Next Article in Journal
A Model to Estimate Willingness to Pay for Harvest Permits for Wild Edible Mushrooms: Application to Andalusian Forests
Next Article in Special Issue
Estimation of Nutrient Exports Resulting from Thinning and Intensive Biomass Extraction in Medium-Aged Spruce and Pine Stands in Saxony, Northeast Germany
Previous Article in Journal
The Biodiversity of Urban and Peri-Urban Forests and the Diverse Ecosystem Services They Provide as Socio-Ecological Systems
Previous Article in Special Issue
Nutrient Resorption and Phenolics Concentration Associated with Leaf Senescence of the Subtropical Mangrove Aegiceras corniculatum: Implications for Nutrient Conservation
Article Menu
Issue 12 (December) cover image

Export Article

Forests 2016, 7(12), 293; doi:10.3390/f7120293

Article
The Effects of Fertilization on the Growth and Physiological Characteristics of Ginkgo biloba L.
Nanjing Forestry University, Co-Innovation Center for Sustainable Forestry in Southern China, 159 Longpan Road, Nanjing 210037, China
*
Author to whom correspondence should be addressed.
Academic Editors: Scott X. Chang and Xiangyang Sun
Received: 2 October 2016 / Accepted: 22 November 2016 / Published: 24 November 2016

Abstract

:
Ginkgo biloba L. is one of the most extensively planted and productive commercial species in temperate areas around the world, but slow-growth is the most limiting factor for its utilization. Fertilization is one of the key technologies for high quality and high forest yield. To better understand the impacts of fertilization on Ginkgo productivity, the effects of fertilization treatments (single fertilizer and combined fertilizer) on growth, nutrient content in Ginkgo leaves, and photosynthesis characteristics were studied in a 10-year-old Ginkgo plantation over two years. The single factor experiments suggested that DBH (diameter at breast height), H (height), NSL (length of new shoots), and V (trunk volume) showed significant differences between the different levels of single nitrogen (N) or phosphate (P) fertilizer application. Orthogonal test results showed that the nine treatments all promoted the growth of Ginkgo, and the formula (N: 400 g·tree−1, P: 200 g·tree−1, potassium (K): 90 g·tree−1) was the most effective. Gs (stomatal conductance) and Pn (net photosynthesis rate) showed significant differences between the different amounts of single N or P fertilizer application, while single K fertilizer only affected Pn. Combined N, P, and K fertilizer had significant promoting effects on Ci (intercellular CO2 concentration), Gs and Pn. N and P contents in Ginkgo leaves showed significant differences between the different amounts of a single N fertilizer application. A single P fertilizer only improved foliar P contents in Ginkgo leaves. A single K fertilizer application improved N and K content in Ginkgo leaves. The effects of different N, P, and K fertilizer treatments on the nutrient content of Ginkgo leaves were different.
Keywords:
Ginkgo; fertilization; growth; photosynthesis; nutrient content

1. Introduction

Nutrient limitations develop when a stand’s potential nutrient use cannot be met by the soil nutrient supply [1]. Improving stand nutrient supply through fertilization is a viable silvicultural option [2]. As an intervention strategy, large-scale application of fertilizers to forests has been implemented to accelerate growth of existing stands and shorten rotation times to overcome future projected timber shortfalls [3]. It is well established that fertilization, in particular nitrogen (N) and phosphate (P) applications, on nutrient limited sites increases tree productivity by increasing photosynthesis in the short term [4,5] and leaf area over the long term [6]. N is a vital constituent in proteins, nucleic acids, chlorophylls, and many secondary metabolites of plants [7]; therefore, it plays an essential role in the enzymatic activities of photosynthetic processes [8]. P plays a central role in almost all aspects of plant metabolism and is one of the nutrients that most commonly limits growth [9]. Potassium (K) is one of important nutrient elements and plays a major role in growth, modifying abundant enzyme activations and controlling cell osmoregulation [10]. Gross primary production (GPP) was also greatly increased by K fertilization as a result of lower stomatal and mesophyll resistance to CO2 diffusion and higher photosynthetic capacity in the leaves [11,12]. In addition, potassium can also alleviate the harmful effects of abiotic stress [13,14,15].
The advantage of using chemical fertilizers is that nutrients are soluble and immediately available to the plants; therefore, the effect is usually direct and fast. Several studies have reported an increase in growing efficiency and higher enzymatic activities following fertilization [16,17]. Many studies have found that growing efficiency is largely unaffected by nutrient additions [18,19]. Different plants do not have the same nutrient demand and specific fertility targets [20]. The fast-growing broad-leaved tree Populus alba × P. glandulosa is more sensitive to increasing N availability [21], while the slow-growing P. popularis is more sensitive to decreasing N availability [22]. Among conifers, the fast-growing spruce families show more plasticity in biomass allocation than do the slowly growing ones under different nitrogen supplies [23], and the fast growing species Pinus radiata allocates more to the aboveground biomass under N and P fertilization [24].
Ginkgo is commonly referred to as Gongsun Tree or Duck Foot Tree, is one of the most ancient gymnosperms in the world, and is native to the temperate forests of China [25]. Ginkgo is an eco-economic tree species which is valuable for food, health care, medicine, timber, landscape, ecological protection, and scientific research. The great environmental adaptability and beauty of Ginkgo have made the tree a favorite species for planting as an ornamental tree throughout the world [26]. Its widespread use has been facilitated by its tolerance of air pollution and soil compaction. Ginkgo has a long history in leaf and nut production. However, it is still in the initial stage for timber cultivation in China. Ginkgo wood has also been highly valued for making furniture and handicraft articles, and Ginkgo wood is also an ideal material for making musical instruments [27]. Nowadays, Ginkgo wood is only used for carving and chopping blocks. The compression of Ginkgo wood was found to be stiffer than that of the other species [28]. Burgert et al. (2004) consequently concluded that there has been an evolutionary trend towards much more flexible compression wood [29]. Gong et al. (2009) reported higher lignin content in Ginkgo than in conifers [30]. Ginkgo wood was once used for pillars and rafters in the palaces and temples in ancient China. Ginkgo also has an anti-dust function, purifying the environment. One important role of Ginkgo is planting in rows in corridors, squares, or on both sides of a street as shade trees, as well as planting in gardens and vestibule entrances as landscape trees. Ginkgo wood has value for many purposes from the help of science and technology. In recent years, with the development of the Ginkgo industry, Ginkgo cultivation area continues to expand; many researchers have developed a variety of optimum fertilization schemes for Ginkgo plantations (especially leaf-producing plantations, nuts plantations, and seedlings) in China. However, studies concentrated on timber plantations are comparatively insufficient.
This study was conducted to examine the relationship between fertilization and growth, photosynthesis characteristics, and foliage nutrient content of pure Ginkgo timber plantations. The main objectives were to assess the effect of fertilization on growth, nutrient content in Ginkgo foliage, and photosynthesis characteristics of new Ginkgo shoots in a 10-year-old Ginkgo plantation over two years. Information generated from this study is expected to be of great value for providing optimal fertilization measures for improving the yield of Ginkgo timber forests and realizing balanced nutrient management for its fast growth. In addition, the application of a suitable fertilizer ratio after foliage nutrient content analysis, photosynthesis, and tree growth characteristics are some of the most effective ways to reduce cost and fertilizer waste.

2. Materials and Methods

2.1. The Study Site

The experimental field was located in Yellow Sea Forest Park, the east-central region of the Jiangsu Province, Eastern China (32°51′ N, 120°51′ E, 5 m above sea level). The study area belongs to a transition zone between a subtropical zone and warm temperate zone, with seasonal pluvial heat and significant monsoon activity. The study area is characterized by a mean annual temperature 15.0 °C, an annual rainfall of 1061.2 mm, an annual sunshine duration of 2209 h, and an annual frost-free period of 220 days. For determining the site fertility, soil samples from the experimental field were collected for physical and chemical characteristics before actual experiments. The soil was characterized as coastal sandy saline-alkali soil with a pH of 8.42, a bulk density of 1.28 g·cm−3, a total nitrogen of 0.75 mg·g−1, a total phosphorus of 0.26 mg·g−1, and a total potassium of 5.25 mg·g−1.

2.2. Materials and Experimental Design

This study was carried out in 2014 and 2015. The test forest was pure Ginkgo forest planted in 2005, with a vine space and row space of 2 m × 8 m. The trees came from the same variety. The experiment with different fertilizer treatments was designed based on a single factor design (EXP.1) and an orthogonal design (EXP.2). Fertilizer was applied to a depth of approximately 10–15 cm (to prevent losses to rain or wind) in several spots in a 70 cm radius circle around each tree in early April 2014 and early April 2015.
Single factor designs (unit: g·tree−1): EXP.1 was designed as single-factor experiment. The dosage of four treatments of single N fertilizer was 600, 400, 200, and 100, respectively. The dosage of four treatments of single P fertilizer was 800, 600, 400, and 200, respectively. The dosage of four treatments of single K fertilizer was 200, 90, 40, and 15, respectively. The amounts of fertilizers were in descending order. The fertilizers used in the experiments were urea (N), superphosphate (P), and potassium sulfate (K). There were a total of 13 treatments, and one of them was CK1 (control, without fertilizer application). Each treatment had 10 Ginkgo trees with three replications in the trial. There were a total of 39 plots and 390 Ginkgo trees (average diameter at breast height was 13.37 cm, average height was 8.04 m, and their growth was uniform.) in the single factor tests. Additionally, there were two guard rows around the test plots.
Orthogonal designs (unit: g·tree−1): Second, the experiment with different fertilizer treatments (EXP.2) was designed based on orthogonal designs with three levels of urea, superphosphate, or potassium sulfate, for a total of 10 treatments one of them was CK2 (control), without fertilizer application, which differed from the CK1 above. Treatments were replicated three times (Table 1). There were a total of 30 plots and 300 Ginkgo trees (average diameter at breast height was 11.62 cm, average height was 5.78 m, and their growth was uniform) in the orthogonal tests. Orthogonal tests plots were in close proximity to the single-factor test spots.

2.3. Tree Growth Indictors’ Measurement

Tree diameter at breast height (DBH), height (H), and length of new shoots (NSL) were measured in November 2015. Tree height was measured using a hypsometer (SGQ-1, Harbin, China). DBH and NSL were measured using diameter tape. We selected 21 Ginkgo trees of different diameter classes (2, 4, 6, 8, 10, 14, and 20) around the experiment plots, cut them down, and measured their DBH and H. Then, according to the standard volume equation and formula (Equation (1)):
V = a0Da1Ha2
we used the R programming language (version 3.0, The University of Auckland, Auckland, New Zealand) software to obtain the trunk volume determination formula (Equation (2)):
LnV = 2.0135 × lnD + 0.5685 × lnH − 9.2452 (R2 = 0.9819)
V: trunk volume (m3), D: DBH (cm), H: height (m). We used this formula to calculate the Ginkgo trunk volume (V) on the test plots.

2.4. Determination of Photosynthetic Indexes

The photosynthetic characteristics were measured with a CIRAS-2 photosynthetic instrument (Hansatech, Norfolk, VA, USA). We selected sunny days in early August 2015 (08:30–11:30), and set the parameters: leaf temperature was not controlled, relative humidity was 85%, cylinder supply CO2 concentration was 380 μmol·mol−1, and the light intensity of an artificial light source was 1200 μmol·m−2·s−1 (exceeding the Ginkgo light saturation point). Five trees were randomly selected from each replicate of each treatment on the test plots. Then, we selected mature healthy leaves of the fully-extended branches in the high position of the canopy. The net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) were measured.

2.5. Determination of Nutrient Concentration in Leaves

The sampling time was in August 2015. We selected five trees randomly from each replicate of each treatment in the test plots. We mined the new shoots in the middle part of the canopy with pole tree pruners. We collected the healthy 8–12 pieces of functional leaves without diseases and pest attack, and immediately put the leaves into an ice box, respectively. After the leaves were brought to the laboratory, the leaves were washed with deionized water, rapid fixed for 15 min at 105 °C, then dried to counterweigh at 70 °C, and, finally, crushed and passed through a 100-mesh sieve, severally (a total of 69 samples). Then, we weighed each sample to 0.1000 g and used concentrated H2SO4-HClO4 to digest them. The nitrogen and phosphorus were analyzed with an AA3 continuous flow analytical system (Bran + Luebbe, Hamburg, Germany); potassium was analyzed via flame atomic absorption spectrometry (WFX-210, Beijing, China).

2.6. Statistical Analysis

Data are reported as the mean of three replicates ± standard deviation (SD), and all tests were performed using the Statistical Product and Service Solution statistical software program (IBM Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) was conducted to compare the effect of fertilization treatments on growth, photosynthetic indexes, and the element contents in leaves. ANOVA was performed at the p < 0.05 level of significance. Duncan’s multiple-range test was performed for each variable (note: different lowercases in the table showed significant differences at the 0.05 level. Treatment means with different lowercases among treatments in the figure are significantly different at the 0.05 level).

3. Results

3.1. Effects of Fertilizer on Growth Indicators

In Yellow Sea Forest Park, DBH, H, NSL, and V in EXP.1 showed significant differences between levels of single N or P fertilizer applications, suggesting that N fertilizer application in excess of 100 g·tree−1 or P fertilizer application in excess of 400 g·tree−1 may be suitable for tree growth (Table 2; p < 0.05). However, growth responses were small and none of the variables showed a significant growth response to K fertilizer (Table 2; p > 0.05). Maximum dosage tended to have the greatest influences on the growth indicators for single N, P, and K fertilizers (N = 600 g·tree−1, P = 800 g·tree−1, or K = 200 g·tree−1). After two years of continuous fertilization, a single N fertilizer application rate at 600 g·tree−1 resulted in an increase in V greater than 17.7% compared with unfertilized plots (CK1). Meanwhile, a single P fertilizer application rate at 800 g·tree−1 resulted in an increase in V greater than 9.7% compared with unfertilized plots (CK1). Therefore, single N or P fertilizer treatments promoted Ginkgo growth indicators significantly, while the promotion effect of single K fertilizer treatment was not significant. Additionally, orthogonal tests in EXP.2 showed that combined N, P, and K fertilizer had significant promoting effects on growth indictors (Table 3; p < 0.05); the maximum effect on the growth of Ginkgo was achieved at a high dosage of N. After two years of continuous fertilization, Treatment 7 resulted in an increase in V greater than 27.7% compared with unfertilized plots (CK2).

3.2. Effects of Fertilizer on Photosynthesis Indicators

In Yellow Sea Forest Park, Pn and Gs showed significant differences between levels of single N or P fertilizer application (p < 0.05), while Tr and Ci were not affected by fertilizer application (Table 4; p > 0.05). However, photosynthesis indicators showed no significant response to single K fertilizer treatment except Pn (Table 4; p > 0.05). After two years of continuous fertilization, a single N fertilizer application rate at 600 g·tree−1 resulted in an increase in Pn greater than 49.5% compared with unfertilized plots (CK1). Meanwhile, single P fertilizer application rate at 800 g·tree−1 resulted in an increase in Pn greater than 27.6% compared with unfertilized plots (CK1). Therefore, single N or P fertilizer treatments promoted Ginkgo Pn significantly, while the promotion effect of single K fertilizer was also significant at 90 g·tree−1 (K2). Additionally, orthogonal tests showed that combined N, P, and K fertilizer had a significant promoting effect on Pn and Gs (p < 0.05); while fertilization was not so important on Tr and Ci (Table 5; p > 0.05) in EXP.2, after two years of continuous fertilization, Treatment 9 resulted in an increase in Pn greater than 36.9% compared with unfertilized plots (CK2).

3.3. Effects of Fertilizer on Leaf N, P, and K Contents

In Yellow Sea Forest Park, N and P contents in leaves showed significant differences between levels of single N fertilizer application (p < 0.05), while K content was not affected by N fertilizer application (Figure 1; p > 0.05). N and K contents showed no significant response to single P fertilizer (p > 0.05), while P content showed a significant difference (Figure 2; p < 0.05). N and K contents showed significant differences between the different amounts of single K fertilizer application (p < 0.05), while P content was not affected by K fertilizer application (Figure 3; p > 0.05). After two years of continuous fertilization, a single N fertilizer application of 600 g·tree−1 resulted in an increase in N content greater than 16.4% and an increase in P content greater than 19.9% compared with unfertilized plots (CK1). Meanwhile, a single P fertilizer application of 800 g·tree−1 resulted in an increase in P content greater than 23.8% compared with unfertilized plots (CK1). A single K fertilizer application of 200 g·tree−1 resulted in an increase in N content greater than 12.2% and an increase in K content greater than 21.8% compared with unfertilized plots (CK1). Therefore, single N fertilizer treatment promoted Ginkgo N and P content significantly, single P fertilizer treatment only promoted Ginkgo P content significantly, and the promotion effect of single K fertilizer treatment on N and K content were significant. Additionally, orthogonal tests in EXP.2 showed that combined N, P, and K fertilizer treatment had a significant promoting effect on N, P, and K content (Figure 4; p < 0.05). After two years of continuous fertilization, Treatment 9 resulted in an increase in N content greater than 13.4% compared with unfertilized plots (CK2). Treatment 6 resulted in an increase in P content greater than 21.5% compared with unfertilized plots (CK2). Treatment 7 resulted in an increase in K content greater than 16.7% compared with unfertilized plots (CK2).

4. Discussion

Nutrient deficiency is generally considered the major factor limiting growth, and fertilization is the main way to supplement the lack of nutrition. The fertilization effects have shown different results under different quantities of fertilizer, the number of years since fertilization treatment, and the nutrition status of the forest site [31]. Our study was carried out in 2014 and 2015. The single factor experiments suggested that DBH, H, NSL, and V showed significant differences between the different levels of single N or P fertilizer application. The orthogonal test results showed that the nine treatments all promoted the growth of Ginkgo, and Treatment 7 (N: 400 g·tree−1, P: 200 g·tree−1, K: 90 g·tree−1) was the most effective one. The response to fertilization in Ginkgo plantations depended on the degree of mismatch between nutrient supply from the soil and the plant nutrient demand [32]. With an increment in the N fertilizer, there was also an increment in the growth, foliar nutrient status, and photosynthesis rate of the Ginkgo plantation. Phosphorus supply affected photosynthesis, leaf metabolites, and allocation to roots versus leaves and growth. In our study, the growth indicators improved with the P fertilizer dosage. However, excess P supply in the soil is a major environmental concern. The accumulation of P in the soil from applications of chemical fertilizer exceed the requirement of plant and can increase the risk of P movement to surface and groundwater [33]. Thus, we should be very circumspect in the application of P fertilizer. Many investigations have shown that improved N and P nutrition increased growth and yield in many tree species [34]. N and P deficiency cause negative effects on plants [35,36]. However, Gotore et al. (2014) proposed that single N application had negative effects on tree growth, while single P had positive effects on Pinus patula growth at Charter Forests. This may be because N is not a limiting factor to tree growth in the first few years after planting and may be readily available in the soil [19]. Additionally, Moilanen et al. (2004) reported clearly that N fertilization is unnecessary on the nitrogen-rich sites, and additional N increased growth only at the most barren sites [37]. In our study, the promotion effect of a single K fertilizer on Ginkgo growth indicators was not significant, though it was better than the unfertilized plots. A previous study showed that fertilization with K was causing a decreased allocation to roots, which enables increased growth in height and leaf number [38]. Moreover, the viewpoint that an optimal potassium nutrition status can reduce the effects of abiotic stresses, such as drought, heat, high light intensity, or salinity has been well established [14,39,40]. The characteristic of our study site is coastal sandy saline–alkali soil; thus, K fertilizer is essential in Yellow Sea Forest Park. In general, N played a key role in the growth of Ginkgo, and P and K were important nutrient elements playing a major role in Ginkgo growth and development. According to the classification standard of soil nutrients in China, the analysis of soil elements in our experimental plots reveals that contents of N, P, and K are basically at low levels. Therefore, supplementary fertilization may be required on the experimental plots, particularly as the soil nutrient availability cannot meet the demand of the trees.
Photosynthesis is the basis of growth and yield formation, and the effects of nutrition on growth may be driven primarily by photosynthesis [41]. Fertilization can increase the photosynthetic efficiency, prolong the duration of photosynthesis, and enlarge the leaf area index (LAI). In the present study, Gs and Pn showed significant differences between the different levels of single N or P fertilizer applications, while single K fertilizer only affected Pn. Combined N, P, and K fertilizers had significant promoting effects on Ci, Gs, and Pn. N played a vital role in the enzymatic activities of photosynthetic processes, and N addition improved the Ginkgo photosynthesis rate and growth response. Among species there is often a strong positive correlation between maximum rates of photosynthesis and N [42]. Greater application of N fertilizer and greater allocation of N to metabolically active tissues, such as leaves and new stems, in the previous study promoted Pn by increasing LAI and chlorophyll concentration of leaves, which, in turn, supported better plant growth [43]. There was also a strong connection between P and the maximum rate of photosynthesis [44]; a partial explanation may lie in a positive relationship between the concentration of P and the amount of Rubisco. Inorganic phosphate (Pi) is a prerequisite for RuBP and also a competitive inhibitor of RUBP [45,46]. Additionally, there was a strong correlation between K concentrations and Rubisco [21]. Zorb et al. (2014) also reported that rates of photosynthesis were positively correlated with application rates of K [47]. K deficiency reduces photosynthesis by decreasing stomatal conductance [48]. However, the differences of stomatal conductance were not significant between different amounts of K fertilizer in our research. Possibly owing to the high mobility of K in both soils and plants, growth is expected to improve in response to added K, as shown in sandy soils [49]. Under this circumstance, deficiency of K may be so severe that fertilization is necessary to sustain tree growth until the end of rotation [50,51]. Transpiration and leaf water status are coordinated to minimize plant water loss and avoid hydraulic failure [52]. Tr of different levels of fertilization had no significant difference in our study. Probably because the climate characteristic of the site belongs to seasonal pluvial heat and significant monsoon, the rainfalls mainly occur in summer. Many studies have shown that growth of Populus was related to increasing water availability and fertilization on nutrient-limited soils [53,54]. Thus, sufficient rainfall and appropriate fertilization contributed to better growth in Ginkgo plantations in Yellow Sea Forest Park.
Nutrient concentrations of foliage have been accepted as adequate indicators of growth and soil fertility in forest stands [55,56]. Maintaining near-optimal foliar nutrient status of trees is especially critical to the maintenance of growth, the establishment of cold tolerance, and the evaluation of soil fertility at sites [56,57]. Our results suggested that N and P contents showed a significant influence of single N fertilizer application. Single P fertilizer only improved foliar P content, and high P fertilizer dosage had an inhibiting effect on K content. Single K fertilizer application improved N and K content in Ginkgo leaves. Effects of different combined N, P, and K fertilizer treatments on the nutrient content of Ginkgo leaves were different. In this study, we found that foliar N concentration was significantly correlated with N fertilizer application, which might result primarily from the supply status of soil nutrient elements. Moreover, foliar N concentration was significantly correlated with K fertilizer application, which might result from K-increased N use efficiency [58]. A previous study has showed that the maximum photosynthetic carbon assimilation rate positively correlated with foliar N concentrations [59]. A greater allocation of N to metabolically-active tissues, such as leaves and new stems in the fertilization treatment, increases the LAI and chlorophyll concentration of leaves, further supporting a better growth of Ginkgo plantations. In N-poor sites, particularly during cold growing seasons, the availability of N for trees may also be low and N deficiencies may be quite common [60,61]. Thus, it is an adaptation to store N in excess of current requirements for photosynthesis that can later be recycled and utilized during periods of lower N supply from the soil. P fertilization improved foliar P contents, and a high P fertilizer dosage had an inhibiting effect on K content. Our findings were consistent with the trend of a previous study of Phoebe bournei seedlings, where foliar N and P concentrations increased, but K concentration decreased as the phosphorus addition increased [62]. The results from Crous et al. (2008) showed a trend of increasing foliar K with an increase in the application of K when no phosphate fertilizer was applied. When P was applied with K on the plots with residual fertilizer, no such trend was observed [63]. Nakashgir (1992) reported nitrogen utilization of maize was accentuated when K application was supplemented [64]. We found that foliar K concentration was significantly correlated with K fertilizer application, which might owe to the high mobility of K in plants and soil. Additionally, light affects the internal redistribution of potassium, leading to higher concentrations in sun-exposed branches than in shaded ones [65,66]. The previous studies reported that potassium plays an important role in stomatal function by maintaining turgor pressure [67]. Growth is expected to improve in response to added K as shown in sandy soils [49]. According to the nutrient content contained in the Ginkgo leaves, the largest demand is N, followed by K, then P in this study. These results suggest that a new compound ratio of fertilizer is needed to optimize the growth of Ginkgo timber forest planted in coastal sandy saline–alkali soil because of different foliar N, P, and K concentrations under different fertilization treatments. According to the actual situation, we can suggest an optimal fertilization formula for improving the yield and quality of Ginkgo timber forests in Yellow Sea Forest Park.

5. Conclusions

The beneficial influences of single N, P, and K fertilization and combined N, P, and K fertilization on Ginkgo nutrition, photosynthesis, and growth were very obvious. This study confirmed the positive foliar nutrient content and the increased photosynthesis and growth responses with sufficient data, which indicated significantly better growth in fertilized stands compared to unfertilized stands. Single N, P, and K fertilizers and the combined N, P, and K fertilizer had positive effects on the growth of Ginkgo. Combined N, P, and K fertilizer and optional formulation are the better choices for achieving balanced nutrition of Ginkgo on our experimental plots. Sufficient nutrition supplements in barren places are significant to guarantee the growth of the forests. Efficient fertilizer regimes require an accurate knowledge of the nutrient status during the growth period to avoid any unforeseen deficiencies.

Acknowledgments

This study was supported by a Grant from the research program “Research on key technology of the cultivation of Ginkgo timber and medicinal forest” (2012BAD21B04) provided by National Science and technology support program, “Research and demonstration of sustainable management technology of Ginkgo timber forest in coastal beach” (BE2013443) provided by Science and technology support program of Jiangsu Province, the Priority Academy Program Development of Jiangsu Higher Education Institution (PAPD) and the Doctorate Fellowship Foundation of Nanjing Forestry University.

Author Contributions

Jing Guo and Yan Lu designed the study and conducted the field trial. Jing Guo, Yaqiong Wu, and Bo Wang were responsible for the samples collection and laboratory analysis. Jing Guo was responsible for the statistical analyses, with contributions from Fuliang Cao and Guibin Wang. Jing Guo wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Pathak, H.; Aggarwal, P.K.; Roetter, R.; Kalra, N.; Bandyopadhaya, S.K.; Prasad, S.; Keulch, H.V. Modelling the quantitative evaluation of soil nutrient supply, nutrient use efficiency, and fertilizer requirements of wheat in India. Nutr. Cycl. Agroecosyst. 2003, 65, 105–113. [Google Scholar] [CrossRef]
  2. Fox, T.R.; Allen, H.L.; Albaugh, T.J.; Rubilar, R.; Carlson, C.A. Tree Nutrition and Forest Fertilization of Pine Plantations in the Southern United States. South. J. Appl. For. 2006, 31, 5–11. [Google Scholar]
  3. Sophie, W.; Leigh, A.K.K.; Grayston, S.J. Effects of long-term fertilization of forest soils on potential nitrification and on the abundance and community structure of ammonia oxidizers and nitrite oxidizers. FEMS Microbiol. Ecol. 2011, 79, 142–154. [Google Scholar]
  4. Gough, C.M.; Seiler, J.R.; Maier, C.A. Short-term effects of fertilization on loblolly pine (Pinus taeda L.) physiology. Plant Cell Environ. 2004, 27, 876–886. [Google Scholar] [CrossRef]
  5. King, N.T.; Seiler, J.R.; Fox, T.R.; Johnsen, K.H. Post-fertilization physiology and growth performance of loblolly pine clones. Tree Physiol. 2008, 28, 703–711. [Google Scholar] [CrossRef] [PubMed]
  6. Samuelson, L.J.; Butnor, J.; Maier, C.; Stokes, T.A.; Johnsen, K.; Kane, M. Growth and physiology of loblolly pine in response to long-term resource management: Defining growth potential in the southern United States. Can. J. For. Res. 2008, 38, 721–732. [Google Scholar] [CrossRef]
  7. Luo, J.; Qin, J.J.; He, F.F.; Li, H.; Liu, T.X.; Polle, A.; Peng, C.H.; Luo, Z.B. Net fluxes of ammonium and nitrate in association with H+ fluxes in fine roots of Populus popularis. Planta 2013, 237, 19–31. [Google Scholar] [CrossRef] [PubMed]
  8. Güsewell, S. N:P ratios in terrestrial plants: Variation and functional significance. New Phytol. 2004, 164, 243–266. [Google Scholar] [CrossRef]
  9. Warren, C.R. How does P affect photosynthesis and metabolite profiles of Eucalyptus globulus? Tree Physiol. 2011, 31, 727–739. [Google Scholar] [CrossRef] [PubMed]
  10. Coskun, D.; Britto, D.T.; Kronzucker, H.J. The physiology of channel-mediated K+, acquisition in roots of higher plants. Physiol. Plant. 2014, 151, 305–312. [Google Scholar] [CrossRef] [PubMed]
  11. Battie-Laclau, P.; Laclau, J.P.; Beri, C.; Mietton, L.; Muniz, M.R.A.; Arenque, B.C.; Piccolo, M.C.; Jordan-Meille, L.; Bouillet, J.P.; Nouvellon, Y. Photosynthetic and anatomical responses of Eucalyptus grandis leaves to potassium and sodium supply in a field experiment. Plant Cell Environ. 2014, 37, 70–81. [Google Scholar] [CrossRef] [PubMed]
  12. Christina, M.; Maire, G.L.; Battie-Laclau, P.; Nouvellon, Y.; Bouillet, J.P.; Jourdan, C.; Goncalves, J.L.M.; Laclau, J.P. Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light-use efficiency in Eucalyptus grandis plantations. Glob. Chang. Biol. 2015, 21, 2022–2039. [Google Scholar] [CrossRef] [PubMed]
  13. Mäser, P.; Gierth, M.; Schroeder, J.I. Molecular mechanisms of potassium and sodium uptake in plants. Plant Soil 2002, 247, 43–54. [Google Scholar] [CrossRef]
  14. Cakmak, I. The role of potassium in alleviating detrimental effects of abiotic stresses in plants. J. Plant Nutr. Soil Sci. 2005, 168, 521–530. [Google Scholar] [CrossRef]
  15. Li, X.Y.; Mu, C.S.; Lin, J.X.; Wang, Y.; Li, X.J. Effect of alkaline potassium and sodium salts on growth, photosynthesis, ions absorption and solutes synthesis of wheat seedlings. Exp. Agric. 2014, 50, 144–157. [Google Scholar] [CrossRef]
  16. Albaugh, T.J.; Allen, H.L.; Dougherty, P.M.; Kress, L.W.; King, J.S. Leaf area and above- and belowground growth responses of loblolly pine to nutrient and water additions. For. Sci. 1998, 44, 317–328. [Google Scholar]
  17. Balster, N.J.; Marshall, J.D. Eight-year responses of light interception, effective leaf area index, and stemwood production in fertilized stands of interior Douglas-fir (Pseudotsuga menziesii var. glauca). Can. J. For. Res. 2000, 30, 733–743. [Google Scholar] [CrossRef]
  18. Samuelson, L.; Stokes, T.; Cooksey, T. Production efficiency of loblolly pine and sweetgum in response to four years of intensive management. Tree Physiol. 2001, 21, 369–376. [Google Scholar] [CrossRef] [PubMed]
  19. Gotore, T.; Murepa, R.; Gapare, W.J. Effects of Nitrogen, Phosphorus and Potassium on the Early Growth of Pinus patula and Eucalyptus grandis. J. Trop. For. Sci. 2014, 26, 22–31. [Google Scholar]
  20. Salifu, K.F.; Jacobs, D.F.; Birge, Z.K.D. Nursery nitrogen loading improves field performance of bareroot oak seedlings planted on abandoned mine lands. Restor. Ecol. 2009, 17, 339–349. [Google Scholar] [CrossRef]
  21. Li, H.; Li, M.; Luo, J.; Cao, X.; Qu, L.; Gai, Y.; Jiang, X.; Liu, T.; Bai, H.; Janz, D. N fertilization has different effects on the growth, carbon and nitrogen physiology, and wood properties of slow-and fast-growing Populus species. J. Exp. Bot. 2012, 63, 6173–6185. [Google Scholar] [CrossRef] [PubMed]
  22. Luo, J.; Li, H.; Liu, T.; Polle, A.; Peng, C.; Luo, Z. Nitrogen metabolism of two contrasting poplar species during acclimation to limiting nitrogen availability. J. Exp. Bot. 2013, 64, 4207–4224. [Google Scholar] [CrossRef] [PubMed]
  23. Miller, B.D.; Hawkins, B.J. Ammonium and nitrate uptake, nitrogen productivity and biomass allocation in interior spruce families with contrasting growth rates and mineral nutrient preconditioning. Tree Physiol. 2007, 27, 901–909. [Google Scholar] [CrossRef] [PubMed]
  24. Bown, H.E.; Watt, M.S.; Clinton, P.W.; Mason, E.G.; Whitehead, D. The influence of N and P supply and genotype on carbon flux and partitioning in potted Pinus radiata plants. Tree Physiol. 2009, 29, 857–868. [Google Scholar] [CrossRef] [PubMed]
  25. Son, Y. Effects of Nitrogen Fertilization on Foliar Nutrient Dynamics in Ginkgo Seedlings. J. Plant Nutr. 2002, 25, 93–102. [Google Scholar] [CrossRef]
  26. Son, Y.; Kim, H.W. Above-ground biomass and nutrient distribution in a 15-year-old ginkgo (Ginkgo biloba) plantation in Central Korea. Bioresour. Technol. 1998, 63, 173–177. [Google Scholar] [CrossRef]
  27. Yuan, J.; Li, Q.; Xiao, G.L.; Zhu, S.H. Discussion on the utilization and development of ginkgo wood. China For. Sci. Technol. 2008, 16, 6–8. [Google Scholar]
  28. Andersson, S.; Wang, Y.; Ponni, R.; Hanninen, T.; Mononen, M.; Ren, H.; Serimaa, R.; Saranpää, P. Cellulose structure and lignin distribution in normal and compression wood of the Maidenhair tree (Ginkgo biloba L.). J. Integr. Plant Biol. 2015, 57, 388–395. [Google Scholar] [CrossRef] [PubMed]
  29. Burgert, I.; Fruhmann, K.; Keckes, J.; Fratzl, P.; Stanzl-Tschegg, S. Structure-function relationships of four compression wood types: Micromechanical properties at the tissue and fibre level. Trees 2004, 18, 480–485. [Google Scholar] [CrossRef]
  30. Gong, Q.L.; Hu, A.H.; Xing, S.Y.; Wang, F. Research on systematic evolution of Ginkgo biloba based on chemical composition of wood. Spectrosc. Spectr. Anal. 2009, 29, 1512–1516. [Google Scholar]
  31. Moilanen, M.; Hökkä, H. The growth response of scots pine to PK fertilization depends on the nutrient status of the stand on drained peatlands. Suo 2009, 60, 111–119. [Google Scholar]
  32. Smethurst, P.; Baillie, C.; Cherry, M.; Holz, G. Fertilizer effects on LAI and growth of four Eucalyptus nitens plantations. For. Ecol. Manag. 2003, 176, 531–542. [Google Scholar] [CrossRef]
  33. Grant, C.; Bittman, S.; Montreal, M.; Plenchette, C.; Morel, C. Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development. Can. J. Plant Sci. 2005, 85, 3–14. [Google Scholar] [CrossRef]
  34. Bussi, C.; Smith, M.A.L. Effects of nitrogen and potassium fertilization on the growth, yield and pitburn of apricot (cv. Bergeron). J. Hortic. Sci. Biotechnol. 1998, 73, 387–392. [Google Scholar] [CrossRef]
  35. Boyce, R.L.; Larson, J.R.; Sanford, R.L. Phosphorus and nitrogen limitations to photosynthesis in Rocky Mountain bristlecone pine (Pinus aristata) in Colorado. Tree Physiol. 2006, 26, 1477–1486. [Google Scholar] [CrossRef] [PubMed]
  36. Turnbull, T.L.; Warren, C.R.; Adams, M.A. Novel mannose-sequestration technique reveals variation in subcellular orthophosphate pools do not explain the effects of phosphorus nutrition on photosynthesis in Eucalyptus globulus seedlings. New Phytol. 2007, 176, 849–861. [Google Scholar] [CrossRef] [PubMed]
  37. Moilanen, M.; Silfverberg, K.; Hökkä, H.; Issakainen, J. Comparing effects of wood ash and commercial PK fertiliser on the nutrient status and stand growth of Scots pine on drained mires. Balt. For. 2004, 10, 2–10. [Google Scholar]
  38. Santiago, L.S.; Wright, S.J.; Harms, K.E.; Yavitt, J.B.; Korine, C.; Garcia, M.N.; Turner, B.L. Tropical tree seedling growth responses to nitrogen, phosphorus and potassium addition. J. Ecol. 2012, 100, 309–316. [Google Scholar] [CrossRef]
  39. Oosterhuis, D.M.; Loka, D.A.; Raper, T.B. Potassium and stress alleviation: Physiological functions and management of cotton. J. Plant Nutr. Soil Sci. 2013, 76, 331–343. [Google Scholar] [CrossRef]
  40. Römheld, V.; Kirkby, E.A. Research on potassium in agriculture: Needs and prospects. Plant Soil 2010, 335, 155–180. [Google Scholar] [CrossRef]
  41. Wang, X.G.; Zhao, X.H.; Jiang, C.J.; Li, C.H.; Cong, S.; Wu, D.; Chen, Y.Q.; Yu, H.Q.; Wang, C.Y. Effects of potassium deficiency on photosynthesis and photo-protection mechanisms in soybean (Glycine max (L.) Merr.). J. Integr. Agric. 2015, 14, 856–863. [Google Scholar] [CrossRef]
  42. Warren, C.R.; Adams, M.A.; Chen, Z.L. Is photosynthesis related to concentrations of nitrogen and Rubisco in leaves of Australian native plants? Funct. Plant Biol. 2000, 27, 407–416. [Google Scholar] [CrossRef]
  43. Pokharel, P.; Chang, S.X. Exponential fertilization promotes seedling growth by increasing nitrogen retranslocation in trembling aspen planted for oil sands reclamation. For. Ecol. Manag. 2016, 372, 35–43. [Google Scholar] [CrossRef]
  44. Warren, C.R.; Adams, M.A. Phosphorus affects growth and partitioning of nitrogen to Rubisco in Pinus pinaster. Tree Physiol. 2002, 22, 11–19. [Google Scholar] [CrossRef] [PubMed]
  45. Kumagai, E.; Araki, T.; Kubota, F. Effects of nitrogen supply restriction on gas exchange and photosystem 2 function in flag leaves of a traditional low-yield cultivar and a recently improved high-yield cultivar of rice (Oryza sativa L.). Photosynthetica 2007, 45, 489–495. [Google Scholar] [CrossRef]
  46. Zafar, M.; Abbasi, M.K.; Khaliq, A. Effect of combining organic materials with inorganic phosphorus sources on growth, yield, energy content and phosphorus uptake in maize at Rawalakot Azad Jammu and Kashmir, Pakistan. Arch. Appl. Sci. Res. 2011, 3, 199–212. [Google Scholar]
  47. Zorb, C.; Senbayram, M.; Peiter, E. Potassium in agriculture: Status and perspectives. J. Plant Physiol. 2014, 171, 656–669. [Google Scholar] [CrossRef] [PubMed]
  48. Terry, N.; Ulrich, A. Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet. Plant Physiol. 1973, 51, 43–47. [Google Scholar] [CrossRef] [PubMed]
  49. Warren, C.R.; McGrath, J.F.; Adams, M.A. Differential effects of N, P and K on photosynthesis and partitioning of N in Pinus pinaster needles. Ann. For. Sci. 2005, 62, 1–8. [Google Scholar] [CrossRef]
  50. Moilanen, M.; Silfverberg, K.; Hokkanen, T.J. Effects of wood-ash on the tree growth, vegetation and substrate quality of a drained mire: A case study. For. Ecol. Manag. 2002, 171, 321–338. [Google Scholar] [CrossRef]
  51. Silfverberg, K.; Issakainen, J.; Moilanen, M. Growth and nutrition of scots pine on drained and fertilized purple moor grass fens in central Finland. Balt. For. 2011, 17, 91–101. [Google Scholar]
  52. Whitehead, D.; Beadle, C.L. Physiological regulation of productivity and water use in Eucalyptus: A review. For. Ecol. Manag. 2004, 193, 113–140. [Google Scholar] [CrossRef]
  53. Dickmann, D.I.; Nguyen, P.V.; Pregitzer, K.S. Effects of irrigation and coppicing on above-ground growth, physiology, and fine-root dynamics of two field-grown hybrid poplar clones. For. Ecol. Manag. 1996, 80, 163–174. [Google Scholar] [CrossRef]
  54. Thornton, F.C.; Bock, B.R.; Behel, A.D.; Houston, A.; Tyler, D.D. Utilization of waste materials to promote hardwood tree growth. South. J. Appl. For. 2000, 24, 230–237. [Google Scholar]
  55. Barrongafford, G.A.; Will, R.E.; Burkes, E.C.; Shiver, B.; Teskey, R.O. Nutrient concentrations and contents, and their relation to stem growth, of intensively managed Pinus taeda and Pinus elliottii stands of different planting densities. For. Sci. 2003, 49, 291–300. [Google Scholar]
  56. Tausz, M.; Trummer, W.; Wonisch, A.; Goessler, W.; Grill, D.; Jiménez, M.S.; Morales, D. A survey of foliar mineral nutrient concentrations of Pinus canariensis at field plots in Tenerife. For. Ecol. Manag. 2004, 189, 49–55. [Google Scholar] [CrossRef]
  57. Jennifer, A.B.; Boerner, R.E.J. Nitrogen fertilization effects on foliar nutrient dynamics and autumnal resorption in maidenhair tree (Gingko biloba L.). J. Plant Nutr. 1994, 17, 433–443. [Google Scholar]
  58. Pettigrew, W.T.; Meredith, W.R. Dry matter production, nutrient uptake, and growth of cotton as affected by potassium fertilization. J. Plant Nutr. 1997, 20, 531–548. [Google Scholar] [CrossRef]
  59. Wright, I.J.; Reich, P.B.; Westoby, M.; Ackerly, D.D.; Baruch, Z.; Bongers, F.; Cavender-Bares, J.; Chapin, T.; Cornelissen, J.H.C.; Diemer, M. The worldwide leaf economics spectrum. Nature 2004, 428, 821–827. [Google Scholar] [CrossRef] [PubMed]
  60. Sundström, E.; Magnusson, T.; Hånell, B. Nutrient conditions in drained peatlands along a north-south climatic gradient in Sweden. For. Ecol. Manag. 2000, 126, 149–161. [Google Scholar] [CrossRef]
  61. Pietiläinen, P.; Kaunisto, S. The effect of peat nitrogen concentration and fertilization on the foliar nitrogen concentration of Scots pine (Pinus sylvestris L.) in three temperature sum regions. Suo 2003, 54, 1–13. [Google Scholar]
  62. Wang, D.G.; Yin, G.T.; Yang, J.C.; Li, R.S.; Zou, W.T.; Jia, R.F. Effects of phosphorus fertilization on growth and foliar nutrient (N, P, K) of Phoebe bournei seedlings. J. Nanjing For. Univ. (Nat. Sci. Ed.) 2014, 38, 40–44. [Google Scholar]
  63. Crous, J.W.; Morris, A.R.; Scholes, M.C. Growth and foliar nutrient response to recent applications of phosphorus (P) and potassium (K) and to residual P and K fertiliser applied to the previous rotation of Pinus patula, at Usutu, Swaziland. For. Ecol. Manag. 2008, 256, 712–721. [Google Scholar] [CrossRef]
  64. Nakashgir, G.H. Influence of potassium on nitrogen utilization by maize under dryland conditions as affected by water storage. Adv. Plant Sci. 1992, 5, 134–142. [Google Scholar]
  65. Nardini, A.; Grego, F.; Trifilò, P.; Salleo, S. Changes of xylem sap ionic content and stem hydraulics in response to irradiance in Laurus nobilis. Tree Physiol. 2010, 30, 136–140. [Google Scholar] [CrossRef] [PubMed]
  66. Sellin, A. Experimental evidence supporting the concept of light-mediated modulation of stem hydraulic conductance. Tree Physiol. 2010, 30, 1528–1535. [Google Scholar] [CrossRef] [PubMed]
  67. Pervez, H.; Ashraf, M.; Makhdum, M.I. Influence of potassium nutrition on gas exchange characteristics and water relations in cotton (Gossypium hirsutum L.). Photosynthetica 2004, 42, 251–255. [Google Scholar] [CrossRef]
Figure 1. Effects of single N fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Figure 1. Effects of single N fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Forests 07 00293 g001
Figure 2. Effects of single P fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Figure 2. Effects of single P fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Forests 07 00293 g002
Figure 3. Effects of single K fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Figure 3. Effects of single K fertilizer application on G. biloba leaf N, P, and K contents in EXP.1.
Forests 07 00293 g003
Figure 4. Effects of combined N, P, and K fertilizer application on G. biloba leaf N, P, and K contents in EXP.2.
Figure 4. Effects of combined N, P, and K fertilizer application on G. biloba leaf N, P, and K contents in EXP.2.
Forests 07 00293 g004
Table 1. Orthogonal trial fertilizer treatments.
Table 1. Orthogonal trial fertilizer treatments.
Treatment No.Fertilization Level (g·tree−1)
UreaSuperphosphatePotassium Sulfate
110020015
210040040
310060090
420020040
520040090
620060015
740020090
840040015
940060040
CK2000
CK2: control in EXP.2.
Table 2. Effects of two years in EXP.1 of N, P, and K fertilizer (F) on the diameter at breast height (DBH, cm), height (H, m), length of new shoots (NSL, cm), and trunk volume (V, m3) of G. biloba in 2014 and 2015 in Yellow Sea Forest Park in China.
Table 2. Effects of two years in EXP.1 of N, P, and K fertilizer (F) on the diameter at breast height (DBH, cm), height (H, m), length of new shoots (NSL, cm), and trunk volume (V, m3) of G. biloba in 2014 and 2015 in Yellow Sea Forest Park in China.
FDBHHNSLV
N1 60015.34 ± 0.396 a9.85 ± 0.383 a26.59 ± 1.204 a0.0146 ± 0.000929 a
N2 40015.11 ± 0.123 a9.27 ± 0.492 b25.56 ± 1.284 ab0.0135 ± 0.000755 ab
N3 20014.96 ± 0.301 a9.17 ± 0.131 b24.64 ± 2.840 ab0.0133 ± 0.000448 b
N4 10014.92 ± 0.407 a9.14 ± 0.068 b21.93 ± 2.635 bc0.0132 ± 0.000369 b
CK1 014.35 ± 0.095 b8.92 ± 0.158 b20.23 ± 2.594 c0.0124 ± 0.000256 b
P1 80014.84 ± 0.063 a9.45 ± 0.257 a25.98 ± 1.33 a0.0136 ± 0.000398 a
P2 60014.42 ± 0.255 ab9.13 ± 0.221 ab24.02 ± 1.86 ab0.0127 ± 0.000408 b
P3 40014.23 ± 0.333 b9.05 ± 0.182 ab24.37 ± 0.688 ab0.0124 ± 0.000514 b
P4 20014.21 ± 0.292 b8.83 ± 0.270 b22.69 ± 0.419 bc0.0121 ± 0.000464 b
CK1 014.35 ± 0.095 b8.92 ± 0.158 b20.23 ± 2.594 c0.0124 ± 0.000256 b
K1 20014.91 ± 0.499 a9.01 ± 0.288 a24.01 ± 0.844 a0.0124 ± 0.000965 a
K2 9014.65 ± 0.428 a8.93 ± 0.195 a23.71 ± 1.29 a0.0117 ± 0.000445 a
K3 4014.66 ± 0.553 a8.88 ± 0.326 a23.35 ± 2.14 a0.0113 ± 0.000699 a
K4 1514.38 ± 0.422 a8.63 ± 0.459 a24.49 ± 0.967 a0.0114 ± 0.000993 a
CK1 014.35 ± 0.095 a8.92 ± 0.158 a20.23 ± 2.59 a0.0124 ± 0.000256 a
Note: different lowercase letters in the table reflect significant differences between treatments. CK1: control in EXP.1.
Table 3. Effects of two years in EXP.2 of combined N, P, and K fertilizer (F) on the diameter at breast height (DBH, cm), height (H, m), length of new shoots (NSL, cm), and trunk volume (V, m3) of G. biloba in 2014 and 2015 in Yellow Sea Forest Park in China.
Table 3. Effects of two years in EXP.2 of combined N, P, and K fertilizer (F) on the diameter at breast height (DBH, cm), height (H, m), length of new shoots (NSL, cm), and trunk volume (V, m3) of G. biloba in 2014 and 2015 in Yellow Sea Forest Park in China.
FDBHHNSLV
113.66 ± 0.908 bcd7.45 ± 0.022 bc24.15 ± 0.832 bcd0.00983 ± 0.000675 cd
213.78 ± 0.825 abcd7.49 ± 0.065 bc26.606 ± 3.250 abc0.00997 ± 0.000679 cd
313.2 ± 0.172 cd7.42 ± 0.168 bc26.00 ± 2.32 abc0.00947 ± 0.000327 de
413.71 ± 0.233 bcd7.65 ± 0.123 ab25.90 ± 1.921 abc0.01013 ± 0.000207 cd
513.88 ± 0.173 abc7.73 ± 0.293 ab25.26 ± 1.705 abc0.01036 ± 0.000261 bc
613.94 ± 0.370 abc7.55 ± 0.046 b22.83 ± 0.656 cd0.01017 ± 0.000304 cd
714.61 ± 0.347 a8.01 ± 0.239 a26.77 ± 4.070 abc0.01130 ± 0.000302 a
814.50 ± 0.423 ab7.81 ± 0.173 ab28.89 ± 2.014 a0.01094 ± 0.000240 ab
914.47 ± 0.208 ab7.81 ± 0.205 ab27.49 ± 1.980 ab0.01092 ± 0.000304 ab
CK212.92 ± 0.231 d7.09 ± 0.0346 c20.23 ± 2.594 d0.00885 ± 0.000161 e
Note: different lowercase letters in the table reflect significant differences between treatments.
Table 4. Average effects of two years N, P, and K fertilizer (F) in EXP.1 on the photosynthesis characteristics, net photosynthetic rate (Pn, μmol·m−2·s−1), transpiration rate (Tr, μmol·m−2·s−1), stomatal conductance (Gs, mol·m−2·s−1), and intercellular CO2 concentration (Ci, μmol·mol−1) in 2014 and 2015 in Yellow Sea Forest Park in China.
Table 4. Average effects of two years N, P, and K fertilizer (F) in EXP.1 on the photosynthesis characteristics, net photosynthetic rate (Pn, μmol·m−2·s−1), transpiration rate (Tr, μmol·m−2·s−1), stomatal conductance (Gs, mol·m−2·s−1), and intercellular CO2 concentration (Ci, μmol·mol−1) in 2014 and 2015 in Yellow Sea Forest Park in China.
FCiTrGsPn
N1 600278.56 ± 8.57 a2.71 ± 0.252 a167.64 ± 3.32 a12.30 ± 0.472 a
N2 400277.33 ± 4.98 a2.68 ± 0.150 a165.78 ± 2.55 a11.74 ± 0.597 ab
N3 200269.78 ± 5.10 a2.43 ± 0.173 a157.78 ± 4.43 a10.25 ± 1.42 b
N4 100267.79 ± 16.65 a2.51 ± 0.284 a156.67 ± 7.86 a10.57 ± 0.635 b
CK1 0267.33 ± 21.73 a2.53 ± 0.208 a127.33 ± 15.5 b8.23 ± 0.833 c
P1 800289.89 ± 3.29 a3.03 ± 0.153 a156.56 ± 5.34 a10.50 ± 1.19 a
P2 600275.11 ± 8.26 a2.80 ± 0.152 a139.78 ± 4.17 b10.22 ± 1.06 ab
P3 400266.89 ± 5.23 a2.62 ± 0. 135 a129.89 ± 8.06 b8.77 ± 1.72 abc
P4 200275.33 ± 19.50 a2.67 ± 0.333 a133.88 ± 6.02 b7.14 ± 0.635 c
CK1 0267.33 ± 21.73 a2.53 ± 0.208 a127.33 ± 15.50 b8.23 ± 0.833 bc
K1 200256.89 ± 1.92 a2.60 ± 0.101 a148.22 ± 11.5 a10.39 ± 0.27 a
K2 90251.00 ± 4.58 a2.54 ± 0.081 a133.11 ± 10.98 a10.44 ± 0.44 a
K3 40265.78 ± 7.93 a2.46 ± 0.102 a123.67 ± 15.94 a8.37 ± 0.62 b
K4 15266.79 ± 9.25 a2.27 ± 0.095 a121.56 ± 16.60 a7.61 ± 0.37 b
CK1 0267.33 ± 21.73 a2.53 ± 0.208 a127.33 ± 15.50 a8.23 ± 0.83 b
Note: different lowercase letters in the table reflect significant differences between treatments.
Table 5. Average effects of two years of N, P, and K fertilizer (F) in EXP.2 on the photosynthesis characteristics, net photosynthetic rate (Pn, μmol·m−2·s−1), transpiration rate (Tr, μmol·m−2·s−1), stomatal conductance (Gs, mol·m−2·s−1), and intercellular CO2 concentration (Ci, μmol·mol−1) in 2014 and 2015 in Yellow Sea Forest Park in China.
Table 5. Average effects of two years of N, P, and K fertilizer (F) in EXP.2 on the photosynthesis characteristics, net photosynthetic rate (Pn, μmol·m−2·s−1), transpiration rate (Tr, μmol·m−2·s−1), stomatal conductance (Gs, mol·m−2·s−1), and intercellular CO2 concentration (Ci, μmol·mol−1) in 2014 and 2015 in Yellow Sea Forest Park in China.
FCiTrGsPn
1239.00 ± 10.40 b2.56 ± 0.34 a122.33 ± 13.39 c9.00 ± 0.91 cd
2246.78 ± 27.03 b2.41 ± 0.20 a127.33 ± 13.00 bc9.22 ± 0.74 bcd
3243.00 ± 25.32 b2.41 ± 0.47 a136.11 ± 7.31 abc9.36 ± 1.02 bcd
4254.00 ± 8.09 b2.61 ± 0.24 a133.56 ± 9.52 bc9.48 ± 0.17 bcd
5247.33 ± 5.20 b2.59 ± 0.34 a141.34 ± 3.51 abc9.71 ± 1.51 abcd
6272.11 ± 17.88 ab2.74 ± 0.15 a140.11 ± 4.40 abc10.11 ± 0.23 abc
7271.78 ± 16.68 ab2.69 ± 0.25 a142.67 ± 3.51 abc10.68 ± 1.22 abc
8272.55 ± 20.51 ab2.69 ± 0.08 a146.89 ± 12.98 ab10.71 ± 0.71 ab
9290.33 ± 16.18 a2.79 ± 0.16 a154.33 ± 12.20 a11.27 ± 0.38 a
CK2265.33 ± 18.73 ab2.50 ± 0.11 a129.13 ± 12.50 bc8.53 ± 0.58 d
Note: different lowercase letters in the table reflect significant differences between treatments.
Forests EISSN 1999-4907 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top