Search Results (266)

Validating the potential of multi-frequency synthetic aperture radar (SAR) data for multi-layer and profile soil moisture (SM) estimation modeling, we conducted an airborne multi-frequency SAR joint observation experiment (AMFSEX) over the Liao River Basin in China. The experiment simultaneously acquired airborne high spatial resolution quad-polarization (quad-pol) SAR data at five frequencies, including the Ka-, X-, C-, S-, and L-band. A preliminary “vegetation–soil” parameter estimation model based on the multi-frequency SAR data was established. Theoretical penetration depths of the multi-frequency SAR data were analyzed using the Dobson empirical model and the Hallikainen modified model. On this basis, a water cloud model (WCM) constrained by multi-polarization weighted and penetration depth weighted parameters was used to analyze the estimation accuracy of the multi-layer and profile SM (0–50 cm depth) under different vegetation types (grassland, farmland, and woodland). Overall, the estimation error (root mean square error, RMSE) of the surface SM (0–5 cm depth) ranged from 0.058 cm³/cm³ to 0.079 cm³/cm³, and increased with radar frequency. For multi-layer and profile SM (3 cm, 5 cm, 10 cm, 20 cm, 30 cm, 40 cm, 50 cm depth), the RMSE ranged from 0.040 cm³/cm³ to 0.069 cm³/cm³. Finally, a multi-input multi-output regression model (Gaussian process regression) was used to simultaneously estimate the multi-layer and profile SM. For surface SM, the overall RMSE was approximately 0.040 cm³/cm³. For multi-layer and profile SM, the overall RMSE ranged from 0.031 cm³/cm³ to 0.064 cm³/cm³. The estimation accuracy achieved by coupling the multi-source data (multi-frequency SAR data, multispectral data, and soil parameters) was superior to that obtained using the SAR data alone. The optimal SM penetration depth varied across different vegetation cover types, generally falling within the range of 10–30 cm, which holds true for both the scattering model and the regression model. This study provides methodological guidance for the development of multi-layer and profile SM estimation models based on the multi-frequency SAR data. Full article

This research aimed to study changes in the diversity of the soil bacterial community in a jujube forest with different years of abandonment. To this end, we took the mountain jujube forest with different abandoned years (1 a, 3 a, 6a and 20 a) in the Qijiashan jujube experimental demonstration base in Yanchuan County as the research object; we used Illumina Miseq high-throughput sequencing technology to analyze the changes in the soil bacterial community structure and reveal the key environmental drivers of bacterial community variation in the abandoned jujube forest in the study area. The results showed the following findings: (1) Phylum Actinomycetota (34%), Proteobacteria (29%), and Acidobacteriota (13%) were the dominant phyla of the soil bacterial community in the abandoned jujube forest. (2) Abandonment altered the composition of soil bacteria at the OTU level in jujube plantations. (3) There are differences in the soil bacterial community structure across different periods of abandonment in the jujube forest. (4) Soil water content is the main factor affecting the bacterial community structure of the abandoned jujube forest. There are differences in the soil water content of abandoned woodlands, which affects the community structure of soil microorganisms. Full article

Understanding the processes of organic nitrogen (N) mineralization to ammonium (NH₄⁺) and NH₄⁺ oxidation to nitrate (NO₃⁻), which, together, supply soil inorganic N (the sum of NH₄⁺ and NO₃⁻), is of great significance for guiding the restoration of degraded ecosystems. This study used space-for-time substitution to investigate the dynamic changes in the rates of organic N mineralization (M_Norg) and nitrification (O_NH4) in soil at different vegetation restoration stages. Soil samples were collected from grassland (3–5 years), shrub-grassland (7–8 years), early-stage shrubland (15–20 years), late-stage shrubland (30–35 years), early-stage woodland (45–50 years), and late-stage woodland (70–80 years) in the subtropical karst region of China during the dry (December) and rainy (July) seasons. The M_Norg and O_NH4 were determined using the ¹⁵N labeling technique. The soil microbial community was determined using the phospholipid fatty acid method. Soil organic carbon (SOC), total nitrogen (TN), NH₄⁺, NO₃⁻, and inorganic N contents, as well as the soil moisture content (SMC) were also measured. Our results showed that SOC and TN contents, and the SMC, as well as microbial community abundances increased markedly from grassland to the late-stage shrubland. Especially in the late-stage shrubland, the abundance of the total microbial community, bacteria, fungi, actinomycetes, and AMF in soil was significantly higher than other restoration stages. These results indicate that vegetation restoration significantly increased soil nutrient content and microbial community abundance. From grassland to the late-stage shrubland, the soil NH₄⁺, NO₃⁻, and inorganic N contents increased significantly, and the NH₄⁺:NO₃⁻ ratios changed from greater than 1 to less than 1, indicating that vegetation restoration significantly influenced soil inorganic N content and composition. As restoration progressed, the M_Norg and O_NH4 increased significantly, from 0.04 to 3.01 mg N kg⁻¹ d⁻¹ and 0.35 to 2.48 mg N kg⁻¹ d⁻¹ in the dry season, and from 3.26 to 7.20 mg N kg⁻¹ d⁻¹ and 1.47 to 10.7 mg N kg⁻¹ d⁻¹ in the rainy season. At the same vegetation restoration stage, the M_Norg and O_NH4 in the rainy season were markedly higher than those in the dry season. These results indicate that vegetation restoration and seasonal variations could significantly influence M_Norg and O_NH4. Correlation analysis showed that the increase in M_Norg during vegetation restoration was mainly attributed to the increase in SOC and TN contents, as well as the total microbial community, bacterial, fungal, actinomycetes, and AMF abundances, and that the increase in O_NH4 was mainly attributed to the increase in M_Norg and the decrease in the F: B ratio. Moreover, the M_Norg and O_NH4 showed a strong positive correlation with inorganic N content. This study clarifies that vegetation restoration in karst regions could significantly increase M_Norg and O_NH4 through enhancing soil carbon and N contents, as well as microbial community abundances, thereby increasing the available soil N supply, which could provide a theoretical basis for soil fertility regulation in future rocky desertification management. Full article

Shrub encroachment in coastal wetlands alters vegetation–soil interactions, yet its impacts on north temperate coastal wetland ecosystems remain poorly quantified. This study investigated the effects of Tamarix chinensis-dominated shrub encroachment in the abandoned Yellow River course wetlands. Encroachment stages (Isolated Tamarix shrub, ITS → Tamarix shrub island, TSI → Tamarix woodland, TWL) were assessed via vegetation surveys and soil sampling (0–60 cm). Encroachment progression significantly increased shrub cover, shrub crown width, and branches per shrub while reducing soil electrical conductivity and soil salt content. Surface soils (0–5 cm) exhibited higher levels of organic carbon (SOC) and elevated total nitrogen (TN) and available nitrogen (AN), while deeper layers (40–60 cm) at the TWL stage exhibited reduced available phosphorus (AP) and total phosphorus (TP). Redundancy analysis (RDA) identified soil bulk density, soil water content, total carbon (TC), and AP as primary drivers of vegetation community restructuring (RDA: 68.68% variance). The average ranges of TC:TN (R_CN), TC:TP (R_CP), and TN:TP (R_NP) were 23.04–92.54, 52.14–92.88, and 0.46–4.29, respectively. T. chinensis encroachment induced nitrogen-limited conditions and reduced deep soil layer phosphorus availability, fundamentally restructuring coastal wetland ecosystems. These findings inform blue carbon ecosystem management in the north temperate zone. Full article

Understanding plant nitrogen (N) uptake strategies during vegetation recovery is essential for restoring and rehabilitating degraded ecosystems. However, there are few studies on plant N uptake strategies in karst regions. In this study, space-for-time substitution was used to investigate the dynamic changes in plant N uptake strategies during vegetation restoration. Grassland, shrub–grassland, shrubland, and woodland naturally recovering in karst ecosystems were chosen as the research objects. The dominant species at each stage were investigated. Dominant plant N uptake rates were measured using the ¹⁵N labeling technique, and plant root functional traits and available soil N were determined. Our results showed that soil inorganic N content and composition varied significantly with vegetation recovery. In early vegetation recovery stages, the soil inorganic N content was low and dominated by ammonium (NH₄⁺), while in the late stages, soil inorganic N content increased, and nitrate (NO₃⁻) became the dominant form. In early vegetation recovery stages, dominant plants preferentially absorbed NH₄⁺, contributing to 90.3%–98.5% of the total N uptake. With vegetation recovery, plants increased the NO₃⁻ uptake ratio from 1.48%–9.42% to 30.1%–42.6%. Additionally, the root functional traits of dominant plants changed significantly during vegetation recovery. With vegetation recovery, specific root lengths and specific root areas decreased, while root N content and plant N uptake rates increased. In summary, plants developed N uptake strategies coordinated with soil N supply by modifying root functional traits following vegetation recovery in karst regions. Full article

Vegetation plays an important role in carbon sequestration in terrestrial ecosystems and is affected by climate change and human activities. As a major factor affecting vegetation growth, the role of soil moisture in the impacts of climate change on vegetation is not well understood. Therefore, the effects of climate change on net primary productivity (NPP) may be underestimated. In this study, we analyzed the spatial distribution of NPP and land use degree comprehensive index (LDCI) in China from 2001 to 2020. The actual and relative contributions of climate change and human activities to NPP variation were explored. The findings indicated that NPP trended upward in 73.12%, 66.78%, and 81.34% of woodland, grassland, and cropland areas, respectively. Most of the woodland and grassland showed a decreasing trend in LDCI, while 48.63% of the cropland showed an increasing trend. The positive joint effects of climate change and human activities increased the NPP of woodlands, grasslands, and croplands by 42.83%, 53.49%, and 45.22%, respectively. Human activities (55.04%) contributed more to NPP than did climate change (44.96%). Analyzing the response of NPP (woodlands, grasslands, and croplands) to climate change and human activities in China is conducive to taking more targeted measures for different land use types to increase carbon sinks in terrestrial ecosystems. Full article

The semi-arid region of North China has undergone extensive afforestation to prevent land degradation. Although afforestation was considered an effective way to improve soil water retention, the mechanism by which it affects soil hydraulic properties remained uncertain. In this study, soil water retention curve (SWRC), soil water-stable aggregates, and other soil physicochemical properties were determined in short-term abandoned cropland (AC), shrubland (SL), and woodland (WL) that had been converted from cropland for 1, 8, and 24 years, respectively. Pearson correlation analysis and partial least-squares structural equation modeling methods were used to identify the main factors affecting soil hydraulic properties. Results showed that the SWRCs of all three land uses were well-fitted by a double-exponential model. The WL and SL land uses exhibited higher soil field capacity (0.33–0.37 cm³ cm⁻³), wilting point (0.20–0.23 cm³ cm⁻³), and available water content (0.13–0.15 cm³ cm⁻³). Surface soil exhibits a more pronounced trend in water retention capacity changes compared to subsoil under vegetation restoration. The WL and SL land uses showed more soil macroaggregates and intra-aggregate pores at surface layers, which mainly explained the variations in hydraulic properties. The main factors influencing soil hydraulic properties were soil aggregates, matrix and structural porosity, soil organic carbon (SOC), and soil bulk density (BD). Overall, afforestation can improve soil hydraulic properties and could be an effective practice for soil and water conservation in the semi-arid region of North China. Full article

The inherent spatial heterogeneity of land types often leads to a class imbalance in remote sensing-based classification, reducing the accuracy of minority class detection. Consequently, current land use datasets are often inadequate for the specific needs of soil erosion studies. In response to the need for soil conservation in dry–hot valley regions, this study integrated multi-source remote sensing imagery and constructed three high-precision imbalanced sample datasets on the Google Earth Engine (GEE) platform to perform land use classification. The degree of class imbalance was quantified using the imbalance ratio (IR), and the impact of sample imbalance on the classification accuracy of different land use types in a typical dry–hot valley was analyzed. The results show that (1) Feature selection significantly improved both classification accuracy and computational efficiency. The period from February to April each year, between 2018 and 2023, was identified as the optimal time window for land use classification in dry–hot valleys. (2) Constructing composite images over longer time scales enhanced classification performance: using a 2020 annual composite image combined with a Gradient Tree Boosting classifier yielded the highest accuracy, indicating that longer temporal synthesis improves classification results. (3) The effect of class imbalance on classification accuracy varied by land type: woodland (the majority class) was least affected by imbalance, whereas minority classes such as cultivated land, garden plantations, and grassland were highly sensitive to imbalance. In imbalanced scenarios, minority classes are prone to omission errors, leading to notable accuracy declines; producer’s accuracy (PA) decreased by 46%, 42%, and 25% for cultivated land, garden plantations, and grassland, respectively, as IR increased (with PA dropping faster than user’s accuracy, UA). Cultivated land was especially sensitive and frequently overlooked under high imbalance conditions compared to gardens and grasslands. Despite overall accuracy improving with higher IR, the accuracy of these minority classes dropped significantly, underscoring the importance of addressing the class imbalance in land use classification for erosion-prone areas. Full article

The purpose of this study was to evaluate the effects of different nitrogen (N), phosphorus (P), and potassium (K) fertilization ratios on the carbon (C), N, and P contents and their ecological stoichiometric characteristics in the leaf–soil–microbial system of Sapindus saponaria and elucidate their relationship with yield. A “3414” experimental design was employed in a 6-year-old Sapindus saponaria woodland located in Fujian Province of China. Fourteen N–P–K fertilization treatments with three replicates were established. Leaf, soil, and microbial samples were collected and analyzed for C, N, and P contents. Redundancy Analysis (RDA), Partial Least Squares Path Modeling (PLS–PM), and the entropy-weighted technique of ranking preferences by similarity to optimal solutions (TOPSIS) were utilized to assess the relationships among variables and determine optimal fertilization strategies. It was found through research that different fertilization treatment methods have a significant impact on both the soil nutrient content and the C, N, and P contents of soil microorganisms. Compared with the control group, soil organic C, total N, and total P, and microbial C, N, and P contents increased by 14.25% to 52.61%, 3.90% to 39.84%, 9.52% to 150%, 6.65% to 47.45%, 11.84% to 46.50%, and 14.91% to 201.98%, respectively. Results from Redundancy Analysis (RDA) indicated that soil organic C, total N, and total P exerted a significant influence on the leaf nutrients. PLS-PM demonstrated that fertilization indirectly affected leaf nutrient accumulation and yield by altering soil properties, with soil total phosphorus and leaf phosphorus being key determinants of yield. Additionally, soil microbial entropy impacted yield by regulating microbial biomass stoichiometric ratios. The entropy-weighted TOPSIS model identified the N₂P₂K₂ treatment (600 kg/ha N, 500 kg/ha P, and 400 kg/ha K) as the most effective fertilization strategy. Optimizing N–P–K fertilization ratios significantly enhances leaf nutrient content and soil microbial biomass C, N, and P, thereby increasing Sapindus saponaria yield. This research clarifies the underlying mechanisms through which fertilization exerts an impact on the C–N–P stoichiometry within the leaf–soil–microbial system. Moreover, it furnishes a scientific foundation for the optimization of fertilization management strategies in Sapindus saponaria plantations. Full article

Research on woodland ecosystem services is the premise of the formulation of regional woodland policies and ecological protection measures in a new round of woodland protection utilization planning. Based on remote-sensing images and socioeconomic data, this study used the InVEST model, geographical detectors, Spearman correlation analysis, and a coupling coordination degree model to evaluate the spatiotemporal changes, driving factors, and trade-off/synergies relationship of habitat quality (HQ), soil conservation (SC), water conservation (WC), and carbon storage (CS) in the woodland of Zhangjiajie City in 1995, 2005, 2015, and 2022. The results show the following: (1) HQ significantly decreased, SC and WC fluctuated and decreased, and CS continued to increase. (2) Natural factors were predominant, and other factors and natural factors interact to increase the driving effect. (3) The four services were dominated by weak synergy, but SC and CS turned into weak trade-offs in 2022. These research results can provide theoretical support for the optimization of the tourism development model, the formulation of ecological compensation policies, and the high-quality sustainable development of woodland in Zhangjiajie City, and provide a case study of the ecological management of world natural heritage sites. Full article

Ecological risk evaluation is a prerequisite for the rational allocation of land resources, which is of great significance for safeguarding ecosystem integrity and achieving ecological risk prevention and control. However, existing research lacks analysis of the ecosystem state after land use simulation within the restricted conversion zone, making it impossible to determine whether ecological risks have been mitigated under these constraints. Therefore, we selected the Dianchi basin as the study area, extracted the ecological defense zone as the restricted conversion zone, and used the PLUS (Patch-generating Land Use Simulation) model to simulate land use for 2030 under multiple scenarios. We then evaluated ecological risks based on landscape pattern indices, and analyzed ecological risks under multiple scenarios with and without the restricted conversion zone. By comparing ecological risks across scenarios with and without constraints, we clarified the critical role of ecological risk evaluation in the rational allocation of land resources. The results show the following: (1) The ecological defense zone was obtained by overlaying no-development zones (such as forest parks and nature reserves), areas of extreme importance in the evaluation of water resource protection, soil and water conservation, and biodiversity, as well as areas of extreme importance in the evaluation of soil and water erosion and rocky desertification sensitivity. (2) Cultivated land and woodland cover significant portions of the Dianchi basin. Overall, ecological risk deterioration was more pronounced in the economic scenario (ES), while the ecological scenario (PS) exhibited lower ecological risk compared to the natural scenario (NS). (3) After importing the ecological defense zone into the PLUS model as the restricted conversion zone for land use simulation, ecological risks in all scenarios showed a trend of improvement. The improvement trend was strongest in the NS, followed by the PS, and weakest in the ES. The results of this study can help to identify the most suitable land use planning model and provide a more effective strategy for ecological risk prevention and control. Full article

Microplastic (MP) pollution has raised global concerns, and biodegradable plastics have been recommended to replace conventional ones. The “plastisphere” has been considered a hotspot for the interactions among organisms and environments, but the differences in the properties of soil microbial communities in the plastisphere of conventional and biodegradable MPs remain unclear. This in situ experiment was conducted to compare the diversity and structure of the bacterial community in the plastisphere of conventional MPs (polyethylene [PE]) and biodegradable MPs (polylactic acid [PLA]) in vegetable fields, orchards, paddy fields, and woodlands. It was discovered that the bacterial α-diversity within the plastisphere was significantly lower than that in the soil across all land use. Significant differences between plastic types were only found in the vegetable field. Regarding the community composition, the relative abundances of Actinobacteriota (43.2%) and Proteobacteria (70.9%) in the plastisphere were found to exceed those in the soil, while the relative abundances of Acidobacteriota (45.5%) and Chloroflexi (27.8%) in the soil were significantly higher. The complexity of the microbial network within the plastisphere was lower than that of the soil. Compared with the soil, the proportion of dispersal limitation in the PLA plastisphere significantly decreased, with the greatest reduction observed in the vegetable field treatment, where it dropped from 57.72% to 3.81%. These findings indicate that different land use types have a greater impact on bacterial community diversity and structure than plastics themselves, and that biodegradable MPs may pose a greater challenge to the ecological function and health of soil ecosystems than conventional MPs. Full article

Ecological restoration projects in the Loess Plateau have significantly altered the underlying surface, which has profoundly affected the regional water cycle. In the context of the ongoing climate change, quantitatively identifying the factors influencing runoff changes and simulating runoff responses to various land management policies are essential for achieving sustainable development in arid/semi-arid regions. Daily hydrological and meteorological data from 1981 to 2020 along with the SWAT model were employed to analyze the attribution of runoff changes in the Yanhe River basin and simulate runoff responses under different climate and land-use scenarios. The results show the following: (1) the improvement of the underlying surface conditions appeared to be the leading factor of runoff retention, with a contribution of 81.21%, while the influence of climate change on runoff was minimal; (2) woodland generally exhibited superior performance in retaining runoff compared to grassland under diverse climate conditions; (3) converting farmland on slopes between 15 and 25 degrees into woodland and farmland on slopes exceeding 25 degrees into grassland demonstrated to be a more effective approach to controlling soil erosion; (4) it is recommended that a balance between water resource utilization and the extent of afforestation should be considered concurrently in future ecological restoration. Full article

This study investigates the diversity and distribution of root endophyte fungi and bacteria across Festuca and Lolium grasses, including open-grassland and forest species. The species examined include perennials such as Festuca arundinacea, F. gigantea, F. pratensis, Lolium perenne, and L. perenne × F. gigantea hybrids and the annuals L. temulentum and L. multiflorum. A total of 21 fungal species (60 isolates) and 26 bacterial taxa (59 isolates) were recovered in the culture (PDA medium for fungi and LB for bacteria) from the root cuttings of these grasses. Microdochium bolleyi fungi and Bacillus sp. bacteria were the most prevalent endophytes, with each being identified in five of the seven plant species examined. The annuals L. multiflorum and L. temulentum exhibited a higher abundance of endophytes than that in their perennial relatives, suggesting the benefits of microbial associations in supporting their short life cycles. The woodland F. gigantea demonstrated the highest fungal endophyte diversity, with six species identified. In contrast, the open-grassland perennials F. arundinacea, F. pratensis, and L. perenne hosted only one to two species. Two Basidiomycota, Coprinellus disseminatus and Sistotrema brinkmannii, were exclusively obtained from the roots of the forest grass F. gigantea. Notably, the open-grassland perennial F. arundinacea exhibited the highest bacterial diversity, with nine species present. However, it showed the lowest fungal diversity, with only one species detected. Overall, our study reveals distinct patterns of fungal and bacterial endophyte diversity in the roots of Festuca and Lolium grasses, with variations linked to host species, growth type traits, and ecological adaptations. Among the root-derived endophytes isolated, several fungi and bacteria are potential candidates for plant growth promotion and biocontrol. Therefore, the findings of this study provide potential implications for improved grassland management and crop breeding strategies aimed at specific climate and/or soil conditions. Full article

Accurate, real-time, and multi-scale soil water content (SWC) monitoring is crucial for understanding terrestrial energy, water, and nutrient cycles. This study assesses the potential of a portable cosmic-ray neutron sensor (CRNS) backpack for measuring SWC in a Mediterranean mountain agroforestry system. Seven field surveys were conducted in northern Spain, covering nine control points under woodland and cropland. CRNS data were compared with in situ SWC measurements from an SM-200 field probe and the NDMI index derived from Sentinel-2 imagery. The results show that the CRNS backpack effectively captures spatial and temporal SWC variations. The CRNS method demonstrated advantages over point-scale sensors by providing integrated measurements at an intermediate scale, while Sentinel-2 data offered valuable insights into moisture variability through vegetation response. The moderate correlations observed among the three methods highlight the complementarity of these approaches for soil moisture monitoring in heterogeneous landscapes. This work underscores the potential of mobile CRNS sensor as a practical tool for field-scale SWC assessment in Mediterranean mountain agroforestry systems, offering new opportunities for cropland and water management in similar landscapes. Full article