Search Results (5)

Afforestation plays a critical role in ecosystem restoration and carbon sequestration. However, there continues to be insufficient knowledge about the long-term effects of different tree species on the forest soil in central subtropical China. In this study, five indigenous afforestation tree species commonly used in the region, including Bretschneidera sinensis, Liriodendron chinense, Schima superba, Phoebe bournei, and Cunninghamia lanceolata, were selected to explore their long-term effects on the forest soil. The soil’s physicochemical properties, organic carbon content, enzyme activity, and respiration were investigated. Our results revealed significant differences in the soil physicochemical properties, enzyme activity, organic carbon content, and soil respiration among the different tree species even with the same tree species types. Broad-leaved species, particularly L. chinense and P. bournei, exhibited superior soil physicochemical properties, higher amounts of organic carbon contents, enzyme activity, and soil respiration compared to coniferous species C. lanceolata. Notably, for the two studied evergreen tree species, P. bournei seemed to improve the forest soil quality more than S. superba. Hence, increasing the proportion of broad-leaved tree species may have a beneficial effect on the soil’s physicochemical properties and microecology. Furthermore, considering tree species’ compositions in afforestation will help to optimize soil quality and ecosystem health. Full article

Bretschneidera sinensis, the sole species of Bretschneidera, belonging to the family Akaniaceae, is a tertiary paleotropical flora. It is considered an endangered species by the International Union for Conservation of Nature (IUCN). It has an important protective and scientific value. The study of its seed dormancy and germination mechanisms contributes to better protection. In this study, the dormancy of fresh mature B. sinensis seeds released via low-temperature wet stratification was studied. In addition, the endogenous phytohormone levels, antioxidant enzyme activity, soluble sugar content, and the key metabolic enzyme activities of seeds at different stratification time nodes were determined. The goal was to analyze the mechanisms of seed dormancy release and germination comprehensively. Results show that low-temperature wet stratification under 5 °C can release seed dormancy effectively. During the seed dormancy release, the seed germination rate was positively correlated with soluble sugar, GA₃, and IAA levels, as well as G-6-PDH, SOD, POD, CAT, and APX activity, but it was negatively correlated with MDH activity and ABA content. These imply that dormancy release might be attributed to the degradation of endogenous ABA and the oxidation of reactive oxygen species induced by low-temperature wet stratification. GA₃, IAA, and the metabolism of energy substrates may be correlated with the induction and promotion of germination. Full article

Aquaporins (AQPs), a type of intrinsic membrane proteins that transport water and small solutes across biological membranes, play crucial roles in plant growth and development. This study presents a first genome-wide identification and comparative analysis of the AQP gene family in papaya (Carica papaya L.), an economically and nutritionally important fruit tree of tropical and subtropical regions. A total of 29 CpAQP genes were identified, which represent five subfamilies, i.e., nine plasma intrinsic membrane proteins (PIPs), eight tonoplast intrinsic proteins (TIPs), seven NOD26-like intrinsic proteins (NIPs), two X intrinsic proteins (XIPs), and three small basic intrinsic proteins (SIPs). Although the family is smaller than the 35 members reported in Arabidopsis, it is highly diverse, and the presence of CpXIP genes as well as orthologs in Moringa oleifera and Bretschneidera sinensis implies that the complete loss of the XIP subfamily in Arabidopsis is lineage-specific, sometime after its split with papaya but before Brassicaceae–Cleomaceae divergence. Reciprocal best hit-based sequence comparison of 530 AQPs and synteny analyses revealed that CpAQP genes belong to 29 out of 61 identified orthogroups, and lineage-specific evolution was frequently observed in Brassicales. Significantly, the well-characterized NIP3 group was completely lost; lineage-specific loss of the NIP8 group in Brassicaceae occurred sometime before the divergence with Cleomaceae, and lineage-specific loss of NIP2 and SIP3 groups in Brassicaceae occurred sometime after the split with Cleomaceae. In contrast to a predominant role of recent whole-genome duplications (WGDs) on the family expansion in B. sinensis, Tarenaya hassleriana, and Brassicaceae plants, no recent AQP repeats were identified in papaya, and ancient WGD repeats are mainly confined to the PIP subfamily. Subfamily even group-specific evolution was uncovered via comparing exon–intron structures, conserved motifs, the aromatic/arginine selectivity filter, and gene expression profiles. Moreover, down-regulation during fruit ripening and expression divergence of duplicated CpAQP genes were frequently observed in papaya. These findings will not only improve our knowledge on lineage-specific family evolution in Brassicales, but also provide valuable information for further studies of AQP genes in papaya and species beyond. Full article

Increasing evidence has shown that introducing broadleaved trees into coniferous plantations can regulate hydrologic stores and fluxes; however, the effects and regulatory mechanisms of species mixing on the water conservation capacity of the litter–soil continuum remain poorly understood, and differences among tree species may appear. Herein, we investigated and compared the water conservation capacity of the litter layer (semi-decomposed and decomposed layer) and soil layer (0–100 cm) in a monoculture plantation (Pinus massoniana) and five mixed plantations (Pinus massoniana mixed with Cercidiphyllum japonicum, Manglietia chingii, Camellia oleifera, Michelia maudiae, and Bretschneidera sinensis) and comprehensively considered their potential influencing factors. We discovered that the identity of broadleaved tree species significantly affected the water storage of litter and soil in the mixed plantations (p < 0.05). The effective water-holding capacity of the litter (13.39 t·ha⁻¹) was low due to the coniferous litter’s simple structure and challenging breakdown, despite the fact that the litter stock of the monoculture plantation was substantially larger than that of the mixed plantation (14.72 t·ha⁻¹). Introducing deep-rooted tree species (e.g., Bretschneidera sinensis and Camellia oleifera) into Pinus massoniana farmsteads improved the soil-pore structure and aggregate stability, thereby significantly increasing the 0–100 cm soil water storage. Furthermore, we found that litter storage, soil organic carbon, and litter thickness, as key influencing factors, have complex effects on the water storage of the litter–soil continuum. Generally, these findings demonstrated that mixed plantations can potentially improve the water conservation capacity of the litter–soil system. Nevertheless, special attention should be given to the complementarity between tree species combinations. Full article

Droughts are becoming more frequent and intense, and the nitrogen deposition rate is increasing worldwide due to human activities. Young seedlings of Bretschneidera sinensis Hemsl. are susceptible to mortality under drought conditions because their root tips have few root hairs. We studied the effect of nitrogen deposition on the physiological characteristics of two-year-old B. sinensis seedlings under drought stress. Seedlings were grown under no nitrogen deposition (control; N0), low nitrogen deposition (N30, 30 kg·hm⁻² year⁻¹), medium nitrogen deposition (N60, 60 kg·hm⁻² year⁻¹), and high nitrogen deposition (N90, 90 kg·hm⁻² year⁻¹), and were subjected to either the normal watering regime (NW) or drought stress (DW). Under DW, the relative conductivity (RC) of seedlings receiving N60 was not significantly different from that of N0 seedlings, and the RC of seedlings receiving N90 was significantly higher than that of N0 seedlings. Under 10 d DW, N60 treatment increased antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and content of soluble protein, chlorophyll a and a + b, with POD activity and soluble protein significantly increasing by 18.89% and 34.66%, respectively. Under DW, the proline (PRO) content of seedlings treated with N90 increased. Our data suggested that moderate nitrogen deposition could alleviate drought stress by decreasing cell membrane permeability, reducing cell membrane peroxidation, increasing the content of osmoregulatory substances, and reducing the tendency for chlorophyll to decline, whereas high nitrogen deposition increased the sensitivity of B. sinensis seedlings to drought stress and aggravated the degree of stress, thereby affecting growth. Full article