Leaf and root litter decomposition has been a major research focus. However, the possible effects of belowground microbial community structure and diversity on this process are poorly understood. Understanding the biochemical mechanisms controlling aboveground decomposition processes is important to predict the changes of soil carbon and nutrient cycling in response to changes of forest management regimes. Here, we explore the biochemical controls of leaf and fine root decomposition in three subtropical plantations (Ford Erythrophleum (Erythrophleum fordii Oliver), Masson Pine (Pinus massoniana Lamb.)), and a mixed plantation containing both species) using the litterbag method, and soil microbial communities were determined using phospholipid fatty acid profiles. Overall, leaves decomposed more rapidly than fine roots, potentially due to the faster degradation of their cellulose component, but not lignin. In addition, leaf and fine root decomposition rates varied among plantations, being higher in E. fordii and lower in P. massoniana. Substrate quality such as N, Ca, lignin concentration, and C/N ratio were responsible for the decomposition rate changes among plantation types. Moreover, we used redundancy analysis to examine the relationships between litter decomposition and soil microbial community composition and diversity. Results revealed that actinobacteria and arbuscular mycorrhizal fungi community were the key determinants affecting leaf and fine root litter decomposition, respectively. Our work demonstrates that litter decomposition was linked to substrate quality and to the structure of soil microbial communities, and evidences the probable role of E. fordii in increasing soil nutrient availability, especially N, P and Ca. Additional data on phospholipid fatty acid (PLFA) or DNA marker groups within the litterbags over time may provide insights into litter decomposition dynamics, which represents potential objectives for future long-term decomposition studies.

The land-use change is a major determinant influencing ecosystem carbon (C) patterns and nutrient cycling in subalpine forests in the Eastern Tibetan Plateau. While some results have been obtained in relation to the influence of land-use change on aboveground components, less is known about the belowground microbial communities and related processes. We assessed the structure and function of soil microbial communities following land-use change from old-growth forest (OF) to secondary forest (SF), plantation forest (PF), and grassland (GL) in the Eastern Tibetan Plateau, China. Phospholipid fatty acid profiles and enzyme activity analysis were used to determine the composition and activities of microbial communities, respectively. Significant differences in physicochemical characteristics, microbial communities, and extracellular enzyme activities in soils under different land uses were observed in this study. pH and total nitrogen (TN) in OF and SF were significantly higher than in GL. PF showed the highest soil organic C (SOC), and significantly higher than in GL. Total phosphorus (TP) and C/N ratio in PF were significantly higher than the other land-use types. OF and PF had significantly higher anaerobic bacteria than in GL. The actinobacteria in SF was significantly higher than in PF. The saprotrophic and ectomycorrhizal (SEM) fungi was significantly lower in GL than the other land-use types. Total microbial biomass and β-glucosidase activities were significantly higher in OF and SF than in GL. GL had significantly higher polyphenoloxidase activities than in OF and PF. Anaerobic bacteria, arbuscular mycorrhizal fungi and SEM fungi were positively correlated with SOC and TP, Gram+ bacteria were correlated with C/P and N/P ratio. N-acetylglucosaminidase activity was negatively correlated with anaerobic bacteria, while polyphenoloxidase activity was positively related to actinobacteria. Furthermore, redundancy analysis revealed that the microbial community composition was primarily regulated by TN and pH. This suggested that altered land-use type initiated changes in the physicochemical characteristics of the soils, which affected the composition of microbial communities and microbial enzyme activities related to nutrient cycling in this area. This provides a scientific basis for the influence mechanism of land use on composition and function of microbial communities, as well as the rational utilization and management of land resources.

Low light intensity can lead to a decrease in photosynthetic capacity. However, could N-fixing species with higher leaf N contents mitigate the effects of low light? Here, we exposed seedlings of Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Castanopsis hystrix and Betula alnoides (non-N-fixing trees) to three irradiance treatments (100%, 40%, and 10% sunlight) to investigate the effects of low irradiance on leaf structure, leaf N allocation strategy, and photosynthetic physiological parameters in the seedlings. Low irradiance decreased the leaf mass per unit area, leaf N content per unit area (N_area), maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max), light compensation point, and light saturation point, and increased the N allocation proportion of light-harvesting components in all species. The studied tree seedlings changed their leaf structures, leaf N allocation strategy, and photosynthetic physiological parameters to adapt to low-light environments. N-fixing plants had a higher photosynthesis rate, N_area, V_cmax, and J_max than non-N-fixing species under low irradiance and had a greater advantage in maintaining their photosynthetic rate under low-radiation conditions, such as under an understory canopy, in a forest gap, or when mixed with other species.

Fine roots play a crucial role in plant survival potential and biogeochemical cycles of forest ecosystems. Subalpine areas of the Eastern Qinghai-Tibetan Plateau have experienced different forest re-establishment methods after clear-cutting primary forest. However, little is known about fine root dynamics of these forests originating from artificial, natural and their combined processes. Here, we determined fine root traits (biomass, production and turnover rate) of three subalpine forest types, i.e., Picea asperata Mast. plantation forest (artificial planting, PF), natural secondary forest (natural without assisted regeneration, NF) and P. asperata broadleaved mixed forest (natural regeneration after artificial planting, MF) composed of planted P. asperata and naturally regenerated native broadleaved species. At the soil depth of 0–30 cm, fine root biomass was the highest in PF and fine root production was the highest in NF, and both were the lowest in MF. Fine root dynamics of the three forest types tended to decrease with soil depth, with larger variations in PF. Fine root biomass and production were the highest in PF in 0–10 cm soil layer but were not significantly different among forest types in the lower soil layers. There were positive correlations between these parameters and aboveground biomass across forest types in soil layer of 0–10 cm, but not in the lower soil layers. Fine root turnover rate was generally higher in mixed forests than in monocultures at all soil depths. In conclusion, the natural regeneration procedure after clear-cutting in the subalpine region of western Sichuan seems to be superior from the perspective of fine root dynamics.

Soil salinity is a worldwide problem that adversely affects plant growth and development. Soil salinization in Xinjiang of China is very serious. Ping’ou hybrid hazelnut, as an important ecological and economic tree species, as well as a salt-tolerant plant, has been grown in Xinjiang for over 20 years. Understanding the salt-tolerance mechanism of Ping’ou hybrid hazelnut is of great significance for the breeding of salt-tolerant varieties and the rational utilization of salinized land. In this study, ‘Liaozhen 7’, a fine variety of Ping’ou hybrid hazelnut, was selected as test material, and seedlings were treated with 0 (control), 50, 100 and 200 mM NaCl. Subsequently, the pattern of NaCl-induced fluxes of Na⁺, K⁺ and H⁺ in the root meristematic zone and their response to ion transport inhibitors were studied using non-invasive micro-test technology (NMT). Different concentrations of NaCl stress significantly increased the Na⁺ concentration in roots, while K⁺ concentration decreased first and then increased with the increase of NaCl concentration. Meanwhile, NaCl stress induced a significant decline in K⁺/Na⁺ ratio. Control and 200 mM NaCl-induced Na⁺ and K⁺ fluxes in roots exhibited an outward efflux, whereas an inward flux was observed for H⁺. Under 200 mM NaCl stress, the average rates of net Na⁺ and K⁺ efflux, as well as H⁺ influx in roots were significantly increased, which were 11.6, 6.7 and 2.3 times higher than that of control, respectively. Furthermore, pharmacological experiments showed that 200 mM NaCl-induced Na⁺ efflux; H⁺ influx was significantly suppressed by amiloride, an inhibitor of plasma membrane (PM) Na⁺/H⁺ antiporter, and sodium vanadate, an inhibitor of PM H⁺-ATPase. Net Na⁺ efflux and H⁺ influx induced by NaCl decreased by 89.9% and 135.0%, respectively. The NaCl-induced Na⁺ efflux was mediated by a Na⁺/H⁺ antiporter using energy provided by PM H⁺-ATPase. The NaCl-induced K⁺ efflux was significantly restricted by tetraethylamine chloride, a K⁺ channel inhibitor, and promoted by sodium vanadate, which decreased by 111.2% and increased by 80.8%, respectively, indicating that K⁺ efflux was regulated by depolarization-activated outward-rectifying K⁺ channels and non-selective cation channels (NSCCs). In conclusion, NMT data revealed that NaCl stress up regulated the root Na⁺/H⁺ antiporter and H⁺ pump (an activity of PM Na⁺/H⁺ antiport system) of ‘Liaozhen 7’, which compelled the Na⁺/H⁺ exchange across the PM and restricted K⁺ loss via depolarization-activated K⁺ channels and NSCCs simultaneously, thereby maintaining the K⁺/Na⁺ homeostasis and higher salt tolerance.