Xiangping Tan

Restoration plantations in subtropical regions, often established with fast-growing tree species such as Acacia auriculiformis A. Cunn. ex Benth and Eucalyptus urophylla S. T. Blake, are frequently developed on highly weathered soils characterized by phosphorus deficiency. To investigate strategies for mitigating nutrient imbalances in such ecosystems, a long-term (≥13 years) fertilization experiment was designed. The experiment involved three fertilization regimes: nitrogen fertilizer alone (N), phosphorus fertilizer alone (P), and a combination of nitrogen and phosphorus (NP) fertilizers. The objective of this study was to investigate the effects of long-term fertilization practices on soil quality in subtropical plantations using a soil quality index (SQI). Consequently, all conventional soil physical, chemical, and biological indicators associated with the SQI responses to long-term fertilization treatments were systematically evaluated, and a principal component analysis (PCA) was conducted, along with a literature review, to develop a minimum dataset (MDS) for calculating the SQI. Three physical indicators (silt, clay, and soil water content), three chemical indicators (soil organic carbon, inorganic nitrogen, and total phosphorus), and two biological indicators (microbial biomass carbon and phosphodiesterase enzyme activity) were finally chosen for the MDS from a total dataset (TDS) of eighteen soil indicators. This study shows that the MDS provided a strong representation of the TDS data (R² = 0.81), and the SQI was positively correlated with litter mass (R² = 0.37). An analysis of individual soil indicators in the MDS revealed that phosphorus addition through fertilization (P and NP treatments) significantly enhanced the soil phosphorus pool (64–101%) in the subtropical plantation ecosystem. Long-term fertilization did not significantly change the soil quality, as measured using the SQI, in either the Acacia auriculiformis (p = 0.25) or Eucalyptus urophylla (p = 0.45) plantation, and no significant differences were observed between the two plantation types. These findings suggest that the MDS can serve as a quantitative and effective tool for long-term soil quality monitoring during the process of forest sustainable management.

The Qinghai–Tibet Plateau, a region susceptible to global change, stores substantial amounts of soil organic carbon (SOC) in its alpine grassland. However, little is known about how SOC is regulated by soil microbial communities, which vary with elevation, mean annual temperature (MAT), and mean annual precipitation (MAP). This study integrates phospholipid fatty acid (PLFA) analysis to simultaneously resolve microbial biomass, community composition, and membrane lipid adaptations along an elevational gradient (2861–5090 m) on the Qinghai–Tibet Plateau. This study found that microbial PLFAs increased significantly with rising MAP, while the relationship with MAT was nonlinear. PLFAs of different microbial groups all had a positive effect on SOC storage. At higher altitudes (characterized by lower MAP and lower MAT), Gram-positive bacteria dominated bacterial communities, and fungi dominated the overall microbial community, highlighting microbial structural adaptations as key regulators of carbon storage. Saturated fatty acids with branches of soil microbial membrane dominated across sites, but their prevalence over unsaturated fatty acids decreased at high elevations. These findings establish a mechanistic link between climate-driven microbial community restructuring and SOC vulnerability on the QTP, providing a predictive framework for carbon–climate feedbacks in alpine systems under global warming.

Restoration plantations in subtropical regions, often established with fast-growing tree species like Acacia auriculiformis and Eucalyptus urophylla, are frequently developed on highly weathered soils characterized by natural phosphorus (P) deficiencies. To investigate strategies for mitigating nutrient imbalances in such ecosystems, a long-term (≥ 13 years) fertilization experiment was designed. The experiment involved three fertilization regimes: nitrogen (N) fertilizer alone, P fertilizer alone and a combination of N and P (NP) fertilizer. The objective of this study was to investigate the effects of long-term fertilization practices on soil quality in subtropical plantations through a soil quality index (SQI). Principal component analysis (PCA) was used along with a literature review to select a minimum dataset (MDS) to calculate SQI. Three physical indicators (silt, clay, soil water content), three chemical indicators (soil organic carbon, inorganic nitrogen, total phosphorus), and two biological indicators (microbial biomass carbon, phosphodiesterase enzyme activity) were chosen as MDS from a total dataset (TDS) of eighteen soil indicators. Our study showed that long-term fertilization did not significantly change the soil quality as measured by SQI in both Acacia auriculiformis (p=0.25) and Eucalyptus urophylla (p=0.45) plantations. However, investigations of individual soil indicators in the MDS suggested that P addition through fertilization (P and NP regimes) strongly increases the P pool in the subtropical plantation soil. The MDS provided a strong representation of the TDS data (R2=0.81), and the SQI was positively correlated with littermass (R2=0.37). These findings suggest that the MDS can serve as a quantitative and effective tool for long-term soil quality monitoring.

Nitrogen‐rich tropical/subtropical forest soil acts as a terrestrial source of nitrous oxide (N₂O), a greenhouse gas commonly affected by soil nitrogen availability and soil moisture. However, in tropical and subtropical regions experiencing both elevated nitrogen deposition and altered precipitation regimes, it is unclear whether nitrogen deposition and precipitation regimes have interactive effects on forest soil N₂O emissions and what roles N₂O‐associated nitrifiers/denitrifiers play in these interactions. We conducted a 2 year field study in a subtropical evergreen broadleaf forest in southern China by applying four treatments: nitrogen addition (N), seasonal precipitation distribution change (PC), both nitrogen addition and seasonal precipitation distribution change (NPC) and a control (C). We found that N₂O efflux from the forest soil was significantly greater in the wet season than in the dry season, but was promoted by 77.4% by the NPC treatment only in the dry season. Soil moisture and pH decreased in the PC and N treatments, respectively. The abundance of nitrifying gene AOA‐amoA and denitrifying gene nosZ in the wet season and the abundance of denitrifying gene nirK in the dry season differed significantly among the four treatments. A structural equation model showed that precipitation change was more important than nitrogen addition in affecting soil properties (e.g., moisture and pH) and N₂O‐associated nitrifiers/denitrifiers, while soil nirK‐ and nosZ‐denitrifiers were the dominant functional microbes in regulating N₂O emissions. The results support predictions of future nitrogen losses (N₂O) in subtropical forests in the context of interactions between elevated nitrogen deposition and altered precipitation regimes.

Background: Grazing exclusion is a practical approach to restore vegetation in degraded grasslands and enhance soil organic carbon (SOC) sequestration. However, the dynamics and drivers of SOC in grasslands after grazing exclusion have not been well documented, especially in ecosystems with cold climates. Methods: Here, we established 14 paired treatments (grazing exclusion vs. free-grazing) along a 600-km transect in the northeastern zone of the Qinghai-Tibet Plateau. After six years, we analyzed vegetation biomass dynamics and measured the soil physicochemical properties and organic C concentration across three depths (0–10, 10–20, and 20–30 cm). Results: Grazing exclusion significantly increased above- and belowground biomass (139.85% and 43.30%, respectively), pH (1.38%), total phosphorus (3.29%), nitrate nitrogen (18.03%), and ammonium nitrogen (17.81%), but significantly decreased soil bulk density (2.43%) and clay content (10.49%), particularly in 0–30 cm. Specifically, SOC concentrations positively responded to grazing exclusion (0–10 cm) in 9 of the 14 sites evaluated. The effects of grazing exclusion on SOC concentrations were significantly higher in areas with a mean annual temperature (MAT) below 0 °C compared to those in sites with a high MAT (> 0 °C). The SOC concentrations significantly correlated with the mean annual precipitation (MAP) in both treatments, but these correlations diminished with increasing soil depth. Ridge regression analysis showed that soil chemical properties (e.g., total nitrogen and phosphorus) positively influenced SOC accumulation, while MAT negatively influenced it after grazing exclusion. Path analysis further revealed that MAT indirectly regulated SOC dynamics via soil chemical properties. Conclusions: Our study highlights that grazing exclusion results in an asynchronous SOC and plant biomass accumulation and may be more beneficial for SOC sequestration in Qinghai-Tibet Plateau grasslands with lower temperatures. Also, humid climates promote SOC concentration in alpine grasslands. These results could help develop management practices and policies that promote sustainable grassland management.

Anthropogenic inputs of nitrogen (N) and phosphorus (P) to terrestrial ecosystems alter soil nutrient cycling. However, the global‐scale responses of soil P fractions to N and P inputs and their underlying mechanisms remain elusive. We conducted a global meta‐analysis based on 818 observations of soil P fractions from 99 field N and P addition experiments in forest, grassland, and cropland ecosystems ranging from temperate to tropical zones. Our global meta‐analysis revealed distinct responses of soil P fractions to N and P enrichment. For studies using the Chang and Jackson inorganic (Pi) method, we found that high N addition promoted the transformation of immobile Pi fractions into Ferrum/Aluminum‐bound Pi and available Pi in surface soils through soil acidification. However, this acid‐induced transformation of Pi fractions by N addition was observed only in Calcium‐rich soils, while in acidic soils, further acidification led to increase P binding. In contrast, additions of P alone or combined with N significantly increased all soil Pi fractions. Regarding the Hedley P fractions, N addition generally decreased labile organic P by enhancing soil acid phosphatase activity. The responses of other P fractions were influenced by soil pH, fertilization rates, ecosystem type, and other factors. P addition increased most soil P fractions. Overall, both P fractionation methods consistently demonstrate that N inputs deplete soil P and accelerate P cycling, while P inputs increase most soil P fractions, alleviating P limitation. These findings are crucial for predicting the effects of future atmospheric N and P deposition on P cycling processes.