Prolonged drought results in serious ecological consequences in forest ecosystems, particularly for soil microbial communities. However, much is unknown about soil microbial communities in their response to long-term consecutive droughts in warm-temperate forests. Here, we conducted a 7-year manipulated throughfall reduction experiment (TFR) to examine the responses of bacterial and fungal communities in terms of richness and networks. Our results show that long-term TFR reduced bacterial, but not fungal, richness, with rare bacterial taxa being more sensitive to TFR than dominant taxa. The bacterial network under the TFR treatment featured a simpler network structure and fewer competitive links compared to the control, implying weakened interactions among bacterial species. Bacterial genes involved in xenobiotic biodegradation and metabolism, and lignin-degrading enzymes were enhanced under TFR treatment, which may be attributed to TFR-induced increases in fine root biomass and turnover. Our results indicate that soil bacterial communities are more responsive than fungi to long-term TFR in a warm-temperate oak forest, leading to potential consequences such as the degradation of recalcitrant organics in soil.

Agroforestry ecosystems are an efficient strategy for enhancing soil nutrient conditions and sustainable agricultural development. Soil extracellular enzymes (EEAs) are important drivers of biogeochemical processes. However, changes in EEAs and chemometrics in rubber-based agroforestry systems and their mechanisms of action are still not fully understood. Distribution of EEAs, enzymatic stoichiometry, and microbial nutrient limitation characteristics of rubber plantations under seven planting patterns (RM, rubber monoculture system; AOM, Hevea brasiliensis-Alpinia oxyphylla Miq; PAR, Hevea brasiliensis-Pandanus amaryllifolius Roxb; AKH, Hevea brasiliensis-Alpinia katsumadai Hayata; CAA, Hevea brasiliensis-Coffea Arabica; CCA, Hevea brasiliensis-Cinnamomum cassia (L.) D. Don, and TCA, Hevea brasiliensis-Theobroma Cacao) were analyzed to investigate the metabolic limitations of microorganisms and to identify the primary determinants that restrict nutrient limitation. Compared with rubber monoculture systems, agroforestry ecosystems show increased carbon (C)-acquiring enzyme (EEA_C), nitrogen (N)-acquiring enzyme (EEA_N), and phosphorus (P)-acquiring enzyme (EEA_P) activities. The ecoenzymatic stoichiometry model demonstrated that all seven plantation patterns experienced C and N limitation. Compared to the rubber monoculture system, all agroforestry systems exacerbated the microbial limitations of C and N by reducing the vector angle and increasing vector length. P limitation was not detected in any plantation pattern. In agroforestry systems, progression from herbs to shrubs to trees through intercropping results in a reduction in soil microbial nutrient constraints. This is primarily because of the accumulation of litter and root biomass in tree-based systems, which enhances the soil nutrient content (e.g., soil organic carbon, total nitrogen, total phosphorus, and ammonium nitrogen) and accessibility. Conversely, as soil depth increased, microbial nutrient limitations tended to become more pronounced. Partial least squares path modelling (PLS-PM) indicated that nutrient ratios and soil total nutrient content were the most important factors influencing microbial C limitation (−0.46 and 0.40) and N limitation (−0.30 and −0.42). This study presented novel evidence regarding the constraints and drivers of soil microbial metabolism in rubber agroforestry systems. Considering the constraints of soil nutrients and microbial metabolism, intercropping of rubber trees with arboreal species is recommended over that of herbaceous species to better suit the soil environment of rubber plantation areas on Hainan Island.

Overuse of chemical nitrogen (N) fertilizers leads to N leaching and soil degradation. Replacing chemical N fertilizers with organic fertilizers can enhance soil nutrition, reduce N loss, and improve soil productivity. However, the effects of combining organic and chemical fertilizers on soil N components and N transformation remain unclear. A 12-year field study included four treatments: no fertilizer (CK), chemical fertilizer alone (CF), 50% chemical N fertilizer combined with co-composted organic fertilizer (CFM), and composted (CFMC) organic fertilizer. The results showed that CFM and CFMC significantly enhanced SOC, TN, LFON, DON, NH₄⁺-N, and MIN levels compared to CF. The CFM and CFMC treatments enhanced the soil N supply capacity and N pool stability by increasing the N mineralization potential (N₀) and decreasing the N0/TN ratio. The CFM and CFMC treatments decreased net N ammonification rates by 108.03%–139.83% and 0.44%–64.91% and net mineralization rates by 60.60%–66.30% and 1.74%–30.38%, respectively. Changes in N transformation have been attributed to increased soil pH, enzyme activity, and substrate availability. These findings suggest that partial organic fertilizer substitution, particularly with co-composted organic fertilizers, is a viable strategy for enhancing soil fertility, improving soil N supply and stability, and reducing N loss in rubber plantations.

Partial organic substitution (POS) is a promising strategy to enhance soil fertility and agricultural sustainability. However, the mechanisms by which varying organic substitution ratios affect soil quality and latex yields in rubber plantations remain unclear. We conducted a two-year field experiment in a rubber plantation with six treatments: no fertilizer (CK), 100% synthetic fertilizer (NPK), and synthetic nitrogen fertilizer substituted with 25% (25 M), 50% (50 M), 75% (75 M), and 100% (100 M) manure. The results indicated that POS treatments significantly increased pH, soil organic carbon (SOC), total phosphorus (TP), total nitrogen (TN), NH₄⁺-N, enzyme activity, and leaf nutrient (C, N, and P) content compared to NPK. Compared with NPK, the soil quality (evaluated through the soil quality index, SQI) increased by 15.30–43.42% under POS across both years, with maximal values observed at 50 M (2020) and 75 M (2021); similarly, the latex yield increased by 2.10–18.60%. SOC, NO₃⁻-N,C:P ratio, TN, and pH are the key factors that influence soil quality and latex yield. Structural equation modeling indicated that fertilization and soil factors collectively explained 82% of the variation in latex yield. These results demonstrated that POS effectively alleviated soil acidity, enhanced soil quality, and improved latex productivity, with 50% manure substitution treatment (50M) identified as the optimal short-term substitution strategy in rubber plantations.

Introduction: Stem CO₂ efflux (E_c) reflects the amount of photo-assimilated carbon released back into the atmosphere and plays a critical role in the carbon balance of tree and forest ecosystems. Despite previous studies indicating that a portion of stem CO₂ originates from root respiration (R_root), the seasonal dynamics of E_c and its relationship with belowground respiration remain poorly understood, particularly in tropical regions characterized by distinct dry and wet seasons.Methods: To address this gap, we investigated E_c in tapping and non-tapped rubber trees, along with environmental factors and physiological traits (sap flow flux density, root respiration, and leaf area index) from 2018 to 2021.Results: Our results showed that tapping activity increased the E_c of rubber trees compared to non-tapped trees, with increases ranging from 10.37% to 233.66%. However, the magnitude of this increase varied between the dry and wet seasons. Although tapping enhanced the E_c, it did not alter the E_c seasonal pattern. Consequently, E_c in both tapped and non-tapped rubber trees displayed an overall single-peak pattern, with significantly lower values during the dry season compared to the wet season, suggesting growth phenology primarily regulates E_c seasonal dynamics. Structural equation modeling revealed that root respiration (R_root), sap flow flux density (F_d), and soil moisture at 50 cm depth as the primary drivers of the E_c variations during the dry season. In contrast, soil moisture at 5 cm depth and air temperature (T_a) were identified as dominant factors influencing E_c in the wet season, with belowground respiration having a negligible influence.Discussion: These results suggest that the relationship between E_c and belowground respiration is environmentally sensitive and exhibits seasonal dependency.