The soils of alpine meadows on the Tibetan Plateau act as significant carbon reservoirs and are particularly vulnerable to warming. Nevertheless, the long-term (≥20 years) warming impact on SOC composition and deep soil dynamics in alpine meadows remains unclear. This study explored the effects of two decades of warming using open-top chambers on various aspects of alpine meadow ecosystems, including plant community composition and biomass, soil physicochemical characteristics, microbial communities, and SOC content in both bulk soil and its fractions. Prolonged warming had no impact on plant-derived C inputs, as indicated by both unchanged above- and below-ground biomass, but it reduced the light fraction carbon (LF-C) in the surface soil layer (0−10 cm) by 25%, with no notable changes observed in bulk SOC or heavy fraction carbon (HF-C) in the surface soil as well as deeper soil layers (10−50 cm). Additionally, long-term warming caused a notable rise in fungal-derived residues and an increase in aromatic carbon, while concurrently decreasing alkyl carbon in the surface soils. These findings imply that prolonged warming acce-lerates the breakdown of more readily decomposable organic matter, shifting the SOC pool towards a more chemically resistant state, even though there was no net change in bulk SOC.

Tropical forests exert the largest influence on the global carbon (C) cycle and climate, and soil microorganisms play an essential role in the feedbacks of the global C cycle and climate. However, the issue of how nutrient limitation of microbial metabolism affects the soil C cycle and its responses to climate change in tropical forests remains poorly understood. Here, we investigated the elevational patterns of microbial metabolic limitations in typical tropical forests by studying ecoenzymatic stoichiometry along three elevation gradients (with an overall elevation range of 100−1400 m above sea level (a.s.l.)) in south China. Results showed that microbial metabolism in tropical forest soils was strongly limited by phosphorus (P) and increased with increasing elevation, suggesting that there was greater microbial P limitation where temperatures were lower. In contrast, microbialC limitation was relatively low and did not show a consistent elevational pattern. Temperature emerged as the most significant predictor of microbial metabolic limitations, showing a positive correlation with microbial C limitation but a negative correlation with microbial P limitation. Based on an investigation of three topical forest elevation gradients (< 1500 m a.s.l.), our findings predict that global warming may alleviate microbial P limitation while exacerbate microbial C limitation.

Ammonia-oxidizing archaea (AOA) are key drivers of soil nitrification, but how they respond to climate warming across northern China’s diverse grassland types remains unclear. To address this, we analyzed 88 soil samples from 22 sites across three northern China grassland biomes based on metagenomic data, quantifying AOA temperature sensitivity as the regression slope of diversity indicators against mean annual temperature (MAT). Our results revealed MAT as the key factor influencing the relative abundance, richness, and composition of the potential AOA community. In alpine grassland, AOA communities exhibited the highest temperature sensitivity, with the steepest slopes of community composition and relative abundance, and a unique decrease in richness. This high sensitivity may reduce the AOA community diversity and destabilize nitrogen cycling in alpine grasslands. Structural equation modeling indicated that MAT impacted AOA communities via a direct route rather than indirect routes. These findings provide a scientific basis for assessing the potential risks of climate warming on grassland nitrogen cycling and informing early-warning and management strategies.

The physicochemical protection of soil organic carbon (SOC) by iron (Fe) (hydr)oxides and clay minerals is crucial to SOC preservation. While clay minerals restrict SOC mineralization, a lack of information exists on the regulatory mechanisms by which clay minerals and their interactions with Fe (hydr)oxides regulate the priming effect (PE). Here, we quantified the PE intensities in two forest soils (i.e., a sandy loam soil and a loam soil), amended without or with Fe (hydr)oxides (goethite) at two levels. The loam soil containing higher clay minerals showed a 26% lower SOC mineralization but a 28% greater PE than the sandy loam soil. This is likely because SOC encapsulated within clay particles serves as a substrate reservoir, which can be decomposed by activated microbes following exogenous C inputs. Contrasting goethite effects on the PE in different soils were detected. High goethite addition intensified the PE in sandy loam soil, while the PE in loam soil declined at both levels of addition. The underlying mechanisms were attributed to alterations in Fe-mediated co-precipitation situation and subsequent microbial metabolism. Overall, this study demonstrates a crucial role of clay minerals in SOC stabilization, with implication for soil management with Fe (hydr)oxides.

Soil microbial necromass carbon (MNC) plays a crucial role in the persistent soil organic carbon (SOC) pool. However, the impact of long-term different water-nitrogen managements on the soil MNC in the greenhouse vegetable production (GVP) remains unclear. Using a 12-year field experiment, coupled with soil physicochemical properties, C- and nitrogen (N)-related enzymatic kinetics and microbial communities’ measurements, the impact of six different water-nitrogen managements on MNC accumulation was examined. Our study showed that MNC constituted 47.7%–71.3% of SOC, with fungal necromass carbon (FNC) contributing 4.2-fold more than bacterial necromass carbon (BNC) on average. Compared to the high irrigation and chemical nitrogen fertilizer practices, water-saving practices under the high fertilization scenario increased BNC/SOC by 18.6% after the 12-year field manipulation. The reduced water-N treatments had the highest MNC/SOC proportions with an average of >60%, which was mainlyattributed to the increased FNC/SOC. The relative importance partitioningresults showed that root biomass, N-acetylglucosaminidase and C-cellobiohydrolase enzyme kinetics were the most important regulators of FNC/SOC, BNC/SOC and MNC/SOC, respectively. The partial least squares path modeling further revealed that soil substrates (e.g., root biomass and dissolved organic carbon) directly promoted FNC/SOC while suppressing BNC/SOC, whereas microbial communities enhanced both fractions. Hence, our study highlights the divergent response of FNC and BNC to the long-term water-nitrogen management in GVP. Therefore, optimized water-nitrogen management sustains crop productivity while enhancing MNC accumulation, thereby promoting SOC persistence and advancing green sustainable development of GVP.

Soil nematodes show the highest abundance among animals on Earth, which can affect plant residue decomposition by influencing plant roots and soil microbes, thus affecting plant- and microbial-derived carbon (C) sequestration. However, the relationships between soil nematodes, plant- and microbial-derived C under long-term fertilization remain unclear. The present work performed a 15-year field fertilization experiment (including four treatments: (1) no fertilizer (CK); (2) nitrogen, phosphorus, and potassium fertilizers (NPK); (3) NPK with straw (SNPK); and (4) NPK with pig manure (MNPK)) for investigating how soil nematodes affected soil plant- and microbial-derived C by determining soil nematode, bacterial, and fungal abundances as well as amino sugar and lignin phenol contents (their biomarkers), and their associated relationships. The results revealed that SNPK treatment increased the abundances of soil bacterivores and bacteria as well as the bacterial necromass C (BNC) content. As revealed by partial least squares path modeling (PLS-PM), bacterivores showed indirect and positive impacts on BNC through influencing the abundance of bacteria. Moreover, SNPK treatment increased fungal abundance and fungal necromass C (FNC) content but did not alter fungivore abundance. FNC was significantly and positively correlated with fungal abundance and bacterivore abundance. PLS-PM revealed that BNC indirectly influenced FNC by affecting fungal abundance; thus, bacterivores play an important role in affecting FNC by affecting BNC. Moreover, all the fertilization treatments increased the lignin phenol content, which was significantly and positively correlated with the bacterivore and plant parasite abundances, indicating that the elevated bacterivore and plant parasite abundances during fertilization may contribute to the formation of plant-derived C. Overall, these findings provide insights for developing fertilization strategies that utilize nematode-mediated C pathways to enhance soil C sequestration in agricultural systems.