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In biodiverse forest ecosystems, plant diversity has been reported to increase plant-derived lignin accumulation and soil organic carbon (SOC) storage. However, little is known about the fate of lignin and its degradation dynamics from plant to soil. This process is critical for the formation of SOC, especially in natural forest ecosystems with diverse plant species. This study presents the lignin biomarker characteristics of several common plant species and in mixed litter. The study was conducted in 45 plots along a plant species diversity gradient in a subtropical forest located in southwest China. Our results demonstrate that lignin content and its biochemical characteristics in plant leaves vary among species, while different plant species also alter the content of lignin and its monomeric compounds in the litter. Lignin compounds are gradually disintegrated from plant leaf to litter and then to soil, further indicating that plant-derived lignin from plant sources contributes to the formation and accumulation of forest SOC. These findings provide novel information on the linkage between tree species diversity and lignin accumulation while indicating the role of plant-derived lignin on SOC storage. These results may be useful in predicting forest soil C dynamics in Earth system models. [ABSTRACT FROM AUTHOR]

The stability of soil organic matter (SOM) plays a critical role in soil carbon (C) dynamics under global warming. However, the factors influencing SOM stability, particularly the significance of bedrock geochemistry and its hierarchical relationship with climate and soil properties, remain poorly understood. To address this gap, we conducted a study along a large climatic gradient (Δtemperature > 9 °C) in the subtropical karst forests of southwest China, quantifying SOM stability using thermal analysis and investigating the contributions of bedrock geochemistry, climate, and soil properties. Our results showed that SOM stability was positively correlated with mineral-associated organic C (MAOC) rather than particulate organic C. Hierarchical partitioning analysis further demonstrated that bedrock geochemistry was the predominant contributor to SOM stability variance, accounting for 23.7%. Following this, soil minerals contributed to 21.1%–22.6% of the variance, the mean annual temperature to 20.3%, and microbial biomass C to 17.2%. In particular, bedrock geochemistry—specifically the presence of calcium-rich bedrock—was found to enhance SOM stability by promoting the accumulation of exchangeable calcium and calcium carbonate in soils. Additionally, high temperature improved SOM stability by increasing the content and proportion of MAOC and soil pH. These results highlight the fundamental role of bedrock geochemistry in controlling SOM stability and emphasize the importance of considering hierarchical relationships among bedrock–soil–climate interactions for evaluating soil C dynamics. [ABSTRACT FROM AUTHOR]

Lithology has such an important effect on the sustainability of soil carbon (C) pools. Forests are an important part of terrestrial C sinks; yet, it is unclear whether their soil carbon sensitivity to temperature changes is regulated by lithology, especially in karst ecosystems, which are widely distributed globally. Along a climate gradient in the subtropical region of southwest China, we compared the contents of soil organic C (SOC) and total N (TN) in karst and non-karst forests. The data were analyzed and processed using ANOVA, regression analysis, and random forest. The results showed that the karst forests had significantly higher SOC and TN contents but lower ratio of SOC to TN (C:N) than non-karst forests, mainly because of the higher soil calcium (Ca) content and microbial biomass. With rising mean annual temperature (MAT), SOC and TN contents in non-karst forests significantly decreased, whereas in karst forests they were not correlated with MAT; while, the opposite was true for C:N. In karst forests, soil Ca constrain warming induced decomposition of SOC and TN by forming stable complexes with SOM through exchangeable Ca, and by promoting aggregate stability through the role of calcium carbonate. The correlation between δ13C and the logarithm of SOC concentration also supported that conclusion. In karst forests compared to non-karst forests, soil C pools are larger and less sensitive to regional temperature change. Nevertheless, climate warming may still accelerate soil C loss in karst forests by increasing microbial C limitation. Thus, soil C sequestration potential and loss risk coexist in karst areas. The ratio of SOC to TN (C:N) is regulated through appropriate management measures in the process of karst vegetation restoration, thus promoting long-term stable sequestration of soil carbon pools. [ABSTRACT FROM AUTHOR]

[Display omitted] • Karst soils are less conducive to GRSP accumulation compared to non-karst soils. • GRSP accumulation decreases with higher temperature gradients in karst soils. • GRSP accumulation increases with higher temperature gradients in non-karst soils. • Temperature-induced changes in soil pH and fertility shape GRSP accumulation. • Lithological constraints on biotic and abiotic factors determine GRSP accumulation. Glomalin-related soil protein (GRSP) is a crucial contributor to the persistent soil carbon (C) pool. However, its response to temperature gradients is contentious due to variations in soil microorganisms, pH, and fertility. Given that soils inherit many properties from the parent lithological material, we hypothesized that bedrock lithology mediates the divergent patterns of GRSP accumulation along temperature gradients. Here, we assessed GRSP content and its contribution to soil organic C (SOC) in forest soils situated atop carbonate rocks (karst) and clastic rocks (non-karst) across a large climatic gradient (Δtemperature > 10 °C). Despite similar SOC content between karst and non-karst soils, the contents of easily extractable and total extractable GRSP, as well as their contributions to SOC, were significantly lower in both bulk soil and the mineral-associated organic matter fraction in karst soils. This discrepancy was attributed to lower plant diversity, higher soil pH, and increased soil fertility (particularly total and alkali-hydrolyzable nitrogen) in karst ecosystems. Additionally, the contribution of GRSP to SOC decreased with increasing temperature gradients in karst soils, whereas it increased in non-karst soils. As temperature gradients rose, karst soils exhibited higher pH and fertility, whereas non-karst soils showed reduced fertility. These changes resulted in contrasting GRSP accumulation patterns along the temperature gradient. Our findings underscore the necessity of considering bedrock lithology when predicting GRSP responses to temperature change and advocate for lithology-specific conservation strategies to enhance glomalin accumulation. [ABSTRACT FROM AUTHOR]

Microbial necromass carbon (MNC) is a key soil organic carbon (SOC) pool. Soil aggregates and minerals play pivotal roles in controlling soil carbon storage. Although soil minerals and aggregates are tightly linked to parent materials, it is uncertain whether the relative importance of aggregates and minerals in governing MNC varies depending on soil parent materials. In this study, we determined the MNC content in forest soils originating from two contrasting soil parent materials, namely karst (carbonate rocks) and non-karst soils (clastic rocks) across a climatic gradient in southwest China. The MNC contents (24.5 ± 0.8 mg g−1 in karst and 24.1 ± 1.8 mg g−1 in non-karst soils) and their respective contribution to SOC (43.7 ± 1.3 % in karst and 41.1 ± 1.4 % in non-karst soils) were similar between the two parent materials. In karst soils, MNC was influenced by aggregates rather than minerals, whereas the opposite was true in non-karst soils. A higher proportion of microaggregates directly increased the MNC content in karst soils, whereas greater mineral contents indirectly increased the MNC through their effects on microbial biomass carbon. The divergent effects of aggregates and minerals on MNC were predominantly attributed to the formation of secondary carbonate crystals in calcium-rich karst soils as well as to the differences in pH between karst and non-karst soils. Additionally, climate (mean annual temperature and precipitation) and vegetation properties (aboveground biomass or richness) indirectly affected the MNC through their effects on aggregates or minerals in karst and non-karst soils. Consequently, the influence of soil aggregates and minerals on microbially derived carbon is mediated by the parent material. Our findings emphasize the importance of considering lithology-dependent drivers in predicting soil carbon accumulation, particularly in relation to the stability of microbial-derived carbon. [Display omitted] • Microbial necromass carbon accumulation is similar between karst and non-karst soils. • Soil aggregates, not minerals, affect microbial necromass carbon in karst soils. • Soil minerals, not aggregates, influence microbial necromass carbon in non-karst soils. • Lithology mediates physical-chemical protection on microbial necromass carbon. [ABSTRACT FROM AUTHOR]

Mosses form a ground layer with a thickness of nearly 1 cm during the first decade of vegetation restoration, but their effects on the belowground microbial community and soil properties and the associated soil carbon (C) and nitrogen (N) accumulation in subtropical areas are unclear. Here, we measured soil C and N variables (soil organic C [SOC], total N [TN], dissolved organic C, ammonium [NH 4 +-N] and nitrate [NO 3 −-N]), soil microbial community and soil properties (soil water content [SWC] and pH) under four treatments (bare soil [BS], bare soil with transplanted moss, moss-covered soil [MS] and moss-covered soil with moss removed) in three vegetation types (forest plantations, forage grasslands and mixed plantations and forage grasslands) in a subtropical climate. We analyzed the effects of native mosses, moss transplantation and removal using BS and MS as references. One year post-treatment, moss transplantation increased NO 3 −-N and NH 4 +-N in the 0–5 cm and 2–5 cm soil layers, respectively. Conversely, moss removal decreased SOC and TN in the 0–2 cm soil layer and SWC in the 0–5 cm soil layer. Compared to BS and MS, native moss presence, moss transplantation and removal decreased the total microbial, bacterial and fungal biomass and altered the soil microbial community composition (ratios of fungi and bacteria and Gram-positive bacteria to Gram-negative bacteria) to varying degrees. Moss properties (biomass, C and N concentrations, C:N ratio and saturated water absorption content), as well as SWC, soil microbial biomass and community composition regulated by mosses affected soil C and N. These findings underscore the crucial role of mosses in facilitating soil C and N accumulation during vegetation restoration. • Both the presence and removal of mosses decreased soil microbial biomass. • Mosses altered soil microbial community composition. • Mosses promoted soil C and N accumulation by affecting soil microbial biomass and community composition. • Mosses are particularly important for soil C and N accumulation in forest plantations. [ABSTRACT FROM AUTHOR]

Protists are commonly considered to be drivers of soil microbial functional groups in terrestrial ecosystems. Although the impact of land use intensity on protist diversity and community composition has been well reported, the response of the protist community to different lithologies is less well understood. We conducted field sampling in forests restored for at least 60 years and long-term maize-cultivated croplands as control, assessing protist diversity, community composition, and interaction patterns in response to lithology across temperature gradients (with temperature differences exceeding 9 °C). In limestone, protist richness in forests and croplands was 22.1 % and 16.4 % significantly (one-way ANOVA, p < 0.05) higher, respectively, than in clastic rock. In croplands, compared to forests, protist richness, Shannon index, and Simpson index were 39.7 %, 24.7 %, and 6.6 % significantly (one-way ANOVA, p < 0.05) higher over limestone and 46.5 %, 20.8 %, and 4.5 % significantly (one-way ANOVA, p < 0.05) higher over clastic rock, respectively. These variations are associated with soil properties, such as soil pH and Ca2+ content. In limestone forest soils, the relative abundance of Cercozoa decreased while Lobosa increased with rising mean annual temperature, indicating their different adaptations to increasing temperature. Limestone exhibited more complex co-occurrence networks than clastic rock in forest environments, suggesting greater stability. This phenomenon is attributed to the crucial role of Apicomplexa, Cercozoa, Conosa, Lobosa, and Ochrophyta, which exhibited numerous connections to other groups in different ecosystems. Future functional studies on protists in fragile ecosystems, together with other microbiomes, carry significant implications for the region's resilience to climate change and the sustainability of ecological restoration efforts. • Protist richness was greater in limestone than in clastic rock under different land use intensities. • Protist diversity was higher in croplands with high land use intensity than in forests with low land use intensity. • In forest ecosystems, limestone substrates fostered stronger connections among protistan taxa than clastic rocks. • With increasing temperature, the relative abundance of Cercozoa decreased, whereas that of Lobosa increased. [ABSTRACT FROM AUTHOR]

• AOB dominated N 2 O production in limestone soils. • AOA and AOB as major contributors to N 2 O production in clastic rock soils. • Comammox contributed more to N 2 O production in clastic rock soils than in limestone. Lithology can strongly influence soil's physical and chemical properties, significantly affecting soil nitrogen (N) transformation rates. Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and complete ammonia oxidizers (comammox Nitrospira) constitute the major producers of soil nitrous oxide (N 2 O), but the importance of different lithology on their relative contributions still poorly understood, especially in terms of newly discovered and widespread comammox. To address this knowledge gap, three nitrification inhibitors, acetylene (ammonia oxidizers inhibitor), 1-octyne (AOB inhibitor) and 3,4-dimethylpyrazole phosphate (DMPP) (both AOB and comammox inhibitor), were used to selectively inhibit the activity of different ammonia oxidation groups in order to discriminate their respective roles in N 2 O production in forest soils developed on different lithologies (limestone and clastic rock). The results showed that AOB dominated N 2 O production (63.5 ± 3.3 %) in limestone soils with ammonium amendment, followed by AOA (34.5 ± 7.6 %), while comammox contributed 1 % of total N 2 O production with N 2 O yield of 0.03 ± 0.04 %. Higher N 2 O production by AOB in limestone soils is associated with higher soil pH, exchangeable calcium/magnesium and lower short-range order iron/aluminum minerals. However, the N 2 O yield by comammox (0.12 ± 0.12 %) in clastic rock soils was comparable to that by AOA (0.15 ± 0.14 %) and AOB (0.20 ± 0.13 %). Based on the results of the correlation analysis, comammox in the clastic rock soils produce greater amounts of N 2 O is closely related to the higher soil organic carbon and available phosphorus. The present study provided evidence that the lithology-driven soil properties markedly affect the N 2 O production from different ammonia oxidizers. [ABSTRACT FROM AUTHOR]