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Background and aims: Long-term nitrogen (N) and phosphorus (P) fertilization could immensely alter plant-soil-microbial properties, thereby impacting the priming effect (PE). However, previous studies mostly simulated PE responses to fertilization by adding nutrient in the laboratory, which could not represent PE changes under long-term fertilization-induced ecosystem alteration. Our aim is to clarify the PE alteration in soils with long-term fertilization history in an alpine meadow. Methods: Soil samples (0–10 cm) were collected from a 9-year field fertilization experiment (including four treatments: control, + N with urea, + P with triple superphosphate, + NP with both fertilizers), and incubated for 30 days with 13C-labeled glucose amendment (2% SOC). Plant-soil-microbial properties were measured before/after incubation. Results: Glucose addition induced a positive PE in all soils with a range from 0.56 to 1.37 mg C g−1 soil. N fertilization did not affect PE intensity due to the microbial adaptation and fast utilization of the added glucose for metabolic needs. P fertilization caused P accumulation in soils, and decreased available N and pH. Such changes inhibited microbes, and glucose activated microbial activities, causing higher PE intensity. Conclusion: Long-term N fertilization did not significantly affect PE, while P fertilization stimulated PE intensity. Overall, we highlight that P fertilization may induce higher risk of CO2 release, which deserves more attention when applying P fertilizers in this alpine meadow. [ABSTRACT FROM AUTHOR]

The priming effects (PEs) of soil organic carbon (SOC) decomposition is a crucial process affecting the C balance of terrestrial ecosystems. However, there is uncertainty about how PEs will respond to climate warming. In this study, we sampled soils along a subtropical elevation gradient in China and conducted a 126‐day lab‐incubation experiment with and without the addition of 13C‐labeled high‐bioavailability glucose or low‐bioavailability lignin. Based on the mean annual temperature (MAT) of each elevation (9.3–16.4°C), a temperature increase of 4°C was used to explore how PEs mediate the decomposition of SOC in response to warming. Our results showed that the magnitude of glucose‐induced PEs (PEglucose) was higher than lignin‐induced PEs (PElignin), with both PEs linearly increasing with MAT. Across the MAT (i.e., elevation) gradient, short‐term warming had a constant magnitude of negative effects on PEglucose, whereas rising MAT exacerbated the negative effects of short‐term warming on PElignin. Moreover, the temperature sensitivity of SOC decomposition decreased after adding glucose and lignin across the MAT gradient, suggesting that fresh C inputs may prime the microbial breakdown of labile SOC under warming. Taken together, warming alleviated SOC loss due to PEs through varying mechanisms depending on substrate bioavailability. Warming mediated the PEglucose by increasing available nitrogen and weakening microbial nitrogen‐mining but inhibited the PElignin by shifting from microbial nitrogen‐mining to microbial co‐metabolization. Our findings highlight the role of warming in regulating the PEs and suggest that incorporating the suppression effect of warming on PEs can contribute to the accurate prediction of soil C dynamics in a warming world. Plain Language Summary: Tropical and subtropical ecosystems have the highest vegetation productivity and diversity on earth and play a crucial role in regulating climate change. However, it is unclear how diverse plant‐derived components stimulate microbial decomposition of soil organic carbon (SOC) via a phenomenon called priming effects (PEs) under climate warming. Here, we added two 13C‐labeled substitutions of plant components (e.g., glucose and lignin) to soils collected from a subtropical elevation gradient and carried out a 126‐day lab‐incubation experiment. Warming consistently harmed glucose‐induced PEs (PEglucose), while amplified the negative effect on lignin‐induced PEs (PElignin) across the elevation gradient, suggesting that warming has stronger negative effects on PElignin at warmer sites. Warming mediates the PEglucose by weakening microbial N‐mining but strengthening microbial preferential substrate utilization. This is achieved by reducing substrate‐built microbial biomass and making more substrate for respiration compared to unwarmed soil. In contrast, warming inhibits lignin‐induced PEs by shifting from microbial N‐mining to microbial co‐metabolization. This shift is supported by the positive association between lignin‐induced PEs and lignin‐derived microbial biomass and available nitrogen. Our measurement suggests that warming decreased the intensity of SOC decomposition by downregulating the primed SOC loss with fresh substrate inputs through varying mechanisms depending on substrate bioavailability. Key Points: Soil C priming effect linearly decreases with elevation in subtropicsHigh‐ and low‐quality substrates play opposite but complementary roles in soil C feedback to climate warmingThe suppression effect of warming on priming can contribute to the accurate prediction of soil C dynamics in a warmer world [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition rates of terrestrial ecosystems have gradually declined but are still high in some areas. Previous studies have reported that N addition elicits diverse impacts on soil organic carbon (SOC) pools. SOC can be divided into different functional fractions, namely, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). The responses of these fractions to N addition should be elucidated to better understand the changes in SOC pools. Here, we conducted a N addition experiment (0, 40, and 80 kg N ha−1 yr−1) in a subtropical Castanopsis fabri forest to simulate N deposition. The surface (0−10 cm) SOC fractions, aboveground litter product, fine root (diameter < 2 mm) biomass, soil exchangeable cation content, and soil enzyme activity under different N addition treatments were measured. The results showed the following: (1) N addition showed a positive effect on POC and SOC contents but did not significantly affect MAOC content; (2) POC content was negatively correlated with pH and soil enzyme activity and positively correlated with aboveground litter product, suggesting that POC accumulation was influenced by aboveground litter input and microbial decomposition; (3) a close negative relationship was observed between exchangeable Al3+ and Ca2+ or K+ contents, indicating that there is likely to be a trade-off between the mineral sorption and desorption, thus resulting in an insignificant reaction of MAOC to N addition. Overall, the accumulation of SOC under short-term N addition was found to be primarily driven by POC, and the response of different SOC functional fractions to N addition was inconsistent. By incorporating these nuances into ecosystem models, it is possible to predict SOC dynamics more accurately in response to global change. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition rates of terrestrial ecosystems have gradually declined but are still high in some areas, and previous studies have reported that N addition elicits diverse impacts on soil organic carbon (SOC) pools. SOC can be divided into different functional fractions, namely particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). The responses of these fractions to N addition should be elucidated to better understand the changes in SOC pools. We investigated the effects of N addition treatments (+0, +40, and +80 kg N ha−1 yr−1) in a subtropical Castanopsis fabri forest to simulate N deposition. The surface (0–10 cm) SOC content in different fractions, aboveground litter biomass, fine root (diameter < 2 mm) biomass, soil exchangeable cation content, and soil enzyme activity under different N addition treatments were measured. The results showed that 1) N addition exerted a positive effect on POC content but did not significantly affect MAOC content. 2) POC content was negatively correlated with pH and soil enzyme activity and positively correlated with aboveground litter biomass, suggesting that POC accumulation was influenced by aboveground litter input and microbial decomposition. 3) Root biomass was unaffected significantly by the addition of N, which could be responsible for the limited response of MAOC to N addition. Furthermore, a close negative relationship was observed between exchangeable Al3+ and Ca2+ or K+ contents, indicating the presence of a trade-off between negative effects of exchangeable cations on SOC bridging and their positive effects on SOC adsorption, thus resulting in an insignificant reaction of MAOC to N addition. Overall, N addition reduces the persistence and increases the nutrient density of SOC, and MAOC with more protection is less vulnerable to N addition than POC with less protection. By incorporating these nuances into ecosystem models, it is possible to more accurately predict SOC dynamics in response to global change. [ABSTRACT FROM AUTHOR]

Background and aims: Grasslands hold one of the most important soil carbon stocks in the world, which is vulnerable to climate change (i.e. precipitation) and human disturbance (i.e. land-use). This study aimed to investigate responses and mechanisms of soil organic carbon (SOC) decomposition and accumulation to precipitation and land-use in an Inner Mongolian grassland. Methods: Using a randomized complete block design with a split plot, an experiment with land-use regimes (fencing, grazing, and mowing, since 2011) and altered precipitation amount (wet, + 50% precipitation; CT, ambient precipitation; dry, −50% precipitation; since 2016) was conducted to explore their impacts on SOC decomposition (represented by soil heterotrophic respiration and extracellular enzyme activities) and accumulation (represented by SOC and its physical fractions) from samples collected in 2019. Results: SOC decomposition significantly increased under wet treatment, but decreased under dry treatment. Wet treatment increased SOC accumulation via the increment of mineral-associated organic carbon (MAOC), and vice versa for dry treatment. Precipitation amount may affect soil microbial biomass and activities via alterations of water supply, plant-derived carbon input, and other soil properties, leading to changes of SOC dynamics. Nevertheless, land-use regimes had little influences on SOC dynamics. Conclusions: Compared to land-use regimes, precipitation treatments can significantly change SOC dynamics. Overall, SOC increased under higher precipitation amount, but decreased with less precipitation. We emphasize that the SOC stock in Inner Mongolia temperate grassland may have an unexpectable fast response to precipitation alteration, but more investigation is still needed in longer terms. [ABSTRACT FROM AUTHOR]

Summary: Soil organic carbon (SOC) is a mixture of various carbon (C) compounds with different stability, which can be distinctly affected by the priming effect (PE). However, little is known about how the PE changes with SOC stability.We address this issue by combining results from two experiments and a metaanalysis.We found that the PE increased with the prolongation of soil preincubation, suggesting that higher PE occurred for more stable SOC than for labile SOC. This was further supported by the metaanalysis of 42 observations. There were significant negative relationships between the difference in PE (ΔPE) between labile and more stable SOC and their differences in SOC, microbial biomass C and soil C : N ratio, indicating that soil C availability exerts a vital control on ΔPE.We conclude that, compared with labile SOC, stable SOC can be more vulnerable to priming once microbes are provided with exogenous C substrates. This high vulnerability of stable SOC to priming warrants more attention in future studies on SOC cycling and global change. [ABSTRACT FROM AUTHOR]

Soil organic carbon storage in soil carbon models is highly sensitive to microbial carbon use efficiency (CUE); thus, to reliably predict C storage requires quantifying the response of CUE to warming. By conducting a meta-analysis of 87 observations from field warming experiments worldwide, we found that field warming has no significant effect on CUE, which remains constant at 0.35 ± 0.19 (mean ± SD) on average. The effect of field warming on CUE is independent of climate factors, incubation temperatures, ecosystem types, warming methods, or CUE measurement methods. The field warming effect on CUE was best explained by the response ratios of microbial biomass–specific growth and microbial biomass–specific respiration according to a multi-model selection, and there was a limited effect of warming on microbial biomass–specific growth and microbial biomass–specific respiration. Overall, the effect of field warming on CUE may be attributed to microbial acclimation. Similarly, insignificant effect of laboratory warming on CUE was observed. Our work highlights that current soil carbon models assuming that CUE decreases with warming may underestimate future soil carbon storage, and calls for more research to explore the regulatory role of microbial community attributes on CUE. • We did a meta-analysis on the response of soil microbial CUE to field warming. • Microbial CUE was 0.39 on average and was not significantly affected by warming. • The effect of warming on CUE is independent of various factors considered. • Such factors include incubation temperature, ecosystem type, warming or measurement method. [ABSTRACT FROM AUTHOR]

Global changes can alter plant inputs from both above‐ and belowground, which, thus, may differently affect soil carbon and microbial communities. However, the general patterns of how plant input changes affect them in forests remain unclear. By conducting a meta‐analysis of 3193 observations from 166 experiments worldwide, we found that alterations in aboveground litter and/or root inputs had profound effects on soil carbon and microbial communities in forest ecosystems. Litter addition stimulated soil organic carbon (SOC) pools and microbial biomass, whereas removal of litter, roots or both (no inputs) decreased them. The increased SOC under litter addition suggested that aboveground litter inputs benefit SOC sequestration despite accelerated decomposition. Unlike root removal, litter alterations and no inputs altered particulate organic carbon, whereas all detrital treatments did not significantly change mineral‐associated organic carbon. In addition, detrital treatments contrastingly altered soil microbial community, with litter addition or removal shifting it toward fungi, whereas root removal shifting it toward bacteria. Furthermore, the responses of soil carbon and microbial biomass to litter alterations positively correlated with litter input rate and total litter input, suggesting that litter input quantity is a critical controller of belowground processes. Taken together, these findings provide critical insights into understanding how altered plant productivity and allocation affects soil carbon cycling, microbial communities and functioning of forest ecosystems under global changes. Future studies can take full advantage of the existing plant detritus experiments and should focus on the relative roles of litter and roots in forming SOC and its fractions. [ABSTRACT FROM AUTHOR]