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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]

Climate warming is becoming an increasingly serious threat. Understanding plant stoichiometry changes under climate warming is crucial for predicting the effects of future warming on terrestrial ecosystem productivity. Nevertheless, how plant stoichiometry responds to warming when interannual rainfall variation is considered, remains poorly understood. We performed a field soil warming experiment (+5°C) using buried heating cables in subtropical areas of China from 2015 to 2018. Stoichiometric patterns of foliar C:N:P:K:Ca:Mg, non-structural carbohydrate, and stable isotope of Cunninghamia lanceolata seedlings were studied. Our results showed that soil warming decreased foliar P and K concentrations, C:Ca, P:Ca, and P:Mg ratios. However, soil warming increased foliar Ca concentration, δ15N value, C:P and N:P ratios. The response ratios of foliar N, C:N, and δ15N to soil warming were correlated with rainfall. Our findings indicate that there was non-homeostasis of N and C:N under warming conditions. Three possible reasons for this result are considered and include interannual variations in rainfall, increased loss of N, and N limitation in leaves. Piecewise structural equation models showed that stoichiometric non-homeostasis indirectly affected the growth of C. lanceolata seedlings in response to soil warming. Consequently, the growth of C. lanceolata seedlings remained unchanged under the warming treatment. Taken together, our results advance the understanding of how altered foliar stoichiometry relates to changes in plant growth in response to climate warming. Our results emphasize the importance of rainfall variations for modulating the responses of plant chemical properties to warming. This study provides a useful method for predicting the effects of climate warming on economically important timber species. [ABSTRACT FROM AUTHOR]

• Foliar C:N:P:K ratios were driven by changes in nutrient concentrations and seasons. • Warming + drought increased foliar N, N:P, and δ15N across seasons. • Drought and warming had significant interactive effects on foliar δ15N but not δ13C. • Foliar δ15N may be a useful indicator of systematic changes in N cycling in forests. Carbon (C), nitrogen (N), phosphorus (P), and, more recently, potassium (K) have been examined in ecological stoichiometry because they are the most abundant elements in organic matter. An increasing number of studies are investigating the potential responses of plants to future global climate change scenarios, and although warming and drought may greatly influence ecosystem function and services, their combined effects on C:N:P:K stoichiometry remain unknown. In the present study, we assessed the stoichiometry of a major subtropical tree species Cunninghamia lanceolata (Lamb.) Hook, in southern China in terms of its responses to warming and drought stresses. To measure C, N, P, and K concentrations, C:N:P:K stoichiometric ratios, and stable isotope abundance, we sampled C. lanceolata needles from seedlings subject to four treatments: control (CT), warming (W, with 5 °C increase in temperature), drought (D, with 50% decrease in precipitation), and the abovementioned warming and drought conditions combined (WD). The warming and drought conditions applied simulated the climate changes predicted for the next decades in southern China. We found that variations in foliar C:N:P:K stoichiometric ratios were driven by changes in nutrient concentration, season, and treatment. Unexpectedly, differences in foliar intrinsic water use efficiency across sampling seasons were not significant. The WD conditions increased foliar N concentration (57%) and the δ15N value (111%) across the different seasons, and significant interactive effects between warming and drought on foliar N concentration and δ15N were clearly demonstrated. The N cycle is likely to accelerate in subtropical forests, with more of the "heavier" N being mobilized for plant use, and thus the combination of warming plus drought may alleviate plant N restrictions in the future. Thus, foliar δ15N might be used as an indicator of the changes in N cycling in C. lanceolata forests. [ABSTRACT FROM AUTHOR]

• Effects of warming and N addition on microbial functional genes were studied. • There was no interaction between warming and N addition on functional genes. • Warming had minimal effect on functional genes associated with soil C and N cycling. • The increase in gene abundance due to N addition was related to pH and available N. Climate warming and nitrogen (N) deposition are expected to increase in the coming decades. The consequences of the interaction between warming and N deposition on forest ecosystems and their functions (i.e., carbon sequestration) remain uncertain. In this study, we examined the composition, diversities, and abundances of soil microbial functional genes in a subtropical forest after four years of exposure to warming and N addition. We found that warming alone did not have a significant effect on the composition, diversities, and abundances of functional genes, suggesting that four years were not long enough to reach the critical threshold that would activate a response to warming from soil functional genes in the subtropical forest. Conversely, warming significantly decreased soil labile carbon (C) content. The application of N in combination with warming significantly enhanced the diversities and abundances of functional genes associated with C and N cycling, leading to an accelerated loss of soil N. Interestingly, the interaction between warming and N addition did not have a significant effect on the diversities and abundances of functional genes associated with C and N cycling. Redundancy analysis indicated that a decrease in pH caused by N addition significantly affected the abundances of those functional genes. Overall, our study fills a research gap by examining the effect of simultaneous warming and N deposition on soil microbial functional genes in subtropical forests. Additionally, the study indicates that microbial functional genes are more sensitive to a combination of warming and N addition than to warming alone. Therefore, the effects of multi-factor global change on soil microbial functional genes cannot be underestimated. [ABSTRACT FROM AUTHOR]

Research Highlights: Warming alters the chemical composition of Cunninghamia lanceolata (Lamb.) Hook, resulting in increased production of macromolecular compounds that protect against heat stress. Background and Objectives: Low latitude forests are experiencing obvious climatic warming; however, the plant physiological responses to warming are not well understood. As warming induces moisture stress, we hypothesized that warming activates metabolites (i.e., lipids, phenolic compounds, amino acids) and causes damage to the leaves, exemplified by the increased concentrations of reactive oxygen species. Materials and Methods: We conducted a warming experiment in a C. lanceolata plantation. Plant physiological traits associated with nutrient status, reactive oxygen species, antioxidant enzymes species, and metabolites were measured. Results: Warming altered the chemical composition of C. lanceolata as it increased C:N ratios of leaves and roots. In particular, the concentrations of N and P in leaves and roots were significantly decreased under the warming condition, which might be related to the biomass production, namely, a dilution effect. Under the warming condition, most of the phospholipid compounds and proteins significantly increased. Leaf C, carbohydrates, amino acids, organic acids, flavonoids, and phenolic compounds were identified to have significantly lower concentrations under the warming treatment than those under the control treatment. These results suggested that moisture stress under the warming treatment may drive C deficiency and metabolic restriction in plants. Conclusions: Under the warming condition, C. lanceolata changed its energy utilization strategy and invested more resources to produce macromolecular compounds for protecting against heat stress. Warming in sub-tropical forests alters plant chemical properties, and thus may have an important consequence for nutrient cycling and soil C sequestration. [ABSTRACT FROM AUTHOR]

• SOC mineralization increased with experimental warming but decreased with increasing elevation. • Short-term temperature sensitivity of SOC mineralization was higher at lower than higher elevations. • Substrate availability and soil microbes are key to the response of temperature sensitivity to experimental warming. Subtropical forest soil exerts a large, but uncertain effect on terrestrial carbon (C) cycling. Global warming is anticipated to alter subtropical soil C cycling but currently, there is no consensus on how warming will affect soil C at different elevations. We conducted a short-term laboratory soil warming incubation experiment (ambient temperature +4 °C) along an elevational gradient in Wuyi Mountains of southeastern China to examine the response of soil organic carbon (SOC) mineralization to rising temperatures. Soil samples were collected from three elevations (630 m, 1450 m and 2130 m), and microbial community composition was determined using phospholipid fatty acids (PLFAs). The SOC mineralization increased with rising mean annual temperature (i.e., with decreasing elevation) and with experimental warming. Unlike most other similar experimental studies, we found that the temperature sensitivity (Q 10) of SOC mineralization to short-term experimental warming significantly decreased with increasing elevation. We also found that temperature sensitivity of SOC mineralization in response to warming depends on substrate availability, as indicated by the significant relationship between dissolved organic carbon (DOC) and Q 10 values. In addition, soil microbial biomass increased significantly with increasing elevations, but was not significantly affected by short-term experimental warming. Experimental warming reduced the abundance of total PLFAs, bacteria, fungi, and actinomycetes in the low-elevation soil. Experimental warming significantly changed soil microbial community composition at low elevation, with increases in the ratios of cyclopropyl to monoenoic precursor fatty acids (cy:pre), saturated to monounsaturated fatty acids (sat:mono), and isomers to trans-isomers fatty acids (i:a), all of which are stress indicators, indicating that warming treatment increased microbial respiration rather than microbial growth, because the microbial respiration per biomass increases under environmental stress. Microorganisms likely altered their membrane fatty acid components and mass in response to changes in available C. The differences in Q 10 associated with short-term warming and among elevations with long-term temperature differences indicate that the effect of warming on SOC mineralization may change through time and this should be taken into account when predicting SOC mineralization in response to continual rising temperatures. [ABSTRACT FROM AUTHOR]