Soil respiration the second-largest carbon flux in terrestrial ecosystems, has been extensively studied across a wide range of biomes. Surprisingly, no consensus exist on how acid rain (AR) impacts the spatiotemporal pattern of soil respiration. Therefore, we conducted a meta-analysis using 318 soil respiration and 263 soil respiration temperature sensitivity (Q10) data points obtained from 48 studies to assess the impact of AR on soil respiration components and their Q10. The results showed that AR reduced soil total respiration (Rt) and soil autotrophic respiration (Ra) by 7.41 % and 20.75 %, respectively. As the H+ input increased, the response rates of Ra to AR (RR-Ra) and soil heterotrophic respiration (Rh) to AR (RR-Rh) decreased and increased, respectively. With increased AR duration, the RR-Ra increased, whereas the RR-Rh did not change. AR increased the Q10 of Rt (Rt-Q10) and Rh (Rh-Q10) by 1.92 % and 9.47 %, respectively, and decreased the Q10 of Ra (Ra-Q10) by 2.77 %. Increased mean annual temperature, mean annual precipitation, and initial soil organic carbon increased the response rate of Ra-Q10 to AR (RR-Ra-Q10) and decreased the response rate of Rh-Q10 to AR (RR-Rh-Q10). However, as the AR frequency and initial soil pH increased, both RR-Ra-Q10 and RR-Rh-Q10 also increased. In summary, AR decreased Rt but increased Q10, likely due to soil acidification (soil pH decreased by 7.84 %), reducing plant root biomass (decreased by 5.67 %) and soil microbial biomass (decreased by 5.67 %), changing microbial communities (increased fungi to bacteria ratio of 15.91 %), and regulated by climate, vegetation, soil and AR regimes. To the best of our knowledge, this is the first study to reveal the large-scale, varied response patterns of soil respiration components and their Q10 to AR. It highlights the importance of applying the reductionism theory in soil respiration research to enhance our understanding of soil carbon cycling processes with in the context of global climate change.

The temperature sensitivity of soil carbon mineralization (Q10) is an important index to evaluate the responses of ecosystem carbon cycling to climate change. We examined the effects of three electron acceptors [SO42-, NO3- and Fe(Ⅲ)] addition on the Q10 value of anaerobic carbon mineralization of Phragmites australis community soil (0-10 cm) in the Yellow River Estuary wetland with the closed culture-gas chromatography method. The results showed that the three electron acceptors addition inhibited the production of CO2 and CH4 during the 48-day culture period, with a decrease of 17.3%-20.8% for CO2 and 29.2%-36.2% for CH4. Generally, the CO2 production differed with the concentrations of electron acceptors, while CH4 production differed with the type of electron acceptors. The CO2:CH4 ratios were significantly different with temperature, indicating an obvious temperature dependence for the anaerobic carbon mineralization pathway. The Q10 values of CO2 and CH4 production under three electron acceptor additions ranged from 1.08 to 1.11 and from 1.19 to 1.37, respectively, showing an increasing trend compared with the control. The type and concentration of electron acceptors affected the temperature dependence of CO2 production, while electron acceptors affected that of CH4 production. It is suggested that the input of reducing salts would retard the mineralization loss of organic carbon in estuary freshwater wetlands under the background of climate change, but enhance the sensitivity of carbon mineralization to increasing temperature.
土壤碳矿化的温度敏感性(Q10)是研究生态系统碳循环响应气候变化的重要指标。以黄河口湿地芦苇群落表层土壤(0～10 cm)为对象,采用室内密闭培养-气相色谱法,研究不同温度和浓度下3种电子受体[SO42-、NO3-和Fe(Ⅲ)]添加对湿地土壤厌氧碳矿化Q10的影响。结果表明: 48 d的培养期内,电子受体添加对厌氧生成CO2和CH4具有不同程度的抑制作用;SO42-、NO3-和Fe(Ⅲ)添加使得CO2和CH4生成量分别下降17.3%～20.8%和29.2%～36.2%;总体上,CO2生成因电子受体浓度而异,CH4生成因电子受体类型而异。CO2∶CH4值在不同温度条件下差异明显,表明厌氧碳矿化途径具有明显的温度依赖性。不同处理中CO2和CH4的Q10值分别在1.08～1.11和1.19～1.37,与对照相比有升高趋势;总体上,CO2的温度敏感性因电子受体类型和浓度而异,CH4的温度敏感性因电子受体类型而异。气候变化背景下,还原性盐离子的输入将在一定程度上减缓河口淡水湿地有机碳的矿化损失,但会增强碳矿化对升温的敏感性。.

The ecosystem respiration and temperature sensitivity (Q10) of paddy soil play very important roles in the emission of greenhouse gases from paddy ecosystems. Under intermittent irrigation and flooding irrigation conditions, a static opaque chamber and gas chromatography method were applied to study the regulation and influence of ecosystem respiration and Q10 using five treatments:no fertilizer (CK), conventional fertilization (NPK), 10t·hm-2 biochar with chemical fertilizer (LBC), 20t·hm-2 biochar with chemical fertilizer (MBC), and 40t·hm-2 biochar with chemical fertilizer (HBC). The results showed that:① The temperature sensitivity coefficients (Q10) of ecosystem respiration under flooding irrigation were 4.45 (CK), 7.40 (NPK), 6.44 (LBC), 4.58 (MBC), and 3.87 (HBC), respectively. Flooding irrigation significantly reduced the Q10 value of the paddy field ecosystem compared to intermittent irrigation (P<0.01). CK, NPK, LBC, MBC, and HBC decreased by 48.6%, 55.2%, 67.9%, 70.3%, and 70.8% under flooding irrigation, respectively. ② Whether intermittent irrigation or flooding irrigation was adopted, the application of fertilizer with biochar increased the respiration of the paddy field ecosystem than conventional fertilization treatment, but the effect of different biochar levels on respiration was not significant. ③ The application of chemical fertilizer with medium or low amounts of biochar increased the temperature sensitivity of respiration compared with no fertilization in the paddy field ecosystems (P<0.05), but both MBC and HBC treatments reduced the Q10 value of paddy field ecosystem compared with NPK. Furthermore, the temperature sensitivity of respiration in the paddy field ecosystem decreased with an increase in the level of biochar application. Therefore, under the two irrigation methods, HBC treatment was more effective than LBC and MBC treatments to inhibit the effect of increasing soil temperature on the respiration of the ecosystem.

An 84-day laboratory incubation experiment was conducted to investigate the effects of different fertilizers (urea; manure), moisture conditions (60%, 75% and 90% water holding capacity) and temperatures (15, 25 and 35℃) on nitrogen mineralization. The experiment included 3 treatments:①CK, unfertilized control; ② Ur, adding urea at N 120 mg·kg-1; 3 UM, adding urea and manure (equal to adding N 120 mg·kg-1). Total inorganic nitrogen and soluble organic nitrogen (SON) were determined at different times throughout the experiment. The results showed that soil temperature and fertilization type had significant impacts on the net mineralization rates, cumulative mineralization, and the potentially mineralizable nitrogen (N0) (P<0.01). In addition, the soil net N mineralization rates and cumulative mineralization significantly (P<0.05) increased by 1.46-8.17 and 2.00-8.15 times, respectively, when fertilizers were added into soils. The soil net N mineralization rates and cumulative mineralization increased with the increase of temperature. Compared with CK treatment, Ur and UM treatments could significantly increase the content of soil soluble organic nitrogen(SON). There was a significant negative correlation between the content of SON and cumulative mineralization. It indicated that SON was involved in soil nitrogen mineralization as a non-negligible component. Increasing the temperature could significantly increase the mineralization rate and mineralization intensity of SON in soil, but the water content had no significant influence on the SON of the soils. Moreover, the authors found that fertilization treatment worked significantly in decreasing the Q10 value for soil N mineralization compared with CK treatment. Further, the Q10 value was significantly lowest in UM treatment(Q10=1.01). The results showed that the application of organic manure significantly reduced the sensitivity of the rate of nitrogen mineralization to temperature changes, which was beneficial in slowing down the release rate of mineral nitrogen under high temperatures and improving the nitrogen utilization efficiency of crops.

Microorganisms dominate the decomposition of organic matter and their activities are strongly influenced by temperature. As the carbon (C) flux from soil to the atmosphere due to microbial activity is substantial, understanding temperature relationships of microbial processes is critical. It has been shown that microbial temperature relationships in soil correlate with the climate, and microorganisms in field experiments become more warm-tolerant in response to chronic warming. It is also known that microbial temperature relationships reflect the seasons in aquatic ecosystems, but to date this has not been investigated in soil. Although climate change predictions suggest that temperatures will be mostly affected during winter in temperate ecosystems, no assessments exist of the responses of microbial temperature relationships to winter warming. We investigated the responses of the temperature relationships of bacterial growth, fungal growth, and respiration in a temperate grassland to seasonal change, and to 2 years\' winter warming. The warming treatments increased winter soil temperatures by 5-6°C, corresponding to 3°C warming of the mean annual temperature. Microbial temperature relationships and temperature sensitivities (Q10 ) could be accurately established, but did not respond to winter warming or to seasonal temperature change, despite significant shifts in the microbial community structure. The lack of response to winter warming that we demonstrate, and the strong response to chronic warming treatments previously shown, together suggest that it is the peak annual soil temperature that influences the microbial temperature relationships, and that temperatures during colder seasons will have little impact. Thus, mean annual temperatures are poor predictors for microbial temperature relationships. Instead, the intensity of summer heat-spells in temperate systems is likely to shape the microbial temperature relationships that govern the soil-atmosphere C exchange.

Understanding soil CO2 flux temperature sensitivity (Q10) is critical for predicting ecosystem-level responses to climate change. Yet, the effects of warming on microbial CO2 respiration still remain poorly understood under current Earth system models, partly as a result of thermal acclimation of organic matter decomposition. We conducted a 117-day incubation experiment under constant and diurnally varying temperature treatments based on four forest soils varying in vegetation stand and soil horizon. Our results showed that Q10 was greater under varying than constant temperature regimes. This distinction was most likely attributed to differences in the depletion of available carbon between constant high and varying high-temperature treatments, resulting in significantly higher rates of heterotrophic respiration in the varying high-temperature regime. Based on 16S rRNA gene sequencing data using Illumina, the varying high-temperature regime harbored higher prokaryotic alpha-diversity, was more dominated by the copiotrophic strategists and sustained a distinct community composition, in comparison to the constant-high treatment. We found a tightly coupled relationship between Q10 and microbial trophic guilds: the copiotrophic prokaryotes responded positively with high Q10 values, while the oligotrophs showed a negative response. Effects of vegetation stand and soil horizon consistently supported that the copiotrophic vs oligotrophic strategists determine the thermal sensitivity of CO2 flux. Our observations suggest that incorporating prokaryotic functional traits, such as shifts between copiotrophy and oligotrophy, is fundamental to our understanding of thermal acclimation of microbially mediated soil organic carbon cycling. Inclusion of microbial functional shifts may provide the potential to improve our projections of responses in microbial community and CO2 efflux to a changing environment in forest ecosystems.