Response Of Soil Microbial Respiration Research Articles

Soil microbial respiration does not respond to nitrogen deposition but increases with latitude

AbstractFacing global changes, substantial modifications in soil microbes and their functions have been widely evidenced and connected. However, the response of soil microbial respiration (MR) to increasing nitrogen (N) deposition and the role of microbial characteristics in controlling this response remain elusive. In this study, we quantified the intensity of the soil MR in terrestrial ecosystems that suffered elevated N deposition. High‐throughput quantitative sequencing and phospholipid fatty acids were employed to analyse microbial community properties and biomass, whilst microbial necromass was quantified using biomarker amino sugars. Our results revealed that soil MR kept stable under N deposition. Microorganisms maintained their respiration rates by modifying the characteristics of enzymes rather than altering microbial community properties or biomass. Notably, soil MR increased with latitude across study sites, which was attributed to the restriction of microbial activity by bacterial necromass. Supporting this observation, the recalcitrance of the soil carbon (C) pool to microbial degradation was evidenced to be the stability mechanism underlying the spatial variations in MR. Overall, we propose that MR is resistant to short‐term N deposition, whilst it exhibits a pronounced latitude dependence as shaped by the recalcitrant C pool. Our findings provide crucial insights into the microbial mechanisms of soil C dynamics under global change, contributing to the advancement of soil C models.

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Cropland abandonment alleviates soil carbon emissions in the North China Plain

Land use change could profoundly influence the terrestrial ecosystem carbon (C) cycle. However, the effects of agricultural expansion and cropland abandonment on soil microbial respiration remain controversial, and the underlying mechanisms of the land use change effect are lacking. In this study, we conducted a comprehensive survey in four land use types (grassland, cropland, orchard, and old-field grassland) of North China Plain with eight replicates to explore the responses of soil microbial respiration to agricultural expansion and cropland abandonment. We collected surface soil (0-10cm in depth) in each land use type to measure soil physicochemical property and microbial analysis. Our results showed that soil microbial respiration was significantly increased by 15.10mg CO2 kg-1day-1 and 20.06mg CO2 kg-1day-1 due to the conversion of grassland to cropland and orchard, respectively. It confirmed that agricultural expansion might exacerbate soil C emissions. On the contrary, the returning of cropland and orchard to old-field grassland significantly decreased soil microbial respiration by 16.51mg CO2 kg-1day-1 and 21.47mg CO2 kg-1day-1, respectively. Effects of land use change on soil microbial respiration were predominately determined by soil organic and inorganic nitrogen contents, implying that nitrogen fertilizer plays an essential role in soil C loss. These findings highlight that cropland abandonment can effectively mitigate soil CO2 emissions, which should be implemented in agricultural lands with low grain production and high C emissions. Our results improve mechanistic understanding on the response of soil C emission to land use changes.

Soil microbial respiration adapts to higher and longer warming experiments at the global scale

Warming can affect soil microbial respiration by changing microbial biomass and community composition. The responses of soil microbial respiration to warming under experimental conditions are also related to background conditions and the experimental setup, such as warming magnitude, duration, and methods. However, the global pattern of soil microbial respiration in response to warming and underlying mechanisms remain unclear. Here, we conducted a global meta-analysis of the response of soil microbial respiration to warming by synthesizing data from 187 field experiments. We found that experimental warming significantly increased soil microbial respiration and microbial biomass carbon by 11.8% and 6.4%, respectively. The warming-induced increase in microbial carbon decomposition was positively correlated with increased microbial biomass carbon, but not community composition. Moreover, the positive response of soil microbial respiration marginally increased with warming magnitude, particularly in short-term experiments, but soil microbial respiration adapted to higher warming at longer timescales. Warming method did not significantly affect the response of microbial respiration, except for a significant effect with open top chamber warming. In addition, the impact of warming on soil microbial respiration was more pronounced in wetter sites and in sites with lower soil pH and higher soil organic carbon. Our findings suggest that warming stimulates microbial respiration mainly by increasing microbial biomass carbon. We also highlight the importance of the combination of warming magnitude and duration in regulating soil microbial respiration responses, and the dependence of warming effects upon background precipitation and soil conditions. These findings can advance our understanding of soil carbon losses and carbon-climate feedbacks in a warm world.

Temperature fluctuation promotes the thermal adaptation of soil microbial respiration.

The magnitude of the feedback between soil microbial respiration and increased mean temperature may decrease (a process called thermal adaptation) or increase over time, and accurately representing this feedback in models improves predictions of soil carbon loss rates. However, climate change entails changes not only in mean temperature but also in temperature fluctuation, and how this fluctuation regulates the thermal response of microbial respiration has never been systematically evaluated. By analysing subtropical forest soils from a 2,000 km transect across China, we showed that although a positive relationship between soil microbial biomass-specific respiration and temperature was observed under increased constant incubation temperature, an increasing temperature fluctuation had a stronger negative effect. Our results further indicated that changes in bacterial community composition and reduced activities of carbon degradation enzymes promoted the effect of temperature fluctuation. This adaptive response of soil microbial respiration suggests that climate warming may have a lesser exacerbating effect on atmospheric CO2 concentrations than predicted.

Response of Soil Microbial Respiration to Spirotetramat Insecticide Under Different Soil Field Capacities

Response of Soil Microbial Respiration to Spirotetramat Insecticide Under Different Soil Field Capacities

Microbial assemblies associated with temperature sensitivity of soil respiration along an altitudinal gradient

Identifying the drivers of the response of soil microbial respiration to warming is integral to accurately forecasting the carbon-climate feedbacks in terrestrial ecosystems. Microorganisms are the fundamental drivers of soil microbial respiration and its response to warming; however, the specific microbial communities and properties involved in the process remain largely undetermined. Here, we identified the associations between microbial community and temperature sensitivity (Q10) of soil microbial respiration in alpine forests along an altitudinal gradient (from 2974 to 3558 m) from the climate-sensitive Tibetan Plateau. Our results showed that changes in microbial community composition accounted for more variations of Q10 values than a wide range of other factors, including soil pH, moisture, substrate quantity and quality, microbial biomass, diversity and enzyme activities. Specifically, co-occurring microbial assemblies (i.e., ecological clusters or modules) targeting labile carbon consumption were negatively correlated with Q10 of soil microbial respiration, whereas microbial assemblies associated with recalcitrant carbon decomposition were positively correlated with Q10 of soil microbial respiration. Furthermore, there were progressive shifts of microbial assemblies from labile to recalcitrant carbon consumption along the altitudinal gradient, supporting relatively high Q10 values in high-altitude regions. Our results provide new insights into the link between changes in major microbial assemblies with different trophic strategies and Q10 of soil microbial respiration along an altitudinal gradient, highlighting that warming could have stronger effects on microbially-mediated soil organic matter decomposition in high-altitude regions than previously thought.

Temperature adaptation of soil microbial respiration in alpine, boreal and tropical soils: An application of the square root (Ratkowsky) model.

Warming is expected to stimulate soil microbial respiration triggering a positive soil carbon-climate feedback loop while a consensus remains elusive regarding the magnitude of this feedback. This is partly due to our limited understanding of the temperature-adaptive response of soil microbial respiration, especially over broad climatic scales. We used the square root (Ratkowsky) model to calculate the minimum temperature for soil microbial respiration (Tmin , which describes the temperature adaptation of soil microbial respiration) of 298 soil samples from alpine grasslands on the Tibetan Plateau and forest ecosystems across China with a mean annual temperature (MAT) range from -6°C to +25°C. The instantaneous soil microbial respiration was determined between 4°C and 28°C. The square root model could well fit the temperature effect on soil microbial respiration for each individual soil, with R2 higher than 0.98 for all soils. Tmin ranged from -8.1°C to -0.1°C and increased linearly with increasing MAT (R2 =0.68). MAT dominantly regulated Tmin variation when accounting simultaneously for multiple other drivers (mean annual precipitation, soil pH and carbon quality); an independent experiment showed that carbon availability had no significant effect on Tmin . Using the relationship between Tmin and MAT, soil microbial respiration after an increased MAT could be estimated, resulting in a relative increase in respiration with decreasing MAT. Thus, soil microbial respiration responses are adapted to long-term temperature differences in MAT. We suggest that Tmin = -5 + 0.2×MAT, that is, every 1°C rise in MAT is estimated to increase Tmin of respiration by approximately 0.2°C, could be used as a first approximation to incorporate temperature adaptation of soil microbial respiration in model predictions. Our results can be used to predict future changes in the response of soil microbial respiration to temperature over different levels of warming and across broad geographic scales with different MAT.

Temperature Affects new Carbon Input Utilization By Soil Microbes: Evidence Based on a Rapid δ13C Measurement Technology

Strong and rapid responses of soil microbial respiration to pulses, such as those from available soil organic matter (SOM) or water input from precipitation (especially in arid areas), are common. However, how soil microbes utilize new SOM inputs and the effects that temperature may have on their activities are unclear owing to the limitation in the application of traditional isotopic techniques at minute scales. In the present study, we developed a system of measuring 12CO2 and δ13C minutely and synchronously under controlled incubation temperatures, i.e., for 48 h at 7, 10, 15, 20, and 25 °C, to explore the carbon utilization strategies of soil microbes. We measured the respiration rates of soil microbes in response to different carbon sources, i.e., added glucose (Rg) and initial SOM (Rs), as well as the total respiration rate (Rt). All responses were rapid and characterized by unimodal curves. Furthermore, the characteristic values of these curves, such as the maximum of rate (R-max), the time required to achieve R-max, and the ratio of the duration of R-max to that of 1/2 R-max, were all dependent on incubation temperature. Interestingly, temperature greatly influenced the strategy that microorganisms employed to utilize different carbon sources. The effects of temperature on the intensity of the microbial respiratory response and the ratio of Rg/Rs are important for evaluating the effect of land-use changes or variations in seasonal temperature on SOM turnover and should be considered in ecological models in future studies.

Influences of N deposition on soil microbial respiration and its temperature sensitivity depend on N type in a temperate forest

Knowledge on temperature sensitivity (Q10) of soil microbial respiration is crucial to improving the accuracy in predicting soil organic carbon (C) dynamics in climate–C models. However, the responses of soil microbial respiration and its Q10 to nitrogen (N) deposition, particularly different N types, remain unclear. Therefore, we incubated surface soils collected from a temperate forest receiving simulated N deposition under 15 °C and 25 °C for 150 days to examine the effects of different types of N deposition on soil microbial respiration and its Q10 and reveal their underlying mechanisms. A mixture of inorganic and organic N had the highest suppression on soil microbial respiration, followed by organic N and inorganic N. This suggested that the suppression effect of atmospheric N deposition on microbial respiration was underestimated by previous studies based on single inorganic N. Q10 values in all soils ranged from 1.96 to 2.76 with a mean of 2.41 at the end of incubation. Inorganic N significantly increased the averaged Q10 values, suggesting that inorganic N caused soil microbial respiration to become more sensitive to climate warming than organic N. Across the incubation period, Q10 values exhibited substantial temporal variation, which depended on the N type. Soil microbial respiration was negatively controlled by NO3−-N and bacteria:fungi and gram-positive:gram-negative bacteria ratios. However, Q10 was positively controlled by soil NH4+-N. Our results highlighted the effects of inorganic and organic N deposition on microbial respiration and its potential mechanisms and implied the necessity of considering the N type when predicting soil C cycling and dynamics in increasing N deposition scenario.

The optimum temperature of soil microbial respiration: Patterns and controls

The temperature response of soil microbial respiration (Rh) is of significance, with the optimum temperature of Rh being the key parameter for accurately modeling how it responds to temperature change under climate warming scenarios. However, knowledge about Topt in natural ecosystems remains limited, especially at large scales, which increases the uncertainty of climate projections. Here, we collected 25 soils from tropical to cold-temperate forests in the northern hemisphere to quantify regional variation in Topt and the controls underlying this variation. Rh was measured at high frequency using a novel system under the mode, with temperature gradually increasing from 5 to 50 °C. The results showed that Topt ranged from 38.5 to 46.0 °C (mean: 42.4 °C). Of note, this study is the first to demonstrate that Topt is far higher than the assumed value used in models (35 °C), varying greatly across different climatic zones and increasing with latitude from tropical to cold-temperate forest soils. To some extent, our results supported the substrate supply hypothesis, and contrast with the climate adaption hypothesis. In addition, climate, nutrient, and soil microorganisms jointly regulate regional variation in Topt, together explaining 53% of variation in Topt. The higher Topt in northern regions indicated that these regions have a greater potential to release more CO2 from soil, which might lead to a positive feedback to global warming. In conclusion, process-based models should incorporate the high variability of Topt across regions to improve predictions of the carbon dynamics of terrestrial ecosystems under climate warming scenarios.

氮添加对高寒草甸土壤微生物呼吸及其温度敏感性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 氮添加对高寒草甸土壤微生物呼吸及其温度敏感性的影响 DOI: 10.5846/stxb201705100859 作者: 作者单位: 南京农业大学,南京农业大学,兰州大学,兰州大学,南京农业大学,南京农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 南京农业大学中央高校基本业务费（0306J0887，KYTZ201404） Effects of nitrogen additions on soil microbial respiration and its temperature sensitivity in a Tibetan alpine meadow Author: Affiliation: Nanjing Agricultural University,Nanjing Agricultural University,Lanzhou University,Lanzhou University,Nanjing Agricultural University,Nanjing Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤氮素的可利用性是控制土壤微生物呼吸的重要因素之一，大量研究已经表明增加土壤活性氮的含量可以降低微生物呼吸，但是土壤氮输入对土壤微生物呼吸温度敏感性的影响还不清楚。以青藏高原高寒草甸为研究对象，通过野外施氮试验和室内控制试验相结合的方式，在5℃、15℃和25℃条件下对3种施氮水平的土壤（对照，0g N m-2 a-1；低氮，5g N m-2 a-1；高氮，15g N m-2 a-1）进行培养，探讨土壤微生物呼吸及其温度敏感性对不同氮添加水平的响应情况。结果表明：（1）3个温度培养下的土壤微生物呼吸速率和累积碳释放量均随施氮量的增加而显著降低（P < 0.05）；（2）氮添加对5℃和15℃培养条件下的微生物呼吸温度敏感性没有显著影响，但显著地增加了15℃和25℃培养条件下的微生物呼吸温度敏感性（P < 0.05）；（3）线性相关分析表明，土壤累积碳释放量与土壤有机碳的难降解性显著负相关（P < 0.05），而15℃和25℃培养条件下的微生物呼吸温度敏感性与土壤有机碳的难降解性显著正相关（P < 0.05）。结果表明，在全球气候变暖的背景下，土壤氮输入将增加预测青藏高原高寒草甸地区土壤碳排放的不确定性。 Abstract:The soil C stock of the Tibetan Plateau is of global significance because of its large pool size and the potential positive feedback to climate warming. Soil microbial respiration is an important carbon (C) flux of the global C cycle, and is greatly affected by soil nitrogen (N) availability. Reactive N inputs often reduce soil microbial respiration, but how they affect the temperature sensitivity of soil microbial respiration is still poorly understood. Here, we examined the effect of N additions on soil microbial respiration and its temperature sensitivity (expressed as Q10), and assessed the relative importance of substrate availability and the chemical composition of soil organic C in explaining the variation in soil microbial respiration and Q10. A 4-year field experiment with four simulated N deposition levels, 0, 5, 10, and 15g N m-2 a-1 was conducted. Soil samples were collected from three levels of nitrogen addition rate (0, 5, and 15g N m-2 a-1) and incubated at 5℃, 15℃ and 25℃ in the laboratory. The results showed that N additions significantly increased soil dissolved organic C and available N (P < 0.05), but did not significantly affect soil pH, soil organic C, total N, available P, and total P. Moreover, N additions did not affect microbial biomass C, but significantly decreased microbial biomass N (P < 0.05). The solid-state 13C nuclear magnetic resonance showed that N additions decreased the relative content of O-alkyl C, but increased the relative contents of alkyl C, aromatic C, and carboxylic C, which resulted in higher aromaticity and aliphaticity of soil organic carbon under N addition treatments than that of the control treatment. We also found that N additions significantly decreased soil microbial respiration rate and cumulative C efflux under three temperatures (P < 0.05), but significantly increased Q10 under the incubation temperature of 15℃ and 25℃ (P < 0.05). Linear correlation analysis showed that microbial respiration was negatively correlated with the complexity of soil organic C, whereas Q10 under the incubation temperature of 15℃ and 25℃ was positively correlated with the complexity of soil organic C. These findings support the prediction based on kinetic theory that soil organic C, with recalcitrant molecular structure, has a high temperature sensitivity of respiration. Together, our results suggest that changes in chemical structure of soil organic C induced by N inputs may play an important role in regulating the response of soil microbial respiration to elevated temperature, and further increase the uncertainty in predicting net soil C losses in the scenario of warming on the Tibetan Plateau. 参考文献 相似文献 引证文献

Long-term nitrogen & phosphorus additions reduce soil microbial respiration but increase its temperature sensitivity in a Tibetan alpine meadow

Nutrient availability may exert major controls over soil microbial respiration, especially in carbon (C)-rich, nitrogen (N)-limited ecosystems in high elevation regions, but how soil organic matter (SOM) decomposition and its temperature sensitivity respond to long-term N & P additions in alpine ecosystems remains unclear. We examined the impact of long-term (15 yr) N & P additions on soil microbial respiration and its temperature sensitivity (Q10), and assessed the relative importance of nutrient-induced alterations in substrate quality and the microbial community composition in explaining the variation in soil respiration and temperature sensitivity. We found that N & P additions significantly reduced microbial respiration rates and cumulative C efflux, but increased the Q10 (15/5 °C). Also, N & P additions reduced the biomass of the whole microbial community, gram negative bacteria and fungi, but increased the aromaticity and aliphaticity of soil organic C substrate. Across the treatments, averaged Q10 was positively correlated with the complexity of SOM as characterized by 13C-NMR, supporting the prediction based on kinetic theory that SOM with recalcitrant molecular structure is with high temperature sensitivity. Together, our results showed that changes in both substrate quality and soil microbial community induced by long-term nutrient inputs may alter the response of soil microbial respiration to elevated temperature. Because the positive effects of increasing temperature sensitivity for use of lower quality substrates on C emission may be offset by lower absolute rates at any one temperature, long-term N & P additions increase the uncertainty in predicting the net soil C losses in the scenario of warming on Tibetan Plateau.

森林土壤融化期异养呼吸和微生物碳变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 森林土壤融化期异养呼吸和微生物碳变化特征 DOI: 10.5846/stxb201511162320 作者: 作者单位: 中国科学院大气物理研究所,中国科学院大气物理研究所,中国科学院大气物理研究所,长安大学地球科学学院,Faculty of Agriculture, Yamagata University, Tsuruoka, Japan 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41175133，21228701，41275166，41321064，41575154） Changes in heterotrophic respiration and microbial biomass carbon of forest soils during thaw Author: Affiliation: Institute of Atmospheric Physics, Chinese Academy of Sciences,Institute of Atmospheric Physics, Chinese Academy of Sciences,Institute of Atmospheric Physics, Chinese Academy of Sciences,College of Earth Science and Resources, Chang'an University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用室内土柱培养的方法，研究在不同湿度（55%和80% WFPS，土壤充水孔隙度）和不同氮素供给（NH4Cl和KNO3，4.5 g N/m2）条件下，外源碳添加（葡萄糖，6.4 g C/m2）对温带成熟阔叶红松混交林和次生白桦林土壤融化过程微生物呼吸和微生物碳的激发效应。结果表明：在整个融化培养期间，次生白桦林土壤对照CO2累积排放量显著高于阔叶红松混交林土壤。随着土壤湿度的增加，次生白桦林土壤对照CO2累积排放量和微生物代谢熵（qCO2）显著降低，而阔叶红松混交林土壤两者显著地增加（P < 0.05）。两种林分土壤由葡萄糖（Glu）引起的CO2累积排放量（9.61-13.49 g C/m2）显著大于实验施加的葡萄糖含碳量（6.4 g C/m2），同时由Glu引起的土壤微生物碳增量为3.65-27.18 g C/m2，而施加Glu对土壤DOC含量影响较小。因此，这种由施加Glu引起的额外碳释放可能来源于土壤固有有机碳分解。融化培养结束时，阔叶红松混交林土壤未施氮处理由Glu引起的CO2累积排放量在两种湿度条件下均显著大于次生白桦林土壤（P < 0.001）；随着湿度的增加，两种林分土壤Glu引起的CO2累积排放量显著增大（P < 0.001）。单施KNO3显著地增加两种湿度的次生白桦林土壤Glu引起的CO2累积排放量（P < 0.01）。单施KNO3显著地增加了两种湿度次生白桦林土壤Glu引起的微生物碳（P < 0.001），单施NH4Cl显著地增加低湿度阔叶红松混交林土壤Glu引起的微生物碳（P < 0.001）。结合前期报道的未冻结实验结果，发现冻结过程显著地影响外源Glu对温带森林土壤微生物呼吸和微生物碳的刺激效应（P < 0.05），并且无论冻结与否，温带森林土壤微生物呼吸和微生物碳对外源Glu的响应均与植被类型、土壤湿度、外源氮供给及其形态存在显著的相关性。 Abstract:Packed soil core incubation experiment was made to study the effects of external carbon (C) (glucose, 6.4 g C/m2) addition on microbial respiration and microbial biomass C (MBC) in soils of a mature broadleaf and Korean pine mixed forest (BKPF) and an adjacent white birch forest (WBF) during thaw under different soil moisture levels (55% and 80% water-filled pore space) and nitrogen (N) supply (NH4Cl and KNO3, 4.5 g N/m2). The results showed that, without C and N addition, cumulative CO2 flux from the WBF soil was significantly higher than that from the BKPF soil during the incubation period. With increasing soil moisture, the cumulative CO2 flux and microbial metabolic quotient (qCO2) decreased in the WBF soil but increased in the BKPF soil without C and N addition(P < 0.05). The glucose-induced cumulative CO2 fluxes from the two forest soils ranged from 9.61 to 13.49 g CO2-C/m2, which was greater than the dose of added C in the form of glucose. The glucose-induced MBC in the two forest soils ranged from 3.65 to 27.18 g C/m2, while glucose addition had little impact on soil dissolved organic C pool. Hence, the extra C released upon addition of glucose may result from the decomposition of soil native organic C. Without N addition and under the two soil moisture levels, the glucose-induced cumulative CO2 flux from the BKPF soil was significantly higher than that from the WBF soil during thaw (P < 0.001). With increasing soil moisture, the glucose-induced cumulative CO2 fluxes from the two forest soils were significantly increased (P < 0.001). The addition of KNO3 alone significantly increased the glucose-induced cumulative CO2 flux (P < 0.01) and the glucose-induced MBC (P < 0.001) in the WBF soil under two soil moisture levels (P < 0.001). Addition of NH4Cl alone significantly increased the glucose-induced MBC in the BKPF soil with low moisture level. Based on the results from the previously reported non-freezing experiments and the results of the present study, it can be concluded that freezing treatment significantly affects the stimulating effects of glucose on soil microbial respiration and MBC under temperate forests. Regardless of whether freezing occurred or not, the responses of soil microbial respiration and MBC to the addition of extraneous C as glucose in temperate forests depend on vegetation type, soil moisture, and the amount and type of N added. 参考文献 相似文献 引证文献

Assessing soil microbial respiration capacity using rDNA- or rRNA-based indices: a review

Understanding soil heterotrophic respiration in relation to microbial properties is not only fundamental to soil respiration modelling, prediction, and regulation through management, but also essential to interpreting microbial community dynamics from an ecologically meaningful perspective. This paper reviewed the recent advances in knowledge and proposed future directions for exploring the respiration-microbe relationships by means of rDNA- or rRNA-based indices (i.e. rDNA copies, rRNA copies, and rDNA- or rRNA-based community structures). We first elucidated the theoretical basis for using rDNA- or rRNA-based indices to probe into soil microbial respiration. Then, the published studies that simultaneously measured soil microbial respiration and the rDNA- or rRNA-based indices were synthesized, extracted, and analysed to further explore the respiration-microbe relationships. At last, the uncertainties and perspectives for establishing the respiration-microbe links were proposed and discussed. The rDNA- or rRNA-based indices are theoretically promising for pinpointing the relationships between soil heterotrophic respiration and microbial properties. Our systematic review suggested that the correlations between bacterial rDNA copies and microbial respiration are inconsistent across studies, while the fungal and archaeal rDNA (or ITS) copies showed moderately positive and negative correlations with soil microbial respiration, respectively. Bacterial 16S rDNA-based community structures were significantly correlated with soil microbial respiration in some studies, but not in some short-term situations. Although rRNA copies are widely used as the proxies of microbial activity, no significant correlations between rRNA copies and soil microbial respiration have been found in previous studies. Bacterial 16S rRNA-based community structures were correlated well with the short-term responses of soil microbial respiration to rewetting or labile carbon amendments and clearly outperformed other rDNA- or rRNA-based indices. As respiration-microbe relationships can be affected by many factors, such as soil physicochemical properties and even the analysis methods of microbial indices, the 69 previous studies included in this review actually provided limited information on them, and the aforementioned results still need to be further confirmed in future studies. Overall, the relationships between soil microbial respiration and rDNA- or rRNA-based indices are still far from being well established. Future research should be directed to systematically understanding the respiration-microbe links, with more attention to the fungus-, archaea- and RNA-related molecular indices. The relationships between microbial specific lineages and total respiration rates should be explored in future studies, and the effects of edaphic properties on the respiration-microbe relationships should also be evaluated.

Response of Soil Respiration to Extreme Precipitation in Semi-arid Regions

Evaluating the response of soil microbial respiration to extreme precipitation event is significant for a better understanding about the influence of the change of precipitation regime on soil carbon cycling under global warming. A simulated experiment of extreme precipitations was conducted during the rainy season (July-September 2015) in the Changwu State Key Agro-Ecological Station, Shaanxi, China. The treatments consisted of three total precipitations in rainy season (600 mm, 300 mm, and 150 mm) and two precipitation regimes (10 mm, 150 mm; P10, P150). Soil microbial respiration varied differently in the same single rainfall event among three precipitations. The variation coefficient of soil microbial respiration under 600 mm total precipitation was 36% (P150) and 33% (P10), and 28% and 22% under 300 mm total precipitation, 43% and 29% under 150 mm total precipitation. Under 600 mm total precipitation, the cumulative soil microbial respiration under P150 was 20% less than that under P10; however, the cumulative soil respiration of P150 under 150 mm total precipitation was 22% more than that under P10; and there was no significant difference between P10 and P150 under 300 mm total precipitation. Therefore, the duration in soil water stress must be considered to estimate soil microbial respirations under extreme precipitations.

Responses of soil microbial respiration to plantations depend on soil properties in subtropical China

Assessing the impact of plantation on microbial respiration (MR) is vitally important to understand the interactions between belowground metabolism and land use change. In this study, cumulative MR was determined by alkali absorption method in 1, 3, 7, 14, 21, 28, 35, 42, 49, and 56 days from the soil in a representative plantations in the subtropical region of China. The treatment of plantations contained no plant (CK), orange trees (Citrus reticulata)+Bahia grass (Paspalum notatum) (GB), orange trees (C. reticulata)+Bahia grass (P. notatum)+soybean (Giycine max (L.) Merrill) (GBH). Results showed that plantation had significant effects on microbial respiration and the responses of microbial respiration to plantation from different soil layers and topographies were different: in 0–20 cm in uphill: GB>GBH>CK; in 20–40 cm in uphill: GBH>CK>GB; in 0–20 cm in downhill: GBH>CK>GB; in 20–40 cm in downhill: GB>CK>GBH. Furthermore, plantation also altered the relationships between MR and soil properties. In CK, microbial respiration was positively correlated with NH4+ and soil total N, and negatively correlated with soil moisture, pH, NO3−, and microbial biomass carbon (MBC). In GB, microbial respiration under GB significantly negatively correlated with dissolved organic carbon (DOC). In GBH, microbial respiration under GBH was positively correlated with NH4+, MBC, total soil carbon (TC), and total soil nitrogen (TN), and negatively correlated with soil moisture (SM), pH, NO3−, and DOC. The underlying mechanisms could be attributed to soil heterogeneity and the effects of plantation on soil properties. Our results also showed that plantation significantly increased soil C storage, which suggested plantation is a key measure to enhance soil C sequestration and mitigate global CO2 emission, especially for the soil with low initial soil carbon content or bared soil.

Strong pulse effects of precipitation events on soil microbial respiration in temperate forests

Precipitation is a critical factor triggering soil biogeochemical processes in arid and semi-arid regions. In this study, we selected soils from two temperate forests—a mature natural forest and a degraded secondary forest—in a semi-arid region. We investigated the pulse effects of simulated precipitation (to reach 55% soil water-holding capacity) on the soil microbial respiration rate (RS). We performed high-intensity measurements (at 5-min intervals for 48h) to determine the maximum value of RS (RS-max), the time to reach RS-max (TRS‐max), and the duration of the pulse effect (from the start to the end of ½RS-max). The responses of RS to simulated precipitation were rapid and strong. RS-max was significantly higher in degraded secondary forest (18.69μgCgsoil−1h−1) than in mature natural forest (7.94μgCgsoil−1h−1). In contrast, the duration of the pulse effect and TRS‐max were significantly lower in degraded secondary forest than in mature natural forest. Furthermore, the accumulative microbial respiration per gram of soil (ARS‐soil) did not differ significantly between degraded secondary forest and mature natural forest, but the accumulative microbial respiration per gram of soil organic C (ARS‐soc) was significantly higher in degraded secondary forest than in mature natural forest. Soil microbial biomass, soil nutrient, and litter nitrogen content were strongly correlated with the duration of the pulse effect and TRS‐max. Soil physical structure, pH, and litter nitrogen content were strongly correlated with RS-max and ARS‐soc. Our results indicate that the responses of soil microbial respiration to simulated precipitation are rapid and strong and that microbial respiration rate per gram C can be used to precisely determine the precipitation pulse of different soil samples as well as the effects of changing precipitation patterns on soil C content under various scenarios of global climate change.

Seasonality, Rather than Nutrient Addition or Vegetation Types, Influenced Short-Term Temperature Sensitivity of Soil Organic Carbon Decomposition.

The response of microbial respiration from soil organic carbon (SOC) decomposition to environmental changes plays a key role in predicting future trends of atmospheric CO2 concentration. However, it remains uncertain whether there is a universal trend in the response of microbial respiration to increased temperature and nutrient addition among different vegetation types. In this study, soils were sampled in spring, summer, autumn and winter from five dominant vegetation types, including pine, larch and birch forest, shrubland, and grassland, in the Saihanba area of northern China. Soil samples from each season were incubated at 1, 10, and 20°C for 5 to 7 days. Nitrogen (N; 0.035 mM as NH4NO3) and phosphorus (P; 0.03 mM as P2O5) were added to soil samples, and the responses of soil microbial respiration to increased temperature and nutrient addition were determined. We found a universal trend that soil microbial respiration increased with increased temperature regardless of sampling season or vegetation type. The temperature sensitivity (indicated by Q10, the increase in respiration rate with a 10°C increase in temperature) of microbial respiration was higher in spring and autumn than in summer and winter, irrespective of vegetation type. The Q10 was significantly positively correlated with microbial biomass and the fungal: bacterial ratio. Microbial respiration (or Q10) did not significantly respond to N or P addition. Our results suggest that short-term nutrient input might not change the SOC decomposition rate or its temperature sensitivity, whereas increased temperature might significantly enhance SOC decomposition in spring and autumn, compared with winter and summer.

The effects of N and P additions on soil microbial properties in paired stands of temperate secondary forests and adjacent larch plantations in Northeast China

The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.