Microbial N2O release during the course of thawing of soil was investigated in model experiment focusing on denitrification, since freeze-thaw has been shown to cause significant physical and biological changes in soil, including a surge of N2O and CO2. The origin of these is still controversially discussed. The increase in denitrification after thawing may be attributed to the diffusion of organic substrates newly available to denitrifiers from disrupted soil aggregates, leading to an increase in microbial activity. Laboratory experiments with upper soil layer of a grassland were conducted in microcosms for real-time gas measurements during the entire phase of freeze and thaw. Shifts in microbial communities were evident on resolution of 16S and 18S rRNA genes and transcripts by denaturing gradient gel electrophoresis (DGGE). Microbial expression profiles were compared by RNA-arbitrarily primed PCR technique and subsequent resolution of amplified products on acrylamide gels. Differences in expression levels of periplasmic nitrate reductase gene (napA) and cytochrome cd1 nitrite reductase (nirS) were observed by most-probable-number-reverse transcription-PCR, with higher levels of expression occurring just after thawing began, followed by a decrease. napA and nirS DGGE profiles showed no change in banding patterns with fingerprints derived from DNA, whereas those derived from cDNA showed a clear succession of denitrifying bacteria, with the most complex pattern being observed at the end of the N2O surge. This study provides insight into the structural community changes and expression dynamics of denitrifiers as a result of freeze-thaw stress. Also, the results presented here support the belief that the gas fluxes observed during thawing is a result of freezing initiated high microbial activity.

Climate change will alter precipitation patterns with consequences for soil C cycling. An understanding of how fluctuating soil moisture affects microbial processes is therefore critical to predict responses to future global change. We investigated how long-term experimental field drought influences microbial tolerance to lower moisture levels ("resistance") and ability to recover when rewetted after drought ("resilience"), using soils from a heathland which had been subjected to experimental precipitation reduction during the summer for 18 years. We tested whether drought could induce increased resistance, resilience, and changes in the balance between respiration and bacterial growth during perturbation events, by following a two-tiered approach. We first evaluated the effects of the long-term summer drought on microbial community functioning to drought and drying-rewetting (D/RW), and second tested the ability to alter resistance and resilience through additional perturbation cycles. A history of summer drought in the field selected for increased resilience but not resistance, suggesting that rewetting after drought, rather than low moisture levels during drought, was the selective pressure shaping the microbial community functions. Laboratory D/RW cycles also selected for communities with a higher resilience rather than increased resistance. The ratio of respiration to bacterial growth during D/RW perturbation was lower for the field drought-exposed communities and decreased for both field treatments during the D/RW cycles. This suggests that cycles of D/RW also structure microbial communities to respond quickly and efficiently to rewetting after drought. Our findings imply that microbial communities can adapt to changing climatic conditions and that this might slow the rate of soil C loss predicted to be induced by future cyclic drought.© 2018 John Wiley & Sons Ltd.

分析冻融作用对土壤微生物养分限制的影响,可为黑土资源可持续利用提供重要支撑。本研究选取位于黑龙江省克山县典型厚层黑土区的坡耕地,测定自然条件下冻融前后土壤养分、土壤微生物生物量和土壤酶活性等,结合¹³⁷Cs示踪技术估算多年平均土壤侵蚀速率,研究冻融作用对土壤微生物养分限制的影响,并分析土壤微生物养分限制对土壤侵蚀速率的响应。结果表明: 1)坡耕地土壤侵蚀速率变化范围为479.31～7802.33 t·km^-2·a^-1,平均值为2751.02 t·km^-2·a^-1。2)冻融作用下坡耕地土壤水溶性有机氮和微生物生物量碳(MBC)分别显著降低了27.9%和37.3%,而冻融作用对土壤有机碳(SOC)、全氮(TN)、全磷(TP)、水溶性有机碳、速效磷、微生物生物量氮和磷均无显著影响。3)冻融作用下坡耕地β-1,4-葡糖苷酶、亮氨酸氨基肽酶和β-1,4-N-乙酰氨基葡糖苷酶活性分别降低了43.2%、11.0%和25.5%。酶计量矢量模型计算结果表明,土壤微生物受到相对碳和磷限制,冻融作用减弱了土壤微生物相对碳限制,而增强了土壤微生物相对磷限制。4)结构方程模型分析表明,冻融作用对土壤微生物相对磷限制和相对碳限制分别存在直接正和负效应;土壤侵蚀速率对土壤微生物相对碳限制存在直接负效应。5)冻融前后土壤SOC和TN、冻融后TP、冻融后MBC和冻融前矢量长度与土壤侵蚀速率呈显著负相关。冻融作用降低了土壤碳氮获取酶活性,进而改变了土壤微生物养分限制状况。本研究加深了黑土区冻融作用对土壤微生物养分限制影响的机理认识,为黑土区坡耕地养分管理提供了重要支撑。

稻田是二氧化碳(CO₂)、甲烷(CH₄)和氧化亚氮(N₂O)等温室气体的重要排放源之一，稻田温室气体产生与排放一直是研究关注的热点和重点。IPCC预测未来全球气候变化主要表现为气候变暖、大气CO₂浓度和近地层臭氧(O₃)浓度升高，三者对稻田温室气体的排放具有不同程度的影响。稻田微生物群落对全球气候变化的响应也很敏感，进而直接或间接影响温室气体的排放。通过文献综述，总结了近年来全球气候变化对稻田温室气体排放和稻田微生物群落的影响、全球气候变化背景下稻田微生物对温室气体排放的效应以及稻田关键微生物在温室气体减排中的应用，指出未来应综合考虑多因子气候变化对稻田温室气体排放的影响并加强对其机制的研究，加强稻田微生物对温室气体排放调控效应和机制研究，以及筛选减排效果显著的微生物类群用以开发成熟的稻田温室气体减排微生物产品。

To understand soil microbial community stability and temporal turnover in response to climate change, a long-term soil transplant experiment was conducted in three agricultural experiment stations over large transects from a warm temperate zone (Fengqiu station in central China) to a subtropical zone (Yingtan station in southern China) and a cold temperate zone (Hailun station in northern China). Annual soil samples were collected from these three stations from 2005 to 2011, and microbial communities were analyzed by sequencing microbial 16S ribosomal RNA gene amplicons using Illumina MiSeq technology. Our results revealed a distinctly differential pattern of microbial communities in both northward and southward transplantations, along with an increase in microbial richness with climate cooling and a corresponding decrease with climate warming. The microbial succession rate was estimated by the slope (w value) of linear regression of a log-transformed microbial community similarity with time (time-decay relationship). Compared with the low turnover rate of microbial communities in situ (w=0.046, P<0.001), the succession rate at the community level was significantly higher in the northward transplant (w=0.058, P<0.001) and highest in the southward transplant (w=0.094, P<0.001). Climate warming lead to a faster succession rate of microbial communities as well as lower species richness and compositional changes compared with in situ and climate cooling, which may be related to the high metabolic rates and intense competition under higher temperature. This study provides new insights into the impacts of climate change on the fundamental temporal scaling of soil microbial communities and microbial phylogenetic biodiversity.

Climatic changes will not only result in higher overall temperature, but also in greater variability in weather conditions. Antarctic soils are subjected to extremely variable conditions in the form of frequent freeze-thaw cycles (FTCs), but the importance of alteration in FTC frequency, compared with increases in average temperature and indirect vegetation-mediated effects on soil microorganisms, is still unknown. We therefore designed two complementary microcosm experiments using undisturbed soil cores from Signy Island (60 degrees 43'S, 45 degrees 38'W) in the maritime Antarctic. The experiments consisted of soil core incubations with or without the overlying vegetation at four different temperatures and six different FTC regimes. We assessed bacterial and fungal density and community structure, as well as the density of several key genes in microbial nutrient cycles using a combination of RNA- and DNA-based molecular fingerprinting and quantitative PCR approaches in addition to enzymatic activity assays. Results showed that bacteria were more affected by warming than by changes in FTC frequency. In contrast, fungal community structure and abundance were mostly influenced by FTC frequency, as well as the presence of vegetation cover. The relative densities of several bacterial gene families involved in key steps of the N-cycle were affected by FTCs, while warming had little or no effect. The FTCs and incubation temperature also strongly influenced laccase enzymatic activity in soil. In total, our results suggest that, in addition to climatic warming, increased climatic variability may also have a profound impact on Antarctic microbial communities. Although these effects are difficult to detect with assays of total bacterial community structure, they do become manifest in the analysis of key functional gene densities.

The colonization of land by plants appears to have coincided with the appearance of mycorrhiza-like fungi. Over evolutionary time, fungi have maintained their prominent role in the formation of mycorrhizal associations. In addition, however, they have been able to occupy other terrestrial niches of which the decomposition of recalcitrant organic matter is perhaps the most remarkable. This implies that, in contrast to that of aquatic organic matter decomposition, bacteria have not been able to monopolize decomposition processes in terrestrial ecosystems. The emergence of fungi in terrestrial ecosystems must have had a strong impact on the evolution of terrestrial bacteria. On the one hand, potential decomposition niches, e.g. lignin degradation, have been lost for bacteria, whereas on the other hand the presence of fungi has itself created new bacterial niches. Confrontation between bacteria and fungi is ongoing, and from studying contemporary interactions, we can learn about the impact that fungi presently have, and have had in the past, on the ecology and evolution of terrestrial bacteria. In the first part of this review, the focus is on niche differentiation between soil bacteria and fungi involved in the decomposition of plant-derived organic matter. Bacteria and fungi are seen to compete for simple plant-derived substrates and have developed antagonistic strategies. For more recalcitrant organic substrates, e.g. cellulose and lignin, both competitive and mutualistic strategies appear to have evolved. In the second part of the review, bacterial niches with respect to the utilization of fungal-derived substrates are considered. Here, several lines of development can be recognized, ranging from mutualistic exudate-consuming bacteria that are associated with fungal surfaces to endosymbiotic and mycophagous bacteria. In some cases, there are indications of fungal specific selection in fungus-associated bacteria, and possible mechanisms for such selection are discussed.

利用黑龙江省水利科学研究院水利试验研究中心综合实验观测场2011年11月-2012年4月整个冻结融化期的实测野外黑土耕层土壤温度和水分数据, 对中-深季节冻土区黑土耕层土壤冻融过程中冻结和融化特征分阴、阳坡进行了分析, 研究了冻融过程中不同深度土壤水分的变化情况, 并探讨了降水对不同深度耕层土壤含水量变化的影响. 结果表明:黑土耕层土壤冻结融化过程分为5个阶段, 历时164 d, 约5.5个月. 阶段I, 秋末冬初黑土耕层土壤开始步入冻结期; 阶段II, 黑土耕层土壤整日处于冻结状态, 阴坡比同样深度的阳坡土壤温度低; 阶段III为黑土耕层土壤稳定冻结期; 阶段IV, 黑土耕层土壤步入昼融夜冻的日循环交替状态, 冻融循环的土层逐渐向深部发展, 阳坡比阴坡融化得更深、更早, 阴坡比阳坡经历冻融循环次数更多; 阶段V为稳定融化期, 在融化过程不存在冻融交替的现象, 直到整个冻层内的土壤全部消融. 各深度位置阴坡土壤温度的最高值出现时间比阳坡晚约0.5 h. 经过整个冻结融化期后, 阴、阳坡各层土壤含水量均大于冻结前, 阴坡土壤含水量比阳坡整体偏低. 在整个冻结融化期, 阳坡地下1 cm、5 cm、10 cm 及15 cm处含水量最大值出现在地下5 cm; 阴坡的含水量整体趋于平稳且在融化期受降水影响明显.

Extracellular degradative enzymes released by psychrophilic marine bacteria (growing optimally at or below 15 degrees C and maximally at 20 degrees C) typically express activity optima at temperatures well above the upper growth limit of the producing strain. In the present study, we investigated whether or not near-zero Arctic environments contain extracellular enzymes with activity optimized to temperatures lower than previously reported. By applying fluorescently tagged substrate analogues to measure leucine-aminopeptidase and chitobiase activity, the occurrence of extracellular enzymatic activity (EEA) with remarkably low temperature optima (15 degrees C) was documented in sea-ice samples. An extremely psychrophilic bacterial isolate, strain 34H, yielded an extract of cell-free protease with activity optimized at 20 degrees C, the lowest optimum yet reported for cell-free EEA from a pure culture. The use of zymogram gels revealed the presence of three proteolytic bands (between 37 and 45 kDa) in the extract and the release of the greatest quantities of the proteases when the strain was grown at -1 degrees C, suggesting a bacterial strategy for counteracting the effects of very cold temperatures on the catalytic efficiency of released enzymes. The detection of unusually cold-adapted EEA in environmental samples has ramifications not only to polar ecosystems and carbon cycling but also to protein evolution, biotechnology and bioremediation.

Root-associated microbes can improve plant growth, and they offer the potential to increase crop resilience to future drought. Although our understanding of the complex feedbacks between plant and microbial responses to drought is advancing, most of our knowledge comes from non-crop plants in controlled experiments. We propose that future research efforts should attempt to quantify relationships between plant and microbial traits, explicitly focus on food crops, and include longer-term experiments under field conditions. Overall, we highlight the need for improved mechanistic understanding of the complex feedbacks between plants and microbes during, and particularly after, drought. This requires integrating ecology with plant, microbiome, and molecular approaches and is central to making crop production more resilient to our future climate.Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

•   Niche differentiation for different soil substrates has been proposed as a mechanism contributing to ectomycorrhizal fungal diversity. This hypothesis has been largely untestable because of a lack of techniques to study the in situ distribution of ectomycorrhizal hyphae. •   We developed a technique involving soil DNA extraction, PCR and terminal restriction fragment length polymorphism (T-RFLP) analysis for species identification to investigate the vertical distribution of fungal hyphae in four distinct layers of the forest floor (lower litter, F-layer, H-layer, and B-horizon) of a Pinus resinosa plantation. •   Fungal communities differed markedly among the four layers. Cluster analysis suggested six different patterns of resource utilization: litter-layer specialists, litter-layer generalists, F-layer, H-layer, and B-horizon species, and multilayer generalists. Known ectomycorrhizal species were found in all six clusters. •   This spatial partitioning observed among ectomycorrhizal fungi along a single, relatively simple substrate-resource gradient supports the niche differentiation hypothesis as an important mechanism contributing to ectomycorrhizal fungal diversity.

为研究棉花秸秆（棉秆）还田配施秸秆腐熟剂及尿素对土壤微生物和土壤酶活性的影响，2021年在山东德州市宁津县设置5个处理，在棉花盛花期和收获期采集土壤样品，测定土壤微生物数量及土壤酶活性。结果显示：在0～20 cm土层中，棉秆还田可以增加土壤中微生物数量，尤其棉秆还田配施秸秆腐熟剂（T3处理）和尿素（T4处理）能显著增加盛花期、收获期土壤中细菌数量和收获期土壤真菌数量；但随着土层深度的增加，微生物总量呈减少趋势。棉秆还田可以提高土壤酶活性，在0～20 cm土层中，棉秆还田配施秸秆腐熟剂、尿素分别显著提高盛花期、收获期的土壤脲酶活性，配施尿素可以显著提高土壤磷酸酶和过氧化氢酶活性；在0～40 cm土层中，增施尿素可显著提高土壤过氧化氢酶活性，但＞20～40 cm土层脲酶和磷酸酶活性在处理间均无显著差异；随着土层深度的增加，土壤酶活性呈下降趋势。结果初步表明，德州地区冬季棉秆还田结合增施秸秆腐熟剂或尿素对棉田土壤微生物数量及土壤酶活性具有正向效应。