西北干旱荒漠区生态系统可持续管理理念与模式

结合对西北干旱区水资源短缺、资源开发中的生态与经济矛盾突出、气候变暖可能加剧干旱区荒漠化以及生态水权与长效保障机制缺失等问题的分析诊断,探讨了荒漠区生态系统可持续管理面临的问题与难点,分析提出了荒漠生态系统植被保育的生态水位与生态阈值,阐述了荒漠-绿洲过渡带生态融合以及绿洲生态系统安全的生态防护梯度等干旱区生态系统管理理念;结合干旱区极端环境自然条件,在多年现场试验基础上,研发集成了退化群落改造与生态多样性构建技术、植物群落结构优化配置、组装与生态融合技术、生态系统恢复水分利用与生态自维持技术以及胡杨萌蘖更新技术等多种适宜荒漠植被恢复与重建的技术模式,并进行了成功实践和试验示范,为干旱荒漠区生态系统可持续管理提供了重要科技支撑。     

荒漠草原盐沼湿地苦豆子土壤细菌群落构建机制及其影响因素

【背景】荒漠草原盐沼湿地是陆地生态系统的重要组成部分,土壤水分和盐分变化是影响该生态系统土壤细菌群落构建的重要因素。【目的】土壤细菌群落构建是由确定性和随机性主导的连续生态过程,阐明荒漠草原盐沼湿地土壤细菌群落的构建机制对于加深微生物作为关键生态系统因子重要性的理解具有积极意义。【方法】以宁夏中部典型荒漠草原盐沼苦水湖湿地为研究对象,对近湖边（near the lake,NL）和远离湖边（far from the lake,FL）苦豆子群落土壤理化特性进行测定并结合土壤细菌高通量测序分析。【结果】NL和FL样地具有明显的水盐梯度变化,NL样地土壤pH、含水量和电导率均显著高于FL样地;变形菌门、放线菌门、厚壁菌门、拟杆菌门和黏菌门是研究区域土壤细菌群落的优势菌门,变形菌门相对丰度随水盐梯度上升而升高,放线菌门和厚壁菌门相对丰度则随之下降,门下成员大多与水盐变化具有明显的相关性;此外,FL样地土壤细菌网络则具有稳定的网络关系;随着NL样地向FL样地的延伸,土壤细菌群落由随机过程主导,并且受pH、电导率和环境变量的影响。【结论】荒漠草原盐沼湿地水分和盐分的变化改变了土壤细菌群落结构;土壤细菌群落通过生态位占据等策略提高逆境下的生存能力;细菌群落构建是随机过程和确定性过程组成的连续统一体,同样受环境变化的影响。本结果揭示了荒漠草原盐沼湿地细菌群落结构和相互关系对环境变化的响应特征,同时阐明了该区土壤细菌群落的构建机制及影响因素,也为相关科学研究提供了一定理论参考。     

锦鸡儿属灌木阻止干旱草地沙漠化生态过程

纵观全球沙漠化的研究进展,从宏观上研究沙漠化现状和后果的报道较多,对沙漠化内在过程的综合研究较少,灌木在阻止干旱区草原沙漠化中的生态作用缺乏研究。研究假设：在干旱地区,灌木的存在提高土壤营养水平,提升土壤保水能力,促进林下植物和土壤生物群落,进而减轻风蚀和固结土壤,这些相互联系的生态过程共同阻止了草原沙漠化。为了验证上述假设,我们以内蒙古阿拉善地区的荒漠化草原为样地,研究锦鸡儿属灌木的固土能力、提高土壤保水能力、改善土壤营养能力和促进生物群落能力,从生物、土壤、水分和沙物质运动等多过程来探讨锦鸡儿属灌木在阻止草原沙漠化中的作用。目的是弄清灌木阻止干旱草地沙漠化的生态过程。在阿拉善荒漠化草原区,锦鸡儿属灌木盖度大约为12.40%。在100 m²的土地上现有灌木固土2.01 m³,固土效率为167 cm³/g鲜重,每年灌木生长可以增加固土能力0.264 m³/100 m²土地。锦鸡儿属灌木提高了土壤湿度(灌丛效应SE=0.120)和土壤对雨水的保持能力(SE 0.155),改善了土...     

Responses of Bacterial Communities to Simulated Climate Changes in Alpine Meadow Soil of the Qinghai-Tibet Plateau

The soil microbial community plays an important role in terrestrial carbon and nitrogen cycling. However, microbial responses to climate warming or cooling remain poorly understood, limiting our ability to predict the consequences of future climate changes. To address this issue, it is critical to identify microbes sensitive to climate change and key driving factors shifting microbial communities. In this study, alpine soil transplant experiments were conducted downward or upward along an elevation gradient between 3,200 and 3,800 m in the Qinghai-Tibet plateau to simulate climate warming or cooling. After a 2-year soil transplant experiment, soil bacterial communities were analyzed by pyrosequencing of 16S rRNA gene amplicons. The results showed that the transplanted soil bacterial communities became more similar to those in their destination sites and more different from those in their “home” sites. Warming led to increases in the relative abundances in Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria and decreases in Acidobacteria, Betaproteobacteria, and Deltaproteobacteria, while cooling had opposite effects on bacterial communities (symmetric response). Soil temperature and plant biomass contributed significantly to shaping the bacterial community structure. Overall, climate warming or cooling shifted the soil bacterial community structure mainly through species sorting, and such a shift might correlate to important biogeochemical processes such as greenhouse gas emissions. This study provides new insights into our understanding of soil bacterial community responses to climate warming and cooling.     

Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska

Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root‐associated, respond to warming. Here, we investigate how long‐term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long‐term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU‐rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium‐distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium‐distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage.     

喀斯特石漠化治理区钙果种植年限对根内细菌群落的影响

存在于健康植物根中的内生细菌不但能够与宿主植物建立共生关系,而且还具有促进植物生长、提升植物对营养元素摄取能力等功能,从而对维持陆地生态平衡、提升喀斯特石漠化综合治理成效具有重要的意义。【目的】探究宿主植物根中的内生细菌群落结构,为深入认识宿主植物-内生细菌的互作机制提供理论依据。【方法】以被引种到喀斯特断陷盆地石漠化综合治理区不同种植年限钙果根中的内生细菌和根际土为研究对象,分析根内生细菌群落特征和根际土理化性质。【结果】钙果种植年限对研究区土壤质量整体有着直接、显著的影响,并间接影响根内生细菌群落。根内生细菌群落以共生互作为主,通过共网络结构识别出种植第一年和第三年的前三位优势属为链霉菌属(Streptomyces)、卡氏伯克霍尔德菌属(Burkholderia-Caballeronia- Paraburkholderia)和噬几丁质菌属(Chitinophaga),种植第五年的前三位优势属为Streptomyces、Chitinophaga和海无柄孢囊黏细菌属(Haliangium)。根内生细菌群落的形成主要由随机性过程中的生态漂变所主导。【结论】不同生长阶段钙果根内生细菌群落结构的差异是由于随机性过程赋予了微生物物种多样化。内生细菌群落的共生互作关系以及优势菌具有生防功能,可增强钙果定殖能力和生长,进而提升钙果在喀斯特断陷盆地石漠化综合治理区的生态效益和经济效益。     

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.     

Contrasting primary successional trajectories of fungi and bacteria in retreating glacier soils

Early community assembly of soil microbial communities is essential for pedogenesis and development of organic legacies. We examined fungal and bacterial successions along a well‐established temperate glacier forefront chronosequence representing ~70 years of deglaciation to determine community assembly. As microbial communities may be heavily structured by establishing vegetation, we included nonvegetated soils as well as soils from underneath four plant species with differing mycorrhizal ecologies (Abies lasiocarpa, ectomycorrhizal; Luetkea pectinata, arbuscular mycorrhizal; Phyllodoce empetriformis, ericoid mycorrhizal; Saxifraga ferruginea, nonmycorrhizal). Our main objectives were to contrast fungal and bacterial successional dynamics and community assembly as well as to decouple the effects of plant establishment and time since deglaciation on microbial trajectories using high‐throughput sequencing. Our data indicate that distance from glacier terminus has large effects on biomass accumulation, community membership, and distribution for both fungi and bacteria. Surprisingly, presence of plants rather than their identity was more important in structuring bacterial communities along the chronosequence and played only a very minor role in structuring the fungal communities. Further, our analyses suggest that bacterial communities may converge during assembly supporting determinism, whereas fungal communities show no such patterns. Although fungal communities provided little evidence of convergence in community structure, many taxa were nonrandomly distributed across the glacier foreland; similar taxon‐level responses were observed in bacterial communities. Overall, our data highlight differing drivers for fungal and bacterial trajectories during early primary succession in recently deglaciated soils.     

Soil prokaryotic community shows no response to 2 years of simulated nitrogen deposition in an arid ecosystem in northwestern China

An arid ecosystem might be sensitive to nitrogen (N) deposition, but the associated ecosystem-specific response of soil microbes is not well studied. To assess the N enrichment effects on plant and prokaryotic community diversity, we performed a two-year NH₄NO₃ treatment in a desert steppe in northwestern China. Results showed that N addition increased plant aboveground biomass and decreased plant Shannon diversity. A C₄ herb (Salsola collina) became dominant, and loss of legume species was observed. The concentrations of soil NH₄⁺-N, NO₃⁻-N, microbial biomass N, and the plant aboveground biomass N pool increased in contrast to total N, suggesting that the N input into the arid ecosystem might mainly be assimilated by plants and exit the ecosystem. Remarkably, the α-diversity and structure of the soil prokaryotic community did not vary even at the highest N addition rate. Structural equation modelling further found that the plant aboveground N pool counteracted the acidification effect of N deposition and maintained soil pH thus partially stabilizing the composition of prokaryotic communities in a desert steppe. These findings suggested that the plants and N loss might contribute to the lack of responsiveness of soil prokaryotic community to N deposition in a desert steppe.     

Diamonds in the rough: Dryland microorganisms are ecological engineers to restore degraded land and mitigate desertification

Our planet teeters on the brink of massive ecosystem collapses, and arid regions experience manifold environmental and climatic challenges that increase the magnitude of selective pressures on already stressed ecosystems. Ultimately, this leads to their aridification and desertification, that is, to simplified and barren ecosystems (with proportionally less microbial load and diversity) with altered functions and food webs and modification of microbial community network. Thus, preserving and restoring soil health in such a fragile biome could help buffer climate change's effects. We argue that microorganisms and the protection of their functional properties and networks are key to fight desertification. Specifically, we claim that it is rational, possible and certainly practical to rely on native dryland edaphic microorganisms and microbial communities as well as dryland plants and their associated microbiota to conserve and restore soil health and mitigate soil depletion in newly aridified lands. Furthermore, this will meet the objective of protecting/stabilizing (and even enhancing) soil biodiversity globally. Without urgent conservation and restoration actions that take into account microbial diversity, we will ultimately, and simply, not have anything to protect anymore.     

Soil moisture effect on bacterial and fungal community in Beilu River (Tibetan Plateau) permafrost soils with different vegetation types

Aim

This study investigated the effects of environmental variables on the bacterial and fungal communities of the Beilu River (on the Tibetan Plateau) permafrost soils with different vegetation types.

Methods and Results

Microbial communities were sampled from meadow, steppe and desert steppe permafrost soils during May, June, August and November, and they were analysed by both pyrosequencing and the use of Biolog EcoPlates. The dominant bacterial and fungal phyla in meadow and steppe soils were Proteobacteria and Ascomycota, whereas Actinobacteria and Basidiomycota predominated in desert steppe soils. The bacterial communities in meadow soils degraded amines and amino acids very rapidly, while polymers were degraded rapidly by steppe communities. The RDA patterns showed that the microbial communities differed greatly between meadow, steppe and desert steppe, and they were related to variations in the soil moisture, C/N ratio and pH. A UniFrac analysis detected clear differences between the desert steppe bacterial community and others, and seasonal shifts were observed. The fungal UniFrac patterns differed significantly between meadow and steppe soils. There were significant correlations between the bacterial diversity (H′) and soil moisture (r = 0·506) and C/N (r = 0·527). The fungal diversity (Hf′) was significantly correlated with the soil pH (r = 0·541).

Conclusion

The soil moisture, C/N ratio and pH were important determinants of the microbial community structure in Beilu River permafrost soils.

Significance and Impact of the Study

These results may provide a useful baseline for predicting the variation in microbial communities in response to climate changes.     

Plant community structure regulates responses of prairie soil respiration to decadal experimental warming

Soil respiration is recognized to be influenced by temperature, moisture, and ecosystem production. However, little is known about how plant community structure regulates responses of soil respiration to climate change. Here, we used a 13‐year field warming experiment to explore the mechanisms underlying plant community regulation on feedbacks of soil respiration to climate change in a tallgrass prairie in Oklahoma, USA. Infrared heaters were used to elevate temperature about 2 °C since November 1999. Annual clipping was used to mimic hay harvest. Our results showed that experimental warming significantly increased soil respiration approximately from 10% in the first 7 years (2000–2006) to 30% in the next 6 years (2007–2012). The two‐stage warming stimulation of soil respiration was closely related to warming‐induced increases in ecosystem production over the years. Moreover, we found that across the 13 years, warming‐induced increases in soil respiration were positively affected by the proportion of aboveground net primary production (ANPP) contributed by C₃ forbs. Functional composition of the plant community regulated warming‐induced increases in soil respiration through the quantity and quality of organic matter inputs to soil and the amount of photosynthetic carbon (C) allocated belowground. Clipping, the interaction of clipping with warming, and warming‐induced changes in soil temperature and moisture all had little effect on soil respiration over the years (all P > 0.05). Our results suggest that climate warming may drive an increase in soil respiration through altering composition of plant communities in grassland ecosystems.     

土壤非保护性有机碳对荒漠草原沙漠化的响应

沙化草地的恢复与重建是干旱半干旱区生态建设的重要内容,分析荒漠草原沙漠化过程中土壤非保护性有机碳分配比例的变异规律对于探讨沙化草地恢复机制具有重要的理论价值。以干旱、半干旱地区荒漠草原不同沙化阶段的土壤为研究对象,分析土壤粗颗粒有机碳、细颗粒有机碳、轻组有机碳含量和分配比例的分布特征、土壤非保护性有机碳转化为保护性有机碳的速率。结果表明:荒漠草原发生逆向演替后,土壤细颗粒有碳含量和分配比例表现为固定沙地荒漠草地半固定沙地流动沙地;粗颗粒有机碳含量表现为荒漠草地半固定沙地流动沙地固定沙地,粗颗粒有机碳分配比例表现为流动沙地半固定沙地荒漠草地固定沙地;轻组有机碳含量和分配比例递减。颗粒有机碳、轻组有机碳、土壤有机碳对草地沙漠化的敏感性不同,颗粒有机碳较轻组有机碳和土壤有机碳敏感性强,其中细颗粒有机碳较粗颗粒有机碳敏感性强。随着草地沙漠化程度的增强土壤非保护性有机碳分配比例呈下降趋势,表明草地沙漠化降低土壤质量。荒漠草地退化至流动沙地土壤非保护性有机碳转化为保护性有机碳的速率整体呈上升趋势。     

Microbial Nonlinear Response to a Precipitation Gradient in the Northeastern Tibetan Plateau

The response of soil microbes to global warming, especially their response to precipitation, remains poorly known. The Tibetan Plateau is very sensitive to climate change. In particular, the northeastern margin of the Tibetan Plateau is an interesting area to test the response of soil microbial communities to precipitation, as there is a distinct gradient in annual precipitation from east to west. We collected soil samples along a precipitation gradient in arid and semi-arid areas of the northeastern Tibetan Plateau. Phospholipid fatty acid (PLFA) technology was used to analyze the microbial community structure and total microbial biomass. With declining precipitation, bacterial biomass decreased significantly, whereas fungal biomass did not show an obvious trend; this result indicates that bacteria are more sensitive to mean annual precipitation (MAP). Overall, the biomass of Gram-negative (G^?) bacteria represented up to 82% of the total bacterial biomass. In the high (260–394 mm yr^?1) MAP areas, bacterial biomass was mainly concentrated at the surface and decreased with increasing soil depth (0–40 cm). In contrast, in the low (36–260 mm yr^?1) MAP areas, bacterial biomass was mainly concentrated in the deep soils. The mean annual precipitation was strongly correlated with soil microbial community in space, with microbial communities in the 0–10-cm soil depth most affected by precipitation. Groundwater may impact microbial communities in the 20–40-cm soil depth of this arid and semiarid region. The clustering of the microbial communities was significantly grouped according to the MAP gradient, revealing that MAP is a major driving force of microbial communities in this arid and semi-arid area. The decline in MAP led to a shift in the structure of the microbial community and an overall reduction in microbial biomass.     

荒漠孑遗植物四合木对土壤古菌群落的影响

土壤是植物定居的场所,也是植物-微生物互作的重要界面。古菌是土壤微生物重要组份,在碳、氮、硫、铁等元素的生物地球化学循环和植物的生长发育、适应生境中发挥重要作用。植物定居对土壤古菌群落的影响研究鲜有开展,孑遗植物在研究植物-微生物-环境互作中具有独特的优势。采用扩增子高通量测序技术,研究以荒漠孑遗植物四合木为建群种或优势种的四合木-红砂-珍珠-针茅群落、四合木-针茅群落和四合木群落等三种荒漠植物群落类型中,四合木根区土壤和光板地土体土壤古菌群落特征,揭示四合木定居对土壤古菌物种数量、多样性、群落组成及功能的影响。结果表明,荒漠孑遗植物四合木定居不仅增加了根区土壤古菌的物种数量,提高了根区土壤古菌群落多样性,而且改变了土壤古菌群落组成,减少了奇古菌门Nitrososphaeraceae科未分类的属氨氧化古菌（unclassified_f_Nitrososphaeraceae）和暂定Nitrososphaera属氨氧化古菌（Candidatus Nitrososphaera）相对丰度,增加了Nitrososphaeraceae科暂定Nitrocosmicus属氨氧化古菌（Candidatus Nitrocosmicus）和广古菌门海洋古菌类群Ⅱ中未分类的属（norank_o_Marine_Group_II）相对丰度,广古菌门热原体纲未分类的属（unclassified_c__Thermoplasmata）相对丰度变化显著。植物群落演替对四合木根区土壤和光板地土体土壤古菌群落均无显著影响。Nitrososphaeraceae科氨氧化古菌是三种不同荒漠植物群落类型中土壤古菌的核心微生物组。四合木定居也显著改变土壤古菌群落的功能,减弱了高丰度功能,增强了低丰度功能,对有氧呼吸、核苷酸合成、氨基酸合成等途径影响显著。荒漠孑遗植物四合木定居改变了土壤古菌群落物种数量、多样性、组成、功能等特征。     

基于系统发育及功能性状的不同坡向荒漠植物群落构建研究——以博湖县沙化封禁保护区为例

荒漠植物群落构建机制的研究有助于荒漠生态系统植物资源的保护及系统平衡稳定的维持。基于系统发育与功能性状相结合的方法,以博湖县沙化封禁保护区植物群落为研究对象,在研究区内纵向沙垄的不同坡向上(丘间、阴坡、阳坡)设置样方,进行植物群落物种功能性状和土壤因子的调查与测定,通过检验植物群落物种功能性状的系统发育信号,分析不同坡向植物群落物种系统发育结构和功能结构的表现模式,利用主成分分析(PCA)和线性回归模型(Linear regression model)筛选出影响物种共存的环境因子,进而揭示研究区干旱荒漠生态系统植物群落物种共存的驱动因素。结果表明：(1)研究区植被主要以耐旱的灌木和藜科草本植物为优势种;不同坡向土壤因子具有异质性,丘间、阴坡土壤养分、水分更为丰富。(2)研究区样地植物群落物种10个功能性状指标的系统发育信号K值均小于1,说明物种功能性状受系统进化影响较小,物种功能性状未表现出系统发育保守性。(3)不同坡向系统发育结构均趋于发散,限制相似性在植物分布中占主导作用;丘间和阴坡上较丰富的土壤肥力是物种功能结构发散的主要原因,阳坡物种功能结构表现为聚集效应,生境过滤为其驱动因素...     

西北荒漠绿洲过渡带土壤细菌结构和氮代谢对梭梭恢复的响应

探究植被恢复过程中土壤微生物群落结构和氮代谢变化,是认识陆地生态系统生物地球化学过程的重要环节。然而,关于干旱区荒漠人工植被种植后土壤微生物功能的研究鲜有报道。选择西北荒漠绿洲过渡带建植时间序列(3、6、11、19、28a和46a)梭梭(Haloxylon ammodendron)林为研究对象,取冠层下表层土样(0-10 cm),流动沙地(Ms)作为对照,采用高通量测序技术,探究土壤细菌群落多样性、结构、氮代谢及功能基因对梭梭恢复的响应,考察土壤细菌群落结构变化的关键驱动因子。结果表明,放线菌门(Actinobacteriota)和变形菌门(Proteobacteria)是所有样地的优势细菌类群。Shannon指数随梭梭种植年限增加显著增加,表明梭梭建立显著提高了土壤细菌群落多样性。样本层级聚类分析显示不同年限梭梭林土壤细菌群落被分为3个小组,非度量多维尺度(NMDS)分析表明梭梭的建立显著改变了土壤细菌群落结构。Spearman相关性分析显示土壤含水量(SM)、有机碳(SOC)、速效磷(AP)和速效钾(AK)显著影响土壤细菌群落结构,且呈显著正相关。土壤细菌氮代谢主要以同化和异化硝酸盐还原为主,硝酸盐还原基因(NRG)丰度是氨氧化基因(AOG)的17.5-126.9倍,表明反硝化速度快于硝化速度。NRG/AOG随梭梭种植年限增加而下降,表明梭梭生长有助于土壤氮的积累。研究结果有助于对干旱荒漠生态系统恢复过程中植物-土壤相互作用方面的理解。     

Photosynthesis and growth reduction with warming are driven by nonstomatal limitations in a Mediterranean semi‐arid shrub

Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming‐induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four‐year manipulative experiment in a semi‐arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near‐average rainfall (75% and 25–40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ¹³C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one‐third in semi‐arid gypsum shrublands dominated by H. squamatum.     

Temperature adaptation of soil bacterial communities along an Antarctic climate gradient: predicting responses to climate warming

Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short‐term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67 °34′S, 68 °08′W), Signy Island (60 °43′S, 45 °38′W) and the Falkland Islands (51 °76′S 59 °03′W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell‐field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth (T_min). Every 1 °C rise in soil temperature was estimated to increase T_min by 0.24–0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q₁₀ values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase T_min by 0.6–1 °C and Q₁₀ (0–10 °C) by 0.5 units.     

水热增加下黑土细菌群落共生网络特征

黑土是有机质含量高且肥沃的土壤类型之一,气候变化会显著改变黑土中微生物群落的结构,同时影响群落间的潜在相互作用关系。[目的] 揭示水热增加对黑土中的细菌群落结构及潜在互作关系的影响。[方法] 基于土壤移置试验,采用16S rRNA高通量测序解析农田黑土（原位黑土、水热增加1和水热增加2）中的细菌群落结构对水热增加的响应;使用CoNet构建微生物群落共生网络,识别共生网络中的枢纽微生物;利用结构方程模型、相关性分析探究水热条件变化下土壤性质、微生物交互作用、多样性之间的直接、间接关系。[结果] 黑土中的微生物以疣微菌、变形杆菌、酸性杆菌和放线菌为主。水热增加下土壤微生物共生网络的拓扑性质发生显著变化,网络中表征微生物潜在竞争关系的负连线随着水热增加而显著增加。气候因素通过改变微生物潜在相互作用影响了群落水平分类多样性。物种竞争增强可能直接导致了土壤有机碳含量的降低。[结论] 水热增加会显著改变黑土中微生物之间的潜在交互作用,枢纽微生物的响应更加敏感。