青藏高原区退化高寒草甸植被和土壤特征

高寒草甸约占青藏高原草地的46.7%,是我国草地生态系统重要的组成部分。近年来,在气候变化和人为活动的影响下,高寒草甸生态系统退化严重,植被和土壤均呈现出不同的退化趋势。在大空间尺度上表现为草地覆盖度下降,杂草类植被增加,土壤退化甚至沙化;在微观尺度上,退化高寒草甸的土壤粒径、土壤微生物和土壤酶也发生改变。本研究从高寒草甸物种多样性、植物群落结构、植被生物量、土壤物理性质、土壤微生物、土壤酶和土壤养分等方面,分析了高寒草甸生态系统退化过程中植被和土壤的变化特征,提出当前研究中存在的一些不确定性和有待深入研究的问题,为全面了解高寒草甸的退化机制和规律、有效干预高寒草甸生态系统和恢复生态功能提供科学依据。     

黄河首曲湿地植物群落生产力、物种多样性及其与生境的关系

近年来，在气候变化与人为干扰等因素的驱动下，高寒湿地退化导致生物多样性的丧失如何影响生态系统功能尚无共识。以黄河首曲高寒湿地为研究对象，基于野外采样数据和植物群落多样性指数，重点分析植物物种多样性、地上生物量空间分布格局及其与土壤因子关系。结果表明：首曲湿地存在一定程度退化，植物群落组成主要集中在菊科和禾本科，莎草科和豆科植物较少；植物群落物种多样性和地上生物量未表现出显著的经纬度和海拔梯度变化；Patrick丰富度指数(R)和Shannon-Weiner多样性指数(H)与地上生物量呈显著正相关，说明保护区植物多样性的保护有利于生产力维持；土壤含水量影响着高寒湿地植被群落结构，与多样性指数呈显著相关性，是高寒湿地植被恢复和重建的关键性因子。该研究结果对于认识黄河首曲高寒湿地植物生物量和物种多样性及土壤因子的空间分异规律具有一定的参考价值，同时为高寒湿地退化生态系统功能的恢复及生物多样性的保护提供科学依据。     

高寒地区煤矿排土场植被恢复研究——以内蒙古扎哈淖尔煤矿为例

高寒煤矿排土场植被恢复是制约我国矿区绿色可持续发展亟待解决问题，内蒙古扎哈淖尔煤矿通过不同的生态措施对排土场进行人工植被恢复的实践。本研究在2020年和2021年对该高寒煤矿排土场75个样地进行野外连续监测，对不同生态恢复措施影响高寒地区内蒙古扎哈淖尔露天煤矿排土场植物恢复过程中的群落组成、盖度、物种多样性进行分析，阐明不同恢复措施在高寒地区煤矿排土场植被恢复中的作用。研究结果表明：从2020年到2021年排土场的植物群落物种数、植被盖度和群落多样性存在显著的季节变化规律；周边原生草原的非人工种植植物随恢复时间增加而不断进入排土场，导致群落物种数显著增加；植物群落多样性在平面、坡面与田字格地形存在显著差异，田字格上Shannon-Wiener多样性指数最低；坡度显著影响群落多样性，同时受到季节变化影响；喷播加灌木种植方式与其他4种播种方式相比显著增加群落香浓维纳多样性指数；但不同坡向、土壤施肥方式和水分灌溉方式对植物群落多样性没有显著影响。本研究结果可为完善草原露天煤矿植被恢复技术提供科学依据。     

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。     

青海省高寒灌丛物种多样性、生物量及其关系

物种多样性对生态系统功能的作用是生物多样性研究的核心领域之一,生物量水平是生态系统功能的重要表现形式,而植物群落的生物量则是生态系统生物量的基础,因此研究植物群落物种多样性与生物量的关系,对于阐明植物多样性对生态系统功能的作用具有重要意义。通过对青海省高寒灌丛生物量、灌丛物种多样性特征以及与生物量的关系调查,得到以下结果:(1)被调查灌木植被群落的40个样地中共出现了207种植物(其中灌木植物18种,草本植物189种),隶属于130属,43科,灌木以蔷薇科、杜鹃花科为主,而草本以菊科、龙胆科、毛茛科和莎草科占优势。(2)群落多样性指数偏低,植物群落结构简单,物种组成稀少。小叶金露梅群落的多样性指数最大,金露梅群落、细枝绣线菊群落和鲜卑花群落次之,百里香杜鹃+头花杜鹃群落最低。(3)不同高寒灌丛类型生物量介于1893.03—7585.41 g/m~2之间,平均值为3775.9 g/m2,其中灌木生物量占灌丛总生物量的73.55%,草本为26.45%。(4)总生物量随草本物种多样性和群落物种多样性的增加而减小;草本生物量随其物种多样性的增加而减小,而灌木物种多样性与其生物量并无显著相关性。     

青藏高原禾草混播对土壤微生物多样性的影响

土壤微生物多样性的形成、维持和变化机理是生态学研究的核心内容, 已有大量研究表明土壤微生物群落构建不仅受到土壤环境的深刻影响, 也与植物群落物种多样性密切相关。由于自然群落中土壤环境和植物多样性协同影响土壤微生物, 难以区分和厘清植物多样性和土壤环境对土壤微生物多样性构建的各自影响。该研究基于在青藏高原高寒草地构建的人工草地群落, 比较分析了3种优势禾本科牧草单播和混播及施肥处理13年后, 土壤细菌和真菌物种多样性及其与植物群落和土壤理化因子的关系。主要结果: 1)与各单播处理相比, 3种牧草两两混播一致显著降低了土壤细菌群落的丰富度和多样性, 其中变形菌门和放线菌门相对丰度显著增加, 而酸杆菌门、拟杆菌门和浮霉菌门相对丰度显著减小; 牧草混播对土壤真菌多样性没有显著影响。2)牧草混播显著降低了土壤pH和土壤全氮含量, 增加了土壤全磷含量; 施肥显著降低土壤pH, 增加了土壤速效磷含量; 但这些土壤理化因子的变化不足以解释土壤细菌和真菌多样性在处理间的差异。3)施肥显著提高了植物群落地上生物量, 降低了植物物种丰富度, 土壤细菌多样性随植物物种丰富度增加而减小, 而与植物生物量变化无关。该研究在野外条件下, 通过长期控制实验揭示了高寒草地禾草混播并不增加土壤微生物多样性, 为高寒地区牧草混播人工草地实践提供了科学依据。     

祁连山中部4种典型植被类型土壤细菌群落结构差异

土壤微生物参与土壤生态过程,在土壤生态系统的结构和功能中发挥着重要作用。2013年7月采集了祁连山中段4种典型植被群落(垫状植被、高寒草甸、沼泽草甸和高寒灌丛)的表层土壤,分析了表层土壤微生物生物量碳氮和采用Illumina高通量测序技术研究了土壤细菌群落结构及多样性,并结合土壤因子对土壤细菌群落结构和多样性进行了相关性分析。结果表明:(1)土壤微生物生物量碳氮的大小排序为:沼泽草甸高寒草甸高寒灌丛垫状植被;(2)土壤细菌群落相对丰度在5%以上的优势类群是放线菌门、酸杆菌门、α-变形菌、厚壁菌门和芽单胞菌门5大门类;(3)沼泽草甸土壤细菌α多样性(物种丰富度和系统发育多样性)显著高于其它3种植被类型(P0.05),而垫状植被土壤细菌α多样性最低;(4)冗余分析和Pearson相关性分析表明,土壤pH、土壤含水量、土壤有机碳和总氮是土壤细菌群落结构和α多样性的主要影响因子。研究结果可为祁连山高寒生态系统稳定和保护提供理论依据。     

玛曲高寒草甸沙化过程中群落结构与植物多样性

针对玛曲高寒草甸沙质荒漠化和水土流失日趋严重的问题,采用群落样方调查的方法,研究了潜在、轻度、中度和重度4种典型高寒沙化草甸的植被结构特征和α多样性与β多样性变化规律。结果表明:随着沙化程度的加剧,1)群落植被盖度持续下降(分别为99.216%,80.078%,49.895%,36.398%)、物种数逐渐减少(分别为53,32,14,13)、群落结构趋向简单(重要值大于1的物种分别有28,16,10,8种),典型高寒草甸优势种和伴生种逐渐退出群落,而适应沙质荒漠的物种逐渐占据群落中的优势地位,玛曲高寒草甸生态系统有向高寒沙质荒漠生态系统转化的趋势,群落以青藏苔草+高山早熟禾群落→青藏苔草+防风+高山嵩草群落→高山嵩草+防风+青藏苔草群落→毛穗赖草+藏虫实+青藏苔草+防风群落的方向演替;2)群落丰富度和植物多样性指数均呈下降趋势,差异显著;均匀度指数先增加后减小,在轻度沙化草甸达到最大,但差异不显著;而群落优势度逐渐增加,在中度沙化草甸增加极显著;3)潜在沙化草甸与沙化草甸之间的Whittaker指数差异极显著,中度沙化草甸与重度沙化草甸之间差异显著,而轻度沙化草甸与中度沙化草甸之间差异不显著。4)潜在沙化草甸与3种沙化草甸和轻度沙化草甸与重度沙化草甸之间群落相异性系数较高(0.705—0.937),群落共有度指数较低(0.034—0.173),而重度沙化草甸与中度沙化草甸、轻度沙化草甸与中度沙化草甸之间群落相异性系数相对较低(0.545—0.553),群落共有度指数相对较高(0.293—0.303)。以上分析表明,玛曲高寒草甸在沙化过程中存在轻度沙化和重度沙化两个关键过程,因此对潜在沙化草甸应采取封育、禁牧、轮牧、抚育等科学管护措施,而对沙化草甸应采取草皮移植、补播、施肥等植被快速恢复措施和流沙治理措施进行生态修复,防止草甸沙化的加剧和蔓延。     

三江源区高寒坡地退化植物群落多样性和地上生物量沿海拔梯度的变化特征

山地生态系统退化对生物多样性和地上生物量,以及相互关系在海拔高度梯度上的格局影响,是认识全球变化和人类干扰引起自然生态系统变化的重要内容。以青藏高原三江源区高寒坡地退化草甸和灌丛为研究对象,探讨退化草甸、灌丛群落物种多样性与地上生物量关系及其沿海拔梯度的变化规律。结果表明:(1)坡地退化的上坡位植被盖度显著大于下坡位(P＜0.05)。坡地退化高寒草甸和高寒灌丛,植物物种多样性沿海拔梯度变化规律一致,均呈现"单峰"分布格局。坡地退化高寒草甸Shannon-wiener指数和Simpson指数二次回归方程解释度达到80%和70%以上(P＜0.05)。(2)坡地退化高寒草甸和高寒灌丛的地上生物量与海拔梯度的变化规律一致,即随海拔升高高寒坡地地上生物量呈先增加后降低的变化趋势。海拔梯度对退化高寒山地地上生物量的解释度达到85%以上(P＜0.05)。(3)物种多样性和地上生物量的关系在两个坡地上表现出一致的规律,呈线性增加的变化趋势。高寒草甸坡地回归方程解释度达到70%,高寒灌丛坡地达到60%(P＜0.05)。坡地退化高寒灌丛植物群落多样性和地上生物量高于高寒草甸植物群落。高寒坡地退化草甸和灌丛植物群落物种多样性以及其与地上生物量之间的关系沿海拔梯度的变化规律一致,海拔梯度造成的环境差异对植物群落物种多样性和地上生物量影响仍较大。该研究对认识三江源区退化山地形成生态学机制,及提出有效的生态恢复措施具有重要参考价值。     

植物多样性对亚热带森林土壤微生物群落的影响

植物群落组成的改变能够直接或间接地影响土壤生态过程并调节参与这些过程的土壤生物,树种特性和多样性是影响土壤微生物多样性和群落结构的关键因素。本项目利用江西新岗山建立的中国亚热带森林生物多样性与生态系统功能(Biodiversity-Ecosystem Functioning Experiment China)BEF-China研究平台,观测了样方水平下不同多样性组成(单物种、2物种、4物种和8物种)对土壤微生物群落结构的影响。结果表明:在森林生态系统演替初期,植物多样性的改变对土壤微生物群落结构具有显著影响,在不同多样性水平处理下,微生物磷脂脂肪酸含量随着植物多样性的增加,表现出先升高后降低的趋势,但各类群微生物磷脂脂肪酸含量并未表现出对植物多样性的明显响应。其中,土壤和凋落物的理化指标能够分别解释微生物群落结构变异的28.4%和12.3%。森林生态系统较高的异质性和地下生态过程响应的滞后性,导致了土壤微生物对植物多样性组成的响应需要较长时间才能显现出来,因此,为了更好地评价地上生物多样性与生态系统功能的关联,应长期监测森林生态系统多样性组成对地下生态过程的影响。     

氮肥添加对高寒藏嵩草(Kobresia tibetica)沼泽化草甸和土壤微生物群落的影响

以藏嵩草沼泽化草甸为研究对象,利用磷脂脂肪酸(PLFA)技术,研究连续6年N素添加对地上植被群落数量特征、土壤微生物群落结构的影响。结果表明:①藏嵩草沼泽化草甸群落生物量、枯枝落叶对施肥处理无明显响应,且莎草科植物对土壤氮素的吸收和利用率较低。②施肥增加了0-10 cm土壤微生物类群PLFAs丰富度尤其细菌和革兰氏阳性菌PLFAs,降低了10-20 cm PLFAs丰富度;③磷脂脂肪酸饱和脂肪酸/单烯不饱和脂肪酸、细菌PLFAs/真菌PLFAs的比值随土壤层次增加而增加;④0-10 cm土层革兰氏阳性菌、真菌PLFAs含量与pH、土壤速效磷、速效氮、土壤有机质显著正相关(P0.05或P0.01);10-20 cm土层,细菌、革兰氏阳性菌、真菌和总PLFAs含量与土壤有机质含量显著正相关(P0.05或P0.01)。表明藏嵩草沼泽化草甸微生物PLFAs含量和丰富度对施肥的响应存在明显的土层梯度效应,土壤微生物PLFAs含量和丰富度主要受表层土壤初始养分含量的影响。     

Soil-covered strategy for ecological restoration alters the bacterial community structure and predictive energy metabolic functions in mine tailings profiles

Native soil amendment has been widely used to stabilize mine tailings and speed up the development of soil biogeochemical functions before revegetation; however, it remains poorly understood about the response of microbial communities to ecological restoration of mine tailings with soil-covered strategy. In this study, microbial communities along a 60-cm profile were investigated in mine tailings during ecological restoration of two revegetation strategies (directly revegetation and native soil covered) with different plant species. The mine tailings were covered by native soils as thick as 40 cm for more than 10 years, and the total nitrogen, total organic carbon, water content, and heavy metal (Fe, Cu, and Zn) contents in the 0–40 cm intervals of profiles were changed. In addition, increased microbial diversity and changed microbial community structure were also found in the 10–40 cm intervals of profiles in soil-covered area. Soil-covered strategy rather than plant species and soil depth was the main factor influencing the bacterial community, which explained the largest portion (29.96%) of the observed variation. Compared directly to revegetation, soil-covered strategy exhibited the higher relative abundance of Acidobacteria and Deltaproteobacteria and the lower relative abundance of Bacteroidetes, Gemmatimonadetes, Betaproteobacteria, and Gammaproteobacteria. PICRUSt analysis further demonstrated that soil-covered caused energy metabolic functional changes in carbon, nitrogen, and sulfur metabolism. Given all these, the soil-covered strategy may be used to fast-track the establishment of native microbial communities and is conducive to the rehabilitation of biogeochemical processes for establishing native plant species.

     

Soil Biological and Chemical Properties in Restored Perennial Grassland in California

Restoration of California native perennial grassland is often initiated with cultivation to reduce the density and cover of non‐native annual grasses before seeding with native perennials. Tillage is known to adversely impact agriculturally cultivated land; thus changes in soil biological functions, as indicated by carbon (C) turnover and C retention, may also be negatively affected by these restoration techniques. We investigated a restored perennial grassland in the fourth year after planting Nassella pulchra, Elymus glaucus, and Hordeum brachyantherum ssp. californicum for total soil C and nitrogen (N), microbial biomass C, microbial respiration, CO₂ concentrations in the soil atmosphere, surface efflux of CO₂, and root distribution (0‐ to 15‐, 15‐ to 30‐, 30‐ to 60‐, and 60‐ to 80‐cm depths). A comparison was made between untreated annual grassland and plots without plant cover still maintained by tillage and herbicide. In the uppermost layer (0‐ to 15‐cm depth), total C, microbial biomass C, and respiration were lower in the tilled, bare soil than in the grassland soils, as was CO₂ efflux from the soil surface. Root length near perennial bunchgrasses was lower at the surface and greater at lower depths than in the annual grass–dominated areas; a similar but less pronounced trend was observed for root biomass. Few differences in soil biological or chemical properties occurred below 15‐cm depth, except that at lower depths, the CO₂ concentration in the soil atmosphere was lower in the plots without vegetation, possibly from reduced production of CO₂ due to the lack of root respiration. Similar microbiological properties in soil layers below 15‐cm depth suggest that deeper microbiota rely on more recalcitrant C sources and are less affected by plant removal than in the surface layer, even after 6 years. Without primary production, restoration procedures with extended periods of tillage and herbicide applications led to net losses of C during the plant‐free periods. However, at 4 years after planting native grasses, soil microbial biomass and activity were nearly the same as the former conditions represented by annual grassland, suggesting high resilience to the temporary disturbance caused by tillage.     

Estimation by PLFA of Microbial Community Structure Associated with the Rhizosphere of Lygeum spartum and Piptatherum miliaceum Growing in Semiarid Mine Tailings

The objective of this study was to compare the microbial community composition and biomass associated with the rhizosphere of a perennial gramineous species (Lygeum spartum L.) with that of an annual (Piptatherum miliaceum L.), both growing in semiarid mine tailings. We also established their relationship with the contents of potentially toxic metals as well as with indicators of soil quality. The total phospholipid fatty acid (PLFA) amount was significantly higher in the rhizosphere soil of the annual species than in the rhizosphere soil of the perennial species. The fungal/bacterial PLFA ratio was significantly greater in the perennial species compared to the annual species. The fatty acid 16:1ω5c, the fungal/bacterial PLFA ratio and monounsaturated/saturated PLFA ratio were correlated negatively with the soluble contents of toxic metals. The cyc/prec (cy17:0 + cy19:0/16:1ω7 + 18:1ω7) ratio was correlated positively with the soluble contents of Pb, Zn, Al, Ni, Cd, and Cu. The results of the PLFA analysis for profiling microbial communities and their stress status of both the plant species indicate that perennial and annual gramineous species appear equally suitable for use in programmes of revegetation of semiarid mine tailings.     

A water-centred framework to assess the effects of salinity on the growth and yield of wheat and barley

We conducted a field experiment in two alpine meadows to investigate the short-term effects of nitrogen enrichment and plant litter biomass on plant species richness, the percent cover of functional groups, soil microbial biomass, and enzyme activity in two alpine meadow communities. The addition of nitrogen fertilizer to experimental plots over two growing seasons increased plant production, as indicated by increases in both the living plant biomass and litter biomass in the Kobresia humilis meadow community. In contrast, fertilization had no significant effect on the amounts of living biomass and litter biomass in the K. tibetica meadow. The litter treatment results indicate that litter removal significantly increased the living biomass and decreased the litter biomass in the K. humilis meadow; however, litter-removal and litter-intact treatments had no impact on the amounts of living biomass and litter biomass in the K. tibetica meadow. Litter production depended on the degree of grass cover and was also influenced by nitrogen enrichment. The increase in plant biomass reflects a strong positive effect of nitrogen enrichment and litter removal on grasses in the K. humilis meadow. Neither fertilization nor litter removal had any impact on the grass biomass in the K. tibetica meadow. Sedge biomass was not significantly affected by either nutrient enrichment or litter removal in either alpine meadow community. The plant species richness decreased in the K. humilis meadow following nitrogen addition. In the K. humilis meadow, microbial biomass C increased significantly in response to the nitrogen enrichment and litter removal treatments. Enzyme activities differed depending on the enzyme and the different alpine meadow communities; in general, enzyme activities were higher in the upper soil layers (0–10 cm and 10–20 cm) than in the lower soil layers (20–40 cm). The amounts of living plant biomass and plant litter biomass in response to the different treatments of the two alpine meadow communities affected the soil microbial biomass C, soil organic C, and soil fertility. These results suggest that the original soil conditions, plant community composition, and community productivity are very important in regulating plant community productivity and microbial biomass and activity.     

Biotic and Abiotic Properties Mediating Plant Diversity Effects on Soil Microbial Communities in an Experimental Grassland

Plant diversity drives changes in the soil microbial community which may result in alterations in ecosystem functions. However, the governing factors between the composition of soil microbial communities and plant diversity are not well understood. We investigated the impact of plant diversity (plant species richness and functional group richness) and plant functional group identity on soil microbial biomass and soil microbial community structure in experimental grassland ecosystems. Total microbial biomass and community structure were determined by phospholipid fatty acid (PLFA) analysis. The diversity gradient covered 1, 2, 4, 8, 16 and 60 plant species and 1, 2, 3 and 4 plant functional groups (grasses, legumes, small herbs and tall herbs). In May 2007, soil samples were taken from experimental plots and from nearby fields and meadows. Beside soil texture, plant species richness was the main driver of soil microbial biomass. Structural equation modeling revealed that the positive plant diversity effect was mainly mediated by higher leaf area index resulting in higher soil moisture in the top soil layer. The fungal-to-bacterial biomass ratio was positively affected by plant functional group richness and negatively by the presence of legumes. Bacteria were more closely related to abiotic differences caused by plant diversity, while fungi were more affected by plant-derived organic matter inputs. We found diverse plant communities promoted faster transition of soil microbial communities typical for arable land towards grassland communities. Although some mechanisms underlying the plant diversity effect on soil microorganisms could be identified, future studies have to determine plant traits shaping soil microbial community structure. We suspect differences in root traits among different plant communities, such as root turnover rates and chemical composition of root exudates, to structure soil microbial communities.     

Responses of Soil Microbial Communities to Experimental Warming in Alpine Grasslands on the Qinghai-Tibet Plateau

Global surface temperature is predicted to increase by at least 1.5°C by the end of this century. However, the response of soil microbial communities to global warming is still poorly understood, especially in high-elevation grasslands. We therefore conducted an experiment on three types of alpine grasslands on the Qinghai-Tibet Plateau to study the effect of experimental warming on abundance and composition of soil microbial communities at 0–10 and 10–20 cm depths. Plots were passively warmed for 3 years using open-top chambers and compared to adjacent control plots at ambient temperature. Soil microbial communities were assessed using phospholipid fatty acid (PLFA) analysis. We found that 3 years of experimental warming consistently and significantly increased microbial biomass at the 0–10 cm soil depth of alpine swamp meadow (ASM) and alpine steppe (AS) grasslands, and at both the 0–10 and 10–20 cm soil depths of alpine meadow (AM) grasslands, due primarily to the changes in soil temperature, moisture, and plant coverage. Soil microbial community composition was also significantly affected by warming at the 0–10 cm soil depth of ASM and AM and at the 10–20 cm soil depth of AM. Warming significantly decreased the ratio of fungi to bacteria and thus induced a community shift towards bacteria at the 0–10 cm soil depth of ASM and AM. While the ratio of arbuscular mycorrhizal fungi to saprotrophic fungi (AMF/SF) was significantly decreased by warming at the 0–10 cm soil depth of ASM, it was increased at the 0–10 cm soil depth of AM. These results indicate that warming had a strong influence on soil microbial communities in the studied high-elevation grasslands and that the effect was dependent on grassland type.     

Seasonal Dynamics of Microbial Community Composition and Function in Oak Canopy and Open Grassland Soils

Soil microbial communities are closely associated with aboveground plant communities, with multiple potential drivers of this relationship. Plants can affect available soil carbon, temperature, and water content, which each have the potential to affect microbial community composition and function. These same variables change seasonally, and thus plant control on microbial community composition may be modulated or overshadowed by annual climatic patterns. We examined microbial community composition, C cycling processes, and environmental data in California annual grassland soils from beneath oak canopies and in open grassland areas to distinguish factors controlling microbial community composition and function seasonally and in association with the two plant overstory communities. Every 3 months for up to 2 years, we monitored microbial community composition using phospholipid fatty acid (PLFA) analysis, microbial biomass, respiration rates, microbial enzyme activities, and the activity of microbial groups using isotope labeling of PLFA biomarkers (¹³C-PLFA). Distinct microbial communities were associated with oak canopy soils and open grassland soils and microbial communities displayed seasonal patterns from year to year. The effects of plant species and seasonal climate on microbial community composition were similar in magnitude. In this Mediterranean ecosystem, plant control of microbial community composition was primarily due to effects on soil water content, whereas the changes in microbial community composition seasonally appeared to be due, in large part, to soil temperature. Available soil carbon was not a significant control on microbial community composition. Microbial community composition (PLFA) and ¹³C-PLFA ordination values were strongly related to intra-annual variability in soil enzyme activities and soil respiration, but microbial biomass was not. In this Mediterranean climate, soil microclimate appeared to be the master variable controlling microbial community composition and function.     

黄土高原退耕地的生态恢复

在刈割干扰下,黄土高原退耕地恢复进程中植被从沙蓬（Agriophyllum arenarium)单优群落向以达乌里胡枝子（Lespedeza davurica)为优势种的群落演替。物种增加速度初期快,后期慢,退耕后恢复初期的新增物种主要是沙蓬和白草（Pennisetum flaccidum);中前期主要是茵陈蒿（Artemisia capillaris),可成为群落的次优势种;中后期新增物种主要是多年生豆科植物,只是群落的伴生种,群落中1年生和多年生植物地上生物量分别以8.8%的年平均速率减少或增加,豆科植物地上生物量及所占比例上升,在退耕地恢复过程中,上层土壤中植物地下生物量比例与变化幅度增加,表现出浅层化趋势,退耕地恢复演替1-7年,土壤粘粒和粉粒减少,砂粒增加,7年后变化趋势相反,退耕地0-100cm土壤含水量在恢复期间呈逐渐上升趋势,中期增幅显著,全N和速效N在恢复前期减少,后期增加,在刈割利用下,退耕地恢复过程中土壤全P,速效P和有机C持续衰竭,退耕地恢复到当前稳定的群落所需时间分别为优势种群8-9年,群落9-11年和土壤11-12年。     

藏北古露高寒草地生态系统对短期围封的响应

过度放牧导致高寒草地生态系统退化,围封是生态保护和恢复的管理手段。以青藏高原那曲县古露镇过牧退化高寒草地为对象,系统分析了高寒草地生态系统的植被特征及土壤理化特性、土壤酶活性、土壤微生物生物量和群落结构对围封的响应。结果表明,短期围封后,(1)植被平均高度、盖度和地上生物量均有极显著增加(P0.01),而生物多样性指数则显著降低(P0.01);(2)土壤的水溶性有机碳含量、土壤物理结构(沙土与粉土的比例)及pH有显著变化(P0.05);(3)土壤酶活性没有明显改善;(4)土壤微生物生物量(细菌、放线菌、真菌)均呈显著增加(P0.05);(5)土壤中细菌的多样性有增加的趋势,其群落组成在门水平上也发生了变化;(6)Manteltest分析显示与土壤细菌群落结构的呈正相关性的环境因子主要为土壤有机碳含量(TOC)、总氮含量(TN)、碳磷比(C/P)与氮磷比(N/P)(P0.05)。这表明围栏封育有利于藏北草地植被、土壤理化特性的恢复,还能维持土壤微生物多样性,促进高寒草地生态系统的可持续发展。