Linking grazing response of species abundance to functional traits in the Tibetan alpine meadow

Whether grazing response of species abundance can be predicted by plant functional trait remains a challenge untested in a specific ecosystem. We measured species abundance and relevant functional traits for 30 common component species in a moderately grazed and a control community over 3 years (2005, 2006 and 2007) in a Kobresia capillifolia dominated alpine meadow on the Tibetan Plateau. Our objective was to examine species response to grazing and to test the relationship between the response of species abundance and functional traits in grazed and control habitats. Our results showed: i) in terms of species relative abundance and saturated height (the maximum height of an adult individual), most component species significantly decrease in response to moderate grazing and the effect differed among species and between functional groups. ii) The response of species abundance was significantly negatively correlated with saturated height, but not correlated with specific leaf area or seed size. We concluded that the response direction of species abundance to grazing can be predicted by functional traits, whereas it is a weak predictor of the extent of grazing response in species abundance.     

Methanotrophic community structure and activity under warming and grazing of alpine meadow on the Tibetan Plateau

Knowledge about methanotrophs and their activities is important to understand the microbial mediation of the greenhouse gas CH₄ under climate change and human activities in terrestrial ecosystems. The effects of simulated warming and sheep grazing on methanotrophic abundance, community composition, and activity were studied in an alpine meadow soil on the Tibetan Plateau. There was high abundance of methanotrophs (1.2–3.4 × 10⁸ pmoA gene copies per gram of dry weight soil) assessed by real-time PCR, and warming significantly increased the abundance regardless of grazing. A total of 64 methanotrophic operational taxonomic units (OTUs) were obtained from 1,439 clone sequences, of these OTUs; 63 OTUs (98.4%) belonged to type I methanotrophs, and only one OTU was Methylocystis of type II methanotrophs. The methanotroph community composition and diversity were not apparently affected by the treatments. Warming and grazing significantly enhanced the potential CH₄ oxidation activity. There were significantly negative correlations between methanotrophic abundance and soil moisture and between methanotrophic abundance and NH₄–N content. The study suggests that type I methanotrophs, as the dominance, may play a key role in CH₄ oxidation, and the alpine meadow has great potential to consume more CH₄ under future warmer and grazing conditions on the Tibetan Plateau.     

高寒草甸物种多样性对藏系牧羊放牧行为的影响

为探究草原植物物种多样性对家畜放牧行为的影响及其机制,在青藏高原高寒草甸开展藏系牧羊轮牧试验,调查植被物种多样性,观察藏系牧羊采食速率、觅食速率和采食时间,并计算藏系牧羊日采食量。结果表明：两年间,植物物种丰富度与藏系牧羊采食速率呈显著正相关关系（P<0.05）;觅食速率、采食时间和日采食量对放牧率响应敏感（P<0.05）,呈夏秋增冬春减的趋势。植物Shannon-Wiener指数与藏系牧羊的采食时间显著负相关（P<0.05）;在暖季或8羊/hm²放牧率下植物Shannon-Wiener指数与藏系牧羊日采食量呈显著正相关（P<0.05）。Pilelou均匀度指数与藏系牧羊采食速率和采食时间显著负相关（P<0.05）;在暖季或8羊/hm²放牧率下Pilelou均匀度指数与藏系牧羊日采食量呈显著负相关（P<0.05）。植物物种丰富度对藏系牧羊放牧行为贡献较大,且放牧藏系牧羊的采食速率和采食时间比觅食速率和日采食量对植物物种丰富度响应更敏感,以用植物物种丰富度为自变量可以更好预测藏系牧羊放牧行为。放牧管理通过影响植被物种多样性从而进一步影响了藏系牧羊放牧行为。放牧行为不仅是评价草地营养价值和家畜生产力的关键指标,也是草地健康管理的基础。因此,明确草原植物物种多样性-藏系牧羊放牧行为的互作机制有助于更好的提高藏系牧羊地生产力,维护草原生态健康。     

藏北高寒草甸群落结构与物种组成对增温与施氮的响应

气候变暖和氮沉降增加作为全球环境问题,将严重影响陆地生态系统的结构与功能.研究发现,近几十年来青藏高原增温显著,其中冬季升温最明显.而已有的研究更多关注全年增温,对冬季增温研究较少.本文基于高寒草甸地区增温和氮素添加影响研究的不足,在青藏高原高寒草甸区开展模拟增温和氮添加试验,研究长期增温与氮添加对高寒草甸群落结构与物种组成的影响.试验布设于2010年7月,地点在西藏当雄高寒草甸区,共有3种增温方式:对照、全年增温、冬季增温;每种增温处理下设置5个氮素添加梯度:0、10、20、40、80 kg N·hm^-2·a^-1,系统研究气候变暖与氮添加对高寒草甸生态系统群落结构与物种组成的影响.结果表明: 2012—2014年,增温与施氮处理均显著影响群落总盖度:全年增温处理降低了群落总盖度;在不施氮处理下,冬季增温降低了群落盖度,但在施氮处理下,随着氮剂量的提高群落盖度逐渐升高.增温与施氮对不同功能群植物的影响不同,增温处理降低了禾草与莎草植物盖度,而施氮提高了禾草植物盖度.相关分析表明,植被群落总盖度与生长旺盛期土壤含水量呈正相关关系,推测在降雨较少的季节增温导致的土壤含水量降低是群落盖度降低的主要原因.半干旱区高寒草甸土壤水分主要受降雨的调控,未来气候变化情景下,降雨时空格局的改变会显著影响植被群落盖度及组成,且大气氮沉降的增加对植被群落的影响也依赖于降雨条件的变化.     

模拟增温对西藏高原高寒草甸土壤供氮潜力的影响

过去几十年青藏高原呈现显著的增温趋势,冬季增温幅度显著高于生长季的季节非对称特征。气候变暖会对生态系统氮素循环产生重要影响,但关于全年增温与冬季增温对高寒生态系统氮循环的不同影响仍缺乏研究。在青藏高原高寒草甸区开展模拟增温试验,研究季节非对称增温对高寒草甸生态系统氮循环的影响。该试验布设于2010年7月,设置3种处理(不增温、冬季增温与全年增温)。研究结果发现,开顶箱增温装置造成了小环境的暖干化:显著提高了地表空气温度和表层土壤温度,降低了表层土壤含水量。冬季增温会加剧土壤中氮素的流失,所以在经历了冬季增温后土壤氮含量显著降低;在生长季节,土壤氮素周转速率受土壤水分的调控,在降雨较少的季节,增温引起的土壤含水量降低会抑制土壤氮周转速率。对于土壤微生物量而言,高寒草甸土壤微生物量碳表现出明显的季节动态,在生长季旺盛期较低,在生长季末期和初冬季节反而较高,这说明为了降低对土壤养分的竞争,高寒草甸植物氮吸收与土壤微生物氮固持在时间上存在分离。研究结果表明,冬季增温导致的土壤养分含量变化会影响随后生长季植物群落的生产力、结构组成与碳氮循环等过程,对生态系统过程产生深远的影响。     

增温对高寒草甸群落凋落物质量动态变化的影响

为了解未来增温条件下,青藏高原高寒草甸凋落物质量如何变化,将有助于增强对高寒草甸生态系统碳源/汇效应的认识.该文通过定位可控的增温试验平台,动态监测了凋落物生物量及其质量的变化.结果表明:增温显著地促进了凋落物的分解速率(F=35.757,P＜0.001),降低了凋落物中的C、N含量及其C/N比,但提高了凋落物中的P含...     

短期氮素添加和模拟放牧对青藏高原高寒草甸生态系统呼吸的影响

氮沉降和放牧是影响草地碳循环过程的重要环境因子,但很少有研究探讨这些因子交互作用对生态系统呼吸的影响。在西藏高原高寒草甸地区开展了外源氮素添加与刈割模拟放牧实验,测定了其对植物生物量分配、土壤微生物碳氮和生态系统呼吸的影响。结果表明:氮素添加显著促进生态系统呼吸,而模拟放牧对其无显著影响,且降低了氮素添加的刺激作用。氮素添加通过提高微生物氮含量和土壤微生物代谢活性,促进植物地上生产,从而增加生态系统的碳排放;而模拟放牧降低了微生物碳含量,且降低了氮素添加的作用,促进根系的补偿性生长,降低了氮素添加对生态系统碳排放的刺激作用。这表明,放牧压力的存在会抑制氮沉降对高寒草甸生态系统碳排放的促进作用,同时外源氮输入也会缓解放牧压力对高寒草甸生态系统生产的负面影响。     

放牧强度对川西北高山草甸两个优势物种凋落物分解的影响

研究了川西北高山草甸两个优势物种垂穗鹅冠草(Roegneria nutans)和四川嵩草(Kobresia setchwanensis)凋落物在不同放牧强度下的分解及其碳氮损失率。经过一年的分解,放牧不同程度地加速了两种凋落物的分解。垂穗鹅冠草凋落物在不放牧、轻牧、中牧和重牧草地的失重率分别为26.0、27.2、29.6和32.8%;川嵩草凋落物的失重率分别为44.0,46.2,50.4和56.2%。不放牧、轻牧、中牧和重牧草地垂穗鹅冠草凋落物碳的损失率分别为26.1%、27.5%、29.4%和32.9%,氮的损失率分别为13.6%、14.4%、17.3%和19.1%;川嵩草凋落物碳的损失率分别为41.9%、44.3%、48.5%和54.4%,氮的损失率分别为39.4%、41.4%、46.4%和52.8%。研究表明,增加的放牧强度加快了两种凋落物的分解速率,加速了凋落物中碳氮的释放;同时也表明,川嵩草凋落物的分解速率要快与垂穗鹅冠草凋落物。     

高山森林土壤微生物群落结构和功能对模拟增温的响应

将高山森林土壤装入PVC管中(土壤有机层在上、矿质土壤层在下)培养10周,以高山森林土壤年均温为对照,采用室内人工气候箱分别模拟增温2和4 ℃,研究土壤微生物群落和土壤酶活性对温度升高的响应.结果表明: 温度升高显著降低了土壤有机层中细菌、矿质土壤层中革兰氏阴性菌(G^-)PLFAs含量,但对土壤真菌无显著影响.温度升高引起革兰氏阳性菌和阴性菌比值(G⁺/G^-)升高,改变了微生物群落结构.增温对漆酶、β-葡萄糖酶、酸性磷酸酶和N-乙酰葡糖胺糖苷酶活性没有显著影响.土壤微生物群落之间呈现出协同增长的趋势,真菌、细菌、G⁺、G^-等微生物群落之间均呈显著正相关.土壤有机层中β-葡萄糖苷酶与土壤微生物群落对碳源利用的竞争,导致β-葡萄糖苷酶活性与土壤有机层细菌、真菌、G⁺呈显著负相关.高山森林不同土壤微生物类群对增温的响应不同,细菌比真菌对温度的响应更敏感,真菌对增温有一定的耐受能力.     

Additive effects of warming and grazing on fine-root decomposition and loss of nutrients in an alpine meadow

增温和放牧对高寒草甸植物细根的分解和养分丧失具有叠加效应 细根的分解是调控生态系统碳循环,影响养分循环以及土壤肥力的关键过程。然而,在自然生态系统中关于增温和放牧影响细根分解的研究十分匮乏。本研究利用非对称增温(即：昼夜和季节性不对称)和适度放牧(约50%饲草利用率)的两因素野外控制试验,探讨增温和放牧对青藏高原高寒草甸为期两年的细根分解和养分丧失的影响。增温和放牧通过提高细根分解促进了碳的循环,并影响了元素循环,但各元素的循环特征各自不同。增温和放牧对细根分解和养分丧失的影响是叠加的。试验两年期间,增温和放牧显著提高了细根累积生物量和总有机碳的丧失量。仅增温并放牧处理显著降低了氮元素百分率丧失量,而无论放牧与否,增温显著降低了磷元素苞粉率丧失量。与对照比较,仅增温或放牧提高了钾、钠、钙、镁的百分率丧失量。增温和放牧对细根分解和养分丧失未呈现交互影响。降低磷丧失较减低氮丧失对温度更加敏感。在未来变暖情景下,细根分解产生的不同养分百分率丧失对温度的敏感性差异可能调整不同养分在土壤中的有效率,进而影响生态系统的结构和功能。     

青藏高原东部高寒灌丛生物量分配对模拟增温的响应

植物生物量分配特征的变化反映了不同环境条件下植物的适应策略,全球气候变暖正在改变青藏高原高寒生态系统植被动态和生物量分配格局。然而,到目前为止,有关青藏高原高寒灌丛生物量分配特征对气候变暖的响应研究较少。为了探究气候变暖对高寒灌丛生物量分配的影响,以青藏高原东部典型的窄叶鲜卑花高寒灌丛为研究对象,分析了高寒灌丛灌木层、草本层和群落水平生物量分配特征对开顶式生长室（OTC）模拟增温的响应。研究结果表明：整个生长季节,模拟增温使空气温度和表层土壤温度分别升高0.6℃和1.2℃,使表层土壤水分含量下降2.7%。模拟增温使草本层和群落地上生物量显著增加57.8%和7.2%,使灌木层、草本层和群落根系生物量显著增加42.5%、105.6%和45.6%。然而,模拟增温没有显著影响灌木层地上生物量。同时,模拟增温使灌木层、草本层和群落总生物量显著增加25.6%、85.7%和28.4%,使灌木层、草本层和群落根冠比显著增加33.2%、30.4%和36.0%。由此可见,模拟增温在促进高寒灌丛生物量生产的同时将显著提高向地下根系部分的分配比例。Pearson相关分析表明,高寒灌丛生物量分配与空气温度、土壤温度和土壤硝态氮含量呈显著正相关关系;多元线性回归分析结果也表明,空气温度、土壤温度和土壤硝态氮含量解释了高寒灌丛生物量分配变异的50.8%以上。这些结果表明,青藏高原东部高寒灌丛植被能够通过调节生物量分配模式应对未来气候变暖。     

Experimental warming causes large and rapid species loss, dampened by simulated grazing, on the Tibetan Plateau

We investigated the independent and combined effects of experimental warming and grazing on plant species diversity on the north‐eastern Tibetan Plateau, a region highly vulnerable to ongoing climate and land use changes. Experimental warming caused a 26–36% decrease in species richness, a response that was generally dampened by experimental grazing. Higher species losses occurred at the drier sites where N was less available. Moreover, we observed an indirect effect of climate change on species richness as mediated by plant–plant interactions. Heat stress and warming‐induced litter accumulation are potential explanations for the species’ responses to experimental warming. This is the first reported experimental evidence that climate warming could cause dramatic declines in plant species diversity in high elevation ecosystems over short time frames and supports model predictions of species losses with anthropogenic climate change.     

Relationship between reproductive allocation and relative abundance among 32 species of a Tibetan alpine meadow: effects of fertilization and grazing

Background

Understanding the relationship between species traits and species abundance is an important goal in ecology and biodiversity science. Although theoretical studies predict that traits related to performance (e.g. reproductive allocation) are most directly linked to species abundance within a community, empirical investigations have rarely been done. It also remains unclear how environmental factors such as grazing or fertilizer application affect the predicted relationship.

Methodology

We conducted a 3-year field experiment in a Tibetan alpine meadow to assess the relationship between plant reproductive allocation (RA) and species relative abundance (SRA) on control, grazed and fertilized plots. Overall, the studied plant community contained 32 common species.

Principal Findings

At the treatment level, (i) RA was negatively correlated with SRA on control plots and during the first year on fertilized plots. (ii) No negative RA–SRA correlations were observed on grazed plots and during the second and third year on fertilized plots. (iii) Seed size was positively correlated with SRA on control plots. At the plot level, the correlation between SRA and RA were not affected by treatment, year or species composition.

Conclusions/Significance

Our study shows that the performance-related trait RA can negatively affect SRA within communities, which is possibly due to the tradeoffs between clonal growth (for space occupancy) and sexual reproduction. We propose that if different species occupy different positions along these tradeoffs it will contribute to biodiversity maintenance in local communities or even at lager scale.     

Moderate grazing increased alpine meadow soils bacterial abundance and diversity index on the Tibetan Plateau

The response of grassland soil bacterial community characteristics to different grazing intensities is central ecological topics. However, the underlying mechanisms between bacterial abundance, diversity index, and grazing intensity remain unclear. We measured alpine meadow soil bacterial gene richness and diversity index under four grazing intensities using 16S rDNA sequence analysis on the Tibetan Plateau. The results suggest that extreme grazing significantly decreased alpine meadow both bacterial gene abundance and diversity index (p < .05). The lowest operational taxonomic unit numbers were 3,012 ± 447 copies under heavy grazing in the growing season. It was significantly lower than heavy grazing with approximately 3,958 ± 119 copies (p < .05). The Shannon index for medium and high grazing grassland bacterial diversity was slightly higher than for light grazing in the growing season. Furthermore, the lowest index was approximately 9.20 ± 0.50 for extreme grazing of grassland in the growing season. The average bacterial gene abundance and diversity index in the dormancy period were slightly higher than that in the growing season. Soil bulk density, pH, ammonium, and nitrate nitrogen were the main positive factors driving grazed grassland bacterial communities. Our study provides insight into the response of alpine meadows to grazing intensity, demonstrating that moderate grazing increases bacterial community diversity in grazed grasslands.     

A test of biotic interactions among two alpine plant species in Australia

This study examines the extent to which interactions among two common alpine/subalpine plant species and their neighbours at the Bogong High Plains in southern Australia are characterized by competition or facilitation. The two target species were Celmisia pugioniformis (Asteraceae) and Carex breviculmis (Cyperaceae). Biotic interactions were examined using vegetation removal manipulations over three growing seasons at five sites across the altitudinal range of tall alpine herbfield communities. Observations recorded growth and mortality. Results for C. pugioniformis clearly indicated facilitation as a dominant process across all sites and seasons. Plants that had their neighbours removed tended to perform worse than plants that had their neighbours left intact. Growth observations for Ca. breviculmis were less clear, but again suggested facilitation. Mortality was distinctly higher among Ca. breviculmis individuals that had their neighbours removed relative to those with neighbours left intact. Results collectively suggest the removal of neighbours acts to reduce growth and increase mortality in C. pugioniformis and Ca. breviculmis throughout the altitudinal range of tall alpine herbfields at the Bogong High Plains. Facilitative and competitive interactions need to be recognized in efforts aimed at mitigating climate change‐associated impacts on the ecology of alpine plant communities. The extent to which biotic interactions may exacerbate or buffer abiotic change is difficult to predict, emphasizing the need for ecological monitoring.     

施肥和放牧对青藏高原高寒草甸物种丰富度的影响

在草地生态系统中, 施肥通常会导致生物多样性下降, 但是关于引起生物多样性下降的机制还存在着很大的争议。该研究基于一个4年的施肥实验, 试图通过个体大小的不整齐性和单位植物氮含量, 定性地揭示青藏高原东部高寒草甸施肥后多样性下降的原因。研究显示: 在封育地, 施肥致使个体大小不整齐性增加了15%, 并不同程度地增加了物种的高度。同时, 施肥使物种间单位植物氮含量存在显著差异的数目降低了65%。施肥后光竞争加剧, 导致大个体植物排斥小个体植物, 进而引起了物种丰富度下降29.6%。与封育地不同, 放牧地施肥并没有改变个体大小不整齐性和物种的高度, 而是使物种间单位植物氮含量存在显著差异的数目增加了11.4%。施肥并没有改变放牧地的光竞争强度, 而是增加了物种间对土壤营养元素氮的竞争强度, 进而引起了物种丰富度下降17.3%。该研究还发现, 放牧施肥地的物种丰富度下降速度和等级显著低于封育施肥地的物种丰富度下降速度和等级, 这表明放牧减缓了施肥对物种丰富度的影响力。     

增温对青藏高原高寒草甸生态系统固碳通量影响的模拟研究

低温被广泛认为是高寒草甸生态系统首要限制性因子,因此增温可能会在某种程度上促进初级生产力,但是也可能由于土壤水分、N素营养状况的改变形成新胁迫而抑制生产力提高。此外,生态系统呼吸由于增温而提高的幅度也可能高于初级生产力提高的幅度,造成总碳库平衡的改变。利用青藏高原海北高寒草甸实测数据对生态系统过程模型Biome-BGC(V.4.2)进行了参数化,并利用研究区实测土壤水分(0-40 cm)和其它观测数据对模型进行了检验,证明模型模拟结果较为可靠。模型使用2005-2008年的海北气象站实测气象数据包括气温、降水等作为驱动数据,模拟了增温1.2-1.7℃下青藏高原海北定位站高寒草甸生态系统碳通量的变化,并整合分析增温试验平台上已发表的试验,与模拟结果进行对比,探讨增温对海北高寒草甸生态系统碳收支的可能影响。结果表明:2005-2008年青藏高原高寒草甸生态系统为弱的碳汇,短期增温导致系统净碳固定增加。增温直接影响系统碳通量,也通过土壤水分和土壤矿化氮变化间接影响碳通量,相比土壤水分和氮素,增温对影响碳通量变化过程中的效应更大;研究也揭示,在增温条件下,植物对土壤矿化氮的吸收量小于有机质分解产生的土壤矿化氮量,土壤矿化氮含量增加。     

放牧作用下高寒草甸群落物种分布与土壤因子的关系

以青藏高原东北缘高寒草甸为对象,研究不同放牧强度下植物群落和土壤因子的变化,以及群落物种分布与土壤物理结构和化学养分因子的定量关系.结果表明: 放牧导致优势种为垂穗披碱草和大针茅的原植物群落发生分异,高强度放牧样地优势种变为矮生嵩草和阴山扁蓿豆,低强度放牧样地变为垂穗披碱草和冷地早熟禾.随放牧强度增加,物种丰富度、重要值和生物量均显著降低.各放牧强度样地重要值的物种序列均可用对数模型进行拟合;随放牧强度增加,植物重要值累积到占整个群落重要值50%时,需要的物种数降低.土壤速效P、速效K、紧实度、含水量、稳定入渗速率和大团聚体指标随放牧强度显著变化,但变化规律不一致.CCA排序表明,土壤紧实度是放牧作用下影响群落物种分布格局的最关键因子.方差分解表明,土壤因子共解释群落物种分布变异的30.5%,其中土壤物理性状单独解释群落物种分布的22.8%,对群落物种分布的贡献率最高,主要影响放牧干扰下高寒草甸植物群落物种的分布格局.     

Warming and grazing interact to affect root dynamics in an alpine meadow

Plant and Soil - Arbuscular Mycorrhizal Fungi (AMF) are ubiquitous soil microorganisms playing a vital role in the functioning of agricultural ecosystems. Although AMF are generally considered to...