放牧对贝加尔针茅草原群落植物多样性和生产力的影响

研究了不同放牧强度对贝加尔针茅草原群落植物多样性和生产力的影响。结果表明,在牧压梯度上,不同的植物表现出不同的生态适应对策,贝加尔针茅种群随着牧压的增加,种群株丛破碎化、小型化,羊草耐牧性较强,在中牧阶段生产力最高。群落初级生产力随着放牧强度的增加逐渐下降。较大的放牧压力下,群落中适口性差、耐牧的杂类草植物渐趋增加。而在更大的放牧压力下,群落逐步被耐牧的小丛生禾草、旱生小苔草、小灌木和灌木所替代。草地群落的稳定性随着放牧强度增加逐渐降低。放牧干扰对群落植物多样性和生产力及其稳定性的影响是不同步的,不对称的。植物群落初级生产力对放牧干扰的响应更迅速,变化更剧烈。     

不同放牧强度下内蒙古温带典型草原优势种植物防御策略

放牧是草原的主要利用方式, 但对牧草造成了一定的生物胁迫。面对生存压力, 牧草会通过调节初级与次级代谢过程启动防御机制。该研究以内蒙古温带典型草原优势种植物为研究对象, 通过测定其在5个放牧水平下不同营养器官中的次级代谢产物及木质素等含量, 探讨大针茅(Stipa grandis)和羊草(Leymus chinensis)的各营养器官在防御机制中的角色及其碳氮权衡策略。结果表明: 面对放牧胁迫, 大针茅和羊草会产生大量的单宁、总黄酮、酚类以及生物碱等次级代谢产物, 并以叶片为主要的合成及储存器官。中度放牧使羊草的化学防御机制得到较充分的诱导及表达。但二者地上部分木质素含量并无显著增加, 因此, 二者在避牧性机制上更倾向于化学防御而非机械防御。由于羊草有更高的氮利用效率, 这使得羊草可以通过碳氮两种代谢途径进行防御, 但大针茅在生长初期并不能将氮高效地分配到化学防御中。大针茅和羊草在生长初期面对轻度放牧胁迫, 较多的资源仍然用于初级代谢, 增加了植物耐牧性。因此, 轻度放牧有利于提高牧草的碳氮资源利用效率、提高生态系统生产力及稳定性。     

Defense strategies of dominant plants under different grazing intensity in the typical temperate steppe of Nei Mongol,China

放牧是草原的主要利用方式, 但对牧草造成了一定的生物胁迫。面对生存压力, 牧草会通过调节初级与次级代谢过程启动防御机制。该研究以内蒙古温带典型草原优势种植物为研究对象, 通过测定其在5个放牧水平下不同营养器官中的次级代谢产物及木质素等含量, 探讨大针茅(Stipa grandis)和羊草(Leymus chinensis)的各营养器官在防御机制中的角色及其碳氮权衡策略。结果表明: 面对放牧胁迫, 大针茅和羊草会产生大量的单宁、总黄酮、酚类以及生物碱等次级代谢产物, 并以叶片为主要的合成及储存器官。中度放牧使羊草的化学防御机制得到较充分的诱导及表达。但二者地上部分木质素含量并无显著增加, 因此, 二者在避牧性机制上更倾向于化学防御而非机械防御。由于羊草有更高的氮利用效率, 这使得羊草可以通过碳氮两种代谢途径进行防御, 但大针茅在生长初期并不能将氮高效地分配到化学防御中。大针茅和羊草在生长初期面对轻度放牧胁迫, 较多的资源仍然用于初级代谢, 增加了植物耐牧性。因此, 轻度放牧有利于提高牧草的碳氮资源利用效率、提高生态系统生产力及稳定性。     

退化草地物种种内和种间功能性状变异对放牧的响应

研究草地植物功能性状变异对放牧干扰的响应机制,有助于解析草地生态系统群落构建和功能多样性维持机制及植物对环境的适应及权衡策略。以科尔沁沙地退化草地为对象,研究围封和放牧草地物种多种功能性状(植株高度、根系长度、叶面积、根面积、叶片干物质含量、地上干物质含量、根系干物质含量、比叶面积、比根长和根冠比)变异特征及其对放牧干扰的响应机制。结果表明: 退化草地物种种间性状变异明显高于种内变异,种间性状变异对总体变异的贡献率占比高达70.2%～95.1%,而种内变异仅为4.9%～29.8%,但群落构建中物种的种内变异仍不可忽视。放牧草地物种种间性状变异低于围封草地,且放牧草地种内变异增加而种间变异减小。放牧导致不耐牧的优良禾本科牧草叶面积和叶片干物质含量下降而比根长增加,但耐牧的杂类草则通过增加叶面积和叶片干物质含量并降低比根长来提高在群落中的优势地位。退化草地对放牧响应较为敏感的功能性状有叶面积、叶片干物质含量、比根长和比叶面积。植物叶片性状和根系性状自身及彼此间均呈显著正相关,但放牧会增强根系性状的协同效应而减弱叶片性状的协同效应。说明放牧会驱动植物个体和种群功能性状权衡策略发生改变,进而起到调控植物群落结构和功能的作用。     

入侵植物乌桕防御策略的适应性进化研究

生长于不同昆虫群落胁迫下的植物地理种群可能进化出不同的防御策略。入侵植物在原产地同时受到专食性昆虫和广食性昆虫的取食危害, 而在入侵地“逃逸”了专食性昆虫的取食危害。入侵植物对不同类型昆虫防御策略的演化可能在其成功入侵的过程中起着至关重要的作用。该文主要以原产中国入侵北美的木本植物乌桕(Triadica sebifera)为例, 并结合其他入侵植物防御策略演化的研究, 从抗性和耐受性、直接抗性和间接抗性、组成抗性和诱导抗性三个方面系统分析不同昆虫选择压力下入侵植物防御策略的演化, 同时探讨入侵植物防御策略演化对生物防治效果的影响, 指出未来的重点研究方向。     

Responses of morphological and physiological traits to herbivory by snails of three invasive and native submerged plants

3种入侵和本地沉水植物形态和生理性状对螺类牧食的响应 沉水植物水盾草(Cabomba caroliniana)已成为中国太湖流域的优势入侵水生植物。与外来物种的原产地环境相比,引入地新环境中存在的专食性天敌较少。外来物种可能会逃避其原产地环境中的天敌牧食,又因为它们的适口性相对较差,从而导致在引入地外来物种通常比本地物种遭受的牧食者影响更低(天敌逃逸假说)。本研究的目的是比较水盾草与共生的本地沉水植物对本地牧食者的响应。我们进行了一个中宇宙尺度实验,研究了水盾草和两种共生的本地沉水植物黑藻(Hydrilla verticillata)和穗花狐尾藻(Myriophyllum spicatum)对两种本地广食性腹足纲螺类萝卜螺(Radix swinhoei)和环棱螺(Sinotaia quadrata)的牧食响应。记录了它们的形态性状指标(总生物量、冠根比和相对生长率)和生理性状指标(叶片总非结构性碳、木质素和纤维素)。研究结果表明,环棱螺对3种沉水植物性状指标的影响较少。随着本地广食性螺类萝卜螺数量的增加,黑藻和穗花狐尾藻大部分植物性状发生了改变,而水盾草的植物性状表现出相对稳定的趋势。水盾草对萝卜螺的牧食更具抵抗力,这与天敌逃逸假说的假设一致。这一发现说明牧食性螺类促进了水盾草的入侵,这可能会改变沉水植物群落中的物种组成。     

季节放牧下内蒙古温带草原羊草根茎叶功能性状的权衡

放牧是草地主要利用方式之一,不同季节放牧通过影响草地功能性状间的权衡从而影响牧后再生及补偿性生长。通过测定内蒙古温带草原优势种羊草(Leymus chinensis)的株高、节间距和分蘖数等软性状及气体交换、抗氧化酶系统和根茎叶渗透调节物质的含量等硬性状,分析了不同季节放牧处理下羊草功能性状的变化及其权衡关系。结果表明,3年短期放牧处理下,类连续放牧(T1)比春季放牧样地(T2)羊草表现出更强的避牧性与耐牧性。类连续放牧与春季放牧样地羊草软性状及光合特性表现出一致性,6月放牧干扰降低了羊草的净光合速率(P_n),8月放牧干扰通过增加电子传递速率(ETR)及光系统Ⅱ(PSⅡ)分配于光化学反应(P)的比值等增大P_n。但春季放牧样地羊草株高较高,且光合产物较多分配于叶片,导致大量有机物质被啃食,不利于牧草再生。而类连续放牧羊草将较多的有机物质分配于根茎,有利于牧草根系吸水及牧后再生。因此,3年短期放牧处理下,类连续放牧更有利于牧草再生及草原的可持续利用。     

草地群落放牧干扰梯度β多样性研究

放牧过程通过牲畜的啃食、践踏作用干扰草场环境,使草地群落的物种组成发生变化,植物种群的优势地位发生更替。结果表明,随放牧干扰强度加重,从盐湿化草甸到典型草原,群落植物种丰富度呈下降趋势。β多样性测度结果显示,盐湿化草甸和羊草杂类草草甸群落物种变化的中度干扰出现在轻牧→中牧阶段,并在整个放牧干扰进程中,表现较低的稳定性;草甸草原和典型草原群落出现在中牧→重牧阶段;而荒漠草原物种变化表现出高度的稳定性,从轻牧到过牧物种替代仅1～3种。各群落放牧干扰植物多样性的稳定性次序是:荒漠草原>典型草原≥草甸草原>盐湿化草甸.     

草地群落放牧干扰梯度β多样性研究

放牧过程通过牲畜的啃食、践踏作用干扰草场环境,使草地群落的物种组成发生变化,植物种群的优势地位发生更替．结果表明,随放牧干扰强度加重,从盐湿化草甸到典型草原,群落植物种丰富度呈下降趋势．β多样性测度结果显示,盐湿化草甸和羊草杂类草草甸群落物种变化的中度干扰出现在轻牧→中牧阶段,并在整个放牧干扰进程中,表现较低的稳定性;草甸草原和典型草原群落出现在中牧→重牧阶段;而荒漠草原物种变化表现出高度的稳定性,从轻牧到过牧物种替代仅１～３种．各群落放牧干扰植物多样性的稳定性次序是：荒漠草原＞典型草原≥草甸草原＞盐湿化草甸     

放牧干扰下若尔盖高原沼泽湿地植被种类组成及演替模式

以若尔盖高原退化沼泽植被为研究对象,应用多重比较、双因素方差分析、物种累积曲线、PCA排序、方差分解等方法分析了不同放牧压力、放牧季节下物种丰富度、多度、生活型组成、群落演替的变化。结果表明:不同放牧季节物种丰富度格局不尽相同,其中6、9、10月在各牧压梯度间无显著差异,7、8月均以极重度和极度阶段(中生草甸)的最高,原生沼泽的最低。在物种累积速率上,沿牧压梯度以极重度和极度阶段的最高,沿放牧季节以7、8月最高;双因素方差分析结果进一步表明物种丰富度与放牧季节无显著关系,但与放牧压力关系显著。放牧压力和放牧季节共解释了物种多度总方差的47.6%,其中放牧压力解释了50.1%,放牧季节以及二者方差交集均为负值;沿牧压梯度,沼泽植被逆向演替模式倾向于沼泽→草甸,沼泽化草甸阶段不明显,但是演替方向未发生变化,建群种替代规律为:乌拉草→木里苔草→栗褐苔草,生活型组成中直立型植物比例较少,莲座型和匍匐型植物增加。总之,放牧季节对物种丰富度无显著影响,但在一定程度上改变了其牧压梯度格局,降低了物种累积速率。放牧压力改变了群落物种丰富度、生活型组成和演替模式,但放牧可能仅为沼泽植物群落物种多样性格局和演替的驱动力之一。     

Herbivory resistance traits in populations of Poa ligularis subjected to historically different sheep grazing pressure in Patagonia

Seeding selected populations with high grazing resistance may foster recovery of plant populations threatened by overgrazing. Resistance to grazing depends on grazing avoidance (escape from grazers) and grazing tolerance (ability to growth after defoliation). Many studies of grazing tolerance defoliate plants at a fixed height instead of removing the same proportion of biomass and therefore confound tolerance with avoidance. For this reason, the information on evolution of tolerance to defoliation at the intraspecific level is remarkably scarce despite the abundance of papers published that evaluate responses to defoliation. The estimation of the cost of tolerance is also troublesome because current methods usually include spurious correlations due to correlation between variables that share common terms. The objectives of this paper were to assess the intraspecific variation in tolerance and in traits associated with avoidance and growth in populations with different sheep grazing histories. We also estimated the percentage of biomass removed when the defoliation treatment was imposed at fixed height in order to separate tolerance and avoidance. Finally, we estimated the cost of tolerance using a new method proposed for spurious correlations. Results of a greenhouse experiment indicated no difference in tolerance among the three compared populations. However, the populations from overgrazed fields had more prostrate growth form, higher specific leaf area, and higher tillering rate (when no defoliated) than populations from exclosures. We confirmed that fixed height defoliation would have removed a higher proportion of shoot biomass from taller than from shorter individual plants, confounding grazing tolerance and avoidance. Regarding the cost of tolerance, we found no differences from a null model of no cost, indicating that the evolution (or future breeding) of more tolerant genotypes would not be constrained by this cost.     

Lack of intraspecific variation in resistance to defoliation in a grass that evolved under light grazing pressure

Grass species frequently show marked intraspecific variation inmorphology and tolerance to defoliation. Remarkably, most of this evidencecomesfrom grasslands with long evolutionary history of grazing. Here, we explore theintraspecific variation in grazing tolerance and morphometric traits associatedwith grazing avoidance of Paspalum dilatatum (Poir.), agrass from the Flooding Pampa (Argentina), where grazing is a novel disturbancein evolutionary time. We performed a clipping experiment in a greenhouse withtwo populations from sites with contrasting short term grazing regime:continuous grazing and 20 year-old grazing exclosure. The populations did notdiffer in their tolerance to clipping, and showed minor differences in the wayclipping affected plant height, a trait associated with grazing avoidance. Ourresults indicate that there are exceptions to the generalized findings of highlevels of intraspecific variation in grazing resistance among populations ofgrasses. These exceptions may be associated to evolutionary history of grazing.     

Grazing responses in herbs in relation to herbivore selectivity and plant traits in an alpine ecosystem

Herbivores shape plant communities through selective foraging. However, both herbivore selectivity and the plant’s ability to tolerate or resist herbivory may depend on the density of herbivores. In an alpine ecosystem with a long history of grazing, plants are expected to respond to both enhanced and reduced grazing pressures, and the interaction between plant traits and changes in species abundance are expected to differ between the two types of alteration of grazing regime. To understand the mechanisms behind species response, we investigated the relationship between sheep selectivity (measured in situ), plant traits and experimentally derived measures of change in species abundance as a response to the enhancement (from low to high density) or cessation (from low to zero density) of sheep grazing pressure over a six-year time period for 22 abundant herb species in an alpine habitat in south Norway. Sheep selected large, late-flowering herbs with a low leaf C/N ratio. Species that increased in abundance in response to enhanced grazing pressure were generally small and had high root/shoot ratios, thus exhibiting traits that reflect both resistance (through avoidance) and tolerance (through regrowth capacity) strategies. The abundance of selected species remained stable during the study period, and also under the enhanced grazing pressure treatment. There was, however, a tendency for selected species to respond positively to cessation of grazing, although overall responses to cessation of grazing were much less pronounced than responses to enhanced grazing. Avoidance through short stature (probably associated with increased light availability through the removal of tall competitors) as well as a certain amount of regrowth capacity appear to be the main mechanisms behind a positive response to enhanced grazing pressure in this study. The plant trait perspective clearly improves our insight into the mechanisms behind observed changes in species abundance when the disturbance regime is altered. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Arbuscular mycorrhizal fungi alter plant community composition along a grazing gradient in Inner Mongolia Steppe

Arbuscular mycorrhizal fungi (AMF) have a significant influence on plant productivity and diversity in non-grazing grassland. However, the interactive effects between grazing intensity and AMF on plant community composition in natural grassland communities are not well known. We conducted a field experiment that manipulated AMF colonization and grazing intensity to study the impact of AMF suppression on plant community composition and nutrient status over 2 years (2015–2016) with contrasting rainfall levels. We found that AMF root colonization was significantly reduced by the application of the fungicide benomyl as a soil drench. Grazing intensity regulated plant community composition and aboveground biomass mainly by reducing the growth of Leymus chinensis over 2 years. AMF suppression increased the growth of Chenopodium glaucum, but it did not alter other plant species across all grazing intensities. The effects of AMF suppression on plant community composition changed along a grazing gradient considerably between years: AMF suppression increased the biomass of C. glaucum across all grazing intensities in 2015, but slightly increased it in 2016. Interactions between AMF suppression and grazing intensity altered the phosphorus concentration of Stipa grandis and Cleistogenes squarrosa in 2015 but not in 2016. AMF suppression decreased the shoot phosphorus content of L. chinensis but increased that of C. glaucum across all grazing intensities. Our results indicate that grazing intensity substantially alters aboveground community biomass and affects growth of dominant species; AMF by itself have limited effects on plant communities along a grazing gradient in typical steppe.     

中国东北样带草地群落放牧干扰植物多样的变化

放牧干扰是草地群落植物多样性变化的主要影响因素之一。中国东北样带９个草地群落放牧干扰植物多样性性变化的研究结果表明：中牧或重牧阶段Ｓhannon指数达最大值。形成中牧（重牧）＞重牧（中牧）＞轻牧＞过牧的规律。群落物种丰富度、均匀度与多样性的相关分析表明,均匀度变化对多样性变化具有更大的贡献率。而丰富度呈下降趋势,即轻牧（中牧）＞中牧（轻牧）＞重牧＞过牧。生活型功能群多样性也表现出明显的变化。中国东北样带草地群落植物多样性的分布格局是：草甸草原＞典型草原＞典型草原＞荒漠草原＞碱化草甸,并且群落物种丰富度对多样性有更大贡献率。     

中国东北样带草地群落放牧干扰植物多样性的变化

放牧干扰是草地群落植物多样性变化的主要影响因素之一。中国东北样带9个草地群落放牧干扰植物多样性变化的研究结果表明：中牧或重牧阶段Shannon指数达最大值,形成中牧（重牧）>重牧（中牧）>轻牧>过牧的规律。群落物种丰富度、均匀度与多样性的相关分析表明,均匀度变化对多样性变化具有更大的贡献率,而丰富度呈下降趋势,即轻牧（中牧）>中牧（轻牧）>重牧>过牧。生活型功能群多样性也表现出明显的变化。中国东北样带草地群落植物多样性的分布格局是：草甸草原>典型草原>典型草原 >荒漠草原>碱化草原,并且群落物种丰富度对多样性有更大贡献率。     

Community attributes along a perturbation gradient in a shortgrass steppe

Abstract. We constructed a perturbation (response) gradient that encompassed several types of disturbances (causes) affecting shortgrass steppe communities, and that was confounded by time scales of initiation and duration. The objectives were to (1) examine the type of disturbance and the relative magnitude of response in relation to the history of the shortgrass steppe, and (2) determine which attributes of the plant communities displayed relationships across the perturbation gradient, rather than across traditional successional - time gradients. Comparisons of disturbance types indicated that long-term heavy grazing by cattle resulted in plant communities which differ less from communities resulting from other disturbances than did long-term ungrazed sites. The removal of grazers from this system promoted attributes of earlier serai stages. Water addition, below-ground grazing by white grubs, and water-plus-nitrogen enrichment had distinct and large impacts on community composition. Nitrogen enrichment resulted in additions but not losses of species. The shortgrass steppe has a high degree of adaptation to both short-term drought and aboveground grazing. Belowground grazing and semi-aridity may be considered antagonistic pressures on the community. Community attributes that displayed a relationship with increasing level of perturbation were decreasing dominance and increasing diversity, and fluctuation in species composition during short-term wet/dry cycles. The level of perturbation was related to negative impacts on the two primary species and a corresponding increase of other warm-season species, but was not related to densities of any other species, life-form, or functional group.     

Interactions between herbivory and resource availability on grazing tolerance of Leymus chinensis

Herbivory and resource interact to influence plant regrowth following grazing, but few detailed investigations on grazing tolerance at population levels are available. We conducted two pot experiments along a simulated grazing gradient (0%, 25%, 50% and 75% of shoot removal) at three water or nutrient levels to determine the interaction of resource and herbivory on Leymus chinensis, a perennial, dominant species in the eastern Eurasian steppes. Interactions between water availability and clipping intensity on the relative height growth rate (RHGR) and bud number were significant. Significant interactions between nutrient and clipping on RHGR, total biomass and specific leaf area (SLA) were also found. Total biomass and bud number, showing a unimodal curve along the clipping gradient in resource-rich environments, were highest at light clipping level, suggesting that this species has the plastic compensatory responses from under- to overcompensation. Interactions between herbivory and water or nutrient were opposite to each other. The “cooperative” interactions between water and herbivory magnified the difference in grazing tolerance of L. chinensis between high and low water treatments. The “antagonistic” interactions between nutrient and herbivory, on the other hand, were reflected in the lower tolerance to heavy clipping in the high nutrient than low nutrient treatments. Results partly support the limiting resource model (LRM). A modified and simplified graphic model of the LRM was proposed based on our results. The new LRM clearly demonstrated that “cooperative” interactions between varying water levels and clipping intensities aggravate the detrimental impacts of herbivores on plant growth and reproduction, whereas “antagonistic” interactions between nutrient and grazing alleviate the negative effects of herbivores. Biomass compensation and density compensation were identified as main mechanisms of herbivory tolerance in this clonal species.     

Grazing response groups among understorey plants in arid rangelands

Abstract. We analysed attributes of the understorey flora in different plant communities along two grazing gradients in arid Australian rangelands. We aimed to determine if there were patterns among species in response to grazing, and easily recognizable ‘indicator response types’ for monitoring grazing-induced change in community composition. Measurements were stratified by vegetation patch type, in woody groves and open patches. Trait selection and analyses followed a hierarchical approach which searched for patterns within major plant life forms. Patch type exerted a dominant influence on both life forms and species attributes, but interacted with grazing. Grazing was associated with loss in differentiation of species composition between patch types, rather than loss in numbers of species overall. Heavy grazing was variously associated with small size, prostrate habit, low meristems, small leaves, coated leaves, high regrowth potential, plasticity in response to grazing, and high fecundity; and light grazing with opposing attributes. Many attributes tended to vary independently of each other and grazing-related attribute syndromes were recognisable only among grasses. This could be because the environmental filters acting on the communities have given rise to many different species with different natural attribute combinations, few of which are closely associated with grazing resistance. For grassy communities ‘large, erect tussocks branching above-ground’ and ‘small, sprawling basal tussocks’ may have potential as response types indicative of light and heavy grazing respectively, but no response types could be identified for herbaceous communities.     

放牧影响下羊草草地主要植物种群生态位宽度与生态位重叠的研究

本文采用Shannon—Wiener和Pianka公式,在土壤水分、土壤含盐量和土壤有机质含量三维生态因子梯度上测定了松嫩草原碱化羊草草地放牧演替系列12种主要植物种群的生态位宽度和生态位重叠。结果表明,植物种群长期适应由放牧引起的群落和土壤环境因子梯度变化是种群生态位分化的主要原因。优势种羊草种群生态位宽度最大,三维上生态位宽度分别为0.910、0.869和0.930。五脉山黧豆和湿生植物生态位宽度均很窄。增加种表现出较强的适应环境能力,生态位宽度都较大。在放牧演替的先锋植物中,只有虎尾草生态位宽度较大(三维上平均0.707),角碱蓬和星星草种群生态位宽度均很窄。生态位宽度较大的物种与其它种群间生态位重叠较大。分布于相同或相邻放牧阶段及具有相同或相似环境要求的物种间生态位重叠较大。放牧条件下,羊草群落的演替过程也就是种群生态位分化的过程。