松嫩草原碱化羊草草地放牧空间演替规律的研究

研究了不同放牧强度对羊草草地的影响。结果表明,过牧条件下,群落地上、地下生物量分别比较牧阶段下降了６７．９６和７５．００％,羊草种群根茎分蘖数和种子产量下降１．０和３．３％,极牧条件下,土壤有机质和水分含量分别下降到轻牧阶段的２１．１和６６．５％,而碱化度和全盐量却分别增加了１倍和８倍。     

放牧影响下羊草种群生殖生态学的研究

在种群水平上系统研究了放牧对松嫩草原关草种群无性繁殖、有性生殖和生物量的生殖分配的影响。结果表明,放牧制约了羊草种群无性繁殖和有性生殖的更新途径,表现在随放牧强度增加,无性繁殖体营养技密度、根茎牙密度和有性生殖体种子生物量、结实数和生殖枝分化率等指标均显著下降,是生牧后下降迅速。随放牧强度增加,关草种群根茎生物量的分配比例显著增加,而同化器官、非同化器官和种子生物量分配比例都显著下降,极牧阶段几科     

短花针茅荒漠草原不同放牧处理地上现存量的对比及拟合优化

为探讨放牧强度季节调控下荒漠草原地上现存量的变化趋势及放牧强度与季节的耦合作用对地上现存量影响,本研究整理2010—2014年9月蒙古高原短花针茅荒漠草原地上现存量观测数据,采用对比分析和回归建模对荒漠草原地上现存量进行了研究。结果表明:荒漠草原地上现存量在试验处理间和年度间均存在极显著性差异(P0.01),且放牧处理效应大于年度间水温变化引起的生物量变化。回归建模分析显示,通过6个试验处理可建立拟合率达到99%以上的通用模型,根据通用模型可以预测27种试验处理组合的地上现存量变化;模型同时显示,春季放牧强度增加可导致草地可持续利用能力下降,且前一季节放牧强度对后一季节放牧存在明显影响,不同放牧季存在影响结果的叠加作用,导致前期的影响作用在放牧季被放大,使得草地在重牧过程后的可恢复能力降低。     

羊草种群生物量分配动态模拟

基于4种密度羊草种群的温室模拟试验,分析了羊草种群地上生物量与地下生物量的动态变化．结果表明：羊草种群的地上生物量与地下生物量随生长期呈增加的趋势,且随密度的增加而增加,但不同密度间羊草地上生物量与地下生物量的相对生长速率没有显著差异;不同密度羊草种群的根冠比随生长进程而增加,但差异不显著,表明环境因子是影响羊草种群根冠比变化的主导因素;单株羊草及羊草种群的地上生物量和地下生物量间存在显著的幂函数关系,但幂函数指数与系数随羊草密度的变化而变化,表明资源竞争引起的微环境差异导致了羊草种群根冠比的动态变化,可为定量研究光合产物分配提供参考．     

氮素对内蒙古典型草原羊草种群的影响

为了研究氮素对内蒙古典型草原植物种群的影响, 在中国科学院内蒙古草原生态系统定位研究站, 实施了长期的氮素添加试验。就两年来不同梯度氮素处理对羊草 (Leymuschinensis) 种群的影响进行了分析。结果表明, 氮素对羊草种群具有显著的调节效应, 随着氮素梯度的增加, 羊草种群密度、种群高度、地上生物量、地下生物量、总生物量均显著增加, 羊草种群地下生物量 /地上生物量比值逐渐降低。氮素对羊草种群构件的生物量分配有显著影响, 随着氮素梯度的增加, 羊草种群生物量向根茎的分配比例显著降低, 向叶片和根系的分配比例显著提高。羊草种群的相对密度和相对生物量也随着氮素梯度的增加而显著提高。     

采用系统聚类分析法对羊草草地放牧演替阶段的划分

系统聚类分析法已被广泛地应用于植物群落分类、演替阶段划分等研究中。本文采用六种聚类分析法将松嫩平原南部羊草草地划分为轻牧、适牧、重牧、过牧和极牧五个放牧演替阶段,其结果与野外实际调查基本一致。     

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.     

水分梯度上放牧对内蒙古主要草原群落功能群多样性与生产力关系的影响

应用样线法对放牧对内蒙古草原沿水分梯度分布的主要植物群落:小针茅(Stipaklemenzii)群落、大针茅(Stipagrandis)群落、羊草(Leymuschinensis)群落和羊草杂类草群落多样性、生产力以及两者关系的影响进行了研究,结果表明,除羊草杂类草群落外,物种多样性、生活型多样性和水分生态类型多样性随放牧强度的加大而降低,但适度放牧增加了羊草杂类草群落的上述多样性指标。群落地上现存量一般随放牧强度的增大而下降,但小针茅群落反之,主要与1年生植物猪毛菜(Salsolacollina)的生物量迅速增加有关。除羊草群落外,其他群落0～10cm地下生物量随放牧强度的变化不显著;放牧显著降低羊草群落和羊草杂类草群落0～30cm地下生物量。多样性和生产力间的关系在群落水平上的趋势是不同的,但放牧影响下内蒙古草原4种群落多样性与生产力总体而言呈线性增加关系;同时两者之间的关系还和采用哪种多样性指标和生产力指标有关,用水分生态类型多样性比物种多样性更能反映与地上地下总生产力间的关系,得到放牧影响下内蒙古草原植物群落地上地下总生物量与水分生态类型多样性的回归方程。     

退化草原冷蒿群落13年不同放牧强度后的植物多样性

放牧过程通过家畜的啃食、践踏干扰草原环境,使草原的物种组成发生变化,植物种群的优势地位发生更替。对退化草原中的冷蒿群落在经历13a不同放牧强度——无牧（0．00只羊,hm^2）、轻牧（1．33只羊／hm^2）、中牧（4．00只羊／hm^2）、重牧（6．67只羊,hm^2）的围栏放牧后的植物群落多样性进行研究,结果表明：经过13a的演替变化,（1）无牧处理下植被密度显著低于其它3个放牧处理下的植被密度,而其它3个放牧处理之间的植被密度差异不显著;（2）无牧处理下羊草成为群落的优势种,轻牧和中牧处理下冷蒿依然是群落的优势种。这3种处理下寸草苔的种群密度最大;重牧处理下优势种变为星毛委陵菜,并且其种群密度最大;随着放牧强度增加,不同放牧退化阶段指示植物的种群密度的变化趋势是：冷蒿为先增大后减小,而星毛委陵菜为先急剧增大,然后平缓增大,最后再急剧增大;（3）植物多样性和均匀度指数在中牧处理下最大,在无牧处理下最小,说明中牧处理下群落的多样性最高,无牧处理下群落的多样性最小。而优势度指数正相反。植物群落结构和多样性的变化主要是由放牧家畜选择性采食、不同植物对放牧响应的不同策略、植物种间的竞争、动植物协同进化以及由放牧改变的土壤理化性质等因素综合决定的。此研究有助于进一步认识退化草原在继续放牧干扰下的演替规律以及为退化草原的保护和恢复提供理论依据。     

放牧对内蒙古锡林河流域草原土壤碳组分的影响

选择内蒙古锡林河流域三种草原,较系统地研究了放牧对微生物量碳(MB-C)和易分解碳(Lab-C)两种碳素组分的影响。结果表明,自由放牧22年后,羊草(Leymus chinensis)草原土壤0~10 cm和10~20 cm土层土壤微生物量碳分别下降了27.9%和12.8%;土壤易分解碳分别下降了22.0%和12.6%,自由放牧没有改变羊草草原土壤活性碳的季节变化形式。大针茅(Stipa grandis)草原0~5 cm表层和5~15 cm下层土壤微生物量碳分别下降了38.2%和12.2%。大针茅草原季节波动出现高峰的时间较羊草草原推后,基本在8月下旬,并且与地上生物量存在明显的正相关关系(p<0.001)。土壤活性碳在表征羊草草原和大针茅草原土壤的动态变化时,要敏感于土壤总有机碳。冷蒿-小禾草草原(Artemisia frigida-short bunchgrasses steppe)连续放牧11年恢复2年后,土壤各碳素组分都没有发生明显变化,但随着放牧率的增加,MB-C/Org-C比值和Lab-C/Org-C比值逐渐降低,表现为轻牧>中牧>重牧,这说明,在表征放牧对冷蒿-小禾草草原土壤的影响指示上,MB-C/Org-C和Lab-C/Org-C要比MB-C和Lab-C敏感。     

Restoration of native vegetation following exclosure establishment on communal grazing lands in Tigray,Ethiopia

Questions: Is plant species richness, diversity and above‐ground standing biomass enhanced after establishing exclosures on communal grazing lands? What factors influence the effectiveness of exclosures to restore degraded native vegetation in Tigray, Ethiopia? Location: Northern Ethiopia. Methods: We used a space‐for‐time substitution approach to detect changes in plant species richness, diversity and above‐ground standing biomass after conversion of communal grazing lands to exclosures. We selected replicated (n=3) 5‐, 10‐, 15‐ and 20‐year‐old exclosures and paired each exclosure with an adjacent communal grazing land to ensure that soil and terrain conditions were as similar as possible among each pair. Results: All exclosures displayed higher plant species richness, diversity and biomass than the communal grazing lands. Differences in plant species richness and biomass between an exclosure age and adjacent communal grazing land were higher in oldest than in youngest exclosures. In exclosures, much of the variability in plant species composition and biomass was explained by a combination of edaphic (total nitrogen, phosphorus, texture and soil pH) and site (precipitation and altitude) variables (R²=0.72–0.82). Edaphic and site variables also explained much of the variability in plant species composition in communal grazing lands (R²=0.76–0.82). Our study shows that all exclosures are at an early stage of succession. The increase in economically important indigenous shrub and tree species with exclosure age suggests that, with time, a valuable afromontane forest may develop. Conclusions: Establishment of exclosures on communal grazing lands is a viable option to restore degraded native vegetation. However, before expanding exclosures, the ecological consequences of additional exclosures should be investigated as further expansion of exclosures could increase grazing pressure on remaining grazing areas. Furthermore, consideration of edaphic and site variables will help optimize selection of areas for establishment of exclosures and enhance natural regeneration in exclosures in the future.     

High impact grazing as a management tool to optimize biomass growth in northern Argentinean grassland

Grasslands are the main source of feed for cattle in Argentina. Standing dead biomass accumulation threatens efficient resource use. The effect and timing of high impact grazing by cattle as a management tool to remove excess standing dead biomass was studied in grasslands of North Eastern Argentina. High impact grazing (HIG) was introduced monthly on adjacent paddocks over the course of the year and its effects were studied for 12 months following the treatment. Dynamics of biomass re-growth and accumulation of green and standing dead biomass were studied. HIG generally improved the green to total biomass ratio and reduced the overall biomass in the paddocks. Strong seasonal dynamics in the biomass growth rates strongly influenced the effects of timing of the HIG. All sub-plots subjected to HIG showed a growth pattern anti-cyclic to control, with an active growth phase during autumn when the biomass in the control sub-plots decreased. Best results in terms of standing dead biomass reduction and dead to green biomass ratios were achieved after HIG in winter. HIG in autumn, however, reduced fodder availability and reduced next year's grassland's productivity. We propose strategically (carefully) timed HIG not only as an alternative method to reduce standing dead biomass, but also as a pathway to sustainable intensification by providing green forage at levels equal or even higher than those achieved under continuous traditional grazing.     

羊草贮藏性物质含量的季节变化及其对不同人为活动影响的反应

羊草(Leymus chinensis)是根茎性禾草,是东北及内蒙东部地区广泛分布的主要建群种之一。以羊草为建群种的羊草群落分布广、面积大、是优良的天然草场。羊草草场的产草量与植物的地下部特别是根茎中贮藏性物质的含量有密切关系。因为多年生根茎性植物所制造的光合产物,除用于当年的生长发育之外,同时将多余的贮藏性物质(主要指可溶性糖     

Strategies of nitrogen cycling of Phragmites australis at two sites differing in nutrient availability

Below-ground biomass and nitrogen content were determined at two genetically homogeneous Phragmites stands differing in morphology, in productivity, and in nutrient supply. Comparable ratios between above-ground standing crop and rhizome biomass were found at both sites, whereas the root biomass/above standing crop ratio was significantly higher at the nutrient poor site. Investigations on the dynamics of nitrogen content revealed distinct differences in nitrogen translocation to the rhizomes between the investigated clones indicating two ecophysiological strategies in storage behaviour. These two strategies could be attached to the “assimilation type” and to the “translocation type”, respectively. A modified definition of both types is presented.     

Aboveground dry-matter allocation in ungrazed and grazed stands of Indigofera spinosa in the arid zone of Turkana, Kenya

The dwarf shrub Indigofera spinosa , indigenous to arid and semi-arid rangelands of northeastern Africa, is an important food source for livestock. Proper management of the shrub requires improved understanding of the effects of grazing and climatic variability on aboveground dry-matter allocation. Between 1986 and 1990, we compared the temporal variability of aboveground dry-matter allocation to different plant biomass compartments. We also compared dry-matter transfers between components; total live biomass to litter, standing dead to litter and live biomass to standing dead between continuously grazed and an ungrazed treatments. Partitioning of combined total dry-matter production among different structural organs (called allocation ratio) is influenced by phenological changes, episodic rainfall and her-bivory. Dry-matter production in the grazed treatment responded more markedly to episodic rainfall events more than in the ungrazed treatment. Exclusion of grazers failed to improve the relative growth rate (RGR) of shrub biomass, while grazing improved it. RGR declined in the ungrazed treatment following the accumulation of standing dead dry-matter, while m the grazed treatment it declined following the shedding of leaves. The shrub allocated more to total live biomass than to standing dead. Greater reduction of total live allocation ratio in the grazed than in the ungrazed treatment occurred during a dry year. The ungrazed treatment had higher standing dead allocation ratio than did the grazed treatment. Plants transferred more dry-matter from total live biomass compartment to litter, than from standing dead to or from total live biomass to standing dead independent of treatment. The rates of transfer were higher in the ungrazed than in the grazed treatment. The results suggest that I spinosa has evolved to respond to climatic variability and grazmgbyallocating dry allocating dry-matter differently between various compartments.     

Effects of experimental season of prescribed fire and nutrient addition on structure and function of previously grazed grassland

Aims Understanding the drivers of grassland structure and function following livestock removal will inform grassland restoration and management. Here, we investigated the effects of fire and nutrient addition on structure and function in a subtropical semi-native grassland recently released from grazing in south-central Florida. We examined responses of soil nutrients, plant tissue nutrients, biomass of live, standing dead and litter, and plant species composition to experimental annual prescribed fire applied during different seasons (wet season vs. dry season), and nutrient additions (N, P and N + P) over 9 years.Methods Experimental plots were set up in a randomized block split-plot design, with season of prescribed fire as the main treatment and nutrient addition as the subplot treatment. Species cover data were collected annually from 2002 to 2011 and plant tissue and plant biomass data were collected in 2002–2006 and 2011. Soil nutrients were analyzed in 2004, 2006 and 2011.Important findings Soil total phosphorus (P) levels increased substantially with P addition but were not influenced by prescribed fire. Addition of P and N led to increased P and N concentrations in live plant tissues, but prescribed fire reduced N in live tissue. Levels of tissue N were higher in all plots at the beginning of the experiment, an effect that was likely due to grazing activity prior to removal of livestock. Plant tissue N steadily declined over time in all plots, with annually burned plots declining faster than unburned plots. Prescribed fire was an important driver of standing dead and litter biomass and was important for maintaining grass biomass and percent cover. Nutrient addition was also important: the addition of both N and P was associated with greater live biomass and woody forbs. Removal of grazing, lack of prescribed fire, and addition of N + P led to a reduction of grass biomass and a large increase in biomass of a woody forb. Annual prescribed fire promoted N loss from the system by reducing standing dead and litter, but maintained desirable biomass of grasses.     

不同海拔云南黄连生物量和主要有效成分变化

研究了不同海拔(2 100～2 700 m)下,野生和人工栽培云南黄连的生物量、主要有效成分含量及产量.结果表明:野生云南黄连根茎和根生物量沿海拔梯度呈上升趋势,但无显著性差异(P>0.05);人工栽培云南黄连根茎生物量平均值在海拔2 600 m和2 700 m处分别为87.5 kg·hm^-2和97.0 kg·hm^-2,显著高于海拔2 300 m处(34.8 kg·hm^-2,P<0.05),且海拔2 300、2 600和2 700 m的人工栽培云南黄连根茎和根生物量均大于野生云南黄连,但无显著性差异(P>0.05). 野生云南黄连的根茎和根生物量均与全株生物量呈显著正相关. 野生云南黄连根茎和根小檗碱含量在海拔2 700 m处最高,分别为4.60%和1.93%; 根茎巴马汀和药根碱含量、根药根碱含量在海拔2 600～2 700 m处最高;根巴马汀含量在2 300 m处最高.人工云南黄连根茎和根小檗碱含量在海拔2 600 m处最高,分别为4.41%和1.90%; 根茎巴马汀含量,根小檗碱、巴马汀和药根碱含量在海拔2 600～2 700 m处最高;根茎药根碱含量在海拔2 300 m处最高.海拔2 600～2 700 m处野生云南黄连根茎和根中各有效成分产量显著高于海拔2 100和2 300 m处(P<0.05). 野生云南黄连分株的根茎生物量、根生物量、叶生物量、总生物量、高度和冠幅沿海拔梯度呈先升后降趋势.增大种植密度和加强人工管理可以提高云南黄连生物量和主要有效成分产量.     

Increasing native, but not exotic, biodiversity increases aboveground productivity in ungrazed and intensely grazed grasslands

Species-rich native grasslands are frequently converted to species-poor exotic grasslands or pastures; however, the consequences of these changes for ecosystem functioning remain unclear. Cattle grazing (ungrazed or intensely grazed once), plant species origin (native or exotic), and species richness (4-species mixture or monoculture) treatments were fully crossed and randomly assigned to plots of grassland plants. We tested whether (1) native and exotic plots exhibited different responses to grazing for six ecosystem functions (i.e., aboveground productivity, light interception, fine root biomass, tracer nitrogen uptake, biomass consumption, and aboveground biomass recovery), and (2) biodiversity-ecosystem functioning relationships depended on grazing or species origin. We found that native and exotic species exhibited different responses to grazing for three of the ecosystem functions we considered. Intense grazing decreased fine root biomass by 53% in exotic plots, but had no effect on fine root biomass in native plots. The proportion of standing biomass consumed by cattle was 16% less in exotic than in native grazed plots. Aboveground biomass recovery was 30% less in native than in exotic plots. Intense grazing decreased aboveground productivity by 25%, light interception by 14%, and tracer nitrogen uptake by 54%, and these effects were similar in native and exotic plots. Increasing species richness from one to four species increased aboveground productivity by 42%, and light interception by 44%, in both ungrazed and intensely grazed native plots. In contrast, increasing species richness did not influence biomass production or resource uptake in ungrazed or intensely grazed exotic plots. These results suggest that converting native grasslands to exotic grasslands or pastures changes ecosystem structure and processes, and the relationship between biodiversity and ecosystem functioning.     

Belowground net primary productivity and biomass allocation of a grassland in Inner Mongolia is affected by grazing intensity

The root system of permanent grasslands is of outstanding importance for resource acquisition. Particularly under semi-arid conditions, the acquisition of water and nutrients is highly variable during the vegetation growth period and between years. Additionally, grazing is repeatedly disturbing the functional equilibrium between the root system and the transpiring leaf canopy. However, very few data is available considering grazing effects on belowground net primary productivity (BNPP) and root-shoot dry mass allocation in natural grassland systems. We hypothesise that grazing significantly reduces BNPP due to carbon reallocation to shoot growth. Root biomass and BNPP were estimated by soil coring in 2004, 2005 and 2006 and from ingrowth cores in 2005 and 2006 at one site which has been protected from grazing since 1979 (UG79), at one winter grazing (WG), and one heavily grazed (HG) site. BNPP was estimated from the summation of significant increments of total and live root biomass and from accumulated root biomass of ingrowth cores. Belowground biomass varied from 1,490–2,670 g m^?2 and was significantly lower under heavy grazing than at site UG79. Root turnover varied from 0.23 to 0.33 year^?1 and was not significantly different between sites. Heavy grazing significantly decreased live root biomass and BNPP compared to site UG79. Taking BNPP estimates from live root biomass dynamics and ingrowth cores as the most reliable values, the portion of dry mass allocated belowground relative to total net primary productivity (BNPP/NPP) varied between 0.50–0.66 and was reduced under heavy grazing in 2005, but not in 2006. The positive correlation between cumulative root length density of ingrowth cores and leaf dry matter suggests that the ingrowth core method is suitable for studying BNPP in this semi-arid steppe system. Grazing effects on BNPP and BNPP/NPP should be considered in regional carbon models and estimates of belowground nutrient cycling.