放牧强度对高寒嵩草草甸土壤养分特性的影响

植物-土壤系统是草地生态和生产服务价值实现的基础,放牧是草地植物群落演替的重要因素。植物、土壤亚系统对放牧的敏感性是评价草地稳定性和提高草地恢复力的重要依据。以不同放牧强度下的高寒嵩草(Kobresia)草甸为研究对象,探讨土壤养分特征对放牧强度的响应及作用位点,结果表明:改变放牧强度可以明显改变植物群落数量特征,但没有明显改变土壤层次分类特征,说明土壤养分特征对一定范围内放牧强度具有自我稳定维持功能;但放牧干扰强度不同时,土壤剖面过渡层养分含量存在差异,说明长期放牧强度的差异会对土壤剖面养分性质产生影响,且这种影响起源于土壤剖面过渡层。在放牧高寒嵩草草甸植物-土壤系统中土壤剖面养分特征较植物群落数量特征更稳定;土壤剖面过渡层养分特征是土壤亚系统中对放牧的敏感因素;而放牧引起土壤剖面养分特征的改变主要表现在各过渡层上,并构成土壤发生层迁移的风险,因此推测,更为持久和更高强度的放牧干扰将最终改变土壤剖面特征及养分性质。     

不同强度牦牛放牧对青藏高原高寒草地土壤和植物生物量的影响

放牧作为家畜饲养方式之一,是草地最简单、有效的利用方式,放牧中的家畜对草地生态系统的影响是全球畜牧生态学研究的焦点。过度放牧导致草地退化严重,虽然在青藏高原地区已有较多放牧对草地影响的研究,但探究连续4年放牧对高寒草地生态系统影响的定位实验却鲜见报道。本研究在青藏高原东缘选取典型高寒草地,使用高原特有且分布最广的牦牛作为大型草食放牧家畜,设置了4个牦牛放牧强度（禁牧：无放牧、轻牧：1头/hm²、中牧：2头/hm²和重牧：3头/hm²）以研究其对高寒草地土壤和植物功能的影响。开展4年试验后的结果表明：放牧条件下土壤含水率显著增加;而土壤容重、全磷和有机质含量对放牧强度均无显著性响应;土壤全氮和pH的响应主要在表层0-20 cm,其中全氮为轻牧和重牧处理分别显著高于中牧,中牧处理下的土壤pH为显著高于轻牧;土壤全钾含量在禁牧处理中显著高于放牧处理;而土壤有效氮和速效钾均为中牧处理显著高于禁牧;放牧可以显著降低植物地上生物量。牦牛放牧强度显著影响土壤含水率、有效养分和植物地上生物量,而对其它土壤理化性质影响较弱。本研究结果揭示放牧对高寒草地土壤理化性质和植物地上生物量的影响,为青藏高原高寒草甸生态系统保护、可持续管理和合理放牧率提供理论依据。     

高寒嵩草草甸植物群落数量特征对不同利用强度的短期响应

以时空转换的方法确定典型高寒嵩草草甸演替过程的4个关键阶段,以此为研究对象,探讨冬春放牧对高寒草甸生态系统植物功能群数量特征的影响,及在现有放牧制度下不同退化程度草甸植物群落数量特征对禁牧和减牧的响应。结果表明:当禾本科功能群在群落中的地位大于等于莎草科功能群时,减牧可以提高禾本科和莎草科功能群而降低杂类草功能群在群落中的地位;禁牧可以提高禾本科和杂类草功能群而降低莎草科功能群在群落中的地位。当莎草科功能群在群落中的地位大于禾本科功能群,且莎草科功能群以根茎密丛型植物为优势种时,放牧强度降低可以提升禾本科功能群但降低莎草科功能群在群落中地位;而莎草科功能群以密丛型植物为优势种时,放牧强度降低可增加莎草科功能群在群落中的地位,而禾本科功能群在群落中地位的变化取决于草地中裂缝的性质,一定强度的裂缝可以增加禾本科功能群在群落中的地位。因此,退化高寒嵩草草甸自我恢复方式的选择取决于可食性牧草组分、地表特征及恢复目标。当可食性牧草以禾本科功能群为优势种(或禾本科同莎草科功能群为共优种)时,减牧容易提高草地的牧用价值,而禁牧容易增加草地中杂类草功能群的比例,不利于畜牧业生产;当高寒嵩草草甸可食性牧草以莎草科功能群为优势种时,禁牧较减牧更容易加快其牧用性的恢复。小嵩草草甸草毡表层开裂期为该演替系列的激变期,而由于冻融交替形成的裂缝是草地恢复的新生带,如加以利用可以加速草地恢复。     

牦牛放牧强度对小嵩草草甸两季轮牧草场植物群落数量特征的影响

基于小嵩草(Kobresia parva)草甸连续2年的牦牛放牧控制试验,研究了暖季和冷季放牧草场植物群落数量特征的变化.结果表明:在2年的放牧期内,小嵩草草甸2季草场优良牧草的盖度随放牧强度的提高呈降低趋势,而杂草的盖度呈增加趋势;2季草场对照、轻度放牧和中度放牧组的优势种均为小嵩草和垂穗披碱草,但暖季草场重度放牧下主要优势种变为鹅绒委陵菜和阿拉善马先蒿,冷季草场重度放牧下小嵩草和鹅绒委陵菜为主要优势种;放牧强度之间的差异越大,2季草场各放牧处理间群落的相似性程度越低,说明放牧强度是引起群落差异的主要原因,也是群落变化的主导因子.2季草场各放牧处理的物种丰富度、多样性指数、均匀度指数在对照组最低,中度放牧组最高,其指数排序为:对照＜轻度放牧＜重度放牧＜中度放牧,这一结果支持“中度干扰理论”.     

高寒矮嵩草草甸地上生物量与气象因子的关系

初级生产量是生态系统研究的主要内容之一。初级生产量的高低,决定了整个系统的生产力。初级生产量一方面取决于群落类型、种类组成、结构特征;另一方面它又受到周围环境条件的制约。高寒草甸是青藏高原上主要的植     

短期牦牛放牧强度对川西北高原高寒草甸土壤细菌群落的影响

气候变化和人类干扰使青藏高原的草地退化日趋严重,特别是过度放牧导致的草地退化现象尤为突出;然而,牦牛作为青藏高原分布广且数量多的重要家畜,其不同放牧强度对高寒草甸土壤理化性质与细菌群落的影响仍不明晰。在川西北高原典型高寒草甸开展牦牛放牧强度试验,设置了对照组(禁牧)、轻度放牧(1头牦牛/hm~2)、中度放牧(2头牦牛/hm~2)和重度放牧(3头牦牛/hm~2)4个放牧强度,每个强度设置3个重复。两年放牧实验后的结果表明：短期的重度放牧导致土壤有效磷显著增加,而其它土壤性质在各放牧强度变化不显著;随着放牧强度的增加,土壤细菌α多样性呈先增加后减少的趋势,其主要原因是牦牛活动为细菌的生长繁殖提供了有利的营养条件,但由于放牧的持续时间较短,变化不显著;就优势菌而言,土壤绿弯菌门中存在光合自养细菌,在重度放牧下显著高于对照组,其它各菌门在不同放牧强度下无显著差异;土壤氮与硝化螺旋菌门呈正相关,速效磷与酸杆菌门也呈显著正相关,均说明放牧强度对土壤细菌类群的影响是通过土壤性质间接实现的。本实验通过研究不同牦牛放牧强度下的土壤细菌群落结构,为放牧策略的制定提供了基础数据支持,为草地退化的防治提供理论...     

放牧强度对草甸草原生产力和多样性的影响

采用比较样地法研究了不同放牧强度对羊草草甸草原群落多样性和生产力的影响。结果表明:α多样性指数随放牧强度的增加表现为先增加后降低的趋势,其值在轻度放牧区最大,支持了"中度干扰理论";β多样性指数随放牧强度的增加而变大;不同放牧强度的草地植物种类相似性变差、草地地上净初级生产力与Alatalo均匀度指数具有显著的线性相关性(P0.05);放牧和气候对草地地上净初级生产力均有较大的影响,但二者的互作效应不显著(P0.05);不放牧不能持续维持草地的健康状况,但健康的草地状况可以有效地缓冲放牧和气候干扰,并能够维持较高的草地生产力和生物多样性。     

青藏高原高寒灌丛植被对长期放牧强度试验的响应特征

在青藏高原中国科学院海北高寒草甸生态系统定位研究站对金露梅高寒灌丛草场植被开展了长期不同放牧强度试验,分别在短期(4年)、中期(11年)和长期(18年)放牧阶段研究不同放牧干扰强度对草地植物物种多样性、群落结构、地上生物量和草场质量的影响.研究表明,在不同放牧阶段,随着放牧强度增加植物群落的高度和盖度都降低.在中期放牧干扰阶段,物种多样性数和均匀度指数随着放牧强度增加呈现典型的单峰曲线模式;在长期放牧干扰阶段,随着放牧强度增加,占优势地位的灌木和禾草被典型杂类草替代,其中的重度放牧干扰简化了高寒灌丛植被群落结构,减少了地上现存生物量,特别是可食优良牧草生物量.植被对放牧的响应除了与放牧强度和放牧时间阶段密切相关外,还与该地区水热条件的变化有一定的相关性.针对长期放牧干扰的反应特性可将金露梅灌丛草场中植物划分为增加型、敏感型、忍耐型和无反应型4种类型.除了丰富度指数、多样性指数和均匀度指数外,其它一些特征参数并不支持著名的中度干扰假说.本研究发现,长期重度放牧促进了青藏高原高寒草地退化,适度放牧有利于高寒灌丛草场的生物多样性保护和牧草利用;"取半留半"的放牧原则在青藏高原草场放牧管理实践中值得推荐,它将有利于防止草场退化,提高牧草利用率和维持较高的生物多样性.     

不同放牧强度对人工草地牧草生殖分配及种子重量的影响

不同放牧强度对白三叶,红三叶,鸭茅的生殖分配及种子千粒重影响极显著,一定强度的放牧干扰有利于提高休牧后三叶草的花序密度,但鸭茅花序密度却随放牧强度却随放牧强度的提高而出现明显下降,放牧草地三种牧草种群的生殖分配均低于对照草地,在放牧草地,随放牧强度的提高,白三叶生殖分配逐渐增加,红三叶及鸭茅生殖分配逐渐减少,提高放牧强度后,三叶草千粒重出现递减趋势,而鸭茅却出现递增趋势,在无放牧干扰草地,三叶草种群趋于生产数量较少的大粒种子,在放牧干扰下,趋于生产数量较多的小粒种子;鸭茅种群则出现相反的变化。     

高寒小嵩草草甸暖季草场主要植物种群的生态位

对高寒小嵩草草甸不同放牧强度下20种植物种群的优势度、生态位宽度及生态位重叠规律进行了研究。结果表明,经过2年的放牧实验,对照、轻度和中度放牧组的主要优势种均为小嵩草和垂穗披碱草,重度放牧组的主要优势种为鹅绒委陵菜和阿拉善马先蒿;由于小嵩草、矮嵩草和线叶嵩草具有耐牧和耐践踏等生物学特点,它们的生态位宽度很大（0．938,0．824,0．815）;垂穗披碱草由于其耐牧和耐旱性较差,生态位宽度相对较小（0．805）,且青海野青茅、异针茅、针茅、紫羊茅和双叉细柄茅等禾本科牧草的生态位宽度在放牧强度梯度上均较小（0．226,0．448,0．445,0．608,0．605）,说明放牧抑制了高大禾草层片的发育,为植株矮小的莎草科牧草的生长创造了条件;异针茅和针茅之间、甘肃马先蒿和阿拉善马先蒿之间生态位重叠较小（0．500,0．572）,这是种间对资源利用上分化的结果。分布于放牧演替系列2个极端的种群间生态位重叠较小,表明物种的分布是既间断又连续的。     

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。     

克氏针茅草原群落物种多样性与生物量关系对放牧强度的响应

放牧强度引起的草原植物群落物种多样性与地上生物量变化是近年来草地生态系统研究的热点问题。以内蒙古锡林郭勒克氏针茅草原为研究对象,探究植物群落结构特征、物种多样性与地上生物量之间相互关系及其对不同放牧强度的响应。结果表明：随着放牧强度的增加植物群落结构逐步向退化方向演替;植物群落高度逐渐降低（P<0.05）,密度逐渐增加（P<0.05）,盖度总体呈下降趋势（P<0.05）;植物群落和原有群落优势种地上生物量总体呈下降趋势（P<0.05）,而退化指示物种的地上生物量逐渐增加（P<0.05）;轻度、中度放牧条件下群落物种Margalef指数、Pielou指数、Simpson指数均显著高于重度放牧（P<0.05）;地上生物量与Shannon-Wiener指数、Margalef指数和Pielou指数呈正相关关系,而与Simpson指数呈负相关关系。综上所述,克氏针茅草原植物群落结构和功能在不同放牧强度下产生不同的响应,适度放牧有利于提高群落物种多样性与生物量。     

Intensity-dependent effects of cattle and sheep grazing in sand grasslands — Does livestock type really matter?

Aims

By analysing cattle- and sheep-grazed sand grasslands, we tested the following hypotheses: (i) livestock type has a stronger effect on the vegetation characteristics than grazing intensity; (ii) sheep grazing results in lower biomass and species and functional diversity than cattle grazing, regardless of intensity; and (iii) increased grazing intensity causes a shift of the trait composition in grasslands.

Location

Sand grasslands in the Nyírség region, East Hungary.

Methods

We selected 26 sand grassland sites grazed by cattle or sheep and classified them into four intensity levels. Vegetation composition was surveyed in 2 m × 2 m plots. We harvested the above-ground biomass from 20 cm × 20 cm plots; then dried and sorted it to live biomass, litter, moss, and lichen. We compared Rao dissimilarity index, species richness, Shannon diversity, evenness, and the community-weighted means of nine vegetative and generative traits along a grazing intensity gradient. We calculated functional richness, evenness, and divergence for comparison.

Results

We found that some diversity metrics and community-weighted means of most studied traits were significantly affected by grazing intensity. Several characteristics were also affected by the interaction of grazing intensity and livestock type, but none of the studied characteristics was affected by livestock type in itself. Increasing Rao dissimilarity index peaking at the fourth grazing intensity level was detected, but for other multitrait indices, no such changes were proven, except for functional divergence, which was the lowest at the first intensity level. Graminoid, forb, and litter biomass were significantly affected by intensity, but none of the biomass fractions was affected by livestock type.

Conclusions

We suggest that for the management of sand grasslands, grazing intensity should be carefully adjusted, considering not only livestock units per hectare. For practical recommendations, well-defined, long-term experiments studying different livestock and habitat types along an intensity gradient would be essential.     

基于三江源高寒草甸群落结构变化评估围栏封育对草地恢复的影响

围栏封育是三江源生态保护与修复主要措施之一,目前缺少基于多样地长时间序列监测数据和从植物群落结构变化角度来评估草地生态保护与修复成效的相关研究。基于多样地各经济类型群2005—2017年的地上生物量及其占总生物量比例数据,对比分析三江源草原围栏封育与放牧区植物群落结构变化差异,评价围栏封育对草地恢复的影响。研究结果表明围栏封育显著提高了地上生物量,在围栏封育期间地上生物量稳定,但群落结构出现恶化趋势,研究时段内禾本科和莎草科优良牧草生物量占比分别减少48.2%和23.9%,毒草增加了230.2%。同期放牧区禾莎草生物量占比先减少后增加,毒草杂草生物量占比先增加后减少,群落的种群结构改善可能与草畜平衡措施的实施有关。现有的持续围栏封育措施不可能但降低了草地的经济价值,也带来了一定的生态风险。因此基于草地实际产草量以及生态保护要求,确定更为合理的载畜量,实施更为精准的草畜平衡管理,应该比切断牲畜与草地关系的长期禁牧封育更为有效。     

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。     

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。     

Satellite remote sensing of grasslands: from observation to management

Aims Grasslands are the world's most extensive terrestrial ecosystem, and are a major feed source for livestock. Meeting increasing demand for meat and other dairy products in a sustainable manner is a big challenge. At a field scale, Global Positioning System and ground-based sensor technologies provide promising tools for grassland and herd management with high precision. With the growth in availability of spaceborne remote sensing data, it is therefore important to revisit the relevant methods and applications that can exploit this imagery. In this article, we have reviewed the (i) current status of grassland monitoring/observation methods and applications based on satellite remote sensing data, (ii) the technological and methodological developments to retrieve different grassland biophysical parameters and management characteristics (i.e. degradation, grazing intensity) and (iii) identified the key remaining challenges and some new upcoming trends for future development.Important findings The retrieval of grassland biophysical parameters have evolved in recent years from classical regression analysis to more complex, efficient and robust modeling approaches, driven by satellite data, and are likely to continue to be the most robust method for deriving grassland information, however these require more high quality calibration and validation data. We found that the hypertemporal satellite data are widely used for time series generation, and particularly to overcome cloud contamination issues, but the current low spatial resolution of these instruments precludes their use for field-scale application in many countries. This trend may change with the current rise in launch of satellite constellations, such as RapidEye, Sentinel-2 and even the microsatellites such as those operated by Skybox Imaging. Microwave imagery has not been widely used for grassland applications, and a better understanding of the backscatter behaviour from different phenological stages is needed for more reliable products in cloudy regions. The development of hyperspectral satellite instrumentation and analytical methods will help for more detailed discrimination of habitat types, and the development of tools for greater end-user operation.     

Effect of nitrogen addition,form and clipping on competitive interactions between grassland species

Aims Although the effects of N addition on plant biomass are well understood, we know a lot less about the importance of N form even though some studies have shown different impacts from reduced and oxidized forms of N. Furthermore, responses to grazing are likely to interact with the response to N addition. This experiment investigates the interactive effects of N addition and form with clipping on competition between three grassland species.Methods The three species (Anthoxanthum odoratum L., Plantago lanceolata L. and Prunella vulgaris L.) were grown alone and in combination with factorial additions of deionized water, sodium nitrate and ammonium chloride, and a clipping treatment. Above- and belowground biomass was harvested after 4 months.Important findings In monocultures, the results show increases in biomass with N addition, but clipping resulted in fewer changes with species displaying varying degrees of growth compensation. A. odoratum was the strongest competitor when grown with other species. In monocultures without clipping, N form was not important, but in the presence of clipping and in different species combinations, N form became important. Significant two- and three-way interactive effects were observed showing that complex interactions exist between N addition, clipping and species identity. The results have important implications when considering the effects of N deposition.     

Influence of nitrogen addition on the primary production in Nei Mongol degraded grassland

Aims Irrational utilization and global climate change have caused degradation of grassland ecosystems in northern China with low soil fertility, decreased vegetation coverage and productivity. Nitrogen addition has been suggested an effective way to enhance restoration of those degraded grasslands. In this study, we selected a typical steppe with three different degrading levels, including lightly, moderately and heavily degraded communities, in East Ujimqin, Nei Mongol. Our objectives of this study are to examine if and how nitrogen (N) addition can enhance restoration of those degraded grasslands Methods Treatments with four levels of N addition (0, 5.0, 10.0 and 20.0 g N·m^-2·a^-1) were conducted to each of the three degraded communities from 2014 to 2015. Nitrogen was applied as urea in June of both years. Aboveground biomass was collected at the species level in 1 m × 1 m plot in August each year, all species biomass was summed as net primary production, and biomass of plant functional groups was calculated by perennial rhizome grasses, perennial bunchgrasses, perennial forbs, shrubs and semi-shrubs, annuals and biennials.Important findings Our results showed that the high (20.0 g N·m^-2·a^-1) and medium level N addition (10.0 g N·m^-2·a^-1) significantly increased the aboveground biomass of the slightly degraded community by 53.1% and 51.6% compared with no N addition. N addition had no significant effects on the moderately and heavily degraded communities. N addition with high and medium levels increased aboveground biomass of perennial rhizome grasses by 45.1% and 47.7%, but decreased that of perennial forbs by 37.4% and 42.1% at the slightly degraded community. Our results indicated that N addition could increase the growth of perennial rhizome grasses, and the growth of perennial forbs was suppressed consequently. Our results suggest that even the application of N fertilizers can only be helpful to restoration of those slightly degraded grasslands. Besides, N addition had no significant effects on species richness in different degraded communities indicating the fact that the study may not last long enough. For the purpose of increasing aboveground biomass of degraded grassland, we should not only consider the type and quantity of fertilization, but also the attribute of the degraded communities. In addition, the response of degraded community in biomass may strongly be impacted by degrading level of studied grassland.