刈割留茬高度和不同播种组合对人工草地初级生产力和物种丰富度的影响

采用7种播种方式(3种单播和4种混播)和3种刈割留茬高度裂区试验,测定了青藏高原高寒地区人工建植3年的垂穗披碱草(Elymus nutans)、中华羊茅(Festuca sinensis)和羊茅(Festuca ovina)草地地上生物量、物种丰富度以及杂草生物量,以分析刈割对青藏高原人工草地初级生产力和物种丰富度的影响。结果显示:(1)在草地建植第2年,不刈割与刈割留茬60和20 mm的草地初级生产力均有显著差异;留茬60和20 mm刈割使单播草地的平均初级生产力分别降低20%和27%,使混播草地的平均初级生产力分别降低29%和37%。(2)草地建植第3年,不刈割、留茬60和20 mm 3个处理间的草地生产力均差异极显著;留茬60和20 mm刈割使单播草地的平均生产力分别降低19%和36%,使混播草地的平均生产力分别降低4%和18%。研究表明,刈割显著降低了人工草地的初级生产力,同时显著增加了垂穗披碱草单播草地的物种丰富度和杂草生物量以及3种牧草混播草地物种丰富度,其他播种草地的物种丰富度和杂草生物量与不刈割草地均无显著差异。     

刈割制度对呼伦贝尔草原群落特征及牧草质量的影响

为确定呼伦贝尔草原高效生产和可持续利用的最佳刈割制度,于2019—2021年在呼伦贝尔草原开展刈割时间(7月31日、8月10日、8月20日、8月30日、9月9日)、留茬高度(3、9、15 cm)及两者交互作用对草原群落特征、牧草产量和品质影响的研究。结果表明: 较晚时间刈割和低留茬刈割会降低翌年群落高度和盖度;低留茬刈割降低翌年地上部分生物量,但刈割时间对其影响不显著。禾草、莎草相对生物量随刈割时间的延迟表现出先增加后减少的趋势,杂类草则与之相反,而豆科植物无明显变化。低留茬刈割在当年能够获得高的干草产量,但翌年的干草产量显著下降;8月30日,留茬3 cm刈割时干草产量达到最高值(469 g·m^-2),高于最低值361.5%。牧草品质中粗蛋白含量在8月30日刈割时亦达到峰值,高于最低值约6.5%,且在高留茬刈割下含量更高;酸、中性洗涤纤维含量随刈割时间延迟逐渐升高,9月9日刈割高于7月31日8.0%、5.9%,并且随留茬高度增加而降低。呼伦贝尔草原刈割制度设置为留茬高度9 cm左右、8月20—30日刈割为最佳,但需更长期的刈割试验观测才能得到更可靠、更客观的结论。     

物种多样性和功能性状驱动高寒草原地上生物量对长期禁牧的响应

围封对草地生物多样性和初级生产力的影响是草地生态学研究的热点问题之一。基于2013—2021年在青藏高原东北部紫花针茅(Stipa purpurea)高寒草原围栏内外植物群落长期调查数据,从物种多样性、功能性状的角度解析了高寒草原地上生物量对长期围封的生态响应过程。结果表明：(1)围封处理对高寒草原物种多样性的负效应具有强烈的时间依赖性。围封处理显著提高地上生物量,但也显著降低了生物量稳定性和异步性,意味着高寒草原稳定的、可持续的生态系统服务功能被长期围封处理削弱。(2)植物功能性状对长期围封处理表现出差异性响应模式;与叶绿素性状相比,叶形态性状对长期围封处理表现出更强的敏感性。(3)物种多样性和功能性状与地上生物量之间均存在显著相关关系,并且物种多样性的影响被功能性状调控进而对地上生物量发挥间接效应,群落加权性状和功能分异度共同对草地生物量发挥直接的主导效应。研究结果证明了植物功能性状通过介导物种多样性与其共同驱动高寒草原地上生物量对长期围封的响应。因此,在未来草地管理过程中,同步研究植物物种和功能属性对于全面揭示生态系统的响应机制至关重要。     

刈割留茬高度对大针茅草原群落结构及稳定性的影响

2014—2018年8月在内蒙古锡林郭勒盟毛登牧场大针茅典型草原,以围封为对照,设置2、5和8 cm 3个刈割留茬高度,研究刈割留茬高度对群落结构及稳定性的影响。结果表明: 群落中共出现15科23属27种植物;优势种为大针茅、知母、羊草及糙隐子草,累计相对重要值为76.1%。多年生杂类草15种,一、二年生植物5种,多年生丛生禾草和灌木半灌木植物各有3种,多年生根茎禾草有1种。大针茅等处于群落上层;知母、羊草等植物处于群落中层;糙隐子草、刺穗藜、猪毛菜等植物处于群落底层。刈割造成大针茅及多年生丛生禾草相对重要值降低,使得糙隐子草、刺穗藜、猪毛菜及一、二年生植物相对重要值增加。留茬2 cm降低羊草相对重要值,而留茬5、8 cm使其增加;留茬5 cm增加知母相对重要值,而留茬2、8 cm使其降低;留茬8 cm降低杂类草相对重要值,而留茬2、5 cm使其增加。物种及功能群多样性年度间差异显著。总体上,刈割对物种丰富度无显著影响,对其物种多样性影响较小,但对功能群多样性存在一定影响。表明在刈割过程中,群落各功能群存在一定的补偿作用,使得群落保持相对稳定。刈割使群落稳定性增加,留茬5和8 cm时群落稳定性较大;留茬5 cm时群落变异性较大,而留茬8 cm时最小。留茬8 cm时群落稳定性高且变异性小,能促进群落长期稳定。     

刈割、施肥对高寒草甸物种多样性与生态系统功能关系的影响及群落稳定性机制

植物群落中不同“功能身份”物种的多样性与特定生态系统功能之间具有何种关系及其作用机制尚不明确。通过在高寒矮嵩草(Kobresia humilis)草甸为期5年的刈割(不刈割、留茬3 cm、留茬1 cm)、施肥(施肥、不施肥)和浇水(浇水、不浇水)控制实验, 研究了刈割与土壤资源获得性梯度上不同“功能身份”物种(群落中所有物种、响应物种、作用物种和共有物种)的多样性变化与群落地上净初级生产力和稳定性的关系以及稳定性机制。研究结果显示: 群落中响应物种、作用物种和共有物种数分别占全部物种数的36.6%、18.3%和64.8%, 物种多样性对生态系统功能具有不同的效应, 净初级生产力主要受响应物种和作用物种的多样性变化影响, 而稳定性则主要由共有物种的多样性变化决定; 群落稳定性的维持主要依赖于共有物种的多样性增加, 其作用机制是投资组合效应, 而超产效应和异步性效应对稳定性并无作用; 刈割和施肥对物种多样性、稳定性和净初级生产力具有相反的影响, 前者能增加物种多样性和稳定性, 并降低净初级生产力, 而后者的作用正相反。这与群落中全部物种的多样性变化受刈割影响较大, 而作用物种的多样性变化受资源获得性影响较大有关。上述结果表明高寒草甸生态系统地上净初级生产力主要由少数影响生产力的作用物种的多样性决定, 而稳定性则由大量共有物种的多样性所掌控。投资组合效应是物种多样性导致稳定性的机制。由于群落中不同物种的多样性效应具有分异性, 对于特定的生态系统功能而言, 物种的“功能身份”可能比物种多样性本身更重要, 不加区别地笼统定义物种多样性与生态系统功能的关系可能欠妥。     

刈割对克氏针茅草原群落优势与亚优势植物的影响

基于内蒙古中部克氏针茅草原长期刈割试验,分析了不同留茬高度下克氏针茅草原植物群落中5个优势及亚优势种地上生物量和群落稳定性的变化.结果表明：留茬高度在10 cm以上时对5种植物地上生物量的影响较小.留茬高度为10 cm适于冷蒿生长,而不利于克氏针茅的生长.糙隐子草在留茬高度为2 cm时表现最佳.黄囊苔草对群落的贡献在留茬高度为5 cm时最大,此时其生物量与刈割年限呈正相关.留茬高度为2和15 cm不利于星毛委陵菜生长.植株较高、竞争力强的多年生植物对干扰的耐受能力较强,刈割的留茬高度不低于10 cm时,有益于维持草原生态系统的稳定性.     

刈割对克氏针茅草原群落优势与亚优势植物的影响

基于内蒙古中部克氏针茅草原长期刈割试验,分析了不同留茬高度下克氏针茅草原植物群落中5个优势及亚优势种地上生物量和群落稳定性的变化.结果表明:留茬高度在10cm以上时对5种植物地上生物量的影响较小.留茬高度为10 cm适于冷蒿生长,而不利于克氏针茅的生长.糙隐子草在留茬高度为2 cm时表现最佳.黄囊苔草对群落的贡献在留茬高度为5 cm时最大,此时其生物量与刈割年限呈正相关.留茬高度为2和15 cm不利于星毛委陵菜生长.植株较高、竞争力强的多年生植物对干扰的耐受能力较强,刈割的留茬高度不低于10cm时,有益于维持草原生态系统的稳定性.     

羊草基因型数目对地下动物及微生物群落的影响

群落建群种的基因型多样性是否具有与物种多样性类似的生态功能已经成为种群生态学非常关注的问题,研究结果能够为种群或群落的保护和恢复提供理论指导。基于已构建并施加不同强度干扰(无刈割、留茬10 cm和留茬5 cm)的不同基因型组合(1-、3-、6-基因型)的羊草种群,本研究采集其地下部土壤研究羊草基因型数目及干扰对地下动物群落和微生物群落的影响。结果表明:(1)羊草基因型数目和干扰强度的交互作用对土壤动物的种类、数量的影响显著(P0.05)。(2)在留茬10 cm处理组中,土壤动物的数量与羊草种群基因型数目呈显著的正相关关系(P0.05),符合"资源化假说"。(3)在无刈割处理组中,羊草的基因型数目对根际土壤中微生物群落的组成和结构具有显著的影响(P0.05)。     

高寒矮嵩草草甸两种主要植物耐牧性的比较

通过野外控制实验,研究了刈割(留茬3 cm、留茬1 cm及不刈割)、施肥(施肥、不施肥)和浇水(浇水、不浇水)处理对高寒草甸矮嵩草(Kobresia humilis)和垂穗披碱草(Elymus nutans)补偿高度、株高相对生长率、比叶面积、叶片净光合速率和地上总生物量的影响.结果表明:2物种的株高和地上总生物量在刈割后均为低补偿响应,但其株高相对生长率显著提高,并均随年份而增加;垂穗披碱草比叶面积、叶片净光合速率和地上总生物量对刈割损伤更加敏感;尽管施肥能显著提高2物种上述各项指标,但在不同处理条件下矮嵩草的耐牧性指数均小于垂穗披碱草;浇水的作用不显著.说明2物种的耐牧性依赖于土壤养分资源获得性,矮嵩草的耐牧性强于垂穗披碱草.     

草地利用方式对草甸草原植被空间异质性的影响

研究不同利用方式下植物群落中物种的分布特征,有助于解释植物在不同利用方式干扰下的演替规律。本研究以内蒙古呼伦贝尔草甸草原为研究对象,通过野外调查,基于幂函数法则,探讨围封、放牧和刈割利用方式下草地植被物种分布状况和群落整体空间分布的变化。结果表明:在放牧和刈割利用及围封下,草甸草原植被物种分布规律符合幂函数法则;与围封相比,放牧增加了群落整体的空间分布异质性,而刈割则降低了这种变化,刈割和放牧草地物种异质性指数高于群落整体异质性指数的物种增多;物种出现频率发生变化,如对糙隐子草(Cleistogenes squarrosa)种群而言,围封地中糙隐子草的出现频率为0.010,刈割和放牧增加了糙隐子草的出现频率(0.151和0.521),刈割和放牧降低了狭叶青蒿(Artemisia dacunculus)的出现频率(0.132和0.028)。     

不同刈割频度对大针茅草原群落特征及土壤元素含量的影响

在草原生态系统中,土壤是植物生长发育最重要的基质,对植物群落动态有显著的影响。刈割是内蒙古典型草原区除放牧外最重要的利用方式。研究不同刈割频度对典型草原区群落特征和若干土壤性质的影响及土壤因子与群落特征的相关性,旨在得出对群落多样性最有利并最适宜生产利用的刈割频度。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原;在2009—2013年进行不同频度的刈割处理,共设置处理,一年两次刈割、一年一次刈割、两年一次(割一年休一年)刈割、围封,在2013年8月采集测定土壤养分的样品。刈割对群落多样性影响显著,割一年休一年Shannon-Wiener多样性指数、Pielou均匀度指数、丰富度指数均高于其他刈割处理(P0.05);不同频度刈割下,一年两次刈割处理下土壤20—30cm和30—40cm的有机质含量显著高于其他处理(P0.05);不同频度刈割处理下土壤中的速效磷和速效氮的含量没有显著差异;一年两次处理的土壤全氮含量显著高于其他处理(P0.05)。Shannon-Wiener多样性指数与有机质含量、全氮含量呈显著负相关;Pielou均匀度指数与土壤元素间无显著相关关系;Richness指数与有机质含量呈显著负相关,与全氮含量为极显著负相关关系。割一年休一年刈割处理下土壤元素含量呈现更好的状态,结合群落物种多样性及生产利用的角度,割一年休一年为最合理的刈割频度。     

Biodiversity, productivity and the temporal stability of productivity: patterns and processes

Theory predicts that the temporal stability of productivity, measured as the ratio of the mean to the standard deviation of community biomass, increases with species richness and evenness. We used experimental species mixtures of grassland plants to test this hypothesis and identified the mechanisms involved. Additionally, we tested whether biodiversity, productivity and temporal stability were similarly influenced by particular types of species interactions. We found that productivity was less variable among years in plots planted with more species. Temporal stability did not depend on whether the species were planted equally abundant (high evenness) or not (realistically low evenness). Greater richness increased temporal stability by increasing overyielding, asynchrony of species fluctuations and statistical averaging. Species interactions that favoured unproductive species increased both biodiversity and temporal stability. Species interactions that resulted in niche partitioning or facilitation increased both productivity and temporal stability. Thus, species interactions can promote biodiversity and ecosystem services.     

Differential roles of species richness versus species asynchrony in regulating community stability along a precipitation gradient

Plant community may provide products and services to humans. However, patterns and drivers of community stability along a precipitation gradient remain unclear. A regional‐scale transect survey was conducted over a 3‐year period from 2013 to 2015, along a precipitation gradient from 275 to 555 mm and spanning 440 km in length from west to east in a temperate semiarid grassland of northern China, a central part of the Eurasian steppe. Our study provided regional‐scale evidence that the community stability increased with increasing precipitation in the semiarid ecosystem. The patterns of community stability along a precipitation gradient were ascribed to community composition and community dynamics, such as species richness and species asynchrony, rather than the abiotic effect of precipitation. Species richness regulated the temporal mean (μ) of aboveground net primary productivity (ANPP), while species asynchrony regulated the temporal standard deviation (σ) of ANPP, which in turn contributed to community stability. Our findings highlight the crucial role of community composition and community dynamics in regulating community stability under climate change.     

Diversity-dependent stability under mowing and nutrient addition: evidence from a 7-year grassland experiment

Anthropogenic perturbations may affect biodiversity and ecological stability as well as their relationships. However, diversity-stability patterns and associated mechanisms under human disturbances have rarely been explored. We conducted a 7-year field experiment examining the effects of mowing and nutrient addition on the diversity and temporal stability of herbaceous plant communities in a temperate steppe in northern China. Mowing increased population and community stability, whereas nutrient addition had the opposite effects. Stability exhibited positive relationships with species richness at population, functional group and community levels. Treatments did not alter these positive diversity-stability relationships, which were associated with the stabilising effect of species richness on component populations, species asynchrony and portfolio effects. Despite the difficulty of pinpointing causal mechanisms of diversity-stability patterns observed in nature, our results suggest that diversity may still be a useful predictor of the stability of ecosystems confronted with anthropogenic disturbances.     

科尔沁沙地封育恢复过程中植物群落特征变化及影响因素

封育是退化沙地植被恢复与生态重建的重要措施, 理解长期处于封育状态下不同类型沙地植物群落特征变化及其影响因素有利于沙地植被恢复和生态重建。该文基于对科尔沁沙地长期封育的流动沙丘(2005年封育)、固定沙丘(1985年封育)和沙质草地(1997年封育)连续多年(2005-2017年)的植物群落调查, 结合土壤种子库、土壤养分以及气象数据, 分析了植物群落特征变化及其对环境变化的响应。研究结果表明流动沙丘植被盖度显著增加, 群落生物量和物种多样性年际间波动变化, 但无明显趋势; 固定沙丘植物群落存在逆行演替趋势, 具体表现为群落生物量、灌木和半灌木以及豆科优势度显著下降, 而一年生和多年生杂类草优势度显著增加; 沙质草地群落物种丰富度和多年生禾草优势度存在降低趋势, 并且一年生杂类草优势度明显高于其他功能群, 群落存在退化现象。3类沙地土壤种子密度变化不显著, 而种子丰富度在流动沙丘显著增加, 在固定沙丘和沙质草地有下降趋势, 土壤养分仅有有效氮和有效磷含量增加。回归分析结果表明气温和降水是影响年内生物量积累的主要因素, 但对年际间群落生物量和物种丰富度变化影响不大。除趋势对应分析结果显示土壤种子库与植物群落之间存在很高的相似性, 典型相关分析结果表明沙质草地植物群落与土壤养分紧密相关, 而固定沙丘群落主要与土壤水分紧密相关。综合以上结果可知, 封育33年的固定沙丘群落和封育21年的沙质草地群落都存在退化现象, 而封育11年的流动沙丘群落正在缓慢恢复, 因此封育年限的设定对退化沙地植被恢复至关重要, 封育时间过长不仅不利于植物群落恢复, 反而会使群落发生逆行演替, 建议封育年限的设定应综合考虑植被退化程度、土壤养分状况、土壤种子库基础以及气候条件等因素的影响。     

Grazing weakens temporal stabilizing effects of diversity in the Eurasian steppe

Many biodiversity experiments have demonstrated that plant diversity can stabilize productivity in experimental grasslands. However, less is known about how diversity–stability relationships are mediated by grazing. Grazing is known for causing species losses, but its effects on plant functional groups (PFGs) composition and species asynchrony, which are closely correlated with ecosystem stability, remain unclear. We conducted a six‐year grazing experiment in a semi‐arid steppe, using seven levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep per hectare) and two grazing systems (i.e., a traditional, continuous grazing system during the growing period (TGS), and a mixed one rotating grazing and mowing annually (MGS)), to examine the effects of grazing system and grazing intensity on the abundance and composition of PFGs and diversity–stability relationships. Ecosystem stability was similar between mixed and continuous grazing treatments. However, within the two grazing systems, stability was maintained through different pathways, that is, along with grazing intensity, persistence biomass variations in MGS, and compensatory interactions of PFGs in their biomass variations in TGS. Ecosystem temporal stability was not decreased by species loss but rather remain unchanged by the strong compensatory effects between PFGs, or a higher grazing‐induced decrease in species asynchrony at higher diversity, and a higher grazing‐induced increase in the temporal variation of productivity in diverse communities. Ecosystem stability of aboveground net primary production was not related to species richness in both grazing systems. High grazing intensity weakened the temporal stabilizing effects of diversity in this semi‐arid grassland. Our results demonstrate that the productivity of dominant PFGs is more important than species richness for maximizing stability in this system. This study distinguishes grazing intensity and grazing system from diversity effects on the temporal stability, highlighting the need to better understand how grazing regulates ecosystem stability, plant diversity, and their synergic relationships.     

Plant community assembly in suburban vacant lots depends on earthmoving legacy,habitat connectivity,and current mowing frequency

In suburban regions, vacant lots potentially offer significant opportunities for biodiversity conservation. Recently, in Japan, due to an economic recession, some previously developed lands have become vacant. Little is known, however, about the legacy of earlier earthmoving, which involves topsoil removal and ground leveling before residential construction, on plant community composition in such vacant lots. To understand (dis)assembly processes in vacant lots, we studied 24 grasslands in a suburban region in Japan: 12 grasslands that had experienced earthmoving and 12 that had not. We surveyed plant community composition and species richness, and clarified compositional turnover (replacement of species) and nestedness (nonrandom species loss) by distance‐based β‐diversities, which were summarized by PCoA analysis. We used piecewise structural equation modeling to examine the effects of soil properties, mowing frequency, past and present habitat connectivities on compositional changes. As a result, past earthmoving, mowing frequency, soil properties, and past habitat connectivity were found to be the drivers of compositional turnover. In particular, we found legacy effects of earthmoving: earthmoving promoted turnover from native grassland species to weeds in arable lands or roadside by altering soil properties. Mowing frequency also promoted the same turnover, implying that extensive rather than intensive mowing can modify the negative legacy effects and maintain grassland species. Decrease in present habitat connectivity marginally enhanced nonrandom loss of native grassland species (nestedness). Present habitat connectivity had a positive effect on species richness, highlighting the important roles of contemporary dispersal. Our study demonstrates that community assembly is a result of multiple processes differing in spatial and temporal scales. We suggest that extensive mowing at local scale, as well as giving a high conservation priority to grasslands with high habitat connectivity at regional scale, is the promising actions to maintain endangered native grassland species in suburban landscapes with negative legacy effects of earthmoving.     

长期围封和自由放牧对高寒草甸土壤微生物群落结构及碳源代谢多样性的影响

土壤微生物群落结构和代谢多样性对于维持草地生态系统的功能和稳定性具有重要意义.本研究运用磷脂脂肪酸法(PLFA法)和Biolog微平板技术,研究了青藏高原长期围封和自由放牧2种草地利用方式下的土壤微生物群落结构和群落碳代谢多样性的差异以及影响机制.结果表明: 1)长期围封和自由放牧草地上的土壤微生物群落结构和碳代谢多样性存在显著差异;2)长期围封显著增加了土壤中总PLFA、细菌、真菌和放线菌生物量;3)长期围封草地土壤微生物的碳代谢活性、多样性和丰富度高于自由放牧草地,而均匀度低于放牧草地;4)与自由放牧相比,长期围封显著增加了土壤微生物对聚合物类、糖类、羧酸类、胺类碳源的利用;5)冗余分析表明,植被盖度显著影响了微生物的群落结构和碳代谢多样性.长期围封草地的土壤微生物量、碳代谢多样性指数和丰富度均高于自由放牧土壤,表明长期围封有利于提高草地生态系统中土壤微生物群落及其对碳源代谢的多样性.