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草原生态系统是我国最大的陆地生态系统,具有调节气候、涵养水源、碳固存、生物多样性保育等不可替代的服务功能[1]。我国草原面积占陆地总面积的42%,是重要的畜牧业生产基地和绿色生态屏障,在保障国家生态安全、粮食安全乃至全球生态平衡中发挥重要作用[1]。尽管气候预测模型结果存在较大的不确定性,但联合国政府间气候变化专门委员会(IPCC)第六次气候科学报告《气候变化2021:自然科学基础》明确指出,在全球气候变暖的背景下,干旱、半干旱地区极端干旱事件发生的频率、强度和持续时间将会显著增加[2],对草甸草地生态系统的结构、功能产生了深远影响。尽管极端干旱事件持续时间较短,但其对植物群落和生态系统的影响可能会超越多年持续性普通干旱的影响[3,4]。因此,21世纪以来,极端干旱如何影响草甸草地生态系统以及草地生态系统如何响应极端干旱成为生态学家和植物学家的关注焦点。
极端干旱事件后,土壤水分与养分等关键资源极度下降,物种间竞争增强,植物迅速占据并利用资源[4, 5]。在长期的进化过程中,草原植物对干旱和半干旱的水分资源波动进化出了各自的适应策略,能够通过改变自身的形态和生理机能提高水分利用效率,适应不同的水分状况,提高自身的竞争能力与生态适应性[6]。在面临极端干旱干扰时,不同物种将采取不同适应策略来应对极端干旱事件[7]。有些物种选择将更多的资源分配到地上部分用于防御环境胁迫(逃避策略),而有些物种将更多的资源贮存于根部用于干旱过后的再生长(忍耐策略)。在干旱发生后,由于忍耐策略物种的超强再生恢复力,逐渐排挤逃避策略的物种,从而成为群落的优势种[8]。
植物功能性状组成是与植物获取和利用资源能力息息相关的属性或特征,最大限度地反映植物对环境变化的适应性信息[9]。因此,群落功能多样性在一定程度上反映物种在资源利用上的生态位互补,可用于探索植物群落应对极端干旱事件的潜在生态学机制[10]。群落功能性状组成的变化由物种内和物种间性状变异共同组成,前者表示种群内个体间性状的差别,后者表示物种间性状的差别[5]。理论上认为,群落水平上多维性状结构组成越复杂,植被在多维生态空间中的配置越多元化,资源配置与利用越合理充分,则植物群落结构和功能的稳定性就越强,反之亦然[11]。因此,基于功能性状的视角,探讨干旱事件对草甸草原生态系统结构和功能的影响不仅可以丰富植被生态适应机理的理论研究,而且对于草甸草原应对干旱事件,开展草地保护与合理利用具有重要的指导意义。
本研究以内蒙古草甸草原植物群落为研究对象,通过控制生长季降雨的干旱模拟实验,旨在探究植物群落性状对干旱胁迫的响应及其对生态系统功能的影响,为预测气候变化下草原生态系统结构和功能提供科学依据。
Responses of Plant Community Traits to Extreme Drought in a Meadow Grassland, Inner Mongolia
doi: 10.12172/202111170002
- Received Date: 2021-11-17
- Available Online: 2022-06-27
- Publish Date: 2022-08-23
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Key words:
- Extreme drought /
- Plant traits /
- Trait diversity /
- Dominant species /
- Adaptive strategy
Abstract: Human activities exert a significant impact on the global atmospheric circulation pattern, resulting in the increasing amplitude, frequency and duration of extreme drought events, which have more negative impacts on grassland ecosystem. In this study, we conducted a four-year extreme drought experiment to investigate the responses of plant community traits to extreme drought as well their consequences on ecosystem functions in a meadow grassland, Inner Mongolia. The results showed that experimental extreme drought exerted no significant effect on plant community traits, which indicated that plant are insensitive to extreme drought and plant community adopted tolerance/conservative strategy under water stress conditions. The relationships between plant community trait diversity and aboveground net primary productivity were not observed under extreme drought conditions, which was inconsistent with the diversity hypothesis. On the other hand, aboveground net primary productivity was mediated by the community-weighted trait means under extreme drought conditions. Specifically, aboveground net primary productivity was positively correlated with community-weighted plant height and negatively correlated with community-weighted leaf carbon concentrations. These results highlighted the great effects of dominated species on ecosystem functions, being in line with mass ratio hypothesis. Overall, these results are of great significance for revealing the processes and mechanisms underlying the functional responses of grassland communities to extreme drought, providing a scientific basis for vegetation protection and management in grassland ecosystem.