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首页> 外文学位 >Drivers of grassland community structure and ecosystem function: The role of biotic factors in determining the ecosystem response to alterations in resource availability.
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Drivers of grassland community structure and ecosystem function: The role of biotic factors in determining the ecosystem response to alterations in resource availability.

机译：草地群落结构和生态系统功能的驱动因素：生物因素在决定生态系统对资源可利用性变化的反应中的作用。

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摘要

Biotic factors, such as plant community composition, trait expression, and trophic interactions, mediate the response of ecosystem functions to alterations in abiotic factors. Here I examine the role of these biotic factors in determining the response of aboveground net primary productivity (ANPP), an ecologically and economically important ecosystem function, to alterations in precipitation, nutrient availability, and space/light at three sites spanning the broad productivity gradient of the U.S. Central Great Plains.;I first show how changes in the plant community with alterations in nutrient availability and seasonal precipitation affect ANPP. I show that across the precipitation gradient of the Great Plains, the abundance of a dominant species, Schizachyrium scoparium, and plant species richness drive the majority of the variation in ANPP. On evolutionary timescales, species abundances and plant species richness are thought to be driven by long-term climate conditions across this precipitation gradient. These communities must then respond to shifts in environmental conditions, such as precipitation and nutrient availability, on ecological timescales. As a result, differences in plant species abundances and richness best predict variation in ANPP by incorporating both the indirect effects of precipitation variability in structuring the plant community as well as the direct effects of specific characteristics of the biota, such as maximum growth rates, height, and/or water use efficiency, that determine ANPP (i.e., height of short grass species will always be less than that of tall grasses, irrespective of precipitation amount). By combining information regarding both the evolutionary history and current physiological responses of species, metrics describing differences in the plant community confer greater power to predict ANPP over abiotic factors alone. In the same vein, I show that the physiological response of the dominant species drove the majority of the production response to experimental nutrient additions across the precipitation gradient, supporting the idea that understanding species abundances and physiological responses to altered environmental conditions is key to predicting ANPP.;I expand upon the effect of resource availability on ANPP through changes in plant trait expression and community composition by determining the response of plant functional traits to chronic alterations in nutrient availability. Across the precipitation gradient studied here, plant species that increase in abundance with chronic nutrient additions had functional trait values associated with faster growth and exhibited more plasticity in their trait expression when exposed to elevated nutrient conditions than plant species that dominate under ambient environmental conditions. This difference in trait expression may underlie the community changes driven by chronic nutrient additions. However, I found that variation in trait expression at the species-level was not enough to drive changes in community aggregate trait expression; rather, species turnover was necessary before changes in trait expression were observed at the community level.;Finally, I examine the role of trophic interactions in determining the ANPP response to alterations in resource availability. I show that vertebrate herbivores tend to promote the growth of forb species, while invertebrate herbivores tend to suppress their growth. In systems where the plant canopy is closed, these effects of vertebrate and invertebrate herbivores on grass:forb ratios interacted with the effects of nutrient availability, resulting in the promotion of grasses with the combined addition of nutrients and removal of vertebrate herbivores and the promotion of forbs with the combined addition of nutrients and the removal of invertebrate herbivores. In contrast, in systems where the plant canopy is open, nutrient additions promote the growth of forbs regardless of herbivore presence.;Invertebrate herbivores not only interact with nutrient additions to affect the plant community, but also are affected by shifts in plant quantity and quality. I show that nutrient additions indirectly increased invertebrate herbivore abundances by increasing plant quantity at the mesic end of the grassland precipitation gradient studied here. However, the increase in plant quality with chronic nitrogen additions resulted in a decrease in the per capita rate of herbivory (selective feeding). The changes observed in invertebrate abundances and feeding behavior with nutrient additions at the mesic end of the precipitation gradient did not have consequences for ANPP due to the trade-off between an increase in abundance of invertebrate herbivores with a decrease in their per capita rate of herbivory resulted in no change in the amount of leaf tissue removed. In contrast, at the xeric end of the precipitation gradient, where leaf tissue C:N is lower relative to the other sites studied, nitrogen and phosphorus additions led to compensatory feeding by chewing herbivores, perhaps because herbivores are limited by another resource, such as carbohydrates, at this site.;Humans are currently having a large impact on abiotic factors worldwide, which can have important consequences for ecosystem function. Here, I show how plant species composition, trait expression, and trophic interactions act to determine the effect of alterations in resource availability in grasslands. The results of my dissertation constitute an important step toward improving our ability to predict how global change will impact grassland ecosystem function in the future.
机译：生物因子，例如植物群落组成，性状表达和营养相互作用，介导了生态系统功能对非生物因子改变的响应。在这里，我研究了这些生物因子在确定地域净初级生产力（ANPP）（生态和经济上重要的生态系统功能）对跨越广泛生产力梯度的三个地点的降水，养分利用率和空间/光照变化的响应中的作用。我首先展示了植物群落的变化以及养分利用率和季节性降水的变化如何影响ANPP。我表明，在大平原的降水梯度上，优势种（Schizachyrium scoparium）和植物物种的丰富度驱动着ANPP的大部分变化。在进化的时间尺度上，物种丰富度和植物物种丰富度被认为是由该降水梯度上的长期气候条件驱动的。然后，这些社区必须在生态时间尺度上应对环境条件的变化，例如降水和养分的获取。结果，通过结合降水变化对植物群落结构的间接影响以及生物群特定特征（如最大生长速率，高度）的直接影响，植物物种丰度和丰富度的差异可以最好地预测ANPP的变化。和/或用水效率，这决定了ANPP（即，短草种的高度始终小于高草的高度，而与降水量无关）。通过结合有关物种的进化历史和当前生理反应的信息，描述植物群落差异的指标赋予了预测仅基于非生物因子的ANPP的更大能力。同样，我证明了优势物种的生理反应在整个降水梯度上推动了对实验性营养物添加的大部分生产反应，支持了这样的观点，即了解物种的丰度和对变化的环境条件的生理反应是预测ANPP的关键通过确定植物功能性状对养分有效性的长期变化的响应，我通过改变植物性状表达和群落组成来扩展资源可利用性对ANPP的影响。在这里研究的降水梯度范围内，与长期环境条件下占主导地位的植物相比，随着长期添加营养物而大量增加的植物物种具有与更快生长相关的功能性状值，并且在暴露于升高的营养素条件下其性状表现出更多的可塑性。性状表达的这种差异可能是由长期添加营养物驱动的群落变化的基础。但是，我发现物种水平上性状表达的变化不足以驱动社区聚集性状表达的变化。相反，在社区一级观察到性状表达变化之前，必须进行物种更新。；最后，我研究了营养相互作用在确定ANPP对资源可利用性变化的反应中的作用。我发现脊椎动物食草动物倾向于促进福布斯物种的生长，而无脊椎动物食草动物倾向于抑制其生长。在植物冠层封闭的系统中，脊椎动物和无脊椎动物草食动物对草：草比率的这些作用与养分利用率的相互作用，从而促进了草的生长，同时增加了养分并去除了脊椎动物的草食动物并促进了草食动物的生长。结合营养物和无脊椎动物的食草动物的去除。相比之下，在开放性植物冠层的系统中，无论草食动物的存在如何，营养物的添加都会促进单穗的生长。无脊椎动物的草食动物不仅会与营养物的添加发生相互作用，从而影响植物群落，而且还会受到植物数量和质量变化的影响。 。我表明，在这里研究的草地降水梯度的中端，通过增加植物数量，营养物的添加间接增加了无脊椎动物的草食动物的丰度。但是，随着长期添加氮肥而提高的植物品质导致人均草食率（选择性饲喂）下降。由于在无脊椎动物食草动物的丰度增加与人均食草率的降低之间进行了权衡，在降水梯度的中端观察到的无脊椎动物丰度和营养添加行为的变化对ANPP没有影响。导致叶片组织去除量没有变化。相反，在降水梯度的干燥端，叶片组织C：N相对于其他研究部位较低，氮和磷的添加通过咀嚼食草动物而导致补给性进食，这可能是因为该地点的食草动物受到另一种资源（例如碳水化合物）的限制。；人类目前对全世界的非生物因子产生重大影响，这可能对生态系统产生重要影响功能。在这里，我展示了植物物种组成，性状表达和营养相互作用如何决定草原资源利用变化的影响。本文的结果是提高我们预测全球变化将如何影响未来草地生态系统功能的重要一步。

著录项

  • 作者

    La Pierre, Kimberly Joy.;

  • 作者单位

    Yale University.;

  • 授予单位 Yale University.;
  • 学科 Biology Ecology.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 226 p.
  • 总页数 226
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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