Collaborative Research: Rainfall variability and the axes of tree-grass niche differentiation

合作研究：降雨量变化和树草生态位分化的轴

• 批准号: 1928875
• 负责人: Jesse Nippert
• 金额: $ 24.07万
• 依托单位: Kansas State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1928875&HistoricalAwards=false
• 关键词: Collaborative; Research; Rainfall; variability; axes

The savanna biome, in which a discontinuous tree layer coexists with a continuous grass layer, has a worldwide distribution. Increasingly, research suggests that the relative proportion of tree and grass biomass in savannas is strongly influenced by rainfall patterns, with higher rainfall leading to greater woody biomass. Despite mounting evidence for rainfall effects, however, it is unclear if more rainfall leads to greater tree biomass in savannas because of deeper water infiltration, changes in rainfall intensity, or because the length of the growing season increases with the amount of annual rainfall. This question is important because we cannot accurately predict future changes to the savanna biome without a detailed understanding of how tree and grass species respond to rainfall patterns. This project will seek answers to this and other questions using a South African savanna as a model system. North American savannas have been largely replaced by forests, and the reasons for this are not fully understood. Results from this project can be used to inform the restoration and maintenance of savannas in North America and elsewhere, as well as to predict with broad generality how the savanna biome might change in the future. The project will also introduce undergraduate students to the ecology of savannas through a multi-year field course and educate local communities about the role of rainfall variability on natural resource availability.The project will combine experimental, observational and modeling approaches to test alternative hypotheses about the relationship between rainfall and tree to grass ratios in savannas. The research has three specific aims: (1) identify the rainfall regimes that favor trees over grasses, (2) identify the functional traits and tradeoffs that differentiate savanna trees and grasses, and (3) develop and test a mechanistic model of tree and grass dynamics as a function of rainfall. The core element of the study will be a field experiment that will manipulate the timing, seasonality and depth distribution of rainfall, and monitor the response of a multi-species assemblage of known-age trees embedded in a grass matrix. In addition, the project will examine functional differences (e.g., drought tolerance, water use efficiency and functional rooting depth) between six tree and six grass species using greenhouse, growth chamber and field experiments. Finally, the project will use parameter estimates from this second component to develop and test a mechanistic model of tree growth and tree to grass ratios based on whole-plant traits, and validate the model under field conditions by comparing modeled and observed changes in tree to grass ratios to rainfall manipulations in the field experiment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

稀树草原生物群分布在世界各地，其中不连续的乔木层和连续的草层共存。越来越多的研究表明，稀树草原树木和草的生物量的相对比例受到降雨模式的强烈影响，降雨量越大，木本植物生物量越大。然而，尽管降雨影响的证据越来越多，但尚不清楚更多的降雨是否会因为更深的水分渗透、降雨强度的变化或生长季的长度随着年降雨量的增加而导致稀树草原上更大的树木生物量。这个问题很重要，因为如果不详细了解树木和草物种对降雨模式的反应，我们就无法准确预测稀树草原生物群未来的变化。该项目将以南非稀树大草原为模型系统，寻求这一问题和其他问题的答案。北美大草原在很大程度上已被森林取代，其原因尚不完全清楚。该项目的结果可用于为北美和其他地区稀树草原的恢复和维护提供信息，以及广泛地预测稀树草原生物群未来可能发生的变化。该项目还将通过为期多年的野外课程向本科生介绍稀树草原的生态学，并教育当地社区了解降雨变化对自然资源可用性的作用。该项目将结合实验、观测和建模方法来测试关于稀树草原降雨量和乔草比之间关系的替代假设。这项研究有三个具体目标：(1)确定有利于树木而不是草的降雨状况；(2)确定区分稀树草原树和草的功能特征和权衡；(3)开发和测试树木和草动态随降雨变化的机制模型。这项研究的核心内容将是一项田间实验，该实验将操纵降雨的时间、季节性和深度分布，并监测镶嵌在草基质中的多物种已知树龄组合的反应。此外，该项目将使用温室、生长箱和田间实验来研究六种树木和六种草的功能差异(例如，耐旱性、水分利用效率和功能生根深度)。最后，该项目将使用来自第二部分的参数估计来开发和测试基于全植物特征的树木生长和林草比的机制模型，并在田间条件下通过比较建模和观察到的林草比的变化与田间试验中的降雨操纵来验证该模型。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。