Climatic Variability and Ecosystem Response: Precipitation Patterns, Soil Moisture Dynamics, and Productivity in Tallgrass Prairie

气候变化是草原生态系统结构和功能的关键驱动力，气候模型表明，由于全球气候变化，降雨量，温度和其他气候参数的变化将增加。然而，未来降雨模式存在不确定性，一些模型预测生长季节降雨量和土壤湿度增加，另一些则减少。降雨量或频率的任何变化都会改变降雨的变异性，并且有几条证据表明，在调节高草草原净初级生产力方面，变异性可能与降雨总量一样重要。事实上，增加降雨量的变化，即使降雨量没有变化，有能力降低植物的性能和生产力，并可能导致高草草原群落组成的变化，因为不可避免的生理和形态的限制，植物的能力，以跟踪和调整不同的资源。本提案中所述研究的目的是以高草草原为模型系统，通过实验确定降雨模式变化对地上和地下草地生产力的影响。我们将施加减少和增加的降雨输入的变化，包含共同的高草草原草和杂类草的微观世界，在16个不同的数量和频率组合的实验浇水。测量将侧重于土壤水分动态，光合性能，冠层发育，根系生长动态，植物繁殖，地上和地下净初级生产力。本实验测试的首要假设是，变异性是高草草原生产力的关键驱动因素，实验将研究几个具体的假设降雨量和频率之间的关系，在草和杂类草生产力。这些知识将拓宽我们对草地生产力调节的理解，并将对生产力/多样性关系、火灾/食草动物相互作用、陆地碳动力学、大气/植被反馈以及全球变化情景中气候要素（降雨、温度和CO2升高）之间的相互作用等研究产生影响。准确了解这些问题对于预测气候变化对草原的影响以及为这些濒危系统制定积极的保护和管理计划至关重要。

Climatic variability is a key driver of ecosystem structure and function in grasslands, and climate models suggest that variability in rainfall, temperature, and other climatic parameters will increase because of global climate change. However, there is uncertainty about future rainfall patterns, with some models predicting increased, others decreased growing season rainfall and soil moisture. Any shifts in rainfall quantity or frequency will change rainfall variability, and several lines of evidence suggest that variability may as important as the total quantity of rainfall in regulating tallgrass prairie net primary productivity. Indeed, increases in rainfall variability, even with no change in rainfall quantity, have the capacity to reduce plant performance and productivity and may cause shifts in tallgrass prairie community composition, because of unavoidable physiological and morphological limitations on plant abilities to track and adjust to varying resources. The objective of the research described in this proposal is to experimentally determine the impact of variability in rainfall patterns on above- and belowground grassland productivity, using tallgrass prairie as a model system. We will impose decreases and increases in variability in rainfall inputs on microcosms containing common tallgrass prairie grasses and forbs, by experimental watering at sixteen different quantity and frequency combinations. Measurements will focus on soil moisture dynamics, photosynthetic performance, canopy development, root growth dynamics, plant reproduction, and above and belowground net primary productivity. The overarching hypothesis tested by this experiment is that variability is a key driver of tallgrass prairie productivity, and the experiment will examine several specific hypotheses about the relationships between rainfall quantity and frequency and productivity in grasses and forbs. This knowledge will broaden our understanding of the regulation of grassland productivity, and will have implications for research on productivity/diversity relationships, fire/grazer interactions, terrestrial carbon dynamics, atmosphere/vegetation feedbacks, and interactions among climatic elements in global change scenarios (rainfall, temperature, and elevated CO2). An accurate understanding of these issues is crucial to predicting climate change impacts on grasslands and developing proactive conservation and management plans for these endangered systems.