LTREB Renewal: Long-term ecosystem responses to directional changes in precipitation amount and variability in an arid grassland

降雨在旱地环境中起着重要作用。气候正在迅速而显著地变化。预计气候将更加干燥和多变，这可能会影响旱地环境。预测新气候对生态系统功能的影响是生态学最紧迫的目标。了解生态系统在这些新条件下的运作方式，对于制定产生最佳社会结果的管理策略是必要的。旱地非常重要，因为它们覆盖了地球表面的40%，提供了宝贵的商品和服务。这些商品和服务的范围从饲料生产到娱乐。该项目将继续进行两项独特的长期实验，研究人员分别在新墨西哥州的沙漠草原上进行了16年的降雨量和变化。这个项目前5年的结果产生了意想不到的结果。干旱对植物物种组成的间接影响抵消了干旱的直接影响。项目的继续将决定这些不同的反应是如何发生的。更广泛的影响包括直接促进代表性不足群体的参与。该项目将与Asombro科学教育研究所合作，在占地960英亩的奇瓦瓦沙漠自然公园建立一个新的示范项目。Asombro是一家非营利组织，每年为新墨西哥州南部和德克萨斯州西部的22,000多名儿童和4,500多名成年人提供获奖的科学教育。这一建议以旱地对降水量和变率变化的响应的两个假设为指导。(1)内源性机制：生物地球化学和人口现象介导种群、群落和生态系统过程的突变或连续变化。(2)外源现象：El Niño事件与低频太平洋年代际涛动（PDO）和大西洋多年代际涛动（AMO）相互作用。这些气候事件与内部机制相互作用。它们共同影响系统的抵抗力，并导致物种组成和生态系统过程的变化。16年后，生态系统似乎处于土壤有机氮形态的十字路口。这种情况可能导致新的氮水限制。该项目将继续进行两个独特的长期降水控制实验，分别对新墨西哥州沙漠草原的降水量和变化进行了16年的控制。降雨量的长期控制是利用雨棚和灌溉系统来完成的。该项目将直接有助于增加代表性不足的少数民族的参与，重点是西班牙裔学生。该项目将与Asombro科学教育研究所合作，在占地960英亩的奇瓦瓦沙漠自然公园建立一个新的示范项目。Asombro是一家非营利组织，每年为新墨西哥州南部和德克萨斯州西部的22,000多名儿童和4,500多名成年人提供获奖的科学教育。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rainfall plays an important role in dryland environments. Climate is changing fast and significantly. A drier and more variable climate is expected, which could affect dryland environments. Predicting the effects of a new climate on the functioning of ecosystems is the most pressing objective of ecology. Understanding, the way ecosystems will function under these novel conditions is necessary to develop management strategies that generate optimal societal outcomes. Drylands are very important because they cover 40% of the terrestrial surface and provide invaluable goods and services. These goods and services range from forage production to recreation. This project will continue two unique long-term experiments, where researchers separately manipulated rain amount and variability in a desert grassland in New Mexico for 16 years. Results from the first 5 years of this project yielded unexpected results. Drought had indirect effects on the composition of plant species that offset the direct effects of drought. The continuation of the project will determine how these different responses occurred. Broader impacts include directly contributing to increasing participation of underrepresented groups. This project will collaborate with Asombro Institute for Science Education by building a new demonstration project at the 960-acre Chihuahuan Desert Nature Park. Asombro is a non-profit organization that provides award-winning science education to more than 22,000 children and 4,500 adults annually in southern New Mexico and western Texas.This proposal is guided by two hypotheses about dryland responses to changes in amount and variability of precipitation. (1) Endogenous Mechanisms: Biogeochemical and demographic phenomena mediate abrupt or continuous changes in populations, communities and ecosystem processes. (2) Exogenous Phenomena: El Niño events at 3-4-year periods interact with changes in low-frequency Pacific Decadal Oscillation (PDO) and Atlantic Multi-Decadal Oscillation (AMO). These climate events interact with internal mechanisms. Jointly, they affect system resistance, and lead to changes in species composition and ecosystem processes. After 16 years, the ecosystem seems to be at crossroads regarding soil organic nitrogen forms. This condition may result in a new N-water limitation. The project will continue two unique long-term precipitation-manipulation experiments that separately manipulated precipitation amount and variability in a desert grassland in New Mexico for 16 years. The long-term manipulations of precipitation amount are accomplished using rainout shelters coupled with irrigation systems. This project will directly contribute to increasing participation of underrepresented minorities with emphasis on Hispanic students. This project will collaborate with Asombro Institute for Science Education by building a new demonstration project at the 960-acre Chihuahuan Desert Nature Park. Asombro is a non-profit organization that provides award-winning science education to more than 22,000 children and 4,500 adults annually in southern New Mexico and western Texas.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.