LTREB: Community reordering alters ecosystem processes in desert grassland

全球环境变化可以通过逐渐改变不同植物物种的存在和丰度，对生态系统造成大规模的破坏。许多生态系统以少数优势植物为特征，但不清楚这些物种是否会随着环境条件的变化而保持优势。优势物种的丧失可能产生巨大的影响，对生态系统的整体结构和功能产生潜在的级联效应。新墨西哥州塞维莱塔国家野生动物保护区正在进行的工作表明，一种常见的沙漠草正在逐渐取代广泛分布的大平原草。为了了解降雨量、降雨时间和变率的变化如何影响优势禾本科植物物种重排序的速率、数量和方向，本项目将物种重排序的影响与碳循环和净初级产量联系起来。实验将改变水、温度和氮的可用性，以测试草原如何应对这些环境变化。旱地生态系统占全球陆地面积的约45%，对全球碳收支具有可测量的影响。由于干旱、空气污染和降雨变异性的增加，旱地正在迅速发生变化。群落重新排序可能是促进对影响美国西南部和其他地区旱地生态系统的不同全球变化因素的理解的关键。在美国大陆，草原覆盖了2.4亿公顷（占陆地面积的33%），为牲畜、野生动物栖息地、水资源、娱乐和碳储存提供了宝贵的资源。三个实验将测试环境变化如何改变两个重要草原的存在、成功和连续性，一个由奇瓦瓦沙漠草（黑色格拉玛）主导，另一个由大平原草（蓝色格拉玛）主导。两者都是重要的牧草，对全球变化的反应不同。其中一项实验将改变干旱的严重程度和降雨的季节性，而另一项实验将在位于蓝色和黑色图共同出现的过渡带的地块上操纵变暖、氮肥和冬季（厄尔尼诺）降雨。第三个实验改变了黑格拉玛草原夏季降雨事件的大小和频率，该草原最有可能经历本地灌木的入侵（物种之间的另一种重新排序）。为了提高对这些物种群落重排序的原因和后果的理解，测量重要的碳过程（根系生产和土壤呼吸）以及添加种子和生物土壤结皮将直接测试植物和微生物群落重排序对生态系统功能的相互作用。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。

Global environmental change can cause large-scale disruptions to ecosystems by gradually shifting both the presence and abundance of different plant species. Many ecosytems are characterized by a few dominant plants, but it is unclear if these species will remain dominants as environmental conditions change. The loss of dominant species may have a large impact, creating a potential cascade of effects on the overall structure and function of the ecosystem. Ongoing work at the Sevilleta National Wildlife Refuge in New Mexico indicates that a common desert grass is gradually replacing a widespread Great Plains grass. To understand how changes in rainfall amount, timing and variability affect the rate, amount and direction of reordering among the dominant grass species, this project will link the effects of species reordering to carbon cycling and net primary production. Experiments will alter water, temperature and nitrogen availability to test how grasslands respond to these environmental changes. Dryland ecosystems, which cover ~45% of global continental land area, have measurable impacts on the global carbon budget. Drylands are changing rapidly in response to droughts, air pollution, and increased rainfall variability. Community reordering may be key to advancing the understanding of different global change factors affecting dryland ecosystems in the southwestern United States and elsewhere. Grasslands cover 240 million ha (33% of land area) in the continental US, providing valuable resources for livestock, wildlife habitat, water resources, recreation, and carbon storage. Three experiments will test how environmental change alters the presence, success and contiuity of 2 important grasslands, one dominated by the Chihuahuan Desert grass, black grama, and the other by Great Plains grass, blue grama. Both are important forage grasses that respond differently to global change. One experiment will alter the severity of drought and seasonality of rainfall, while a second experiment manipulates warming, nitrogen fertilization and winter (El Nino) rainfall on plots located in the ecotone where blue and black grama co-occur. The third experiment alters the size and frequency of summer rain events in black grama grassland, which is most likely to experience future invasion by native shrubs (another kind of reordering among species). To improve understanding of the causes and consequences of community reordering among these species, measurements of important carbon processes (root production and soil respiration) along with additions of seeds and biological soil crusts will directly test for interactive effects of plant and microbe community reordering on ecosystem function.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.