Collaborative Proposal: Aeolian Processes: An Overlooked Driver of State Change in Drylands?

草原转变为灌木稀少的沙漠，或荒漠化，正在世界各地发生。在许多情况下，荒漠化用牲畜和野生动物难以消化的灌木取代了它们喜欢吃的植物。因此，这一问题威胁到农民和牧场主的生计，同时也危及野生动物的栖息地。尽管荒漠化现象普遍存在，但很难查明其确切原因。许多科学家认为，当食草动物选择吃草而不是灌木时，灌木就会取而代之。然而，荒漠化往往发生在没有牲畜的地区，因此荒漠化可能有多种原因。这项研究旨在发现降雨量低的地区（往往是沙质）的荒漠化是否是由于风吹沙（喷砂）。风沙可以做两件事，可能会导致荒漠化：1）侵蚀土壤，降低其肥力和2）破坏草植物。因为草需要更肥沃的土壤，而且比灌木更脆弱，所以灌木可能在风力更大、土壤肥力更低的地方占据优势。通过这项研究，本科生和博士后研究人员将被培养。本研究将对K-12教师和学生进行外展，并将包括来自代表性不足群体的个人。本研究测试了以下假设：1）叶片特性决定喷砂对植物调节水分流失和碳吸收能力的影响，并在夜间和休眠期保持不透水的屏障以防止水分流失;（2）生长形态，特别是株高和生长点的暴露，决定了对风沙的脆弱性：（3）草和灌木对水分和氮的需求不同，使灌木在风蚀土壤上具有优势;（4）新植物对风沙危害的脆弱性在草和灌木之间存在差异，这种脆弱性与土壤氮素状况有关;（5）叶片和植物效应将导致植物种群的长期变化，最终导致从草向灌木优势的转变。将对广泛的草和灌木生长形式进行实地试验。在一系列的实验中，已建立的植物将被放置在一个控制喷砂水平的风洞中。在另一项研究中，将对具有不同土壤表面特征的地点上的幼苗建立和生长进行量化，这些土壤表面特征与对比长期的风载运输水平有关。这些实验的结果将使用模型加以综合，以定量评估这些过程在推动荒漠化方面的作用。

The conversion of grassland to a desert with sparse shrubs, or desertification, is occurring in areas across the world. In many cases, desertification replaces plants that livestock and wildlife prefer to eat with shrubs that are difficult for them to digest. This problem therefore threatens the livelihood of farmers and ranchers while also jeopardizing wildlife habitat. Despite the widespread occurrence of desertification, the exact causes are difficult to pinpoint. Many scientists suggest that when grazing animals choose to eat grasses over shrubs, the shrubs take over. However, desertification has often been observed in areas without livestock, so there may be multiple causes for desertification. This research intends to discover if desertification in areas with low rainfall (which tend to be sandier) is due to sand being blown by the wind (sandblasting). Windblown sand can do two things that might cause desertification: 1) erode soil and decrease its fertility and 2) damage grass plants. Because grasses require richer soils and are more fragile than shrubs, shrubs may be at an advantage where there is more wind and soil fertility is lower. Through this research, undergraduate students and a postdoctoral researcher will be trained. Outreach to K-12 teachers and students will be conducted, and will include individuals from underrepresented groups.This research tests the following hypotheses: 1) leaf properties determine the effect of sandblasting on the plant's ability to regulate water loss and carbon uptake and to maintain an impermeable barrier to water loss during nighttime and dormant periods; 2) growth form, specifically plant height and exposure of growing points, determines vulnerability to sandblasting; 3) seedling water and nitrogen demands differ between grasses and shrubs, giving shrubs the advantage on wind-eroded soils; 4) vulnerability of new plants to sandblasting damage differs between grasses and shrubs and this vulnerability is related to soil nitrogen status; and 5) leaf and plant effects will lead to long-term changes in plant populations, culminating in a shift from grass to shrub dominance. Field experiments will be conducted on a wide range of grass and shrub growth forms. In one series of experiments, established plants will be placed in a wind tunnel that manipulates levels of sand blasting. In another, seedling establishment and growth will be quantified on sites with different soil surface characteristics associated with contrasting long-term levels of windborne transport. Results from these experiments will be integrated using models to quantitatively assess the role of these processes in driving desertification.