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

草原变成稀疏灌木的沙漠，或荒漠化，在世界各地都在发生。在许多情况下，沙漠化用难以消化的灌木取代了牲畜和野生动物更喜欢吃的植物。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栖息地。尽管荒漠化现象普遍发生，但确切的原因很难确定。许多科学家建议，当食草动物选择吃草而不是灌木时，灌木会占据主导地位。然而，沙漠化往往发生在没有牲畜的地区，因此沙漠化的原因可能是多方面的。这项研究旨在发现，降雨量少(往往沙化程度更高)地区的沙漠化是否是由于风吹沙(喷沙)造成的。风沙可以做两件可能导致荒漠化的事情：1)侵蚀土壤，降低其肥力；2)破坏草本植物。由于草需要更肥沃的土壤，而且比灌木更脆弱，灌木可能在风多、土壤肥力较低的地方处于优势地位。通过这项研究，将培养本科生和博士后研究员。这项研究测试了以下假设：1)叶片特性决定了喷沙对植物在夜间和休眠期间调节水分损失和碳吸收的能力的影响；2)生长形式，特别是植株高度和生长点的暴露，决定了植物对喷沙的脆弱性；3)苗木对水分和氮素的需求在草和灌木之间不同，使灌木在风蚀土壤上具有优势；4)新植物对喷沙伤害的脆弱性在草和灌木之间不同，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，最终从草本优势转变为灌木优势。将在多种草和灌木生长形式上进行田间试验。在一系列实验中，已建立的植物将被放置在风洞中，以控制喷砂的水平。在另一项研究中，苗木的建立和生长将在具有不同土壤表面特征的地点进行量化，这些土壤表面特征与长期风载运输水平的对比有关。这些实验的结果将使用模型综合起来，以定量评估这些过程在驱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.