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

世界各地都在发生草地向具有稀疏灌木的沙漠或荒漠化的转变。在许多情况下，沙漠化取代了牲畜和野生动物喜欢吃的植物，取而代之的是难以消化的灌木。因此，这个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，荒漠化经常发生在没有牲畜的地区，因此荒漠化可能有多种原因。这项研究的目的是发现在降雨量少的地区（往往沙子较多）的沙漠化是否是由于风吹沙（喷沙）。风吹来的沙有两种可能导致沙漠化：1)侵蚀土壤，降低其肥力；2)损害草类植物。因为草需要更肥沃的土壤，而且比灌木更脆弱，所以在风多、土壤肥力低的地方，灌木可能更有优势。通过这项研究，将培养本科生和一名博士后研究员。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。本研究验证了以下假设：1)叶片特性决定了喷砂对植物调节水分流失和碳吸收以及在夜间和休眠期维持水分流失不透水屏障的能力的影响；2)生长形式，特别是植物高度和生长点的暴露，决定了喷砂的易损性；3)禾本科和灌丛幼苗对水分和氮的需求不同，灌丛在风蚀土壤上具有优势；4)禾草灌木新植物对喷砂破坏的易损性不同，其易损性与土壤氮态有关；叶片和植物的影响将导致植物种群的长期变化，最终导致从草为主向灌木为主的转变。将对各种草和灌木生长形式进行实地试验。在一系列实验中，已建立的植物将被放置在一个风洞中，风洞可以控制喷砂的水平。另一方面，幼苗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运水平的对比有关。将利用模型综合这些实验的结果，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.