Desert Fertilization Experiment: investigation of Sonoran desert ecosystem response to atmospheric deposition and experimental nutrient addition, ongoing since 2006

Launched in 2006 with support from the National Science Foundation (NSF) and leveraged by the CAP LTER, the Carbon and Nitrogen deposition (CNdep) project sought to answer the fundamental question of whether elemental cycles in urban ecosystems are qualitatively different from those in non-urban ecosystems. Ecosystem scientists, atmospheric chemists, and biogeochemists tested the hypothesis that distinct biogeochemical pathways result from elevated inorganic nitrogen and organic carbon deposition from the atmosphere to the land. To test the hypothesis, scientists examined the responsiveness of Sonoran desert ecosystems to nutrient enrichment by capitalizing on a gradient of atmospheric deposition in and around the greater Phoenix metropolitan area. Fifteen desert study sites were established, with five locations each west and east of the urban core, and in the urban core in desert preserves. In addition to the gradient of atmospheric deposition in and around the urban core, select study plots at each of the fifteen desert locations receive amendments of nitrogen, phosphorus, or nitrogen + phosphorus fertilizer. Measured variables include soil properties, perennial and annual plant growth, and atmospheric deposition of nitrogen. At the close of the initial grant period, the CAP LTER assumed responsibility for the project, renamed the Desert Fertilization Experiment, which provides a remarkable platform to study the long-term effects of nutrient enrichment on desert ecosystem properties.

该碳氮沉降（Carbon and Nitrogen deposition, CNdep）项目于2006年启动，获美国国家科学基金会（National Science Foundation, NSF）支持，并由CAP LTER负责实施，旨在解答一个核心科学问题：城市生态系统的元素循环是否在本质上有别于非城市生态系统。生态学家、大气化学家与生物地球化学家对如下假说展开验证：大气向陆地沉降的无机氮与有机碳通量升高，会形成独特的生物地球化学循环路径。为验证该假说，研究人员依托大凤凰城都会区及其周边的大气沉降梯度，探究了索诺兰沙漠生态系统对养分富集的响应。研究共设立15个沙漠样地：城市核心区以西、以东各设5个样地，城市核心区内的沙漠保护地另设5个样地。除依托城市核心区及其周边的大气沉降梯度外，研究人员还对15个样地中的部分样地施加了氮肥、磷肥或氮磷复合肥料。观测指标涵盖土壤理化性质、多年生与一年生植物生长状况，以及大气氮沉降量。初始资助周期结束后，CAP LTER接管了该项目，并将其更名为沙漠施肥实验（Desert Fertilization Experiment），该平台为探究养分富集对沙漠生态系统特征的长期影响提供了绝佳的研究载体。