Department of Biology, University of New Mexico, Albuquerque, New Mexico, United States of America.
School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, United States of America.
PLoS One. 2019 Nov 8;14(11):e0224804. doi: 10.1371/journal.pone.0224804. eCollection 2019.
The infiltration of stormwater runoff for use by urban trees is a major co-benefit of green infrastructure for desert cities with limited water resources. However, the effects of this passive irrigation versus regular, controlled moisture inputs, or active irrigation, is largely unquantified. We monitored the ecohydrology of urban mesquite trees (Prosopis spp.) under these contrasting irrigation regimes in semiarid Tucson, AZ. Measurements included soil moisture, sap velocity, canopy greenness, and leaf-area index. We expected both irrigation types to provide additional deep (>20 cm) soil moisture compared to natural conditions, and that trees would depend on this deep moisture for transpiration and phenological activity. Results show that active irrigation supported higher soil moisture throughout the study than passive irrigation. Passive irrigation only provided additional deep moisture when green infrastructure features received impervious runoff from a city street. Sap velocity and greenness were similar under both irrigation types, outside of isolated periods of time. These differences occurred during the extremely wet summer 2017 when passively irrigated trees exhibited a greenness peak, and the dry conditions of spring when actively irrigated trees had higher sap flow and relative greenness. Finally, it was not determined that deep soil moisture had a stronger relationship with mesquite productivity than shallow moisture, but both relationships were stronger in the spring, before summer rains. This study aims to contribute empirical observations of green infrastructure performance for urban watershed management.
城市树木利用雨水的渗透是水资源有限的沙漠城市绿色基础设施的一个主要附带好处。然而，这种被动灌溉与常规的、有控制的水分输入或主动灌溉的效果在很大程度上是无法量化的。我们在亚利桑那州图森的半干旱地区，监测了这些具有对比性灌溉模式下城市牧豆树（Prosopis spp.）的生态水文学特征。测量包括土壤湿度、液流速度、冠层绿色度和叶面积指数。我们预计这两种灌溉类型都会比自然条件提供更多的深层（>20 厘米）土壤水分，并且树木会依赖这种深层水分进行蒸腾和物候活动。结果表明，主动灌溉在整个研究过程中提供的土壤湿度都高于被动灌溉。只有在绿色基础设施设施接收来自城市街道的不透水径流时，被动灌溉才能提供额外的深层水分。在液流速度和绿色度方面，两种灌溉类型在孤立的时间段之外都很相似。这些差异发生在极其湿润的 2017 年夏季，此时被动灌溉的树木表现出绿色峰值，以及在春季干旱条件下，主动灌溉的树木具有更高的液流和相对绿色度。最后，并没有确定深层土壤水分与牧豆树生产力的关系比浅层水分更紧密，但这两种关系在春季（在夏雨之前）都更强烈。本研究旨在为城市流域管理提供绿色基础设施性能的经验观察。
