Mechanisms and Ecological Consequences of Predawn Soil-Plant Water Potential Disequilibrium in Desert Shrubs

在许多生境中，水是限制植物生长和分布的主要因素。因此，植物水分状况和水分关系特征与植物生长性能密切相关，特别是在干旱生境中。由于黎明前植物水势与土壤水势处于平衡状态，日出前植物水分状态的测量被称为植物黎明前水势，作为比较不同生境植物水分有效性的标准。pi从野外和受控环境研究中获得证据，至少有两种沙漠灌木物种显示出与预期的土壤-植物黎明前水势平衡的重大偏离，即使水力连续性（土壤-根接触）不是限制因素，pi将这种现象称为“黎明前不平衡”。研究物种的黎明前不平衡为研究一套可能解释偏离经典生理预期的机制以及研究这些机制的生态后果和适应意义提供了焦点。研究灌木为黄菊花。不含盐、非盐生的consimilis和盐生的Sarcobatus vermiculatus在生活史和生根特性上相似。在温室和野外研究中，需要测试的机制包括缺乏夜间恢复时间、夜间蒸腾作用、夜间根部水分外排、生长诱导的植物水势降低以及细胞间隙的溶质积累。然后，pi将通过检查其与光合作用、蒸腾作用和水利用效率的关系，评估黎明前不平衡对植物碳增益的影响。该项目将有助于在经典解释失败的地区更准确地理解基本的植物水关系。这种认识的提高对于对野生植物的水关系适应作出有效的生态解释是必不可少的。

Water is the primary factor limiting plant growth and distribution in many habitats. Thus, plant water status and water relations characteristics are closely related to plant performance, particularly in arid habitats. Measurements of plant water status just before sunrise, called plant predawn water potential, are used as a standard for comparing plant water availability in different habitats because of the expectation that predawn plant water potential is in equilibrium with soil water potential. The PIs have evidence from field and controlled environment studies that at least two desert shrub species show major departures from the expected soil-plant predawn water potential equilibrium, even when hydraulic continuity (soil-root contact) is not a limiting factor, and the PIs call this phenomenon "predawn disequilibrium." Predawn disequilibrium in the study species provides a focal point for investigating a suite of mechanisms that may account for departure from classical physiological expectations and for study of ecological consequences and adaptive significance of those mechanisms. The study shrubs are Chrysothamnus nauseosus ssp. consimilis (salt-excluding, non-halophytic) and Sarcobatus vermiculatus (salt-accumulating, halophytic) which are similar in life history and rooting characteristics. Mechanisms to be tested, in both greenhouse and field studies, include lack of time for overnight recovery, nighttime transpiration, nocturnal efflux of water from roots, growth-induced reduction in plant water potential, and solute accumulation in intercellular spaces. The PIs will then assess the plant carbon gain consequences of predawn disequilibrium by examining its relationship to photosynthesis, transpiration and water-use-efficiency. This project will contribute to a more accurate understanding of fundamental plant water relations in areas where classical interpretations fail. This improved understanding is essential for making valid ecological interpretations of water relations adaptations of wildland plants.