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

在许多生境中，水分是限制植物生长和分布的主要因素。 因此，植物的水分状况和水分关系特征与植物的生产性能密切相关，特别是在干旱生境中。 测量植物水分状况日出前，称为植物黎明前的水势，被用作比较植物水分在不同的栖息地，因为期望黎明前的植物水势是在平衡与土壤水势的标准。PI从实地和受控环境研究中获得的证据表明，至少有两种荒漠灌木物种显示出严重偏离预期的黎明前土壤-植物水势平衡，即使水力连续性（土壤-根系接触）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系列机制提供了一个焦点，这些机制可以解释偏离经典生理预期的原因，并研究这些机制的生态后果和适应意义。研究的灌木是Chrysothamnus daminosus ssp. consimilis（不耐盐，非盐生）和Sarcobatusvermiculatus（耐盐，盐生）的生活史和生根特性相似。 在温室和田间研究中，有待测试的机制包括缺乏过夜恢复的时间，夜间蒸腾，夜间从根部流出的水，生长诱导的植物水势降低，以及细胞间隙中的溶质积累。 然后，PI将通过检查其与光合作用，蒸腾作用和水分利用效率的关系来评估黎明前不平衡的植物碳增益后果。 这个项目将有助于更准确地了解基本植物水的关系，在经典的解释失败的地区。这一认识的提高是必不可少的，使有效的生态学解释的水关系适应的荒地植物。

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.