UCLA

Among the many constituents of a plant’s environment, water is critical to the functionality of most of a plant’s physiological processes. Therefore, it is imperative to clarify how plants acquire, retain, utilize, and lose water to understand how these organisms will perform in a changing environment. Improving the capacity to determine tissue water status at organ, whole plant, canopy, and regional scales is necessary to resolve the drought responses and water requirements of crop and wild species, for agricultural and urban sustainability of water use. The most salient metrics of plant responses to dehydration at leaf scale are pressure volume (PV) curve traits, estimated from the relationship between water potential of a leaf (Ψleaf) and relative water content (RWC). These indices are correlated for a given dehydrating leaf; and notably, Ψleaf can provide mechanistic insight of the driving force for water movement within tissues. Pressure-volume curves have long been used for detailed analysis of tissue water status and its determinants (e.g., modulus of elasticity (ε), leaf water potential at turgor loss point (πtlp), and cell capacitance before wilting (Cft)), exhibiting many physical relationships among parameters. However, while pressure-volume traits are central in the analysis and prediction of drought tolerance there has been much less characterization of the variation of PV parameters across leaves within species. Further, estimation of Ψleaf and RWC require destruction of leaf tissues, whereas remote sensing tools provide opportunities to improve throughput and enable water stress measurements at coarser scales. Therefore, in this dissertation, I constructed a model to discern and explain the patterns of changes in water status as Ψleaf scaled from water content measured by terahertz radiation in-situ remote sensing. Then, I estimated the impact of intraspecific variation and inter-relationships of pressure volume curve parameters on prediction and interpretation, establishing a novel concept of baseline variation among sun leaves on similarly grown plants of 50 species. Last, I quantified intraspecific plasticity in the osmotic potential at full turgor (πo) (Δπ, or osmotic adjustment), an important drought tolerance trait, among ecotypes of a model species, Arabidopsis thaliana, and test for associations among osmotic adjustment, drought survival, growth under well-watered conditions, and native climate. This work provides new resolution of the determinants of tissue water status, with applications at both the leaf scale, such as clarifying the mechanistic traits underlying drought tolerance within species, and at ecosystem scales, such as for spectroscopic estimation of plant water status.