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Plant functional traits and resource economies describe plant strategies and performance in a semi-arid shrubland


Functional traits are defined as those having a direct impact of plant fitness, mediating the interaction between species and environments. Thus, they have become an important tool for understanding resource allocation strategies in individuals in the face of a changing climate. Economic models of carbon, nitrogen, and water use have significantly advanced our understanding of the constraints on plant trait strategies, placing plants on a continuum of fast to slow resource use and short to long tissue life span. While economic spectra have been developed for different plant tissue types, less is known about the coordination of resource economies across tissue types and how coordination may impact performance. This is especially true when considering roots for which recent work has described a multidimensional trait framework. Additionally, it is not clear how dynamic these trait strategies may be in response to endogenous (i.e., ontogeny/age) and exogenous (i.e., plasticity to environmental heterogeneity) factors. The coastal sage scrub plant community of Southern California offers a ripe testing ground for questions of resource use as plants from this community have adopted diverse sets of traits and trait responses to manage the region’s pulse-driven water availability. To this end, I investigated 1) aboveground and belowground trait coordination, and 2) shifts in xylem anatomy due to age and differential rainfall. I found aboveground traits ran along an expected fast to slow economic spectrum while roots occupied a two-dimensional trait space. Furthermore, root traits explained variation in the performance metrics of growth and stress tolerance while aboveground traits only explained variation in stress tolerance, suggesting discoordination between tissues. In examining trait responses to differential water availability, we found xylem traits in the shrub Artemisia californica were plastic with respect to age and watering treatment. In general, xylem traits became more conductive as plants got older and under higher water availability, with convergence in trait values as plants aged and in water abundant scenarios. These changes in xylem anatomy established strong potential conductivity trajectories and point to the importance of xylem trait plasticity during establishment. These changes will be important to consider under future precipitation regimes as they may impact plant function and ultimately population age structure. Understanding resource use economies in drylands provides evidence for the mechanisms controlling plant establishment and community assembly and structure, information valuable for earth system modeling and land management.

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