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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2021)

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.

    Cover page: Plant functional traits and resource economies describe plant strategies and performance in a semi-arid shrubland
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2021)

    Background and aims

    Leaf functional traits are strongly tied to growth strategies and ecological processes across species, but few efforts have linked intraspecific trait variation to performance across ontogenetic and environmental gradients. Plants are believed to shift towards more resource-conservative traits in stressful environments and as they age. However, uncertainty as to how intraspecific trait variation aligns with plant age and performance in the context of environmental variation may limit our ability to use traits to infer ecological processes at larger scales.

    Methods

    We measured leaf physiological and morphological traits, canopy volume and flowering effort for Artemisia californica (California sagebrush), a dominant shrub species in the coastal sage scrub community, under conditions of 50, 100 and 150 % ambient precipitation for 3 years.

    Key results

    Plant age was a stronger driver of variation in traits and performance than water availability. Older plants demonstrated trait values consistent with a more conservative resource-use strategy, and trait values were less sensitive to drought. Several trait correlations were consistent across years and treatments; for example, plants with high photosynthetic rates tended to have high stomatal conductance, leaf nitrogen concentration and light-use efficiency. However, the trade-off between leaf construction and leaf nitrogen evident in older plants was absent for first-year plants. While few traits correlated with plant growth and flowering effort, we observed a positive correlation between leaf mass per area and performance in some groups of older plants.

    Conclusions

    Overall, our results suggest that trait sensitivity to the environment is most visible during earlier stages of development, after which intraspecific trait variation and relationships may stabilize. While plant age plays a major role in intraspecific trait variation and sensitivity (and thus trait-based inferences), the direct influence of environment on growth and fecundity is just as critical to predicting plant performance in a changing environment.
      Cover page: Leaf traits and performance vary with plant age and water availability in Artemisia californica
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2020)
      When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.
        Cover page: Global gene flow releases invasive plants from environmental constraints on genetic diversity
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