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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2018)

In many plants from arid and semi-arid ecosystems in both temperate and tropical regions, green photosynthetic stems appear to have evolved as a response to water shortage at least during one period of the year. My work addresses the question of whether plants with photosynthetic stems respond differently to drought. In my first chapter I studied the coordination between photosynthesis and hydraulics in plants with photosynthetic stems in southern California. This topic is critical because photosynthetic stems have been proposed to be more tolerant to drought than leaves, and given the predictions of global climate change, plants in arid ecosystems may face die-back and eventual local extinction if they cannot cope with the detrimental effects of drought. Using drought survival traits, I can predict what species are more likely to survive extreme droughts. My second chapter addresses the question of how carbon and water dynamics differ in green versus non-green-stemmed plants. It is obvious that having photosynthetic stems increases the carbon gain of the whole plant, but what are the costs associated with it? They might have higher water costs than plants without green stems, raising the question of the existence of trade-offs in carbon and water resources in plants with photosynthetic stems. I found that plants with green stems have the same carbon gain as plants without green stems, and both had the same water-use efficiency. However, cuticular conductance was higher in green stems than leaves and brown stems of non-green-stemmed species, raising questions about the possible costs of having green stems in terms of water balance. In my third chapter I studied photosynthetic and hydraulic traits of plants with photosynthetic stems in a subtropical arid ecosystem in Mexico. I found that green stems had higher photosynthetic capacity than fleshy ones, but that fleshy stems had higher hydraulic capacity and water storage capacity. The results show that different photosynthetic stem syndromes can have different physiological outputs. Overall, green stem physiology resembles leaf physiology and the advantages of extra carbon gain are offset by water costs.

    Cover page: Do Plants With Photosynthetic Stems Respond Differently to Drought? An Ecophysiological Evaluation of Desert Communities
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2019)
    Woody plants with green photosynthetic stems are common in dry woodlands with the possible advantages of extra carbon gain, re-assimilation of CO2, and high water-use efficiency. However, their green stem tissue may also incur greater costs of water loss when stomata are closed. Our study focussed on evaluating the costs and benefits of having green stems in desert plants, addressing the water-use efficiency hypothesis. We measured water status, carbon and water exchange, and carbon, nitrogen and oxygen isotopic composition of 15 species in a desert wash scrub in Joshua Tree National Park, California, USA. We found that all woody species that have green stems relied on their green stems as the sole organ for carbon assimilation for most of the study period. Green stems had similar photosynthetic rate (Amax), stomatal conductance (gs) and intrinsic water-use efficiency (WUEi) to leaves of the same species. However, Amax, gs and cuticular conductance (gmin) were higher in green stems than in leaves of non-green stemmed species. Carbon isotopic composition (δ13C) was similar in both leaves and green stems, indicating no difference in integrated long-term WUE. Our results raise questions about the possible trade-off between carbon gain and water loss through the cuticle in green stems and how this may affect plant responses to current and future droughts.
      Cover page: Costs and benefits of photosynthetic stems in desert species from southern California.
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2017)
      Coordination between stem photosynthesis and hydraulics in green-stemmed desert plants is important for understanding the physiology of stem photosynthesis and possible drought responses. Plants with photosynthetic stems have extra carbon gain that can help cope with the detrimental effects of drought. We studied photosynthetic, hydraulic and functional traits of 11 plant species with photosynthetic stems from three California desert locations. We compared relationships among traits between wet and dry seasons to test the effect of seasonality on these relationships. Finally, we compared stem trait relationships with analogous relationships in the leaf economics spectrum. We found that photosynthetic and hydraulic traits are coordinated in photosynthetic stems. The slope or intercept of all trait relationships was mediated by seasonality. The relationship between mass-based stem photosynthetic CO2 assimilation rate (Amass ) and specific stem area (SSA; stem surface area to dry mass ratio) was statistically indistinguishable from the leaf economics spectrum. Our results indicate that photosynthetic stems behave like leaves in the coordination of multiple traits related to carbon gain, water movement and water loss. Because of the similarity of the stem Amass -SSA relationship to the leaf Amass -specific leaf area relationship, we suggest the existence of a photosynthetic stem economic spectrum.
        Cover page: Stem photosynthesis and hydraulics are coordinated in desert plant species
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2022)
        The study of plant functional traits and variation among and within species can help illuminate functional coordination and trade-offs in key processes that allow plants to grow, reproduce and survive. We studied 20 leaf, above-ground stem, below-ground stem and fine-root traits of 17 Costus species from forests in Costa Rica and Panama to answer the following questions: (i) Do congeneric species show above-ground and below-ground trait coordination and trade-offs consistent with theory of resource acquisition and conservation? (ii) Is there correlated evolution among traits? (iii) Given the diversity of habitats over which Costus occurs, what is the relative contribution of site and species to trait variation? We performed a principal components analysis (PCA) to assess for the existence of a spectrum of trait variation and found that the first two PCs accounted for 21.4 % and 17.8 % of the total trait variation, respectively, with the first axis of variation being consistent with a continuum of resource-acquisitive and resource-conservative traits in water acquisition and use, and the second axis of variation being related to the leaf economics spectrum. Stomatal conductance was negatively related to both above-ground stem and rhizome specific density, and these relationships became stronger after accounting for evolutionary relatedness, indicating correlated evolution. Despite elevation and climatic differences among sites, high trait variation was ascribed to individuals rather than to sites. We conclude that Costus species present trait coordination and trade-offs that allow species to be categorized as having a resource-acquisitive or resource-conservative functional strategy, consistent with a whole-plant functional strategy with evident coordination and trade-offs between above-ground and below-ground function. Our results also show that herbaceous species and species with rhizomes tend to agree with trade-offs found in more species-rich comparisons.
          Cover page: Above and belowground functional trait coordination in the Neotropical understory genus Costus
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2022)

          Premise

          Adaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation.

          Methods

          We combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real-time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation.

          Results

          We found that drought-adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi-drought-deciduousness and a fast economic strategy. Although the two species do not differ in water-use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light-saturated photosynthetic rates. These fast economic strategy traits align with both field-based observations and experimental dry-down results. During drought, C. villosissimus displays facultative drought-deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season.

          Conclusions

          We revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.
            Cover page: Flexible drought deciduousness in a neotropical understory herbCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2024)
            Environmental variation commonly drives functional trait diversity within species, among species, and across communities. Climate and shared evolutionary history can both influence trait–environment relationships. We studied variation in plant functional traits among closely related Costus species occurring across environmental gradients, the extent to which this variation occurs within single species, and how that variation may be influenced by shared evolutionary history. We measured leaf, aboveground stem, rhizome, and fine root traits of 17 species of Costus in eight sites in Costa Rica and Panama, which varied in elevation, temperature, and precipitation. We then assessed the relationships among traits and environmental variables and estimated the phylogenetic signal of the traits. We observed significant relationships between functional traits and climate. Stomatal conductance decreased, but stem density and rhizome dry matter content increased with decreasing mean annual temperature and precipitation seasonality in both cross-species and single-species analyses. This suggests that herbaceous species have a similar trade-off between plant hydraulic efficiency and safety as found in woody plants. Mean annual temperature was a stronger driver of trait variation than mean annual precipitation. We also found phylogenetic signal in leaf and stem structural traits (i.e., closely related species are more similar than distantly related species), but not in physiological or belowground traits. Our results demonstrate significant trait variation within and among species of Costus, a widespread understory and herbaceous genus in the tropics, which is driven by both climate and shared evolutionary history.
              Creative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2018)
                Cover page: Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars
                • Article
                • Peer Reviewed
                UC Riverside Previously Published Works (2018)
                Abstract:Isotopic composition of leaf carbon (δ13C) and nitrogen (δ15N) is determined by biotic and abiotic factors. In order to determine the influence of leaf habit and site on leaf δ13C and δ15N in the understorey of two Atlantic forests in Brazil that differ in annual precipitation (1200 and 1900 mm), we measured these isotopes in the shaded understorey of 38 tropical tree species (20 in the 1200-mm site and 18 in the 1900-mm site). Mean site values for δ15N were significantly lower at the 1200-mm site (−1.4‰) compared with the 1900-mm site (+3.0‰), and δ13C was significantly greater in the 1200-mm site (−30.4‰) than in the 1900-mm site (−31.6‰). Leaf C concentration was greater and leaf N concentration was lower at 1200-mm than at 1900-mm. Leaf δ15N was negatively correlated with δ13C across the two sites. Leaf δ13C and δ15N of evergreen and deciduous species were not significantly different within a site. No significant phylogenetic signal for any traits among the study species was found. Overall, site differences were the main factor distinguishing traits among species, suggesting strong functional convergence to local climate and soils within each site for individuals in the shaded understorey.
                  Cover page: Isotopic composition of leaf carbon (δ13C) and nitrogen (δ15N) of deciduous and evergreen understorey trees in two tropical Brazilian Atlantic forests
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