Is it plastic or just fantastic? Understanding the role of plasticity and local adaptation in the drought tolerance of Bouteloua gracilis

2017 Summer.Includes bibliographical references.The ability of an organism to tolerate or acclimate to drought may become a major driver of changes in community composition, carbon and water cycles and ecosystem services as we encounter increasing severity and frequency of droughts in the face of global change.  Drought tolerance traits allow us to quantify functional attributes of individual species, but the expected variability of drought tolerance traits within a species is uncertain.  Although some variability in plant traits are expected, it is unknown whether the local adaptation of populations can explain the expected variability.  The objective of this study is the quantification of plasticity of drought tolerance responses across populations of Bouteloua gracilis to different soil moisture levels.  B. gracilis is a C4 perennial grass that dominates grasslands across a range of climates and is a major contributor of ecosystem function and services within these systems. Populations from less arid sites showed greater osmotic adjustment and higher midday water potentials when grown under limited soil moisture conditions. Populations from arid sites did not adjust osmotic potential but showed more negative midday water potentials while maintaining higher growth rates. This variation in response to lowered soil moisture indicates a potential shift in water use strategy across an aridity gradient that has implications for land managers seeking to restore B. gracilis dominated ecosystems with drought tolerant material

Trading water for carbon in the future : effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland

The effects of climate change on plants and ecosystems are mediated by plant hydraulic traits, including interspecific and intraspecific variability of trait phenotypes. Yet, integrative and realistic studies of hydraulic traits and climate change are rare. In a semiarid grassland, we assessed the response of several plant hydraulic traits to elevated CO2 (+200 ppm) and warming (+1.5 to 3°C; day to night). For leaves of five dominant species (three graminoids and two forbs), and in replicated plots exposed to 7 years of elevated CO2, warming, or ambient climate, we measured: stomatal density and size, xylem vessel size, turgor loss point, and water potential (pre-dawn). Interspecific differences in hydraulic traits were larger than intraspecific shifts induced by elevated CO2 and/or warming. Effects of elevated CO2 were greater than effects of warming, and interactions between treatments were weak or not detected. The forbs showed little phenotypic plasticity. The graminoids had leaf water potentials and turgor loss points that were 10% to 50% less negative under elevated CO2; thus, climate change might cause these species to adjust their drought resistance strategy away from tolerance and toward avoidance. The C4 grass also reduced allocation of leaf area to stomata under elevated CO2, which helps explain observations of higher soil moisture. The shifts in hydraulic traits under elevated CO2 were not, however, simply due to higher soil moisture. Integration of our results with others' indicates that common species in this grassland are more likely to adjust stomatal aperture in response to near-term climate change, rather than anatomical traits; this contrasts with apparent effects of changing CO2 on plant anatomy over evolutionary time. Future studies should assess how plant responses to drought may be constrained by the apparent shift from tolerance (via low turgor loss point) to avoidance (via stomatal regulation and/or access to deeper soil moisture)

Trait selection and community weighting are key to understanding ecosystem responses to changing precipitation regimes

Plant traits can be used to predict ecosystem responses to environmental change using a response\u2013effect trait framework. To do this, appropriate traits must be identified that explain a species' influence on ecosystem function (\u201ceffect traits\u201d) and the response of those species to environmental change (\u201cresponse traits\u201d). Response traits are often identified and measured along gradients in plant resources, such as water availability; however, precipitation explains very little variation in most plant traits globally. Given the strong relationship between plant traits and ecosystem functions, such as net primary productivity (NPP), and between NPP and precipitation, the lack of correlation between precipitation and plant traits is surprising. We address this issue through a systematic review of >500 published studies that describe plant trait responses to altered water availability. The overarching goal of this review was to identify potential causes for the weak relationship between commonly measured plant traits and water availability so that we may identify more appropriate \u201cresponse traits.\u201d We attribute weak trait\u2013precipitation relationships to an improper selection of traits (e.g., nonhydraulic traits) and a lack of trait-based approaches that adjust for trait variation within communities (only 4% of studies measure community-weighted traits). We then highlight the mechanistic value of hydraulic traits as more appropriate \u201cresponse traits\u201d with regard to precipitation, which should be included in future community-scale trait surveys. Trait-based ecology has the potential to improve predictions of ecosystem responses to predicted changes in precipitation; however, this predictive power depends heavily on the identification of reliable response and effect traits. To this end, trait surveys could be improved by a selection of traits that reflect physiological functions directly related to water availability with traits weighted by species relative abundance. A plain language summary is available for this article