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

Abstract

Plant traits can be used to predict ecosystem responses to environmental change using a response–effect trait framework. To do this, appropriate traits must be identified that explain a species' influence on ecosystem function (“effect traits”) and the response of those species to environmental change (“response traits”). 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 “response traits.” We attribute weak trait–precipitation 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 “response traits” 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 http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13135/suppinfo is available for this article.

Compensatory mechanisms to climate change in the widely distributed species Silene vulgaris

“…Under dry conditions, plants are expected to decrease their leaf surface and SLA to prevent the evaporation of water and thus enhance the water‐use efficiency. However, these leaf traits have also been shown to be highly species‐specific (Griffin‐Nolan et al., ) which impedes the prediction of general drought responses. Flower number decreased significantly with lower precipitation in our experiment.…”

Mimicking a rainfall gradient to test the role of soil microbiota for mediating plant responses to drier conditions

“…This suggests that dry-adapted microbial species may be buffering plants from water and nutrient limitations (Vurukonda et al 2016a), and thereby reducing the demand for increasing leaf construction costs (LDMC) or belowground biomass allocation (root-to-shoot ratio). Recent work has highlighted the importance of identifying appropriate response traits to climatic variables such as precipitation (O'Brien et al 2017b, Griffin-Nolan et al 2018. Our results suggest that leaf and allocation traits measured here are less useful for assessing trait shifts in this semiarid system than physiological traits such as nonstructural carbohydrate concentrations or hydraulic conductance.…”

“…In addition, functional traits may be good metrics to gauge population responses to climatic variables (O'Brien et al 2017b, Griffin-Nolan et al 2018. For example, leaf dry matter content (LDMC), which is associated with photosynthetic capacity, relative growth rate and leaf longevity (Cornelissen et al 2003), is regulated by construction costs related to plant water status.…”

Plant Hydraulic Trait Covariation: A Global Meta-Analysis to Reduce Degrees of Freedom in Trait-Based Hydrologic Models

“…Understanding strategies of water use and acquisition, often termed hydraulic strategies, and the functional traits that define them is critical to understanding the roles different types and species of vegetation play in the carbon and water cycles, predicting vegetation responses to climate change, and predicting the impacts of drought, disturbances, and other extreme events on the land surface [18]. To that end, Griffin-Nolan, et al [19] demonstrated that hydraulic traits can be used to predict ecosystem-level responses to changing precipitation patterns. In the context of our changing climate, vegetation regulated feedbacks between the biosphere and atmosphere are expected to change with changing temperature and precipitation [20][21][22][23][24].…”