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      Responses of plant leaf economic and hydraulic traits mediate the effects of early- and late-season drought on grassland productivity

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          Abstract

          Drought can occur at different times during the grassland growing season, likely having contrasting effects on forage production when happening early or later in the season. However, knowledge about the interacting effects of the timing of drought and the development stage of the vegetation during the growing season is still scarce, thus limiting our ability to accurately predict forage quantity losses. To investigate plant community responses to drought seasonality (early- vs. late-season), we established a drought experiment in two permanent grasslands of the Swiss Jura Mountains that are used for forage production. We measured three plant functional traits, including two leaf traits related to plant economics (specific leaf area, SLA; leaf dry matter content, LDMC) and one hydraulic trait related to physiological function (predicted percentage loss of hydraulic conductance, PLCp), of the most abundant species, and plant above-ground biomass production. Plant species composition was also determined to calculate community-weighted mean (CWM) traits. First, we observed that CWM trait values strongly varied during the growing season. Second, we found that late-season drought had stronger effects on CWM trait values than early-season drought and that the plant hydraulic trait was the most variable functional trait. Using a structural equation model, we also showed that reduction in soil moisture had no direct impacts on above-ground biomass production. Instead, we observed that the drought-induced decrease in above-ground biomass production was mediated by a higher CWM PLCp (i.e. higher risk of hydraulic failure) and lower CWM SLA under drought. Change in CWM SLA in response to drought was the best predictor of community above-ground biomass production. Our findings reveal the importance of drought timing together with the plant trait responses to assess drought impacts on grassland biomass production and suggest that incorporating these factors into mechanistic models could considerably improve predictions of climate change impacts.

          Abstract

          Plant hydraulic traits measured at the community scale have rarely been used to assess grassland responses to drought. Here, the use of percentage loss of conductivity (PLCp) as a plant community hydraulic trait allowed us to observe its interactions with more commonly used plant leaf economic traits (SLA, LDMC) and its direct effects on grassland productivity under drought. Using a structural equation model, we showed that reduction in soil moisture had no direct impacts on above-ground biomass production. Instead, we observed that the drought-induced decrease in above-ground biomass production was mediated by a higher PLCp and lower SLA under drought.

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          Most cited references64

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          Benefits of plant diversity to ecosystems: immediate, filter and founder effects

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            Convergence across biomes to a common rain-use efficiency.

            Water availability limits plant growth and production in almost all terrestrial ecosystems. However, biomes differ substantially in sensitivity of aboveground net primary production (ANPP) to between-year variation in precipitation. Average rain-use efficiency (RUE; ANPP/precipitation) also varies between biomes, supposedly because of differences in vegetation structure and/or biogeochemical constraints. Here we show that RUE decreases across biomes as mean annual precipitation increases. However, during the driest years at each site, there is convergence to a common maximum RUE (RUE(max)) that is typical of arid ecosystems. RUE(max) was also identified by experimentally altering the degree of limitation by water and other resources. Thus, in years when water is most limiting, deserts, grasslands and forests all exhibit the same rate of biomass production per unit rainfall, despite differences in physiognomy and site-level RUE. Global climate models predict increased between-year variability in precipitation, more frequent extreme drought events, and changes in temperature. Forecasts of future ecosystem behaviour should take into account this convergent feature of terrestrial biomes.
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              Rainfall variability, carbon cycling, and plant species diversity in a mesic grassland.

              Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.
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                Author and article information

                Journal
                AoB Plants
                AoB Plants
                aobpla
                AoB Plants
                Oxford University Press (UK )
                2041-2851
                June 2019
                04 April 2019
                04 April 2019
                : 11
                : 3
                : plz023
                Affiliations
                [1 ]Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), Laboratory of Ecological Systems (ECOS), Switzerland
                [2 ]Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Lausanne, Switzerland
                [3 ]Agroscope, Grazing Systems Group, Route de Duillier, Nyon, Switzerland
                [4 ]Université Grenoble Alpes, Irstea, LESSEM, Grenoble, France
                [5 ]Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Community Ecology, Zuercherstrasse, Birmensdorf, Switzerland
                [6 ]Université Clermont Auvergne, INRA, PIAF, Clermont-Ferrand, France
                [7 ]ITEIPMAI, Domaine de la Vesc, Montboucher-sur-Jabron, France
                [8 ]UMR BIOGECO, INRA–UB, University of Bordeaux 1, Bat, Talence, France
                [9 ]Laboratoire de Chrono-Environnement, UMR CNRS 6249, UFR des Sciences et Techniques, Université de Franche-Comté, Besançon, France
                Author notes
                Corresponding author’s e-mail address: amarante.vitra@ 123456epfl.ch
                Article
                plz023
                10.1093/aobpla/plz023
                6499892
                31065332
                608ffb8f-32be-4151-9f39-1e0c7b0c3be0
                © The Author(s) 2019. Published by Oxford University Press on behalf of the Annals of Botany Company.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 23 November 2018
                : 29 March 2019
                Page count
                Pages: 15
                Categories
                Studies

                Plant science & Botany
                drought timing,grassland productivity,plant functional traits,plant hydraulic status,precipitation manipulation,rainout shelter,vegetation dynamics,water limitation

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