Grassland | EPFL Graph Search

A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica and are found in most ecoregions of the Earth. Furthermore, grasslands are one of the largest biomes on earth and dominate the landscape worldwide. There are different types of grasslands: natural grasslands, semi-natural grasslands, and agricultural grasslands. They cover 31–69% of the Earth's land area. Definitions Included among the variety of definitions for grasslands are:

"...any plant community, including harvested forages, in which grasses and/or legumes make up the dominant vegetation."
"...terrestrial ecosystems dominated by herbaceous and shrub vegetation, and maintained by fire, grazing, drought and/or freezing temperatures." (Pilot Assessment

Responses of permanent grasslands to drought during the plant growing season: combining agronomic, functional and ecophysiological approaches

Amarante Vitra

Extreme summer drought events are predicted to increase in intensity and frequency within the current century. The resulting water scarcity could dramatically impact human activities related to agriculture, due to the strong relationship between precipitations and plant biomass production. However, little is known about the interactions between timing of drought and vegetation dynamics along the growing season. In Switzerland, were grasslands are at the core of the agriculture, droughts could have severe economical consequences. Thus, farmers should be provided with insights on how to adapt and optimize their management to the changing climate. In order to further our understanding on the response of grasslands to different timing of drought and its interaction with other factors such as management intensity, productivity or soil characteristics, we developed the GRASSALT project -which was the context of this PhD- as a joint venture between AGROSCOPE, EPFL and WSL, with the aim to investigate this challenge through a multidisciplinary perspective at the crossroad between applied and fundamental research. The setup of a realistic drought experiment in three semi-natural grasslands in the Swiss Jura Mountains (even though this thesis is focusing mainly on two) where 70% of the precipitations were removed during two months at two different (during the peak of vegetation growing season vs after this peak later in the season) and two management intensities were applied, enabled us to investigate how grassland communities responded to drought at different timings and sites and investigate its interacted with management. To perform this investigation we adopted a combined agronomic, functional and ecophysiological approach that leads us to analyse the effect of drought from the plant community level to the physiological level and to the analysis of the aboveground-belowground interaction. The main findings of this thesis were the following: (i) a drought event occurring later in the growing season leads to stronger reduction in aboveground productivity than a drought event occurring during the peak of growing season. (ii) The decrease in aboveground productivity is mediated by an intraspecific variability in the functional traits of the most abundant plant species. (iii) the effect of drought is more deleterious under higher mowing intensity. (iv)The effect of drought on plant aboveground and belowground productivity is dependent on soil types and modulated through the effects on microbial communities in response to climate. Altogether the presented work has shown that timing of drought plays a big role on the impact of drought on the productivity of grasslands per se or by interacting with otherfactorsand that this requires further in-depth studies to offer efficient management strategies to farmers.

EPFL2019

Nutrient limitations induced by drought affect forage N and P differently in two permanent grasslands

Alexandre Buttler, Claire Emilie Deléglise, Pierre Rémi Mariotte, Amarante Vitra

Drought events can strongly affect ecosystem functioning by modifying relationship between plants, microbes and soil chemistry, with consequent impacts on nutrient cycling. However, the potential impacts of a soil moisture reduction on the nitrogen (N) and phosphorus (P) cycling in grasslands remain poorly understood, especially in regard to. forage production. To fill this knowledge gap, a drought experiment was carried out using rainout shelters in two permanent grasslands, characterized by similar vegetation communities but contrasted soil nutrient limitations. Drought treatments were applied during two months, either when plant growth was highest (Early-season drought) or after the peak of biomass production (Late-season drought). Dry matter production, forage N status (NNI) and P content as well as N and P contents in microbial biomass and soil were determined. Both early and late-season drought significantly reduced soil moisture during the vegetation growth period. Forage yield was also reduced by drought, but only when it occurred late in the season. Using a structural equation model, we showed that soil moisture reduction had a direct effect on forage N status, suggesting that water shortage induced lower transpiration and water fluxes. Soil moisture reduction also affected forage P by reducing the availability of soil P. However, other mechanisms played a larger role and were site-specific. At the more fertile site, reduction in soil moisture directly impaired forage P, suggesting that water stress mainly resulted in lower diffusion rates to roots, while at the less fertile site, an indirect reduction of forage P through a pathway implying microbes (decrease in microbial P) was detected. Our results suggest that the two grasslands suffered mainly from water shortage per se, but also from drought induced nutrient deficiency (mainly P), which amplified yield losses and further decreased forage quality. Overall, our findings emphasize the need for further research on the plant-soil-microbe system functioning, in order to secure a sustainable and resilient forage production in the context of climate change.

ELSEVIER2019