The Pasture Simulation model – evaluation of plant acclimatory effects on grassland systems in France

Session B2: Advances in Agricultural Modelling

The temperature responses of plant photosynthesis and respiration observed on single-plant species can be assumed to occur at the scale of a grassland ecosystem (which is a dynamic and competitive associations of plants). Based on the model for a single, fully expanded leaf as derived from experimental evidence and to gain insights into acclimatory and modulatory effects of growth temperature, we have: 1) improved a complex soil-vegetation-management model of grasslands, PaSim (Pasture Simulation model), and 2) evaluated it on multi-year datasets of plant biomass and C-water- energy fluxes in managed grassland systems. Illustrative results are presented for the French grassland site of Laqueuille, by comparing two grazing management treatments: high animal stocking rate and high nitrogen fertilisation (intensive) and low animal stocking rate with no fertilization (extensive). Model performances (reflected by mean square error, index of agreement and correlation coefficient) showed that accounting for plant acclimatory effects may help improving water and respiratory fluxes. However the pattern of results is generally complex (e.g. differences between management options), and a substantiation of results is required by assessing model performances on a range of sites and contrasting conditions (as listed in the paper).