Do plant functional types based on leaf dry matter content allow characterizing native grass species and grasslands for herbage growth pattern ?
Résumé
Abstract Few studies have focused on vegetation characteristics of importance to feeding domestic herbivores, mainly the seasonal pattern of herbage growth at spring. Our objective is to establish and to evaluate a simple method of ranking grassland communities for these characteristics. We combined approaches at plant species level (comparison of grass species growing in a pure stand) and plant community level (comparison of grasslands differing mainly in their nutrient availability). Firstly, we ask if the ranking of species by leaf dry matter content (LDMC), a functional parameter used to assess the plant strategy for resource acquisition and use, is consistent with a classification of the species using three plant features that determine plant growth pattern at spring (beginning and ending of stem elongation, leaf lifespan). Secondly, for three network soft natural grasslands, we test whether there is consistency when ranking them by their dominant plant functional type (PFT A, B or C) established previously at species level, and by the three agronomic characteristics. For species growing in pure stands, there was a significant effect of PFT for the three plant features. For species having a low LDMC (A and B PFT), there were earlier stem elongation in the season, earlier flowering and shorter leaf life span. The opposite was observed for species having a high LDMC (C and D PFT). For grassland communities dominated by A-PFT, the ceiling yield for leaves and stems occurred earlier in spring than for those dominated by C-PFT. Results were consistent at plant and community levels. Scaling up from plant to community was well mediated by PFT. Plant features which characterize species for resource acquisition and use are consistent with herbage growth patterns at plant community level. These results show that herbage growth pattern and composition depend on PFTs and that knowing the PFT dominance is of great importance to plan the use of grasslands. We can expect to use the PFT approach to perform vegetation diagnosis at field level when the objective is to rank grassland communities for their agronomic characteristics.