Root functional traits and their plasticity drive grasslands' Fabaceae capacities to face phosphorus shortage

Fabaceae performances in low fertility agro systems rely on their capacity to acquire phosphorus (P) since their growth is highly limited by P shortage. Recent work conducted on grassland’s legumes demonstrated, that different roots strategies exist within fabaceae family resulting in a large range of responses to P stress. Our objective is to evaluate to what extend rhizospheric soil phosphatase activity is related to Fabaceae response to P limitation. In that purpose, we grew in a green house, 13 grassland Fabaceae species under two levels of P availability for more than 100 days. At harvest, rhizospheric soil were sampled then analysed for alkaline phospho-monoesterase activity together with bulk soil (control). Results show a significant effect of plant on species identity on rhizospheric phosphatase activity, Anthylis vulneraria and Vicia cracca induce high phosphatase activity in their rhizsospheric soil while Securigera varia and Trifolium pratense induce low phosphatase activity. There is also a significant and negative effect of P supply on phosphatase activity of rhizospheric soil. The activity measured for the bulk soil is always significantly lower than the one measured for the rhizospheric soil. It was interesting to notice that phosphatase activities measured for Fabaceae are not different from those obtained for Poaceae grown under similar conditions. We showed that Fabaceae species induce au strong increase of the phosphatase activity in their rhizospheric soil in comparison to bulk soil. However, further work is needed to understand the link between rhizospheric soil activity and P stress tolerance