Plant and soil microbial responses to defoliation in temperate semi-natural grassland

There is much interest in understanding the nature of feedback mechanisms b etween plants and soil organisms in grazed ecosystems. In this study, we ex amine the effects of different intensities of defoliation on the growth of three dominant grass species, and observe how these plant responses relate to the biomass and activity of the microbial community in the root zone. Ou r data show that grassland plants with varying tolerances to grazing have m arkedly different growth responses to defoliation, and that these responses vary with the intensity of cutting. Defoliation of grasses which are toler ant to grazing, namely Festuca rubra and Cynosurus cristatus, leads to a re duction in root mass and an increase in the allocation of resources to shoo ts. In contrast, defoliation of a grass with low tolerance to grazing, Anth oxanthum odoratum, had little effect on root mass, but increased the relati ve allocation of resources below-ground. In all plant species, defoliation led to an increase in soil microbial biomass and C use efficiency in the ro ot zone. This response was greatest in the root zone of A. odoratum and is likely to be related to changes in root exudation pattern following defolia tion. The significance of these changes in relation to soil nutrient dynami cs and plant nutrient uptake during regrowth require further exploration.