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

There is much interest in understanding the nature of feedback mechanisms between plants and soil organisms in grazed ecosystems. In this study, we examine 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. Our data show that grassland plants with varying tolerances to grazing have markedly different growth responses to defoliation, and that these responses vary with the intensity of cutting. Defoliation of grasses which are tolerant to grazing, namely Festuca rubra and Cynosurus cristatus, leads to a reduction in root mass and an increase in the allocation of resources to shoots. In contrast, defoliation of a grass with low tolerance to grazing, Anthoxanthum odoratum, had little effect on root mass, but increased the relative allocation of resources below-ground. In all plant species, defoliation led to an increase in soil microbial biomass and C use efficiency in the root 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 defoliation. The significance of these changes in relation to soil nutrient dynamics and plant nutrient uptake during regrowth require further exploration.