Plasticity in leaf and stem nutrient resorption proficiency potentially reinforces plant–soil feedbacks and microscale heterogeneity in a semi-arid grassland

1. The potential resorption of substantial amounts of nutrients from all vegetative organs of plants has large implications for the plant nutrient economy and for biogeochemical cycles. So far, most studies have focused on leaf nutrient resorption only. Besides, while evidence is growing that soil fertility changes impact on leaf nutrient resorption at a large spatial scale, hardly anything is known of such coupling at a small spatial scale. 2. Here we show that nitrogen (N) in culms of four dominant grasses of northern Chinese steppes contributed from 17% to 36% to the total pool of N resorbed from above-ground senescing parts and accounted for 25-52% of above-ground litter N. These results demonstrate the tremendous importance of non-leaf organs for plant nutrient economy and ecosystem nutrient cycling. 3. More importantly, we found that even microscale variations in resource availability (soil inorganic N; soil moisture) can strongly impact on both leaf and culm N resorption proficiencies (RP) and absolute leaf N resorption of grasses. Moreover, plasticity was responsible for 86% and 43% of within-site variance in leaf and culm RP, respectively, with the remainder owing to interspecific differences between the four grasses. These results imply a much larger role of plant plasticity in driving ecosystem functioning than previously assumed. 4. Synthesis. Our results suggest that plant litter quality varies even at the microscale with heterogeneity in soil resource availability, thereby potentially feeding back on soil properties and sustaining microscale soil fertility patchiness. In parallel, plants of more fertile patches resorbed a greater absolute amount of N, likely benefiting their competitive and reproductive abilities. © 2011 The Authors. Journal of Ecology © 2011 British Ecological Society