Nutrient remobilization in tree foliage as affected by soil nutrients and leaf life span

Nutrient remobilization is a key process in nutrient conservation in plants and in nutrient cycling in ecosystems. To predict the productivity of terrestrial ecosystems, we thus need to improve our understanding of the factors that control remobilization. We studied the remobilization rates of several major nutrients (N, P, S, K, Ca, and Mg) in 102 forest ecosystems representing large environmental gradients at the country scale (France). Total amounts or availability of nutrients in soils were correlated with nutrient remobilization: the larger the soil nutrient pool, the lower the remobilization rate (e.g., P remobilization decreased with increasing total or extractable inorganic P in soils). Soil type and soil parent material influenced nutrient remobilization indirectly through their effect on soil nutrients. Nutrient remobilization was also affected by the quality of soil organic matter (C:N and C:P ratios) and K-Ca-Mg antagonisms. In addition to soil properties, plant-related parameters (nutrient concentrations in foliage and leaf life span) and climate variables (e.g., precipitation and actual evapotranspiration) were also correlated with nutrient remobilization. Using multivariate analysis, we found that soil nutrient richness and the life span of the leaf were generally the two most important factors controlling nutrient remobilization. As a whole, the nutrient remobilization rate is regulated by soil nutrients through negative feedback. This general ecological pattern is modulated by ecophysiological constraints of plants, mainly leaf life span or the capability of plants to move Ca through the phloem sap.