Changes in nutrient concentrations of leaves and roots in response to global change factors

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Abstract

Global change impacts on biogeochemical cycles have been widely studied, but our understanding of whether the responses of plant elemental composition to global change drivers differ between above- and belowground plant organs remains incomplete. We conducted a meta-analysis of 201 reports including 1,687 observations of studies that have analyzed simultaneously N and P concentrations changes in leaves and roots in the same plants in response to drought, elevated [CO2], and N and P fertilization around the world, and contrasted the results within those obtained with a general database (838 reports and 14,772 observations) that analyzed the changes in N and P concentrations in leaves and/or roots of plants submitted to the commented global change drivers. At global level, elevated [CO2] decreased N concentrations in leaves and roots and decreased N:P ratio in roots but no in leaves, but was not related to P concentration changes. However, the response differed among vegetation types. In temperate forests, elevated [CO2] was related with lower N concentrations in leaves but not in roots, whereas in crops, the contrary patterns were observed. Elevated [CO2] decreased N concentrations in leaves and roots in tundra plants, whereas not clear relationships were observed in temperate grasslands. However, when elevated [CO2] and N fertilization coincided, leaves had lower N concentrations, whereas root had higher N concentrations suggesting that more nutrients will be allocated to roots to improve uptake of the soil resources not directly provided by the global change drivers. N fertilization and drought increased foliar and root N concentrations while the effects on P concentrations were less clear. The changes in N and P allocation to leaves and root, especially those occurring in opposite direction between them have the capacity to differentially affect above- and belowground ecosystem functions, such as litter mineralization and above- and belowground food webs.

We analyzed global data by a meta-analysis to investigate whether the responses of plant elemental composition to Global Change drivers differ between above- and belowground plant organs. The response of N and P in leaves and roots differed among vegetation types. In temperate forests CO2 fertilization was related with lower N concentrations in leaves and higher in roots. In temperate grasslands CO2 decreased leaf N concentrations and in croplands elevated CO2 decreased N root concentration. When CO2 and N fertilization coincided, leaves had lower N concentrations whereas root had higher N concentrations. The changes in the N and P allocation to foliar and root concentrations, especially those occurring in opposite direction between leaves and roots have the capacity to differentially affect above- and below-ground ecosystem functioning, for example by differentially affecting litter mineralization and above- and belowground food webs.

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