Tree – Open Grassland Structure Drives Carbon And Nitrogen Cycling In Mediterranean Wood Pastures of The Iberian Peninsula

Abstract Purpose: Mediterranean wood pastures are the largest agroforestry system in Europe. Traditional silvo-pastoral uses shaped these systems into a mosaic of trees and open grassland. However, little is known about how this structure may influence ecosystem carbon (C) and nitrogen (N) dynamics, considering different canopy types and interactions with the herbaceous layer. Aims: To unravel the canopy effect on C and N dynamics (1) under representative canopy types, including traditional Quercus stands and Pinus pinea L. plantations; and (2) in interaction with the herbaceous plant functional types (PFT). Methods: We analysed C and N content and the isotopic natural abundance on soil and plant materials at the open grassland and under the different tree canopies. Results: Under the canopy, soil C and N content, and N availability for the herbaceous layer increased. The canopy effect performed differences between Quercus and P. pinea plots, as detected on the belowground biomass C content. Also, the canopy effect was more pronounced with increasing environmental constraints, highlighting the relevance of trees in more restrictive environments. PFT ecophysiological characteristics interacted with tree canopies, as reflected the enhanced efficiency taking-up N, and/or exploiting symbiotic N of grasses, which was probably one of the causes of their dominancy under the canopy, at higher N availability. Conclusion: Changes in the tree coverage and tree species will significantly change ecosystem C and N storage and cycling. Therefore, it is highly advisable to preserve a balance between trees and open grassland, and traditional Quercus stands, to keep ecosystem services provisioning.