Maximum distance evaluation of nutrient uptake in tropical forest formations using 15N as tracer

Abstract

Climate changes have caused alterations in temperature and in precipitation regimes around the world. This increases the probability of exceptional drought periods, which may result in tree mortality over large areas. Therefore, it is necessary to improve our knowledge about the processes that explain the tree behaviour under extreme drought. This work aims to assess the maximum distance of the trunk and the maximum depth of nutrient and water absorption by tree roots in forests growing on deep Ferralsols in the Sao Paulo state. The absorption of 15N-NO3- injected at several soil depths will be studied in eucalypt plantations during the dry season for trees of contrasting social status (comparing dominant trees and dominated trees of the same genotype in a monoclonal forest) and in native savannah (Cerrado) for three tree species (comparing dry and rainy seasons). Furthermore, the existence of a niche complementarity in the soil among the three studied Cerrado species will be evaluated, analysing the absorption of the tracer in different soil layers, depending on the species, on dry and rainy seasons. The 15N tracer will be applied in the middle of the inter rows: a) in a 1-year-old eucalypt stand, at 4 depths (down to 9 m) and 3 repetitions of 15N application per depth; b) in the same stand at 2 years of age, at 5 depths (down to 12 m) and 3 repetitions; c) in another eucalypt stand - same genetic material - at the end of the rotation (between 5 and 6 years of age), at 6 depths (down to 15 m) and 3 repetitions. In Cerrado, 15N will be applied at 36 positions: 2 seasons (dry and rainy) * 3 repetitions * 6 depths (down to 12 m). The 15N application positions will have a minimum distance of 40 m between each other to make sure that the roots of the trees where 15N will be evaluated have access only to the 15N applied at the closest position.