Evidence of short-term belowground transfer of nitrogen from Acacia mangium to Eucalyptus grandis trees in a tropical planted forest

Abstract

The short-term belowground transfer of nitrogen from nitrogen-fixing trees to companion trees has never been studied in the field. A 15 N pulse-labeling study was conducted in a mixed plantation of Acacia mangium and Eucalyptus grandis at the peak of leaf area, 26 months after planting. 15 NeNO 3 À was injected into the stem of one big Acacia tree in three plots. 15 N was traced over 2 months in the labeled Acacia tree as well as in neighboring Eucalyptus trees. For both species, young leaves were sampled, as well as fine roots and the rhizosphere at a distance of 0.75 m and 2.25 m from the labeled tree. The 15 N atom% was also determined in the wood, bark, branches and total foliage of the 3 labeled Acacia trees and 9 Eucalyptus trees, 60 days after labeling. Most of the leaves, fine roots and rhizosphere samples of both species were 15 N enriched from 5 days after labeling. The d 15 N values were higher at a distance of 0.75 m than at 2.25 m in Acacia roots, but were similar at both distances in Eucalyptus roots and the rhizospheres. The wood and bark of Eucalyptus trees sampled at a distance of 6.2 m from the labeled Acacia trees were 15 N enriched. This shows belowground N transfer from Acacia to Eucalyptus trees in the field during the first few days after labeling. This facilitation process may provide a significant amount of the nitrogen requirements of trees close to N-fixing trees in mixed forests.

Shifts in the bacterial community composition along deep soil profiles in monospecific and mixed stands of Eucalyptus grandis and Acacia mangium

“…A possible solution is the co-cultivation of Eucalyptus and leguminous trees in mixed systems [5–7] to provide an additional supply of nitrogen (N) for Eucalyptus [6, 8–10]. This strategy for N 2 fixation is well described and is promoted by nodules found in Acacia mangium [11], the most commonly used legume in experimental stands of mixed plantations with E . grandis in Brazil [6, 12].…”

Enhanced decomposition and nitrogen mineralization sustain rapid growth of Eucalyptus regnans after wildfire

“…While this has been observed for some Eucalyptus spp. (Paula et al 2015), most of the N fixed by Acacia spp. is taken up by E. regnans after the N is released through decomposition of Acacia litter (Forrester et al 2006).…”

High diversity mixed plantations in Brazil: <em>Eucalyptus</em> intercropped with native tree species

“…This indicates that the higher the number of N-fixing neighbors, and the larger they are, the larger Eucalyptus will grow in mixtures. These N-fixing neighbors may increase the amount of N available in the system (Siddique et al, 2008) that can be acquired by Eucalyptus after decay or below-ground transfer (Paula et al, 2015) and result in higher foliar N concentration and photosynthetic rates. Species grown in mixtures generally have greater above-ground nutrient content (Richards et al, 2010).…”

“…Considering the numerous examples of how non-fixing trees can benefit from the proximity of nitrogen-fixers (Binkley et al, 2003;Epron et al, 2013;Paula et al, 2015), we hypothesized that (i) Eucalyptus trees were facilitated by N-fixing native tree species;…”