Nitrogen Pools in Tropical Plantations of N2-Fixing and Non-N2-Fixing Legume Trees under Different Tree Stand Densities

Kelly Nery Bighi,Diego Lang Burak,Marcos Vinícius Winckler Caldeira,Eduardo De Sá Mendonça,Fabiano De Carvalho Balieiro,Paulo Henrique De Souza,Ranieri Ribeiro Paula,William Macedo Delarmelina

doi:10.3390/nitrogen2010006

Abstract

We investigated the nitrogen pools in monocultures of legume species widely used in reforestation in Brazil that have contrasting growth and nitrogen acquisition strategies. The plantations were established with the slow-growing and N2-fixing tree Anadenanthera peregrina var. peregrina, and the fast-growing and non-fixing tree Schizolobium parahyba var. amazonicum. The measurements of N pools in the tree biomass and the soil followed standard methods and were carried out on 54 experimental plots. The N2 fixation pools were evaluated by abundance natural of 15N and the N accretion methods. The soil N content was of similar magnitude between species and stand densities. The species showed similar amounts of N in the biomass, but divergent patterns of N accumulation, as well as the 15N signature on the leaves. S. parahyba accumulated most N in the stem, while A. peregrina accumulated N in the roots and leaves. However, the N accumulation in biomass of A. peregrina stand was less constrained by environment than in S. parahyba stands. The percentage of N derived from N2 fixation in A. peregrina stands decreased with the increase of stand density. The biological N2 fixation estimates depended on the method and the response of tree species to environment.

Highlights

The expansion of forest restoration is expected for this decade in tropical regions as one important way to improve many ecosystem services [1,2]
The Atlantic Forest biome has experienced an increase in forest cover, with the new land-cover map revealing the cover of 28% of native vegetation [3], 12–17% higher than the previously available estimates [4]
This study aimed to quantify the N accumulated in the biomass and topsoil of monocultures of Anadenanthera peregrina (L.) Speg. var. peregrina and Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby grown under three stand densities (625, 1111, and 1666 trees ha−1), and to estimate the percentage of N derived from biological N2 fixation for A. peregrina using the 15N natural abundance and the N accretions methods

Summary

Introduction

The expansion of forest restoration is expected for this decade in tropical regions as one important way to improve many ecosystem services [1,2]. In addition to socioeconomic drivers, such as farm credit and economic development, part of this expansion was attributed to Atlantic Forest remnants, and the vicinity of eucalyptus plantations [5]. The choice of the tree stand density is a relevant question that directly affects biomass and nutrient accumulation. As pointed out by some authors [13], the fast-slow plant economics spectrum predicts that faster-growing species has a large biomass accumulation rate per individual trees, and nutrient uptake and water consumption (high-rate acquisition resources), while the resistance to environmental stress is in general higher from slow-growing species (with higher tissue density, long tissue lifespan and lower rates of resource acquisition) [13]

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Discussion

Conclusion