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

Author(s)

Rafael Costa Pinheiro

• Document type: Doctoral Thesis
• Press: Botucatu. 2020-06-01.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agronômicas. Botucatu
• Defense date: 2019-04-02
• Advisor: Jean Paul Laclau; Iraê Amaral Guerrini

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 the dynamics of water and nitrate uptake by the rootsthat explain the tree behaviour under extreme drought. This study aimed to assess the maximum distance of the trunk and the maximum depth of nutrient and water uptake by tree roots in forests growing on very deep Ferralic Arenosols through 15N tracer. The consequences of the social status of trees, comparing dominant and suppressed trees of the same genotype in a monoclonal forest, were studied in plantations of the same clone of the Eucalyptus urophylla x Eucalyptus grandis hybrid over the dry season. The effects of seasonality (comparing dry and rainy seasons) were studied in three native savanna (Cerrado) species: i) Xylopia aromatica (Lam.) Mart.; ii) Coussarea hydrangeifolia (Benth.) Müll.Arg.; and iii) Miconia albicans (Sw.) Steud,. Furthermore, the existence of a niche complementarity in the soil among the three studied Cerrado species was evaluated, with the analysis of the tracer uptake in different soil layers, depending on the species. The NO3--15N tracer was applied in 7-month-old, 1.2-year-old, 2.2-year-old and 6.4-year-old eucalypt stands at several soil depths, with three repetitions per depth at 60 positions. In the Cerrado, NO3--15N tracer was applied at 36 positions: 2 seasons (dry and rainy), 6 depths (down to 12 m) and 3 repetitions. All the plots were allocated at a distance > 50 m between them. The tracer was applied at only one location in the centre of each plot. Five months after tracer application, 15N was determined from the δ15N values in leaves sampled in dominant and supressed trees at different distances from each injection area. The results show that fertilizers must be applied close to the trunks (within 2 m) in Eucalyptus plantations to be taken up by all trees, regardless of stand age and tree social status. Fertilization (and weed control) in half of the inter-rows during the rainy season could be sufficient to make it possible for all the trees to take up the applied nutrients which could reduce the cost of a conventional commercial fertilization., Nitrates leached in deep sandy soils can be taken up by tree roots at a depth of 6 m between 0.6 and 2.5 years after planting in commercial Eucalyptus plantations. However, the velocity of exploration of deep soil layers depends on the social status of the trees. The labelled nitrates were taken up at different depths and distances from the trunk depending on the species in the Brazilian savanna studied, which showed a niche complementarity throughout the soil profile down to a depth of at least 6 m. Only trees with a DBH of more than 5 cm were able to take up the NO3--15N tracer injected at depths of more than 1.5 m. Unexpectedly, trees did not take up the labelled nitrates more deeply in the dry season than in the rainy season. (AU)

• FAPESP's process: 15/25946-0 - Maximum distance evaluation of nutrient uptake in tropical forest formations using 15N as tracer
• Grantee: Rafael Costa Pinheiro
• Support Opportunities: Scholarships in Brazil - Doctorate