Nitrogen isotopic patterns in tropical forests along a rainfall gradient in Northeast Brazil

作者：Santiago de Freitas Ana Dolores; de Sa Barretto Sampaio Everardo Valadares; de Souza Ramos Andresa Priscila; de Vasconcellos Barbosa Maria Regina; Lyra Rosangela Pereira; Araujo Elcida Lima

来源：Plant and Soil, 2015, 391(1-2): 109-122.

DOI：10.1007/s11104-015-2417-5

• N-15 depletion
• Soil and plant delta N-15
• High temperature
• Symbiotic nitrogen fixation

Background and aims The interpretation of ecosystem nitrogen isotopic patterns is subject to controversies since there are few surveys of signals along climate gradients within the same region. We determined the effects of a rainfall gradient, under high temperatures, on the soil and plant delta N-15 signals in Northeast Brazil.
Methods Nitrogen, carbon and delta N-15 signals were determined from coastal perennial to subhumid and semiarid deciduous forests to savanna - deciduous forest transition.
Results Soil C and N concentrations were linearly related and both related quadratically with mean annual rainfall while delta N-15 concentrations decreased with higher rainfall (16 to 4%). Plant delta N-15 was 1-3% lower than soil delta N-15 (Delta delta N-15) in all areas. Only in the deciduous forests, leaves of target species had significantly lower N-15 signals than those of non-fixing species, allowing estimation of fixation.
Conclusions In the perennial forests the low signals indicated that the N-15 natural abundance method was not suitable to estimate fixation, while in the savanna - deciduous forest transition, high signals indicated that the legume species were not fixing. The smaller Delta delta N-15 than those reported in cooler areas and the absence of rainfall effect indicates that, when high, temperature overrides the rainfall effect.

• 出版日期2015-6