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

• Published in: Plant and soil Vol. 391; no. 1/2; pp. 109 - 122
• Main Authors: de Freitas, Ana Dolores Santiago, de Sá Barretto Sampaio, Everardo Valadares, de Souza Ramos, Andresa Priscila, de Vasconcellos Barbosa, Maria Regina, Lyra, Rosângela Pereira, Araújo, Elcida Lima
• Format: Journal Article
• Language: English
• Published: Cham Springer 01.06.2015; Springer International Publishing; Springer Nature B.V
• Subjects: Analysis; Biomedical and Life Sciences; Brazil; carbon; climate; Deciduous forests; Ecology; Ecosystems; Forest ecology; High temperature; Isotopes; leaves; legumes; Life Sciences; Nitrogen; nitrogen content; Nitrogen cycle; Plant Physiology; Plant Sciences; Plant-soil relationships; Rain; Rainfall; Rainforests; Regular Article; Savannahs; savannas; soil; Soil Science & Conservation; Surveys; temperature; Tropical forests; Brazil; ASW, Brazil; High temperature; Symbiotic nitrogen fixation; Soil and plant δ; N; N-15 depletion
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-015-2417-5

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 δ15N signals in Northeast Brazil. Methods Nitrogen, carbon and δ15N 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 δ15N concentrations decreased with higher rainfall (16 to 4‰). Plant δ15N was 1–3‰ lower than soil δ15N (Δδ15N) in all areas. Only in the deciduous forests, leaves of target species had significantly lower 15N signals than those of non-fixing species, allowing estimation of fixation. Conclusions In the perennial forests the low signals indicated that the 15N 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 Δδ15N than those reported in cooler areas and the absence of rainfall effect indicates that, when high, temperature overrides the rainfall effect.