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

Freitas, Ana Dolores Santiago de; Sampaio, Everardo Valadares de Sá Barretto; Ramos, Andresa Priscila de Souza; Barbosa, Maria Regina de Vasconcellos; Lyra, R. P.; Araújo, Elcida de Lima

doi:10.1007/s11104-015-2417-5

Cited by 27 publications

(20 citation statements)

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“…4a) agree well with the range of data reported from earlier investigations in the same study region (Amundson et al, 2003;Zech et al, 2011), but with our study involving more ecosystems, replicate sites, and a far larger spatial sampling domain. Overall, the δ 15 N values for montane tropical forest ecosystems in Mount Kilimanjaro are considerably lower than the mean values reported for a broad variety of tropical lowland forests worldwide (soil values ranging from 3 ‰ to 14 ‰; de Freitas et al, 2015;Martinelli et al, 1999;Nardoto et al, 2014;Piccolo et al, 1996;Sotta et al, 2008). Rather, the δ 15 N values observed in the montane forests investigated are in the same range of temperate forest ecosystems reported in a comprehensive literature review by Martinelli et al (1999).…”

Section: Variation Of δ 15 N Values Along the Elevational And Land-usmentioning

confidence: 51%

“…This may be due to the C limitation of heterotrophic microbial N retention under low C/N ratios (Butterbach-Bahl and Dannenmann, 2012). However, nitrate leaching is quite a relevant process that discriminates only slightly against 15 N (Denk et al, 2017), which may confound the interpretation of soil δ 15 N values. Indeed, Gütlein et al (2018) have recently shown that nitrate leaching may be quite significant in Mount Kilimanjaro's semi-natural forests.…”

Section: Factors Controlling Soil δ 15 N Along the Elevational And Lamentioning

confidence: 99%

“…atmospheric deposition and fertilizer additions) prevent substantial gaseous and/or leaching N losses. In contrast, open ecosystem N cycling is characterized by significant inputs and losses of N. On the one hand, gaseous N losses from soils are strongly depleted in 15 N due to the high fractionation factors associated with these processes (Denk et al, 2017). This results in high δ 15 N values of the residual substrate, which consequently leaves less importance to impacts of external N additions (Robinson, 2001;Zech et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

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Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania

et al. 2019

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Abstract. Variations in the stable isotopic composition of carbon (δ13C) and nitrogen (δ15N) of fresh leaves, litter, and topsoils were used to characterize soil organic matter dynamics of 12 tropical ecosystems in the Mount Kilimanjaro region, Tanzania. We studied a total of 60 sites distributed along five individual elevational transects (860–4550 m a.s.l.), which define a strong climatic and land-use gradient encompassing semi-natural and managed ecosystems. The combined effects of contrasting environmental conditions, vegetation, soil, and management practices had a strong impact on the δ13C and δ15N values observed in the different ecosystems. The relative abundance of C3 and C4 plants greatly determined the δ13C of a given ecosystem. In contrast, δ15N values were largely controlled by land-use intensification and climatic conditions. The large δ13C enrichment factors (δ13Clitter − δ13Csoil) and low soil C∕N ratios observed in managed and disturbed systems agree well with the notion of altered SOM dynamics. Besides the systematic removal of the plant biomass characteristic of agricultural systems, annual litterfall patterns may also explain the comparatively lower contents of C and N observed in the topsoils of these intensively managed sites. Both δ15N values and calculated δ15N-based enrichment factors (δ15Nlitter − δ15Nsoil) suggest the tightest nitrogen cycling at high-elevation (> 3000 m a.s.l.) ecosystems and more open nitrogen cycling both in grass-dominated and intensively managed cropping systems. However, claims about the nature of the N cycle (i.e. open or closed) should not be made solely on the basis of soil δ15N as other processes that barely discriminate against 15N (i.e. soil nitrate leaching) have been shown to be quite significant in Mount Kilimanjaro's forest ecosystems. The negative correlation of δ15N values with soil nitrogen content and the positive correlation with mean annual temperature suggest reduced mineralization rates and thus limited nitrogen availability, at least in high-elevation ecosystems. By contrast, intensively managed systems are characterized by lower soil nitrogen contents and warmer conditions, leading together with nitrogen fertilizer inputs to lower nitrogen retention and thus significantly higher soil δ15N values. A simple function driven by soil nitrogen content and mean annual temperature explained 68 % of the variability in soil δ15N values across all sites. Based on our results, we suggest that in addition to land-use intensification, increasing temperatures in a changing climate may promote soil carbon and nitrogen losses, thus altering the otherwise stable soil organic matter dynamics of Mount Kilimanjaro's forest ecosystems.

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Section: Variation Of δ 15 N Values Along the Elevational And Land-usmentioning

confidence: 51%

Section: Factors Controlling Soil δ 15 N Along the Elevational And Lamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania

et al. 2019

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“…No Semiárido brasileiro, as plantas que não se associam com bactérias diazotróficas (não fixadoras) apresentam valores de δ 15 N altos e pouco variáveis dentro de um mesmo local, tanto espacialmente quanto entre espécies (Freitas et al, 2010a). Este padrão isotópico não é encontrado em outros ambientes do Nordeste (Freitas et al, 2015) e é ideal para estudos da FBN, facilitando a seleção de plantas referência e os procedimentos de amostragem.…”

Section: Técnica Da Abundância Natural Do 15 N Para Estimativa Da Fbnunclassified

Biological nitrogen fixation in the Brazilian Semiarid

Freitas

Sampaio²,

Santos³

et al. 2015

Revista Brasileira De Geografia Física

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A fixação biológica de nitrogênio (FBN) é a principal forma de entrada de N em ecossistemas naturais e em sistemas agrícolas de subsistência, como os praticados predominantemente no Semiárido brasileiro. Estimativas dos aportes de N na Caatinga e em cultivos de importância para a região ainda são escassas, em parte pela dificuldade de medir simultaneamente as proporções de N derivadas da atmosfera (%Ndda) e as produções de biomassa no mesmo sistema. Estudos pioneiros indicam que diversas espécies de leguminosas, herbáceas e arbóreas, nativas e/ou cultivadas, podem fixar elevadas proporções de seu N. Em Caatinga bem preservada, os aportes de N em leguminosas arbóreas foram estimados em 11 kg ha-1 ano-1 , um valor relativamente baixo devido à baixa densidade de plantas fixadoras. Entretanto, a densidade de leguminosas fixadoras na vegetação não é o único fator definindo o aporte de N, pois há observações de ausência de FBN em áreas de Caatinga em regeneração, dominadas por espécies fixadoras. No estrato herbáceo, os aportes de N podem chegar a 6 kg ha-1 ano-1 , nas áreas com menor cobertura de arbóreas. As quantidades de N fixadas nos diferentes sistemas de cultivo são pouco conhecidas. Para o feijão-caupi, a FBN pode se aproximar dos 30 kg ha-1 , em cultivos consorciados com milho, chegando a 45 kg ha-1 , em cultivos solteiros. Em cultivos irrigados, adubos verdes podem adicionar 185 kg ha-1 , superando a quantidade exportada nas colheitas. Em sistemas agroflorestais, a adição anual de N pode chegar a 40 kg ha-1. Não existem estimativas do N fixado em gramíneas na região, mas algumas espécies apresentem potencial de FBN. Palavras-chave: abundância natural do N-15, agricultura de corte e queima, micro-organismo diazotróficos, rizóbios, simbiose. Biological nitrogen fixation in the Brazilian Semiarid A B S T R A C T Biological nitrogen fixation (BNF) is the main N input in natural ecosystems and in subsistence agricultural systems, such as those commonly practiced in the Brazilian semiarid region. Estimates of N inputs in Caatinga and the main regional crops are still scarce, partly due to the difficulty in measuring concomitantly the proportion of plant N derived from the atmosphere (%Ndfa) and the amount of biomass produced in the same system. Pioneer studies indicate that several legume species, herbs and trees, native and/or cultivated, can fix large proportions of their N. In mature Caatinga, N inputs in tree legumes were estimated at 11 kg ha-1 year-1 , a relatively low value due to the low plant density of the legume species. However, plant density is not the only factor defining N input, since absence of fixation has been reported in regenerating Caatinga, even in those dominated by potentially fixing species. In the herb stratum, N input up to 6 kg ha-1 year-1 has been reported in areas with lower tree cover. Inputs in crop systems are largely unknown. Fixation in cowpea can reach 30 kg ha-1 , in plants consortiated with corn, and 45 kg ha-1 , in single crop. Under irrigation, green manure crops can add 185...

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“…Among all native plants from Caatinga, legume (Fabaceae) is the most abundant family with 86 genus and more than 320 species (Queiroz, 2009). Several of these species is able to associate symbiotically with a wide range of indigenous nitrogen fixing bacteria (collectively called of rhizobia) (Reis Júnior et al, 2010;Teixera et al, 2010;Freitas et al, 2014;Freitas et al, 2015) and these associations can be exploited to increase success of the seedlings establishment in the field.…”

Section: Introductionmentioning

confidence: 99%

Seedling development of nodulating and non-nodulating native legumes in soils from Brazilian Caatinga biome

et al. 2015

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This study aimed to evaluate the initial development of the nodulating legumes jurema-rosa (Mimosa verrucosa Benth.) and angico [Anadenanthera colubrina (Vell.) Brenan] and the non-nodulating legumes umburana-de-cheiro [Amburana cearensis (Allemao) A.C. Smith] and caatingueira-verdadeira [Poincianella pyramidalis (Tul.) L.P. Queiroz]. Plants were grown in pots containing soil samples from six areas in Brazilian Caatinga biome region. Differences at the nodulation in plant roots were observed among the soils studied, pointing out a Vertisol covered by an introduced legume. The leaf gas exchange evaluations also showed differences among the plants grown in the different soils used as substrate mainly to angico and caatingueira-verdadeira.

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

Cited by 27 publications

References 50 publications

Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania

Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania

Biological nitrogen fixation in the Brazilian Semiarid

Seedling development of nodulating and non-nodulating native legumes in soils from Brazilian Caatinga biome

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