Isotopic view of vegetation and carbon and nitrogen cycles in a cerrado ecosystem, southeastern Brazil

Abstract

Carbon and nitrogen biogeochemical cycles in savannas are strongly regulated by the seasonal distribution of precipitation and pulses of nutrients released during the wetting of the dry soil and are critical to the dynamics of microorganisms and vegetation. The objective of this study was to investigate the spatial and temporal variability of C and N isotope ratios as indicators of the cycling of these elements in a cerrado sensu stricto area, within a protected area in a State Park in the state of São Paulo, Brazil. The foliar δ 13 C and δ 15 N values varied from -33.6 to -24.4 ‰ and -2.5 to 4.5 ‰, respectively. The δ 13 C values showed a consistent relationship with canopy height, revealing the importance of structure of the canopy over the C isotopic signature of the vegetation. Carbon isotopic variations associated with the length of the dry season indicated the importance of recent fixed C to the integrated isotopic signature of the leaf organic C. The studied Cerrado species showed a depleted foliar δ 15 N, but a wide range of foliar Nitrogen with no difference among canopy heights. However, seasonal variability was observed, with foliar δ 15 N values being higher in the transition period between dry and rainy seasons. The variation of the foliar C and N isotope ratios presented here was consistent with highly diverse vegetation with high energy available but low availability of water and N. Key words: cerrado, carbon, nitrogen, stable isotopes, woody savanna VISÃO ISOTÓPICA DA VEGETAÇÃO E OS CICLOS DO CARBONO E NITROGÊNIO NUM ECOSSISTEMA DE CERRADO, SUDESTE DO BRASILRESUMO: Os ciclos biogeoquímicos do carbono e do nitrogênio em savanas são fortemente regulados pela distribuição sazonal de precipitação e pulsos de nutrientes liberados após eventos de chuva, que são críticos para o comportamento dos microrganismos e da vegetação. Investigou-se a variabilidade espacial e sazonal dos isótopos estáveis de C e N como indicadores da ciclagem destes elementos em uma área de cerrado sensu stricto de uma área protegida em um Parque Estadual no estado de São Paulo, Brasil. Os valores de δ 13 C e δ 15 N foliar variaram de -33,6 a -24,4 ‰ e -2,5 a 4,5 ‰, respectivamente. Os valores de δ 13 C apresentaram uma relação consistente com a altura do dossel, mostrando a importância da estrutura da vegetação na assinatura isotópica do C da vegetação. A variação isotópica do Carbono associada com a duração da estação seca indica a importância do C recentemente fixado para integrar a assinatura isotópica do C orgânico da folha.

Functional differences between woodland savannas and seasonally dry forests from south-eastern Brazil: Evidence from 15N natural abundance studies

“…Consistent with previous studies in several ecosystems with contrasting N availability, we found a large range of leaf d 15 N values in both cerradão and SDF sites (Michelsen et al 1996;Nadelhoffer et al 1996;Bustamante et al 2004;Ometto et al 2006;Coletta et al 2009). The N-poor cerradão site had a larger range of leaf d 15 N values in comparison to the SDF; however, this difference seems very small (1.6‰) to characterize a higher diversity of N use strategies in the N-poor cerradão site.…”

“…Moreover, plants associated with mycorrhizal fungi tend to have lower d 15 N values than nonmycorrhizal plants, mainly because discrimination against 15 N occurs during fungal N assimilation (Högberg et al 1996;Hobbie et al 2000). Legume trees, which might obtain substantial amounts of their N inputs by association with N-fixing bacteria, tend to present higher leaf N concentration relative to nonlegumes (Vitousek et al 2002;Bustamante et al 2004;Bai et al 2009;Coletta et al 2009). In addition, legumes would presumably have d 15 N values between 0 and 2‰ (Högberg 1997), because there is no isotopic discrimination during biological fixation of atmospheric N2, which has a d 15 N of near 0‰ (see Dawson et al 2002).…”

Declining foliar and litter δ15N diverge from soil, epiphyte and input δ15N along a 120 000 yr temperate rainforest chronosequence

“…Samples were filtered (0.45 lm) immediately and frozen from £ 6 h after collection until they were chemically and isotopically analyzed. Our sampling design does not allow us to capture seasonal or within-canopy variation in d 15 N. However, our main trends are much larger than observed seasonal changes in other systemstypically 1-2‰ at most (Ometto et al, 2006;Coletta et al, 2009;Bragazza et al, 2010) -and within-canopy variation reported elsewhere (Bergstrom & Tweedie, 1998) is negligible.…”

Vegetation and soil carbon‐13 isoscapes for South America: integrating remote sensing and ecosystem isotope measurements

“…13 C measurements contribute to our understanding of plant ecophysiology, e.g., how plants respond to water stress or differences in light availability, as well as canopy-level CO 2 gradients and exchanges (Buchmann et al 1996, Buchmann et al 1997, Dawson et al 2002, Coletta et al 2009). At continental and global scales, d…”