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Photosynthetic pathway variation among C4 grasses along a precipitation gradient in Argentina

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Abstract Aim 

Based on the biochemical and physiological attributes of C4 grasses, and on the close association between decarboxylation pathways and the taxa in which they evolved, the hypotheses tested were: (1) that C4 grasses would become progressively more abundant as precipitation decreased, with grasses of the NADP-me subtype more abundant in wetter sites and those of the NAD-me subtype more common in arid regions; and (2) that the distribution of grass subfamilies would also be correlated with annual precipitation. Location 

The study was conducted along a precipitation gradient in central Argentina, from the eastern Pampas (>1000 mm year−1) to the western deserts and semi-deserts near the Andes (<100 mm year−1). Methods 

Percentage of species and relative cover of C3 and C4 grasses (including C4 subtypes) in local floras from 15 lowland sites of central Argentina were obtained from our own unpublished data and from recently published floristic surveys. Pearson correlation coefficients were obtained between grass distribution parameters and the available climatic data. Results 

The percentage of C4 grasses increased towards the arid extreme and showed a strong negative correlation with annual rainfall (r = −0.74, P <0.01). Within the C4 subtypes, the NADP-me species showed a higher proportional representation at the wetter extreme, whereas the representation of NAD-me species increased towards the more arid extreme. The relationship of PEP-ck species with climatic parameters in central Argentina was less evident. The distributions of the Panicoideae and Chloridoideae subfamilies along the precipitation gradient were diametrically opposed, with the Panicoideae positively (r =0.86, P <0.001) and the Chloridoideae negatively (r = −0.87, P <0.001) correlated with annual precipitation. Main conclusions 

Our data are consistent with the broad observation that C4 grasses tend to dominate in areas where the wet season falls in the warmer summer months. In agreement with previously reported results for Africa, Asia, Australia and North America, we describe here for the first time a significant relationship between annual precipitation and the prevalence of the NADP-me and NAD-me photosynthetic pathways along climatic gradients for the Neotropics. We also report for the first time that correlations between C4 species and annual rainfall are stronger when the relative cover of grass species is considered. The association of grass subfamilies Panicoideae and Chloridoideae with rainfall is as strong as that recorded for the NADP-me and NAD-me variants, respectively, suggesting that characteristics other than decarboxylation type may be responsible for the geographic patterns described in this study.

Keywords: C4 grasses; C4 photosynthesis; Central Argentina; Chloridoideae; NAD-me photosynthesis; NADP-me photosynthesis; PEP-ck photosynthesis; Panicoideae

Document Type: Research Article


Affiliations: 1: Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba, CC 5009, 5000 Córdoba, Argentina 2: Facultad de Agronomía y Veterinaria, Universidad Nacional de Río Cuarto, Ruta Nacional No. 36, KM 601, 5800 Río Cuarto, Córdoba, Argentina 3: Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, CC 14, 2123 Zavalla, Santa Fe, Argentina 4: Instituto Multidisciplinario de Biología Vegetal, Universidad Nacional de Córdoba – CONICET, CC 495, 5000 Córdoba, Argentina

Publication date: 2008-01-01

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