Soil salinity determines the relative abundance of C3/C4 species in argentinean grasslands

FELDMAN, S.R.; BISARO, V.; BIANI, N.B.; PRADO, D.E.

Global Ecology and Biogeography

Blackwell Publishing

Lugar: Hoboken, New Jersey; Año: 2008 vol. 17 p. 708 - 714

1466-822X

1. Aim: The C4+CAM pathways are adaptations to compensate high rates of photorespiration and water and carbon deficiency. This is the first attempt to compare the relative abundance of C3 vs. C4+CAM species in temperate and subtropical grasslands across a latitudinal gradient in central Argentina. We predict that under the same rainfall regime C4+CAM plants will have larger soil coverage in highly saline soils than in neighboring non-saline ones. 2. Location: Data were taken from three phytogeographical provinces in the Santa Fe province of Argentina: Chaquenian, Pampean and Espinal. 3. Methods: The salinity of the soil was estimated through the aqueous solution conductivity. The proportions of species belonging to C3/C4+CAM photosynthetic pathways were compared among halophyte and non- halophyte communities with a 2 homogeneity test. The sum of cover percentages corresponding to the C3 and C4+CAM photosynthetic pathways were calculated and compared using ANOVA. 4. Results: The soil conductivity values were higher in the halophyte than in the non-halophyte communities for the same phytogeographical area. The C4+CAM plants had much higher soil coverage values in halophyte than in non-halophyte communities in the Pampean and Espinal phytogeographical provinces. The differences were not statistically significant in the Chaquenian province. 5. Main conclusions: The soil drought provoked by the soil salinity results in a much higher soil cover by C4+CAM plants in regions with positive to neutral water balance (i.e.: Pampean and Espinal). This differential abundance pattern in C4+CAM functional group is not observed in areas where a pronounced water-deficit exists per se (Chaquenian region), and therefore C4+CAM predominate in all environments regardless of soil salinity. Our results suggest that probably one of the main environmental forces driving the C4 species upsurge in Argentinean grasslands might have been the strong local soil salinity gradient. 6. Keywords: C3. C4. Chaco. Cover-abundance. Espinal. Functional groups. Grasslands. Pampas. Photosynthetic pathways