Environmental and species-specific controls on δ13C and δ15N in dominant woody plants from central-western Argentinian drylands

Abstract

Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ13C) in photosynthetic tissues of C3 plants is an indicator of time-integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ15N) is an indicator of the main source of plant N (soil N vs. atmospheric N2). Previous studies in drylands have documented that plant δ13C and δ15N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in 15N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ13C, δ15N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central-western Argentinian drylands. Noticeably, plant δ13C and δ15N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ13C and δ15N. The short-term environmental conditions may interact with species-specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ13C and δ15N widely reported in drylands.