¹³C Natural Abundance in Plant Communities Along a Rainfall Gradient: a Biological Integrator of Water Availability

Abstract

Carbon isotope natural abundance (δ¹³C) has been previously used as a powerful tool in the study of water-using processes at the leaf, individual and within-community levels. We analysed 348 species from 12 plant communities along a 900 km-long rainfall gradient in southern Queensland. Although the range of δ¹³C values found in a given community was large, variability in the δ¹³C signature of plants within a community was relatively small given the large numbers of species sampled (mean n per site of 29) and the taxonomic diversity in each. The community-averaged δ¹³C signature ranged from -25.60 in a brigalow (Acacia harpophylla) dominated community in western Queensland to - 31.20 in subtropical rainforest in eastern Queensland. A strong relationship was found between the δ¹³C value averaged for each site and rainfall within the range 350-1700 mm per annum. Foliar δ¹³C was also related to the number of rain days per annum and moisture balance (rainfall - evaporation). The strength of these relationships varied only slightly according to the rainfall parameter used, with values for r² of 0.78, 0.70, 0.70 and 0.74 for the relationship between δ¹³C and long-term rainfall average, 5-year rainfall average, number of rain days and moisture balance, respectively. Despite considerable taxonomic variability within a given plant community, the averaged δ¹³C signature for that community gives a strong indication of moisture availability.