Stable isotope natural abundances (δ13C and δ15N) and carbon-water relations as drought stress mechanism response of taro (Colocasia esculenta L. Schott)

Taro (Colocasia esculenta L. Schott) is an important staple food crop in tropical and developing countries, having high water requirements. The purpose of this study was to evaluate the feasibility of using carbon and nitrogen isotopic composition (δ13C and δ15N) as a physiological indicator of taro response to drought, and elucidation of the relationship between the water use efficiency (WUE) under drought conditions and carbon isotope discrimination (Δ13C). As an alternative to WUE determination, obtained by measuring plant growth and water loss during an entire vegetative cycle, we have used Δ13C to determine the tolerance of C3 taro plants to drought. Seven taro accessions from Madeira, Canary Islands and the Secretariat of the Pacific Community (Fiji) collections were grown under greenhouse conditions and subjected to different watering regimes during a one-year cycle. Total plant biomass (TPB), WUE and δ15N were determined at the whole-plant level (WP). Corms and shoots were evaluated separately for nitrogen content (N), δ13C, Δ13C and δ15N. WUE showed positive correlation with TPB (r = 0.4) and negative with Δ13C (r = −0.3); Corm δ15N showed positive correlations with WP δ15N (r = 0.6) and corm N (r = 0.3). Accordingly, the taro plants with enhanced WUE exhibited low Δ13C and δ15N values as a physiological response to drought stress. The approach used in the present study has developed new tools that could be used in further research on taro response to environmental stresses.