Peanut genotypic variation in transpiration efficiency and decreased transpiration during progressive soil drying

Peanut (Arachis hypogaea L.) is commonly grown on sandy soils in warm climates where water-deficit can impose a limitation on yield. Identification of plant traits related to increased productivity under water-deficit conditions could be used to increase yields in these water-limited environments. Two traits were examined among 17 peanut genotypes. Transpiration efficiency (TE), ratio of mass increase to water transpired, was the first trait examined. TE was measured both under well-watered conditions (greenhouse) and soil drying (outdoors in pots) conditions. Virtually no difference was observed in TE among genotypes under well-watered conditions indicating the gas exchange properties were similar. However, under soil drying conditions there were substantial differences among genotypes. These results indicated that TE with drying soil might interact with traits associated with water loss on drying soils. Therefore, the second trait examined in this study was the fraction transpirable soil water (FTSW) content at which the decline in transpiration with soil drying was observed. This greenhouse experiment showed large variability among the 17 genotypes. A second-order polynomial described the relationship between TE under soil drying conditions and the threshold for the decline in transpiration. The FTSW for maximum TE was 0.55, but this value is expected to depend on the environmental conditions to which the plants influence TE.