The genetic architecture of leaf stable carbon isotope composition in Zea mays and the effect of transpiration efficiency on leaf elemental accumulation

With increased demand on freshwater resources for agriculture, it is imperative that more water-use efficient crops are developed. Leaf stable carbon isotope composition, d¹³C, is a proxy for transpiration efficiency and a possible tool for breeders, but the underlying mechanisms effecting d¹³C in C₄ plants are not known. It has been suggested that differences in specific leaf area (SLA), which potentially reflects variation in internal CO₂ diffusion, can impact leaf d¹³C. Furthermore, although it is known that water movement is important for elemental uptake, it is not clear how manipulation of transpiration for increased water-use efficiency may impact nutrient accumulation. Here, we characterize the genetic architecture of leaf d¹³C and test its relationship to SLA and the ionome in five populations of maize. Five significant QTL for leaf d¹³C were identified, including novel QTL as well as some that were identified previously in maize kernels. One of the QTL regions contains an Erecta-like gene, the ortholog of which has been shown to regulate transpiration efficiency and leaf d¹³C in Arabidopsis. QTL for d¹³C were located in the same general chromosome region, but slightly shifted, when comparing data from two different years. Our data does not support a relationship between d¹³C and SLA, and of the 19 elements analyzed, only a weak correlation between molybdenum and d¹³C was detected. Together these data add to the genetic understanding of leaf d¹³C in maize and suggest that improvements to plant water use may be possible without significantly influencing elemental homeostasis.