Apple Δ13C Discrimination Is Related to Shoot Ash Content

Plant ash content has been highly correlated with plant water use efficiency (WUE) and Delta C-13 (Delta) in field crops and grassland species and proposed as a selection criteria for WUE. delta O-18 (delta) has also been correlated with transpiration in herbaceous plants. The objectives of the study were to 1) evaluate the relationship of shoot ash (ASH) with Delta and delta in 'Empire' apple over a 3-year period; 2) determine if yearly variation significantly affected the relationship of ASH with Delta and delta; and 3) evaluate the value of the relationship between ASH content with Delta and delta for a population of Mains sieversii. 'Empire' leaf area index (LAI) was negatively correlated with ASH content and positively correlated with Delta. Delta was negatively correlated with 'Empire' ASH. There were no yearly effects at a site. Within the Malus sieversii accessions, there was a grouping based on ASH that could be identified and this outlier group also had the lowest delta of the accessions. There were no correlations of leaf area, number, length, width, or stomata number with delta, Delta, or ASH for the Malus sieversii accessions. Rather than a substitute for Delta measurement in assessing WUE, ash content analysis adds an additional dimension to understanding the dynamics of WUE in apple. This work has identified a unique population of Malus meriting further study.