Dynamic changes in leaf wax n-alkanes and δ13C during leaf development in winter wheat under varied irrigation experiments

Leaf wax n-alkanes serve as biomarkers that record environmental information with their carbon isotopic composition (delta C-13(alk)) recording water availability. Agricultural and paleoclimate applications would benefit from a greater understanding of how water shortages are recorded in delta C-13(alk) across the growing season, and controlled experiments can contribute to understanding as they constrain cause and effect, although they represent highly simplified versions of natural ecosystems. In this study, we use fieldgrown winter wheat (Triticum aestivum L.) under three water treatments (full irrigation, deficit irrigation and dry/rain-fed) to investigate the changes of flag (top) leaf traits including leaf mass per area, wax nalkanes and carbon composition of bulk leaf and n-alkanes (delta C-13(alk)) during leaf development. We find that leaf wax n-alkane synthesis ceases when the leaf reaches its maximum area (fully expanded) under dry conditions. However, fully expanded leaves can still increase their n-alkane concentrations by 42% and 70% under deficit and full irrigation, respectively. Total leaf wax n-alkane concentrations and delta C-13(alk) show no difference at leaf flush between rain-fed (dry) and deficit irrigation treatments, but delta C-13(alk) under full irrigation is more depleted as expected, with more pronounced offsets between the experiments developing during the growing season. delta C-13(alk) decreases logarithmically during leaf development perhaps indicating a shift from stored carbohydrate to fresh photosynthate and shoot growth related responses. Our results indicate that the water information at leaf flush is not `locked-in' to the delta C-13(alk) signal carried by the leaf wax n-alkanes. Instead, the first flush likely reflects the signal of stored carbohydrate more so than ambient environmental conditions. Total leaf wax n-alkane concentrations and delta C-13(alk) at the mature stage carry a more complete record of differences in water use efficiency experienced during the growing season. (C) 2020 Elsevier Ltd. All rights reserved.