Experimental study of leaf wax n-alkane response in winter wheat cultivars to drought conditions

Leaf wax forms the boundary between plant leaf and atmosphere. The properties of the wax layer reflect physiological and biochemical adaptation and response to environmental stress, including drought. Agricultural field cropping experiments provide an intermediary between complex natural ecosystems and controlled laboratory growth experiments, routinely involving translocation of species, irrigation and the harvest of fully grown plants. Investigation of plant wax traits including leaf n-alkane chain length, total n-alkane concentrations, and compound specific carbon and hydrogen isotopic analyses of n-alkanes as well as bulk leaf carbon isotope response to environment in irrigated winter wheat (Triticum aestivum L.), a common agricultural monocot, provides a framework for drought-sensitivity tests for biomarker indices used to reconstruct paleoenvironments. We conducted field-growth studies of winter wheat, sampling flag leaves from ten cultivars under full and deficit irrigation (13 and 25% reduction in irrigation) in two regions of Texas, USA (Winter Garden, Uvalde and High Plains, Amarillo). We quantified leaf trait response to environment and isotopic evidence for water use efficiency (WUE) under different irrigation treatments and between sites. Leaf mass per area, bulk leaf δ13C values, leaf wax n-alkane concentration and δ13C values were responsive to irrigation treatment and environmental variables, whereas leaf wax n-alkane δD values were relatively insensitive. We found around 50% higher n-alkane concentration at the higher and drier site (Amarillo), leading us to suggest that crop breeding may want to select for high n-alkane concentration for drought-adaptation. Bulk leaf and leaf wax n-alkane δ13C analyses yielded broadly similar insights for plant WUE, however the value of n-alkane δ13C analyses is towards understanding past drought conditions as recorded by these biomarkers in soils. Our two-location, field-growth experiments tested the drought responsiveness of leaf wax properties in winter wheat, which is an extensive part of the human-modified ecosystem and thus of modern input to soils and sediments.