Age-related changes in nitrogen resorption and use efficiency in the perennial new crop Physaria mendocina (Brassicaceae)

Domestication of desert-adapted species and their development into perennial crops has been proposed as an alternative to increase cropping intensity in arid lands, while reducing nitrogen inputs and losses. Among traits involved in nitrogen conservation much attention has been drawn to resorption patterns. However, understanding of intra-population variability in resorption and nitrogen use efficiency is required prior to the development of new crops. Here we evaluate age-related changes in resorption patterns and nitrogen use efficiency (NUE) within a wild population of Physaria mendocina (Brassicaceae). We generated a relative age index, based on morphological traits, and we use it as an independent variable to regress nitrogen concentrations in roots and leaves (green and senesced), nitrogen resorption efficiency and use efficiency. Nitrogen in green and senesced leaves decrease with age, resorption efficiency did not change, and nitrogen use efficiency increased. The lower nitrogen concentration in green leaves and higher proficiency (lower nitrogen concentrations in senesced leaves) of older plants might be due to a decrease in acquisition capacity. Constant efficiency is explained by the lack of differences in concentration in green and senesced leaves slopes. Higher proficiency in older plants resulted in higher NUE; this relationship would be modulated by nitrogen concentration in green leaves, which, in turn, is controlled by nitrogen availability and acquisition. These findings have implications in the domestication process, since in perennial species biomass production and internal plant nitrogen turnover over multiple seasons, are central key to physiological functions such as plant re-growth and winter survival. We identified a few questions as directions for future research.