Foliar Nitrogen Dynamics and Nitrogen Resorption of a Sandy Shrub Salix gordejevii in Northern China

Resorption of nitrogen (N) from senescing leaves is an important conservation mechanism that allows plants to use the same N repeatedly. Seasonal variations in leaf nitrogen of mature green and senescing leaves and N resorption in Salix gordejevii Chang, a sandy shrub in northern China, were studied. Our objective was to compare N resorption of this Salix species that successfully occupy different habitats (shifting sandland, fixed sandland and lowland) with differences in soil N availability and moisture. Nitrogen concentrations in green and senescing leaves were higher in June and July. N resorption efficiency (percentage reduction of N between green and senescing leaves) was highest at shifting sandland, intermediate at fixed sandland, and lowest at lowland. There was a clear seasonal variation in N-resorption efficiency, with a lower value at the early growing season and a higher value during summer. N resorption efficiency was lower at the sites with higher soil N availability, suggesting that the efficiency of the resorption process is determined by the availability of the nutrient in the soil. Resorption from senescing leaves may play an important role in the nitrogen dynamics of sandy plants and reduce the nitrogen requirements for plant growth. We conclude that N resorption from senescing leaves in S. gordejevii was correlated to soil characteristics and higher N resorption on poor soils is a phenotypic adjustment by this species to maximize N-use at low availability.