Nutrient resorption responses to water and nitrogen amendment in semi-arid grassland of Inner Mongolia, China

Plant growth and ecosystem processes in semi-arid and arid areas are typically limited by nutrient and water availability. Alleviation of these resource stresses by future increases in reactive nitrogen and precipitation may affect internal plant nutrient cycling. The effect of increased nitrogen and water supply on foliar N and P concentrations, resorption efficiency and proficiency in four dominant species was studied in semi-arid grassland in northern China. Four treatments (Control, N addition, water addition and N plus water additions) were replicated in five 4 x 4 m plots per treatment. We found significant interspecific differences in leaf nutrient and resorption variables. N addition and water addition increased N concentration but had no effect on P concentration in green leaves. Both N addition and water addition reduced plant N resorption proficiency. N addition increased and water addition had no effect on P resorption proficiency. N addition and water addition decreased N resorption efficiency while increasing P resorption efficiency, but responses to N and water addition differed among species. N addition significantly interacted with water addition to affect N resorption efficiency and proficiency but did not affect that of P. These results suggest that species identity, N availability and water availability interact to affect plant nutrient resorption processes. Our analyses provide a better understanding of plant internal nutrient retranslocation in response to potential changes in nitrogen and water availability.