Leaf stoichiometry and resorption of N and P in Lucerne at different growth stages under different water supplies

Drought affects not only nutrient cycling but also the internal cycling in the plant. We conducted a greenhouse experiment with lucerne at low, moderate and high soil water levels (LW, MW and HW). Green-leaf N:P (N:P-gr) decreased at squaring and flowering stages as water supply increased, while senesced-leaf N:P (N:P-sen) increased mostly. N:P-gr increased with the growth at LW and MW, while hardly changed at HW. N:P-sen increased and then decreased with the growth at LW and HW, but increased at MW. Water supply may affect soil N or P limitation in a growth stage-specific way. Water supply barely affected leaf N resorption of lucerne, while enhanced leaf P resorption. P resorption was positively correlated with soil P limitation, while there was no relationship of N resorption with N limitation. Therefore, increased water supply would lead to enhanced P resorption to ameliorate the restriction of soil P limitation to lucerne growth.