Abstract:We studied Pinus elliottii, Casuarina equisetifolia, Eucalyptus urophylla × E. grandis, Acacia cunninghamia and A. aulacocarpa plantations in the coastal sandy land of Fuzhou City, measured their water use efficiency by stable carbon isotope method, and explored water use efficiency (WUE), nitrogen (N) and phosphorus (P) status of foliar as well as their relationships. The results showed that:(1)There were significant differences in foliar δ13C between P. elliottii and E. urophylla × E. grandis, A. cunninghamia and E. urophylla × E. grandis (P<0.05). However, there was no significant difference in foliar δ13C among P. elliottii, C. equisetifolia, A. cunninghamia and A. aulacocarpa. The foliar δ15N of A. cunninghamia and A. aulacocarpa were significantly higher than those of P. elliottii, C. equisetifolia and E. urophylla × E. grandis.(2)WUE varied with different tree species in the order of P. elliottii>A. cunninghamia>C. equisetifolia>A. aulacocarpa>E. urophylla × E. grandis. The WUE of foliar of P. elliottii was significantly higher than that of E. urophylla × E. grandis 36.87%, but there was no significant difference in water use efficiency between P. elliottii and other species.(3)The foliar N concentration of each species in turn was A. cunninghamia>A. aulacocarpa>E. urophylla × E. grandis>C. equisetifolia>P. elliottii. There was a significant difference between A. cunninghamia and P. elliottii, A. aulacocarpa and P. elliottii. The foliar P concentration of each species in turn was E. urophylla × E. grandis>A. cunninghamia>A. aulacocarpa>P. elliottii>C. equisetifolia. There was a significant difference between E. urophylla × E. grandis and P. elliottii, E. urophylla × E. grandis and C. equisetifolia, E. urophylla × E. grandis and A. aulacocarpa. The foliar N/P of C. equisetifolia and A. aulacocarpa was significantly higher than that of E. urophylla × E. grandis. There was no significant difference in foliar N/P among the other tree species.(4)The foliar δ13C showed a significant seconddegree parabola correlation with the foliar N concentration. The foliar δ15N was extremely significantly positively correlated with the foliar N concentration(P< 0.01). The study found that there was a significant difference among WUE, foliar N concentration, foliar P concentration, and N/P. In addition, WUE had significantly negative correlation with foliar N concentration and foliar P concentration. The foliar N and foliar P concentration would be key factors affecting WUE in coastal shelterbelt tree species in coastal sandy land.