[Leaf nitrogen and phosphorus stoichiometry in typical desert and desertified regions, north China]

Characteristics of leaf nitrogen and phosphorus stoichiometry at regional scale is key factors to understand spatial pattern, forecast change trends and reveal responses of terrestrial ecosystem to global change. In this study, pattern of leaf nitrogen and phosphorus of 214 plants was investigated to elucidate their relationships with rainfall and temperature in typical desert and desertified regions of northern China. The results showed that average leaf nitrogen concentration, average leaf phosphorus concentrations, and leaf N/P of 214 species are (24.45 +/- 8.1) mg/g, (1.74 +/- 0. 88) mg/g, 15.77 +/- 7.5 in these regions of northern China, respectively. Compared with other studies at global, national or regional scale, leaf nitrogen and phosphorus concentrations are significantly higher in this study (p < 0.001). However, leaf N/P didn't show any significant differences with other studies. This implies that leaf N/P is generally well-constrained. One-way ANOVA analysis showed that leaf N, P, and N/P varied significantly among trees, shrubs, graminoids, and forbs. Leaf N concentration in shrubs, forbs and leaf P concentration in forbs are averagely higher than those in other life-forms, respectively. This implies that nutrient use strategies are significantly different among plant life-forms. There are no significant differences in leaf nitrogen concentration among each typically desert and desertified region. However, Leaf phosphorus concentration and leaf N/P are significantly different among each typically desert and desertified regions. Leaf phosphorus concentrations are relatively high in Kerqin Sand Land and Mowuso Sand Land. Leaf N/P of most species in Talimu basin, Zhunger Basin, and Alashan is higher than 16, and lower than 14 of most species in Kerqin Sand land. This means that nutrient constraining in different regions varies greatly. Correlations analysis showed that leaf N, P, and N/P are significantly correlated with annual precipitation, but not significantly correlated with annual mean temperature in desert and desertified regions of northern China.