Leaf Traits of Orchids in Relation to Life Form in Karst Area of Southwestern China Variation in relationships between SLA and Leaf C, N, P stoichiometry in Machilus pauhoi among locations Response of foliar δ13C of Quercus spinosa to altitudinal gradients Effects of nitrogen and phosphorus fertilization on leaf carbon, nitrogen and phosphorus stoichiometry of Arabidopsis thaliana