Effects of ecological restoration on stoichiometric characteristics and nutrient resorption efficiency of Pinus massoniana foliage

Carbon( C),nitrogen( N),and phosphorus( P) content are important indexes for forest management that respond positively to environmental conditions. In recent years,stoichiometry has received considerable attention. However,few studies have reported the patterns of soil-plant stoichiometry and nutrient resorption during ecological restoration. The goal of the study was to investigate the effects of ecological restoration on stoichiometric characteristics and nutrientresorption efficiency of Pinus massoniana foliage. We used P. massoniana as our research species and determined variations in leaf C,N,and P content. The content of foliar N and P were used to estimate stoichiometric ratios,homeostatic indexes,and nutrient resorption efficiencies across years during ecological restoration at five sites. Four of the five P. massoniana woodlands were restored at 0( CK1),13,30,and 33 years,and one was a secondary forest( CK2). These study sites were expected to differ based on the level of ecological restoration( years) in the typical eroded red soil region in Hetian Town,Changting County,Fujian Province. The results revealed no considerable changes in the C,N,or P content of one-year old foliage of P. massoniana during the restoration process on degraded red soil. The same observations were made for the C : N,C : P,and N : P ratios because P. massoniana has strong homeostatic mechanisms( N and P homeostatic indexes were 7.57 and 3.89,respectively). The N : P of foliage at the five sites was between 11.0 and 13.4. There may have been some degree of N and P co-limitation of P. massoniana growth in the eroded red soil region. However,N resorption efficiency was significantly lower than P resorption efficiency. This was related to P. massoniana nutrient use efficiency, nutrient requirements for growth,and soil nutrient availability. In addition,there was a negative correlation between the ratios( C : N and C : P) and resorption efficiency of one-year old foliage of P. massoniana. Furthermore,one-year old foliage of P. massoniana substantially exhibited lower N and P use efficiencies as the C : N and C : P ratios increased. As such,more nutrients could be resorbed. The opposite occurred when C : N and C : P ratios were low. Furthermore,the C : N and C : P ratios of one-year old foliage of P. massoniana were negatively correlated with tree height and diameter at breast height,respectively. This suggests that nutrient demands for the growth of P. massoniana affect the st