生态恢复对马尾松叶片化学计量及氮磷转移的影响

为了解生态恢复对侵蚀红壤恢复的马尾松林叶片碳氮磷化学计量及氮磷养分转移的影响,在福建省长汀县河田镇典型侵蚀红壤区选取恢复13、30、33a的马尾松林为研究对象,并以未治理侵蚀地(CK1)和次生林(CK2)分别作为恢复前和恢复后的对照,通过测定马尾松叶片的碳、氮、磷含量,计算其计量比,内稳性指数和氮磷转移率,分析了侵蚀红壤生长的马尾松养分限制与养分转移的关系。结果表明:在侵蚀红壤恢复过程中,马尾松1年龄叶片C、N、P含量及1年龄叶片C∶N、C∶P、N∶P变化较小,这与马尾松较高的内稳性有关(N和P内稳性指数分别为7.57和3.89)。所有实验地马尾松1年龄叶片N∶P处于11.0—13.4之间,表明马尾松的生长受N、P共同限制,其中马尾松叶片N转移率显著低于P转移率,这与生态恢复过程中马尾松养分利用效率、生长需求以及土壤养分供应状况有关。1年龄叶片C∶N、C∶P分别与马尾松N、P转移率成负相关关系,当马尾松叶片C∶N、C∶P较低时,表明N、P利用效率较低,叶片衰老时更多的N和P被转移利用;反之,则N、P利用效率较高,转移率低。同时,C∶N、C∶P分别与树高、胸径成显著负相关关系,即马尾松生长对N、P的需求同样会影响化学计量比的变化,从而影响养分转移。虽然侵蚀地生态恢复过程中土壤N、P含量增加,但仍较贫瘠,不足以满足马尾松的生长,马尾松养分转移率较高,因此,为了提高侵蚀地恢复的马尾松林的生产力,建议下一步恢复措施中适当施加N肥和P肥。该研究将侵蚀红壤不同生态恢复年限的马尾松叶片C、N、P化学计量及养分转移结合,有助于全面、系统地揭示生态恢复过程马尾松林的养分循环,对指导侵蚀红壤恢复和提高马尾松生产力具有重要意义。

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 nutrient resorption 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 stoichiometric ratios and N and P resorption. In brief, the N and P contents increased during the restoration process in degraded red soil; in other words, this explains the slow recovery and still relatively infertile status of eroded areas. The soil nutrients cannot sufficiently support the growth of P. massoniana, which leads to relatively higher N and P resorption rates. Thus, in order to improve P. massoniana forest productivity, we suggest increasing N and P fertilizer to increase soil fertility. This study helped to clarify the nutrient cycling of P. massoniana woodlands by combining P. massoniana foliage C, N, and P stoichiometric characteristics and nutrient resorption in a comprehensive and systematic manner. Therefore, it is important to manage the ecological restoration of eroded red soil, and efforts improve the productivity of forest systems should be conducted.