不同林龄杉木人工林植物-凋落叶-土壤C、N、P化学计量特征及互作关系

以贵州8年、16年、28年生杉木人工林为研究对象,分析植物-凋落叶-土壤的C、N、P化学计量特征及其内在联系,探讨林龄对杉木人工林生态化学计量的影响,为杉木人工林可持续经营提供参考。结果表明:(1)杉木人工林植物-凋落叶-土壤均呈高C低N、P元素格局,两两组分间差异显著(P0.05);成熟叶C/N(38.58)、C/P(376.67)偏低,其养分利用效率较低;与成熟叶相比,凋落叶N、P偏低,C/N、C/P偏高;土壤C/P、N/P偏低,C/N较高,说明土壤P素分解较快而N保存较好,反映了凋落叶分解不利。(2)成熟叶C、P以及根、凋落叶、土壤的C、N、P、C/N、C/P、N/P均受林龄的显著影响;从8年到28年,C、N、P含量在植物体呈先增后减趋势,而在土壤中相反,呈先减后增趋势,但在凋落物中C、P显著减小,且C/P,N/P显著增加,反映杉木林早期对养分需求旺盛,随年龄增大需求减小,凋落物分解受制于P素,加剧中幼期杉木生态系统养分供需矛盾。(3)成熟叶与凋落叶N、C/N、N/P之间显著正相关,凋落叶养分源自成熟叶;成熟叶重吸收率P(0.518—0.645)N(0.292—0.488),即对P的利用效率高于N。凋落叶与土壤C、C/N之间显著负相关,表明土壤C、N来源于凋落叶分解,但凋落叶分解缓慢,导致大量元素滞留于凋落叶,土壤损耗元素得不到补给,两者间养分循环缓慢。土壤与根C、P、C/N、C/P、N/P之间均显著正相关,土壤与成熟叶的C、N、P均不相关,表明土壤养分是杉木生长养分的主要来源,但土壤C、N、P含量对成熟叶C、N、P含量影响不大。

C, N, and P stoichiometry and their interaction with plants, litter, and soil in a Cunninghamia lanceolata plantation with different ages

In this study, three different stand ages of Cunninghamia Lanceolata plantations in Guizhou Province, including 8-year-old, 16-year-old and 28-year-old, were selected as the objects. In order to provide the scientific basis for sustainable management of Cunninghamia Lanceolata plantations, we explored carbon (C), nitrogen (N) and phosphorus (P) ecological stoichiometry and their interaction of plant, litter and soil, to indicate the effects of stand ages on the stoichiometry. Our results showed that, (1) The nutrient stucture of leaf, litter and soil presented high concentration of C and low concentration of N and P in Cunninghamia Lanceolata plantations. The concentration and stoichiometric ratio of C, N, and P were significant different among plant, litter and soil (P < 0.05).The C/N (38.58) and C/P (376.67) of leaf were lower than those of other coniferous trees, demonstrating that nutrient use efficiency of Cunninghamia Lanceolata was poor. Conversely, C/N and C/P of litter were higher than those of leaf, on account of N and P concentrations of litter were lower than those of leaf. The soil C/P and N/P were lower and C/N was higher, indicated that N release was inhibited but P decomposition was reversely accelerated in soil, and it suggested that the condition would inhibit the litter decomposition and nutrients release. (2) The C, N, and P concentrations and stoichiometric ratios of root, litter, and soil, as well as C and P concentrations of mature leaf, were significantly different among the three age groups. From 8 to 28 years old, the C, N and P concentrations of plant increased firstly and then decreased, but the results were converse in soil, suggesting that plant nutrient uptake significantly increased firstly and then decreased. This could result in soil nutrients being transformed from consumption to accumulation. The C and P concentrations of litter significantly decreased, and litter C/P and N/P ratios significantly increased, suggesting that P was the main factor that constrains litter decomposition. Thus, P may have inhibited nutrient return and intensified the contradiction between the nutrients supply and demand in young and middle aged forests. (3) N concentration, C/N and N/P of matured leaf had significantly positive correlations with those of litter, indicating that the nutrients of litter were sourced from the matured leaf. Resorption efficiency of P (0.518-0.645) was significantly greater than that of N (0.292-0.488) (P < 0.05), indicating that utilizing efficiency of P was greater than that of N in the plantations. C concentration and C/N of litter had significant negative correlations with those of soil, suggesting that C and N concentrations of soil was sourced from litter decomposition. However, litter decomposition was a slow process, accompanied with a plentiful nutrients reserved in litter, which delayed nutrient return from litter to soil. Concentrations of C and P, C/N, C/P and N/P of root had significantly positive correlations with those of soil, meanwhile, concentrations of C, P and N of soil had no significant correlations with those of matured leaf,suggesting that soil nutrients were the main sources of plant nutrients, but had less influence on concentrations of C, N, and P of matured leaf.