陕西黄土高原刺槐枯落叶生态化学计量学特征

生态系统元素平衡是当前全球变化生态学和生物地球化学循环研究的焦点和热点,生态化学计量学结合了生物学、物理学和化学等基本原理,是研究生物系统能量平衡与多重化学元素平衡的科学,为研究元素在生物地球化学循环与生态过程中的规律及其之间的计量关系提供了一种综合的方法。以陕西黄土高原人工刺槐林为研究对象,结合纬度和坡向两个因素,分析了三原、淳化、耀州区、宜君、黄陵、洛川、富县、甘泉、宝塔区、安塞、米脂、神木12个县区的刺槐枯落叶生态化学计量学特征。结果发现,阳坡刺槐枯落叶C、N、P含量的变化范围分别为318.34—428.01 g/kg、13.27—24.07 g/kg、1.66—2.57 g/kg;阴坡刺槐枯落叶C、N、P含量的变化范围分别为306.70—433.68 g/kg、12.55—24.39 g/kg、1.62—2.99 g/kg。阳坡刺槐枯落叶C∶N、C∶P、N∶P的变化范围分别为14.23—24.61、148.67—215.92、7.37—14.47;阴坡刺槐枯落叶C∶N、C∶P、N∶P的变化范围分别为16.87—26.54、130.06—234.41、7.05—13.22。随着纬度的升高,刺槐枯落叶C、N显著下降,刺槐枯落叶P、C∶N、C∶P、N∶P无明显差异。刺槐枯落叶C、N、P之间呈显著正相关。刺槐枯落叶C、N、P、C∶N、C∶P、N∶P在阴坡和阳坡之间无明显差异。研究区,阴坡和阳坡的刺槐枯落叶N∶P均较低,刺槐林土壤的全氮平均含量也低于全国平均水平,推测陕西黄土高原刺槐林的生长可能主要受到氮素的限制。

Ecological stoichiometry characteristics of leaf litter of Robinia pseudoacacia in the Loess Plateau of Shaanxi Province

The balance between various elements of the ecosystem has been the focus of research related to the ecology of global change and biogeochemical cycles. Ecological stoichiometry is the study of the balance of energy and elements in biological systems and is based on the general laws of physics, chemistry and biology. Ecological stoichiometry provides an integrated approach to investigating the stoichiometric relationships and rules in biogeochemical cycling and ecological processes. Robinia pseudoacacia, a leguminous tree, is the main species used for afforestation in the Loess Plateau of China. R. pseudoacacia has some special features, such as a rapid growth, being easy to propagate, being very adaptable to various environmental conditions and an strong ability to fix nitrogen in a biologically useful form, allowing it to be widely planted in the Loess Plateau. To explore ecological stoichiometric characteristics of leaf litter of R. pseudoacacia in the Loess Plateau, R. pseudoacacia forests scattered across 12 counties (listed below) on both sunny and shady slopes were selected for study. Data were collected at each site on latitude, slope and aspect, light conditions, temperature, water and soil conditions. The C, N, and P contents of R. pseudoacacia leaf litter were studied from sites scattered from south to north in the Loess Plateau of Shaanxi Province, including Sanyuan, Chunhua, Yaozhou, Yijun, Huangling, Luochuan, Fuxian, Ganquan, Baota, Ansai, Mizhi and Shenmu counties. The results showed that C, N, and P contents of R. pseudoacacia leaf litter from sites on sunny slopes range from 318.34 to 428.01 g/kg, 13.27 to 24.07 g/kg, and 1.66 to 2.57 g/kg, respectively. Leaf litter C, N, P content of shady slopes ranged from 306.70 to 433.68 g/kg, 12.55 to 24.39 g/kg, and 1.62 to 2.99 g/kg, respectively. Leaf litter C:N, C:P, N:P ratios on sunny slopes ranged from 14.23 to 24.61, 148.67 to 215.92, and 7.37 to 14.47, respectively. Leaf litter C:N, C:P, N:P ratios on shady slopes ranged from 16.87 to 26.54, 130.06 to 234.41, and 7.05 to 13.22, respectively. C and N contents decreased significantly in R. pseudoacacia leaf litter with increasing latitude in the 12 counties, although P content in the leaf litter did not change significantly among the 12 counties. The same trend was observed between R. pseudoacacia leaf litter and soil when latitude increased. The C, N and P content in R. pseudoacacia leaf litter were positively correlated to each other. The C:N, C:P, N:P ratios were not significantly different in R. pseudoacacia leaf litter among the 12 counties with increasing latitude. Slope aspect had no effect on the C, N and P content of R. pseudoacacia leaf litter and soil. The leaf N:P ratio can be used as an ecological indicator for shortages of these two nutrients at the individual plant and community levels. In this research, the ratios of N:P in R. pseudoacacia leaf litter on both sunny and shady slopes were small. In addition, the soil N content of this study area was less than average for all of China, which implies that available N was the main factor limiting the distribution of R. pseudoacacia in the Loess Plateau of Shaanxi Province. Further research should be conducted to determine whether this conclusion can be applied over a broader spatial scale.