天山北坡植物土壤生态化学计量特征的垂直地带性

生态化学计量工作专注于植物与土壤的元素比例关系及其环境解释等问题上,还需要分析在连续环境梯度上元素比例关系的变化规律以进一步加深已有的认识。受水热梯度的影响,植被与土壤在天山北坡均存在明显的垂直地带性,这为探讨植物土壤生态化学计量特征的垂直带谱提供了有利条件。在天山中段北坡海拔1000—3840m范围内,按海拔梯度对植物和土壤分别采样,测定其C、N、P含量。结果表明:(1)随海拔的升高,植物C、N、P含量及其计量比变化规律各不相同,C含量随海拔变化保持不变,仅山地针叶林显著低于亚高山灌丛草甸、高山垫状植被和山前灌木(P0.05);N含量、C∶P、N∶P随海拔先升高后降低,山地针叶林和亚高山灌丛草甸显著高于山地荒漠草原、山地草原、高山垫状植被(P0.05);P含量、C∶N则是随海拔先降低后升高,高山垫状植被显著高于其他植被类型,山地荒漠草原、山前灌木和高山草甸显著高于山地草原、针叶林和亚高山灌丛草甸(P0.05)。(2)从生活型角度,乔木、灌木和草本C、N含量、C∶N差异不显著,灌木P含量、C∶P、N∶P显著高于草本(P0.05);乔木和灌木更受P限制,草本更受N限制。(3)随海拔的升高,土壤C、N、P含量、C∶P、N∶P均先升高后降低,其中山地针叶林和亚高山灌丛草甸均显著高于山地荒漠草原和山地草原(P0.05),土壤C∶N表现为一直降低,山地荒漠草原显著高于其他植被类型(P0.05)。(4)植物C、N、P及计量比与土壤相关性分析中,仅植物C∶P与土壤C∶P相关性显著,且植物C、N、P含量与土壤相关系数小于植物C∶P、N∶P与土壤相关系数。在垂直地带性上,土壤主要通过生态化学计量比影响植物的生长。

Plant and soil ecological stoichiometry with vertical zonality on the northern slope of the middle Tianshan Mountains

The proportional relationships of nutritional elements with plants, soil, and the environment have been studied intensely. Relationships that occur along continuous environmental gradients should be analyzed to better understand these issues. There are obvious differences in plant and soil types at different points along the hydrothermal gradient, which provide a unique advantage to examine the vertical spectrum of plants and soil ecological stoichiometry. In this study, we examined organic carbon (C), total nitrogen (N), and total phosphorus (P) in plant and soil samples collected along the altitude gradient of the north slopes of the middle Tianshan Mountains (the altitude of which varies from 1000 to 3840 m). The results showed that (1) with increasing altitude, C, N, and P content and the stoichiometric ratios in plants leaves differed. C levels were almost invariant, and only the mountain needle leaf forest had significantly lower C levels than the subalpine shrub meadow, alpine cushion vegetation, and piedmont scrub (P<0.05). Second, N content and C:P and N:P ratios first increased and then decreased with altitude, and levels in the mountain needle leaf forest and subalpine shrub meadow were significantly higher than in the mountain desert steppe, mountain steppe, and alpine cushion vegetation (P<0.05). Finally, P content and C:N ratio first decreased and then increased with altitude, and were significantly higher in the alpine cushion vegetation than in the other vegetation types. Moreover, levels in the mountain desert steppe, piedmont scrub, and alpine meadow were significantly higher than in the mountainous steppe, mountain needle leaf forest, and subalpine shrub meadow (P<0.05). (2) There was no significant difference in C content among trees, shrubs, and herbs, and this also true for N and C:N ratio. However, P levels and C:P and N:P ratios were significantly higher in shrubs than in herbs (P<0.05). Trees and shrubs were largely limited by P, and herbs were limited by N. (3) With increasing altitude, soil C, N, and P content and the C:P and N:P ratios first increased and then decreased, and were significantly higher in mountain needle leaf forest and subalpine shrub meadow than in mountain desert steppe and mountainous steppe (P<0.05). The C:N ratio decreased with altitude, and was significantly higher in the mountain desert steppe than in the other vegetation types (P<0.05). (4) Plant C:P ratios were significantly correlated with the soil C:P ratio, and the correlation coefficients of plant and soil C, N, and P content were less than that of the plant stoichiometric ratio and soil. These results suggest that plants are mainly influenced by soil through stoichiometric ratios in the vertical zone.