云杉碳氮化学计量比对土壤水分和氮有效性的响应

以西南亚高山针叶林优势种——粗枝云杉(Picea asperata)为研究对象,探究不同土壤水分状况和氮添加下云杉碳氮化学计量比的变化及其响应过程。采用两因素(水分×氮素)随机区组实验,设置5个土壤水分梯度和3个氮添加浓度,其中土壤水分梯度分别是土壤田间持水量的40%(W1)、50%(W2)、60%(W3)、80%(W4)和100%(W5),氮添加浓度分别为0(N0)、20(N1)、40(N2)gNm~(-2) a~(-1)。结果表明:(1)土壤水分和氮添加显著影响了云杉碳氮化学计量比(P0.05),具体为:云杉植株和器官碳氮比在N0W4处理下最大值,随土壤水分有效性的降低而减小,随氮添加浓度的增加而降低。(2)随土壤水分有效性的降低,根和叶的碳含量显著升高(P0.05),茎和叶的碳含量随着氮添加浓度的增加而降低。此外,土壤水分有效性的降低显著提高了根和茎的氮含量(P0.05),各器官的氮含量随着氮添加浓度的增加而增加。在相同水分和氮添加浓度处理下表现为碳含量:叶茎根,氮含量:叶根茎。(3)云杉净光合速率随土壤水分有效性的降低先升高后降低,随氮添加浓度增加而增加,在N2W4达到最大。(4)根对NH~+_4和NO~-_3的净吸收速率随土壤水分有效性的降低而减小,随氮添加浓度的增加而显著增加(P0.05)。此外,根对NH~+_4的净吸收速率与土壤有效氮含量呈显著负相关关系(P0.05)。本研究表明,土壤水分和氮添加影响了云杉的碳同化和氮吸收过程,改变植物的碳、氮分配策略和养分利用效率,从而导致碳氮比的变化。

Response of C : N stoichiometry of Picea asperata to soil water and nitrogen availabilities

To study the variation and response of C: N stoichiometry under different soil water and nitrogen availabilities, we used Picea asperata, the dominant species in subalpine coniferous forests of western Sichuan, China, as material to conduct the experiment. A two-factor (water and nitrogen) randomized block experiment was set up, including five water gradients (40% (W1), 50% (W2), 60% (W3), 80% (W4), and 100% (W5) of soil field capacity, respectively) and three nitrogen application concentrations (0 (N0), 20 (N1), and 40 (N2) gN m^-2 a^-1, respectively). The results showed that: (1) soil water availability and nitrogen application significantly affected C: N stoichiometry of P. asperata. Specially, C: N stoichiometry of the whole plant and organs reached the highest value under N0W4 treatment, which decreased with the decline of soil water availability as well as the increase of nitrogen application. (2) with the decrease of soil water availability, the carbon concentration of roots and leaves significantly increased, whereas, those of stem and leaves showed a decline with the increase of nitrogen application. In addition, the decline of soil water availability markedly promoted the nitrogen concentration of roots and stem, and nitrogen concentration of organs increased gradually with more nitrogen application. The carbon and nitrogen concentration decreased consistently in the order of leaves > stem > roots and leaves > roots > stem under the same treatment. (3) the net photosynthetic rate of P. asperata rose first and then decreased with the decline of soil water availability, and increased with more nitrogen application, which reached the maximum value under N2W4 treatment. (4) net fluxes of NH₄⁺ and NO₃^- in roots decreased obviously with the decline of soil water availability, and increased with more nitrogen application. besides, net flux of NH₄⁺ in roots was correlated negatively with soil available nitrogen concentration. The results showed that soil water and nitrogen availabilities affected carbon assimilation and nitrogen uptake processes of P. asperata, and changed the nutrient utilization efficiency and carbon and nitrogen concentration, which resulted in changes of C: N stoichiometry.