N、P施肥对塔里木河上游绿洲棉花C、N、P生态化学计量特征的影响

施肥通过外源物质的添加直接干预了农田生态系统中作物元素的运移循环过程。通过野外N、P施肥试验,测定棉花各生育期碳(C)、氮(N)、磷(P)元素含量及其生物量,分析棉株C、N、P元素的分配规律,探讨棉株对生长速率调控的内在机制,获得棉株体内N、P元素的内稳性指数,并判断其限制性元素类型。结果表明:棉花C、N、P元素平均含量分别为388.7、20.97、3.43 g/kg;棉花比生长速率与N∶P、C∶P间均存在负相关关系,棉花生长符合生长速率假说;N、P元素内稳性指数H分别在1.02—5.28、1.01—4.55范围内。叶片N∶P可表征植物限制性元素类型,棉花最大生长速率所对应的叶片N∶P为13,是判断限制元素的标准;综合棉花生长速率和内稳性指数研究可知研究区棉花生长受到N、P元素的共同限制,同时,在生长前期更易受P元素的限制,生长后期更易受N元素的限制。

Effects of nitrogen and phosphorus fertilizers on carbon, nitrogen, and phosphorus stoichiometry of oasis cotton in the upper reaches of Tarim River, Xinjiang, China

C, N, and P are the basic elements required for plant growth and regulation and their balance and stability plays an important role in many physiological functions. Ecological stoichiometry combines the first law of thermodynamics, the theory of evolution by natural selection, and the central dogma of molecular biology and has organically integrated biological studies at the scales of molecules, cells, species groups, communities, and ecosystems. C, N, and P stoichiometry of plants reflects a complex interplay that is the result of adaptation of plants to changing biological and abiotic environments during the process of evolution. Therefore, it is important to investigate the patterns of stoichiometric flexibility within and among plant species. Homeostasis and the growth rate hypothesis (GRH) have always been considered as the two important theories of ecological stoichiometry. Homeostasis is the ability of organisms to maintain relatively stable chemical compositions regardless of the environmental changes. The growth rate hypothesis considers that there is a close relationship between C:N:P stoichiometry and growth rate and it proposes that fast-growing organisms have low biomass C:P and N:P ratios. Fertilization by the addition of exogenous substances directly disturbs the migration of elements and circulation of crop in the farmland ecosystem. To further understand the response of crop growth to fertilization, in this study, we measured the cotton C, N, and P contents and the biomass of cotton plant in a pot experiment involving the addition of N and P fertilizers, conducted in the upper reaches of Tarim River. Our results showed that the mean content of C, N, and P was 388.7, 20.97, and 3.43 g/kg, respectively. The growth rate of cotton decreased with increasing leaf N:P or C:P, and the growth of cotton was consistent with GRH. Plants with higher H (H is the homeostasis index) have stronger homeostasis, that is, they have stronger control over element change. The values of H in cotton ranged from 1.02 to 5.28 for N and from 1.01 to 4.55 for P. Researchers have reported that homeostasis is gradually enhanced from prokaryotic to eukaryotic organisms. H of cotton was between those of prokaryotic and eukaryotic organisms, and was consistent with the results of earlier studies. The leaf N:P ratios have been widely used to indicate the availability and limitation of soil nutrients. Cotton growth was mainly restricted by N and P. For cotton, the value of leaf N:P was 13 at the maximum growth rate, which was the standard of judging the limiting element. It conformed to the law of demand for cotton growth.