三峡库区消落带4种典型草本植物的生态化学计量特征

为研究三峡水库消落带优势植物的养分利用特征及其对生境的适应策略,选择消落带分布最多的4种草本植物为研究对象,分析了植物根、茎、叶的碳(C)、氮(N)、磷(P)、钾(K)含量和化学计量比特征。结果表明:(1)相比陆地系统和自然湿地系统,消落带植物具有较低的C含量和较高的N、P、K含量,C/N、C/P、C/K均较低,表明植物具有低固碳和高养分积累、低养分利用效率和高生长速率的特征;(2)4种植物的养分含量和计量比存在一定差异,其中狗牙根具有较低的N、P、K含量和较高的C/N、C/P、C/K,且变异系数均低于其他3种植物,其低养分需求、高养分利用效率以及较强的内稳性可能是其在库区分布最广的重要机制;(3)4种植物在不同器官的养分分配策略相似,均表现为叶片C含量低于根和茎,而N、P、K含量则显著高于根、茎;同时,与根、茎相比,叶片C/N、C/P、C/K较低,N/P、N/K较高,且在不同生境条件下变异系数较小,表现出相对较高的稳定性;(4)落消带植物的养分含量及计量比从全库区上游至下游的空间变异性较强,其中N、C/N、N/P变异性较大,而C、P、K变异性较小,表明植物N含量受生境变化的影响较大,加之消落带不同植物生长均受到严格的N限制,因此N供给可能是影响消落带生态系统结构的重要因子。三峡库区消落带植物生态化学计量特征具有明显的变异性和特殊性,是植物群落演替及生态系统功能变化的重要驱动因素。

Ecological stoichiometry of four typical herbaceous species in the Littoral Zone of Three Gorges Reservoir

The littoral zone of the Three Gorges Reservoir (TGR), a water level fluctuation zone with 348.93 km², has gradually formed a special ecosystem with a few dominant species due to the water transfer mechanism of long-term flooding in winter and drought in summer. However little is known about the effect of plant community evolution on ecological function of the littoral zone of TGR. Therefore, this study aims to reveal the characteristics of nutrient utilization and their adaptation to the ecological environment of dominant species in the water level fluctuation zone of TGR. Based on field investigation, we selected four representative species of plants that widely distributed in littoral zone of TGR, including Cynodon dactylon, Bidens tripartite, Abutilon theophrasti and Xanthium sibiricum, and collected their root, stems and leaf respectively in 11 sampling sections along the Yangtze River and three main tributaries. Then, total carbon (C), total nitrogen (N), total phosphorus (P), potassium (K) contents and stoichiometric ratio of all samples were analyzed and calculated to explore the nutrition distribution mechanism of the dominant plants in the littoral zone, and their spatial variation characteristics in different habitats. The results showed that: 1) compared with the plants in the terrestrial ecosystem and the natural wetland ecosystem, the four dominant species in the littoral zone of TGR had the lower C contents, C/N, C/P and C/K ratio, but the higher N, P and K contents. It indicated that the plants were featured with lower carbon sequestration and nutrient utilization efficiency but high nutrient accumulation and growth rate. Meanwhile, such stoichiometric characteristics of the four selected plants were closer to the wetland ecosystem, but deviated from the terrestrial. 2) There were some differences in nutrient contents and stoichiometric characteristics among the four selected plants. Particularly, the contents of N, P and K of Cynodon dactylon were much lower than those of the other three species of plants, while its C/N, C/P and C/K were comparatively high, demonstrating that Cynodon dactylon, as the most widely distributed plant species in the littoral zone of TGR, had the characteristics of low nutrient demand and high nutrient utilization efficiency. In addition, the variation coefficients of measurement parameters in Cynodon dactylon were lower than those in other three plants, represented Cynodon dactylon having a strong homeostasis to adapt to habitats change. These adaptive characteristics might result in Cynodon dactylon becoming the most widely distributed dominant species around the littoral zone of the TGR. 3) The four dominant species of plant had the similar nutrient allocation strategies for different plant organs, with that the leaves had the comparatively low C contents but the highest contents of N, P and K compared with roots and stems. As a related result, C/N, C/P as well as C/K in leaves were lower, while the N/P and N/K were higher compared with roots and stems. The coefficient of variations of the most stoichiometric parameters in leaves was smaller than that in roots and stems. It revealed that plants under stress environment had the characteristic that priority was given to improving the stability of nutrient content by reducing the sensitivity of leaves to environmental changes. 4) Affected by the N limiting of soil, topography and other geographical factors, the spatial variability of nutrient content and stoichiometric characteristics among different plants was obvious, and the variability of N, C/N as well as N/P were high, while the variability of C, P, and K were weak. Ecological stoichiometric characteristics of the littoral zone plants of the TGR had obvious variability and particularity, would play an important driving force for the succession of plant communities and the evolution of ecosystem functions.