哈巴湖国家级自然保护区油蒿群落生态化学计量特征对群落生物量和物种多样性的影响

Effects of ecological stoichiometry on biomass and species diversity of the Artemisia ordosica community in Habahu National Nature Reserve

以宁夏哈巴湖国家级自然保护区内的油蒿群落为研究对象,测定了油蒿群落不同发育阶段植物叶C、N、P含量,分析了植物叶C∶N∶P比化学计量特征,探讨了油蒿群落生态化学计量特征对物种多样性和生物量的影响。结果表明,在哈巴湖国家级自然保护区,油蒿群落发育早期,植物生长受N限制,发育中后期,植物生长受P限制;油蒿群落发育早期阶段的植物具有较高的叶C∶N比和较低的叶N∶P比,而油蒿群落发育后期阶段的植物具有较低的叶C∶N比和较高的叶N∶P比。随着叶C∶N比的增大,油蒿群落生物量呈指数函数显著降低,物种多样性呈对数函数降低的趋势,但不显著;而随着叶N∶P比的增大,油蒿群落生物量和物种多样性均呈幂函数显著增加,表明生态化学计量特征对油蒿群落的物种多样性和生物量有重要影响。

Ecological stoichiometry represents the balance of multiple chemical elements in ecological interactions and processes. Theoretically,if there are clear relationships between the C ∶ N ∶ P ratios and maximum relative growth rate,relationships between life history evolution,the physiological demand for major elements,and even ecosystem processes would be expected as well. Indeed,many studies have shown clear relationships between plant growth rates and plant N ∶ P ratios. However,whether C ∶ N ∶ P ratios can affect species diversity and community biomass remains unclear,and requires testing. We therefore investigated several Artemisia ordosica communities from sandy soils in the Ningxia Habahu NationalNature Reserve. More specifically,we chose an（ 1） A. ordosica-Corispermum deslinatum ＋ Salsola sp. community,（ 2） A.ordosica-Calamagrostis pseudophragmites community,（ 3） A. ordosica-Pennisetum centrasiaticum ＋ Aneurolepidium dasystachys community,（ 4） A. ordosica-P. centrasiaticum community,（ 5） A. ordosica-Sophora alopecuroides community,and an（ 6） A. ordosica-A. scoparia-S. alopecuroides community. From these communities,1 and 2 represent the early successional stages of an A. ordosica community; 3 and 4,the middle stages; 5 and 6,the final stages. We determined foliar C,N,and P concentrations of the plants from the investigated communities,and analyzed the relationships between the plant leaf C ∶ N ∶ P ratios and the corresponding community biomass and species diversity. The results showed that,in the early stages of A. ordosica community development,the plant growth was primarily limited by N,whereas in the middle and final stages,plant growth gradually changed from being N limited to being P limited. The early stage plants had the highest foliar C ∶ N ratios,and the lowest N ∶ P ratios,whereas the final stage plants had the lowest C ∶ N ratios and highest N ∶ P ratios. Plant growth is often limited by N or P element in sandy soil due to the sterile nutrition regime and lower N and P concentration in soil. According to Growth Rate Hypothesis,the rapidly growing organisms commonly have lower biomass N ∶ P ratios. And our results show that the plants have a lower biomass N： P ratio in early stage while a higher biomass N ∶ P ratio in final stage of A. ordosica community. In other words,the plants grow more rapidly in early stage but more slowly in final stage,which is in line with the actual investigation. For early stage plants,the soil water is more abundance,and the low biomass N ∶ P ratio promotes the rapid growth of the plants,while in final stage,the soil is relatively short of water,therefor more P in plant is needed to resist the water stress by protein synthesis,thus higher biomass N ∶ P ratio limits plant growth. In this paper,the results of regression analysis show that with increasing foliar C ∶ N ratios,community biomass decreased significantly,and species diversity deceased as well. In contrast,with increasing foliar N ∶ P ratios,the biomass and diversity both significantly increased. In sum,the ecological stoichiometry has an important effect on species diversity and biomass in A. ordosica communities.