Research Center of Forest Management Engineering of State Forestry and Grassland Administration, Beijing Forestry University, Beijing, 100083, China.
College of Life Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
Ecol Appl. 2019 Oct;29(7):e01965. doi: 10.1002/eap.1965. Epub 2019 Jul 30.
Biodiversity has a close relationship with ecosystem functioning. For most biodiversity-ecosystem-functioning studies, biodiversity has been linked to a single indicator variable of ecosystem functioning. However, there are generally multiple ecosystem processes contributing to ecosystem functioning and they differ in their dependence on biodiversity. Thus, the relationship between biodiversity and ecosystem functioning can be stronger when multiple rather than single ecosystem processes are considered. Using both mass-balance and stable-isotope approaches, we explored the effects of plant diversity on nitrogen (N) removal sustained by multiple N-cycling processes in experimental microcosms simulating constructed wetlands, an ecosystem treating wastewater with high N loading. Four species were used to assemble different plant communities, ranging in richness from one to four species. The removal of N, indicated by low levels of total inorganic N concentration (TIN) present in the effluent, was considered as an integrated measure of ecosystem functioning, combining three constituent N-cycling processes: plant uptake, denitrification, and substrate adsorption. Our results showed that (1) species richness had a positive effect on N removal, in particular, the four-species mixture reduced effluent TIN to a lower level than any monoculture; however, polycultures (two-, three-, and four-species mixtures) did not outperform the most efficient monoculture when each of the three constituent N-cycling processes was considered by itself; (2) species identity had significant impacts on single processes. Communities with the species Coix lacryma-jobi showed the greatest capacity for N uptake and communities with Phragmites australis had the highest denitrification rates; (3) isotope fractionation in the rhizosphere of Coix lacryma-jobi was primarily due to microbial denitrification while multistep isotope fractionation was detected for Phragmites australis and Acorus calamus (indicating recycling of N), suggesting that species differed in the way they transformed N; (4) the enhanced N removal at high diversity may be due to mutualistic interactions among species belonging to different functional types. Our findings demonstrated that although plant species richness had negligible effects on individual N-cycling processes, it enhanced the overall ecosystem functioning (N removal) when these processes were considered collectively. Our study thus contributes to improve the treatment efficiency of constructed wetlands through proper vegetation management.
生物多样性与生态系统功能密切相关。对于大多数生物多样性-生态系统功能研究，生物多样性与生态系统功能的单一指标变量相关联。然而，通常有多个生态系统过程有助于生态系统功能，它们在对生物多样性的依赖程度上有所不同。因此，当考虑多个而不是单个生态系统过程时，生物多样性与生态系统功能之间的关系可能更强。本研究采用质量平衡和稳定同位素方法，在模拟人工湿地的实验微宇宙中，探讨了植物多样性对受多种氮循环过程支撑的氮（N）去除的影响，人工湿地是一种处理高氮负荷废水的生态系统。使用四种物种来组装不同的植物群落，从一种到四种物种不等。通过低水平的总无机氮浓度（TIN）存在于流出物中，将 N 的去除被认为是生态系统功能的综合衡量标准，它结合了三个组成的氮循环过程：植物吸收、反硝化和基质吸附。研究结果表明：（1）物种丰富度对 N 去除有积极影响，特别是四物种混合物将出水 TIN 降低到比任何单种培养物更低的水平；然而，当单独考虑三个组成的氮循环过程中的每一个时，多物种培养物（二、三、四物种混合物）并没有优于最有效的单种培养物；（2）物种身份对单个过程有显著影响。含有薏苡的群落具有最大的 N 吸收能力，而含有芦苇的群落具有最高的反硝化速率；（3）在薏苡的根际中存在同位素分馏主要是由于微生物反硝化，而在芦苇和菖蒲中检测到多步同位素分馏（表明 N 的再循环），这表明物种在转化 N 的方式上存在差异；（4）高多样性下增强的 N 去除可能是由于不同功能类型的物种之间的互利相互作用。本研究表明，尽管植物物种丰富度对单个氮循环过程几乎没有影响，但当综合考虑这些过程时，它会增强整个生态系统的功能（N 去除）。因此，本研究通过适当的植被管理有助于提高人工湿地的处理效率。
