DOI: 10.5061/dryad.80nf679
title: Data from: Plant diversity increases N removal in constructed wetlands when multiple rather than single N processes are considered

description: 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.
description: Multiple N processes in
 the microcosmsThis data file includes
 rates of N removal and three key processes contributing to N removal
 (plant uptake, denitrification and substrate adsorption) in response to
 changes in plant diversity (plant species richness, identity and
 composition). Pa, Phragmites australis; Ta, Typha angustifolia; Cl, Coix
 lacryma-jobi; and Ac, Acorus calamus.Multiple N
 processes.xlsx