Nitrogen availability and plant functional composition modify biodiversity-multifunctionality relationships

The ability of an ecosystem to deliver multiple functions at high levels (multifunctionality) typically increases with biodiversity but there is substantial variation in the strength and direction of biodiversity effects, suggesting context-dependency. A better understanding of the drivers of this context dependency is essential to predict effects of global change on ecosystems. To determine how different factors modulate the effect of diversity on multifunctionality, we established a large grassland experiment with 216 communities, crossing a manipulation of plant species richness (1, 4, 8, 20 species) with manipulations of resources (nitrogen enrichment), plant functional composition (gradient in mean specific leaf area [SLA] to manipulate abundances of exploitative, fast-growing vs. conservative, slow-growing species), plant functional diversity (variance in SLA) and enemy abundance (foliar fungal pathogen removal). We measured ten above- and belowground functions, related to productivity, nutrient cycling and energy transfer between trophic levels, and calculated ecosystem multifunctionality. Plant species richness and functional diversity both increased multifunctionality, but their effects were context dependent. Species richness increased multifunctionality only when communities were assembled with fast growing (high SLA) species. This was because slow species were more redundant in their functional effects, whereas different fast species tended to promote different functions. Functional diversity also increased multifunctionality but this effect was dampened by nitrogen enrichment. However, unfertilised, functionally diverse communities still delivered more functions than low diversity, fertilised communities. Our study suggests that a shift towards fast-growing exploitative communities will not only alter ecosystem functioning but also the strength of biodiversity-functioning relationships, which highlights the potentially complex effects of global change on multifunctionality.

Methods
Datasets used in "Nitrogen availability and plant functional composition modify biodiversity-multifunctionality relationships" 

from Noémie A. Pichon, Seraina L. Cappelli, Tosca Mannall, Thu Zar Nwe, Norbert Hölzel, Valentin H. Klaus, Till Kleinebecker, Santiago Soliveres, Hugo Vincent and Eric Allan

Initial manuscript can be found on bioRxiv: https://www.biorxiv.org/content/10.1101/2020.08.17.254086v1 

This experiment manipulates in a full factorial design species richness (1, 4, 8 species), nitrogen enrichment (0, 100 kg ha-1 year-1), fugicide spraying (unsprayed, sprayed) and initial community composition in SLA (gradient in growth strategies).

See methods for more info on the design. If you have further questions: [e-mail]