Biodiversity effects on ecosystem functioning in a 15-year grassland experiment: Patterns, mechanisms, and open questions

Abstract

In the past two decades, a large number of studies have investigated the relationship between biodiversity and ecosystem functioning, most of which focussed on a limited set of ecosystem variables. The Jena Experiment was set up in 2002 to investigate the effects of plant diversity on element cycling and trophic interactions, using a multi-disciplinary approach. Here, we review the results of 15 years of research in the Jena Experiment, focussing on the effects of manipulating plant species richness and plant functional richness. With more than 85,000 measures taken from the plant diversity plots, the Jena Experiment has allowed answering fundamental questions important for functional biodiversity research. First, the question was how general the effect of plant species richness is, regarding the many different processes that take place in an ecosystem. About 45% of different types of ecosystem processes measured in the ‘main experiment’, where plant species richness ranged from 1 to 60 species, were significantly affected by plant species richness, providing strong support for the view that biodiversity is a significant driver of ecosystem functioning. Many measures were not saturating at the 60-species level, but increased linearly with the logarithm of species richness. There was, however, great variability in the strength of response among different processes. One striking pattern was that many processes, in particular belowground processes, took several years to respond to the manipulation of plant species richness, showing that biodiversity experiments have to be long-term, to distinguish trends from transitory patterns. In addition, the results from the Jena Experiment provide further evidence that diversity begets stability, for example stability against invasion of plant species, but unexpectedly some results also suggested the opposite, e.g. when plant communities experience severe perturbations or elevated resource availability. This highlights the need to revisit diversity–stability theory. Second, we explored whether individual plant species or individual plant functional groups, or biodiversity itself is more important for ecosystem functioning, in particular biomass production. We found strong effects of individual species and plant functional groups on biomass production, yet these effects mostly occurred in addition to, but not instead of, effects of plant species richness. Third, the Jena Experiment assessed the effect of diversity on multitrophic interactions. The diversity of most organisms responded positively to increases in plant species richness, and the effect was stronger for above- than for belowground organisms, and stronger for herbivores than for carnivores or detritivores. Thus, diversity begets diversity. In addition, the effect on organismic diversity was stronger than the effect on species abundances. Fourth, the Jena Experiment aimed to assess the effect of diversity on N, P and C cycling and the water balance of the plots, separating between element input into the ecosystem, el...

Biodiversity‐ecosystem functioning relationships in a long‐term non‐weeded field experiment

“…Moreover, in contrast to many other biodiversity studies, both under experimental (see, e.g., Tilman et al 2014, Weisser et al 2017) and natural conditions (Grace et al 2016, Duffy et al 2017, in our experiment we observed very few or negative relationships between diversity and biomass production. Moreover, in contrast to many other biodiversity studies, both under experimental (see, e.g., Tilman et al 2014, Weisser et al 2017) and natural conditions (Grace et al 2016, Duffy et al 2017, in our experiment we observed very few or negative relationships between diversity and biomass production.…”

“…F. VEEN ET AL. 8 experiments (e.g., Lehman and Tilman 2000, van Ruijven and Berendse 2005, Tilman et al 2006, Hector et al 2010, Weisser et al 2017 or natural conditions (Duffy et al 2017, Gross et al 2017, we found very few relationships between diversity and ecosystem functioning and the ones we found were generally negative, for both taxonomic and functional diversity. 99,No.…”

“…Ecology,Vol. Our experiment differs fundamentally from weeded biodiversity experiments, as weeded experiments are targeted to study species extinction (Weisser et al 2017), while our experiment allows colonization and hence the reappearance of "extinct" species. 8 experiments (e.g., Lehman and Tilman 2000, van Ruijven and Berendse 2005, Tilman et al 2006, Hector et al 2010, Weisser et al 2017 or natural conditions (Duffy et al 2017, Gross et al 2017, we found very few relationships between diversity and ecosystem functioning and the ones we found were generally negative, for both taxonomic and functional diversity.…”

Recommendations for establishing global collaborative networks in soil ecology

“…Shannon et al 2019), we here provide an example from our own observations that made us aware how gender representation changes along the scientific career. In the Jena Experiment (http://www.the-jena-experiment.de/), a large research consortium studying the ecosystem consequences of biodiversity loss funded by the German Research Foundation (Weisser et al 2017, Eisenhauer et al 2019), we noticed that the percentage of female scientists drops sharply from the level of PhD students (75%) to postdocs (42%) to PIs (35%, a percentage that still is far above the proportion of female professors at many German universities). Please note that these numbers are not supposed to be representative, but just an example.…”

Linking ecology and plant pathology to unravel the importance of soil-borne fungal pathogens in species-rich grasslands

“…A higher microbial diversity is expected to reduce invasion of pathogens and increase antagonism in soils, thereby reducing the impact of plant pathogenic fungi (Larkin 2015;Mallon et al 2015). In fact, an increase in plant diversity in the Jena biodiversity experiment (Weisser et al 2017) enhanced the activity of antagonistic bacteria in the soil against the soil-borne fungal pathogen R. solani (Latz et al 2012). Also in natural grasslands, the diversity of neighbouring plants has been found to affect Streptomyces spp.…”