Producer–decomposer co-dependency influences biodiversity effects

Abstract

Producers, such as plants and algae, acquire nutrients from inorganic sources that are supplied primarily by decomposers whereas decomposers, mostly fungi and bacteria, acquire carbon from organic sources that are supplied primarily by producers. This producer-decomposer co-dependency is important in governing ecosystem processes, which implies that the impacts of declining biodiversity on ecosystem functioning should be strongly influenced by this process. Here we show, by simultaneously manipulating producer (green algal) and decomposer (heterotrophic bacterial) diversity in freshwater microcosms, that algal biomass production varies considerably among microcosms (0.0-0.67 mg ml(-1)), but that neither algal nor bacterial diversity by itself can explain this variation. Instead, production is a joint function of both algal and bacterial diversity. Furthermore, the range in algal production in microscosms in which bacterial diversity was manipulated was nearly double (1.82 times) that of microcosms in which bacterial diversity was not manipulated. Measures of organic carbon use by bacteria in these microcosms indicate that carbon usage is the mechanism responsible for these results. Because both producer and microbial diversity respond to disturbance and habitat modification, the main causes of biodiversity loss, these results suggest that ecosystem response to changing biodiversity is likely to be more complex than other studies have shown.

Bacterial diversity in relation to secondary production and succession on surfaces of the kelp Laminaria hyperborea

“…However, microbial diversity has rarely been studied in the context of productivity of microbial communities (Naeem et al, 2000;Langenheder et al, 2010;Peter et al, 2011). Similarly, the process of primary succession, where freshly formed habitats become colonized by a sequence of organisms, has a long-standing tradition of study in the ecology of macroscopic organisms, yet is only since recently emerging as a topic in microbial ecology (Fierer et al, 2010).…”

Food-web constraints on biodiversity–ecosystem functioning relationships

“…Understanding the impacts of consumer diversity on ecosystem functioning is particularly important because extinction threats are often higher for animals than for plants (14,15). Recent experiments suggest that changes in biodiversity may affect ecosystem processes through trophic interactions among species (16)(17)(18)(19). Countervailing effects of autotroph diversity and heterotroph diversity were observed recently in some studies; addition of heterotrophs can remove the positive relationship between diversity and production found in autotroph-only treatments (16,20), and algal biomass was reduced by increasing grazer diversity in a seagrass system (21).…”

Integrating Different Organizational Levels in Benthic Biodiversity – Ecosystem Functioning (BEF) Studies

“…However, diverse communities were more likely to contain temperature-tolerant species and therefore retained more species than depauperate ones (Petchey et al, 1999). Further, the simultaneous manipulation of two trophic levels showed that neither algal nor bacterial species richness alone could explain the significant differences among microcosms, but that the algal biomass was a joint function of both algal and bacterial diversity implying important interactions among functional groups (Naeem et al, 2000). Studies on microbial communities are very useful as they can be carried out at very high species richness levels (Bell et al, 2005).…”

“…Their study system consisted of semi-permanent rain pools from the base of European beech trees. In another approach, algal (producer) and bacterial (decomposer) species diversity were manipulated simultaneously, and algal biomass was measured as a proxy of primary production (Naeem et al, 2000). Algae were chosen randomly from a pool of eight, and bacteria were chosen from a pool of 12 species.…”