More Than Just Earthworms: Decomposers and Their Contribution to Plant Biodiversity

In recent years, it has become a widely accepted notion among the conservationist community that Earth’s ecosystems are facing catastrophic losses of biodiversity.This is concerning because humans rely on ecosystems throughout the world for the numerous (and free) services they provide. It is important to preserve biodiversity because, in doing so, we are also preserving these services. A team of scientists consisting of Nico Eisenhauer (University of Minnesota; Technische Universität München), Peter B. Reich (University of Minnesota; Hawkesbury Institute for the Environment, University of Western Sydney) and Forest Isbell (University of Minnesota) recently postulated that plant productivity and ecosystem functions increase as the biodiversity of decomposers increases. Through their research, they established that high levels of decomposer biodiversity led to higher levels of plant productivity because decomposers eased competition between different species of plants. This occurred because decomposers replenish nutrients in the soil (such as nitrogen) that plants have to compete for, and because decomposers also reduce the amount of biomass in the soil, therefore freeing up more space for the roots of plants to grow. 

In order to evaluate their hypothesis Eisenhauer, Reich, and Isbell devised an experiment involving several microcosms meant to test the effects of plant and decomposer species diversity on plant productivity and ecosystem functionality. Through the use of microcosms, Eisenhauer, Reich, and Isbell were able to control otherwise incidental environmental conditions and to regulate natural conditions by regulating soil and water quality, the frequency of irrigation and the exposure to sunlight. The same amount of ground-level ‘plant litter’ (presumably dead plant matter such as leaves) was scattered at the top of the soil in each microcosm. The team devised multiple treatments demonstrating different degrees of plant and decomposer biodiversity through varied levels of species richness (Species richness refers to the number of actual species of decomposers and plants, not the total number of plants and decomposers.) Each microcosm was then left to sit for fourteen weeks. After fourteen weeks, the researchers disturbed the microcosms and calculated the amount of surface level decomposition, the amount of microbial biomass in the soil, and counted the decomposers present. The results indicated that the microcosms with the most decomposer species richness had the most surface litter decomposition, supporting Eisenhauer, Reich, and Isbell’s hypothesis that plant productivity and ecosystem functioning are impacted by decomposer biodiversity.

The scientists also suggested the fact that high levels of species richness of decomposers promote high levels of plant productivity and biodiversity could in turn lead to more decomposer biodiversity, forming a positive feedback loop. Potentially, this makes increasing and preserving decomposer biodiversity a viable means of preserving entire ecosystems. Eisenhauer, Reich, and Isbell’s findings could open new doors in the field of conservation when it comes to preserving biodiversity. In the future, the ideas established in their research could allow for the focus of conservation efforts on a single thing: the preservation of decomposer biodiversity. By preserving these organisms, conservationists are also promoting biodiversity in other trophic levels. Earthworms could be one of conservation biology’s most useful soldiers in the fight to protect the Earth’s biodiversity. 

Article:

Eisenhauer, N., Reich, P. B., & Isbell, F. (2012).Decomposer diversity and identity influence plant diversity effects on ecosystem functioning. Manuscript submitted for publication, Retrieved from http://www.esajournals.org/doi/pdf/10.1890/11-2266.1

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