Soil Animals Increase Leaf Decay in Warmer, Wetter Regions with Unexpected Effects Related to Global Warming

A Colorado State University researcher spearheaded a global experiment to determine if unseen species found in soil are important on a global scale in increasing leaf decay and making a greater impact in warm regions’ climate change. The findings: those species make a significant impact.

Soil animals and their importance have long been ignored. Many scientists have wondered, do they really have any significance from beyond the backyard?

Results show that soil animal impacts are climate dependent; they increase leaf decay in temperate and wet tropical locations and have neutral effects in other regions. This suggests that in ecosystems where climates are projected to be warmer and wetter, the effects could be faster decomposition rates and higher releases of carbon dioxide.  

Alternatively, global changes affecting soils such as land-use change, which alter soil animal diversity or biomass, may negatively impact decomposition rates in warm, wet climatic regions.

The study, published in the latest issue of "Global Change Biology," was directed by Diana Wall, ecosystem scientist and director of CSU’s School of Global Environmental Sustainability. Wall organized a volunteer scientific network around the world to see if soil animals matter beyond local scales.

For many years, scientists questioned the importance of soil animals in the release of carbon dioxide to the atmosphere as the animals help dead leaves and wood rot.  Without soil organisms to rip, tear, shred and dissolve leaves and wood, the falling leaves would stack up on the ground causing less carbon to be stored in soil. As leaves and wood rot, they break down into smaller fragments, and at every step of decay, carbon is released as atmospheric carbon dioxide, used as food for organisms or stored in soil. Too much global atmospheric carbon dioxide contributes to greenhouse gases.

For the experiment, Wall’s lab worked to assemble more that 2,000 mesh bags filled with dead plant material and shipped them to scientists worldwide where they were placed on the surface of soil. Scientists identified more than 80,000 animals found in 30 sites in 18 countries around the world, from Namibia to Brazil and Canada to Russia. Soil animals include earthworms, termites, pill bugs, millipedes, centipedes, ants and smaller, less well-known invertebrates like mites, springtails and nematode roundworms.

"Climate and plant chemistry are primary drivers of terrestrial decomposition rates, and the release of soil carbon dioxide to the atmosphere is factored into global decomposition models," said Wall. "The role of soil fauna in plant litter decomposition at the global scale was unresolved, although evidence indicates they are key actors in determining how quickly dead plant litter will decay and rot at local scales."

The study’s findings further support the need to include soil animal data in global climate change models, particularly when predicting how fast dying vegetation will decay and release carbon dioxide to the air.

In terrestrial ecosystems, biological diversity of soils is poorly known, but it is estimated to be greater than in above-ground systems. Soil biota is known to regulate vital ecosystem processes such as carbon sequestration, nutrient cycling and decomposition.

Mark Bradford from the University of Georgia, Athens was a lead co-author of the study.

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