ITES PROFESSOR

Xiaoming Zou

In a feature article in Inventio 2.1, Xiaoming Zou, Ph.D., ITES ecology professor, shared his groundbreaking research linking increased carbon dioxide release from soil with increased exotic earthworm activity in the tropics Since then, Zou has expanded his research on soil biota and CO₂, a greenhouse gas that causes global warming, and has collected three years of data from tropical Yunnan, China. His results challenge the way ecologists have been predicting the effect of future climate change on CO₂ release from soil.

“The decomposition of soil organic carbon, or soil respiration, has been recognized in the scientific community as a control. There is one factor called the Q₁₀ value, which equals the rate of change when temperature changes by ten degrees,” says Zou. In the past, ecologists had assumed that the Q₁₀ value was affected solely by temperature.

“This value is important because when we project global climate change, we need to know how soil respiration or CO₂ efflux comes out from soil, or how much carbon still remains in the soil. So it is a crucial number to know. People use Q₁₀ value of two throughout the world for different ecosystems. A Q₁₀ value of two is chemically correct for all chemical reactions. If you change a chemical process by ten degrees, the rate will double for all chemical reactions.” Zou investigated whether the rate, the same Q₁₀ value, would be the same for biological processes if biota were involved. In other words, is the Q₁₀ value of soil respiration affected by biological processes in addition to temperature change?

The biological processes he examined were plant litter input, root carbon input, or root exudates (what is secreted out from plant roots), and plant uptake of water and nutrients. He studied how the biological processes affect CO₂ efflux from the soil and the Q₁₀ value. “My experiment separated the three processes. There were three treatments for the experiments:

1) a girdling of tree trunks, which basically cut off transport of complex carbohydrates to the roots, so there would be no root exudates; 2) litter exclusion, where we had a tent to intercept litter fall; and 3) root trenching, in which we cut plots of land so that there would be no roots getting into them.” Root trenching cuts off two processes, secretion, or exudates, from roots and plant uptake.

“My findings show that both root exudates and plant litter input affect Q₁₀ value. The broader conclusion is that Q₁₀ value of soil respiration is not only a function of temperature—biota also can affect Q₁₀ values. And for modeling future climate change, using Q₁₀ value of two is no longer valid. It could cause severe deviation.”

Zou’s next project will address one of the fundamental questions in the field of ecology: explaining the gradient increase in biodiversity around the latitudinal gradient, or why tropical ecosystems are more diverse in flora and fauna than other ecosystems. There are different hypotheses to explain this. Zou’s future experiments will test an existing hypothesis and expand it at a more basic level through observations and the examination of tropical soils.

xzou@uprrp.edu

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