Physical protection of soil organic carbon (SOC) relating to soil aggregates is an important factor controlling SOC decomposition. However, plant roots are considered to be one of the most important drivers of aggregate turnover, including both aggregate formation and destruction processes. On the other hand, plant roots can significantly influence SOC decomposition via the so-called "rhizosphere priming effect (RPE)".
"To our best knowledge, mainly due to methodological difficulties, no studies have investigated the role of root-driven aggregate turnover in regulating the RPE yet," said Prof. WANG Peng from the Institute of Applied Ecology of the Chinese Academy of Sciences.
In a recent research, his team conducted an experiment by employing a 13C natural abundance approach combined with a rare earth oxide tracer method. They thus were able to simultaneously quantify the transformation rates among aggregate fractions and the RPE.
They found that both plant growth and species identity significantly affect aggregate turnover rates. Overall, the extent of the formation to bigger aggregates was larger than that of the destruction to smaller aggregates, consequently leading to an increase in aggregation. The dynamics of soil aggregate turnover could be associated with fine root traits.
Furthermore, differences in the RPE between species were concurrent with that of soil aggregate turnover, indicating the tight association between the RPE and aggregate turnover.
"Based on these findings, we develop a new framework centered on root-driven aggregate turnover acting as a 'key' in regulating SOC dynamics, particularly the RPE: accelerated aggregate turnover by living roots acts as a 'key' where aggregate breakdown may open the 'lock' of SOC decomposition via the positive RPE, and simultaneously aggregate formation may open the other 'ock' of turning root-derived carbon into occluded carbon resulting in carbon sequestration. The balance of the above two processes may determine the net change in SOC," said Prof. WANG.
A new framework centered on root-driven aggregate turnover (Image by WANG Peng)
"We propose that changes in aggregate turnover are likely affect soil carbon cycle, which should merit greater consideration and be incorporated into biogeochemical models," said Prof. WANG.
The results were published in a paper entitled "Rhizosphere priming is tightly associated with root-driven aggregate turnover" in Soil Biology & Biochemistry.
This study was supported by the National Key R&D Program of China, the National Basic Research Program of China and the National Natural Science Foundation of China.
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