Rhizodeposition of labile organic carbon (C) is one of the main pathways linking above- and below-ground biota to affect soil C cycling. Rhizodeposition is also a strategic physiological process for plants to cope with environmental stress, such as nutrient deficiency and drought, via the interaction with microbes. Nevertheless, separating decomposition of rhizodeposit C from root respiration in intact plant-soil systems has not yet been achieved due to methodological limitations, even though rhizosphere respiration has been intensively investigated. 

Recently, Prof. Yong Jiang’s Lab from the Institute of Applied Ecology of Chinese Academy of Sciences, used a novel approach to separate soil respiration into root respiration, decomposition of rhizodeposit C, and decomposition of soil organic C (SOC).  

The researchers applied a ¹³C pulse label to intact plant-soil cores and measured δ¹³C values of the separate components of soil respiration simultaneously (i.e., root respiration, decomposition of rhizodeposit C, and decomposition of SOC). Then two-source isotopic mixing models were used to sequentially separate root respiration and then decomposition of rhizodeposit C from total soil respiration rates in planted pots.  

They found that the cumulative rhizodeposit C decomposition and root respiration, respectively, accounted for 7-31% and 52-76% of the cumulative soil respiration.  

Moreover, the cumulative rhizodeposit C decomposition was of a similar magnitude to the cumulative SOC decomposition, indicating that rhizodeposit C decomposition is a fundamental process that should not be overlooked in studies of the terrestrial C cycle. 

The study entitled “A novel ¹³C pulse-labelling method to quantify the contribution of rhizodeposits to soil respiration in a grassland exposed to drought and nitrogen addition” has been published online in New Phytologist as a Methods paper. 

This study was financially supported by the Australian Research Council, the National Natural Science Foundation of China, and Youth Innovation Promotion Association CAS.