Root turnover, organic rhizodeposition

J. Swinnen, Rhizodeposition and turnover of root-derived organic material under conventional and integrated management. Agriculture, Ecosystems and Environment 5/ l 15 (1994). 

Several authors have applied in situ pulse labeling of plants (grasses and crops) with C-CO2 under field conditions with the objective of quantifying the gross annual fluxes of carbon (net assimilation, shoot and root turnover, and decomposition) in production grasslands and so assess the net input of carbon (total input minus root respiration minus microbial respiration on the basis of rhizodeposition and soil organic matter) and carbon fixation in soil under ambient climatic conditions in the field. 

According to the mechanisms of release, organic rhizodepositions may be grouped into these major fractions lysates, leachates from sloughed-off cells, and dead tissues as a consequence of root turnover. In contrast, root exudates (2-10% of translocated carbon) are released from intact root cells either passively as diffusates or actively as excretions or secretions with specific functions (Grayston et al., 1996 Neumann... 

Organic compounds released from sloughed-off root cells and tissues are a major carbon source for rhizosphere microorganisms but may indirectly have an impact as microbial metabolites on nutrient availability and on exclusion of toxic elements in the rhizosphere (Brimecombe et al., 2007). Continuous root turnover is a general feature of plant development, and insoluble root debris may comprise 50-90% of total rhizodeposition (Darrah, 1991). 

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