Root turnover

In a perennial grassland there is a relatively constant rate of root turnover (21). A low level relatively constant input of substrate allows... 

Leigh MB, JS Fletcher, X Fu, FJ Schmitz (2002) Root turnover an important source of microbial substrates in rhizosphere remediation of recalcitrant metabolites. Environ Sci Technol 36 1579-1583. 

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. 

R. Fogel, Root turnover and productivity of coniferous forests, Plant Soil 71 75 (1983). 

Besides their influence on P availability, plants also influence the size of the total organic P pool, mainly through the rate and quality of organic input from aboveground litter and root turnover. The rate of organic P input with litter depends on the size and P status of the plants. P-deficient plants usually have less... 

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). 

Janssens, I. A., Sampson, D. A., Curiel-Yuste, J., Carrara, A. Ceulemans, R. (2002). The carbon cost of fine root turnover in a Scots pine forest. Forest Ecology and Management, 168, 231-40. 

Tierney, G. L. Fahey, T. J. (2002). Fine root turnover in a northern hardwood forest a direct comparison of the radiocarbon and minirhizotron methods. Canadian Journal of Forest Research, 32, 1692-7. 

The second major ecosystem role of decomposition is in the formation and stabilization of humus. The cycling and stabilization of SOM in the litter-soil system is presented in a conceptual model in Figure 2. Parallel with litterfall and most root turnover, detrital processing is concentrated... 

Figure 2 Conceptual model of carbon cycling in the litter-soil system. In each horizon or depth increment, SOM is represented by three pools labile SOM, slow SOM, and passive SOM. Inputs include aboveground litterfall and belowground root turnover and exudates, which will be distributed among the pools based on the biochemical nature of the material. Outputs from each pool include mineralization to CO2 (dashed lines), humification (labile slow passive), and downward transport due to leaching and physical mixing. Communition by soil fauna will accelerate the decomposition process and reveal previously inaeeessible materials. Soil mixing and other disturbances can also make physically protected passive SOM available to microbial attack (passive slow).

SD of mean listed for cool temperate steppe ecosystems in Post et al. (1982). Estimated from root turnover rates listed for tropical forests in Gill and Jackson (2000). 

Gill R. A. and Jackson R. B. (2000) Global patterns of root turnover for terrestrial ecosystems. New Phytol. 147(1), 13-31. 

Vogt, K. A., and Bloomfield. J. (1991). Tree roots turnover and senescence. In Plant Roots The Hidden Half, ed. Waisel, Y., Eshel, A., and Kafkafi. U.. Marcel Dekker. New York, 287-306. 

Darrah, P. R., and Staunton, S. (2000). A mathematical model of root uptake incorporating root turnover, distribution within the plant and recycling of absorbed species.TJwr. J. Soil Sci. 51, 643-653. 

Modeling experiments allowed us to control for factors that might cause variation in field-based estimates of woody plant age-SOC relationships. Model estimates of SOC accumulation were comparable to field estimates for upland patch types and substantially lower than field estimates for lowland patch types (Table 4). Model estimates of soil N accumulation were substantially lower than field estimates, especially in lowlands. Given that woody patch age explained only 26-68% of the variance in soil C and N content, our field estimates of accumulation rates cannot be taken as definitive. Model results underestimated field observations, especially for N. Reliability of model estimates of soil carbon could likely be improved with a better understanding of how turnover of the substantial root mass (Table 2) might differ among patch types. Model estimates of soil N are likely constrained by lack of information on inputs associated with N, fixation, atmospheric N deposition, translocation between uplands and lowlands, and root turnover. 

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