Distribution and turnover of recently fixed photosynthate in ryegrass rhizospheres

The cycling of root-deposited photosynthate (rhizodeposition) through the soil microbial biomass can have profound influences on plant nutrient availability. Currently, our understanding of microbial dynamics associated with rhizosphere carbon (C) flow is limited. We used a 13C pulse-chase labeling...

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Bibliographic Details
Published in:Soil biology & biochemistry 2004-02, Vol.36 (2), p.371-382
Main Authors: Butler, Jessica L., Bottomley, Peter J., Griffith, Stephen M., Myrold, David D.
Format: Article
Language:English
Subjects:
13C-labeling
Agronomy. Soil science and plant productions
Biochemistry and biology
Biological and medical sciences
carbon
Chemical, physicochemical, biochemical and biological properties
dry matter partitioning
Fundamental and applied biological sciences. Psychology
isotope labeling
Lolium multiflorum
microbial activity
Microbial biomass
Microbiology
photosynthesis
Physics, chemistry, biochemistry and biology of agricultural and forest soils
plant growth
Pulse-labeling
Rhizodeposition
rhizosphere
root exudates
Root exudation
root growth
shoots
soil microorganisms
soil nutrient dynamics
Soil science
soil-plant interactions
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Summary:The cycling of root-deposited photosynthate (rhizodeposition) through the soil microbial biomass can have profound influences on plant nutrient availability. Currently, our understanding of microbial dynamics associated with rhizosphere carbon (C) flow is limited. We used a 13C pulse-chase labeling procedure to examine the flow of photosynthetically fixed 13C into the microbial biomass of the bulk and rhizosphere soils of greenhouse-grown annual ryegrass ( Lolium multiflorum Lam.). To assess the temporal dynamics of rhizosphere C flow through the microbial biomass, plants were labeled either during the transition between active root growth and rapid shoot growth (Labeling Period 1), or nine days later during the rapid shoot growth stage (Labeling Period 2). Although the distribution of 13C in the plant/soil system was similar between the two labeling periods, microbial cycling of rhizodeposition differed between labeling periods. Within 24 h of labeling, more than 10% of the 13C retained in the plant/soil system resided in the soil, most of which had already been incorporated into the microbial biomass. From day 1 to day 8, the proportion of 13C in soil as microbial biomass declined from about 90 to 35% in rhizosphere soil and from about 80 to 30% in bulk soil. Turnover of 13C through the microbial biomass was faster in rhizosphere soil than in bulk soil, and faster in Labeling Period 1 than Labeling Period 2. Our results demonstrate the effectiveness of using 13C labeling to examine microbial dynamics and fate of C associated with cycling of rhizodeposition from plants at different phenological stages of growth.
ISSN:0038-0717
1879-3428
DOI:10.1016/j.soilbio.2003.10.011