TY - JOUR

T1 - 13CO2 pulse labelling of plants in tandem with stable isotope probing: methodological considerations for examining microbial function in the rhizosphere

AU - Griffiths, Robert I

AU - Manefield, Mike

AU - Ostle, Nick

AU - McNamara, Niall

AU - O'Donnell, Anthony G

AU - Bailey, Mark J

AU - Whiteley, Andrew S

PY - 2004/7

Y1 - 2004/7

N2 - Recently developed 13CO2 pulse labelling and stable isotope probing (SIP) methods offer the potential to track 13C-labelled plant photosynthate into phylogenetic groups of microbial taxa in the rhizosphere, permitting an examination of the link between soil microbial diversity and carbon flow in situ. We tested the feasibility of this approach to detect functional differences in microbial communities utilising recently fixed plant photosynthate in moisture perturbed grassland turfs. Specifically, we addressed two questions: (1) How does moisture perturbation (three treatments; continual wetting, drying, and drying followed by rewetting) affect the assimilation of 13C-labelled exudates carbon into the soil microbial community?; (2) Can 13C deposited in soil from pulse-labelled plants be used to identify microbes utilising plant exudates using SIP methodologies? Net CO2 fluxes showed that prior to 13CO2 pulse labelling, all treatments were photosynthetically active, but differences were observed in night time respiration, indicating moisture treatments had impacted on net CO2 efflux. Measurements of pulse-derived 13C incorporated into soil RNA over 2 months showed that there was only evidence of 13C enrichment in the continuously wetted treatments. However, isotopic values represented only a 0.1–0.2 13C at.% increase over natural abundance levels and were found to be insufficient for the application of RNA–SIP. These findings reveal that in this experimental system, the microbial uptake of labelled carbon from plant exudates is low, and further optimisation of methodologies may be required for application of SIP to natural plant–soil systems where 13C tracer dilution is a consideration.

AB - Recently developed 13CO2 pulse labelling and stable isotope probing (SIP) methods offer the potential to track 13C-labelled plant photosynthate into phylogenetic groups of microbial taxa in the rhizosphere, permitting an examination of the link between soil microbial diversity and carbon flow in situ. We tested the feasibility of this approach to detect functional differences in microbial communities utilising recently fixed plant photosynthate in moisture perturbed grassland turfs. Specifically, we addressed two questions: (1) How does moisture perturbation (three treatments; continual wetting, drying, and drying followed by rewetting) affect the assimilation of 13C-labelled exudates carbon into the soil microbial community?; (2) Can 13C deposited in soil from pulse-labelled plants be used to identify microbes utilising plant exudates using SIP methodologies? Net CO2 fluxes showed that prior to 13CO2 pulse labelling, all treatments were photosynthetically active, but differences were observed in night time respiration, indicating moisture treatments had impacted on net CO2 efflux. Measurements of pulse-derived 13C incorporated into soil RNA over 2 months showed that there was only evidence of 13C enrichment in the continuously wetted treatments. However, isotopic values represented only a 0.1–0.2 13C at.% increase over natural abundance levels and were found to be insufficient for the application of RNA–SIP. These findings reveal that in this experimental system, the microbial uptake of labelled carbon from plant exudates is low, and further optimisation of methodologies may be required for application of SIP to natural plant–soil systems where 13C tracer dilution is a consideration.

KW - Stable isotope probing

KW - Soil

KW - C

KW - RNA

KW - Bacteria

KW - Rhizosphere

KW - Drought

U2 - 10.1016/j.mimet.2004.03.011

DO - 10.1016/j.mimet.2004.03.011

M3 - Article

VL - 58

SP - 119

EP - 129

JO - Journal of Microbiological Methods

JF - Journal of Microbiological Methods

SN - 0167-7012

IS - 1

ER -