Impact of soil matric potential on the fine-scale spatial distribution and activity of specific microbial degrader communities

Abstract

The impact of the soil matric potential on the relationship between the relative abundance of degraders and their activity and on the spatial distribution of both at fine scales was determined to understand the role of environmental conditions in the degradation of organic substrates. The mineralization of (13) C-glucose and (13) C-2,4-dichlorophenoxyacetic acid (2,4-D) was measured at different matric potentials (-0.001, -0.01 and -0.316 MPa) in 6 × 6 × 6 mm(3) cubes excised from soil cores. At the end of the incubation, total bacterial and 2,4-D degrader abundances were determined by quantifying the 16S rRNA and the tfdA genes, respectively. The mineralization of 2,4-D was more sensitive to changes in matric potential than was that of glucose. The amount and spatial structure of 2,4-D mineralization decreased with matric potential, whilst the spatial variability increased. On the other hand, the spatial variation of glucose mineralization was less affected by changes in matric potential. The relationship between the relative abundance of 2,4-D degraders and 2,4-D mineralization was significantly affected by matric potential: the relative abundance of tfdA needed to be higher to reach a given level of 2,4-D mineralization in dryer than in moister conditions. The data show how microbial interactions with their microhabitat can have an impact on soil processes at larger scales.

Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate

“…Our scenarios generated a high but still realistic variability in biodegradation response. The coefficient of variation of 44% found here for 10-days CO 2 emissions was close to values obtained in experimental studies exploring the effect of spatial heterogeneity on the mineralization of soluble substrates at the millimeter scale: Monard A C C E P T E D M A N U S C R I P T et al obtained slightly lower CV for glucose (14-22%) [8], while CV values ranging from 25 to 160% have been found for the soluble pesticide 2,4-D [3,4,8].…”

“…The combined effect of substrate location and water potential was illustrated by experimental works based on the incubation of soluble substrates, such as glucose and 2,4-D [8], and benzoate [7]. Dechesne et al found cumulative effects of the water potential and the biomass distribution, with high water potential and dispersed distribution both stimulating the mineralization of benzoate [7].…”

“…The heterogeneity of the arrangement of soil particles (inter-aggregate vs intra-aggregate porosity) and the variation of water saturation conditions contribute to maintain gradients in abiotic conditions (nutrients, pH and redox conditions) and therefore locally promote or not the growth of microorganisms [6]. The patchy distribution patterns of bacteria in soils can result in spatial disconnection between organic residues and decomposers and thereby influence the kinetics of decomposition of organic compounds, as has been shown experimentally by [7,8]. The sinuous water diffusion pathways in the soil pore space through which nutrients can be transported can thus play a major role in these situations [9,10] although this can be mitigated by cells migration mechanisms allowing the microorganisms to reach distant resources [11][12][13][14].…”

The millimetre-scale distribution of 2,4-D and its degraders drives the fate of 2,4-D at the soil core scale

“…In this case, intermediary metabolites must move into the soil to come into contact with the different degraders. Monard et al (2012) showed that an increase in soil water content led to a reduction in the spatial heterogeneity of pesticide mineralization, presumably by increasing the probability of degrader and substrate encounters.…”

Increasing soil carbon storage: mechanisms, effects of agricultural practices and proxies. A review

“…At the plot scale, agricultural practices and plant species are the determinants of heterogeneity (Etema and Wardle 2002;Chevallier et al 2000). At the fine process scale, the degree of heterogeneity depends on the soil physical structure, which corresponds to the spatial arrangement of solid particles (mineral particles, OM) and pores in which fluids, decomposers and soluble compounds circulate (Chenu and Stotzky 2002;Monard et al 2012). Understanding how the soil physical structure affects OM dynamics is crucial with a view to preserving or even increasing organic C stocks in soils.…”