Spatial location of carbon decomposition in the soil pore system

Abstract

We sought to examine the distribution of carbon (C) decomposition within the framework of the soil pore system. Soils were sampled from a transect having a natural gradient in pore-size distribution. After the addition of labelled wheat straw ( 13 C) the repacked soil columns were incubated (25 C) at soil water matric potentials of either À75 kPa or À5 kPa and for either 4 or 90 days. Pore-size distribution was determined for each soil column after incubation and soils were then analysed for soluble C, label-derived residual C, label-derived and native biomass C, nematode abundance, and ergosterol concentration as an indicator of fungal biomass. Overall, the data suggested that pore-size distribution and its interaction with soil water give rise to a highly stratified biogeography of organisms through the pore system. This results in different rates of decomposition in pores of different size. Added plant material seemed to decompose most rapidly in soils with a relatively large volume of pores with neck diameters c. 15-60 m and most slowly in soils with large volumes of pores with neck diameters < 4 m. Regression analysis suggested that at matric potentials of both À75 kPa and À5 kPa the fastest decomposition of organic substrate occurred close to the gas-water interface. This analysis also implied that slower rates of decomposition occur in the pore class 60-300 m. Correlations between the mass of soil biota and the pore volume of each pore class point to the importance of fungi and possibly nematodes in the rapid decomposition of C in the pores c. 15-60 m during the early stages of decomposition.

Carbon Storage and DNA Adsorption in Allophanic Soils and Paleosols

“…17.1d) provide a haven for SOM so that a portion of SOC is poorly accessible to microbes or enzymes and thus protected. Calabi-Floody et al (2011) showed that significant SOC, which resisted the treatment of hydrogen peroxide, was strongly held by allophane and imogolite in Andisols, a finding consistent with studies of the physical protection and stabilisation of SOM within larger micro-and macroaggregates (Elliott, 1986;Strong et al, 2004). It is possible that SOC is protected against the attack of enzymes in the narrowest interstices, such as in nanoaggregates, because the diffusion pathway for the passage of enzymes is constrained (McCarthy et al, 2008;Chevallier et al, 2010).…”

Modeling Microbial Dynamics in Heterogeneous Environments: Growth on Soil Carbon Sources

“…Soil structure is a dynamic hierarchy of aggregates of different sizes that contain microbial cells [34][35][36]53]. Physical structure and geometry of soil pores [40,46,49] dictate how nutrients may penetrate and diffuse within the soil, and spatial heterogeneities can create local variations in substrate availability. This may lead to the formation of preferable residence sites for microbial organisms [36].…”

Storage and Turnover of Organic Matter in Soil

“…This type of protection is largely a function of soil structure, occurring primarily within meso-and microaggregates, pores with spaces or entrances too small for soil organisms or enzymes to pass (Oades 1988;Mayer et al 2004;Strong et al 2004). Additionally, highly tortuous diffusional paths may reduce the viability of bacterial 'foraging' using enzymes, potentially reducing the likelihood that otherwise degradable SOM is degraded (e.g., Vetter et al 1998).…”