Decomposition of 14C-labelled glucose and legume material in soils: properties influencing the accumulation of organic residue C and microbial biomass C
1992
Amato, M. | Ladd, J.N.
Relationships were established between the properties of 23 soils. Particularly identified were those soil properties correlated with (i) native biomass C, with (ii) the extent of decomposition of added [14C]glucose and [14C]Medicago littoralis plant residues after 44 and 66 weeks incubation respectively, and with (iii) the concentrations of substrate-derived C found in the microbial biomass and non-biomass residues. The native biomass C and biomass 14C from glucose and M. littoralis were highly correlated with each other and with soil clay content and other related soil properties, e.g. CEC and total soil pore space. For glucose-amended soils total residual 14C was also correlated with soil clay content. Differences between soils in the concentration of total residual organic 14C were due entirely to differences in the amounts of 14C present in the microbial biomass. Thus, statistically non-biomass 14C accounted for a constant proportion of input 14C. In contrast with glucose decomposition, total residual organic 14C from M. littoralis decomposition was not significantly correlated with clay content and related properties except when the statistical analyses were confined to soils of neutral to alkaline pH. Soils of mildly acidic pH retained more residual non-biomass 14C than did neutral to alkaline soils of similar clay contents. The close direct correlations between biomass 12C, and biomass 14C from glucose and plant material metabolism, and soil properties indicated that soil charge or structure or both are important factors influencing microbial biomass accumulation in soils. These factors may override such influences as substrate type, concentration and efficiency of utilisation in determining biomass C concentration in soils after long (1 yr) incubation.
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