Detritusphere effects on P availability and C mineralization in soil

This paper investigates two possible processes in the detritusphere: the effect of various fresh plant materials on extractable phosphorus in soil and the effect of decomposing litter on mineralization of soil microbial residues. The objective was to quantify these two poorly-studied processes. The work was done in a soil at two different fertility levels following 30 years of different fertilizer practice, as we have previously observed effects of fertilizer history on soil carbon dynamics. We incubated fresh leaf material from Lupinus, Raphanus and Rumex separated from the soil by a fine mesh. At 4, 7, 14 and 28 days after incubation, extractable phosphate was measured in 1-mm soil layers at increasing distance from the litter. In order to establish a labelled microbial residue pool, the soil had been labelled with C-14-glucose 3 weeks prior to incubation, and respiration was measured throughout the incubation. Extractable soil phosphorus (P) increased up to 3 mm from the litter layer, most in Rumex and least in Lupinus. Extractable soil P increased throughout the sampling period, corresponding to a maximum of 20% of the P lost from the plant litter layer. Measurement of residue-derived organic acids in the soil showed no specific pattern. The study did not indicate any solubilization of soil P as the increase in soluble P can be fully accounted for by leakage from the litter. Mineralization of soil C-14 in the form of microbial biomass and microbial residues was significantly accelerated by the addition of litter. The magnitude was correlated with decomposition of the plant litter, and corresponded to a maximum of 5% of the soil C-14. Because of the localized impact of litter on the detritusphere soil layer, the impact on soil C-14 in this soil fraction was potentially even greater. In conclusion, the decomposition of litter had significant effects on soil carbon mineralization, although we could not demonstrate an effect of plant-derived compounds on soil P availability, beyond the direct contribution of litter P.