Short-term decomposition, turnover and retention of residue-derived carbon are influenced by the fertility level in a sandy loam soil

The straw residue amendment to soil is documented as an effective measure for integrated fertility management, and residue's decomposition dynamics are closely related to the physical, chemical and biological properties of soil. This paper aimed to investigate the effects of soil fertility on residue-derived carbon (C) decomposition, turnover and retention, and to identify the linkages between these processes and soil aggregation as well as microbial community. Arable soils following 27-year applications of compost and inorganic NPK along with a control (no fertilizer) were collected to divide into the corresponding high, medium and low fertility levels, and an in situ incubation was set up with these soils amended with and without C-13-labeled maize residues. During the whole incubation, the residue decomposition was significantly affected by the fertility level, and the retentions of residue-C in soils were ranked as high fertility soil > medium fertility soil > low fertility soil. Adding straw residue and improving the fertility level were favorable for the formation of water-stable macroaggregates. Following the addition of C-13-labeled residues, although the residue-C was preferentially incorporated into the large macroaggregate (> 2000 mu m) and then translocated to smaller aggregates, the large macroaggregate made the greatest contribution to the residue-C retention. The distinct microbial community dynamics determined their residue-derived C-13 incorporations into microbial biomass. The increasing C-13 incorporations into gram positive (G(+)) bacteria, fungi and anaerobes and decreasing C-13 incorporations into gram-negative (G(-)) bacteria, actinobacteria and aerobes corresponded to improving fertility levels. Consequently, soil aggregation and microbial community composition collectively explained 92% of the variation in residue-C retention, and their interaction exerted the largest effect. It can be concluded that residue return could effectively enhance soil fertility, which in turn contributes to residue-C retention by associating with macroaggregation and microbial community in a sandy loam soil.