Amino sugar distribution in brown earth’s aggregates as affected by different maize residues

Objectives Carbon and nitrogen contents differ in the shoot and root of maize residues, and returning these plant parts to soils of different fertilities could have a different effect on the distribution of amino sugars in soil aggregates. Studying the effects of different maize residues on the distribution of amino sugars in aggregates of brown earth with different fertility and the dynamics of fungal and bacterial community composition in soil aggregates using the ratios of glucosamine to muramic acid would helpful to understand the microbial mechanism of soil carbon and nitrogen cycling and distribution under the condition of maize residues returning.

Methods An incubation experiment was conducted for 360 days at 25℃. Maize root (R) and shoot plus leaf (S) were incorporated into high fertility and low fertility brown earth. Soil samples were taken at 0, 30, 60, 180, and 360 days of incubation and divided into macro-aggregates (size ≥250 μm) and micro-aggregates (size <250 μm) by the dry-sieved method. Carbon and nitrogen contents were determined, and amino sugar content and the ratio of glucosamine to muramic acid were also analyzed.

Results The amino sugar content in macro-and micro-aggregates (P<0.05) increased with increasing maize residue addition to the soil. A higher amino sugar content was recorded in high fertility soil than low fertility soil. The addition of shoots resulted in higher amino sugar content than roots. The ratio of glucosamine to muramic acid was higher in low fertility soil than in high fertility soil. Root addition had higher ratio in macro-aggregates while shoot addition enhanced that in micro-aggregates.

Conclusions The addition of maize residue was beneficial to accumulating amino sugars in soil aggregates. High fertility soil was more conducive to the accumulation of amino sugars. The accumulation of amino sugars was higher under shoot addition than root addition. Further, high fertility soil was conducive to the survival of bacteria, while low fertility soil was conducive to the survival of fungi. Roots and shoots increased the contributions of fungal residues to soil carbon and nitrogen in macro- and micro-aggregates, respectively.