Linkages between straw decomposition rate and the change in microbial fractions and extracellular enzyme activities in soils under different long-term fertilization treatments.

In order to study the linkages between straw decomposition rate and the change in soil biological properties after straw addition to different fertilized soils, we collected soils from three long-term fertilization treatments (no-fertilizer, CK; nitrogen, phosphorus, and potassium fertilizers, NPK; NPK plus straw (S), NPKS), and incubated maize straw with these soils at 25°C for 75 days. The average straw carbon dioxide (CO2) emission rate in the CK+straw (S), NPK+S, and NPKS+S treatments was 0.58±0.51, 0.66±0.53, and 0.74±0.58 μg C g-1soil h-1, respectively. The average increase in the contents of fungi, bacteria, and Actinomycetes under straw addition treatments than the control soils (CK, NPK, and NPKS, respectively) changed in the order of CK+S≤NPK+S <NPKS+S, while bacteria and Actinomycetes peaked later in the CK+SthanNPK+S and NPKS+S treatments. Bacterial abundance unchanged, Actinomycetes abundance decreased, but fungal abundance significantly increased in soils after straw addition. The average increase in the activities of β-glucosidase (BG), β-D-cellobiosidase (CB), and β-xylosidase (XYL) differed as: CK+S<NPK+S ≤ NPKS+S, and the highest activities and increments of them occurred later in the CK+S than NPK+S and NPKS+S treatments. Straw CO2 emission rate was poorly correlated with changes in the contents of microbial fractions across all straw addition treatments, but it was significant positively correlated with the increased activities of BG, CB, and XYL under the NPK+S and NPKS+S treatments. Our results indicated that chemical fertilization and straw return soils differently increased straw decomposition because of the different increases in microbial fractions and soil enzyme activities when compared to the no-fertilizer soil, and the decomposition process was more closely correlated with C-obtaining enzymes than microbial fractions.