Evident variations of fungal and actinobacterial cellulolytic communities associated with different humified particle-size fractions in a long-term fertilizer experiment

Cellulose is the dominant form of carbon (C) existing in arable soils, however the ecology of its degradation in soil is still relatively poorly understood. Here, community abundance and composition of fungal and actinobacterial cellulolytic genes (cbhl and GH48) from glycoside hydrolase family 7 and 48 together with characterization of fulvic acid (FA) and humic acid (HA) determined by cross polarization magic angle spinning (CPMAS) C-13 nuclear magnetic resonance (NMR) spectroscopy were explored in five soil particle-size fractions (large macroaggregate, coarse sand, fine sand, silt and clay), collected from a 33-yr mineral and organic fertilizer experiment. The results revealed the significant effects of particle-size fraction and fertilization on the distribution of soil humus and cellulolytic microbial community abundance. Strong correlations were detected between C content and structure of soil humus with cellulolytic microbial abundance. Generally, larger fractions (>63 mu m) especially fine sand, which showed a lower degree of humification with higher aromaticity, lower HA/FA ratio, aliphaticity and alkyl/O-alkyl ratio of HA, were associated with greater abundance of cellulolytic microbes. However, smaller fractions (<63 mu m), especially the clay fraction, showed lower cbhl and GH48 gene abundances with a greater degree of humification indicated by C-13 NMR spectra. Phylogenetic analysis of the obtained nucleotide sequences revealed undiscovered sequences of both fungal and actinobacterial cellulolytic microbes. However, no clear clustering of sequences from particular particle-size fraction or fertilizer treatment was observed, even though combined application of chemical fertilizer and manure significantly increased cellulolytic gene abundances. (C) 2017 Published by Elsevier Ltd.