Trichoderma Bio-Fertilizer Decreased C Mineralization in Aggregates on the Southern North China Plain

Trichoderma bio-fertilizer is widely used to improve soil fertility and carbon (C) sequestration, but the mechanism for increasing C accumulation remains unclear. In this study, effects of Trichoderma bio-fertilizer on the mineralization of aggregate-associated organic C were investigated in a field experiment with five treatments (bio-fertilizer substitute 0 (CF), 10% (BF10), 20% (BF20), 30% (BF30) and 50% (BF50) chemical fertilizer nitrogen (N)). Aggregate fractions collected by the dry sieving method were used to determine mineralization dynamics of aggregate-associated organic C. The microbial community across aggregate fractions was detected by the phospholipid fatty acid (PLFA) method. The results indicated that Trichoderma bio-fertilizer increased organic C stock across aggregate fractions and bulk soil compared with CF. Cumulative mineralization of aggregate-associated organic C increased with the increasing bio-fertilizer application rate. However, the proportion of organic mineralized C was lower in the BF20 treatment except for <0.053 mm aggregate. Moreover, the PLFAs and fungal PLFA/bacterial PLFA first increased and then decreased with increasing bio-fertilizer application rates. Compared with CF, the increases of bacteria PLFA in >2 mm aggregate were 79.7%, 130.0%, 141.0% and 148.5% in BF10, BF20, BF30 and BF50, respectively. Similarly, the PLFAs in 0.25–2, 0.053–0.25 and <0.053 mm aggregates showed a similar trend to that in >2 mm aggregate. Bio-fertilizer increased the value of fungi PLFA/bacteria PLFA but decreased G+ PLFA/G− PLFA, and BF20 shared the greatest changes. Therefore, appropriate Trichoderma bio-fertilizer application was beneficial to improving soil micro-environment and minimizing risks of soil degradation.