Effects Of Chinese Fir Litter And Its Biochar On Soil CO₂ Emission, Microbe And Enzyme Activity

In this paper, an investigation was conducted of impacts of fir ?Cunninghamia lanceolata? litter and its biochar on soil CO₂ emission, microbial community structure and enzyme activity in a fir plantation in the Jianou Wanmulin Nature Reserve of Fujian Province, in the hope of providing some valuable information for rational utilization of the biomass resources and management of carbon sequestration in the artificial forest in Subtropical China. The biochar was produced from fir litter through pyro lysis at three different temperatures,350 ?,550 ? and 750 ?. Soil samples were collected from the plantation, and prepared into eight treatments by amending fir litter, biochar or both, separately, and the litter and biochar was added both at a rate of 2% of the dry soil mass. All soil samples were incubated in the dark at 25 ? for 364 d. We used the alkali absorption method to observe soil CO₂ emission dynamic during the incubation. At the end of the incubation, the soil samples were analysed for soil properties and enzyme activity using conventional methods, and for soil microbial biomass and community structure using the phospholipid fatty acid method.Results showed that the pyrolysis temperature of biochar only significantly influenced soil total CO₂ emission at the early stages of incubation ?p<0.05?, and the soil total CO₂-C emission rates with addition of BC350 ?biochar produced at 350 ?? were higher than with BC550 ?biochar produced at 550 ?? and BC750 ?biochar produced at 750 ??, and biochar produced at lower temperature ?BC350? resulted in more cumulative soil total CO₂-C emission. The cumulative soil total CO₂-C emission with biochar was higher than that without biochar at the early stages of incubation, however, it was lower at the late stages. Native soil organic carbon mineralization rates declined with the incubation time in Treatment S+BC, and biochars stimulated the native soil organic carbon mineralization at the early stages of incubation ?1-14 d?, but suppressed the native soil organic carbon mineralization at the late stages ?224-364 d?. CO₂ mineralization rate from biochar declined with the incubation time, While the mineralization rates were slightly higher in Treatment S+L+BC than in Treatment S+BC. The cumulative mineralization ratio of biochars was significantly lower in Treatment S+BC than in Treatment S+L+BC, and the cumulative mineralization ratio of BC750 was significantly lower than BC350 and BC550.The pH and C/N ratio was higher in Treatment S+BC and Treatment S+L+BC ?regardless of preparation temperature? than Treatment S. And the effect was more significant in Treatment S+L+BC750 than in Treatment S+L+BC350. The amendments, regardless of which, increased soil total carbon and total nitrogen, but the effect on total carbon was more significant in Treatment S+BC than in Treatment S+L, and in Treatment S+BC350 than in Treatment S+BC750. From the perspective of one year, Treatment S+BC had no significant effect on the decomposition of native soil organic carbon, whereas Treatment S+L stimulated it. Treatment S+L+BC promoted the decomposition of biochar, and the soil organic carbon content derived from Treatment S+L+BC750 was more than Treatment S+L+BC350.Phospholipid fatty acid analysis showed that Treatment S+L and Treatments S+L+BC were both significantly higher than Treatment S in total PLFAs, fungi abundance and fungi to bacteria ratio, and Treatments S+BC and Treatments S+L+BC were significantly higher than Treatment S in ratio of gram positive bacteria to gram negative bacteria. However, Treatment S+L and Treatments S+L+BC were lower than Treatment S in abundance of actinomycetes, but Treatments S+L+BC were much higher than Treatment S+L in abundance of actinomycetes. Principal component analysis ?PCA? shows that microbial community structure varied significantly with type of the amendment. Canonical correspondence analysis ?CCA? shows that the amendments changed soil properties, including soil pH, C/N, total carbon, total nitrogen, dissolved organic carbon ?DOC? and dissolved organic nitrogen ?DON?, which in turn affected the soil microbial community structure. The effects of amendment increasing soil total carbon, C/N and soil pH were more significant in Treatment S+BC than in Treatment S+L, but the effect of increasing soil microbial biomass was more in Treatment S+L than in Treatment S+BC, and so was the effect on soil microbial community structure.The activity of ?-glucosidase ?PG?, ?-N-acetylglucosaminidase ?NAG? and acid phosphatase ?AP? in Treatment S+L was significantly higher than in Treatments S, and slightly higher than Treatment S+BC and Treatment S+L+BC. There was significant positive correlation between ?G, NAG and AP, respectively. There was significant positive correlation between NAG and soil total nitrogen content. ?G, NAG and AP had a significant positive correlation with DOC, separately. The activity of ?G and NAG was positively correlated with the content of gram positive bacteria, gram negative bacteria, fungi, and total PLFAs. However, AP was positively correlated with the content of fungi and total PLFAs.