Responses Of Soil Organic Carbon Mineralization Under Long-term Fertilization Regimes To Temperature Changes And Cattle Manure Addition

The mineralization of soil organic carbon(SOC) is an important part of carbon cycle in the terrestrial ecosystem, and it is directly related to the nutrient cycling and utilization in the soil, crop productivity, greenhouse gases emission, and SOC storage and so on. It is reported that the SOC mineralization is significantly affected by the environmental factors such as temperature, the exogenous organic matter addition and so on, and even small changes of it can lead to higher impact on the dynamics of soil ecosystems. In this study, the effects of temperature changes and cattle manure addition on SOC mineralization, soil labile organic carbon and nitrogen fractions, and soil enzyme activities in a long-term fertilizer experiment, which was established in 1986 in Yucheng site, Shandong province, China, were conducted by using the indoor incubation method, and then the relationships between soil labile OC fractions, enzyme activities and environmental factors were analyzed with redundancy analysis, in order to reveal the impact mechanisms of them. This research provides an important implication of how to enhance soil fertility, maintain and improve soil biological ecosystems. The main results are as follows:1. Long-term fertilization significantly increased the contents of SOC, total nitrogen, available phosphorus and potassium, but decreased soil p H value over 28 years. And all these soil chemical properties were higher in treatments with the application of organic manure over time including standard rate of organic manure treatment(SMA), half-standard rate of organic manure plus half-standard rate of mineral fertilizer treatment(1/2(SMA + SMF)), and double standard rate of organic manure(DMA)) than those in the mineral fertilized treatments(standard rate of mineral fertilizer treatment, SMF; double standard rate of mineral fertilizer treatment, DMF), moreover, they increased with the increasing rate of organic manure addition. In addition, they also increased with the increasing rate of mineral fertilizer application.2. Long-term fertilization significantly increased soil microbial biomass carbon(MBC) and nitrogen(MBN) contents, dissolved organic carbon(DOC) and nitrogen(DON) contents, particulate organic carbon(POC) and nitrogen(PON) contents, and easily oxidizable carbon(EOC) contents as well as carbon management index(CMI). The contents of carbon and nitrogen in soil labile organic matter and CMI were increased with increasing organic manure application. Long-term fertilization significantly increased the activities of most soil hydrolytic enzymes and peroxidase, but decreased the phenol oxidase activity. And treatments with long-term organic manure application had much more significant effects on SOC, soil labile OC fractions and soil enzyme activities than treatments with mineral fertilizer application over time.3. Fertilization, temperature and the interaction of them, significantly affected SOC content, labile OC fractions and enzyme activities in different fertilizer treatments, respectively. During incubation, the contents of SOC and labile OC fractions decreased with temperature increasing, and the enzyme activities were significantly different at different temperatures. Soil hydrolytic enzyme activities decreased with increasing temperature in long-term fertilizer treatments except for 1/2(SMA+SMF) treatment, however, peroxidase and phenol oxidase showed the opposite trend with soil hydrolytic enzymes. RDA revealed that the dominant factors of SOC and soil labile OC fractions affecting soil enzyme activities were POC and SOC at 5℃, DOC and POC at 15℃, DOC and SOC at 25℃, and MBC, DOC, and SOC at 35℃.4. Cattle manure addition significantly increased the contents of SOC, total nitrogen(TN), MBC, DOC, POC, PON and EOC contents, but significantly reduced the contents of MBN and DOC. Additionally, the effects of cattle manure addition on the changes in soil labile OC fractions in SMA and 1/2(SMA+SMF) treatments were less than those in CK and SMF treatments.5. Cattle manure addition significantly enhanced CO2-C release rates and increased the amounts of cumulative mineralized CO2-C in different fertilized soils. And the priming effects in CK and SMF treatments were 48.56% and 48.43%, much higher than those in the SMA and 1/2(SMA+SMF) treatments. Moreover, the priming effects were investigated to be significantly affected by changes in the contents of soil nutrients and the C/N ratios of soil labile organic matter fractions in different fertilized soils.