施肥方式和土壤水分变化对秸秆降解特征及微生物秸秆碳利用效率的影响

为探究华北平原施肥方式和土壤水分对玉米秸秆降解特征及微生物秸秆碳利用效率的影响，从长期定位实验站采集施用9 t/hm²牛粪的有机肥和等养分含量的化肥处理(N、P、K肥)的表层土壤，将¹³C标记的玉米秸秆分别添加到2种施肥方式的土壤中，在恒湿(田间持水量(WHC)60%)和干旱胁迫(WHC 30%)条件下培养56 d，测定来源于秸秆和土壤本底的CO₂排放和微生物量碳(MBC)的动态变化，并分析微生物秸秆碳利用效率和代谢熵。结果表明:添加秸秆后，随着培养时间的延长，土壤总CO₂-C排放通量先降低后趋于稳定，土壤总MBC先增加后降低。相比恒湿条件，干旱胁迫显著降低了来源于秸秆和土壤本底(培养第1、3天除外)的CO₂-C累积排放量，却显著提高了微生物秸秆碳利用效率；培养前期(第1—7天)，干旱胁迫显著降低了土壤总MBC，但后期(第14—56天)对土壤总MBC影响不显著。恒湿条件下，施用有机肥的土壤中秸秆(培养第1天除外)和土壤本底(培养第1、3天除外)来源的CO₂-C累积排放量、微生物代谢熵均显著高于化肥处理，但在培养第3天微生物秸秆碳利用效率显著低于化肥处理；而干旱胁迫条件下2种施肥方式间秸秆(培养第56天除外)和土壤本底来源的CO₂-C累积排放量、微生物代谢熵和秸秆碳利用效率差异均不显著。综上，恒湿条件下，施用化肥可显著降低秸秆和土壤原有有机碳的累积矿化量，在培养第3天微生物秸秆碳利用效率显著升高，有利于秸秆碳在土壤中的固存；而在干旱胁迫下，化肥和有机肥施用均有利于秸秆碳的固存。

Effects of long-term fertilization and soil moisture on straw decomposition and microbial straw-carbon use efficiency

To investigate the effects of fertilization regimes and moisture changes on the degradation characteristics of maize straw and the microbial straw-carbon use efficiency in north China Plain. In this study, surface soil treated with organic fertilizer(9 t/hm² cow manure)and chemical fertilizer(N P K fertilizer)with equivalent nutrient content was collected from long-term experimental field. The ¹³C labeled maize straw was separately added to the soil under the two fertilization regimes, and soil was subjected to constant humidity(60% water holding capacity, WHC)and drought stress(30% WHC)conditions for 56 d. The dynamics of CO₂ emissions derived from straw and background soil, and microbial biomass carbon(MBC)were determined, and microbial straw-carbon use efficiency and metabolic quotient were analyzed. The results showed that: After the addition of straw, soil total CO₂-C flux initially decreased and then stabilized, while total MBC initially increased and then decreased with incubation time. Compared to constant humidity, drought stress significantly reduced the cumulative CO₂-C emissions derived from straw and background soil(except on day 1 and day 3 of incubation), while significantly increased microbial straw-carbon use efficiency. Drought stress significantly decreased soil total MBC during the early incubation period(day 1 to 7), and there was no significant difference between the drought stress and constant humidity treatments during the later incubation period(day 14 to 56). Under constant humidity conditions, the cumulative CO₂-C emissions derived from straw(except on day 1 of incubation)and background soil(except on day 1 and day 3 of incubation), as well as the microbial metabolic quotient were significantly higher in soil with organic fertilizer treatment compared to soil with chemical fertilizer treatment. However, the microbial straw-carbon use efficiency was significantly lower in soil with organic fertilizer treatment compared to soil with chemical fertilizer treatment on day 3 of incubation. Under drought conditions, there were no significant differences in the cumulative CO₂-C emissions derived from straw(except on day 56 of incubation)and background soil, microbial metabolic quotient and straw-carbon use efficiency between the two fertilization regimes. In conclusion, under constant humidity conditions, the application of chemical fertilizer significantly reduced cummulative the mineralization of straw and native soil organic carbon, and significantly increased microbial straw-carbon utilization efficiency on day 3 of incubation, thereby was beneficial to the sequestration of straw carbon in soil. Both chemical and organic fertilizers were beneficial to the sequestration of straw carbon under drought conditions.