采用室内培养方法, 以西藏拉萨地区选取的草地、农田为对照, 测定并比较日光温室土壤碳、氮矿化特征, 揭示草地和粮田转变为日光温室菜地后土壤矿化演变过程, 为西藏高原设施菜地土壤管理提供科学依据。结果表明, 草地、农田、1年温室、5年温室土壤有机碳矿化速率均在培养前期(0~7 d)日均矿化量最快, 且草地土壤显著高于农田和5年温室土壤(P<0.05), 温室土壤间无差异(P>0.05); 在培养28 d后, 农田土壤有机碳矿化释放的CO2-C累积量高于草地, 草地高于1年温室和5年温室, 但不同类型土壤碳矿化释放的CO2-C累积量间差异不显著(P>0.05)。无论是草地、农田还是温室, 4种土壤氮矿化都主要发生在培养的前期(0~3 d), 之后随着培养时间的延长, 不同利用类型土壤氮素转化以氮素的固定为主; 至培养结束时, 草地、农田、1年温室、5年温室土壤无机氮含量分别为培养0 d的29.04%、75.94%、66.86%、65.70%, 说明草地土壤氮素矿化能力较农田和温室强, 而温室土壤氮素矿化能力随着温室利用年限的延长而不显著升高, 农田氮矿化能力最弱。方差分析表明, 土壤氮矿化能力因土壤类型而异但矿化过程不因土壤类型而存在差异。
Soil carbon and nitrogen in vegetable fields are the core elements of soil quality and environmental pollution. The decrease of soil C/N ratio of vegetable fields under greenhouse conditions causes an imbalance in soil carbon and nitrogen content. An effective way of adjusting soil carbon and nitrogen conditions in vegetable fields has been by improving soil quality and decreasing environmental pollution. Furthermore, there has been little research on soil carbon and nitrogen mineralization under greenhouse conditions in the Tibetan region. After transformations of alpine meadows and farmlands into solar greenhouse vegetable fields, there was the need to study the characteristics and processes of soil mineralization. In this study therefore, carbon and nitrogen mineralization in soils of alpine grassland, farmland and greenhouse (1-year, 5-year) were analyzed in an indoor incubation experiment. The results showed that soil carbon mineralization in different soil types mainly occurred during the first seven days (0 7 d) after treatment. Soil carbon mineralization was higher under alpine grassland than in farmland and 5-year greenhouse conditions (P < 0.05). There was no significant difference between the 1-year greenhouse and 5-year greenhouse soil conditions in terms of carbon mineralization (P > 0.05). This was attributed to soil nutrient and soil microbial environment sensitivity to temperature. Soil CO2-C accumulation in farmland soil was higher than in alpine grassland soil. It was also higher in alpine grassland soil than in the 1-year greenhouse and 5-year greenhouse soils. However, the differences in soil organic carbon mineralization and accumulation among alpine grassland, farmland, 1-year greenhouse and 5-year greenhouse soil conditions were not significant (P > 0.05) at 28 days after treatment. Soil nitrogen mineralization mainly happened in different soil types during the first three days (3 d) after treatment. With delayed incubation, the main process of soil nitrogen mineralization was nitrogen fixation. Soil inorganic nitrogen content in alpine grassland, farmland, 1-year greenhouse and 5-year greenhouse soils at 28 days after incubation were 29.04%, 75.94%, 66.86% and 65.70% of that at 0 day, respectively. The results showed that soil nitrogen mineralization capacity of alpine grassland soil was stronger than farmland, 1-year greenhouse and 5-year greenhouse soils. Soil nitrogen mineralization capacity of farmland was weaker than alpine grassland, 1-year greenhouse and 5-year greenhouse. Also soil nitrogen mineralization capacities of 1-year greenhouse and 5-year greenhouse were similar. Moreover, soil mineralization processes were similar among different soil conditions.