长期保护性耕作可提高表层土壤碳氮含量和根际土壤酶活性

【目的】 研究不同长期耕作措施对作物根际和非根际土壤碳氮元素含量和土壤酶活性的影响，以及土壤碳氮元素与碳氮转化相关酶之间的相互联系，对认识土壤酶响应土壤碳氮变化的机制和选择合理有效的耕作技术具有重要的理论和实践意义。 【方法】 长期耕作试验始于1999年，位于河南孟津县，属于黄土高原东部边缘，土层深厚 (50—100 m)，土壤类型是壤质黄绵土。试验处理有草地 (GL)、传统耕作 (CT)、免耕覆盖 (NT)、深松覆盖 (SM)，于2016年采集根际土和非根际土0—20 cm、20—40 cm，分析了土壤总碳、有机碳和总氮含量，以及β-葡萄糖苷酶 (BG)、β-纤维二糖苷酶 (CBH)、β-木糖苷酶 (BXYL)、乙酰氨基葡萄糖苷酶 (NAG) 和亮氨酸氨基肽酶 (LAP) 的活性，并进行了土壤碳氮元素含量与酶活性的相关性分析。 【结果】 1) 与传统耕作相比，免耕和深松显著提高了根际和非根际0—20 cm土壤的总碳、有机碳和总氮含量，显著降低了非根际20—40 cm土壤的总碳、有机碳和总氮含量。草地显著提高了根际土壤总碳、有机碳和总氮含量，显著提高了非根际0—20 cm土壤的有机碳含量，显著降低了非根际土壤的总碳含量和非根际20—40 cm土壤中的有机碳含量。深松显著降低了作物根际和非根际土壤C/N，免耕和草地处理显著降低了作物非根际20—40 cm土壤中的C/N，但草地处理显著提高了作物非根际0—20 cm土壤C/N。2) 与传统耕作相比，草地、免耕和深松显著提高了根际土壤中β-葡萄糖苷酶、β-纤维二糖苷酶、β-木糖苷酶和乙酰氨基葡萄糖苷酶的活性。草地显著提高了根际土壤的亮氨酸氨基肽酶活性，免耕和深松显著降低了根际土壤的亮氨酸氨基肽酶活性。3) 碳氮转化相关酶之间均存在正相关关系 (除β-纤维二糖苷酶与亮氨酸氨基肽酶之间)。碳氮转化相关酶与土壤总碳、总氮和有机碳之间均存在正相关关系 (除亮氨酸氨基肽酶与总碳之间)，与C/N之间均存在负相关关系。 【结论】 土壤碳氮转化酶之间存在相互促进的关系，共同参与土壤碳氮的转化。长期保护性耕作 (免耕和深松) 可以有效提高土壤表层的总碳、有机碳和总氮含量，提高根际土壤酶活性，有利于营养元素 (有机质、碳氮元素) 的循环转化和作物的吸收利用，以深松效果最好，免耕次之。

Long-term conservation tillage improves surface soil carbon and nitrogen content and rhizosphere soil enzyme activities

【Objectives】 Long-term tillage affects the C and N contents and enzyme activities in rhizosphere and non-rhizosphere soils of crops, and then affects the correlation between soil C and N contents and the activities of enzymes associated with C and N transformation. The paper compared the effect of different tillage measures to provide reference for selecting rational and effective tillage technology in the tested area. 【Methods】 The long-term tillage experiment, began in 1999, was conducted in Mengjin County, Henan Province, which is located at the east edge of Loss Plateau, the soil was loam Loessal and 50?100 m in depth. The tillage treatments included: weed field (GL), conventional tillage (CT), no-tillage and mulch (NT) and sub-soiling and mulch tillage (SM). Samples of 0?20 cm and 20?40 cm deep in non-rhizosphere and rhizosphere soil were collected in 2016. The contents of total C, organic C and total N, and the activities of β-glucosidase (BG), β-D-cellobioside (CBH), β-xylosidase (BXYL), β-N-acetylglucosaminidase (NAG) and leucineaminopeptidase (LAP) were analyzed. The correlation between soil C and N content and enzyme activity was analyzed. 【Results】 1) Compared with the CT, the total C, organic C and total N contents in the 0?20 cm non-rhizosphere and rhizosphere soils were significantly increased by NT and SM, but those in the 20?40 cm non-rhizosphere soil were significantly decreased. The contents of total C, organic C and total N in rhizosphere soil, organic C content in 0?20 cm non-rhizosphere soil were significantly increased in GL, but the total C content in non-rhizosphere soil and organic C content in 20?40 cm layer of non-rhizosphere were significantly reduced. SM significantly decreased the C/N in rhizosphere and non-rhizosphere soil. NT and GL significantly decreased C/N in 20?40 cm layer non-rhizosphere, but GL significantly increased C/N in 0?20 cm non-rhizosphere. 2) Compared with CT, the activities of BG, CBH, BXYL and NAG in rhizosphere soil were significantly increased by NT and SM. The LAP activity in rhizosphere soil was significantly increased in GL, but significantly decreased by NT and SM. 3) There was a positive correlation between carbon conversion enzymes and nitrogen conversion enzymes (except CBH with LAP). The activities of C and N transformation enzymes were significantly and positively correlated with the soil total C, total N and organic C (except LAP with TC) and negatively correlated with C/N. 【Conclusions】 Soil enzymes associated with carbon and nitrogen transformation have mutually reinforcing relationship and participate in the transformation of soil carbon and nitrogen. Long-term conservation tillage (No tillage and mulching, Sub-soiling and mulching) can effectively increase the total carbon, organic carbon and total nitrogen contents in surface soil, increase the enzyme activities in the rhizosphere soil, facilitate the circulation and transformation of carbon and nitrogen, as well as the absorption and utilization of crops. Long-term conservation tillage is a reasonable and effective tillage method.