减氮条件下生物炭对甜菜盐碱胁迫的缓解效应

  【目的】  通过模拟盐碱胁迫环境，在施用生物炭、减施氮肥的条件下，研究甜菜根际土壤微生物数量、甜菜氮代谢相关酶活性、块根产量和含糖率的变化，明确生物炭对盐碱胁迫的缓解作用，以及盐碱胁迫下施加生物炭后是否可减少氮肥的施用， 为今后盐碱地改良以及甜菜合理施肥提供理论依据和技术支撑。  【方法】  试验于2018年在黑龙江哈尔滨东北农业大学试验站进行。以甜菜品种KWS0143为试验材料，在土壤中添加盐碱处理以中性盐 (Na₂SO₄、NaCl) 和碱性盐 (Na₂CO₃、NaHCO₃) 模拟盐碱胁迫土壤 (Na+含量为3 g/kg)。采用桶栽试验，每桶装土10 kg，共设6个处理，以在盐碱胁迫土壤施N 180 kg/hm2为对照 (CK)，其余5个处理土壤中均加入生物炭30 g/kg, 施氮量依次为N180、162、144、126和108 kg/hm2。子叶完全展开后测定甜菜出苗率，3对真叶后每隔20天左右测定土壤微生物数量及叶片硝酸还原酶 (NR)、谷氨酰胺合成酶 (GS)、谷氨酸合成酶 (GOGAT) 活性，收获后测定块根产量和含糖率并计算产糖量。  【结果】  盐碱胁迫下，施加生物炭显著提高了土壤真菌和细菌数量；BC+N180处理显著提升放线菌数量，在施BC基础上随着施氮量的降低，各时期土壤放线菌含量呈降低趋势。施加生物炭能够显著提高盐碱胁迫下甜菜出苗率，施氮量对出苗率的影响不大；施加生物炭后氮代谢相关酶活性显著提高，其中BC+N162和BC+N144各时期NR活性均高于CK，BC+N144除播种后第117天、第138天外，叶片GS活性均显著高于CK，BC+N144叶片GOGAT活性始终显著高于CK，BC+N126除播种后第53天和第138天外，GOGAT活性显著高于CK；施加生物炭后除BC+N108处理外, 各施加生物炭处理甜菜的块根产量、含糖率、产糖量均显著高于对照，减施氮肥10%～20%的甜菜产量与BC+N180相当，BC+N162的产糖量与BC+N180差异不显著，但显著高于其他处理；而BC+N126和BC+N108的产量与产糖量均显著低于BC+N180。  【结论】  施加生物炭可有效缓解盐碱胁迫对土壤微生物数量及甜菜氮代谢相关酶活性的影响，提高甜菜产量、含糖率、产糖量。在本试验条件下，施加土壤风干质量3%的生物炭，可节约氮肥施用量的10%～20%，提高甜菜的产糖量。

Mitigative effect of biochar on saline-alkali stress in sugar beet under reduced nitrogen condition

  【Objectives】  The paper studied the effects of biochar on soil microbial population, the activities of enzymes related to nitrogen metabolism, yield and sugar content of sugar beet under saline-alkali stress, in order to clarify the mitigation effect of biochar on saline-alkali stress and the possibility of reducing nitrogen fertilizer input.  【Methods】  A pot experiment was conducted at the Experimental Station of Northeast Agricultural University in Harbin, Heilongjiang Province in 2018. The sugar beet cultivar of KWS0143 was used as the test material, and neutral and alkaline salts were added to make a saline-alkali stress soil for the experiment. There were total of six treatments, among them, saline-alkali soil applied with N 180 kg/hm2 was used as control (CK), and in the other five treatments, biochar were added in rate of 30 g/kg soil, and N were applied in rates of 180, 162, 144, 126 and 108 kg/hm2 in turn. The seedling emergence rate of sugar beet was measured when cotyledon was fully expanded. The population of soil bacteria and fungi were measured every 20 days since the six-leaf stage of sugar beet, and the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthetase (GOGAT) in leaves were analyzed at the same time. Sugar content was analyzed after harvest.  【Results】  The population of soil fungi and bacteria were significantly increased by the application of biochar under saline-alkali stress. BC+N180 treatment significantly increased the amount of actinomycetes, BC+N126 treatment increased the amount of bacteria, but BC+N162 treatment was more suitable for the survival of fungi in the soil. After the application of biochar, the activities of enzymes were significantly improved, and the activities of NR in BC+N162 and BC+N144 treatments were higher than that in CK. Except the 117th and 138th day after sowing, the activity of GS in BC+N144 treatment was significantly higher than that in control, and the activity of GOGAT in BC+N144 treatment was always significantly higher than that in CK. Except the 53th and 138th day after sowing, the activity of GOGAT in BC+N126 treatment was significantly higher than that in CK. Applying biochar increased the sugar beet root yield and sugar content significantly, except that in BC+N108 treatment. At the base of applying biochar, BC+N162 treatment obtained similar root and sugar yield as BC+N180 treatment, and significantly higher root and sugar yield than BC+N144 and BC+N108 treatments.  【Conclusions】  The application of biochar is effective to alleviate the saline-alkali stress on the population of soil microorganisms and increase the activities of enzymes related to the metabolism of beet nitrogen, and improve the yield and sugar content consequently. Under the condition of the experiment, the application of 3% biochar in soil can save 10%–20% of nitrogen fertilizer input.