熏蒸剂溴甲烷对农田土壤微生物的影响

土壤微生物是反应土壤健康状况最敏感的生物学指标,溴甲烷残留不仅消耗臭氧层,影响生态平衡,还会造成土壤质量恶化和微生物群落结构的变化。为明确溴甲烷对农田土壤微生物群落结构及生态过程的影响,以兰州市红古区连续两年种植草莓的土壤为研究对象,测定熏蒸剂溴甲烷处理后土壤微生物量碳、基础呼吸、诱导呼吸和微生物代谢熵等相关指标,并运用磷脂脂肪酸法(PLFA)测定不同类群微生物的变化。结果表明:经溴甲烷熏蒸处理至培养结束(第90天)时土壤微生物基础呼吸和诱导呼吸分别下降0.6%和16.2%,并且与对照皆差异显著(P 0.05);微生物量碳培养结束时与对照差异显著(P 0.05),且减少5.6%;总体上微生物基础呼吸、诱导呼吸和微生物量碳都呈现先下降后逐渐恢复的趋势;微生物代谢熵(q CO_2)第15天后都高于对照,但随培养时间延长,处理组和对照组的差值逐渐降低,到培养期结束仍未恢复,相差5.1%。溴甲烷对土壤细菌(B)、真菌(F)和革兰氏阴性菌(GN)、革兰氏阳性菌(GP)都存在抑制作用; B、F含量分别较对照下降0.64%—8.72%、0.03%—5.61%;到培养期结束时,GP的量下降0.26%,GN下降10.42%,GN对溴甲烷的敏感性强于GP,且GN的变化具有滞后性;溴甲烷处理降低了B/F和GN/GP,但对GN/GP影响比对B/F的更为显著,土壤微生物压力指数增加。综上,说明施用溴甲烷使农田土壤微生物受到了长期的、持续的外源压力胁迫,溴甲烷在对有害微生物杀死的同时,也对有益微生物造成极大的伤害,不利于土壤优良性状的保持,使土壤中微生物丰富度和多样性下降。因此,实际应用中应充分考虑溴甲烷对土壤微生物带来的负面影响。

Effects of the fumigant methyl bromide on farmland soil microbial community structure and ecological processes

Methyl bromide is a commonly used insecticide and fungicide, which is typically used for the fumigation of farmland soil. Methyl bromide residues not only deplete the ozone layer and affect ecological balance but also contribute to the deterioration of soil quality and changes in the community structure of soil microorganisms, which are sensitive biological indicators of soil health. In order to clarify the effect of methyl bromide on the microbial community structure and ecological processes in farmland soil, we examined soil planted with strawberry in the Hong-gu District of Lanzhou City over two consecutive years, and measured related indicators such as soil microbial biomass carbon, basic respiration, induced respiration, and microbial metabolic entropy. The mechanisms of different microbial groups were determined using the phospholipid fatty acid (PLFA) method. The results indicated that over a culture period of 90 days following methyl bromide fumigation treatment, microbial basal respiration and induced respiration decreased by 0.6% and 16.2%, respectively, which were significantly different from the control values (P < 0.05). At the end of the microbial carbon culture, there was a 5.6% decrease in biomass carbon, which was significantly different from the control value (P < 0.05). Generally, microbial basal respiration, induced respiration, and microbial biomass carbon all showed a trend of gradual recovery after an initial decline, and microbial metabolic entropy (qCO₂) was higher than that of the control on the 15th day. However, the difference between the treatment group and the control group decreased gradually with the prolongation of culture time, although it had still not recovered at the end of the culture period, the difference being 5.1%. Methyl bromide has inhibitory effects on soil bacteria (B), fungi (F), gram-negative bacteria (GN), and gram-positive bacteria (GP). The soil contents of bacteria and fungi decreased by 0.64%-8.72% and 0.03%-5.61% respectively, in response to methyl bromide treatment. By the end of the training period, the amounts of GP and GN had decreased by 0.26% and 10.42%, respectively. The sensitivity of GN to methyl bromide was stronger than that of GP, although the change in GN was delayed. Methyl bromide treatment reduced both B/F and GN/GP ratios, although the effect on the GN/GP ratio was more significant than that on the B/F ratio, and there was an increase in the soil microbial pressure index. In summary, our findings indicate that the application of methyl bromide exerts long-term and persistent exogenous pressure stress on farmland soil microorganisms. Methyl bromide kill harmful microorganisms, and also cause considerable harm to beneficial microorganism, which is unfavorable to the maintenance of favorable soil conditions and decreases the richness and diversity of microorganisms in the soil. Accordingly, the negative effects of methyl bromide on soil microorganisms should be fully considered in practical applications.