新疆绿洲农田不同连作年限棉花根际土壤微生物群落多样性

以南北疆不同连作年限棉花根际土壤为研究对象,采用Biolog技术,并结合传统平板培养法和土壤酶的测定,研究连作对棉花根际土壤微生物群落多样性的影响。Biolog分析结果表明,不同连作年限棉花根际土壤微生物碳源利用和功能多样性差异显著。荒地土壤微生物活性较低;在连作年限较短时(5—10a),根际土壤微生物群落的平均颜色变化率(AWCD)和Shannon指数较高;长期连作(15—20a),则呈明显下降趋势。主成分分析表明,不同连作年限的棉花根际土壤微生物碳源利用特征有明显不同。第一、二组开垦与未开垦土壤分别在PC1和PC2上出现差异,未开垦土壤得分均为负值,开垦土壤均为正值;而正茬与连作多年的棉花土壤在PC1上差异显著。其中在PC1上起分异作用的碳源主要是羧酸类和聚合物类,这两类碳源可能是影响连作棉花根际土壤微生物的主要碳源。可培养微生物数量的测定结果表明,荒地细菌数量最少;在连作年限较低时(5—10a左右),细菌数量呈上升趋势;而长期连作(>15a)后,细菌数量呈现下降趋势。真菌数量在连作多年后(10—15a)也开始增加。放线菌变化趋势不明显。四种土壤酶活性在连作的初中期(5—15a),连作障碍表现明显,土壤酶活性呈下降(过氧化氢酶和磷酸酶)或先升高后下降(脲酶和蔗糖酶)趋势,但随着连作年限的延长(15—20a),这4种土壤酶活性均表现出增高趋势。综上所述,棉花长期连作使棉花根际土壤微生物群落多样性降低,发生连作障碍,进而导致棉花产量降低。

Microbial community diversity of rhizosphere soil in continuous cotton cropping system in Xinjiang

This study investigated effect of various durations of contton cropping on microbial community diversity of rhizosphere soil in south and north parts of Xinjiang by Biolog method, cultured-based microorganism and soil enzyme measurements. Biolog analysis showed that there were significant differences in microbial carbon utilization and functional diversities of microbial community of rhizosphere soils under various durations of contton cropping. Soil microbial activity of uncultivated soils were lower than that of cultivated soils. The AWCD of rhizosphere microbial community and Shannon(H) index were higher under 5-10 years than under 15-20 years of continuous contton cropping. The principal component analysis showed that there was significant differences in carbon utilizations of soil microbial community. The significant differences existed on PC1 and PC2, respectively, between cultivated and uncultivated soils in group one and group two, and the coefficients of uncultivated soils were negative,those of cultivated soils were positive. However significantly differences in PC1 were found between soils under rotation system and continuous cotton cropping.The differences of carbon sources in PC1 were mostly caused by carboxylic acid and polymers, which were probably the main carbon sources affectting soil microbial community under continuous cotton cropping.The results of count of soil culturable microorganism showed that numbers of bacteria in the uncultivated soils were less than that in the cultivated soils. Nevertheless, numbers of bacteria were larger under 5-10 years than under 15-20 years of continuous contton cropping. The numbers of fungi increased after 15-20 years continuous contton cropping. However, numbers of Actinomyces did not change obviously between cultivated and non-cultivated soils. Soil enzyme activities were decreased significantly after 5-15 years of continuous contton cropping, then, increased after 15-20 years of continuous contton cropping. It is concluded that soil microbial community diversities were decreased in rhizosphere soils under long-term continuous cotton cropping, and this might be the main cause of yield decrease of cotton in Xinjiang.