干旱胁迫对不同根型苜蓿根系生长及根际土壤细菌的影响

为明确干旱胁迫对根茎型清水紫花苜蓿、直根型陇东紫花苜蓿、根蘖型公农4号杂花苜蓿根系生长及根际土壤细菌群落的影响，采用盆栽试验，运用16S rRNA基因测序技术，研究了幼苗期干旱胁迫下各根型苜蓿根系生长及根际土壤细菌群落结构的变化。结果表明：干旱胁迫下各根型苜蓿的Chao1和ACE丰富度指数均在中度胁迫下最大，Simpson和Shannon-wiener多样性指数各处理间差异不显著；根际土壤细菌群落均以变形菌门、绿弯菌门、类杆菌门、放线菌门和厚壁菌门为主，干旱胁迫均显著增加了变形菌门和厚壁菌门的相对丰度，显著降低了绿弯菌门的相对丰度，但类杆菌门和放线菌门先提高后下降。统计学分析显示，幼苗期干旱胁迫显著影响各根型苜蓿生长发育，随胁迫程度增加，其株高、地上生物量、地下生物量、根系活力、根体积、根系总长均显著降低，根冠比先增加后下降且在中度胁迫时达到最大值。重度胁迫下，清水苜蓿的株高、根系活力显著大于其他品种，而根冠比、根系干重显著小于其他品种；陇东苜蓿的根长、根尖数均显著大于其他品种；根系平均直径、根系总表面积各根型苜蓿间差异不显著。研究结果为植物的抗干旱胁迫以及提高各根型苜蓿在干旱胁迫下的水分利用提供参考。

Influence of root growth and bacterial community in the rhizosphere of different root types of alfalfa under drought stress

To study the effect of drought stress on morphological characteristics of alfalfa root and bacterial community structure and diversity in alfalfa rhizosphere soil, pot experiment using three root types of alfalfa (rhizomatous rooted Medicago sativa cv.Qingshui, tap rooted M. sativa cv.Longdong, creeping rooted M. varia Martin.cv.Gongnong No.4) as the experimental materials was conducted to set up the drought treatment experiments. The total DNA of the seedling rhizosphere soil was extracted and deep sequencing of V4 region of 16S rRNA gene was performed to characterize the bacterial community structure of drought-treated alfalfa. Compared to the normal condition (CK), the richness index of Chao1 and Ace was the highest under moderate stress, whereas the diversity index of Simpson and Shannon Wiener was not significant under different drought stress. Proteobacteria, Chloroflexi, Bacteroidota, Actinobacteria, and Firmicutes were the special bacteria. The relative abundance of Proteobacteria and Firmicutes dramatically increased, while that of Chloroflexi evidently decreased, whereas that of Bacteroidota and Actinobacteria significantly firstly increased then decreased. The plant height, aboveground and underground biomass, root activity, root volume, and total root length were significantly decreased with increasing of drought concentration, while root shoot ratio increased first and then decreased and reached the most under moderate stress. Under severe stress, the plant height and root activity of M. sativa cv.Qingshui were significantly higher than those of other varieties, while root shoot ratio and underground biomass were significantly lower than those of other varieties. The root length and root tip number of M. sativa cv.Longdong were significantly higher than those of other varieties. There was no significant difference between average root diameter and total root surface area among three root types of alfalfa. Results from this study would present reference to the resistance of plants to drought stress and the improvement of water use of three root types of alfalfa under drought stress.