Arbuscular mycorrhizal fungi alter root and foliar responses to fissure-induced root damage stress

Abstract

Ground subsidence caused by coal mining can produce large amounts of surface ground fissures which may damage the surrounding plant roots. Here, a device was used that simulates root damage and we observed the growth of maize roots in real time, the morphological responses of roots and leaves to fissure-induced root damage stress, and the effects of arbuscular mycorrhizal fungi (AMF). Time series of root and leaf growth and hormonal changes in mycorrhizal and control plants with damaged root systems were observed for the first time. Indole-3-acetic acid (IAA) and cytokinin (CTK) levels in roots and leaves decreased significantly one week after ground fissuring. Abscisic acid (ABA) levels increased and the growth of roots and leaves was inhibited. Arbuscular mycorrhizal fungi (AMF) reversed these trends and significantly increased the percentages of root tips and fine roots compared with uninoculated controls. IAA and CTK levels declined significantly in roots and leaves six weeks after ground fissuring but ABA levels remained unchanged. AMF inoculation significantly increased both IAA and CTK levels but decreased ABA levels. The spatial distribution of roots was affected by fissures in addition to the changes in hormones. The negative impacts of ground fissures on maize growth were alleviated by AMF inoculation at harvest with increased shoot and root biomass. The results suggest that the ameliorative effects of AMF on root damage stress may be related to the regulation of hormone levels and an increase in the percentage of fine roots which was conducive to the growth of roots and leaves and increased plant resistance to environmental stress. In addition, analysis of variable distributions shows that the ameliorative effects of AMF were affected by the degree of root damage.