Physiological mechanism of regulating root growth of pepper and promoting plant restoring under root cutting stress

【Objective】To investigate the physiological mechanism of self-storing process of the roots of pepper under different root cutting degrees and restoring times, which could provide theoretical basis for selecting suitable mechanical tillage methods for pepper and similar crops.【Method】In this study，Reyin No. 1 pepper seedlings were selected as the research object，and a single factor randomized block design was adopted. Four treatments were set up: no root cutting（control，CK），mild root cutting，moderate root cutting and severe root cutting. The root endogenous hormone content，antioxidant enzyme activity，morphological and vitality indexes，leaf photosynthetic rate and plant growth were determined 15，30 and 60 d after root cutting respectively. And the relationship among indexes was analyzed.【Result】Compared with CK，at 30 and 60 d after root cutting，the fresh weight growth of plants with mild root cutting and moderate root cutting was significantly increased（P<0.05，the same below），and the leaf photosynthetic rate at 60 d after root cutting was significantly increased，and the plant height growth at 60 d after mild root cutting was significantly increased. Root cutting significantly increased the growth of root morphological indexes，among which the increase of average root diameter at 30 d and increase of total root length，increase of surface area and increase of average root diameter at 60 d of moderate root cutting were significantly higher than CK. At 60 d after root cutting，the root activity of mild root cutting and moderate root cutting was significantly higher than that of CK，which was 92.0% and 66.6% higher than that of CK respectively，and had a significant restoring advantage over severe root cutting. Root cutting treatment had obvious regulatory effect on root endogenous hormone contents. Severe root cutting significantly increased gibberellin（GA）content at 15， 30 and 60 d after root cutting，and severe root cutting also significantly increased cytoknin（CTK）content at 15 and 30 d after root cutting. At 15 d after root cutting，the activities of superoxide dismutase（SOD）and peroxidase（POD）in moderate and severe root cuttings were significantly higher than those in CK. At 30 and 60 d after root cutting，the POD activity of 3 root cutting treatments was significantly higher than that of CK. The results of structural equation model analysis showed that root cutting affected the biomass traits indirectly through the effects of endogenous hormone content，antioxidant enzyme activity and root traits, but the influence indexes and paths were different under different restoring times. 【Conclusion】The growth restoring of pepper after root cutting is the result of interaction of growth and physiological indexes. In the early stage，endogenous root hormones promote root growth，or indirectly promote root growth and start root restoring through positive regulation of antioxidant enzyme activity. In the late stage，root cutting treatment and endogenous hormones negatively regulate the activity of antioxidant enzymes to promote root growth and restoring. Mild root cutting and moderate root cutting have compensation or super compensation effects on pepper growth restoring， while time efficiency of severe root cutting is low , and the restoring is completed only after 60 d.