Clonal growth response of Hippophae rhamnoides ssp. sinensis to irrigation intensity and its hormone regulation mechanism

Studies of the clonal growth regulation of Hippophae rhamnoides ssp. sinensis have been confined to the external mechanisms. This aim of this study was to investigate the response of clonal growth to irrigation intensity and the relationship between the internal mechanism and hormone regulation. With increasing irrigation intensity,the growth capacity,clonal propagation,and clonal expansion of the ramets first increased but then decreased. This trend was also observed for IAA（Indole-3-acetic acid）,ZR（Trans-zeatin-riboside）,and GA3（Gibberellic acid）,and their ratios to ABA（Abscisic acid）,while ABA content showed the opposite trend. The growth capacity,clonal propagation,and clonal expansion were significantly positively correlated with the contents of IAA,ZR,and GA3,and the ratios of IAA/ABA,ZR/ABA,and GA3/ABA,while significantly negatively correlated with ABA content. Deficient or excessive irrigation lowered the contentsof IAA,ZR,and GA3 and the ratios of IAA/ABA,ZR/ABA,and GA3/ABA and increased ABA content. Clonal growth potential was inhibited and the populations were small ramets,showing a low quantity（sparse distribution） and weak expansion（horizontal root extension and branching）. The clone growth was patterned as "guerrilla,"and the population was prone to presenility. Appropriate irrigation intensity increased the contents of IAA,ZR,and GA3,and their ratios to ABA and decreased the ABA content,indicating the cloning growth potential. The populations were characterized as having large ramets,high quantity（density distribution）,and strong expansion ability. The clone growth was patterned as"aggregation,"and populations were stable. With increased irrigation from deficiency to adequacy to excess,the clonal growth was patterned from guerrilla to aggregation to guerrilla in response to the irrigation intensity by regulation of hormone conditions,and the population stability changed from low to high to low. The change in endogenous hormones,which was induced by irrigation intensity,regulated the clonal growth pattern,which determined the population stability.