关键词: 马缨杜鹃, 水分胁迫, 生长过程, 生理机制, 数量关系

Abstract: Aims The Rhododendron as a high ornamental value genus has a great potential for resources development and utilization in China which provided the most abundant rhododendron resources in the world. The risk of drought stress is rapidly increasing in the context of global warming, it is necessary to deep understand how drought stress impacts the rhododendron growth through affecting related plant physiological indicators. In this paper, the height and ground diameter growth increment of R. delavayi under the drought stress were studied, and the numerical relationship of the growth increment response to the physiological indicators were established to provide a theoretical basis for the future protection and management of rhododendron. Methods Pots experiment with 2-3 years old seedlings of R. delavayi were carried out from March 11th to October 15th, 2022. The drought stress gradient was set as15% (10%-20%)、25% (20%-30%)、35% (30%-40%)、50 (40%-60)%、70% (60%-80%)、90% (80%-100%) of the field water holding capacity respectively. The height and ground diameter of each R. delavayi were measured in early and late of March, April, May and in the middle of June, July and October. The physiological index of antioxidant system (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activity, malondialdehyde (MDA) content), photosynthesis system (photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (Tr)) and osmotic system (proline (Pro), soluble sugar (Ss), soluble protein (Sp) content), were measured in June, July, and August by randomly selecting five seedlings in each treatment. Important findings 1) The equations of rhododendron height and ground diameter response to the day of year (DOY) were established under each drought gradient with the fitting accuracy between 0.94-0.99. The mortality was the highest under the treatment of 15% of the field water holding capacity. 2) The equations of the relative cumulative tree height response to the soil water content were established with the unimodal curve variation. While that of ground diameter response to the soil water content shows the “U” shape variation with the increase of soil water content before DOY161, the linear pattern with that between DOY161-201, and the unimodal curve variation after DOY201. 3) With the increase of soil water content, SOD activity, CAT activity, POD activity, Pn, gs, Tr and Pro content increased firstly and then decreased, the SOD activity, CAT activity, POD activity and Pro content reach the maximum value at field water holding capacity of 20%-30%, Pn, gs and Tr reach that value at 60%-80%; MDA content gradually decreases; Ci, Ss and Sp content decrease first and then increase, reaching the minimum value at field water holding capacity of 60-80%. 4) Based on the regression analysis of the daily increment of ground diameter and the physiological indexes, the significant regression relationship index includes MDA content, Pn, gs, Tr and Ss content, except the quadratic function relationship, the other physiological indexes are power equation, the fitting accuracy is Tr > Pn > MDA content > gs > Ss content. The cumulative growth (diameter increment) of R. delavayi was the most when the soil content was 68% of the field water holding capacity. With the soil water varying, the growth was mainly promoted by Tr, Pn and gs, but inhibited by Ss content. The MDA content promoted the growth when it was lower than 33.53 nmol?g-1, but it turned inhibited the growth when it was higher than 33.53 nmol·g-1. This has further explained the physiological mechanism of R. delavayi seedlings growth.