Comparison of low light tolerance and high temperature resistance among eight grape cultivars based on analysis of photosynthetic charac- teristics

Abstract:【Objective】Protected cultivation is an important cultivation mode in grape production. Poor light and high temperature stresses are two urgent problems to be solved in protected cultivation. Photo- synthesis is a very important metabolic process in plants, which can be used as an index to judge plant growth and stress resistance. In order to provide theoretical support for selection of suitable cultivation modes for different grape varieties, photosynthetic characteristics of eight cultivars were studied to eval- uate their low light tolerance and high temperature resistance.【Methods】One-year-old grapevines of Shine Muscat, Summer Black, Ruiduhongyu, Miguang, Wagamichi, Sweet Sapphire, Gold Finger, and Jumeigui planted in pots were used as the experimental materials. After the plants was above one meter in height, the mature leaves in the middle of shoots were selected to determine the light response curve, and diurnal variation of net photosynthetic rate (Pn) under natural, shade or high temperature conditions in single-span greenhouse using a portable photosynthesis system on sunny days. The light compensa- tion point (LCP), dark respiration rate (Rd), apparent quantum efficiency (AQY), light saturation point (LSP) and maximum net photosynthetic rate (Pm) were calculated through a hyperbolic modified model from the light response curves. Meanwhile, the light intensity and air temperature were recorded with a portable HOBO recorder【. Results】The net photosynthetic rate of the eight grape varieties increased first and then tended to be stable with the increasing of the photon flux density (PFD). Different grape varieties showed different Pn under the same PFD. The LCP, Rd, AQY, LSP and Pm could be good indica- tors to reflect photosynthetic performance of different grape varieties under low light and high light in- tensities. The LCP of Jumeigui was the highest of all, which was 58.7 μmol · m- 2 · s- 1. The LCPs of Wa- gamichi, Summer Black, Shine Muscat and Ruiduhongyu were medium. Miguang, Sweet Sapphire and Gold Finger had lower LCPs than the other varieties, which ranged from 29.6 μmol · m- 2 · s- 1 to 35.9μmol·m-2 ·s-1. The Rd ranged from 1.60 μmol·m-2 ·s-1 to 2.02 μmol·m-2 ·s-1 in the eight grape varieties. Those of Wagamichi, Jumeigui, Shine Muscat, Summer Black and Miguang were higher than the other grape varieties, and Gold Finger had the lowest Rd. The AQY of Sweet Sapphire, Gold Finger, Miguang and Shine Muscat was higher than the other varieties, which was above 0.050; that of Wagamichi, Sum- mer Black and Ruiduhongyu was medium; and Jumeigui had the lowest AQY, which was 0.038. There was a significant positive correlation between LCP and Rd, and an extremely significant negative corre- lation between LCP and AQY. Under shade condition, the Pn of Wagamichi and Jumeigui were lower than that of the other varieties, and Gold Finger and Ruiduhongyu had the highest Pn among the tested varieties, which was consistent with the results of the LCP for most of the varieties. The LSP of Jumei- gui was the highest, which was 1 409.1 μmol · m-2 · s-1. LSP of Summer Black and Ruiduhongyu was low- er than that of the other varieties, which had a LSP below 1200 μmol · m- 2 · s- 1. Different grape varieties had different Pm. The Pm of Sweet Sapphire and Wagamichi, which was 15.6 μmol · m- 2 · s- 1 and 14.3μmol·m-2·s-1,respectively,washigherthanthatoftheothervarieties.Pm ofRuiduhongyu,ShineMus- cat, Jumeigui and Summer Black was lower than the other varieties. The daily maximum Pn of Sweet Sapphire and Gold Finger was the highest, which was 15.9 μmol·m-2 ·s-1 and 15.7 μmol·m-2 ·s-1, respec- tively. The daily maximum Pn of Miguang, Ruiduhongyu and Wagamichi was medium, and that of Sum- merBlack,ShineMuscatandJumeiguiwerethelowest,below12.0 μmol·m-2·s-1.Pn wasgenerallycon- sistent with Pm for most of the varieties. Under high temperature conditions in the greenhouse, the Pn of Gold Finger, Miguang and Ruiduhongyu were higher than that in the open field at most of the time points, while the Pn of Jumeigui, Shine Muscat, Summer Black, Sweet sapphire and Wagamichi in the greenhouse were lower than that in the open field at most of the time points.【Conclusion】Gold Finger and Ruiduhongyu have good low light tolerance and high temperature resistance and are suitable for protected cultivation. Sweet Sapphire has good low light tolerance, but poor high temperature resis- tance, and is suitable for early and delayed protected cultivation. Miguang has medium low light tolerance and good high temperature resistance, and is suitable for rain-shelter cultivation. Summer Black and Shine Muscat have medium low light tolerance and poor high temperature resistance, which are suitable for early protected cultivation. Wagamichi and Jumeigui have poor low light tolerance and high temperature resistance, and are not suitable for protected cultivation.