Effect of calcium application on growth and physiological property of blueberry cutting seedlings

Abstract:【Objective】Calcium is a crucial regulator of growth and development in plants, the myriad processes dealing with the calcium ion participation are involved in nearly all aspects of plant development. The calcium supplements have increasingly been used in other fruit trees, such as apple, pear, grape, peach and so on. Blueberry, as a kind of Vaccinium L. in Ericaceae, vaccinioideae, is suggested to be planted only in low calcium soil because it is considered to be a calcifuge plant. However, the previous studies reported that the calcium application increased calcium- content of the leaves and improved the fruit quality in some blueberry cultivars. The mechanisms of the effects of calcium application on the growth and fruit quality in blueberry is still unclear. The study aimed to detect the effects of calcium application on the growth, photosynthesis and physiological characteristics of blueberry cutting seedlings.【Methods】The experiment was carried out during July to December, 2020 in Dalian Senmao Modern Agriculture Limited Company. The local main variety Daguo Lanjin was used as the experimental material. The cutting seedlings were uniformly cultured in Hoagland and Arnon basic nutrient solution (calcium- deficient), the pH of hydroponic nutrient solution was adjusted to 4.0- 4.5 with vitriol. The experiment included six treatments of calcium application: 0 (CK), 2.9 mmol·L^-1 (Ca-1), 5.8 mmol·L^-1 (Ca-2), 8.7 mmol· L^-1 (Ca-3), 11.6 mmol· L^-1 (Ca-4), 14.5 mmol· L^-1 (Ca-5). CaSO4 was the test source of calcium and saturation concentration is the limiting concentration of our study. The cutting seedlings were irrigated with 500ml hydroponic nutrient solution every 7 days in the beginning of the growth, and every 4 days in the period of vigorous growth. The photosynthetic parameter [net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and transpiration rate (Tr)] were measured on 0, 10, 20, 30 and 40 days after CaSO4 application by the portable photosynthesis of LI-6400/XT, at 8:30-11:00 a.m . The plant height, base diameter, root volume, calcium content of the stem and calcium content of the leaf were tested on 0, 40 days after CaSO4 application. The leave and stem samples were collected on 40 days when the experiment is accomplished, and were brought back to the laboratory for the measurements of the leave moisture content, stem moisture content, above-ground biomass, total biomass, root activity, superoxide dismutase (SOD) activity and catalase (CAT) activity. The adopted experimental design was a randomized block with five repeats of each treatments (three plants per repeat were used). The differences between means were evaluated by using Tuckey’s test (p ＜ 0.05), the data were all mean ± standard error, statistical analysis was performed using SPSS statistical package (SPSS Statistics for Windows, Version 26.0. SPSS Inc), prism®8 (GraphPad Software, Inc.) were used to make the figure of the test.【Results】Our results showed that low calcium concentrations (2.9 mmol·L^-1 and 5.8 mmol·L^-1 ) notably enhanced the photosynthetic properties such as transpiration rate (Tr) and stomatal conductance (Gs) (p ＜ 0.05) of the cutting seedlings, the leaf net photosynthetic rate (Pn ) increased by 10.47% and 11.24% , compared with the control. The root volume with calcium application of 5.8 mmol·L^-1 and 8.7 mmol·L^-1 was 3.23 and 2.84 times as much as that of the control, the plant height increased by 5.41% and 25.13%, the basal diameter increased by 5.13% and 10.26% respectively, while 5.8 mmol·L^-1 and 8.7 mmol·L^-1 calcium applications had little effect on the above- ground biomass and total biomass. However, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), basal diameter, aboveground biomass and total biomass were significantly reduced with the increase of calcium concentrations ranging from 11.6 mmol·L^-1 to 14.5 mmol·L^-1 . The leaf moisture content displayed the tendency of first rising and then declining with the range of calcium concentrations from 2.9 mmol·L^-1 to 14.5 mmol·L^-1 , whereas calcium application had little effect on the stem moisture content and calcium content of the blueberry cutting seedings. The root activity was significantly higher than that of the control when the plants treated with 8.7 mmol·L^-1 and 11.6 mmol·L^-1 calcium ion. However, low calcium ion (2.9 mmol·L^-1 , 5.8 mmol·L^-1 ) and high calcium ion (14.5 mmol·L^-1 ) were unfavorable for the root activity. In addition, the calcium application had significantly enhanced the SOD, CAT activities compared with the control, the SOD activity was the strongest when the calcium ion concentration was 8.7 mmol·L^-1 , CAT activity increased gradually with the increase of calcium concentrations.【Conclusion】 CaSO4 application promoted the development of blueberry seedlings with appropriate calcium ion environment (5.8-8.7 mmol·L^-1 ), effectively regulated the stomatal opening and improved the transpiration rate (Tr ), net photosynthetic rate (Pn), plant height, basal diameter, root volume and leaf moisture content, it also improved the root activity and the activities of superoxide dismutase (SOD), catalase (CAT). However, the plant calcium ion concentrations (11.6-14.5 mmol·L^-1 ) significantly inhibited photosynthesis and plant growth.