Study on the photosynthetic characteristics of apricots in different ecological groups

Abstract:【Objective】The objective of this study was to compare the photosynthetic characteristics of apricots in different ecological groups, and to screen high photosynthetic efficiency resources for mining excellent germplasm and breeding.【Methods】The Pn (net photosynthesis rate, μmol·m^-2·s^-1) , Tr (transpiration rate, μmol·m^-2·s^-1) , Gs (stomatal conductance, μmol·m^-2·s^-1) and Ci (mesophyll CO2 concentration, μmol·m^-2·s^-1) of 103 cultivars in 4 ecological groups were detected using LI-6400 XT. The measurements were conducted by the same person and under the same conditions with a light intensity of 1 500 μmol·m^-2·s^-1 (red and blue light sources) , a leaf chamber temperature of 26 ℃ and a gas flow rate of 500 mmol·s^-1. The Pn, Gs, Ciand Trof 1-year-old shoots in the middle canopy were determined with a Li-6400 XT portable photosynthesis analyzer at 08:30—11:00 am on 3 to 5 leaves selected from each apricot plant. Water use efficiency (WUE) and carboxylation rate (CE) were calculated: WUE=Pn/Tr; CE=Pn/Ci.【Results】Pn, Gs, Ciand Trin different apricot cultivars showed a normal distribution pattern, indicating that photosynthetic traits are typical quantitative traits and controlled by polygenes.Based on F test, the differences in Pn, Gs, Ciand Tramong the cultivars were significant, suggesting strong genetic background of photosynthetic traits. The average photosynthetic rate of the apricot cultivars was 9.86 μmol·m^-2·s^-1 and its range was 10.18 μmol·m^-2·s^-1, indicating that there was a significant genetic variation in photosynthetic characteristics. Pnranged from 7.81 to 15.75 μmol·m^-2·s^-1 in the ecological group of Northeast Asia, and its average photosynthetic rate was higher than those of the otherthree ecological groups. The difference in Gsbetween different ecological groups was small, and the Gs of Northeast Asia group was the highest in the four ecological groups. The order of Ciin different ecological groups was Central Asian sub > North China > Northeast Asia Ecosystem > European. The largest range of Ciwas found in the North China group, which was from 156.52 to 294.77 μmol·m^-2·s^-1.The average transpiration rate in the North China group was the lowest (4.28 μmol·m^-2·s^-1) , and the highest was in the European ecological group (4.35 μmol·m^-2·s^-1) . The photosynthetic parameters in different ecological groups had extreme values, which provide potential for breeding of better apricot cultivars. There were significant differences in WUE among different ecological groups, and its range was4.45 in the North China group, indicating genetic variation among apricot cultivars in the North China group was large. The correlation between Pn, Gsand Trin the Northeast Asia group was generally stronger than that in the other three groups. The correlations of WUE, carboxylation rate and photosynthetic parameters of apricots in different ecological groups, suggested that WUE was negatively correlated with Pn, Gs, Ci, and Tr (except for Pnof North China Ecological group) , and the correlation of WUE with Trwas stronger than with Pn, Gsand Ci, but none of them was significant. The CE was positively correlated with Pn, Gs, and Tr, and the correlation of CE with Pnwas higher than with Gsand Tr, and the correlation between CE and Pnin the North China group and the Central Asia ecological group was significant. There were significant positive correlations between Pnand Gs, Ci, and Trin different ecological groups (except for Ciof the Northeast Asia and the Central Asia group) . The correlations between Pn and Gsand Trin the Northeast Asia group was generally higher than those in the other three ecological groups. The correlation coefficients among Pn, Gsand Trwere high in each ecological group, and that between Pnand Ciwas relatively lower, and there was a similar pattern in the other three ecological groups, indicating that Pnwas mainly affected by Gsand Tr. Using photosynthetic rate as the main indicator, and other photosynthetic parameters as reference indicators, 5 cultivars with high photosynthetic performance were screened out from the ecological group of North China. Their photosynthetic rate was at least 47% higher than the average of all the cultivars tested.【Conclusion】Pn, Gs, Ciand Trare strongly affected by the genetic background. The average Pnand WUE in the ecological group of Northeast Asia were higher than in the other ecological groups. Five cultivars with high photosynthetic performance were screened.