Impact of summer shading on net photosynthetic rate of Actinidia chinensis ‘Hongyang’ and its related eco-physiological factors

CHEN Yansong; YUAN Hualing; WEI Wenyuan; LIU Siqin; CHEN Jiawei; YAO Chenglin

doi:10.13925/j.cnki.gsxb.20160430

Abstract：[Objective] The study explored the diurnal changes in photosynthetic parameters of Actinidia chinensis ‘Hongyang’ under different shading treatments in summer.[Methods] 0％ (control),35％ and 70％ shading levels were used in this study,and the treatments began on June 10,2015.Gas exchange characteristics of the plants were detected on sunny days (July 13 to14 and August 3 to 4,2015) from 6:00 to 18:00 at 1.5 h intervals.Photosynthesis related parameters including Pn,transpiration rate (Tr),stomatal conductance (Gs),intercellular CO2 concentration (Ci),leaf temperature (T1oaf) and environmental factors including photosynthetic active radiation (PAR),air temperature (ta),air CO2 concentration (Ca),and air relative humidity (RH) were automatically measured and recorded with a portable photosynthesis system with an air flow rate of 0.3 L· min-1 and an open system (CI-340,CID Inc.,USA).Central portion of each leaf was used for photosynthesis measurement to ensure sample uniformity.Measurements were replicated 6 times (n =6) for each treatment.[Results] (1) A typical double-peak pattern of diurnal changes in Po with an obvious midday depression was recorded in the control and the 35％ shading treatment.The value of the first peak of Po occurred at 9:00 and was the highest.In the control and under 35％ shading treatment,this peak value was 11.198 and 14.715 μmol· m-2· s-1,respectively,and the value of the second peak occurring at 15:00 was 7.817 and 8.980 μmol· m-2· s-1,respectively.In contrast,a single-peak diurnal curve of Po was found in the 70％ shading treatment,the peak value of which was 10.982 μmol· m-2· s-t appearing at 9:00.The daily average value of Pn was 7.889,6.058,and 3.921 μmol· m-2· s-1 in the 35％ shading treatment,the control and the 70％ shading treatment,respectively.However,the value of PN was significantly higher in the control than in the 35％ and 70％ shading treatments at 6:00 and 18:00.(2) The 94.8％ and 99.3％ of the variations inPn could be separately explained by 6 eco-physiological factors,such as PAR,Ca,T,,Gs,Ci,and Tloaf in the control and the 35％ shading treatments,respectively.97.3％ of the variation in Pn could be explained by Ca,RH,Gs and Ci under 70％ shading treatment.Further,significant negative effects of PAR,Ci,and Tloaf but significant positive effects of Co,Tr,and Gs on Po were found in the control and under the 35％ shading treatment.As for the 70％ shading treatment,negative factors and the direct positive factors were Ci,RH and Ca,Gs,respectively.According to the decision coefficient,PAR,Gs,Ci and Tleaf were the four inhibitors and Ca and Tr were the 2 determinants which affected the Pn of A.chinensis ‘ Hongyang’ in the control.The inhibitors and the determinants were PAR,Tleaf and Tr,Gs and Ci under the 35％ shading treatment,respectively,and were Ci,RH and Ca,Gs under the 70％ shading treatment,respectively.[Conclusion] In summer,there was an obvious midday depression of Po in A.chinensis ‘Hongyang’,which was caused by stomatal limitation.The Pn could be effectively improved by 35％ shading treatment except in the early morning or at dusk.PAR and Tleaf were the major inhibitors affecting the Po ofA.chinensis ‘Hongyang’,while Tr was its main determinant.We suggest that,for the cultivation of the A.chinensis ‘ Hongyang’,it is better to select an open region with a good air circulation,such as flat terrain or less slope gradient and southern side of hills,and to use moderate shading treatment in day time but avoiding shading in the early morning and at dusk during summer.