Studies on photosynthetic characters and their relationship with yield in two late season walnut cultivars
[Objective] The purpose of the study was to explore the relationship between photosynthetic characters and productivity in two late season walnut cultivars in order to provide theoretical reference for high yielding cultivation.The changes in the photosynthesis,chlorophyll fluorescence and yield per plant in the two cultivars were studied in this experiment.[Methods]The two late season walnut cultivars,‘Qingxiang’ and ‘Jinlongl’,were used as the materials.The trees grown at a space of 5 m×6 m were ten years old and cultivated according to the conventional management.The soil was sandy loam,and water and fertilizer management was poor in orchard.Determination of changes in photosynthetic and fluorescence parameters,fruit yield and kernel yield per plant was under normal circumstances.Photosynthetic and environmental parameters were determined using a portable photosynthetic analyzer (Li-6400,USA) and a chlorophyll fluorescence analyzer (PAM-2100,Germany).The experiment was conducted in July 2016 in a walnut orchard in south mountain of Chengxian,Longnan.The measurements were carried out on July 1 and 2,July 11 and 12 and July 21 and 22.Three grafted walnut seedlings were selected for each cultivar,and the fifth or sixth functional leaves of the middle compound leaves from three new branches in the same growth direction of the outer canopy of each tree were measured.The diurnal variation of photosynthesis was measured at one hour interval from 80' clock to 18 O' clock,and the parameters measured included net photosynthetic rate (Pn,μmol·m-2· s-1),intercellular CO2 concentration (Ci,μmol·mol-1),stomatal conductance (Gs,mol· m-2· s-1),and transpiration rate (Tr,mmol· m-2· s-1).Besides,the environmental parameters including atmospheric temperature (ta,℃),air CO2 concentration (Ca,μmol· mol-1),atmospheric relative humidity (RH,％) and light intensity (PAR,μumol·m-2·s-1),and water use efficiency (WUE,mmol·mol-1)were also collected.The light response curve of Pn was constructed by measuring Pn at 2 000,1 800,1 600,1 400,1 000,500,200,150,100,50,20 and 0 μmol· m-2· s-1.SPSS software was used to obtain the regressed light response curve.According to the regression equation,light compensation point (LCP) and saturation point (LSP),maximum photosynthetic rate (Pmax),and apparent quantum yield (AQY) could be obtained.The diumal variations of fluorescence parameters were measured at one hour interval from 80' clock to 18 O'clock at the same time with the measurement of photosynthetic parameters.The fluorescence parameters included PS Ⅱ maximum photochemical efficiency (Fv/Fn),PS Ⅱ photon yield (Yield),photochemical quenching (qP),non-photochemical quenching (qN) and so on.The number of fruit and yield in each investigated tree were collected when walnut were ripe.30 fresh walnuts were randomly collected for calculation of the average single fruit weight after fully dried in the middle of September in the same year.Finally,walnut yield and kernel yield per plant were calculated.All the data were analyzed using Excel 2010 and SPSS 21.0.[Results]The diurnal changes in Pn in both walnut cultivars exhibited a double peak curve with a clear "mid-day rest" around 13 o'clock.The LSP,LCP,AQY,and Pmax in ‘Jinlong1’ and ‘Qingxiang’ were 1 612.5 and 1 716.7 μmol·m-2·s-1,37.32 and 49.27 μmol·m-2·s-1,0.031 8 and 0.037 6,and 11.40 and 18.68 μmol· m-2· s-1,respectively.The data indicated late season walnut trees need strong light and was insensitive to weak light,and therefore should be planted in low density.The variety of ‘Qingxiang’ showed a higher photosynthetic capacity.Fv/Fm,Yield,and qP were low,while qN was high around 13 O' clock,when photosynthetic efficiency decreased with significant photoinhibition but no significant damage on photosynthetic system.Fv/Fm,qP,qN and Yield in ‘Qingxiang’ were generally higher than in ‘ Jinlong1 ’ throughout the day,suggesting that the former had a better light conversion efficiency and stress tolerance and thus more suitable for planting in Longnan mountain.The yield per plant and yield per hectare were also significantly different between cultivars,and productivity of ‘Qingxiang’ was 1.77 times that of ‘Jinlong1’.Pn,Fv/Fm,Yield,qP,qN and yield per plant of the two late season walnut cultivars had strong correlations.[Conclusion]The mid-day decrease in Pn in both cultivars was caused by non-stomatal limitation under extreme environmental conditions.Photosynthetic capacity and plant productivity were significantly positively correlated.Their requirement for strong light with low sensitivity to low light indicated that they were suitable for sparse planting.
Late fruiting walnutsPhotosynthetic characteristicsFluorescence characteristicsYield
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