The Effects Of Shading On Photosynthetic Characteristics And Fruit Quality Of Peach

The experiment was carried out with ‘Yan Hong’ and ‘Baojiahong’(Prunus persica cv. Yan Hong) cultivar to study the effects of shading on fruit quality and photosynthetic characteristics of peach. The main results were presented as follows:1. In the study of light intensity, compared with the controls, fruit quality was not affected by 80% of full sunlight. Fruit interior quality was significantly affected by 60% of full sunlight. For instance, firmness, soluble sugar, ascorbic acid, and anthocyanin were significantly reduced, the contents of titratable acid and soluble starch were significantly increased. Fruit overall quality was severely affected by 20% and 40% of full sunlight. For instance, fruit mass, the vertical and transverse diameter, color, firmness, soluble sugar, ascorbic acid, and anthocyanin were significantly decreased, the contents of titratable acid and soluble starch were significantly increased.In the study of shading period, fruit exterior quality such as fruit mass, shape size and color were not significantly affected by 40% of full sunlight during the young fruit stage and stone hardening stage. While fruit mass, shape size and color were significantly decreased during the late fruit development stage and the whole stage. The interior quality such as fresh firmness, the content of soluble solid, soluble sugar and anthocyanin were significantly reduced, the content of titratable acid was increased by 40% of full sunlight during the different stages. Through comprehensive studying, shading affected more on fruit quality at the late fruit development stage and the whole stage than at the young fruit stage and stone hardening stage.2. Under different shading levels at different leaf growth stages, leaf quality and nutrient content were not affected by 80% of full sunlight, but gradually significantly decreased by 20%, 40% and 60% of full sunlight with the increasing degree of shade. It was mainly presented as follows: specific leaf weight, dry matter content, soluble solid content, soluble starch content and soluble protein content were significantly decreased.In terms of chlorophyll content, there was no significantly statistical difference on chlorophyll a content(chl.a), chlorophyll b content(chl.b) and chlorophyll a+b content chl.(a+b) between full sunlight and 80% full sunlight at different leaf growth stages. Chl.a, chl.b and chl.(a+b) were significantly decreased under 40% and 60% of full sunlight. Chlorophyll content under 20% of full sunlight treatment was significantly lower than full sunlight treatment, but chl.b was significantly higher than 40% of full sunlight treatment. Chlorophyll a/b(chl.a/b) was gradually increased from 100% to 40% of full sunlight with the increasing degree of shade, but significantly decreased by 20% of full sunlight.3. In the study of light intensity, compared with the controls, the diurnal variation of net photosynthetic rate(Pn) appeared to be a single peak curve under the shading treatments, which suggested that photosynthetic ‘noon break’ phenomenon vanished. With the increase of shading level, the net photosynthetic rate gradually decreased. Under full sunlight, Pn was decreased at noon, this was closely related with much too high light intensity, much too transpiration water loss, declined stomatal conductance and decreased intercellular CO2 concentration. Pn was not decreased by 80% of full sunlight, but decreased by 60% and lower than 60% of full sunlight because of decreased light intensity.The diurnal variation of net photosynthetic rate(Pn) appeared to be a ‘noon break’ phenomenon under full sunlight at Ⅱ, Ⅲ period. With the increase of shading level, the net photosynthetic rate gradually decreased at different leaf growth periods. The diurnal variation trend of stomatal conductance and transpiration rate were similar to the diurnal variation trend of net photosynthetic rate, but the diurnal variation trend of intercellular CO2 concentration had an opposite trend.Compared with the controls, maximum net photosynthetic rate(Pmax), light saturation point(LSP), light compensation point(LCP), dark respiratory rate(Rd) were decreased by the shading treatments. Apparent quantum efficiency(φc) presented a trend of increasing first and then decreasing with decreased light intensity.4. With the decreasing of light intensity, the maximum fluorescence gradually increased. In terms of PSⅡ energy distribution ratio, low light intensity significantly increased the value of φEo, but decreased the value of φDo. In terms of PSⅡ reaction center activity, low light intensity significantly decreased the values of ABS/RC, TRo/RC, ETo/RC, DIo/RC. Diurnal variations of the maximum photochemical efficiency(Fv/Fm) decreased at noon under the different light intensity treatments at different growth periods. And the higher light intensity, the greater the reduction of Fv/Fm. This suggested that peach leaves produced photoinhibition. Under low light intensity, the antenna pigment of peach leaves reduced the absorption flux and the trapped energy flux, and decreased PSⅡ reaction center activity, but added energy distribution ratio of electron transport in order to improve the light efficiency.