Effect Of Soil Moisture Contents And Brassinolide Spraying On Leaf Photosynthetic And Antioxidant Characteristics In Huangguan Pears

Water-saving irrigation and drought-resistant growing in pear orchard are key issuesin high-efficient fruit growing in the future. This experiment examined the effect of soilmoisture contents on net photosynthetic rate and antioxidant abilities in Huangguan pearleaves, so as to figure out a way to increase the antioxidant ability and simulanously thephotosynthetic efficiency of pear leaves.The experiment was conducted with potted‘Huangguan’ pear trees, and the effect of different soil moisture contents and brassinolidespraying on leaf Pn and antioxidant ability in leaves were investigated. The main resultsare as fellows:1. A colse relationship existed between leaf photosynthetic and antioxidantcharacteristics in pears. Under soil water stressed conditions, the oxidative stress wasaggrevated with an increas of LOX activity and MDA content. By foliar spray with BR, theleaf antioxidant capacity was enhanced, which raised leaf Pn significantly.2. Application of BR can also change the dynamic pattern of diurnal Pn changes inpear leaves. A single-peak curve displayed with BR application and a double-peak curveexisted with the control.3. When the soil moisture content maintained approximately75%or so, the maximumleaf Pn was observed, being22.0%,78.5%and70.9%higher than65%,55%and40%soilmoisture treatments, respectively. As soil moisture contents decreased, the netphotosynthetic rates reduced but when the content reached55%or below, the leaf Pnremained a lower level without significant changes. When the soil moisture contentdecreased from75%to65%, Ci decreased by38.5%and reached a very significant level.When the soil moisture content decreased from55%to40%, Ci decreased by56.67%andreached a very significant level.4. When soil moisture content maintained75%or so, a lower level of SOD and APXactivities were found but as soil moisture contents decreased, the activity of both enzymesincreased and when the soil moisture content reached55%, the activity achieved themaximum. However, when the soil moisture content decreased to40%, the activityreduced significantly. Under either stressed or unstressed soil moisture conditions, sprayingbrassinosteroids (BR) could significantly increase leaf SOD and APX activities, with SOD activity from four soil moisture treatments increasing by39.1%~113.3%and APX by28.8%~141.7%. The AsA contents in leaves showed a increasing trend with a decrease ofsoil moisture contents.5. By comparing to four different soil moisture treatments，the results showed that,when the soil moisture content maintained about75%or so, the maimum leaf Pn wasreached, and when the soil moisture content decreased to65%, the net photosynthetic ratesdecreased. When the soil moisture content maintained about55%or so, LOX and SODactivities reached a maximum. Therefore, it is suggeated that75%soil moisture was moreappropriate for pear trees to carry out photosynthesis under the present experimentalconditions.