Effects Of Root Excision Mulched With Film On Morphology And Photosynthetic Characteristics Of Poplar In Agriculture Shelterbelts

Root excision mulched with film is an effective method which can decrease crop production in negative-effect area.However,the measure may have adverse effects on the cropland shelterbelt.The forest belt growth,fine root distribution,photosynthetic and stomatal characteristics and chloroplast ultrastructure of poplar were discussed in shelterbelts of black soil region in Heilongjiang Province.The poplars were treated with the root excisions mulched with film from the trunk 0.5 m,1 m,2 m and 3 m in the 3 rows and 6 rows forest belt,compared with no treatments(CK).The results indicated that:(1)Growth rate of DBH of treated poplars were decreased,the influence of growth rate increased with the increasing root excision strength.Compared with the CK,except the 6 rows of forest belts 0.5 m treatment,growth rate of DBH of other treated poplars were decreased significantly after root excision in the first year.Second years after root excision,growth rate of DBH of treated poplars gradually recovered,except the 3 rows of forest belts 0.5 m and 1 m treatments,growth rate of DBH of other treated poplars had no significant difference from CK.Root excisions mulched with film had less influence on the height growth rate of 6 rows of forest belts,treated poplars was not different markedly against the CK in the first and second years.Height growth rate of 3 rows of forest belts were significantly lower than CK after root excision in the first year,the decreasing degree enhanced with the increasing root excision strength.Second years after root excision,the decreasing degree of height growth rate was significantly reduced;only 0.5 m treatment was still significantly lower than CK.Overall,two years after root excision,the 3 rows of forest belts 0.5 m and 1 m treatments growth rate of DBH and volume were significantly lower than CK;growth rate of DBH?height and volume of other treated poplars had no significant difference from CK.(2)Root excisions mulched with film had less influence on the fine root(<2mm diameters)morphology and distribution on the shelterbelt inside.On the shelterbelt outside,Root excisions mulched with film had obvious promoted in fine root growth,the promoted was significant associations with root excision distance.Two years after root excision.fine root biomass of 6 rows of forest belts 0.5 m treatment,3 rows of forest belts 0.5 m and 1 m treatments were increased notable,the relative distribution of fine root biomass in 0?10 cm and 0?20cm soil were also increased.Compared with 1?2 mm fine root,the<1 mm fine root biomass was more sensitive to root excisions mulched with film.(3)Root excision mulched with film has not significant effect on poplar leaf water content.One month after root excision,the time of peak and trough in the treatments were earlier than CK.Different treatments of root excision mulched with film made daily average value of net photosynthetic rate of poplar leaves significantly lower than CK,and there were significant differences among different treatments.After three months of treatments,root excision mulched with film induced daily average value of net photosynthetic rate of poplar leaves still lower than CK,but the lowered range was somewhat reduced,root excision mulched with film in the distance from the trunk 3 m had no significant difference from CK.After root excision mulched with film,transpiration curve appeared in many forms,when the distance from the trunk 2 m and 3 m,daily average value of transpiration rate of poplar leaves had no significant difference from CK,and when the distance from the trunk 0.5 m and 1 m,the decrease in transpiration rate was greater than that of photosynthetic rate after one month,the water use efficiency of the other treatments was significantly higher than CK.Compared with CK,the daily dynamics of water use efficiency of the other treatments had no change,but daily average value of water use efficiency of the other treatments had significant changed,some of the changes are adverse.The net photosynthetic rate of treated poplars declined,with the stomatal resistance of leaves increasing and the intercellular CO2 concentration decreasing.These phenomena suggested that the decreasing net photosynthetic rate was mainly caused by stomatal limitation.(4)Except the 6 rows of forest belts 2 m and 3 m treatments,The stomatal density of the upper and lower epidermis of the poplar leaves were obviously decreased than CK after one month.Two months later,with the stomatal density increasing continuously,the lower epidermis of the poplar leaves was significantly higher than CK.Chloroplast ultrastructure of 6 rows of forest belts 1 m,2 m and 3 m treatments had no significant difference from CK.After one month of other treatments,chloroplast ultrastructure of poplar leaves was significantly changed.With the root excision strength increasing,the phenomena were as followed:the chloroplast showed expansion,the plasmolysis was more evident,lamellae of chloroplast were blurred,starch grain volumes became smaller and the quantity was reduced,the number of the osmiophilic granules has increased enormously.Chloroplast ultrastructure of the treated poplar leaves was recovered well and the number and volume of starch granules in the chloroplasts were significantly increased in the treatments of root excision mulched with film from the unk 1 m and 2 m in the 3 rows forest belt after three months.The structural and functional injuries of treated poplar leaves were reversible.The photosynthetic characteristics,the stomatal morphology and the chloroplast ultrastructure of poplar leaves have adapted the water stress causing by root excision mulched with film.These changes were correlated with the intensity of root excision.