Effects Of Soil Drought On Seedling Growth And Physiology Of Dogwoods

Dogwoods(Cornus), belonging to the Cornaceae, are widely used as ornamental plants due to their attractive horticultural traits. In the present study, the growth and physiological reponses to soil drought were assessed for C. florida and C. kousa by pot experiments under controlled conditions. The seedlings of two species were subjected to 19 d drought continuously, followed by 7d normal watering. The indexes of growth, photosynthesis and physiology were monitored and compared for two species during the process of drought treatment and re-watering. These results would provide the basic knowledge for introduction and application of excellent ornamental varieties. The test results showed as followings:(1)The soil relative water content of two dogwoods decreased gradually with the increase of drought time, and the soil relative water content of C. kousa was significantly lower than C. florida at the time of severe drought(soil relative water content<30FC%). Compared with CK, the soil relative water content of C. florida and C. kousa were decreased by 84.8% and 90.0% on the 19 th day of drought, respectively. Meanwhile, the leaf relative water content of two dogwoods was significantly decreased with the continuous drought, which C. kousa decreased more than C. florida did. Compared with CK, the leaf relative water contents of C. florida and C. kousa were decreased by 30.2% and 48.7%, respectively. However, the soil relative water content and the leaf relative water content could restore to normal level after rewatering 7d.(2)The relative growth rate of height and basal diameter for C. florida and C. kousa were significantly decreased under soil drought, and the effects on C. florida was more than on C. kousa. Compared with CK, the relative growth rate of height and basal diameter for C. florida and C. kousa were decreased by 75.2%, 62.1% and 36.0%, 40.4%, respectively. Moreover, the leaf area and leaf biomass of two dogwoods were decreased significantly, and two indexes of C. kousa decreased more than C. florida did. Compared with CK, the leaf area and biomass for C. florida and C. kousa were decreased by 30.12%, 29.7% and 34.9%, 39.5%, respectively.(3) Leaf relative conductivities of C. florida and C. kousa were significantly increased with the continuous drought, and the value of C. kousa was than that of C. florida. Compared with CK, the leaf relative conductivity of two dogwoods were increased by 40.9% and 175.0% at the end of drought treatment, respectively. Compared with CK, the contents of chlorophyll a content, chlorophyll b and total chlorophyll were increased by 40.7%, 85.9% and 53.0%, respectively, when C.kousa was suffered from severe soil drought. Mild and moderate drought(soil relative water content>30%FC) had no significant effect on the contents of soluble sugar content, the contents of soluble protein, MDA and SOD activity of C. florida and C. kousa. However, under severe soil drought, the contents of soluble sugar, soluble protein and MDA of C. florida were increased by 90.8%, 15.8% and 16.2%, respectively, compared with CK; while the contents of soluble sugar, soluble protein, MDA and SOD activity of C. kousa were increased by 193.3%, 50.8%, 81.7% and 3.84%, respectively. All physiological indexses expcept for souble sugar content of C.kousa could restore to normal level after rewatering.(4)The LSP of C. florida and C. kousa decreased significantly while the LCP increased with the continuous soil drought, and C. kousa was more affected than C. florida. Compared with CK, the LSP of C. florida and C. kousa decreased by 27.6% and 46.8%,respectively, and the LCP increased by 14.3% and 200.0%,respectively. Mild drought or moderate drought had no significant effect on Pn, Gs, Ci, Tr, WUEi, Fv/Fm, Fv/F0, q P and q N. However, Pn, Gs, Ci, Tr, Fv/Fm, Fv/F0 and q P decreased significantly under severe drought, while q N increased significantly. The differences of these indexes between two dogwoods were no significant, and those could restore to normal level after rewatering.(5)Both seedling growth and physiology of C. florida and C. kousa were affected by soil drought. The response of growth indexes to soil drought indicate that C. florida has more drought tolerance than C. kousa has. Mild drought or moderate drought had no significant on physiology for two dogwoods. However, severe drought had significant effect on the response of physiology. We concule that the seedlings of C. florida and C. kousa can tolerate mild and moderate soil drought, and the inhibition of C. florida was more than C.kousa under severe drought. However, most of physiological indexes would recover to CK standard after rewatering.