Eco-Physiological Effects Of Simulated Rocky Desertification Soil On Dalbergia Odorifera Root System

Dalbergia odorifera has strong drought-tolerance and stress-tolerance that can grow in both mountain ridge and poor land with exposed rock,which is an excellent afforestation tree species in limestone karst mountains.However,it is rare to find studies of Dalbergia odorifera on the mechanism of how to adapt to the rocky desertification environment.In this study,a layered simulation column was used to simulate the rocky desertification type Ⅰ(surface rocky desertification type with different thickness loam and bottom limestone in the bottom)and simulates rocky desertification type Ⅱ(Rocky desertification types with limestone crevices)with fan-shaped simulation column.Annual seedlings of Dalbergia odorifera were used to study the effects of different simulated rocky desertification conditions on the spatial distribution,morphological and physiological characteristics.It will provide scientific basis for the introduction of Dalbergia odorifera in the rocky desertification area of Southwest Karst and the promotion of regional economic development.The results were as following:(1)Dalbergia odorifera showed a certain degree of adaption in different simulated stony desertification soil that there was no significant difference plant’s biomass in 10cm thick gravel substrate and fan-shaped substrate comparing with control group,but plant’s biomass dropped significantly in 15cm thick gravel substrate and full gravel substrate.With the reduce of topsoil thickness,the proportion of biomass distribute increased in root and leaf,and the root-crown ratio also increased.Meanwhile,its roof biomass distribution on third-class root increased.(2)In vertical direction,root weight density in 10 cm thick topsoil substrate and fan-shaped substrate did not change significantly when soil depth was increased.But the density changed considerably in 15 cm thick topsoil substrate and 5 cm thick topsoil substrate.In 15cm thick topsoil substrate,the root weight density increased firstly and then decreased with increase of soil depth.In 5 cm thick topsoil substrate,root weight density centrally distributed in loan layer which range from 0 cm to 5 cm deep in the soil,but the density decreased sharply in gravel layer which range from 5 cm to 20 cm deep in the soil.In horizontal direction,root weight density decreased as horizontal distance increase,and it concentrates in 0 cm to 5 cm away from its trunk.Expecting 10 cm thick gravel substrate,the density of area which was 5 cm to 10 cm far from trunk had no significant difference compared with area that was 10 cm to 15cm away from trunk.These features indicated that Dalbergia odorifera had more strong penetration ability than extension ability.(3)In different simulated stony desertification,the length of roots which have diameter less than 0.5mm varied significantly.In 10cm thick topsoil substrate and fan-shaped substrate,root with diameter less than 0.5mm was the longest,which differed from other substrates significantly.Meanwhile,the proportion of root length which had diameter less than 0.5mm increased with the increase of gravel thickness.To some extent,gravel improved the growth of small-diameter root,as it can enhance root activity so that plant can absorb nutrients better even in poor land.With the increase of gravel thickness,both root surface area and root tips raised firstly and then declined.This implied that Dalbergia odorifera had limited stress-tolerance.(4)In different simulated stony desertification,root activity had upward trend with the increase of gravel thickness.Root activity reached the peak in full-gravel substrate but met the lowest in whole gravel substrate.Comparing with control group,root activity in 15 cm thick topsoil,10cm thick topsoil and fan-shaped substrate did not have significant difference,but root activity in 5 cm thick topsoil substrate had significant difference.(5)With the reducing of topsoil thickness,contents of soluble sugar and soluble protein of Dalbergia odorifera root had downward trend.Stony desertification had little impact on POD activity,but greater impact on SOD activity.SOD activity improved as gravel thickness increasing.In summary,Dalbergia odorifera had great eco-physiological adaptability.Extremely high or low gravel thickness will make a bad influence on root’s spatial distribution and largely constrained by the spatial heterogeneity of the soil,but root can improve its activity to absorb more nutrients by rising root-shoot ratio to transfer more biomass to third-class root and increasing length of small-diameter root and creating more root surface area and root tips.The soil matrix with gravel involvement,root activity,SOD enzyme and POD enzyme activity will improve root system to perform various life metabolic activities.