Analysis Of Four Species Of Commelinaceae Adaptability And Response Strategies Under Different Light Intensities

Four species(Commelina purpurea,Tradescantia zebrina,Tradescantia flurnuensis’Variegata’ and Tradescantia flurnuensis ’Vairidia’)from Commelinaceae,with good shade tolerance,are used as ground cover plants in landscaping in South China,and as underwood in indoor tourist greenhouses in Northeast China,but the degree of shade tolerance and light adaptation strategy of each plant is still unknown,therefore,five light environments(full light,shade 25%,50%,75%,95%)were set up for light treatment,and the morphological and structural characteristics,biomass distribution,physiological biochemistry and photosynthetic physiological indexes of the four plants were analyzed under different light intensities,and the strategies and potentials of the four plants for light adaptation were explored.It provides a scientific basis for cultivation applications in gardens and further widespread dissemination.The main results are as follows:(1)With the decrease of light intensity,the colorful leaf parts of the four plants gradually degraded and green parts gradually increased,with an overall increasing trend in leaf length,leaf area,specific leaf area,plant height,and leaf angle,but the leaf length and leaf area of Commelina purpurea decreased significantly at shading 95%;Shading reduced the thickness of the upper and lower epidermal thickness and leaf thickness of the four plants,but the palisade thickness and spongy thickness ratio was not significant change;In terms of biomass accumulation and distribution,the total biomass of four plants was largest at shading 25%or 50%,and lowest at shading 95%.With the decrease of light intensity,the biomass gradually accumulated above ground,the root dry weight decreased significantly,and the crown-root ratio reached the largest at shading 95%.Among which the growth rate of Tradescantia flurnuensis’Vairidia’ was largest(345.05%).(2)Although different degrees of shading environment have different effects on the epidermal thickness,cortex thickness,vascular bundle diameter,medulla diameter and stem thickness of four plants,the ratio of tissue structure to stem thickness remained relatively stable.The decreasing light intensities increased significantly the myeloid and cortical cell lengths,but the myeloid and cortical cell widths significantly decreased;With the decrease of the light intensity,four plants showed a significant increase in internodal length and a significant decrease in relative cellulose content,phenylalanine ammonialase(PAL)activity,bending properties,organizational structure intensity,and compressive strength.(3)With the decrease of light intensity,the soluble protein and malondialdehyde content of the four plants decreased significantly,the free proline content decreased and then increased,while the soluble sugars showed different trends;The O2·-content of 4 plants and the H2O2 content of Tradescantia zebrina showed a decreasing trend with the decrease of light intensity,while the H2O2 content of other three plants showed a decreasing and then increasing trend,with the highest H2O2 content under full light exposure.Four plant antioxidants maintained high levels under full light conditions,among which SOD and POD activities and ASA content were positively correlated with the light intensity,with the exception of the CAT activity of Tradescantia flurnuensis ’Variegata’,which decreased significantly,the CAT activity of the other three plants decreased and then increased with the decrease of light intensity.In terms of the mesophyll ultrastructure,the plasma membrane structure was damaged by full light exposure,the number of chloroplasts and mitochondria was significantly reduced,and the number of starch granules,osmophilic granules,and cell wall thickness were significantly increased.(4)With the decrease of light intensity,the anthocyanin content of the four plants decreased significantly.The contents of chlorophyll a,chlorophyll b and total chlorophyll of Commelina purpurea and Tradescantia zebrina showed a increased and then decreased trend,while the Tradescantia flurnuensis ’Variegata’ and Tradescantia flurnuensis ’Vairidia’ increased significantly;Different light environments had less effect on the vertical axis length and horizontal axis length of the four plants stomata and more effect on the stomatal aperture and density,with the smallest stomatal aperture under full light and larger stomatal aperture at shading 25%-75%.Meanwhile,the Pn,Ci,Tr,WUE,Fv/Fm,and ΦPSⅡ of the four plants under this condition were generally higher than those under full light and shading 95%conditions,but the NPQ and qP of four plants decreased significantly with decreasing light intensity.