Study On Shade Tolerance Of Four Ground Cover Plants

In recent years,people’s living environment has been greatly improved,and the demand for urban green coverage is also increasing.However,due to the blockage of high-rise buildings,urban green areas are mostly located in the buildings.Therefore,greening under the forest has become a popular trend in today’s greening.The shade-tolerant ground cover plants are characterized by their outstanding adaptability,high ornamental value,and easy cultivation and planting.It can quickly and effectively alleviate the large-scale undergrowth space that appears due to the growth of the trees,which constitutes a patchwork landscape level,satisfies the landscape effect,and provides people with a beautiful living environment.Therefore,the study of shade-tolerance of plants is significant for urban landscaping and rational use of under-forest space for plant landscape.Four species of ground cover plants Nepeta cataria,Ranunculus japonicus,Sedum kamtschaticum,and Scutellaria baicalensis were selected for the study.Different shading treatments were applied to the four plants（optical blocking rates:30%,50%,70%,and90%,with full light as a control）.After 4 months of shading treatment,the external morphology,physiological and biochemical indices,photosynthetic parameters and fluorescence parameters of the four ground cover plants were affected to varying degrees.Through comprehensive evaluation analysis,the main findings are as follows:（1）Different shade treatments have affected the phenophase and morphological characteristics of plants.The time for the four species of plants to enter the early flowering stage under different shade treatments was delayed,and the number of flowering days was prolonged and the flowering amount was reduced.Nepeta cataria and Scutellaria baicalensis do not bloom under 90%shading treatment.The increments of leaf length,leaf width,leaf area,and plant height of the four ground cover plants all showed a trend of increasing first and then decreasing with increasing shading degree.Among them,Nepeta cataria and Ranunculus japonicus were at their maximum under 50%shading treatment.Sedum kamtschaticum and Scutellaria baicalensis reached the maximum under 70%and30%shading treatments respectively.The specific leaf weights of the four species of ground cover gradually decreased with the increase of the shading intensity,and the values were the smallest when the shade degree was 90%.（2）Different shading treatments have an effect on the physiological and biochemical characteristics of plants.With the continuous increase of shading intensity,the leaf water content of four kinds of ground cover plant gradually increased.The water content of leaves increased gradually with the increase of shading strength and reached the maximum under 90%shading treatment.The relative electrical conductivity increased first and then decreased with the increase of shading degree.Among them,Nepeta cataria,Ranunculus japonicus,and Scutellaria baicalensis reached the maximum under 30%shading treatment,and Sedum kamtschaticum was the largest under 50%shading treatment.The contents of soluble sugar and soluble protein decreased with increasing shading intensity.Chlorophyll content changes trend,the chlorophyll content of Nepeta cataria and Sedum kamtschaticum increased with the increase of shading intensity,and the chlorophyll content of Ranunculus japonicus and Scutellaria baicalensis first increased and then decreased with increasing shading intensity.（3）Different shading treatments have an effect on the diurnal variation of photosynthetic plants.The daily changes of net photosynthetic rate,daily changes of leaf stomatal conductance,and diurnal changes of transpiration rate of Nepeta cataria and Sedum kamtschaticum were all shown as bimodal curves.The daily change of net photosynthetic rate,the daily change of leaf stomatal conductance,and the daily change of transpiration rate of Ranunculus japonicus and Scutellaria baicalensis membranaceus were shown as single-peak curves.The intercellular CO₂ concentration of the four ground cover plants was negatively correlated with the change of the net photosynthetic rate.（4）Different shade treatments have an impact on the plant’s light response curve parameters.The light response curves measured by the four ground cover plants under different degrees of shading were parabolic.According to further analysis,With the increase of shading degree,the light saturation point,light compensation point,surface light quantum efficiency,and dark respiration rate of the four species of ground cover gradually decreased.（5）Different shade treatments have an effect on the chlorophyll fluorescence parameters of plants.The change trends of the Fv/Fm and Fv/Fo values of the four ground cover plants were the same,and they all increased first and then decreased with the increase of shade degree.Nepeta cataria and Sedum kamtschaticum have the largest Fv/Fm and Fv/Fo values under 50%shading.Ranunculus japonicus have the largest Fv/Fm and Fv/Fo values under 30%shading.Scutellaria baicalensis have the largest Fv/Fm and Fv/Fo values under 70%shading.At the same time,the Fv/Fm and Fv/Fo values of 4 plants under90%shading treatment were significantly lower than under full light conditions.（6）Correlation analysis of each index showed that there were significant or extremely significant correlations between morphological,physiological,photosynthetic,and fluorescence characteristics.Comprehensive analysis,Nepeta cataria may be grown under normal light blocking ratio is 30%to 50%environment.Ranunculus japonicus can grow normally under the light-shielding rate of 30%⁷0%.Sedum kamtschaticum can grow normally in a 50%to70%environment.Scutellaria baicalensis can grow normally at a light-shielding rate of30%to 70%.To further illustrate,these four ground cover plants can be planted under the sparse forest and can achieve landscape effect.However,if the shade intensity is too high,the normal growth of the plant will be inhibited,and even death will occur.