Adaptability and Tolerance Thresholds of Green Wall Plants under Summer High temperature Stress

Green wall is an important approach to mitigating the urban heat island effect and improving ecological quality. Chengdu suffers from prominent high-temperature stress in summer, and micro-environments vary significantly with building orientations. However, existing studies lack quantitative analysis on plants’ environmental adaptation mechanisms and tolerance thresholds. To clarify the adaptability and directional response rules of perennial herbs under high-temperature wall microclimate, 12 perennial herb species were selected as test materials, and continuous in-situ monitoring was implemented on wall surfaces with four orientations throughout summer. Indicators including green leaf area ratio, crown width and net photosynthetic rate were measured. Correlation analysis and curve fitting were adopted to explore the driving effects of environmental factors and corresponding tolerance thresholds. In addition, the average ranking method was adopted to quantify the relative contribution of different environmental factors. The results showed that combined abiotic stress differentiated by building orientation induced significant divergence in plant growth, photosynthetic carbon fixation and water utilization. Chlorophytum comosum and Nephrolepis cordifolia maintained stable performance across all orientations; Thaumatophyllum bipinnatifidum adapted preferably to east-facing walls, while Pilea notata showed superior fitness on west-oriented substrates. Plant growth was jointly regulated by air temperature, soil temperature and humidity, and light intensity. Canopy width of Chlorophytum comosum on north-facing walls was mainly controlled by soil temperature, while that of Philodendron selloum on east-facing walls was dominated by soil moisture. Plants had distinct critical thresholds in response to key environmental factors. The crown width of Pilea notata peaked at soil temperature of 32℃ on west walls; photoinhibition occurred in Nephrolepis cordifolia when leaf illuminance exceeded 5 000 lx on south walls; the growth of Thaumatophyllum bipinnatifidum was markedly promoted when soil moisture was above 77% on east walls. The results reveal the adaptation rules and response characteristics of perennial herbaceous plants to high temperatures and different orientations in summer in Chengdu, which can provide a scientific basis for plant selection and engineering application of green walls.