Study On Eco-photosynthetic Characteristics And Ecological Effects Of Common Landscape Plants In Chongqing, China

Aimed at providing theoretical bases and technical references for the choosing, configuration and maintenance of garden greening tree species, this article studied diurnal changes in the photosynthesis and transpiration of 14 common landscape plants by employing Li-6400 photosynthesis system. Combined with leaf area index (LAI) and cluster analysis, this article also makes a primary assessment and evaluation on carbon fixation and oxygen production, temperature decrease and humidity increase. By fitting the light response curves of photosynthetic and determining other physiological indices of the plants, such as chlorophyll content and leaf mass per area (LMA), it analyzed the differences in types and months of the maximum net photosynthetic rate (Pn max), apparent quantum yield (AQY), light compensation point (LCP), light saturation point (LSP), chlorophyll content, chlorophyll a/b (Chi a/b) and LMA of the plants. Based on the research, a primary discussion is made on the plants' photosynthetic characteristics under rainy and cloudy conditions.The main results were as follows:1. Under cloudy and rainy conditions, all net photosynthesis rate (Pn) of the plants tend to be low with obvious differences.The Pn of Ficus virens var. sublanceolata gets the maximum, approximately 62.16%, while Loropetalum chinense var. rubrum gets the minimum, approximately 12.04%. On the other hand, Chlorophyll content rises more or less in all plants while Chl a/b falls. All the plants'LMA decreases except Magnolia soulangeana and Ficus virens var. sublanceolata.2. There is a difference in diurnal changes characteristics of Pn and transpiration rate (Tr) in July and September. The diurnal change curves of a certain plant varies in different months with double-peak or single-peak curves, mainly reflecting on the time of peak values, daily assimilation quality, daily transpired water quality. When the durnal changes of Pn are double-peak curves, the photosynthesis midday depression phenomena are obvious at noon. The causes of midday depression differ in types of plants. For example, in July, Magnolia soulangeana is non-stomata limited factors, while Ficus virens var. sublanceolata is stomata limited factors; Moreover, the causes of a certain plant differ in different months. For example. Camellia sasanqua is non-stomata limited factor in July, while it is stomata limited factors in September.3. In most cases, the volume of daily assimilation quality and daily transpired water quality in July is more than that in September. Rhododendron mucronatum varies most in daily assimilation quality while Photinia serrulata does least. Cinnamomum camphora, Loropetalum chinense var. rubrum and Ficus virens var. sublanceolata get the maximum in average assimilation quality,while Rhododendron mucronatum gets the minimum. Rhododendron mucronatum varies most in daily transpired water quality while Ficus virens var. sublanceolata varies least; Ligustrum lucidum, Pittosporum tobira, Cinnamomum camphora, Loropetalum chinense var. rubrum and Phoenix canariensis get the maximum in average transpired water quality, while Camellia sasanqua, Osmanthus fragrans and Rhododendron mucronatum get the minimum.The diurnal changes of efficiency for solar energy utilization (PE) performs a "U" line with varying most, and Magnolia grandiflora, Ligustrum lucidum and Ficus virens var. sublanceolata varying least.Cinnamomum camphora, Ficus virens var. sublanceolata, Phoenix canariensis and Loropetalum chinense var. rubrum get the maximum of the average of the two months, while Camellia sasanqua, Rhododendron mucronatum and Osmanthus fragrans get the minimum of it. The diurnal changes of water use efficiency (WUE) occurs double-peak or single-peak or changeable curves, Pittosporum tobira and Ligustrum lucidum varies most.but they get the minimum of WUE.Compared to that, Ficus virens var. sublanceolata and Cinnamomum camphora get a higher WUE. According to such physiology indexes, cluster analysis shows that Cinnamomum camphora and Phoenix canariensis have exceptional photosynthetic physiology characteristics in arbor and palm trees; while Loropetalum chinense var. rubrum and Photinia serrulata have exceptional photosynthetic physiology characteristics in shrubs.4. Except Magnolia soulangeana, all plants have the same change direction in LSP and Pn max with obvious positive correlation. On the other hand, except Loropetalum chinense var. rubrum, all plants have the same change direction in AQY and LCP with slight positive correlation. The LCP of arbor and palm trees is between 20-50 umol·m-2·s-1, and their LSP is between 800-1600μmol·m-2·s-1, from which we can judge them to be typical sunny plants. Among the plants, the LCP and LSP of Phoenix canariensis is high.Compared with the low LCP, high LSP and adaptability to lighting environment of Ficus virens var. sublanceolata and Ficus concinna, while Magnolia grandiflora and Livistona chinensis have high LCP, low LSP, and they adapt badly to lighting environment. The LCP of shrubs trees is between 16～35μmolm·-2·s-1, and their LSP is between 700～1600μmol·m-2·s-1. All the shrubs trees are sunny plants except Rhododendron mucronatum, which has bad adaptability to lighting environment, and is intermediate between sunny and shade plants.5. Shown in the comparison of July and September, Chlorophyll content tends to rise in most of the plants without obvious relevance to daily assimilation quality.Livistona chinensis, Ficus virens var. sublanceolata and Phoenix canariensis have the highest Chlorophyll content in July and September, while Magnolia soulangeana and Rhododendron mucronatum have the lowest. The Chl a/b of most plants tend to fall with more Chl b and increasing ability of emplying weak light.The average Chla/b of Magnolia soulangeana and Ficus virens var. sublanceolata is above 3.0. In most cases, LMA in September is higher than July. Camellia sasanqua, Magnolia grandiflora and Pittosporum tobira have a larger average LMA of the two months while Magnolia soulangeana, Rhododendron mucronatum and Loropetalum chinense var. rubrum have a smaller average LMA.6. Among the 14 landscape plants, Ficus virens var. sublanceolata, Ficus concinna and Cinnamomum camphora get a higher LAI, while Rhododendron mucronatum, Magnolia soulangeana and Pittosporum tobira get a lower one.As to the oxygen releasing and carbon fixation effects unit ground area of arbor and palm trees, Cinnamomum camphora and Ficus virens var. sublanceolata have the strongest in arbor and palm trees, while Loropetalum chinense var. rubrum has the strongest in shrubs. Concerning temperature decrease and humidity increase effects unit ground area, Cinnamomum camphora has the strongest in arbor and palm trees, while Ligustrum lucidum and Loropetalum chinense var. rubrum have the strongest in shrubs. According to amount of carbon fixation, amount of oxygen releasing, temperature decrease effects and humidity increase effects unit ground area, a comprehensive evaluation is made to give a ranking list of the 14 landscape plants. Among arbor and palm trees, Cinnamomum camphora get the maximum of photosynthetic ecological effect, while Ficus virens var. sublanceolata, Ficus concinna and Phoenix canariensis get a medium of it, and Magnolia grandiflora, Osmanthus fragrans, Osmanthus fragrans and Magnolia soulangeana get the minimum of it. In shrubs, Loropetalum chinense var. rubrum and Ligustrum lucidum have the strongest photosynthetic ecological effect, followed by Photinia serrulata and Pittosporum tobira, and Camellia sasanqua and Rhododendron mucronatum have the least.