Study On Transpiration Characteristics And Ecological Effects Of Ginkgo Biloba In Urban Gardens

The 21st century was a century of urbanization.China was one of the countries with the fastest urbanization development in the world.Although urbanization can promote social and economic development,people need to pay attention to the resource and environmental problems caused by urbanization.The urban landscaping construction could improve the urban environment and improve the ecological quality.It was an effective measure to promote urban development and protect the environment.The research on different regions,climatic conditions and gardening vegetation could improve the level of chemical management of urban greening and ecological benefits of gardening vegetation.At present,there were still relatively few studies on the transpiration and water consumption as well as the ecological benefits of garden greening vegetation in Guanzhong Urban Agglomeration.This study selected Yang Ling as the research location and Ginkgo biloba as the research target,which was commonly used as the main landscape.In this study,the thermal diffusion probe TDP was used to monitor the trunk sap flow.At the same time,the dynamic characteristics of transpiration water consumption of G.biloba at different ages and its response to environmental factors were analyzed.The soil evaporation between vegetation trees was measured by the micro-lysimeter,and the proportion of evapotranspiration in gardens was calculated.The photosynthetic parameters of vegetation were measured by photosynthetic measurement system,the resource utilization efficiency of vegetation was calculated,and the benefits of carbon fixation,oxygen release,humidification and cooling of vegetation were quantified.The main conclusions were as follows:（1）The potential evapotranspiration,soil water content and soil evaporation of urban gardens had a certain seasonal variation law.The variation range of potential evapotranspiration was 1.07-6.74 mm d^-1.There was a significant negative correlation between potential evapotranspiration and soil water content of G.biloba green space at the age of 24 and 29（P<0.05）.The variation range of soil water content of the two garden green spaces was 18.56%-28.92%.Tree age had no significant effect on soil water content,and the soil water content of 0-300 cm showed moderate variation.The highest value of soil evaporation occurred from in August,the maximum daily soil evaporation between trees was2.70 mm.The average daily soil evaporation of 24-year-old G.biloba was greater than that of 29-year-old G.biloba.The influences mechanism of environmental factors on soil evaporation were different on different time scales.There was a significant positive correlation between air temperature.On the daily scale,soil evaporation was significantly correlated with air temperature,5cm soil temperature,solar radiation and other environmental factors.On the monthly scale,the correlation between soil evaporation and environmental factors was small,and there was a significant negative correlation with leaf area index（P<0.05）.（2）The stem sap flow velocity of G.biloba shows circadian rhythm and seasonal difference.The liquid flow rate in clear day was higher than that in rainy day,and in summer was the highest,followed by spring and autumn.The hourly variation of liquid flow rate responded to meteorological factors but had certain time lag,which was 70 min ahead of air temperature,50 min ahead of difference of saturated water pressure and 60 min behind solar radiation.Its response to environmental factors could be better explained by building a multiple regression model on the hourly scale.On the daily scale,there was a highly significant correlation between the trunk fluid flow and potential evapotranspiration,air temperature,solar radiation,as well as saturated water vapor pressure（P<0.01）.On the monthly scale,there was a significant positive correlation between G.biloba fluid flow and the leaf area index（P<0.05）,and the correlation with environmental factors decreased.The transpiration water consumption of G.biloba was the largest in June.The monthly transpiration water consumption of G.biloba of two tree ages reached 245.88 kg and 383.71kg respectively,accounting for 20.18%and 18.70%of the annual water consumption respectively.（3）During the experiment,the diurnal variation trend of the net photosynthetic rate of two kinds of vegetation with different tree ages from May to September was the same,and the net photosynthetic rate of 29-year-old G.biloba was higher than that of 24-year-old G.biloba.The diurnal variation curve of the net photosynthetic rate in May and September was"single peak type",and the diurnal variation curve of the net photosynthetic rate from June to August was"double peak type".The phenomenon of"midday depression of photosynthesis"occurred at noon,resulting in the decline of the net photosynthetic rate of G.biloba.The main regulation mode in this period was stomatal regulation.The analysis of the diurnal variation of water use efficiency of G.biloba shows that because the water use efficiency of the two kinds of tree age G.biloba was high around 16:00,considering the lag of water absorption,16:00 was the appropriate time for irrigation.The correlation analysis between photosynthetic indexes and environmental factors showed that the two physiological factors of leaf transpiration rate and stomatal conductance were most closely related to the net photosynthetic rate of G.biloba,and the two environmental factors of solar radiation and air temperature were also closely related to the net photosynthetic rate.（4）The leaf expansion period of G.biloba was from March 25 to April 10,and the leaf defoliation period was from October 5 to October 20.The radial growth of G.biloba had a seasonal law.The DBH growth period was from May to October.G.biloba at the age of 29had higher ecological benefits.The ecological benefits of G.biloba were positively correlated with net photosynthetic rate,leaf transpiration rate,stomatal conductance,solar radiation,air temperature,saturated water vapor pressure difference and DBH of vegetation（P<0.01）.In summary,the climate conditions in Guanzhong Region were suitable for the growth and development of G.biloba.The transpiration water consumption and photosynthetic characteristics of vegetation with different tree ages were different.Landscaping vegetation played an important role in improving urban ecological environment and maintaining urban ecological balance.In the context of rapid urbanization,in order to further enhance the diversified value of landscaping,the research on the physiological characteristics and ecological benefits of urban garden vegetation should be carried out in an all-round way.