Study On Photosynthetic Characteristics And Ecological Effects Of Main Tree Species Of Robinia Pseudoacacia In Yan'an,China

In July,August,and September of 2018,the GFS-3000 portable photosynthetic apparatus?Germany?was used to measure photosynthetic data of the main tree species of Robinia pseudoacacia in Yan'an City,for example,net photosynthetic rate?A??transpiration rate?E??stomatal conductance,etc,in order to analyze the indicators of Robinia pseudoacacia.On this basis,the chlorophyll content,free water,bound water and other data were measured.According to the calculation of the data,this article also made a primary evaluation on carbon fixation and oxygen production,temperature decrease and humidity increase.The objective of the study was to study the photosynthetic characteristics and ecological benefits of the main tree species of Robinia pseudoacacia plantation in Yan'an,in order to provide the basis for the construction of Robinia pseudoacacia plantation in northern Shaanxi.The results showed:?1?In July,August,and September,the net photosynthetic rate?A?of the Robinia pseudoacacia showed a"double peak"curve,showing a clear photosynthetic"midday depression"phenomenon.There are many reasons for the photosynthetic"midday depression"phenomenon,such as stomatal conductance?Gs?,ambient temperature?Tr?,air relative humidity?RH?,and air CO₂ concentration?Ca?,etc.In this thesis,it was found that ambient temperature,photosynthetically active radiation,water pressure deficit,and stomatal conductance all cause photosynthetic"midday depression"of Robinia pseudoacacia to varying degrees.Moreover the cause of same plant differ in different months.Robinia pseudoacacia is stomata limited factor in July,while it is non-stomata limited factors in August.?2?The light saturation point?LSP?of the Robinia pseudoacacia is above540umol·m^-2s^-1,the light compensation point is?LCP?is between 10-100 umol·m^-2s^-1,and the value of chlorophyll a/b is between 0.629-1.595.The light compensation point is low,the light saturation point is high,and the chlorophyll a/b is low.From which we can judge it to be typical sunny and shade plants.It is adapt well to lighting environment.?3?The ratio of Robinia pseudoacacia in bound water/free water in August is high,the plant metabolism is slow,and the drought resistance is strong.While in July and September,the ratio of bound water/free water is low,and the plant metabolism is faster and grows faster.Under the same conditions,the Robinia pseudoacacia has a high net photosynthetic rate?A?and a high water use efficiency?WUE?.They have the strong ability to resist drought and adapt to the environment.?4?Different ecological characteristics,environmental factors and growth stages of plants cause plants to have different carbon fixation and oxygen production,temperature decrease and humidity increase in different months.The daily carbon fixation and oxygen production of Robinia pseudoacacia are the largest in July,the second in September and the smallest in August.The daily transpiration rate in August is the highest,so the ability of temperature decrease and humidity increase in August is the strongest.The annual carbon fixation of Robinia pseudoacacia is 3523.382 g and the annual transpiration water is 939.737 Kg,which indicates that Robinia pseudoacacia has strong ability of carbon fixation,oxygen production and temperature decrease and humidity.The results showed that the photosynthetic characteristics of Robinia pseudoacacia were determined by different external ecological factors and internal various physiological factors,there is an interaction between them.Robinia pseudoacacia has strong photosynthetic capacity,drought resistance,carbon fixation and oxygen production capacity,temperature decrease and humidity increase capacity and adaptability to the environment.Robinia pseudoacacia can be used as dominant species in the selection and allocation of plantation in Yan'an,then multiple tree species combine,in order to improve the ecological effect of Plantation.