Effects Of Simulated Warming On Photosynthetic Characteristics And Product Distribution Of Cunninghamia Lanceolata

Since the industrial revolution,global warming has been increasing due to the large amount of greenhouse gases such as CO₂.According to the fifth report of IPCC,it is expected that by the end of the 21st century,the global atmospheric temperature may increase by 0.3-4.8°C.Subtropical forest vegetation has abundant carbon reserves and high forest productivity,which plays an important role in the carbon cycle of terrestrial ecosystems.Due to the close relationship between forest and climate,subtropical forest vegetation is particularly important for global warming response.However,the impact of global warming on leaf photosynthetic characteristics and photosynthetic product distribution in different leaf ages of subtropical forest vegetation is still unclear.This study is based on the experiment of soil warming?cable heating,+4??carried out in the Chenda observation point of the Forest Ecosystem and Global Change Research Station of Sanming City,Fujian Province.The effects of warming on the distribution characteristics of photosynthetic products in different organs of Cunninghamia lanceolata?4 years old?were investigated by using ¹³CO₂ to carry out field in situ pulse labeling of C.lanceolata in the growing stage.In addition,the gas exchange characteristic parameters,light response parameters,CO₂ response parameters,chlorophyll content,and carbon and nitrogen contents of different leaf ages of C.lanceolata were also determined.Differences between characteristics and response patterns to warming.The aim is to reveal the response mechanism of subtropical forest vegetation growth under global warming.The main results of this paper are as follows:?1?The net photosynthetic rate of different leaf ages of C.lanceolata had different responses to temperature increase,and the reasons were also different.Among them,the decrease of net photosynthetic rate of C.lanceolata leaves was mainly attributed to non-stomatal limiting factors,while the reason for the significant increase in net photosynthetic rate of C.lanceolata 1 and 2 year old leaves after warming was stomatal factor.?2?After warming,the change of the maximum net photosynthetic rate of different leaf ages of C.lanceolata was consistent with the change of net photosynthetic rate,which also indicated that warming increased the photosynthetic potential of 1 and 2 year old leaves.The warming reduced the apparent quantum efficiency of the current old leaves,and the 1 year old leaves increased,indicating that the 1 year old leaves had higher light energy utilization efficiency after warming.The dark respiration rate of leaves at different leaf ages showed an increasing trend after warming.?3?After warming,the maximum carboxylation rate,maximum electron transport rate,triglyceride utilization rate,net photosynthetic rate and maximum net photosynthetic rate of different leaf ages of C.lanceolata were basically the same.The light respiration of 1 year old leaves also increases after warming,which may enhance the ability of C.lanceolata to consume organic matter.In addition,the content of Ch1 and N in leaves of different leaf ages of C.lanceolata decreased after warming.?4?Under different treatments,the photosynthetic capacity of C.lanceolata leaves decreased with the increase of leaf age.At the same time,the dark breathing of the leaves of Chinese fir also showed a decreasing trend with the increase of leaf age.?5?The warming decreased the average value of?¹³C value and ¹³C net increase ratio of C.lanceolata in 1-21d after labeling,indicating that the warming reduced the retention ability of C.lanceolata to photosynthetic carbon.In addition,the decrease in the¹³C net increase ratio and?¹³C value in the aboveground part of ¹³C in the 1-21d after warming treatment was greater than that in the control treatment,while the root system of¹³C was higher than the control treatment,indicating that the warming and the input of photosynthetic carbon to the underground part.?6?Under different treatments,the average values of?¹³C value and ¹³C net increase ratio of leaves and branches after 1-21d were decreased with the increase of age,It indicated that the photosynthesis products of the current old leaves and branches of the C.lanceolata were more and used for self-growth,while the photosynthetic products absorbed of the 1 and 2 year old leaves were more transported to other organs.?7?Compared with the control,the net growth of the ground diameter and the height of C.lanceolata showed no significant decrease.It indicated that the warming had a certain inhibitory effect on the growth of C.lanceolata in the growth stage,which is consistent with the?¹³C value and ¹³C net increase ratio of various organs...