Effect Of Gradient Warming On Growing Season Net Ecosystem Productivity In A Paddy Field In Northeast China

Global warming substantially impacts ecosystems,whereas there is a lack of understanding about how it impacts ecosystem processes.As an important part of the ecosystem carbon cycle,net ecosystem productivity(NEP)and its components play a key part in the global carbon cycle.Analysing the impacts of global warming on NEP will improve our understanding of how warming affects global carbon cycle and ecosystem processes.In this study conducted in 2018 and 2019,five temperature treatments were manipulated(0 W,500 W,1000 W,1500 W,and 3000 W)using far infrared open warming over three repetitions in a paddy field in Northeast China.NEP and its two related components,gross primary productivity(GPP)and ecosystem respiration(ER),were measured using the static chamber-infrared gas analyser method to explore the effects of different warming magnitudes on NEP.The main results are as follows:(1)Measuring times(date,year),warming treatments and their interactions significantly affected the air temperature,and there were significant differences between different measuring times and warming treatments.Warming significantly increased the air temperature,and the air temperature responded linearly to different warming magnitudes.(2)Measuring times(date,year),warming treatments and their interactions significantly affected the aboveground biomass,and there were significant differences between different measuring times and warming treatments.Warming significantly increased the aboveground biomass,but the maximum increases in aboveground biomass occurred at 1500 W warming.(3)Measuring times(date,year),warming treatments and their interactions significantly affected NEP and its components,and there were significant differences between different measuring times and warming treatments.Warming significantly increased NEP and its components,but the maximum increases in NEP and its components occurred at 1500 W warming.(4)NEP and its components responsed non-linearly to different warming magnitudes.The maximum increases in NEP occurred at 28°C.In addition,NEP responsed linearly to its components,and GPP showed a closer relationship with NEP than ER.(5)NEP and its components were significant differences between different measuring years.The inter-annual difference in temperature was the main reason for the inter-annual difference in NEP and its components.The based temperature in 2018 was significantly higher than that in 2019.In addition,the temperature after warming of each treatment in 2018 was significantly higher than 2019.Therefore,NEP and its components in 2018 were significantly higher than that in 2019.In this study,we investigated the responses of NEP to different warming magnitudes based on the relationship between NEP and air temperature,aboveground biomass and its components.Results showed that warming significantly promoted air temperature,aboveground biomass,NEP and its components in the paddy field in Northeast China.However,GPP and ER responded non-linearly to gradient warming resulted in a non-linear response of NEP.This study enhances our understanding of the carbon cycle process of the ecosystem and provides the basis for predicting the response of the carbon cycle in future climate events.