The Influence Of AM Fungi On Plant Photosynthetic Characteristics In Songnen Grassland Under Warming And Nitrogen Addition Conditions

The concentrations of CO₂,CH4 and other greenhouse gas increased caused by nature and human activities,and the temperatue elevated significantly in the last decades.Meanwhile,more and more nitrogen?N?inputted terrestrial ecosystem due to fossile fuel and fertilizer utilization.Global warming and nitrogen deposition affected the ecosystem function and stability.Arbuscular mycorrhizal fungi is one of the most important soil microbes which form mycorrhizal associations with most of high plants.AM fungi can improve plant growth via increasing the uptake of nutrients,water,etc.However,the effects of AM fungi on plant photosynthesis under warming and N addition conditions are still not clear.To test the influence of AM fungi on plant photosynthetic characteristics,an in situ experiment was conducted in Songnen meadow with simulated warming and N addition.The main results are present as the followings:?1?AM fungi increased the net photosynthetic rate?Pn?,stomatal conductance?Gs?and leaf transpiration rate?Tr?of Leymus chinensis,but reduced the intercellular CO₂concentration?Ci?of leaves under warming.However,AM fungi decreased the net photosynthetic rate?Pn?,stomatal conductance?Gs?and intercellular CO₂ concentration?Ci?of L.chinensis under N addition.AM fungi also improved the photosynthesis of L.chinensis under warming plus N addition.AM fungi increased the net photosynthetic rate?Pn?and stomatal conductance?Gs?of Phragmites australis under warming and N addition.AM fungi reduced the net photosynthetic rate?Pn?and stomatal conductance?Gs?of P.australis?P?0.05?,weakened the photosynthesis of P.australis under warming plus N addition conditions.?2?In the 2015-2016 two growing seasons,the effect of AM fungi on the net CO₂ exchange capacity?NEE?,the total ecosystem productivity?GEP?and the transpiration rate of ecosystems?ET?changed from inhibition to promotion,and enhanced the carbon sinks under warming and N addition.AM fungi increased the net CO₂ exchange capacity?NEE?,the total ecosystem productivity?GEP?,but had no significant effect on the ecosystem respiration?ER?under warming plus N addition.?3?AM fungi increased the content of chlorophyll a and the total chlorophyll content under warming.AM fungi increased chlorophyll a content,chlorophyll b content and total chlorophyll content,enhanced the ability of light absorption and transport,improved the photosynthesis of L.chinensis under warming plus N addition.AM fungi significantly reduced the chlorophyll a content and total chlorophyll content of P.australis?P?0.05?,and decreased the photosynthetic capacity of P.australis under warming and N addition.?4?AM fungi increased soluble sugar content of L.chinensis under warming and N addition.However,AM fungi increased the soluble sugar content of L.chinensis leaves,promoted the plant to accumulate more organic matter,enhanced plant resistance,and whichis beneficial to the growth and development of L.chinensis under the conditions of warming plus N addition.AM fungi increased the soluble sugar content of P.australis,significantly under warming and N addition.In summary,AM fungi had different impacts on the photosynthetic characteristics of plants and populations under warming and N addition,which can reduce the negative effects of warming and N addition on plant growth via affecting the plant photosynthesis and increase plant net primary productivity.