Effects Of Changes In Precipitation Amount On Soil Respiration And Photosynthesis In A Coastal Wetland In The Yellow River Delta,China

The coastal wetland has shallow underground water level and is affected by the fresh water and salt water in vertical direction.The changes in precipitation amount can alter the conditions of soil water and salt,thus affecting soil respiration and plant photosynthesis.In order to clarify the effect of the changes in precipitation amount on soil respiration and photosynthetic characteristics,we used rainout shelters and rainwater pipes to manipulate precipitation amount in the coastal wetland in the Yellow River Delta.And measured seasonal dynamics of soil respiration and light response curve of Phragmites australis during the growing season in 2015.Moreover,environmental factors including soil temperature,soil water content and soil salt content were measured simultaneously.The results are as follows:During the growing season,in the treatment of increased precipitation,soil moisture was significantly increased by 10.5% and soil salt was decreased by 24.3% compared with that in control.Diversity index and richness index of plant community was significantly increased.While in the treatment of decreased precipitation,soil moisture was significantly decreased by 24.6% and soil salt was increased by 20.8% compared with that in control.Diversity index and richness index of plant community was significantly decreased and soil respiration was significantly decreased by 38.9%.There was no significant difference in light response curve of Phragmites australis between two treatments during the growing season.The results showed that,according to soil moisture condition,the whole growing season could be divided into three periods: drought period,flooding period and wet period.The effect of changes of rainfall on soil respiration and photosynthetic characteristics of Phragmites australis was controlled by soil moisture condition.(1)During the drought period,water stress and salt stress engender the main adverse effects on the growth of plants and the process of underground biochemistry.increased precipitation increased soil respiration significantly by 31.8% greater than the control.In addition,increased precipitation also increased stomatal conductance(Gs)and photosynthetic capacity of plant leafcompared with those in the control.While decreased precipitation decreased soil respiration significantly by 41.1% compared with that in control.Meanwhile,decreased precipitation decreased the stomata obstruction and photosynthetic capacity of Phragmites australis.(2)During the wet period,the treatment of increased precipitation significantly increased soil moisture by 9.9%,while the treatment of decreased precipitation decreased by 14.2%.Increased,both of them lead to soil respiration temperature sensitive index(Q10)decreased.Soil respiration in decreased precipitation significantly decreased soil moisture by 41.3%.There was no significant difference in light response curve of Phragmites australis between two treatments.(3)During the flooding period,increased and decreased precipitation amount had no significant effect on soil respiration.However,increased and decreased precipitation aggravated and reduced the flood damage in reed plants,respectively.The net photosynthetic rate of Phragmites australis was from high to low as the PR > CK > PA.