Effects Of Experimental Warming On Morphology And Growth Of Fine Roots In A Phragmites Australis Wetland Of The Yangtze Estuary

Under the background of global warming,the change of fine roots in costal wetland is yet unclear.Taking the Phragmites australis wetland in Chongming Dongtan of the Yangtze River Estuary as the research object,we used the open-top chamber method to investigate the effects of warming on the amount,morphology,growth,and turnover of fine roots of P.australis.From May to November in 2019,the methods of minirhizotron and soil auger were used to determine the total length,total surface area,specific root length,specific root surface area,average diameter,and biomass of fine roots(fibrous roots of P.australis with the diameter ? 2 mm)in the 0—40 cm soil layer.The net growth rate and turnover rate of fine roots were also calculated.Meanwhile,the above-ground growth,morphology and photosynthetic traits of P.australis were also observed to analyze the correlation between above-ground traits and fine root traits under the condition of elevating temperature.The results showed that:(1)In general,the elevated temperature significantly increased the total root length,total surface area and total biomass of fine roots of reeds in the 0-40 cm soil layer,and also significantly increased the net growth rate of fine roots of P.australis.Yet for the traits that indicate water and nutrient absorption efficiency of fine roots(specific root length,specific surface area,average fine root diameter),there was no significant effects caused by elevating temperature.Elevated temperature significantly increased the turnover rate of fine roots of reed in the 0-40 cm soil layer.Meanwhile,due to the increase in the total amount of fine roots involved in fine root turnover,the root organic carbon input of the P.australis wetland in the whole 0-40 cm soil layer under elevated temperature increased significantly.(2)On time scale,the total biomass,total root length,and total surface area of fine roots of P.australis wetland continued to increase month by month,resulting in accumulation.For morphology traits of fine root(specific root length,specific surface area,average root diameter),there were no significant difference between ET and CK.But there were similar seasonal dynamics for morphology traits,and both ET and CK reached the relative peak in August when the growth was most vigorous.(3)On spatial distribution,the elevated temperature changed the spatial distribution of the fine root traits of P.australis.The differences between different soil layers were not significant in CK,but the elevated temperature significantly improved the fine roots total root length,total surface area,total biomass,and net growth rate of the0-20 cm soil layer,which caused the fine roots of P.australis wetland to gather more to the surface 0-20 cm.At the same time,the elevated temperature did not significantly affect the specific root length,specific surface area and the spatial distribution of the average fine root diameter of P.australis.The turnover rate of fine roots of P.australis was only significantly increased in the 20-40 cm soil layer under the condition of elevated temperature.However,due to the increase of fine roots number participating in turnover in all 3 soil layers,the root organic carbon of each soil layer increased significantly.(4)Warming had no significant effect on the above-ground growth and morphological traits of P.australis,but only changed the plant height,plant height to stem ratio,bottom leaf height and leaf length-to-width ratio which reflect the leaf morphology.However,warming significantly improved the photosynthesis of P.australis,which indicated that the photosynthate were preferentially allocated to fine roots that were more sensitive to warming.Through correlation analysis,it was found that the above-ground growth and morphological traits of P.australis had significant correlation with fine root growth traits,but the photosynthetic traits had poor correlation with fine root growth traits.Only Cond,Ci and WUE had significant correlation with fine root growth traits under CK.After experimental warming,in addition to these 3 traits,the correlation between Tr and fine root growth traits also became significant.