| Climate warming is one of the main trends in global climate change.Climate warming affects the physiological and biochemical processes of plants,plant growth and development,and population expansion patterns,and then affects the changes of plant biomass.In this paper,Chongming Dongtan Wetland was selected as the research area,and the open top chamber(OTC)was used to simulate the atmospheric temperature increase in situ(the average increase of air temperature in OTC was 1.56±0.15°C in 2016,and 1.60±0.17 ° C in 2017,respectively),the target species were the local dominant wetland plants Phragmites australis and Spartina alterniflora.During the two growth seasons of P.australis and S.alterniflora(2016-2017),the changes of photosynthetic characteristics,growth indexes and biomass of P.australis and S.alterniflora were measured and analyzed,and biomass accumulation and allocation of P.australis and S.alterniflora were estimated by mathematical model.The results are helpful to understand the dynamics of the biomass of the P.australis and S.alterniflora in the coastal salt marsh of the Yangtze River estuary.The main findings of this paper are as follows:1.Regardless of warming treatment or not,photosynthetic indicators(maximum net photosynthetic rate,light saturation point,dark respiration rate,stomatal conductance,transpiration rate)of P.australis and S.alterniflora increased gradually and then decreased gradually in the two-year growing seasons,except for light compensation point and water use efficiency.Compared with the control,the two-year warming significantly increased the photosynthetic capacity of P.australis and S.alterniflora,whereas the extent and duration(i.e.,months)of increase of S.alterniflora was higher than those of P.australis,implying that S.alterniflora was more sensitive to warming treatment than P.australis.2.Over the two growth seasons,regardless of warming treatment or not,morphological parameters(i.e.,the plant height,base diameter and number of leaves)of these two species increased firstly and then stayed stable.In comparison,the leaf area of single plant and leaf area index increased firstly and then decreased later in the growing season.Compared with the control,the warming treatment increased the total leaf area of single plant and leaf area index of P.australis and S.alterniflora significantly(P<0.05).Additionally,and in the second year,the warming treatment increased the plant height of S.alterniflora by 3.36%(P<0.05).Compared with the first year,morphological parameters(i.e.,the plant height,base diameter and leaf area index)of S.alterniflora increased significantly(P<0.05).3.In the two-year growing season,leaf biomass,stem biomass and consequent aboveground biomass,belowground biomass and total biomass of P.australis and S.alterniflora increased firstly and then stayed stable later in the growing season,and the maximum values appeared in October.Compared with the control,the warming treatment increased the aboveground and total biomass of S.alterniflora significantly(P<0.05).In comparison,warming treatment increased the belowground biomass of P.australis significantly(P<0.05).Although warming treatment increased the values of above-ground and total biomass of P.australis,but the statistics were not significant(P>0.05).Compared with the control,the warming treatment increased the steam biomass of S.alterniflora significantly(P<0.05),and leaf biomass of S.alterniflora in the later growing season(September-October).Warming treatment increased the leaf biomass of P.australis in the middle and late growing season(August-October)significantly(P<0.05).4.The results of biomass model estimation showed that the total biomass of P.australis and S.alterniflora have the same trend in the growth season regardless of the temperature treatment or not,which increased firstly and then stayed almost stable with the maximum values appearing in October.The maximum growth rate of P.australis and S.alterniflora occurred in July and September,respectively.The trend of total biomass estimated by the model is basically in line with the trend of measured biomass.Compared with the control,the warming treatment increased the total biomass of P.australis from July to September significantly(P<0.05),the value of increase was approximately 32.27%,and then the value of increase by warming treatment decreased later gradually.Whereas the temperature increased the total biomass of S.alterniflora significantly(P<0.05),the value of increase reached 20.31%.5.By fitting the distribution index,it can be seen that regardless of the warming or not,the proportion of the aboveground part of the Phragmites australis gradually decreases linearly,and the underground part gradually increases;while the proportion of the upper part of the Spartina alterniflora increases first and then decreases and peaks in August.At the same time,the proportion of the lower part of the ground gradually decreased and then gradually increased,and August was the bottom value.It can be seen from the shoot index of the shoots that the biomass of the stems of the Phragmites australis first decreased and then rose,reaching the bottom value in September,and the leaves were opposite.The trend of Spartina alterniflora is contrast to Phragmites australis,stem biomass first rises and then falls,peaking in August,and opposite to leaves.Compared with the control,the analysis of the distribution index showed that the warming significantly increased the aboveground biomass of the Phragmites australis,significantly reducing the biomass of Spartina alterniflora. |
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