Responses Of Photosynthesis And Biomass Allocation Of Phragmites Australis And Spartina Alterniflora To Planting Patterns

For shore fixing and siltation,greening and other ecological engineering needs,the alien plant Spartina alterniflora was introduced to China.After more than three decades of proliferation,it is now widely distributed throughout the coastal wetlands of our country.Are there differences in the competitive patterns and processes of mixed populations under different proportions during the competitive process of S.alterniflora and native plants?What are the reasons for the difference?At the moment we don't know.In order to explore the physiological,growth dynamics and relationship to the structural dynamics of Phragmites australis-Spartina alterniflora mixed community under different proportions,in this paper,the local plant P.australis and invasive plants S.alterniflora in the Yangtze River estuary wetland are used as research objects.The different mixed proportions of P.australis and S.alterniflora are used to simulate the different mixed states of P.australis and S.alterniflora in the real situation of coastal wetlands.Through long-term monitoring of photosynthesis?maximum net photosynthetic rate,transpiration rate,stomatal conductance?,growth?plant height,basal diameter,total leaf area per plant,number of tillers?and biomass?aboveground biomass,belowground biomass,spike biomass?of both species?June 2016-December 2018?,this paper studied the structure and dynamics of mixed communities of P.australis and S.alterniflora under different mixed proportions.At the same time,we constructed biomass growth and distribution models for P.australis and S.alterniflora under proportions based on continuous environmental and meteorological data,with a view to continuously and dynamically simulating the biomass accumulation and distribution dynamics of P.australis and S.alterniflora under different mixed communities,and ultimately enriching our understanding of the process and mechanism of S.alterniflora invasion.The main conclusions of this article are as follows:1.S.alterniflora shows the eco-physiological advantages related to growth.In the single mode,the maximum net photosynthetic rate,stomatal conductance,and transpiration rate of S.alterniflora were significantly higher than those of P.australis in the middle of the growing season,and the maximum net photosynthetic rate was still higher in the late growing season,while that of P.australis was significantly lower in the late growing season.In terms of morphology,S.alterniflora had a higher shoot height and leaf area growth rate than P.australis,and in terms of reproduction,S.alterniflora had a significantly higher spike rate and tiller number than P.australis,and in terms of biomass accumulation,S.alterniflora had higher single plant biomass than P.australis,and the single plant biomass was still increasing late in the growing season.2.In different planting modes,S.alterniflora showed competitive advantages.In mixed communities,S.alterniflora had higher asexual reproduction?number of tillers?and biomass accumulation than P.australis,and this phenomenon intensified with an increase in the proportion of S.alterniflora.This is also manifested in that S.alterniflora has a higher maximum net photosynthetic rate,plant height,and leaf area per plant than P.australis,but the effect of P.australis on biomass accumulation and reproduction?sexual and asexual?of S.alterniflora is not significant?P>0.05?.At the same time,P.australis did not have a significant effect on the photosynthetic index and morphological index of S.alterniflora.3.Under single-planting model,the inter-annual root-shoot ratio of P.australis increased year by year?P<0.05?,while the root-shoot ratio of S.alterniflora was not significantly different?P>0.05?;Under mixed-planting model,because of the inter-species competition of rice grass,P.australis had a higher root-shoot ratio and tended to distribute more photosynthetic products to the underground part to obtain nutrients.However,P.australis had no significant effect on the root-shoot ratio of S.alterniflora.At the same time,different planting ratios had no significant effect on the root-shoot ratio of the two species.4.The biomass accumulation model showed that the biomass growth curves of P.australis and S.alterniflora showed a similar trend,increasing first and then tending to be flat.The maximum biomass of P.australis community appeared in September,which was 1050.70 g·m^-2,and the maximum absolute growth rate and relative growth rate of biomass both appeared in June,which were 16.51 g·m^-2·d^-1 and 0.0205g·g^-1·d^-1 respectively.The maximum biomass of S.alterniflora community appeared in October at 1325.02 g·m^-2,and the maximum absolute growth rate and relative growth rate appeared in July at 11.83 g·m^-2·d^-1 and 0.0283 g·g^-1·d^-1,respectively.In the mixed community,S.alterniflora inhibited the growth of P.australis biomass significantly,and the P.australis growth rate was the lowest in the community where the ratio of P.australis to S.alterniflora was 1:3.However,the effect of P.australis on S.alterniflora was relatively limited,and the relative growth rates of mixed and single species communities did not show significant differences.5.Through the simulation of the biomass allocation index,it was found that the biomass allocation index on the P.australis and S.alterniflora showed a trend of increasing first and then decreasing.The above-ground biomass allocation index of reeds all reached the maximum in July,and the above-ground biomass allocation index changed between 0.60-0.73.The above-mentioned allocation index of mixed species communities was lower than that of single species communities overall and decreased with the lower proportion of P.australis gradually.The community where the ratio of P.australis to S.alterniflora was 1:3 decreased the most,compared with the single species by 4.34%-10.46%.The biomass allocation index on S.alterniflora reached its maximum value in August,later than the P.australis.The above-ground biomass allocation index varied between 0.55-0.63,and there was no significant regularity among different planting ratios.The stem biomass allocation index of P.australis decreased first and then increased,and the stem biomass was always higher than that of leaves.S.alterniflora and P.australis had a different trend,and the stem biomass first increased and then tended to be flat,increasing from 0.32 to 0.57.This study enriches our understanding of the interspecific competition pattern,process,and mechanism of P.australis and S.alterniflora in coastal wetlands,and provides a reference for the dynamic simulation of community biomass in a mixed state.