| Poyang Lake is the largest freshwater lake in China.Under the influence of human activities and climate change,the degradation trend of wetland vegetation is gradually increasing,and the biodiversity is decreasing,which leads to the decline of ecosystem function.Especially in recent years,extreme water level occurs frequently,causing serious damage or even death of submerged macrophytes.In order to study the growth process and suitable growth mechanism of submerged macrophytes under different flooding conditions in Poyang Lake,the paper taked the dominant submerged macrophytes of Vallisneria verticillata and Hydrilla verticillata in Poyang Lake wetland as the research objects,collected hydrological data of Poyang Lake in the past 50 years.The V.natans group,H.verticillate group and the mixed group of V.natans group and H.verticillate were 1.5 m,2.5 m,3.0 m,6.0 m,and 7.0 m,5.5m for the control experiment.Ecological simulation and outdoor culture methods were adopted to analyze the influence degree and recovery process of flood season on the growth and process of V.natans group and H.verticillate seedlings.The growth indexes,photosynthetic pigment indexes,antioxidant enzyme indexes content were measured,and the effects of typical wetland plants in Poyang Lake on chlorophyll fluorescence parameters of submerged macrophytes under different flooding conditions were discussed.The response process and suitable growth mechanism of V.natans group and H.verticillate to hydrological factors in typical wetlands of Poyang Lake in different hydrological periods are expounded.The research results were of great significance for maintaining plant diversity in Poyang Lake wetland under the new era and extreme hydrological background.The main conclusions were as follows:（1）From the aspect of growth morphological indicators,there were significant differences in the plant height,biomass,root length and number of ramets of submerged plants（P<0.05）.With the increase of water depth,the value first increased and then decreased.There were significant differences between the same plant under different flooding conditions;（2）From the aspect of photosynthetic pigments,the content of pigments increased first and then decreased with water depth.The maximum occured in May and the minimum occured in September.The content of each pigment in H.verticillate was higher than that of V.natans.（3）From the aspects of antioxidant enzyme index,SOD activity and POD enzyme activity were observed.The water depth increased and the MDA content was reversed,which was consistent with the growth index and photosynthetic pigment index.The correlation between water depth and Chlorophyll a+b,Chlorophyll a/b,Carotenoids and POD showed significant negative correlation at P<0.01 level,and significant positive correlation with MDA at P<0.05 level.There are different degrees of correlation among the indicators.（4）From the chlorophyll fluorescence parameters,the Fv/Fm decreased with the increase of water depth.Except for the control group and the DH water depth at 1.5 m,the other groups were less than 0.8,indicating that plants were subjected to external stress,resulting in different degrees of damage to PSII reaction center.The photosynthetic rate declined gradually.The Fv/Fm of H.verticillate was significantly higher than that of V.natans,suggesting that the conversion efficiency of H.verticillate was higher in PSII reaction center than that of V.natans;the growth trend of Y（II）and qP was consistent with the Fv/Fm,and gradually decreased with the increase of water depth.qN and NPQ are opposite to the Fv/Fm,and their values increase with the increase of water depth;（5）From the photosynthetic response curve,it can be seen that with the increase of PAR,rETR of V.natans and H.verticillate increased rapidly and decreased slowly.When PAR is 295μmol·m-2·s-1,rETR reaches saturation.The photosynthetic efficiency of H.verticillate was higher than that of V.natans,which indicated that the light tolerance of H.verticillate was better than that of V.natans.The correlation of chlorophyll fluorescence parameters showed that water depth was negatively correlated with Fv/Fm,Y（II）,qP and rETR at P<0.01 level,positively correlated with NPQ at P<0.01 level,and positively correlated with DK,HK and DH qN at P<0.01 level.There was a significant positive correlation between mixed black qN and P<0.05.There are different degrees of correlation among the indicators.（6）From the results of mixed planting,because of intraspecific competition rather than interspecific competition,there is a clear competition relationship between V.natans and H.verticillate.The height of H.verticillate is higher than that of V.natans,and the illumination in the canopy of V.natans is lower than that of H.verticillate.H.verticillate is more competitive than V.natans.That is to say,H.verticillate is superior to V.natans.From different planting patterns,single planting is better than mixed planting.Combining with the competitive relationship,that is,DH>HH>DK>HK. |
