| Global warming,inducing an increase in ocean temperature and polar glaciers melting,results in an accelerated rise in global average sea level.Sea level rise causes seawater intrusion,changes hydrological conditions,and soil physicochemical properties,affecting the structure and function of plant communities,ecological processes including ecological stoichiometry,biogeochemical processes in the coastal wetlands.How plants in the coastal wetland respond to the ecological environment changes has become a hot topic in ecological research.Ecological stoichiometric characteristics can be used to determine the distribution of nutrient elements,utilization efficiency and limiting elements of plants.In order to explore the response and adaptation of coastal wetland plants to environmental changes,sample sites were set up in the T.chinensis coastal wetland of the Yellow River Delta(YRD,Xianhe Town,Dongying City,China).Based on the shallow groundwater level,salinity and soil physical and chemical properties in the study area,the sample points were divided into I(groundwater salinity 51.87±2.27 g/L,soil conductivity 3.27±0.16 m S/cm),II(underground water salinity32.99±1.83 g/L,soil conductivity 2.92±0.18 m S/cm),III(underground water salinity25.33±2.55 g/L,soil conductivity 2.61±0.07 m S/cm)three groups,to analyze the seasonal changes in the ecological chemometric characteristics of T.chinensis and the impact of shallow groundwater on the ecological chemometric characteristics of T.chinensis,and analyze the key environmental factors affecting the ecological chemometric characteristics of plants in the YRD,It provides a theoretical basis for wetland restoration and biodiversity protection in Yellow River Delta.The main results of this study were as follows.(1)The shallow groundwater level in the study area is high and the seasonal fluctuation is significant.The salinity of shallow groundwater is between 22.34～58.15 g/L.With the increase of distance from the coast,the salinity of shallow groundwater generally shows a downward trend.Shallow groundwater level and salinity will significantly affect the physical and chemical properties of wetland soil.With the decrease of shallow underground mineralization,soil conductivity significantly decreases,and soil conductivity decreases with the increase of soil depth,indicating a phenomenon of‘surface aggregation’of soil salt.In the study area,the soil C,N,and P contents were 4.46 g/kg,0.40 g/kg and 0.64 g/kg,respectively,and the nutrient content was the highest in the surface layer of the soil,which decreased with the increase of soil depth.With the decrease of groundwater salinity,the C and N content of the soil gradually increase,while the P content shows a trend of first decrease and then increase.(2)With the decrease of groundwater salinity,the species number of T.chinensis community increased gradually,but the aboveground biomass and importance value of T.chinensis decreased gradually.The aboveground biomass and important value of T.chinensis in group I(2.34±0.65 kg/m~2,0.10±0.02)were significantly higher than those in group III(1.49±0.32 kg/m~2,0.09±0.01).With the decrease of groundwater salinity,the average height,base diameter,east-west crown width and north-south crown width of T.chinensis gradually decreased.Although the downward trend of the three is different,group I were significantly greater than groupⅢ(P<0.05).(3)During the growing season,the leaf C content and stem xylem P content of T.chinensis in the study area increased first and then decreased.And the contents of N and P in leaves,C and N in stem xylem,C,N and P in stem bark and root were opposite.During the growing season,the C:N,C:P,N:P of leaves,stem bark and roots and the C:N of stem xylem increased first and then decreased;the C:P and N:P in stem xylem were opposite.T.chinensis showed the same seasonal variation trend under different groundwater salinity conditions.There were significant differences in nutrient content in different organs of T.chinensis.The C content and C:N content were as follows:stems(476.70±22.32 g/kg,55.72±21.74)>roots(424.46±12.54 g/kg,38.69±13.74)>leaves(417.40±17.72 g/kg,17.29±3.57).The N content was as follows:leaves(25.45±5.17 g/kg)>roots(12.41±3.96 g/kg)>stems(9.98±3.28 g/kg).P content showed leaf(1.05±0.26 g/kg)>stem(0.46±0.24 g/kg)>root(0.40±0.22 g/kg),C:P and N:P showed root(1644.86±1217.73,42.4±22.54)>stem(1280.79±731.94,27.69±18.35)>leaf(421.52±109.38,25.93±6.74).The N:P ratios of root(42.42±22.54),stem bark(29.69±17.47),stem xylem(25.26±19.22)and leaf(25.93±6.74)of T.chinensis in the study area were all greater than 16,indicating that the growth of T.chinensis in the study area was generally limited by P.(4)The growth of T.chinensis was significantly affected by the salinity of shallow groundwater.The stoichiometric characteristics of T.chinensis under brine groundwater condition(group I)were significantly different from those under saline groundwater condition(groupⅡand groupⅢ).Under brine groundwater condition(group I),the contents of C and P in T.chinensis leaves(411.04±18.09 g/kg,1.02±0.19 g/kg)<group II(416.20±15.24 g/kg,1.04±0.29 g/kg)<group III(423.90±14.71 g/kg,1.09±0.27 g/kg),N content(26.20±5.28g/kg)>II(25.24±5.07 g/kg)>III(25.09±5.24 g/kg).With the decrease of the salinity of shallow groundwater,the C content in the stem bark and xylem of T.chinensis showed an increasing trend,while the N and P showed a decreasing trend.The C content in the stem bark of T.chinensis under brine groundwater condition(group I)(496.91±8.53 g/kg)was less than that under saline groundwater condition(group II、III)(499.81±11.05 g/kg,500.73±7.50g/kg),and the N content(12.85±2.23 g/kg)and P content(0.58±0.30 g/kg)were higher than those under saline groundwater conditions(11.80±2.40 g/kg,0.51±0.28 g/kg).The C content(454.91±3.72 g/kg)in the xylem of T.chinensis under brine groundwater conditions was lower than that under saline groundwater conditions(457.64±3.87 g/kg),and the N content(8.74±2.45 g/kg)was higher than that under saline groundwater conditions(7.40±2.52 g/kg).With the decrease of the salinity of shallow groundwater,the content of C and N in the root of T.chinensis increased gradually,and the content of P decreased gradually.Under brine groundwater condition,the C and N contents of T.chinensis roots(422.38±11.78 g/kg,11.88±4.51 g/kg)<group II(425.37±7.96 g/kg,12.75±3.79 g/kg)<group III(426.68±16.13g/kg,13.03±3.72 g/kg);the content of P(0.49±0.27 g/kg)was higher than that of root P content(0.37±0.19 g/kg,0.33±0.18 g/kg)in groupsⅡandⅢ.(5)With the decrease of salinity of shallow groundwater,the C:N and N:P of T.chinensis leaves increased,and C:P decreased.With the decrease of the salinity of shallow groundwater,the C:N and C:P of T.chinensis stem bark increased significantly,and the N:P decreased first and then increased;the C:N of stem xylem increased first and then decreased with the decrease of shallow groundwater salinity,and the C:P and N:P showed a decreasing trend with the decrease of shallow groundwater salinity.The C:N of T.chinensis roots decreased with the decrease of shallow groundwater salinity,while C:P and N:P increased with the decrease of shallow groundwater salinity.(6)Groundwater salinity,soil electrical conductivity,and soil C and P contents were the dominant factors affecting the stoichiometry of T.chinensis.RDA analysis showed that the total cumulative interpretation rates of the first and second ordination axes on the ecological stoichiometric characteristics of T.chinensis leaves and roots were 62.4%and 79.0%,respectively,indicating that groundwater salinity,soil conductivity and soil C content had significant effects on the stoichiometric characteristics of T.chinensis leaves and roots.The total cumulative interpretation rates of the first two environmental factors on the stoichiometric characteristics of the stem bark and stem xylem of T.chinensis were 62.2%and68.9%,respectively,indicating that groundwater salinity,soil conductivity and soil P content were the key factors affecting the stoichiometric characteristics of the stem bark and stem xylem of T.chinensis.In summary,the shallow groundwater level and salinity in the YRD will affect the physical and chemical properties of wetland soil,and then affect the community and ecological stoichiometry of T.chinensis. |
