Effects Of Nitrogen And Phosphorus Addition On Ecological Stoichiometric Characteristics Of Different Types Of Halophytes

Under the joint influence of human activities and natural conditions,the nitrogen and phosphorus deposition of the wetland natural ecosystem in the Yellow River Delta changed accordingly.Ecological stoichiometry theory shows that plants will actively adjust their nutrient requirements and element abundance to adapt to environmental changes,and there were differences among different regions and different species.Therefore,the study of the response mechanism of different halophytes to the rapid change of external nutrient conditions in the Yellow River Delta region is of great benefit to the assessment of ecological risks faced by vegetation and even the ecosystem in this region.In this study,the secretohalophyte Aeluropus sinensis,the euhalophyte Suaeda salsa,and the pseudohalophyte Phragmites communis which were in the Yellow River Delta were selected as the research subjects.Eight nitrogen and phosphorus addition methods were used.The four nitrogen supplemental levels were N0(0.00 g/m2),N1(5.00 g/m2),N2(15.00 g/m2),and N3(45.00 g/m2),and the two phosphorus supplemental levels were P0(0.00 g/m2)and P1(1.00 g/m2).There were eight treatments in total: N0P0,N1P0,N2P0,N3P0,N0P1,N1P1,N2P1,and N3P1.Controlled by field test and analysis of laboratory test,the method of combining with characteristics of plant ecological stoichiometric and biomass index,soil ecological characteristics of chemical metrology and physical and chemical properties,the correlation of plant and soil factors were analyzed,such as the nitrogen and phosphorus add processing under different types of halophytes ecological characteristics of chemical measurement mechanism change,The differences of different halophytes and their communities in soil ecological stoichiometry were discussed to reveal the correlation between plants and soil environmental changes under nitrogen and phosphorus addition conditions,providing the theoretical basis for the restoration of halophytes in the Yellow River Delta wetland ecosystem.The main conclusions are as follows:(1)The accumulation capacity of C,N and P elements in the three halophytes in the Yellow River Delta was weak,and the plant community was restricted by N elements partially,while the leaves of the secretohalophyte Aeluropus sinensis,were mainly restricted by both N and P elements.The content of C in each organ of Suaeda salsa was lower than that in the secretohalophyte Aeluropus sinensis and the pseudohalophyte Phragmites communis,and the content of C in the stem of Aeluropus sinensis and Phragmites communis was higher than that in other organs.(2)N supplementation significantly increased the content of N in each organ of different and decreased the content of C:N in plants.N:P increased with the increase of N supplemental level in Suaeda salsa and Phragmites communis,and the peak value of N:P in leaves was 40.03 and 33.34 when P and high concentration of N were added together.The nutrient use efficiency of Aeluropus sinensis and Suaeda salsa were improved to some extent by P addition.The interaction between N addition and P addition significantly affected the ecological stoichiometric characteristics of each organ of the three halophytes,and there was a coupling mechanism between the effects of N and P addition on the ecological stoichiometric characteristics of plants.(3)Soil N:P<14 of the three halophyte communities in the Yellow River Delta showed N restriction.Soil N element is scarce in the region,but the utilization and transformation efficiency of N element is high,while the assimilation efficiency of P element is low.Shortterm N and P addition had certain effects on soil ecological stoichiometry and physicochemical properties.For the soil of secretohalophyte Aeluropus sinensis community,high concentration N supplementation promoted the increase of P content in rhizosphere soil,while medium and high concentration N supplementation significantly decreased soil organic matter content.For the soil of the euhalophyte Suaeda salsa community,P addition promoted the increase of P content in the whole soil and C and N content in the nonrhizosphere soil.Medium concentration N addition significantly increased the C and N content in the rhizosphere soil,and N addition alone significantly increased the N content in the non-rhizosphere soil.For the soil of pseudohalophyte Phragmites communis community,the addition of N and P decreased the content of C and N in the whole soil,while the simultaneous addition of high concentration of N and P promoted the increase of available P in the rhizosphere soil.(4)The addition of N and P promoted the growth and development of halophytes.The addition of N significantly promoted the increase of aboveground biomass,underground biomass,total biomass,and plant height of the three halophytes,and the joint addition of N and P further promoted the increase of plant height of the three halophytes.The addition of P and medium and high concentration N significantly reduced the root-shoot ratio of plants,and halophytes were more inclined to transport and accumulate nutrients to the aboveground parts under the condition of adequate nutrition.(5)Under N and P addition,there was a certain correlation between the changes of rhizosphere soil and non-rhizosphere soil of halophytes,and there were differences in the correlation between rhizosphere soil and non-rhizosphere soil of halophytes.Both Aeluropus sinensis and Suaeda salsa show that,there was a significant positive correlation between total carbon in non-rhizosphere soil and total carbon and total nitrogen in rhizosphere soil(P<0.05),and there was a significant positive correlation between total nitrogen in nonrhizosphere soil and total carbon in rhizosphere soil(P<0.05).(6)Total carbon,total nitrogen,and total phosphorus in some organs of different halophytes were significantly positively correlated with plant biomass accumulation(P<0.05).There was an internal coupling mechanism between the stoichiometric characteristics of organs of the three types of halophytes,and there was a significant correlation between the ecological stoichiometry of different types of halophytes and soil factors.The ecological stoichiometric characteristics of the pseudohalophyte Phragmites communis were more closely correlated with soil factors than those of secretohalophyte Aeluropus sinensis and euhalophyte Suaeda salsa.