Effects Of Winter Mowing On Phragmites Australis Growth And Ecological Stoichiometry Of Nitrogen And Phosphorus In The Yellow River Delta

Mowing is an important management method of natural ecosystem.Different mowing frequency and time have different influence on soil properties,individual species,biological community structure,biodiversity and productivity in the ecosystem.The changes of ecological stoichiometry and distribution of key elements caused by mowing can also be adjusted by the changes of perennial rhizome plant size.Phragmites australis is a perennial gramineous herb widely distributed in the Yellow River Delta.Winter mowing is a common local management measure and is considered to be an important method for the rejuvenation of P.australis community.However,the effects of winter mowing on the growth of P.australis varied in different regions.The effects of mowing and the resulting biomass retention on plant growth and community diversity need to be further studied.This study was conducted in the Yellow River Delta coastal wetland ecological research station of the Chinese Academy of Sciences,through a three-year field control experiment from 2018 to 2020.Three treatments,no mowing(CK),mowing + no litter removal(MY)and mowing + litter removal(MN),were set to study the effects of winter mowing on soil properties,community diversity,individual traits and ecological stoichiometry of P.australis community,in order to explore its ecological and environmental effects on P.australis communities in the Yellow River Delta,with the purpose of providing advice for the management and sustainable utilization of P.australis resource in the Yellow River Delta.The main results are as follows:(1)Winter mowing,whether the aboveground biomass was retained or not,had no significant effect on the soil p H,EC,organic matter,total nitrogen and phosphorus content during the three-year experiment period.However,the above indicators had significantly differences in different years.Compared with 2018 and 2020,the soil total nitrogen and total phosphorus content in 2019 decreased significantly,which may be related to the loss of nitrogen and phosphorus caused by the strong wind and heavy rainfall of typhoon liqima in 2019.(2)Whether the aboveground biomass was retained or not,winter mowing had no significant effect on the species composition of P.australis community,community diversity index and the important value of P.australis in the three-year experimental period.However,the variation between repetitions of MY and MN treatments was significantly higher than CK(P<0.05),indicating that mowing may increase the contingency of community succession direction.There was no significant difference in P.australis density,biomass and biomass of other species among the treatments.The total biomass of the community was significantly affected by winter mowing,with the highest in MY treatment and the lowest in MN treatment,there was significant difference between them(P<0.05),but no significant difference between the two treatments and CK(P>0.05).Compared with CK,MY treatment reduced the difference of community biomass between treatments,but increased the variation degree of P.australis biomass and other species biomass.The variation degree of P.australis community traits in MN treatment increased significantly.(3)MY treatment and MN treatment had significant effects on the individual characters of P.australis,which would lead to the dwarfing of P.australis plants.The phosphorus content of P.australis leaves was more affected by mowing than nitrogen content,and the N:P of leaves in three treatment were greater than 16,indicating that the growth of P.australis was limited by P.In 2019,there was little difference in traits and ecological stoichiometry between MY and MN treatments,and the difference increased by 2020.The single leaf mass,stem diameter,stem mass,plant height,total mass,leaf nitrogen content,leaf phosphorus content,whole plant P.australis phosphorus content and nitrogen leaf-stem distribution ratio of MY treatment were significantly higher than MN treatment,but the stem N: P and whole plant P.australis N:P of MN treatment were significantly higher than MY treatment.The plasticity index of individual plant traits and ecological stoichiometry of P.australis under MN treatment was higher than MY treatment,and the biomass retention after mowing had a greater impact on individual plant traits of P.australis.P.australis after winter mowing showed the characteristics of plant dwarfing,but the community biomass of P.australis had not changed significantly,which may be related to the intensification of intraspecific competition caused by the increase of P.australis density after mowing.The change of individual traits of P.australis may be a trade-off between population density.(4)Principal component analysis(PCA)showed that total biomass,single leaf mass,stem mass and plant height were the main indexes to measure the plant size of P.australis.By 2020,the plant size of P.australis among CK,MN and MY treatments decreased successively and the difference was significant.The plant size of P.australis was significantly correlated with the content of nitrogen and phosphorus in plant tissue,which first increased and then decreased with the increase of plant size.The ratio of nitrogen to phosphorus in aboveground biomass had no significant correlation with plant size.The ratio of nitrogen to phosphorus in stem first decreased and then increased with the increase of plant size,while the ratio of nitrogen to phosphorus in leaf first increased gradually with the increase of plant size.There was no significant correlation between P.australis size and the ratio of leaf to stem distribution of nitrogen and phosphorus.(5)The retention of biomass after mowing had a greater impact on the individual traits of P.australis,and the density and biomass were relatively low.Taking into account the elimination of fire safety hazards and P.australis rejuvenation,the removal of aboveground parts after winter mowing is a better management method,which can improve P.australis density and biomass to a certain extent.However,in the actual management process,it should also be combined with ecological effects.For example,some birds nests are built in P.australis clusters,and birds breeding in early spring also need P.australis as shelters.Mowing every other year or in blocks may have practical significance for the scientific management of P.australis resources.