| As the source of Kaidu river,special water conservation in northern Xinjiang and many endangered and rare birds' main habitat,Bayanbulak grassland plays a very important role in ecology.But since 2000,native species Pedicularis kansuensis Maxim.occurred here and had been expanding rapidly,threatening the local livestock industry.Therefore,the local government and Bayanbulak grassland research station of Chinese academy of science together conducted several methods on P.kansuensis Maxim.control include chemical control,but the effect was not ideal because of its root hemiparasitism.Furthermore,chemical mearsure also existed certain risks and hidden dangers because of the Bayanbulak grassland's special geographic and ecological position.According to the failure control before,we proceeded with its hemiparasitic peculiarity in this experiment.Therefore,we laied belt transect perpendicular to the river,and took samples in different soil texture to obtain the seed's distribution and regularity in different soil,conduct clipping,removing P.kansuensis Maxim.species biotic factor experiments and nutrient addition,warming and along the soil water gradient abiotic experiments,to obtain the change and compose of community and soil nutrient before and after the experiments,the difference between them,and compared with distribution areas of Q inghai Province,to research the soil nutrient difference between infected areas and non-infected areas,and attempt to find out the main ecological factor of P.kansuensis Maxim.' expanding and hoping to provide theoretical basis on P.kansuensis Maxim.integrated control.The results showed that:(1)P.kansuensis Maxim.seeds was very small(thousand seed weight was 0.64±0.02 g),easy to spread by wind,and had higher fructification percentage,each of individuals could produce more than 600-2000 seeds,it meant that they had stronger fecundity,laboratory simulation showed that the best germination period of P.kansuensis Maxim.seed was in late May and early June;the closer the source of water,the more P.kansuensis distribution,and the more seeds there were.There was a significant positive correlation between the number of seeds of P.kansuensis Maxim.and soil water content,it meant that soil water content was one of the key factor in P.kansuensis Maxim.'s growth,production and spatial expansion;the vertical distribution of soil seed number turned out that: the litter layer>humus layer>subsoil layer,and the highest number of P.kansuensis Maxim.seed turned up in the litter layer of loam,then were sandy soil,gravel and marsh,respectively.(2)There was no difference between clipping and non-clipping treatment's soil nutrient factors and the species composition of community;clipping had little effect on the species number and coverage of graminoids plant and forbs,but reduced P.kansuensis Maxim.coverage obviously;mowing treatment could also reduce the total aboveground biomass of P.kansuensis Maxim.while reducing the total aboveground biomass.Enclosure could increase the biomass of graminoids plant significantly,suppress the expansion of P.kansuensis Maxim.meanwhile.(3)There were no difference among removed P.kansuensis Maxim.,parasitized and non-parastized treatments' s soil nutrient;there were no obvious difference in three treatments' s species number and coverage;the occurance of P.kansuensis Maxim.would decrease the graminoids proportion in its community,but had no influence on forbs;P.kansuensis Maxim.turned up again in the non-parastized plots in the second growing season,and its ratio in total coverage was just like the parasitized plots,it showed that P.kansuensis Maxim.was spreading movability,and its seeds had over-year living peculiarity meanwhile.(4)Influence of soil nutrient status and leaf carbon content,nitrogen content and phosphorus did not have a clear pattern on occurrence and expansion of the root hemiparasite,respectively;total aboveground plant biomass in heavily-infected areas were generally higher than non-infected areas,despite of the parasitism by a large number of P.kansuensis Maxim.;aboveground biomass of P.kansuensis Maxim.negatively correlated with graminoid aboveground biomass,but positively correlated with that of forbs;P.kansuensis Maxim.occurred more frequently in graminoid-dominated areas.More studies are required for a better understanding of the driving forces for spatial expansion of the damaging root hemiparasite.(5)Although fertilization showed marked influence on plant foliar element concentrations and dramatically altered N :P ratios in the first growing season,effects of fertilization on plant community composition and productivity became robust only in the second season.Dramatical suppression of the hemiparasite was observed in blocks fertilized with nitrogen(particularly HN).Fertilization with phosphorus had no significant influence on plant density and canopy cover of the hemiparasite,but significantly reduced its above-ground biomass.HN significantly reduced plant diversity,with the species number of forbs being halved while that of graminoids hardly affected.Other fertilization regimes showed no notable influence on plant diversity.Fertilization with both nitrogen and phosphorus showed marked promoting effects on plant productivity,particularly above-ground biomass of graminoids.Competition from the vigorous growth of graminoids that benefited more from the imbalanced N :P ratios due to fertilization may explain the suppression of P.kansuensis Maxim.and the altered surrounding plant community.(6)There existed highly significant difference between warming and CK's flower allocation and stem leaf allocation of P.kansuensis Maxim.;warming surpressed P.kansuensis Maxim.aboveground part certainly,and would limit the growth of the smaller individuals roots,but would play a driving role in roots growing with the enlargement of the individual;the closer the source of water,the higher of P.kansuensis Maxim.density,coverage and biomass;soil water content significant positively correlated with P.kansuensis Maxim.density,the influence of soil water content on graminoids and forbs was relatively small;the difference of community evenness index were evident with the decreasing of soil water content,but species diversity index had little change.Above-mentioned results,we had the following conclusion: global warming is an indisputable fact,the germinate time of P.kansuensis Maxim.seeds was ahead of time with the warming,and prolonged its period of duration meanwhile.Extreme weather took place frequently made Bayanbulak accumulated snow melt rapidly in short-term.P.kansuensis Maxim.mainly distributed in higher altitude zone of Bayanbulak originally,but it removed to lower altitude with the snowmelt.O vergrazing led to poor soil nutrients,but it had no influence on P.kansuensis Maxim.population because of its peculiarity of root hemiparasite,and it had the superiorit y to survive in the barren soil,overgrazing of livestock has significantly reduced the amount of coverage aboveground,plants increased the investment of belowground biomass.Underground,P.kansuensis Maxim.haustoria produced successful in favour of a large number of roots;aboveground,P.kansuensis Maxim.competed for light with its host plants was in a dominant position because of the lower coverage.At the same time,both the powerful soil seeds and highly fertility of P.kansuensis Maxim.provided strong supporting for its spreading rapidly. |
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