Allelopathic Potential Of Major Poisonous Weeds And Grasses In Alpine Meadows

The application of allelopathy in the study of alpine grassland degradation to reveal its potential role in community succession has important theoretical and practical significance for the restoration and sustainable utilization of degraded grassland.This research aimed at the practical problems of seeded pasture degradation in the Sanjiangyuan area,and focused on the perspective of allelopathy.The shortcomings of existing research methods were partly improved.Six poisonous weeds(Pedicularis kansuensis,Aconitum pendulum,Oxytropis ochrocephala,Ajuga lupulina,Anaphalis lactea and Leontopodium nanum)and five grasses(Elymus sibiricus cv.Tongde,Elymus nutans,Poa crymophila cv.Qinghai,Poa pratensis cv.Qinghai and Festuca sinensis cv.Qinghai)were used as experimental materials.The allelopathic potential of water extracts from poisonous weeds,grass plants and rhizosphere soil on the seed germination and seedling growth of grasses were investigated by laboratory bioassay.The general goal was to reveal the potential allelopathic effects of driving grassland degradation and provide theoretical basis for restoration of degraded grassland and establishment of seeded pasture.The results and conclusions of the study are as follows:(1)The allelopathic effect index of whole plant water extract of Pedicularis kansuensis on the Elymus sibiricus cv.Tongde and Poa pratensis cv.Qinghai was 0.08 and 0.01,presenting a weak promotion effect.The allelopathic effect index of the whole plant water extract of Ajuga lupulina on the seed germination and seedling growth of Elymus nutans was 0.08,showed a weak promoting effect.In contrast,the powder water extracts of Pedicularis kansuensis and Ajuga lupulina showed inhibitory effects on the five grasses.The allelopathic indices of both whole plant water extract and powder water extracts of Aconitum pendulum,Oxytropis ochrocephala,Anaphalis lactea and Leontopodium nanum on seed germination and seedling growth of five grasses were all less than 0,showing inhibitory effects,and the inhibitory effects of powder water extract on five grasses were stronger than those of whole plant water extract.(2)The whole plant water extract of Elymus sibiricus cv.Tongde increased its own seed germination rate by7.6%,showed a weak promotion effect,but the whole plant water extract had an inhibitory effect on its seedling height,root length and dry weight,and the inhibitory rates were 12.2%,54.7% and 42.9%,respectively.In contrast,the powder water extracts of Elymus sibiricus cv.Tongde had an inhibitory effect on seed germination and seedling growth.The whole plant and powder water extracts of Elymus nutans,Poa crymophila cv.Qinghai,Poa pratensis cv.Qinghai and Festuca sinensis cv.Qinghai all showed inhibition on germination of their own seeds and seedling growth.(3)The allelopathic effect indices of rhizosphere soil water extract of poisonous weeds on the seed germination and seedling growth of five grass species were negative values and showed an inhibitory effect.The allelopathic effect of the extract from the rhizosphere soil Aconitum pendulum on Festuca sinensis cv.Qinghai was the strongest,with an allelopathic effect index of-0.62,and the allelopathic effect of the water extract from the rhizosphere soil of Pedicularis kansuensis on Elymus nutans was the weakest,with an allelopathic effect index of-0.03.The effect of grass rhizosphere soil water extracts on the germination of their own seeds varied from species to species.The rhizosphere soil extract of Elymus sibiricus cv.Tongde has a significant promotion effect on its own seed germination.The rhizosphere soil water extracts of Elymus nutans,Poa crymophila cv.Qinghai,Poa pratensis cv.Qinghai and Festuca sinensis cv.significantly reduced their own germination rate.In conclusion,all the water extracts of whole plant,powder and rhizosphere soil of the poisonous weeds had potential allelopathic effects on seed germination and seedling growth of the tested grasses and the allelopathic effect of powder water extracts was stronger than that of the whole plant extracts.Different poisonous weeds show different allelopathic potentials,and the sensitivity of the same grass to extracts from different treatments was different.Except for whole plant water extract of Elymus sibiricus cv.Tongde,which can promote the germination of its own seeds,other extracts from whole plants,powder and rhizosphere soil of grasses had autotoxic effects on their own seed germination and seedling growth.The restoration of degraded grassland and establishing seeded pasture,and related management on alpine meadow region should not only consider the effects of poisonous weeds,but also the autotoxicity of grass species.