Ecological Adaptability Of Invasive Plant Solidago Canadensis To Environments And Its Control Strategy

Solidago canadensis(Canada goldenrod),a rhizomatous perennial plant (family,Compositae)originating from North America,was introduced into China as a horticultural plant in 1930s.S.canadensis began to spread rapidly as an important weed in the 1980s and has now infested many districts in eastern China and the species was listed as one of the harmful alien plants in China.In the process of invasion,S.canadensis initially forms numerous "satellite model" populations,produces clones of individual plants with the aid of the underground rhizomes to fill the interspace,and,finally,forms a single dominant species population supplanting the native species.It has caused grievous damages to the ecosystems.In recent years,the studies and control of S. canadensis have been paid more attention in China.To date,the research on S. canadensis has mainly focused on its physio-ecological adaptation,allelopathic effects on native plants and the genetic diversity.In this paper,we studied the ecological adaptability of S.canadensis to the soil water content,light intensities, the distribution pattern of its populations,and the the methods of its biological control,chemical control and physical controls.The main results are as follows:1.The growth response of the seedling of S.canadensis to the water content in the soils and light intensities were determined under controlled conditions.We found:(1)The seedling height of S.canadensis was affected greatly by water content in the soils and light intensities,mesophytic habitats and habitats with lower light intensity are good for the species to increase its height,while xeric habitats and habitats with higher light(100%)are not;(2) The leaf number of S.canadensis reached maximum when it grew in moist habitat,but was less affected by the light intensities.(3)Soil water content has greatly effect on the leaf area of S.canadensis,which reached the biggest when it grew in the mesophytic,habitat,but smallest in the aquatic habitat.The habitats with moderate light intensity(45%)are good for S.canadnesis to increase the leaf area,but those with high light intensity(100%)or low light intensity(15%,5%)are not.(4)The indices of leaf mass per area are not significant different among the plants growing in the soils with different water contents,but increased with the increase of the light intensity;(5)The biomass of the seedlings reached maximum in the mesophytic habitat,but with the minimum in the aquatic habitat.The habitat with 45%light intensity is best for the biomass accumulation of S.canadensis,while the seedlings in the habitat with 5%light intensity almost did not grow and perished at last.2.The coverages of S.canadnesis populations in different colonized periods and habitats were surveyed by the successive sampling.The deviation coefficients were calculated and the pattern scale and pattern grain were analyzed.The results showed:(1)The populations of S.canadensis were obvious clumpy distributed;(2)The number of the population patches of S. canadensis followed an order as less→more→less,which was related to its sexual reproduction at initiatory invaded period and asexual reproduction at latter period.3.The eco-physiological indices of S.canadensis after being parasitized by C.japonica were measured under the experimental conditions,and the anatomical features of the parasitism were also observed.The main results were as follows:(1)the parasitic roots of Cuscuta japonica were able to parasitize the stems and leaves of S.canadensis by penetrating the stem and leaf epidermis to the pith of S.canadensis,and therefore,absorb a large amount of water and nutrition from the host,which enhanced its biomass and stunt the host;(2)after being parasitized for 50 to 60 days,compared with the control,the maximal net photosynthesis rate of S.canadensis decreased to 58.81%,the light compensation increased by 153.39%,the proline by 287.57%,and MDA content by 128.64%;but the content of dissoluble protein and sugar declined 43.45% and 44.47%respectively;(3)the normal individuals of S.canadensis entered into flower bud stage in the middle of September,and full flowering stage in the middle of October;in contrast,those parasitized by C.japonica produced flower buds late to the end of October,and their inflorescence length was only one-tenth of the controls.The dividuals of S.canadensis were unable to produce flower buds if the biomass(dry weight)of its parasitic plant(namely,C. japonica)exceeded 13.14%of its dry weight.The results above showed that C. japonica could restrain the growth and sexual reproduction of S.canadensis effectively.Therefore,C japonica might be a promising species for controlling the invasiveness of S.canadensis.4.We collected the pollens of S.canadensis in its anthesis,examined the activety of pollen and the influences of herbicides(Glyphosate,Ethephon,2, 4-D,Paraquat)on pollen germination and pollen tube growth.We found:(1)the culture medium containing 0.5%agar,20%sucrose and 10 mg·L^-1boracic acid was favorable for the pollen germination and the pollen tube growth of S. canadensis,and the pollen germination rate is higher than 50%,the pollens of S. canadensis survived for 3-4 d under natural conditions;the culture medium with proper concentration of Ca²⁺has no effects on pollen tube germination,but accelerated the growth of pollen tube distinctly.Based on their inhibitory effects (from high to low)on pollen germination and pollen tube growth,the 4 herbicides are ranked as Glyphosate＞Ethephon＞2,4-D＞Paraquat.5.In order to better understand the response of S.canadensis to human disturbance,we determined:(1)the content of chlorophyll,Proline,MDA, conductivity of leaves of S.canadensis after sprayed with herbicides;(2)the survival and reproductive capacity of its rhizomes under different incision intensities,dry and waterlogged treatments;(3)its shoot number,capability of sexual reproduction of S.canadensis after cut at different intensities in different stages.We found:(1)Glyphosate(11,250-22,500g.ha^-1)is more effective than 2,4-D(450-1050g.ha^-1)in the control of S.canadnesis;(2)The vegetative reproductive capacity of its rhizomes varies among different stages,with highest from February to March and lowest from November to December,suggesting that the period from November to December is a good stage to control S. canadensis by mechanical methods;(3)With the decrease of water content in rhizomes,their survival rate falls gradually;When the water in rhizomes lost by over 50%of the fresh weight,their survival rate falls sharply.Therefore,tillage in dry and sunny period is a good practice to control the rhizome of S. canadensis;(4)Under soakage condition,the rhizome of S.canadensis could stand short-term stress of low concentration of salt solution,has wider adaptation breadth to pH,especially high tolerance to the acid environment;thus the soakage of the rhizome at temperature of 30℃(Rice/dry crop rotation Systems)is a choice for us to control rhizome of S.canadensis;(5)Little effect on the growth and sexual reproduction of S.canadensis could be found if the plant cut with different intensities at the early stages of vegetative growth;but, in its middle stage of the vegetative growth,for instance,May,the number of its shoots and seeds would increase greatly;the shoot number and seeds could increase more if the plants cut with light intensity before inflorescence.The above results provided new and practical information in the control of S. canadensis.