| Bidens frondosa,native to North America,is an alien noxious weed in China in recently.This weed has invaded in many habitats,such as arable land,roadside and waste land etc.,it has brought bad effects on local agriculture and environments.In this paper,Morphology,growth,biomass and its allocation,and their phenotypic plasticity of B.frondosa among invasive populations and between it and its congeners were compared under different light and water conditions by common garden experiments.In addition,growth and competitive response of B.frondosa to its congeners(B.pilosa,B.biternata and B.tripartita)were also studied by plant experiments.The results will be helpful to explore the invasive mechanism and provide fundamental materials for prevention and control of B.frondosa.The results are as follows:1.Plant height,branch number,specific leaf area,total biomass and its allocation,relative growth rate and photosynthetic pigment of B.frondosa from different invasive populations were varied under different light and water conditions.These parameters exhibited different plasticity.Plant height and branch number of all populations at high light level were higher than those at low light level.But their specific leaf areas were larger at low light level than at high light level.Total biomass of all populations was the highest under high light and high water conditions,and was the lowest under low light and low water conditions.Biomass allocation varied with the light and water changing.Stem mass ratio at high light level was the highest and leaf mass ratio at low light level was the highest in all structure mass ratios.Root mass ratio at high light level was higher than that at low light level.This indicated that light have strong effects on mass allocation of B.frondosa.Relative growth rate of all populations was higher at high light level than at low light level.Photosynthetic pigment content varied with light and water changing and different chlorophyll has different change rule.At different water conditions,plasticity index of most traits was the highest for Hebei population and was the lowest for Jiangsu population,the mean plasticity index values were 0.52 and 0.35,respectively.At different light levels,the plasticity index of all populations was over 0.5,it was the highest for Guangxi population and was the lowest for Jiangsu population,the mean plasticity index value were 0.63 and 0.54,respectively.The plasticity index under different light and water conditions was different among the studied population,indicated that there were variation for phenotypic plasticity among populations.B.frondosa has invaded diverse habitats and adapt to different introduced range,so that their adaptability produce variation.These made this weed can adapt to and invade a wider range.2.Morphology,growth,biomass and its allocation,and their phenotypic plasticity under different light and water conditions were different between B.frondosa and its congeners(B.pilosa and B.biternata).There were no significant difference for plant height and specific leaf area between B.frondosa and its congeners under high light and high water conditions.But branch number of B.frondosa was higher than that of its congeners.At high light and low water,plant height of B.frondosa was lower than that of its congers,but branch number and specific leaf area of B.frondosa were higher than that of its congener.At low light level,plant height and branch number was lower in B.frondosa than in its congeners,but their specific leaf area was similar,even higher in B.frondosa than in its native congenr B.biternata under low light and high water.Morphological parameters of the three species varied with light and water changing.Plant height and branch number were higher and specific leaf area was lower significantly in high light than in low light level.Total biomass of the three species was significantly higher at high light than at low light level.At high light and high water conditions,the total biomass of B.frondosa was lower than that of invasive species B.pilosa and was similar to that of native species B.biternata.Shoot mass ratio was no significant difference between Bidens frondosa and its congeners under all light and water conditions except for under high light and low water level.Leaf mass ratio of Bidens frondosa was significant lower under high light and high water conditions but was remarkable higher under high light and low water level than that of B.biternata.However,shoot and leaf mass ratios among the three species were similar at low light level.Relative growth rate of the three species was higher in high light than in low light level.It always the largest in B.pilosa at all light and water conditions.But the relative growth rate of B.frondosa was higher in high light level and was lower in low light level than that of B.biternata.There was no significant difference in photosynthetic pigment B.frondosa and native B.biternata at high light level.But at low light level,all photosynthetic pigment except carotenoid was lower in B.frondosa than in B.biternata.Light compensate point and saturation point,the maximum photosynthetic rate,dark respiration rate were significant higher at high light level than at low light level.At different water conditions,the mean plasticity indexs were similar among the three species;they were 0.36,0.35 and 0.35 for B.frondosa,B.pilosa and B.biternata,respectively.But at different light levels,they were 0.63,0.60 and 0.53,respectively.The mean plasticity indices were higher at different light levels than at different water conditions.This indicated that B.frondosa and its congeners were more adaptive to light changing than to water changing.3.Morphology,biomass and its allocation at all nutrient levels were different between B.frondosa and its congeners(B.pilosa,B.biternata and B.tripartita).Competitive response of B.frondosa to native congener B.biternata was also varied with nutrient level changing.Plant height,branch number,total biomass and specific leaf area of the three species were higher at higher nutrient level than at low nutrient level.Biomass allocation of B.frondosa and B.pilosa at high nutrient level were significantly different from those at low nutrient level.But they had no significant difference between middle nutrient level and high nutrient levels.Whether it was at high or at low nutrient levels,biomass allocation were constant in B.biternata.Plant height and biomass of B.frondosa was lower than that of B.pilosa,but it was similar to that of B.biternata,and higher than that of B.tripartita.Specific leaf area and reproductive mass ratio of B.frondosa were the highest at all nutrient levels.They were significantly higher than that of it congeners.Plant height,branch number,total biomass and specific leaf area of different B.frondosa populations were higher at high nutrient level than at low nutrient level.Plant height,branch number,total biomass were the highest in Guangxi population and were the lowest in Hebei population.They had significant difference between the two populations.They were secondary in Jiangsu population.Reproductive mass ratios of the three populations were higher at low nutrient level than at high nutrient level.It was the highest in Hebei population;especially it was significantly higher than that in Guangxi and Jiangsu populations at low nutrient level.Competitive responses of the three B.frondosa populations to native species B.biternata were varied.At high nutrient level,plant height,branch number,root mass,reproductive mass and total biomass of Guangxi had no significant difference between with and without competitor.But reproductive mass and total biomass of Jiangsu and Hebei populations were significantly different between with and without competitor.At low nutrient level,all trait parameters of the three populations had significant difference between with and without competitor.This indicated that native B.biternata had more competitive effects on B.frondosa at low nutrient level,but the effects decreased with nutrient increasing.In summary,at different water conditions,the mean plasticity index of different traits were similar among the B.frondosa and its relatives,but the mean plasticity index value of B.frondosa were higher than that of B.pilosa and B.biternata under different light conditions.This exhibited that B.frondosa were more adaptive to light and water changing than its congeners.Furthermore,there was variation for plasticity among populations,which made the alien weed adapt to a wider range and increase its ability to invade and spread.Especially,when resources such as light,water and nutrient were abundant,morphology,growth,biomass and specific leaf were performed best.In addition,high nutrient enhanced the competitive ability of B.frondosa.High reproductive allocation could be attributed to high seed production strategy of B.frondosa,and ensure survival,establishment and colonization.All above characters were benefit to the invasion of B.frondosa. |
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