Effects Of Enhanced Ultraviolet-B Irradiance On Physiology,Compositions,Resource Allocation,Construction Cost And Allometry Of Amaranthus Retroflexus

Resources allocation and allometry of plants are critical to study the ecological adaptation strategies and enhanced UV-B radiation has become a hot spot of global change problem while research has not refered to the influence of enhanced UV-B radiation on resources allocation and allometry.First,the effects of two dosages(2.8 kJ·m^-2.d^-1 and 4.2 kJ·m^-2·d^-1) of enhanced UV-B radiation on biomass allocation,chemical compositions, construction cost,energy accumulation and allocation of Amaranthus retroflexus were studied under field conditions and discussed from the aspect of morphology and physiology. Secondly,the effects of enhanced UV-B radiation(2.8 kJ·m^-2·d^-1) and competition on plant allometry as well as on the distributions aspects of size,morphology and biomass of Amaranthus retroflexus were studied under field conditions.The results indicated that:(1) Branch number,leaf number,plant height and stem diameter of Amaranthus retroflexus were not affected by enhanced UV-B radiation at four growth phases.(2) The activity of CAT in plants under enhanced UV-B is significantly higher than that of the control.Enhanced UV-B radiation has no statistically significant influence on the activity of SOD.The activity of POD was significantly increased only by the low dosage supplemental radiation,and the contents of MDA were increased remarkably after UV-B radiation treatment.(3) When harvested at stages of maturity,the proportion of biomass partitioned to leaf increased significantly under the lower dosage of UV-B radiation due to increased SLW,but allocated less to root which might be involved with reducing root number,length and activity. However,the high dosage radiation had no significant influence on the proportion of biomass.(4) Most of chemical composition in root,stem and leaf were notably influenced by enhanced UV-B radiation.Soluble protein,lignin and fat in leaf,lignin in root,cellulose,lignin in stem were increased,while starch in leaf,soluble sugar,starch,fat in stem were decreased by UV-B radiation.This may result in the decomposition rate of leaf and stem slow down.(5) Carbon and nitrogen concentration,ash,Ash-free heats of combustion and construction cost were not affected by enhanced UV-B radiation.Root,stem,fruit-spike and whole-plant energy content under enhanced UV-B were significantly lower than that of the control,and was lowest in low dosage.The pattern of energy allocation changed in low dosage,the proportion of energy partitioned to stem and leaf increased significantly but allocated less to root and fruit-spike.However,the high dosage radiation had no significant influence on the proportion of energy,expect root.(6) At two intensity of intraspecific competition,the UV-B radiation lead to a negatively skewed of the height frequency distribution,while the radiation had not caused the skewed of stem diameter frequency distribution.At high intensity of competition,the UV-B radiation lead to the positively skewed of the biomass frequency distribution and had been recovered gradually with the growth of seedlings.The radiation did not influence the biomass frequency distribution at low intensity of competition.At two intensity of competition,there is a tendency to lower the coefficient variation of height,stem diameter and biomass by UV-B radiation.(7) At low intensity of competition,UV-B radiation caused a deflection in the height-to-stem diameter relationship at initial stage,but the deflection recoverd gradually.The radiation did not influence this relationship at high intensity of competition.The stem diameter-to-biomass relationship under the UV-B radiation and the controls lie in the same area.It is indicated that Amaranthus retroflexus has strong ability to recover and adapt the influence produced from external pressure.In a word,this study found that low dosage of UV-B radiation have significant influence on the proportion of biomass partitioned to leaf and root,and have a certain impact of height-to-stem diameter,height-to-biomass relations in initial stages.These results are of great significance for the evaluation of ecological consequences from enhanced ultraviolet radiation.