The Responses Of Alternanthera Philoxeroides And Its Natural Enemy Agasicles Hygrophila To Elevated CO₂

Plant and insect have related responses to elevated CO₂.This study explored the responses which were growth characteristics and foliage compositions of alligator weeds?Alternanthera philoxeroides?grew under different CO₂ concentrations?420 ?L/L,550 ?L/L and 750 ?L/L?,and indirectly effects on flea beetle?Agasicles hygrophila?larvae growth enzymes activity and adults selecting feeding from CO₂.Additionally,we researched the indirect responses and direct-indirect responses of A.hygrophila to different CO₂ concentrations.Elevated CO₂ accelerated the growth of alligator weeds and its photosynthesis,and made its foliage compounded chemical nutriments which were benefit for flea beetle larvae growth and development,and parts of detoxification enzymes whose expression quantity were less after larvae eating it,female and male adults both preferred to eat A.philoxeroides grew under elevated CO₂.CO₂ concentration elevates,it will accelerate growth of A.philoxeroides.In 42nd day,the heights of A.philoxeroides were 35.60 cm and 40.04 cm at 550 ?L/L and 750 ?L/L CO₂ concentrations,respectively,1.75 times and twice of control group?420 ?L/L,19.83 cm?.Elevating CO₂,the SPAD value added,photosynthesis was stronger;foliage soluble sugar content was increased,nitrogen-containing compounds?protein and total amino acid?and tannin contents were decreased,so the C:N was increased.When they fed on A.philoxeroides grew under elevated CO₂,the increasing speed of A.hygrophila larvae weight was faster than the controls';and the 3rd instar acetylcholine esterase?AChE?and glutathione peroxidase?GSH-PX?activities,both of them related to 750 ?L/L CO₂ concentration were significantly lower than others,both of the latters had no significant difference,however,the catalase?CAT?and total superoxide dismutase?T-SOD?activities of 3rd instar related to 3 CO₂ concentrations all were no significant difference;the females and males emerged in the same day,showing the same feeding selectivity,both of them preferred to feed A.philoxeroides grew under higher CO₂ concentration?750 ?L/L?.A.hygrophila was indirectly affected by higher CO₂ concentration,its longevity had no significant change,but it put up advantageous responses on its pre-adult survival and population reproduction.As CO₂ indirectly affected,these whole developmental times from 1st instar to pupa,female adult life times and total longevities all had no significant difference among 3 kinds of CO₂ concentrations,male adult life times and total longevities related to 750?L/L CO₂ concentration all were significantly prolonged;about adult pre-oviposition period?APOP?was significantly shortened with CO₂ concentration going up;but the total pre-oviposition period?TPOP?,it was the longest only at ambient CO₂ concentration;the oviposition period of fertile female and the average fecundity of per female were significantly added with elevated CO₂ concentration.About population parameters,its net reproductive rate?R0?,intrinsic rate of increase?r?and finite rate of increase???all were significantly increased as CO₂ concentration elevated,but mean generation times?T?,the ratios of male:female?sex ratio?and fertile female ratios associated with 3 kinds of CO₂ concentrations all were no significant difference,the pre-adult survival rate related to 750 ?L/L CO₂ concentration was the highest,70%.Comparing values,the sex ratio and fertile female ratio were increased with elevated CO₂.A.hygrophila was directly-indirectly affected by elevated CO₂,its longevity was short,but it put up disadvantageousness on its pre-adult survival and population reproduction.As CO₂ directly-indirectly affected,750 ?L/L CO₂ concentration had made whole developmental times from larva to pupa,female adult life times and total longevities,but male adult life times,male total longevities,the oviposition period of fertile female and the average fecundity of per female all were significantly decreased with elevated CO₂ concentration;adult pre-oviposition period?APOP?was prolonged with elevated CO₂;3 kinds of total pre-oviposition period?TPOP?had no significant difference.About population parameters,its net reproductive rate?Ro?,intrinsic rate of increase?r?,finite rate of increase???,pre-adult survival rate and fertile female ratio all were significantly decreased as CO₂ concentration elevated,while mean generation time?T?related to 750 ?L/L CO₂concentration was the significantly shortest,32.10 days;the ratio of male:female?sex ratio?increased a little with CO₂ concentration going up,but they were no significant difference.Elevated CO₂ had a positive role to A.philoxeroides,when it acted on the growth and development and population reproduction of A.hygrophila,the indirect influence way had a positive role,but the direct-indirect influence way was negative effect.It means the control ability of A.hygrophila would be significantly decreased to A.hygrophila which would be crazy to grow and sprawl if atmosphere CO₂ concentration elevate and A.hygrophila and A.philoxeroides are in the same environment.