Impacts Of Elevated CO₂ On The Interaction Among Tri-trophic System: Cotton, Aphis Gossypii Glover And Lysiphlebia Japonica Ashmead

Along with the atmospheric CO₂ concentration increases and global warming,concerns have arisen rapidly over plant resistance in different cultivars.Elevated CO₂ not only affects the growth and development of resistant plants,but also changes their chemical component contents and compositions,which was supposed to have indirect impact on herbivore insects, and would influence the further trophic levels(ie.natural enemies) by food chain.How does herbivore natural enemy response to elevated CO₂ by cascade effects was largely unknown. In this study,we performed a systematical experiment to examine the effects of elevated CO₂ on cotton cultivar,cotton aphid Aphis gossypii Glover,and Lysiphlebia japonica Ashmead,as well as their interactions in open-top chambers(OTC).The results as follows:1) Effects of elevated CO₂ on the foliar chemical compounds of three cotton cultivarsThe CO₂ level,cotton cultivar(high 'M9101',medium 'HZ401',and low gossypol content 'ZMZ13') and interaction between them significantly influenced the foliar chemical compounds in the plant leaves.Significantly increase in C/N,and decreases in water content and free amino acid contents were observed in 'M9101' leaves grown in elevated CO₂, compared with those in ambient CO₂.Foliar TNCs and C/N were significantly higher,and nitrogen content and soluble protein was significantly lower in 'HZ401' with CO₂ rising. Furthermore,No significantly changes in foliar chemical components of low level gossypol cultivar 'ZMS13' grown in elevated CO₂,compared with those in ambient CO₂.Moreover, significantly increases in foliar gossypol and tannin content were found in all three cultivars grown in elevated CO₂,compared with those in ambient,and soluble protein was significantly higher but free amino acid contents was significantly lower in 'ZMS 13' than in 'M9101' and 'HZ401' with CO₂ rising,which indicate elevated CO₂ will strengthen the resistant effect of 'M9101'.2) Effects of elevated CO₂ on SOD,CAT,AChE activity in cotton aphid,Aphis gossypii fed on different cotton cultivarsThese three enzyme activity in Aphis gossypii Glover show the diverge response to elevated CO₂.Higher CAT,AChE and lower SOD activity were found in cotton aphids fed on 'M9101' with CO₂ rising.Three enzymes activity were all increased in cotton aphids fed on 'HZ401' in elevated CO₂,compared with that in ambient CO₂.However,CAT,AChE and SOD activity were all significantly decreased in cotton aphids fed on 'ZMS13' with CO₂ rising.Furthermore,these three enzyme activity were significantly higher in cotton aphid fed on 'HZ401' in elevated CO₂,compared with that fed on 'M9101' and 'ZMS13',and higher CAT activity was observed in cotton aphid fed on 'M9101' in elevated CO₂, compared with that fed on 'ZMS13'.3) Effects of elevated CO₂ on the developmental time,fecundity and life table parameters of two successive generations of the cotton aphid fed on different cotton cultivarsSignificantly shorter nymphal stage for the first generation were observed in cotton aphids fed on all three cultivars grown in elevated CO₂,but along with generation increasing, the cotton aphids show the diverge response to elevated CO₂.More specific,in the treatment of aphids fed on 'M9101' grown in elevated CO₂,significantly longer nymphal stage, shorter adult life span and decrease in fecundity for the second generation of cotton aphids were found compared with those in first generation.It may indicate that elevated CO₂ positively affect neither developmental time nor fecundity of the cotton aphids.Besides, significantly decrease was found in the aphid r_m with generation increasing,which suggested fitness of the cotton aphids was reduced.However,significantly shorter nymphal stage with generation increasing was found when the aphids were fed on 'ZMS13'. Moreover,in the second generation,longer nymphal stage and parameter T,as well as lower r_m were observed in cotton aphids fed on 'M9101',compared with those fed on 'ZMS13'. The results indicate elevated CO₂ will shorten the nymphal stage of cotton aphids fed on all three cotton cultivars.At the same time,high gossypol in the cotton plant has a negative effect on cotton aphids in elevated CO₂.4) Effects of elevated CO₂ on the developmental time and the parasiting ability of Lysiphlebia japonica Ashmead parasitized the cotton aphid from different cotton cultivarsSignificantly shorter in the developmental time of Lysiphlebia japonica Ashmead parasitize the cotton aphids from different cotton cultivars in elevated CO₂.Moreover,the parasitism rate(%),female proportion(%),number of wasp emergences and number of wasp female per hundred-aphids were increased,and wasp emergence(%) of Lysiphlebia japonica Ashmead was decreased when parasitize aphids from 'M9101' grown in elevated CO₂,compared with those in ambient CO₂.Significantly higher in the parasitism rate(%) and decrease in other parameters were found in Lysiphlebia japonica Ashmead parasitize aphids fed on 'HZ401' with CO₂ rising.However,significantly lower parasiting ability of Lysiphlebia japonica Ashmead parasitize aphids fed on 'ZMS13' grown in elevated CO₂. Furthermore,significantly increase in number of wasp female per hundred-aphids was observed in Lysiphlebia japonica Ashmead parasitize aphids from 'M9101' compared with those from 'ZMS13'.The results suggested that elevated CO₂ will positively affect the growth and development of Lysiphlebia japonica Ashmead at the third trophic level,and high gossypol in the cotton host plant will strengthen the wasp ability of pest control.Our results indicate high gossypol in cotton plant negatively affects A.gossypii,while shows a positive effect on growth and development of Lysiphlebia japonica Ashmead with CO₂ rising.This suggests elevated CO₂ will strengthen effect of pest control in high gossypol cotton cultivar.