| Temperature and CO2concentrationrisingare characteristic of the climate change.Climatebiologystudies have indicated that an increase in C availability in soils and then consequent change in C/N ratio in plants are influential on N contents in plant tissues,leading to theso-called’nitrogen dilution effect’.Such an effectcan result in a decrease in concentration of leaf protein and therefore reduce nutritionfor herivores,whose growth,development and reproduction can be impaired.In addition,reductions in herbivore performance under CO2enrichment can lead to higher mortality by increasing the sensitive period to attacks by natural enemies.These changes in life history traits have consequences on population growth.So far,we have had little knowledge about the effect of climat change on insect interaction ecology.Empirical advances in climate change biology of insects have mostly been obtained through manipulated experiments in laboratory(e.g.environmental chambers),some through semi-natural experiments in the field(e.g.open-top chambers),and a few w through open field experiments(e.g.Free-Air-CO2-Enrichment,FACE).To date,FACE has not been employed in research of rice pests in paddy field.Im my thesis research Ⅰ made both laboratory and open field experiments to focus on interactions between main rice planthopers,including the small brown planthopper[SBPH]Laodelphax striatellus(Fallen),the brown planthopper Nilaparvata lugens(St?l)[BPH],and the white brown planthopper(WBPH)Sogatella furcifera(Horvath).In addition,I investigated arthropod biodiversity in paddy field plots under CO2 by temperature treatments.Specifically,followingquestions are addressed:(1)How do CO2elevation and N fertilization affect development,survival and reproduction of SBPH?(2)How does CO2elevation affect intra-and inter-specific competition between BPH and WBPHin survival and wing dimorphism?(3)How do temperature and CO2 elevation influence survivaland wing dimorphismof SBPH and BPHunder interaction in open paddy field?(4)How do temperature and CO2 elevation impact arthropod diversity in open paddy field?Following results and conclusions are obtained from this research.1.Effects of elevated CO2 and nitrogen fertilization on development and reproduction of Laodelphax striatellusLaboratory experiments were conducted examing the effect of CO2(ambient 390 μl/L and elevated 780 μl/L)andnitrogen fertilizer application(80,120,and 160 mg/L amendments to soils at seedling)on SBPH survival and oviposition across five generations.Thethree-way ANOVA on the effect of CO2,nitrogen and generation showed that CO2,generation and its quadratic,interaction between CO2and nitrogen application influenced SBPH fecundity.Under both ambient and eleved CO2 the fecundity increased gradually from first to third generation and then declined toward fifth generation across all nitrogen levels,showing higher fecundity at increasing N levels.Under the ambient CO2,nymphal survival increased from 51.56%at the low Nlevelto 60.54%at the high Nlevel;under the elevated CO2,the survival reduced from 69.53%to 59.38%across the N levels.Nymphal survival was not obviously higher in the 3rd and 5th generation than the 2nd under the elevated CO2 compared with the ambient CO2.The results from this experiment suggest that increasing application of N fertilizer under the elevated CO2 may impair nymphal survival of SBPH but not adult fecundity.2.Effects of elevated CO2 on intra-and inter-specific competition of BPH and WBPHLaboratory experiments were conducted in microcosms under two CO2 concentrations(ambient 390 μl/L and elevated 780 μl/L)and different densities(4,8,16 and 32neonate nymphs per seedling/glass tube)treatments.Neonate BPH and WBPHnymphs were released into the tubes either alone(intra-specific competition)or in mixing(inter-specific competition)and their survival by wing dimorphism was calculated.Theresultsshoweda significant effect of CO2 and density on intra-and inter-specific competition.Inter-specific competition resulted in lower nymph survival rate and higher proportion of macropterous individuals with an increase in density under both ambient and elevatedCO2.The density-related intra-specific competition resulted in lower nymph survivalrate,higher proportion of female macropterous individuls ofthe two planthoppers,and lower proportion of male macropterous individuls ofBPH,underthe ambientCO2.However,the declineof the two planthoppers’ nymph survival rate and proportion of macropteran male BPH is not as much while the proportion of macropteran female increased underthe elevated CO2.The density-related intra-specific competition lead toa lower nymph survival rate and higher proportion of macropterous SBPHunder theambient CO2,while a higher nymph survival rate and proportion of macropterous WBPH femalesundethe relevated CO2.The results suggest that CO2elevation may favor WBPH in its competition with BPH.3.Effects of elevated CO2 and temperature on nymph survival and wing polymorphism in BPH and SBPHunder interaction in paddy fieldA field experiment was made in a free air CO2 and temperature elevation plotsin a paddy field in eastern China.A factorial combination of two CO2 concentrations(ambient and500μL/L)and two temperatures(ambient and+2℃)treatments were manipulated with three replicated plots for each treatment.BPH and SBPH were released into a organza-covered cage either alone by50 second-instarnymphs or in mixure byratios of BPH/SBPH=13/37,25/25 and 37/13.The observation showed that BPH nymphal survival increased under the elevated CO2&temperature and the elevated CO2 treatments,but both planthoppers decreased under theelevated temperature.With an increasein proportion,BPH survival rate decreased but SBPH increased.Under the elevated CO2,macropterous SBPH females and BPH males increased in proportion;under the elevated CO2&temprature”,macropterous SBPH females increased in proportion,but macropterous BPH males decreased in proportion.The results of this study suggest that elevated temperature and CO2 may have negative impacts on survivorship of BPH,but positive on SBPH by increasing proportion of macropterous adults.4.Effects of elevated CO2 and warming on arthropod diversity in paddy fieldA survey of arthropods was made in free-air CO2 and temperature elevation plots in a paddy field eastern Chinafrom August toNovember 2011 during the rice growing season.Samples were randomly taken from field plots.The survey found 96 species from 55 families in 11 orders,2 classes,among which were 71 insect species from 42 families in 10 orders and 25 arachnid species from 8 families in 1 order.Analysis of overall arthropod community showed that species evenness and abundance obviously increasedunderthe elevated CO2&temperature treatment,which had varying impacts on species diversity indicesin the rice growing season.Species diversity reduced under elevated CO2&temperature treatments.Richness of herbivorous and detritivorous insectsdecreased under the elevated CO2;abundances of parasitoid and detritivorous insects increased underthe elevated CO2&temperature.The results of this study suggest thatarthropod diversitychanges somewhat when both CO2 and temperature are elevatedin paddy fields,a dissimilar consequence thanwhen either of the two factorswas elevated. |
