Interactive Effects of [CO2] and Temperature on Plant Chemistry of Transgenic Bt Rice and Population Dynamics of a Non-Target Planthopper, Nilaparvata lugens (Stål) under Different Levels of Soil Nitrogen

Abstract

Gaining a better understanding of the interactive effect of projected atmospheric CO2 level increase and the Earth’s rising temperature on plant chemistry (nutritional and defensive characteristics) of transgenic crops is essential when attempting to forecast the responses of target and non-target insects to climate change. In this study, effects of carbon dioxide (CO2; elevated versus ambient), temperature (T; high versus low), and their interactions on leaf nitrogen content (N%) and C:N ratio of transgenic Bt rice and its non-Bt isoline grown under low- and high-N fertilizer were systematically analyzed together with the resulting insect population dynamics of a non-target planthopper Nilaparvata lugens (Stâl) in open-top-chamber experiments. The results indicated that under low-N treatment, elevated CO2 at low T (i.e., eCO2) (compared to ambient CO2 at low T, i.e., CK) significantly decreased N% and Bt-toxin content and significantly increased C:N ratio in leaf sheath and leaf of Bt rice, especially during the tillering stage, whereas inverse effects of high T were shown on the plant chemistry of Bt rice, especially during heading stage. The combination of elevated CO2 and high T (i.e., Combined) (in contrast to CK) significantly increased N% and decreased C:N ratio in leaf sheath of Bt rice during the heading stage under low-N fertilizer, while significantly decreased N% and increased C:N ratio in leaf of Bt rice during the tillering stage, regardless of fertilizer-N level, and significantly increased Bt-toxin content in leaf sheath and leaf during the tillering stage under both low- and high-N. Moreover, no discernable relationships between Bt-toxin content and N% or leaf C:N ratio were observed at any CO2 or N levels evaluated. Furthermore, transgenic treatment, temperature and fertilizer-N level interactions, and CO2 and fertilizer-N level interactions all significantly affected the population dynamics of N. lugens. Specifically, high-N significantly enhanced the population dynamics of N. lugens fed on non-Bt rice grown under eTemp and Bt cultivar significantly reduced the population dynamics of N. lugens under eCO2 regardless of N fertilizer levels. The study demonstrates that the planting of transgenic Bt rice would not increase the risk of increased N. lugens severity under the combined condition of elevated CO2 and increased temperature, particularly under moderate level of N fertility.

AMF Inoculation Can Enhance Yield of Transgenic Bt Maize and Its Control Efficiency Against Mythimna separata Especially Under Elevated CO2

“…Plant nitrogen uptake, nitrogen-level status, and C: N ratio could affect the production of exogenous Bt toxins for Bt crops (Gao et al, 2009;Jiang et al, 2013). Numerous studies have shown that eCO 2 can significantly reduce the exogenous Bt protein content of Bt cotton and Bt rice, while increasing their yield (Coviella et al, 2000(Coviella et al, , 2002Chen et al, 2005b;Wu et al, 2011a,b), and also found the "dilution effect" on exogenous Bt protein or inhibition on Bt-transgene expression (Chen F. J. et al, 2011;Jiang et al, 2017;Liu et al, 2019). Moreover, elevated CO 2 also affected the production of primary and secondary metabolites, and the defense mechanisms of crop plants (e.g., JA and SA) (Stiling and Cornelissen, 2007;Sun et al, 2016).…”

“…In this study, the results showed that e CO 2 significantly increased maize ear weight per plant and grain weight per ear, while it did not significantly affect the 100-grain weight. It is mainly because e CO 2 can enhance photosynthesis and in turn, has a positive effect on crop biomass and production (Guo et al, 2016 ; Liu et al, 2019 ). Although the maize yield was improved, the comprehensive nutritional quality of maize grain (100-grain weight) could not be improved; it may be due to the decreased nitrogen content at high CO 2 levels.…”

“…Moreover, elevated CO 2 also affected the production of primary and secondary metabolites, and the defense mechanisms of crop plants (e.g., JA and SA) (Stiling and Cornelissen, 2007 ; Sun et al, 2016 ). In this study, e CO 2 significantly decreased the ECI and RGR of M. separata larvae fed on non- Bt maize without F. caledonium inoculation, and was almost adverse to all the measured indices of growth and development of M. separata ; it is mainly due to the increased secondary defense substances (i.e., JA and SA) in plants and the declined food nutrient level (e.g., fewer N) under elevated CO 2 (Armstrong et al, 1995 ; Coviella et al, 2002 ; Liu et al, 2019 ). Many studies found that elevated CO 2 had adverse effects on the developmental duration, pupation, and eclosion of cotton bollworm, H. armigera (Akbar et al, 2016 ), and reduced the oviposition number of borers and semilooper (Stange, 1997 ; Rao et al, 2013 ).…”

“…Elevated CO 2 may enhance or weaken plant defense against herbivorous insects, at least partly due to the changes in C- and N-based defensive metabolites, as well as plant nutrients, especially protein content (Kretzschmar et al, 2009 ). Some studies have shown that jasmonic acid (JA), ethylene (ET), and salicylic acid (SA) are secondary defense substances of plants against aphids under e CO 2 (Sun et al, 2013 ; Guo et al, 2014 ), and reported that e CO 2 caused a significant reduction of N-based compounds (i.e., Bt toxin proteins) in Bt crops (Chen et al, 2005b ; Wu et al, 2011a ; Liu et al, 2019 ). Hence, it is speculated that under the condition of climate change, transgenic Bt crops will face a new risk that the effective control of the target pests will be reduced.…”

Arbuscular mycorrhizal fungi alter the food utilization, growth, development and reproduction of armyworm (Mythimna separata) fed on Bacillus thuringiensis maize

“…This phenomenon can be explained by the fact that AMF inoculation promoted the absorption and utilization of soil nutrients in maize plants, thus improving the nutrient level (e.g., nitrogen, phosphorus and potassium) of plant leaves Hodge, Helgason & Fitter, 2010; Rodriguez & Sanders, 2015). Many studies have shown that the nitrogen metabolism and nitrogen level of transgenic Bt crops could affect the expression of Bt toxin protein (Wang et al, 2012; Liu et al, 2019). Stimulating in plant N uptake can increase biomass N relative to C and enhance the nitrogen metabolism enzyme (e.g., nitrate reductase, nitrite reductase, and so forth) activity, transgene expression and Bt toxin production of Bt crops (Stitt & Krapp, 1999; Gao et al, 2009; Jiang et al, 2017).…”