Climate Change Will Increase Pest Attacks on Soybeans
26 Jul, 2007 02:44 pm
Under natural field conditions, elevated [CO2] increased susceptibility of soybean to herbivory by the invasive species Japanese beetle and enhanced the performance of these beetles.
During the last annual meeting of the American Society of Plant Biologists in Chicago (July 7-11, 2007), scientists Jorge A. Zavala, Clare L. Casteel, May R. Berenbaum and Evan H. De Lucia from the University of Illinois, USA have shown that elevated CO2 may negatively impact the relationship between some plants and insects. CO2 is one of the most important gases involved in global warming, the greenhouse effect. However, not only temperature, but also CO2 concentrations itself can affect ecosystem functions, including plant-insect interactions.
By 2050, soybean (Glycine max) the world’s most widely grown seed legume will grow in an atmosphere with a 50% higher carbon dioxide concentration ([CO2]) and could affect plant-insect interactions. Insect’s attack produces high economic costs to field crops. Soybeans respond to insect attack by producing defense compounds that inhibit digestive enzymes (proteinases) in the gut of insects, reducing their performance and crop damage. The production of this antidigestive compounds are regulated in plants by the hormone jasmonic acid (JA). However, elevated [CO2] levels disrupt this equilibrium in plant-insect interactions and benefit the herbivore.
This study, supported by the Department of Energy, Office of Science, found that when soybeans were exposed to elevated [CO2] the crop became more susceptible to Japanese beetle (Popillia japonica) colonization, producing more leaf damage. The study was conducted with soybean grown in traditional field conditions but with additional exposure to ambient [CO2]. The results showed that the expression of genes related to antidigestive compounds and their inhibitory activity decreased when soybeans were exposed to elevated [CO2]. This interesting result was explained by a reduction of JA biosynthesis produced by elevated [CO2]. Interestingly, beetles that fed on soybean grown under elevated [CO2] had higher proteinase activity in the guts, increasing their capacity to digest proteins.
Our results suggest that elevated [CO2] increased the susceptibility of soybean to invasive insects by down-regulating the expression of hormones related with defense, which down-regulate important defense compunds against beetles,” Zavala said.
Zavala also explained, “Under natural field conditions, elevated [CO2] not only increased susceptibility of soybean to herbivory by the invasive species Japanese beetle, but also enhanced the performance of these beetles.”
Recently it has been suggested that field experiments in free-air concentration enrichment (FACE) for exposure to elevated [CO2] result in lower yield stimulation under elevated [CO2] exposure compared to previous chamber experiments. FACE experiments provide free access to herbivores, which increases damage by arthropods and explain the observed reduction in productivity, perhaps due to decreased resistance to herbivores. Thus predicted increase in soybean productivity under projected [CO2] levels may be reduced due changes in gene expression that reduces soybean resistant to herbivory in the field. Increased susceptibility of this important crop by elevated [CO2] to insect attack is an indirect effect of anthropogenic atmospheric change that may have implications for future agricultural productivity.
Reference: Presentation at the American Society of Plant Biologists in Chicago, July 7-11, 2007, Jorge A. Zavala, et al.