Phloem phytochemistry and aphid responses to elevated CO₂, nitrogen fertilization and endophyte infection

Abstract

1 Rising atmospheric CO 2 has been shown to alter plant nitrogen metabolism, growth and secondary chemistry. We hypothesized that altered aphid performance under elevated CO 2 is linked to phloem nitrogen chemistry. 2 Rhopalosiphum padi performance on endophyte-infected or uninfected tall fescue was examined under three levels of CO 2 (ambient, 800 and 1000 p.p.m.) and high and low nitrogen fertilization. Ethylenediaminetetracetic acid-facilitated exudation was used to sample phloem sap, followed by quantification of relative amino acid concentrations using reverse-phase high-performance liquid chromatography. 3 Aphid abundance was reduced at 800 p.p.m. relative to ambient CO 2 but returned to baseline at 1000 p.p.m. The density of aphids was reduced in both the elevated CO 2 treatments. Aphids were unsuccessful at colonizing endophyte-infected plants, possibly as a result of the presence of loline alkaloids. 4 Multivariate analysis showed that certain groups of phloem amino acids were altered by nitrogen fertilization and CO 2 . We found that four amino acids (valine, arginine, glutamine and aspartate) were correlated with aphid performance. These findings partially explained the effect of plant nitrogen fertilization and elevated CO 2 on aphids. 5 The present study represents a first step toward providing a mechanistic explanation of the aphid performance changes that may result from rising atmospheric CO 2 .

Mutualism effectiveness of a fungal endophyte in an annual grass is impaired by ozone

“…, ; Whittaker , ; Hughes & Bazzaz ; Ryan et al . ) and effects of ozone on the interactions between plants and aphids have been unclear and highly idiosyncratic (Holopainen ; Valkama, Koricheva & Oksanen ; Lindroth ). Effects of ozone on herbivore performance may be direct by affecting their physiology, or indirect through phytochemical changes of exposed plants (Lindroth ).…”

“…As a result, efforts have been made on predicting the consequences of environmental variables such as temperature, precipitation and CO 2 , on different aspects of plant-herbivore interaction. Reaction with CO 2 (see Bezemer, Jones & Knight 1998;Bezemer et al 1999;Newman et al 1999Newman et al , 2003Whittaker 1999Whittaker , 2001Hughes & Bazzaz 2001;Ryan et al 2014) and effects of ozone on the interactions between plants and aphids have been unclear and highly idiosyncratic (Holopainen 2002;Valkama, Koricheva & Oksanen 2007;Lindroth 2010). Effects of ozone on herbivore performance may be direct by affecting their physiology, or indirect through phytochemical changes of exposed plants (Lindroth 2010).…”

Elevated CO2 Levels Impact Fitness Traits of Vine Mealybug Planococcus ficus Signoret, but Not Its Parasitoid Leptomastix dactylopii Howard

“…Higher atmospheric levels of CO 2 have been shown to result in a higher biomass, increased yield, and lower nutritional values in grapevine and other plants [2,5,44]. However, plant tissues and fluids vary in their response to elevated CO 2 [2,3,45] and influence different feeding guilds of herbivores in different ways [3,7]. Leaf-chewing herbivores generally perform worse and phloem-feeders have been shown to be less affected by rising CO 2 concentrations [3,46].…”

Fungal symbiont effects on dune plant diversity depend on precipitation

“…; Ryan et al . ; but see Emery & Rudgers ). Ultimately, benefits provided by microbial mutualists may ameliorate the negative, direct effects of climate change on plants (Singer, Travis & Johst ).…”

“…For example, while epichloid endophytes can confer drought tolerance to plants (Malinowski & Belesky 2000), possibly improving plant performance in warmer, drier climates, little work has directly tested fungal endophyte benefits in the context of future climate manipulations (reviewed by Kivlin, Emery & Rudgers 2013). Thus far, studies have focused on agronomic systems (Newman et al 2003;Hunt et al 2005;Brosi et al 2011;Ryan et al 2014; but see . Ultimately, benefits provided by microbial mutualists may ameliorate the negative, direct effects of climate change on plants (Singer, Travis & Johst 2013).…”