Johnson Scott N, Lopaticki Goran, Hartley Susan E
Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, New South Wales, Australia.
York Environmental Sustainability Institute, Department of Biology, University of York, York, United Kingdom.
PLoS One. 2014 Mar 20;9(3):e90251. doi: 10.1371/journal.pone.0090251. eCollection 2014.
Predicted increases in atmospheric carbon dioxide (CO2) concentrations often reduce nutritional quality for herbivores by increasing the C:N ratio of plant tissue. This frequently triggers compensatory feeding by aboveground herbivores, whereby they consume more shoot material in an attempt to meet their nutritional needs. Little, however, is known about how root herbivores respond to such changes. Grasslands are particularly vulnerable to root herbivores, which can collectively exceed the mass of mammals grazing aboveground. Here we provide novel evidence for compensatory feeding by a grass root herbivore, Sericesthis nigrolineata, under elevated atmospheric CO2 (600 µmol mol(-1)) on a C3 (Microlaena stipoides) but not a C4 (Cymbopogon refractus) grass species. At ambient CO2 (400 µmol mol(-1)) M. stipoides roots were 44% higher in nitrogen (N) and 7% lower in carbon (C) concentrations than C. refractus, with insects performing better on M. stipoides. Elevated CO2 decreased N and increased C:N in M. stipoides roots, but had no impact on C. refractus roots. Root-feeders displayed compensatory feeding on M. stipoides at elevated CO2, consuming 118% more tissue than at ambient atmospheric CO2. Despite this, root feeder biomass remained depressed by 24%. These results suggest that compensatory feeding under elevated atmospheric CO2 may make some grass species particularly vulnerable to attack, potentially leading to future shifts in the community composition of grasslands.
大气中二氧化碳（CO₂）浓度的预计升高通常会通过提高植物组织的碳氮比来降低食草动物的营养质量。这经常引发地上食草动物的补偿性取食，即它们会消耗更多的地上部分物质以满足其营养需求。然而，关于地下食草动物如何应对这种变化却知之甚少。草原尤其容易受到地下食草动物的影响，它们的总体质量可能超过地上放牧哺乳动物的质量。在这里，我们提供了新的证据，表明在大气CO₂浓度升高（600 μmol mol⁻¹）的情况下，一种禾本科地下食草动物——黑线金龟（Sericesthis nigrolineata）会对C₃ 禾本科植物（细叶米草，Microlaena stipoides）进行补偿性取食，但对C₄禾本科植物（曲序香茅，Cymbopogon refractus）则不会。在环境CO₂浓度（400 μmol mol⁻¹）下，细叶米草根系的氮（N）含量比曲序香茅高44%，碳（C）浓度低7%，昆虫在细叶米草上的表现更好。CO₂浓度升高降低了细叶米草根系中的氮含量，提高了碳氮比，但对曲序香茅根系没有影响。在CO₂浓度升高的情况下，地下取食者对细叶米草表现出补偿性取食，消耗的组织比在环境大气CO₂浓度下多118%。尽管如此，地下取食者的生物量仍下降了24%。这些结果表明，在大气CO₂浓度升高的情况下进行补偿性取食可能会使一些禾本科植物特别容易受到攻击，这可能会导致未来草原群落组成的变化。
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