Friday, March 1, 2013

Plant Fungus Recycles Insects

The common soil fungus Metarhizium may just be a plant's new best friend.  Imagine a naturally occurring common fungus that not only kills insects but literally feeds their nitrogen to the plant.  An article published in the journal Science describes how this was found and proven.

Bug infected with Metarhizium- K. Knight.
Metarhizium fungus is found around the world in a mutualistic association with plants, meaning that they both benefit from the relationship.  This is somewhat like a marriage, although my editor/wife is still trying identify what her benefits are.  And like a marriage, the fungus actually lives with the plant in its roots.  Like when I spray the wasps living by the front door (at last a benefit!), the fungus kills some of the plant's insect pathogens.
Metarhizium spores-

Normally plants absorb nitrogen from the soil which is produced by nitrogen fixing bacteria- think clover and legumes.  Nitrogen is also produced by bacteria breaking down decaying plant material and in some cases by fire.  A few plants such as the Venus flytrap and pitcher plants have even been able to catch their own nitrogen by collecting insects.

In the study reported in scientists inserted a nitrogen marker isotope into waxmoths Galleria mellonella.  They had planted "Phaseolus vulgaris, the quick-growing haricot bean, and Panicum virgatum, a slower-growing perennial bunchgrass" in sterilized soil.  Then they introduced waxmoth larvae infected with either Metarhizium fungus or Aspergillus flavus which is a non endophytic insect fungus.  Plants without any larvae served as controls.

They found that the plants with the Metarhizium fungus infected waxmoth larvae had higher levels of the nitrogen isotope in their leaves than those sterile or Aspergillis infected larvae.  The plants are essentially being fed the digested and processed nitrogen isotope by the Metarhizium fungus.  Now that's marriage with benefits.

Science journal abstract.

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