The flow of carbon through soil is ten times greater than theamount of carbon moved around by the burning of fossil fuel but untilnow how this happens was at best poorly understood. Soil was almostliterally a black box to scientists interested in carbon. Nowresearchers at the University of Warwick have been able to shed lightin that black box by getting a particular class of insects to exposethe key underground carbon traffic system - by eating it.
TheUniversity of Warwick team worked with researchers from Aberdeen,Lancaster and Sheffield, to try and establish if plant associated fungi- arbulscar mycorrhizal (AM) fungi - found on the roots of 80% of allland plants had any role in the movement of atmospheric carbon to soil(fixed by plants in the form of CO2). AM fungi produce filaments thatspread widely throughout the soil (sometimes referred to as themycorrhizosphere) and they are known to be important for effectiveuptake by plants of water and phosphates but they were not known toplay any role in the movement of carbon through the soil.
Theresearchers developed novel soil cores that were engineered withopenings covered by nylon mesh with tiny pores just big enough to allowAM mycelia to grow into them but too small for any insects or othermicro-fauna (including Collembola, soil mites) to get into the cores.The cores were then filled with soil which was frozen -80oC to kill anyother insects/microfauna and inserted into experimental grassland toenable colonization by AM fungi from the surrounding plants. Twentymites from the order Collembola, which would view the AM mycelia asfood stuff, were introduced to half of the cores. After another fourweeks the grassland was exposed to a particular form of carbon dioxide(a stable isotope of carbon, 13C) for 7 hours, a technique called pulselabelling. Concentration of 13C in cores was then analysed. The soilcores which were exposed to the mites were found to have 32% less 13Cthan the control cores. This showed that Collembola's consumption ofthe arbulscar mycorrhizal mycelia had disrupted a key pathwaytransporting carbon from plants to soil.
As a final check theresearchers examined both the cores with and without Collembola for aparticular phospholipid fatty acid (PLFA) that is characteristic for AMmycelia. They found that this particular PLFA contained significantamounts of 13C in cores not exposed to Collembola. However those soilcores that were exposed to collembola which fed on the mycorrhizalmycelia did not have 13C enriched PFLAs..
This researchestablishes that arbuscular mycorrhizal mycelia provide a major highwayin terms of transporting carbon from plants to soil. This newunderstanding of how both mycorrhizal mycelia and the insect populationof soil impact on the transport of carbon will assist researcherstrying to understand what preserves a healthy soil and providesrecycled carbon for supporting below ground biodiversity. It will alsoopen up a new understanding of the food-webs and nutrient flow in soilwhich is fundamental to sustainable agriculture.
Note foreditors: The research paper Soil Invertebrates Disrupt Carbon FlowThrough Fungal Neworks is in Science vol 309, 2005, p. 1047
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