Transfer of recent photosynthate into mycorrhizal mycelium of an upland grassland: short-term respiratory losses and accumulation of ¹⁴C

The movement of carbon from plants into their natural communities of arbuscular-mycorrhizal (AM) fungi was investigated. Mesh-bound cores, which allowed in-growth of AM mycelium to be controlled but excluded roots, were inserted into turf monoliths removed from an upland grassland and were exposed to (CO2)-C-14. Flux of C-14-labelled carbon from plants to hyphae of AM fungi for 70 h post-labelling was measured by (a) trapping CO2 released from soil cores containing AM hyphae linked to the plants compared to cores from which AM hyphal connections to the plant roots had been severed, and (b) quantification of the total amount of C-14 in the cores. Release of (CO2)-C-14 from the cores colonised by active AM mycelium was highest for 0-28 h from the onset of labelling and declined rapidly thereafter. The amount of C-14 allocated into mycorrhizal mycelium 0-70 h after labelling accounted for 3.4% of the C-14 initially fixed by the plants. The results confirm the rapidity of photosynthate allocation to AM mycelium and demonstrate the importance of the short-term dynamics of C fluxes in undisturbed grasslands. (C) 2002 Elsevier Science Ltd. All rights reserved.