| Plants can obtain soil resources via arbuscular mycorrhizal fungi (AM). Thus, one may expect beneficial effects of AM on growth, and on resistance to stress, pathogens and disturbance. However, the AM depends on the host to supply the assimilate required for its growth, maintenance and functioning. Therefore it is questionable whether colonisation by AM is always beneficial to the fitness of the host. In particular it is unclear (1) if the host plant has effective control over the AM, (2) if that control is a direct function of the resource needs of the host, (3) if resource acquisition via AM is always less costly than without AM, and (4) if AM can supply relevant amounts of water to the host.
The present project aimed at answering these questions through detailed analysis of the resource economy of mycorrhizal and non-mycorrhizal plants. To that end, we combined state-of-the-art methodology including (1) mesocosm-scale steady-state 13C/12C-CO2 labelling and gas exchange facilities and (2) 'split-soil' systems with different compartments which can be manipulated in terms of resource content and accessibility to roots and mycorrhizal hyphae.
The studies yielded detailed data on C, N, P and water fluxes between functionally distinct plant compartments, between host and AM, and between plant and environment. Effects of AM on plant growth were analysed on leaf growth zone physiology, morphological parameters and whole plant carbon balance. Effects of AM on water use efficiency were determined by gas exchange measurements and analysis of 13C discrimination.
The regulation of AM by the host was assessed by:
Part 1: comparison of cost/benefit relationships of resource acquisition of mycorrhizal and non-mycorrhizal plants in different stress and disturbance scenarios with perennial ryegrass
Part 2: measurement of N, P and water uptake through extraradicular hyphae in 'split-soil' systems in scenarios of water shortage with barley.
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