Continuous measurement of stem-diameter growth response of Pinus pinea seedlings mycorrhizal with Rhizopogon roseolus and submitted to two water regimes

Linear variable differential transformer (LVDT) sensors were used to detect continuous diameter growth responses of Pinus pinea (stone pine) seedlings inoculated with the ectomycorrhizal fungus Rhizopogon roseolus. Colonised and non-colonised seedlings provided with sensors were submitted to differe nt water regimes in two consecutive experiments established in a controlled -temperature greenhouse module (cycle 1), and in an adjacent module without temperature control (cycle 2). Under regular irrigation, colonised seedlin gs showed significantly higher growth than non-colonised seedlings. Water-s tressed seedlings showed no benefit from inoculation in terms of growth. Al so, seedlings with a high colonisation level recovered more slowly from wat er stress than control seedlings. A significant positive relationship betwe en maximum daily shrinkage (amplitude of the daily stem contraction) and gl obal radiation was observed only in the first water-stress period in cycle 1 and in regularly irrigated seedlings in both cycles. However, no differen tial responses due to inoculation were observed. The mycorrhizal colonisati on of the seedlings at the end of the experiment was related with the initi al colonisation level. Mycorrhizal colonisation by R. roseolus in old roots was maintained at significantly higher levels in seedlings which had an in itial colonisation level >50% than in seedlings with <50% initial colonisat ion. Also, more newly formed roots became colonised in seedlings which had an initial colonisation level >50% than in seedlings with an initial coloni sation <50%, which had almost no new root colonisation. From the results ob tained, it can be concluded that LVDT sensors can be used to detect a diffe rential response of plants according to water supply, mycorrhizal status an d, in some cases, to their colonisation level. The results are discussed in relation to the predictive possibilities of the method for the selection o f efficient mycorrhizal fungi for the promotion of plant growth.