Use of commercial mycorrhizal fungi in stress-free growing conditions of potted olive cuttings

Biofertilizers of mycorrhizal fungi have been mainly tested in nutrient-limited soils or harsh environmental conditions, which have helped to highlight their beneficial role in plant growth. However, their benefits in stress-free growing conditions have not yet been properly proven. In this work, a commercial mycorrhizal fungi, composed of 18 ecto and endomycorrhizal fungi, was tested in a pot experiment with young olive cuttings, under an experimental apparatus allowing the evaluation of dry matter yield and plant nutritional status after one and two years of growth. The results highlighted the role of the mycorrhiza in increasing P bioavailability, either evaluated by soil P labile fraction or through tissue P concentration. The role of mycorrhiza in increasing soil organic C was also relevant (7% higher than the control). Mycorrhiza had little effect on the uptake of other nutrients and on the alleviation of excessive levels of metals, in particular Fe, in the shoots. Instead, olive showed its own exclusion mechanisms, registering root Fe levels 50 times higher than in shoots. Mycorrhiza did not improve plant growth compared to the other fertilized treatments. The increase in plant dry matter observed in the mycorrhiza treatment in comparison to the control was probably due to the initial content of the commercial product of N, P and K (3% N, 3% P2O5 and 3% K2O). Under the conditions of this experiment, the farmer would not benefit from the use of this mycorrhizal fungi, but it nevertheless proved its value for agriculture, suggesting that commercial products should be targeted more towards specific purposes, than for generalized uses.This research was funded by the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UIDB/00690/2020) and CITAB (UIDB/04033/2020). The research was integrated in the activities of the Operational Group “Novas práticas em olivais de sequeiro: estratégias de mitigação e adaptação às alterações climáticas”, funded by PT2020 and EAFRD (European Agricultural Fund for Rural Development).