Drought acclimation of beech seedlings depends largely on their rooting patterns and less on the fungal communities in soils

Aims: The composition of soil fungal communities is known to impact tree performance. However, fungal communities differ among soils with different precipitation histories and may change during drought. This study aimed to determine the influence of soil origin and associated climate adaptation of fungal communities on European beech seedlings’ drought responses. Methods: Seedlings were established from the same seed source and grown in three soils with different precipitation histories but similar water retention properties. One year after establishment, half of the seedlings were exposed to a two-month drought with predawn leaf water potentials of about –1.5 MPa, the other half remained well-watered (control). Before and during the drought, soil and root fungal community composition, root architecture, seedling growth, carbon allocation and leaf physiology were determined. Results: The drought effect on the fungal community composition was the lowest in dry region soils, suggesting a natural adaptation of the fungal communities to dry environments. Nevertheless, contrary to our expectations, the seedlings grown in dry region soils with respective adapted fungal communities were most affected by drought. This was evidenced by a lower predawn water potential, probably due to shorter root systems with higher root branching compared to those grown in moist region soils where a greater taproot length was observed. Conclusion: Beech seedlings´ drought responses depend largely on their different rooting patterns and less on the soil fungal communities that are adapted to long-term precipitation conditions. Yet, microbial effects cannot be excluded. Future research should focus more on the role of specific microbial species on plant root growth and drought responses.