Plant–soil feedbacks in mixed pine-oak Mediterranean forests under drought conditions

Abstract

Background and aimsPine-oak mixed forests are characteristic of the Mediterranean landscape. Understanding which types of plant-soil feedbacks (PSFs) operate in these communities and how such PSFs could be altered by severe summer droughts is needed in the face of current climate change.MethodsWe conducted a fully reciprocal PSF experiment using eight Mediterranean pine and oak species. Seedlings were grown under controlled conditions in substrate containing sterilised soil and a small amount of soil collected under congeneric or heterogeneric mature trees. Half of the seedlings were subjected to a severe drought during the second growing season.ResultsDifferences in plant biomass and responses to drought were linked to fungal communities in the rhizosphere. Negative PSFs were detected amongst pines and oaks. Pine and oak seedlings grew better in heterogeneric soil than in congeneric soil. Fitness differences correlated with a higher relative abundance of growth-promoting ectomycorrhizal fungi (EMF) in heterogeneric soils. Under severe drought, no differences in seedling biomass, seedling survival or stomatal conductance were observed between seedlings growing in heterogeneric or congeneric soil.ConclusionSeedlings grew better in heterogeneric soils which suggests that Mediterranean pine-oak mixtures could be maintained by negative PSFs. Severe drought could decrease the strength of the negative PSFs, implying that tree diversity in Mediterranean forests could decline in a drier climate.

This research was part of the PADRINO and CLARA projects funded by the grants RTI2018-095711-B-I00 and PID2021-127328OB-I00 from the Spanish Ministry of Science and Innovation. DS was supported by the European Union's H2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 801586. MC was supported by the AGAUR FI fellowship 2021FI_B00223 from the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia and the European Social Fund. JO was partially supported by the 'Ramon y Cajal' fellowship RYC-2015-17459 from the Spanish Ministry of Science and Innovation.