Resumen de Effects of forest management, tree growth and climate on fungal communities
Fungi are vital to both human well-being and forest ecosystem functioning due to the ecosystem services delivered by them: provisioning (e.g., edible mushrooms), regulating (e.g., carbon sequestration), supporting (e.g., soil formation) and cultural services (e.g., leisure). To provide further insights into fungi-soil-plant interactions in forest ecosystems, it is still necessary to understand the links between the dynamics of above- and below-ground fungal components together with stand dynamics under anthropogenic disturbances. The main objective of this thesis was to understand, describe and quantify the coupled effects of forest thinning, tree growth and climate on fungal biomass, productivity and community composition.
The doctoral thesis was mainly conducted in a long-term experimental set-up of 28 forest plots, located in the Natural Park of Poblet (Catalonia, Spain), which where thinned with different intensities in 2009. These plots were located in 52 – 57-year-old Pinus pinaster Ait. planted stands covering different sites and stand characteristics (e.g., slope, basal area). From 2008 to 2019, we collected sporocarps in each plot on a weekly basis from September to December, and extracted, in December 2014, wood cores from 10-15 dominant trees belonged to each plot. This fungal and dendrochronological information aimed to describe the relationships between mushroom production and forest growth. A similar methodology was conducted in different European regions and forest ecosystems to inspect such fungi-tree relations under other climatic conditions and vegetation composition. Additionally, soil samples (i.e., eight soil cores per plot) were collected in the P. pinaster stands, over 5 years. These soil samples were analysed by molecular techniques such as high-throughput DNA sequencing (PacBio RS II, Illumina MiSeq), and biochemical techniques such as ergosterol extraction. The belowground data obtained by the latter techniques together with the sporocarp data was used to inspect above- and below-ground fungal community dynamics under the effects of thinning intensity.
The results showed that the latewood intra-annual density fluctuations frequency was the best predictor of ectomycorrhizal (ECM) mushroom yield, i.e., better than early- or latewood width (EW and LW, respectively). The analysis also revealed that the precipitation of late summer and early autumn as well as forest thinning were mediating the relationship between tree growth and ECM mushroom production. Unlike in the boreal and temperate regions, this interaction between ECM fungi and the growth of host trees was more significant in Mediterranean regions, with positive correlations particularly between LW growth and mycorrhizal mushroom productivity. Thinning also showed in the Mediterranean plots a prolonged negative effect belowground, both inter- and intra-annually, on total fungal biomass and on the biomass of ECM fungi, but not on saprotrophic fungi. Moreover, belowground fungal biomass of total and ECM fungi were negatively correlated with total and ECM mushroom yields, respectively. Differences between the above- and below-ground biomass increased with higher thinning intensities. Finally, the total fungal sporocarp community composition, unlike the sporocarp diversity (i.e., richness, evenness), showed short-term (< 2 years) changes mainly under heavy and light thinning intensities compared to unthinned stands. The unexpected compositional change caused by light thinning intensities has been exclusively related to particular commercial ECM fungi (Lactarius group deliciosus). Climatic factors, mostly the mean temperature of September and October, modulated the compositional response to thinning.
Based on these results, it can be concluded that: (i) only under more water-limited conditions, both the tree growth (mostly LW) and the mushroom productivity (mainly ECM) are more sensitive to precipitation events, resulting in higher synchrony between both processes; (ii) models may be used to reconstruct mushroom production along historical periods based on dendrochronological information, but also to predict future mushroom yields based on climate-sensitive tree and stand growth predictions; (iii) forest thinning may cause potential short-term shifts in resource allocation of fungi from below- to above-ground structures, i.e., prioritizing increasing reproduction rather than colonizing the surrounding soil; and (iv) forest thinning practices with a careful removal of trees does not compromise the sporocarp diversity, but lead to short-term successional changes in fungal assemblages.
