Drought in the forest breaks plant–fungi interactions

Abstract

Drought in the forest is not only a prolonged state of water shortage, but also an occasion where interactions between plants and fungi are affected. Water efficiency accelerates a range of pathologies in interactions between organisms, influencing the ecosystems and their interacting biological components. This study focuses on the role of mycorrhizal and endophyte fungi in alleviating the effects of soil water shortage, and on the impact of their altered activity during drought on the health of trees. The issues presented here show the fundamental role of the mycorrhizal mycelium and the mechanism of water transport to the plant in the course of other phenomena (withering, pathogenesis, endophytes biology) that occur in trees under influence of drought, with particular attention on managed coniferous stands. Conclusions resulting from published information on this topic emphasize the negative impact of soil moisture deficiency on the ectomycorrhizal fungi functioning and, in contrast, on the promotion of the growth of some endophytes, pathogens and hemi-parasitic mistletoes (Viscum spp.).

Plant–Fungi Interactions: Where It Goes?

“…Moreover, they have recognized that mycorrhizal interactions help Aleppo pine to overcome water stress. In contrast, Boczoń et al [ 150 ] further highlighted that the water shortage can shift the endophytic phase of Cenangium ferruginosum to phytopathogenic and saprotrophic lifestyles. This stressed environment activates C. ferruginosum and causes pine dieback disease as the plant reduces its resistance mechanism against the pathogen.…”

“…Nevertheless, it is enthralling to know how mycorrhizal fungi take up the necessary water. According to Boczoń et al [ 150 ] this could have happened because of the ability of mycorrhizal hyphae to explore small water pores in the soil, where plant roots are not accessible, thus improving plant water status under low water availability. Added to this explanation, Bennett and Classen [ 132 ] reported that mycorrhiza support the plant via improved apoplastic water flow facilitated water uptake through fungal water channels, increased stomatal conductance in host plants, and modified host gene expression of drought-related genes encoding plant aquaporins.…”

Tree growth is better explained by absorptive fine root traits than by transport fine root traits

“…Another possible explanation could be a higher SRL for EM species (Figures 1 and S5), which again highlights efficiently exploring a substantial soil volume, resulting in greater resource uptake (Comas et al, 2012; Ostonen et al, 2007). In the same direction, mycelium of the EM species efficiently penetrates the capillary pores and explores water-depleted zones around the root, resulting in the utilization of soil water reservoirs (Boczoń et al, 2021).…”

Soil fungal communities contribute to the positive diversity–productivity relationship of tree communities under contrasting water availability

“…Similarly, we expected that the relationship between fungal diversity and productivity would strengthen under water stress. Additionally, mycorrhizal fungal species vary in their ability to increase tree drought tolerance and facilitate the transport of water between trees (Boczoń et al, 2021; Prieto et al, 2016); therefore, we expected the relationship between mycorrhizal diversity and productivity to be stronger under low water and that their role in shaping the diversity–productivity relationship would become more pronounced because of their role in plant–water relations (Lehto & Zwiazek, 2011). In contrast, we expected that the influence of plant pathogenic fungi would be greatest under high water availability, where pathogen impacts are expected to be strongest (Velásquez et al, 2018) (Figure 1).…”