Spatial patterns of soil pathogens in declining Mediterranean forests: implications for tree species regeneration

Abstract

Summary• Soil-borne pathogens are a key component of the belowground community because of the significance of their ecological and socio-economic impacts. However, very little is known about the complexity of their distribution patterns in natural systems. Here, we explored the patterns, causes and ecological consequences of spatial variability in pathogen abundance in Mediterranean forests affected by oak decline.• We used spatially explicit neighborhood models to predict the abundance of soil-borne pathogen species (Phytophthora cinnamomi, Pythium spiculum and Pythium spp.) as a function of local abiotic conditions (soil texture) and the characteristics of the tree and shrub neighborhoods (species composition, size and health status). The implications of pathogen abundance for tree seedling performance were explored by conducting a sowing experiment in the same locations in which pathogen abundance was quantified.• Pathogen abundance in the forest soil was not randomly distributed, but exhibited spatially predictable patterns influenced by both abiotic and, particularly, biotic factors (tree and shrub species). Pathogen abundance reduced seedling emergence and survival, but not in all sites or tree species.• Our findings suggest that heterogeneous spatial patterns of pathogen abundance at fine spatial scale can be important for the dynamics and restoration of declining Mediterranean forests.

Impact of tree decline on spatial patterns of seedling-mycorrhiza interactions: Implications for regeneration dynamics in Mediterranean forests

“…We found that in woodland sites an important fraction of Q. suber seedlings did not show any ECM colonization (25% of the seedlings) or had low colonization values (37% of the seedlings had <20% of root tips colonized). Therefore, in these sites a higher seedling investment in ECM associations in response to tree decline could be justified in terms of an expected gain in performance, particularly taking into account that seedlings established in defoliated and dead neighborhoods are severely impaired due to stressful microclimatic conditions (Ibáñez et al, 2015) and high soil-borne pathogen loads (Gómez-Aparicio et al, 2012). This result also agrees with the ''intermediate host-plant stress hypothesis'' (Swaty et al, 2004), which postulates that stress can promote the establishment of mycorrhizal associations, at least until a certain threshold at which hosts can no longer support the C costs of the association.…”

Analyses between Reproductive Behavior, Genetic Diversity and Pythium Responsiveness in Zingiber spp. Reveal an Adaptive Significance for Hemiclonality

“…The fungal and oomycete pathogens are predicted to account a greater share of the disease catastrophes caused by ecological degradations (Giraud et al, 2010; Fisher et al, 2012). Upsurges of epidemics caused by soil microbiota (Klironomos, 2002), particularly the species of the oomycete necrotroph Pythium may critically affect the demography and diversity of an ecosystem (Gómez-Aparicio et al, 2012). Thus, the ongoing habitat fragmentation and climate change may trigger a drastic shift in the reproductive strategy, host resistance and demography in natural populations in the near future.…”

Virulence of oomycete pathogens from Phragmites australis‐invaded and noninvaded soils to seedlings of wetland plant species

“…From the few studies that have focused on pathogen populations, it is becoming clear that species within the oomycete genus Pythium can be significant regulators of native plant communities (Mills and Bever 1998; Packer and Clay 2000, 2003, 2004; Augspurger and Wilkinson 2007; Gómez-Aparicio et al. 2012) and, at the same time, facilitate invasiveness of a number of plant species (Reinhart et al. 2005, 2010a,b, 2011; Reinhart and Clay 2009; Butof and Bruelheie 2011).…”