Arbuscular mycorrhizal fungi counteract the Janzen‐Connell effect of soil pathogens

Abstract

Soilborne pathogens can contribute to diversity maintenance in tree communities through the Janzen-Connell effect, whereby the pathogenic reduction of seedling performance attenuates with distance from conspecifics. By contrast, arbuscular mycorrhizal fungi (AMF) have been reported to promote seedling performance; however, it is unknown whether this is also distance dependent. Here, we investigate the distance dependence of seedling performance in the presence of both pathogens and AMF. In a subtropical forest in south China, we conducted a four-year field census of four species with relatively large phylogenetic distances and found no distance-dependent mortality for newly germinated seedlings. By experimentally separating the effects of AMF and pathogens on seedling performance of six subtropical tree species in a shade house, we found that soil pathogens significantly inhibited seedling survival and growth while AMF largely promoted seedling growth, and these effects were host specific and declined with increasing conspecific distance. Together, our field and experimental results suggest that AMF can neutralize the negative effect of pathogens and that the Janzen-Connell effect may play a less prominent role in explaining diversity of nondominant tree species than previously thought.

Belowground top-down and aboveground bottom-up effects structure multitrophic community relationships in a biodiverse forest

“…Although plant communities can strongly shape the habitat conditions for taxa at higher trophic levels 33, 36 , feedback effects of both plant antagonists and mutualists might result in an overall strong top-down control of plant community composition 27, 29 . Our findings are in line with observations in other species-rich forests that have indicated strong effects of soil fungal pathogens, bacteria, and mycorrhizae on plant community composition 28–30 . An important role of top-down effects is indicated by strong links between microorganisms and plants in the top-down model that are not found or less evident in the bottom-up model, such as for Alphaproteobacteria and Bacteroidetes.…”

How belowground interactions contribute to the coexistence of mycorrhizal and non-mycorrhizal species in severely phosphorus-impoverished hyperdiverse ecosystems

“…However, increasing evidence over the last few decades has shown that mycorrhizas can also offer their hosts defence against pathogens (Marx 1972;Maherali and Klironomos 2007;Sikes et al 2009;Wehner et al 2010;Albornoz et al 2016b). They can provide physical barriers around roots against soil-borne pathogens (Marx 1972), produce antimicrobial compounds (Duchesne et al 1988a, b), or neutralise the negative effects of pathogens for seedling survival and growth (Liang et al 2015). In this section, we summarise the current evidence of pathogen defence of both ECM and AM fungi, and discuss their implications for plant-plant interactions in hyperdiverse ecosystems.…”

Arbuscular mycorrhizal fungal communities in an iron mining area and its surroundings: Inoculum potential, density, and diversity of spores related to soil properties

“…Revegetation can provide the biodiversity necessary for recovery of areas impacted by mining. In this context, arbuscular mycorrhizal fungi (AMFGlomeromycota phylum) represent important components of the soil biota that promote diverse services in the ecosystem (Pellegrino;Bedini, 2014), such as better plant nutrition and growth (Thirkell;Cameron;Hodge, 2016), soil aggregation (Leifheit;Verbruggen;Rillig, 2015) and an increase in plant tolerance to biotic stresses (e.g., pathogens) (Liang et al, 2015) and abiotic stresses (e.g., potentially toxic elements in the soil) (Cabral et al, 2015), and assume an important role in the rehabilitation process of areas affected by mining.…”