Phenolics of the understory shrub Cotinus coggygria influence Mediterranean oak forests diversity and dynamics

Abstract

Chemical interactions in forested ecosystems play a role in driving biodiversity and ecosystem dynamics. Plant phenolics released by leaching can influence surrounding plants and soil organisms such as bacteria, fungi or arthropods. However, our knowledge about such chemically-mediated biotic interactions in Mediterranean oak forests is still limited, in particular whether they play a role in the limited forest regeneration. In this study, we analyzed how phenolics of Cotinus coggygria, a dominant shrub of Mediterranean downy oak (Quercus pubescens) forests, influence understory herbaceous plant species, downy oak regeneration and soil organisms in order to obtain a more integrative view of possible direct and indirect interactions triggered by this shrub species. We performed a series of experiments testing the effect of aqueous extracts of C. coggygria, mimicking natural leachates, on these organisms. Cotinus coggygria contained a high quantity of phenolics in green and senescent leaves but much less in leaf litter. Extracts from C. coggygria leaves stimulated bacterial communities, exhibited few effects on both saprophytic and symbiotic fungi, and negatively affected Collembola. Herbaceous species growth was particularly impaired by extracts from green and senescent leaves, although these effects were alleviated in the presence of soil microorganisms. In both greenhouse and field experiments, C. coggygria affected early oak seedling establishment in particular through a reduced root growth, but exhibited no effect on later seedling and sapling growth. We discussed the implication of these results for the balance between competition and facilitation in oak forests and concluded that C. coggygria has the potential to strongly alter biotic interactions, understory plant diversity and oak forest dynamics.

Allelopathic effects of volatile organic compounds released from Pinus halepensis needles and roots

“…Regarding seedling growth, root length (mm) was measured for each individual 5 days after germination (Fernandez et al, , ; Hashoum et al, ). We calculated a relative allelopathic effect (RAE) index to determine the intensity of the allelopathic effect on seed germination and seedling growth (Gavinet et al, ; Hashoum et al, ). The RAE index was calculated as (O − C)/C × 100, where O is the value of the plant trait (germination or growth) when a target species is exposed to allelopathic compounds and C the mean value of that trait under control conditions.…”

“…Seed germination percentage was calculated as [(number of germinated seeds)/(number of sown seeds)] × 100 (Bousquet-Mélou et al, 2005;Gavinet et al, 2019;Santonja, Le Rouzic, et al, 2018). Regarding seedling growth, root length (mm) was measured for each individual 5 days after germination (Fernandez et al, 2006(Fernandez et al, , 2013Hashoum et al, 2017).…”

“…Regarding seedling growth, root length (mm) was measured for each individual 5 days after germination (Fernandez et al, 2006(Fernandez et al, , 2013Hashoum et al, 2017). We calculated a relative allelopathic effect (RAE) index to determine the intensity of the allelopathic effect on seed germination and seedling growth (Gavinet et al, 2019;Hashoum et al, 2017). The…”

“…A strong attention has been paid during the last decades to allelopathy, demonstrating the key implication of plantplant chemical interaction as a driver of plant community structure and ecosystem functioning (Inderjit, Wardle, Karban, & Callaway, 2011;Meiners, Kong, Ladwig, Pisula, & Lang, 2012;Wardle, Nilsson, Gallet, & Zackrisson, 1998). Seed germination and seedling performance are the main life stages usually affected by allelochemicals, and frequent negative allelopathic effects are inhibition of seed germination (Fernandez et al, 2013;Herranz, Ferrandis, Copete, Duro, & Zalacain, 2006), delay of seed germination (Fernandez et al, 2013;Hashoum et al, 2017), and inhibition of seedling growth (Gavinet et al, 2019;Santonja, Le Rouzic, & Thiebaut, 2018) by altering physiological processes (e.g., photosynthesis, nutrient uptake, cell division, or elongation; Inderjit & Duke, 2003). However, the persistence, availability, and biological impacts of the allelochemicals could be modulated by soil microbial communities (Cipollini, Rigsby, & Barto, 2012;Inderjit, 2005).…”

Autotoxicity Hinders the Natural Regeneration of Cinnamomum migao H. W. Li in Southwest China

“…Autotoxicity is regarded as a negative effect on plant growth, and secondary metabolites produced by maternal plants could hinder the growth of their seedlings [12]. Phenolics and terpenoids released by woody plants play a key role in these interactions by influencing the structure and diversity of plant and soil communities [13][14][15]. Soil microorganisms can be directly affected by plant phenolics [16], but they can also use these phytochemicals as carbon sources, thereby modifying the chemical plant-plant interactions [17].…”