No allelopathic effect of the dominant forest‐floor lichen Cladonia stellaris on pine seedlings

Abstract

Summary 1.The lichen Cladonia stellaris forms dense mats and dominates the forest-floor vegetation in latesuccessional oligotrophic boreal forests. This lichen is rich in polyphenolic secondary compounds, and through allelochemical effects of these compounds the dense mat formed by C . stellaris is assumed to have negative effect on forest regeneration and soil microbial functioning. 2. We examined the effect of C . stellaris and its secondary metabolite usnic acid on nutrient uptake and growth of pine ( Pinus sylvestris ) seedlings in symbiosis with the ectomycorrhizal fungus Suillus variegatus and in non-symbiotic condition. 3. Contrary to our expectations, usnic acid had no effect on nitrogen uptake and growth in pine seedlings. The addition of lichen fragments into the growth substrate significantly increased biomass accumulation in mycorrhizal pine seedlings and needle nitrogen acquisition in nonmycorrhizal seedlings. 4. These results suggest that lichen mats do not have direct allelopathic effects on pine seedling nitrogen acquisition or growth.

Lichen-plant interactions

“…It has been recognized for a long time that nutrient dissolution from the plant substrate provides mineral nutrition to epiphytic lichen communities (Des Abbayes 1951;Nash 2008), but the inhibition of lichens by bark compounds has also recently been claimed (Koopmann et al 2007). Several in vitro studies suggest that competitive relationships between terricolous lichens and plants depend on allelopathic interferences (Lawrey 1984(Lawrey , 1986(Lawrey , 2009), but recent ecological investigations do not support this finding (Kyto¨viita and Stark 2009). …”

The contradictory role of understory vegetation on the success of Scots pine regeneration

“…Brown and Mikola (1974) showed that lichens have negative allelopathic effects on mycorrhizas and tree seedlings. In contrast, recent studies have revealed that the effects of lichens are either neutral or even beneficial (Stejlen et al 1995;Kytöviita and Stark 2009). However, the interplay between reindeer grazing and vegetation might create complex interactions that in turn have various effects on the establishment, initial growth, and survival of pine seedlings (Väre et al 1996;Jonsson 1999).…”

Understory vegetation-environment relationships of lichen-rich forests in north-central British Columbia.

“…This is because the concentrations of largely hydrophobic allelochemicals leaching into mineral soils from lichen mats rarely reach toxic (or even detectable) levels (Kershaw 1985, Stark et al 2007, Kytoviita and Stark 2009. Studies have shown the removal of lichen mats to be more detrimental to tree growth than their presence (Bonan and Shugart 1989, Lawrey 1995, Crittenden 2000.…”

“…Kershaw (1985) explored many of the microclimatic influences of lichen mats, and concluded that lichen mats generally decreased temperature fluctuation and rates of evaporation at the soil surface, as compared to non-vegetated surfaces. This soil-climate buffering may favour the gradual development of moss or vascular plant components of the system, and has been suggested as the mechanism responsible for increased growth of mycorrhizae and their associated trees in boreal forests (Bonan 1990, Crittenden 2000, Stark et al 2007, Kytoviita and Stark 2009. Similarly, feathermosses act as a moisture-regulating buffer between the atmosphere and soil, and in doing so may facilitate the dominance of spruce canopies over pine in later stages of forest development in some systems.…”

“…Lichens are also known to produce a myriad of organic acid compounds, albeit mostly hydrophobic ones (Huneck 1999), which may have a similar effect. Although recent studies have shown that there is little evidence to support allelopathy as a mechanism as being functionally important in the field (Stark et al 2002, Stark et al 2007, Kytoviita and Stark 2009 It is has often been stated that feathermosses are more likely to reduce soil nutrient availability than increase it; potential mechanisms for this include mosses acting as a barrier to nutrient deposition (in crown leachate or rainfall), maintaining efficient internal recycling (Turetsky 2003), being able to quickly reabsorb nutrients lost to solution (Startsev and Leiffers 2006), having relatively slow decomposition of dead tissues Ehrenfeld 2005, Turetsky 2003), or by maintaining lower soil temperatures which inhibit microbial activity (Bonan 1990, Turetsky 2003). Yet, more recent research has shown that mosses, and feathermosses in particular, may actually increase nitrogen availability in ecosystems due to their association with nitrogen fixing cyanobacteria and their apparent utilization of nutrient enriched crown leachate solution (Turetsky 2003, Nilsson and Wardle 2005, Hart and Chen 2006, Houle et al 2006.…”