Questions How do mat thickness, physical structure and allelopathic properties of terricolous mat‐forming lichens affect recruitment of vascular plants in dwarf‐shrub and lichen heath vegetation? Location The mountains of Dovrefjell, central Norway. Methods In autumn, seeds of ten vascular plant species were collected and sown in a common garden experiment with mats of six lichen species and bare soil controls as experimental treatments. We recorded growing season soil temperature and moisture, and seedling recruitment and growth after one year. The effect of lichen secondary compounds on germination was tested in a growth chamber experiment and compared to the lichen–plant interactions detected under field conditions. Results The lichen mats buffered extreme soil temperatures and soil drying in dry weather, with soils below the thickest mats (Cladonia stellaris and C. rangiferina) experiencing the lowest temperature fluctuations. Seedling recruitment and seedling growth in the field and seed germination in the lab were species‐specific. Seedling recruitment rates were overall higher within lichen mats than on bare soil, but the c. 6.5‐cm‐thick mats of C. stellaris reduced recruitment of many species. The lab experiment suggested no overall strong effect of lichen allelopathy on seed germination, and effects on seed germination were only moderately correlated with the lichen–plant interactions observed for seedling recruitment in the field. Conclusions In harsh environments like alpine dwarf‐shrub and lichen heaths, the presence of lichens and the resulting amelioration of the microclimate seem more important for vascular plant recruitment than are allelopathic effects often reported in lab experiments. We might therefore expect most terricolous lichens, depending on the plant species in focus, to facilitate rather than hamper the early stages of plant recruitment into lichen‐dominated arctic‐alpine heath vegetation.
Dollar spot, caused by at least five Clarireedia species (formerly Sclerotinia homoeocarpa F. T. Benn.), is one of the economically most important turfgrass diseases worldwide. The disease was detected for the first time in Scandinavia in 2013. There is no available information from Scandinavian variety trials on resistance to dollar spot in turfgrass species and cultivars (http://www.scanturf.org/). Our in vitro screening (in glass vials) of nine turfgrass species comprising a total of 20 cultivars showed that on average for ten Clarireedia isolates of different origin, the ranking for dollar spot resistance in turfgrass species commonly found on Scandinavian golf courses was as follows: perennial ryegrass = slender creeping red fescue > strong creeping red fescue > Kentucky bluegrass = velvet bentgrass > colonial bentgrass = Chewings fescue ≥ creeping bentgrass = annual bluegrass. Significant differences in aggressiveness among Clarireedia isolates of different origin were found in all turfgrass species except annual bluegrass (cv. Two Putt). The U.S. C. jacksonii isolate MB-01 and Canadian isolate SH44 were more aggressive than C. jacksonii isolates from Denmark and Sweden (14.10.DK, 14.15.SE, and 14.16.SE) in velvet bentgrass and creeping bentgrass. The Swedish isolate 14.112.SE was generally more aggressive than 14.12.NO despite the fact that they most likely belong to the same Clarireedia sp. The U.S. C. monteithiana isolate RB-19 had similar aggressiveness as the Scandinavian C. jacksonii isolates, but was less aggressive than two U.S. C. jacksonii isolates MB-01 and SH44. Thus, aggressiveness of Clarireedia isolates was more impacted by their geographic origin and less by species of the isolate and/or the host turfgrass species.
Seed mixtures with a nurse grass that germinates quickly at low soil temperatures can be an option for faster establishment of Agrostis stolonifera (AS) putting greens after winter damage. From 2015 to 2018 Poa trivialis (PT) 'Dark Horse' and Lolium perenne (LP) 'Chardin' were evaluated as nurse grasses in comparison with pure AS 'Independence' at two experimental sites in each of the two major climatic zones of the Nordic countries. Poa annua (PA) 'Two-Putt' was also included as a nurse grass in the northern zone. As an overall trend, establishment was faster with AS+LP than with AS+PT and AS+PA, which both had faster establishment than pure AS. In the northern zone, AS+PT produced better turf quality than pure AS in the seeding year and year after and tended to be superior even on average for the entire trial period (mean value 6.0 versus 5.8 for pure AS, 5.3 for AS+LP, and 4.6 for AS+PA; scale 1-9 where 9 is the highest quality). Within the same zone, AS+PT also suffered less overall winter damage than the other combinations and was less infected with microdochium patch than pure AS. In the southern zone, PT and especially LP were far more persistent than in the northern zone and compromised turfgrass quality compared with pure AS. In conclusion, we recommend PT as a nurse grass for faster establishment of AS putting in the northern zone, but not in the southern zone where AS should rather be seeded in a pure stand.
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