Distribution patterns of soil entomopathogenic and birch symbiotic ectomycorrhizal fungi across native woodland and degraded habitats in Iceland

Abstract

In Iceland, extensive afforestation programmes have been initiated, often involving the outplanting of nursery seedling stock on eroded land. In some areas high seedling mortality, to a large extent due to root damage caused by Otiorhynchus spp. larvae, has been reported. Even though recent studies have shown that inoculation with entomopathogenic and ectomycorrhizal fungi may reduce the effects of Otiorhynchus spp. on seedling mortality, information on the occurrence and distribution of these key fungal species in Icelandic soils is limited. The present study reports findings of a targeted survey on the occurrence and distribution of entomopathogenic fungi and birch (Betula pubescens) root symbiotic ectomycorrhizal fungi in Icelandic soils from key habitats representing birch woodland, heathland and degraded/eroded land. Entomopathogenic fungi were isolated from soil by baiting with Tenebrio molitor and Galleria mellonella larvae. Identification to species was achieved based on standard morphotyping of cultures that included conidiophores and conidia. Birch seedling root symbiotic ectomycorrhizal fungal distribution in eroded and birch woodland soil was determined following baiting with birch seedlings over 9 months and classification based on gross morphology. Significant lower frequency and diversity of both entomopathogenic and ectomycorrhizal fungi were detected in soil collected from eroded areas compared to soil from vegetated areas (birch and heathland). Three species of entomopathogenic fungi, Beauveria bassiana, Metarhizium anisopliae and Isaria farinosa were present in soil samples collected from the birch woodland and heathland sites. In contrast, no insect pathogenic fungi were found in soil collected from the eroded sites. B. bassiana and M. anisopliae were recorded for the first time in Iceland. The incidence of mycorrhizal root tips was higher on seedlings grown in soil from birch woodland than in soil from eroded land and a higher diversity of ectomycorrhizal morphotypes was found in birch soil. The importance of these findings is discussed in relation to afforestation in Iceland.

Á sumum nýskógræktarsvæðum hefur borið talsvert á afföllum á trjáplöntum, sem orsakast af rótarskemmdum af völdum ranabjöllulirfa. Nýlegar rannsóknir benda til þess að hægt sé að draga úr slíkum skemmdum með því að smita plöntur með svepprót og skordýrasníkjusveppum. Hins vegar er lítið vitað um útbreiðslu slíkra sveppa í íslenskum vistkerfum. Því var útbreiðsla svepprótarsveppa á birki (Betula pubescens) og skordýrasníkjusveppa könnuð í þremur mismunandi vistkerfum; birkiskógum, lyngmóum og á rofnum svæðum. Lirfur tegundanna Tenebrio molitor og Galleria mellonella voru notaðar sem beita til að veiða skordýrasníkjusveppi úr jarðvegi. Sveppirnir voru síðan greindir til tegunda. Tegundagreining byggði á stöðluðum aðferðum við mat á útlitsgerð sveppagróa. Ungar birkiplöntur voru notaðar til að veiða svepprótarsveppi úr jarðvegi birkiskóga og jarðvegi af rofnum svæðum og sveppirnir flokkaðir gróflega eftir útlitsgerð. Tíðni og fjölbreytni sveppa var minni í jarðvegi af rofnum svæðum en af grónum svæðum (birkiskógur og lyngmói). Þrjár tegundir skordýrasníkjusveppa (Beauveria bassiana, Metarhizium anisopliae og Isaria farinosa) fundust í birki- og lyngvistkerfum en engir sníkjusveppir fundust í jarðvegi af rofnum svæðum. Tvær þessara tegunda, B. Bassiana og M. anisopliae höfðu ekki áður fundist hér á landi. Tíðni og fjölbreytni svepprótarsveppa var hærri á birkiplöntum sem ræktaðar voru í jarðvegi af birkisvæðum en þeim sem ræktaðar voru í jarðvegi frá rofnum svæðum. Mikilvægi þessara rannsókna í tengslum við nýskógrækt á Íslandi er rætt.