The mycorrhizal condition of weakened Scots pine saplings grown on ploughed sites in northern Finland

Abstract

The mycorrhizal condition of nursery-grown containerized Scots pine (Pinussylvestris) saplings planted in clear-cut and ploughed sites in northern Finland was investigated. The saplings, 15 years old on average, were classified on the basis of shoot condition into injured and healthy-looking saplings on the ploughed sites and control saplings on the adjoining natural sites. Ploughing after clear-cutting resulted in reduced mycorrhiza formation, the average percent infection being below 20 for injured saplings and between 60 and 85 for the control saplings. Formation of the mantle and Hartig net was weak in the injured saplings and reduced in the healthy-looking saplings compared with the control saplings, where the mantle had a mean thickness of 31.3 μm and the Hartig net was fully developed. The number of short roots and the short root biomass were greatly reduced in the healthy-looking saplings compared with the control saplings. These results indicate that the practice of ploughing in the clear-cut areas of northern Finland had caused a marked reduction in the growth of the whole short root system and in the formation of mycorrhizae in both the injured and healthy-looking saplings. The poor formation of mycorrhizae is clearly linked to the reduced growth of shoots at these sites.