Demography of mycorrhizal short roots in a Norway spruce stand in SW Sweden.

DAMM, EVA¹, HOOSHANG MAJDI² & JAN-ERIK NYLUND¹

¹ Department of Forest Mycology & Pathology, SLU, Box 7026, SE-750 07 Uppsala, SWEDEN. ²Department of Ecology and Environmental Research, SLU, Box 70 72, SE-750 07 Uppsala, SWEDEN.

Short root dynamics were studied at a Norway spruce (Picea abies (L.) Korst.) stand in SW Sweden from 1991 to 1995 using minirhizotron technique. Root intersections were recorded with a video camera once a month during the vegetation period. The following parameters were studied: longevity of mycorrhizal roots at 0-20, 20-40 and 40-85 cm depth, occurrence of unbranched mycorrhizae (1), main axis of branched mycorrhizae (2), branches of the same (3), and relationship between occurrence of long roots and mycorrhizal short roots.
A marked ingrowth of long roots into the field of view was noted in 1991 - 93, and a corresponding emergence of short roots in 92 - 93. In 1994 and 1995, short root production was only 19% and 6% of that of 1992.
92% of the short roots were scored as mycorrhizal. All mycorrhiza recorded were whitish without rhizomorphs. Only in 1995 was a single mycorrhizal type with strands found. However, it only colonized three short roots among several hundreds. No winter suberization could be seen on mycorrhizal short roots. No grazing or clear pathogen attacks to mycorrhizal roots was recorded. The mean age of long roots for developing mycorrhizal roots was 3.5 months. The median life span for the mycorrhizal roots were 360, 720 and 720 days, for types 1, 2 and 3, respectively. Short roots at 0-20 cm depth had significantly lower longevity than those at 20-40 and 40 80 cm .