Morphometric analysis of Pinus banksiana Lamb. root anatomy during a 3-month field study

Tree roots are variable in their growth rates, alternating between periods of elongation and dormancy. This variability may have a strong influence on root anatomy. In the present study, field-grown Pinus banksiana Lamb. roots were divided into four distinct anatomical regions (i.e. white without mycorrhizae, white with mycorrhizae, condensed tannin, and cork). Changes in root growth, the proportions of the root system occupied by the various regions, and cortical plasmalemma surface area (CPSA) were determined for 6- to 9-month-old ectomycorrhizal P. banksiana seedlings during a 3-month period (August through October) in northern Ontario. The region in which the greatest change in length occurred was the condensed tannin zone, which was also the dominant contributor to root length (up to 74% of total). The roots of seedlings grown under artificial conditions had the same zones but in different proportions compared to roots in the field. A correlation was noted between increased root growth, low metacutization, and high soil water availability. The CPSA data were assumed to be a factor influencing ion uptake capacity in a positive manner. Interestingly, increases in CPSA were not directly correlated with changes in root length for field-grown seedlings. The primary contributor to CPSA in the field-grown roots was the ectomycorrhizal zone (approximately 80%). In comparison, the bulk (85%) of the CPSA in the chamber-grown roots was found in the white root region. The conditions under which the seedlings were grown strongly influenced the anatomy of their roots. Received: 27 April 1999 / Accepted: 6 December 1999