CONTRIBUTION OF ECTOMYCORRHIZA TO THE POTENTIAL NUTRIENT-ABSORBING SURFACE OF PINE

The increase in potential nutrient-absorbing surface area of loblolly pine (Pinus taeda L.) seedlings as a result of ectomycorrhizal develop ment was quantified. In one experiment, loblolly pine seedlings were i noculated with Pisolithus tinctorius Pers. Coker (Pt) after having fir st been grown from seed for 8 wk under a low phosphorus (P) nutrient r egime. Eight weeks following inoculation, seedlings were harvested and all components of the nutrient absorbing system (including the fungal mycelium) were quantified. External mycelium accounted for only 5 % o f the potential absorbing-system dry weight, but this mycelium compris ed 75 % of the potential absorbing system area and over 99 % of the ab sorbing length. In a second experiment, the P uptake and contribution to potential absorbing surface of Pt was compared to Cenococcum geophi lum Fr. (Cg). Seedlings inoculated with Pt differed from those inocula ted with Cg in that they (i) absorbed almost twice the P, (ii) had a h igher frequency of fine-root branching, (iii) developed an extensive n etwork of rhizomorphs, and (iv) had over 1.5 times the mycelial absorb ing surface area and over 3 times the mycelial length of Cg. We conclu de that for both Pt and Cg inoculated plants, external mycelium made b y far the greatest contribution to the overall potential absorbing sur face area of the pine seedling. Differences in total mycelial surface area and mycelial length may account for differences in P uptake betwe en seedlings inoculated with Pt and those inoculated with Cg.