Growth and nutritional responses of containerized sugar and Jeffrey pine seedlings to controlled release fertilization and induced mycorrhization

Abstract Two controlled release nutrient formulations, Sierra 17-6-10+Minors and High N 24-4-8, and ectomycorrhizal inoculation with pelletized basidiospores of Pisolithus tinctorius (Pers.) Coker & Couch were evaluated for their effects on containerized sugar pine (Pinus lambertiana Dougl.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) seedlings. Low, medium, and high application rates of each amendment formulation were tested. Peters 20-10-20 water soluble nutrients, also applied with three rates, plus unfertilized and uninoculated seedlings of each species provided for comparison of treatment effects on growth and nutrition. Shoot growth in both sugar and Jeffrey pine, as indicated by dimensions, volume, and mass, increased with amendment application rate, and the response to controlled release nutrients exceeded that to the water soluble formulation. Jeffrey pine root growth, in terms of mass and total length, paralleled that of the shoots, but in sugar pine, the three fertilizers produced comparable root growth that did not increase with application rate. For both species, however, the Sierra formulation produced the greatest specific root lengths among fertilized seedlings. Inoculated sugar pine seedlings generally exhibited smaller dimensions and volume and less shoot and root mass than uninoculated sugar pine. Jeffrey pine with induced mycorrhization were also generally smaller in shoot dimensions and volume but had greater shoot and root mass than uninoculated seedlings. Total root length and specific root length were increased substantially in both species by mycorrhizal inoculation. The Sierra formulation applied at the high rate resulted in the most P. tinctorius mycorrhizae in Jeffrey pine, but in sugar pine, mycorrhizal counts and the percentages of root length colonized declined as fertilization rates rose although nutrient additions increased both relative to that found in unfertilized seedlings. Foliar analysis for a broad array of macro- and micronutrients revealed a coupled increase in nutrient concentrations, notably of N but also P and S among others, and amendment application rates in sugar and Jeffrey pine, which at least in part probably explains the growth responses to fertilization noted above. The High N amendment, which excelled in elevating N uptake, also had a propensity to depress P concentrations in both species, however. Inoculated sugar pine had higher foliar N and K but lower Ca and Mn overall than uninoculated seedlings, while inoculated Jeffrey pine had higher K and Zn but lower N, P, Ca, Mg, and S than their uninoculated counterparts. In the latter species, however, the depressed macronutrient uptake in inoculated seedlings was frequently offset by fertilization with specific formulations and/or application rates. Overall, these results indicate that the high rate of the Sierra amendment produced the most favorable array of attributes in both sugar and Jeffrey pine, but that P. tinctorius is likely a more promising mycobiont for inoculation of the latter species than the former.