When looking at the effects of CO2 the different seedling treatments were combined. When looking at the effect of CO2 on any growth or weathering parameters, only planted columns were considered. Statistical analysis was performed using JMP software version 5.01a . Two way ANOVA was used to determine treatment and interaction effects. Significant differences between CO2 treatments were assessed with a student T test, and significant differences between ectomycorrhizal treatments with Tukey’s HSD test, using a one way ANOVA.Upon harvest we observed highly variable rates of mycorrhizal colonization. We classified the seedlings as abundantly colonized , moderately colonized , or sparsely colonized . Of the 20 seedlings in the mycorrhizal treatments 6, 4, and 10 seedlings were abundantly, moderately, and sparsely colonized, respectively, at the time of harvest. While the root systems extended 12S21 cm down the 30 cm columns, no mycorrhizae were found deeper than 6 cm. There were no extraradical hyphae or ectomycorrhizae resembling Piloderma& fallax or Suillus&variegatus observed in the non mycorrhizal treatment, but there were turgid, smooth,maceta cuadrada plastico black root tips observed in the non mycorrhizal treatments that may have been Thelephoroid mycorrhizae. Chitin analysis of roots and growing medium showed almost no chitin in our unplanted controls, and significant chitin in both mycorrhizal treatments . There were also significant amounts of chitin in the non mycorrhizal planted treatments. In both mycorrhizal treatments most chitin was found in the mineral mix, whereas in the non mycorrhizal treament most chitin was found in the rhizosphere and roots. Combining the two mycorrhizal treatments we found moderately more chitin in the elevated CO2 treatment, 86 mg chitin/column vs. 50 mg chitin / column . When the chitin content was expressed as total chitin content per gram seedling biomass , we see that the mycorrhizal treatments did have significantly more chitin than the non mycorrhizal treatment, and that elevated CO2 was associated with a higher chitin content in the Piloderma treatment.Formic, lactic, and acetic acids made up the majority of measured low molecular weight organic acids , comprising 82%, 12%, and 4% of total LMWOA’s, respectively.Much smaller amounts of malonate, oxalate, fumarate, and succinate were occasionally detected, but their occurrence in measurable quantities was not associated with any treatment. Nonplanted columns had significantly lower LMWOA levels than planted columns while P.&fallax columns had significantly higher LMWOA concentrations than non-planted, but significantly lower levels than either the nonmycorrhizal or S.&variegtus columns . These differences were driven by differences in the production of formate and lactate . Columns exposed to elevated CO2 produced significantly more total LMWOA’s , and this difference was driven primarily by significantly greater formic acid production . When amounts of LMWOA are calculated per gram seedling DW there are no significant differences between mycorrhizal or CO2 treatments .Solution pH was measured for the leachate from 7 sampling dates. Leachate pH was consistently alkaline . The nutrient solution used to water the columns was pH 5. There was no significant difference between elevated and ambient CO2 treatments nor between the non mycorrhizal treatments and the mycorrhizal treatments in leachate pH, but the leachate of the non planted controls was significantly lower in pH than the planted treatments on 5 of the 7 sampling dates and moderately but not significantly lower on the other two sampling dates. The pH of the column leachate from the planted columns did not change appreciably over time, while the leachate from the unplanted columns decreased slightly over time .The needle concentrations of Ca, K, Mg, Fe, and P were all at or above deficiency thresholds for P.&sylvestris , though P is near the lower limit of optimal growth. CO2 treatment had no effect on needle nutrient concentrations and mycorrhizal treatment only affected needle [Ca] . Neither CO2 level nor mycorrhizal treatment had a significant effect on total seedling contents of Ca, K, or Mg despite significant differences in seedling biomass between CO2 treatments. The differences in seedling Ca and K contents between treatments correlated tightly with seedling DW, while the opposite trend was found with Mg. Ectomycorrhizal colonization, particularly with Piloderma, increased seedling Mg concentration.Whole column weathering budgets for the 4 elements: Si, Ca, K, and Mg show no effect of CO2 on total weathering losses . The presence of seedlings, mycorrhizal or not, did significantly enhance weathering losses compared to nonSplanted controls.More Si and Mg were weathered in columns planted with P.&fallax inoculated seedlings, but these differences were not significant . The major pool of weathering losses for Mg, K, and Ca in the seedling treatments was uptake into the growing seedlings; losses of magnesium were particularly dominated by seedling uptake . Silica losses were fairly evenly distributed between ΔCEC and column leachate, while seedling uptake was negligible . As stated previously, ΔCEC was negative for calcium and slightly negative for some K and Mg treatments. When the nutrients added during watering were subtracted from the final budgets the net weathering losses of Ca, K, and Mg in the non planted treatment are negative or only slightly positive ,maceta 7 litros suggesting a “missing sink” for weathering products.Elevated CO2 increased the biomass of the Pinus&sylvestris seedlings. Other studies on coniferous seedlings have generally found a growth stimulation with elevated CO2 , and this trend includes several studies on mycorrhizal Pinus&sylvestris seedlings , although some other studies have failed to find an effect of elevated CO2 on growth . We found a slight reduction in root:shoot with elevated CO2. Most studies on ectomycorrhizal P.& sylvestris seedlings which have noted a growth stimulation from elevated CO2 also found an increase in root:shoot . A decrease in root:shoot does not necessarily indicate reduced below ground C allocation as carbon could be allocated to EM fungi rather than root biomass. If we use Ekblad and Nasholm’s estimate that 9.5% of fungal biomass is chitin, then our observed 21 mg average difference in chitin between elevated and ambient CO2 treatments would correspond to 220 mg more fungal biomass supported by seedlings in the elevated CO2 treatment. This difference would bring the root: shoot ratios of the two CO2 treatments to near parity. Additionally, a given amount of ectomycorrhizal biomass typically has a significantly higher respiration rate than the same mass of fine roots and thus represents more below ground carbon allocation This same explanation for potentially higher below ground carbon allocation despite lower root:shoot applies to our findings of slightly lower root: shoot in the two mycorrhizal treatments vs. the nonmycorrhizal treatment. Low molecular weight organic acid production was strongly associated with seedling biomass across both CO2 and mycorrhizal treatments. While EMF are often mentioned in the literature to produce significant amounts of LMWOA’s, our findings seem to fall in line with the majority of studies examining the EMF role in LMWOA production which fail to find an increase in LMWOA production when comparing EMF and nonSEMF seedlings . However, many of these studies do find that EMF significantly alter the composition of LMWOA’s produced, particularly increasing oxalic acid concentrations , which we did not. Similar to Fransson and Johansson , we did not find that elevated CO2 increased LMWOA production beyond its effect on seedling biomass. Elevated CO2 was associated with significantly increased chitin content in seedlings colonized by Piloderma&fallax, but not with seedlings colonized by Suillus& variegatus;&this increase was due to elevated chitin levels found in the growth matrix, not on the seedling roots. Increased mycorrhizal growth is commonly found in elevated CO2 treatments . Many studies show that this response is highly fungal speciesS specific . It is interesting to note that Fransson and Johansson , in which they assessed the effects of elevated CO2 on mycorrhizal growth of 5 ectomycorrhizal species, also found this strain of Piloderma&fallax responded far more to elevated CO2 than any other fungal species examined. Our finding of no increase in seedling biomass in the mycorrhizal seedlings is not uncommon. Despite the fact that Pinus&sylvestris is considered obligately mycorrhizal, many studies have also found a growth depression of P.&sylvestris with mycorrhizal colonization when mycorrhizal and non mycorrhizal seedlings are compared . Given the high needle nutrient concentrations in our non mycorrhizal seedlings, and the very dense rooting we observed, it seems likely that high nutrient availability, and a very restricted rooting zone were the primary reasons we observed no growth stimulation by mycorrhizaeThe generally low levels of mycorrhizal colonization we observed were likely a result of nutrient levels being too high , or insufficient drainage . The significant amounts of chitin observed in the non mycorrhizal treatments may indicate either the presence of thelephoroid mycorrhizal contamination or saprotrophic fungi growing in the mineral mix. Our visual observations of shiny, turgid, smooth, black roots, and the fact that the majority of the chitin found in the non mycorrhizal treatments was found in the roots and not in the mineral mix suggests some thelephoroid mycorrhizal contamination. The larger size of the non mycorrhizal seedlings and their lower chitin levels indicates that thelephoroid infection was minor. Nutrient levels were sufficient for healthy balanced growth. Leachate concentrations of nutrient cations were steady suggesting that we increased the nutrient amounts sufficiently to keep up with the increasing nutrient demand of the growing seedlings. The fact that none of the needle nutrient concentrations were below sufficiency threshold further suggests that none of the seedlings had severe nutrient deficiencies that could have compromised carbon allocation physiology.The overall negative weathering observed for some mineral nutrients suggests a missing sink somewhere in our weathering budget. The two most likely possibilities are the formation of secondary precipitates that were not extracted upon harvest or a large pulse of weathering in the initial 3 weeks of equilibration , before seedlings were planted. We used a chemical speciation and equilibria model Visual MINTEQ to determine if secondary precipitates may have formed. Given the makeup of LMWOA’s observed, the pH’s measured and the elemental concentrations in the drainage as input parameters the only compound likely to have precipitated would have been Caoxalate, but only in very small quantities <3 uM. This leaves the initial “equilibration flush” as the likely missing sink in our weathering budget. All the columns were treated equally before planting so this missing sink should not affect the merit or interpretation of our results. Overall, and in every individual elemental flux , seedlings had a significant effect on weathering. For the nutrient cations K, Mg, and Ca, extra weathering products were taken up by the seedlings, while for Si, which was not taken up in appreciable quantities , extra weathering products were found on exchange sites in the mineral matrix. Mycorrhizal colonization did not significantly increase weathering rates or nutrient uptake, but seedlings colonized by Piloderma&fallax did exhibit a trend toward increased weathering. More Si and Mg were mobilized in the P.&fallax treatment despite the fact that P.&fallax colonized seedlings were on average smaller, though these differences were not statistically significant. P.&fallax colonized seedlings also had significantly higher Mg concentrations. Elevated CO2 had no effect on the weathering losses of Ca, K, or Si, but increased Mg losses . While seedlings grown in elevated CO2 did have higher plant and fungal biomass, and higher total seedling elemental contents, these increases in nutrient uptake were balanced by reduced leaching losses and not by enhanced mineral dissolution. Soil biota are capable of stimulating weathering of alumina silicate minerals by four distinct mechanisms. Proton&promotion: positively charged hydronium ions exuded by biota bind with partially charged negative surface sites on minerals, displacing cations from the mineral surface and destabilizing Si or Al on mineral surfaces, facilitating their release into solution. Plant growth is generally seen as a net acidifying phenomenon as a plant’s greater uptake of positively charged nutrient cations than negatively charged nutrient anions leads to a plant’s net exudation of protons. Ligand8promotion: an anion, either inorganic or organic, binds to mineral surface cations, again destabilizing the bond energy at the mineral surface stimulating release of surface cations and framework Si or Al. Removal&of&transport&limitation: the removal of weathering products from the surface boundary layer via nutrient uptake or enhanced solution flow eliminates or reduces the constant readsorption of these mineral weathering products that occurs in concert with dissolution, enhancing net dissolution.