Soil solution chemistry in lodgepole pine (Pinus contorta ssp. latifolia) ecosystems,southeastern Wyoming,USA

Concentrations of the principal inorganic and organic solutes in the soil root-zone were measured in six contrasting lodgepole pine (Pinus contorta ssp.latifolia) forest ecosystems for five years (1979–1983). Consistent temporal changes in the principal inorganic solutes (Ca, Mg, K, Na, SO₄, Cl) were observed in all the forest stands and years of study: high concentrations at the initiation of snowmelt in the spring were followed by rapid declines to rather constant values in the mid to late stages of snowmelt. Except for K, concentrations of these solutes differed significantly between sites and between years. Sulfate was the principal mobile anion in the root-zone soil solutions, but contributions of bicarbonate and organic anions also were important.The pH of root-zone solutions was relatively high (6.0), did not change significantly as snowmelt proceeded, and was significantly lower in high-clay soils. No consistent trends in bicarbonate alkalinity were observed and soil atmosphere CO₂ concentrations were only about 10 to 20 times above atmospheric levels, peaking at the end of the snowmelt interval. Concurrent changes in the concentrations of dissolved organic carbon, non-volatile acid-neutralizing capacity, and total Al and Fe indicated that these soil-forming metals were transported vertically in the soil as organic complexes. Precipitation of these complexes was more rapid and more complete in the soils with high clay content than in the coarser soils. Moreover, organic anions comprised up to 30% of the total anionic charge in the coarse-textured soils but less than 10% in the fine soils.Little seasonal or spatial variation of inorganic N and P concentrations was observed in root-zone solutions, probably as a result of high biotic demand for these limiting nutrients. Flux of N and P in these ecosystems was predominately via organic forms so that losses of these nutrients was strongly linked to the mobility of dissolved organic carbon. However, a two-fold increase in the organic N:P and C:P ratios was observed during passage of melt water from the forest floor to mineral soil, evidence of more rapid mineralization of organic P.