Print PageCalcium (Ca) is an essential element that shapes forest structure and function, and is of particular interest in forests subject to Ca depletion from high levels of acidic deposition and/or repeated biomass removal. Calcium can exist in several chemical forms in plants and soils, including the insoluble biomineral calcium oxalate, yet few studies have characterized the contribution of calcium oxalate to whole-ecosystem calcium pools and dynamics. We measured Ca-oxalate in plants, litter, and soils of two Douglas-fir forests of contrasting nutrient status in the Oregon Coast Range to address three questions: 1) How much Ca-oxalate exists in live biomass, decaying tissues, and soil? 2) What is the decomposition rate of Ca-oxalate in the forest floor? 3) Does site Ca status influence Ca-oxalate pools and concentrations?
Results/Conclusions
Our preliminary data indicate that Ca-oxalate was a large portion (30-50%) of total Ca in live biomass, and the majority (60-70%) of Ca flux between trees and soil via leaf litter. The low-Ca site had a greater proportion of total Ca existing as Ca-oxalate in both biomass and in soil, as compared to the high-Ca site, suggesting that Ca-oxalate may be more important in shaping physiology and biogeochemistry in lower Ca-status sites. Our data reveal Ca-oxalate in the high-Ca source litter decomposed rapidly, losing 66% in two years, indicating the potential for quick Ca-oxalate degradation and release from detritus. The rapid decomposition of Ca-oxalate in the high Ca source litter was not expected, considering that Ca-oxalate is a highly insoluble crystal. Our data suggest that Ca-oxalate degradation occurred primarily via microbial degradation, rather than chemical changes as the pH of the leaf litter did not decrease over time. Because Ca-oxalate makes up a large portion Ca in biomass pools, the formation and degradation of Ca through oxalate-mediated physiological and biogeochemical pathways is likely to have a strong influence ecosystem Ca dynamics.
