Foliar Nitrogen and Phosphorus Level Related to Site Quality in a Northern Minnesota Spruce Bog

Abstract

Channels of relatively rapid water movement, termed "water tracks," in black spruce bogs in former glacial Lake Agassiz are often associated with a rich flora and shallow peat. Adjacent areas of lesser water movement are characterized by a depauperate, less productive flora and deeper peats. Black spruce foliage, collected from transects running from the good site in the water track with vigorous stands to the very poor muskegs bearing stunted trees one—fourth mile distant, was analyzed for 13 mineral elements. Nitrogen and phosphorus levels were significantly correlated with site quality; potassium displayed an inverse correlation. Levels of N and P were low, generally below the point at which deficiency symptoms have been reported for this or other spruces. The inverse relationship of potassium is a growth dilution effect, since the levels appear sufficient on all sites. The higher levels of nitrogen on good sites may be attributed to nitrogen fixation by speckled alder, which is abundant on the good sites but absent on poorer sites. More rapid decomposition of litter, indicated by lesser depth of peat accumulation, movement of enriched water, and nearness of mineral subsoil, may influence the level of N and P in the water track. Other elements were not related to site quality for black spruce.