Chemical influences on 14C and 15N primary production in an arctic lake

Summary Twelve 24 h bioassay experiments were conducted in 1980 and 1981 to evaluate seasonal influences of NO₃^-, NH₄⁺, PO₄^3-, N+P, vitamins, trace metals, a synthetic chelate and common salts on ¹⁴C and ¹⁵N primary production in Toolik Lake, Alaska. Addition of N+P, NO₃^-or NH₄⁺significantly increased ¹⁴C primary production over all other treatments on most dates. Only on three occasions did any other treatment have any statistically significant effect on ¹⁴C primary production. ¹⁵NO₃^-and ¹⁵NH₄⁺primary production were each significantly enhanced by PO₄^3-enrichement relative to all other nutrient applications on seven dates. Significantly depressed ¹⁵NO₃^-primary production consistently resulted from NH₄⁺addition but enrichment with NO₃^-gave significantly depressed ¹⁵NH₄⁺primary production in just three experiments. Other treatments significantly influenced ¹⁵N primary production on two occasions only. The general stimulatory influence of N+P, NO₃^-and NH₄⁺on ¹⁴C primary production as well as the similar effect of PO₄^3-on ¹⁵N primary production had no seasonal pattern. The total data show that nitrogen and phosphorus are the most important chemical regulators of primary production in Toolik Lake.