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Effects of Divalent Metal Chlorides on Respiration and Extractable Enzymatic Activities of Douglas-Fir Needle Litter¹

ABSTRACT

The rates of CO₁ evolution from Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) needle litter, following application of divalent metal (Hg, Cd, Pb, Ni, Zn, and Cu) chlorides at rates of 10, 100, and 1,000 µg/g and Ca chloride at 7, 68, and 683 µg/g, were monitored at 2- to 3-day intervals for 4 weeks; extractable enzymatic activities were also measured on additional samples at 1 day, 2, and 4 weeks following treatment. All metals except Pb inhibited respiration when applied at the highest level. Cellulase activity was depressed by treatments of 1,000 µg/g of either Hg or Cd after 4 weeks but was not affected initially (1 day after). After 4 weeks, xylanase activity was also depressed by the 1,000-µg/g Hg treatment. Apparently these enzymatic activities declined due to decreased enzyme synthesis associated with inhibited microbial growth rather than by direct enzymatic inhibition. Although addition of Hg or Cu chlorides directly to litter extracts caused marked inhibition of most enzymatic activities, equivalent levels, when applied to the needle litter, produced no inhibitions in extracts after 1 day, except for invertase activity. lnvertase activity was depressed at all intervals and β-glucosidase activity was elevated at all intervals by Hg at the 1,000-µg/g level. The level of extractable ninhydrin-reactive compounds was elevated by this Hg treatment at all intervals similar to the effect of fumigation of soil or litter. Regardless of treatment, cellulase and xylanase activities were correlated (r = 0.70, n = 192).

Key Words: heavy metals • litter decomposition • enzyme inhibition

¹ Contribution from Corvallis Environ. Res. Center, Corvallis, OR 97330.

² National Research Council Resident Research Associate, USEPA, Corvallis Environ. Res. Center, Corvallis. Present address: Environ. Sci. Div., Oak Ridge Natl. Lab. (Operated by Union Carbide Corp. under contract W-7405-eng-26 with the U.S. Dep. of Energy), Oak Ridge, TN 37830.

Received for publication April 10, 1978.