DECOMPOSITION OF SPARGANIUM-EURYCARPUM UNDER CONTROLLED PH AND NITROGEN REGIMES

The objective of this study was to examine the combined effect of acid ity and nitrogen (N) concentration on decomposition of Sparganium eury carpum Engelm. litter. Decomposition was examined in the laboratory fo r 200 days with a factorial arrangement of three pH levels (pH 4, 6 an d 8) and two N regimes (high and low) in water surrounding Sparganium litter. Increasing acidity inhibited decomposition (47.5%, 27.9% and 7 .3% dry weight remaining after 200 days at pH 4, 6 and 8, respectively ), but N fertilization had no overall effect on weight loss. Under all treatments, both N and phosphorus (P) were exported from decaying lit ter. After 200 days, maximum export of N and P from decaying tissues o ccurred at pH 8 (maximum losses of 13.07 mg N g-1 and 1.22 mg P g-1 of initial litter mass). Conversely, the least export occurred at pH 4 ( minimum losses of 4.79 mg N g-1 and 0.68 mg P g-1). The effects of N f ertilization on nutrient export varied with pH. After 200 days, nitrog en export was virtually the same between high and low N treatments at pH 4; however, at the two higher pH regimes, less N was exported in th e high N treatment (as much as -2.12 mg N g-1 less at pH 8). For P, lo sses were actually higher (+0.14 mg P g-1) under the high N treatment at pH 4, but lower under high N conditions at pH 6 (-0.02 mg P g-1) an d 8 (-0.26 mg P g-1) after 200 days. In each case the effects of acidi fication and N fertilization were greater after 100 days of decomposit ion. In summary, low pH slowed N and P export from decaying litter and N fertilization seemed to retard N and P export at high pH.