James Hohmann’s research while affiliated with Eastern Michigan University and other places

The objective of this study was to examine the combined effect of acidity and nitrogen (N) concentration on decomposition of Sparganium eurycarpum Engelm. litter. Decomposition was examined in the laboratory for 200 days with a factorial arrangement of three pH levels (pH 4, 6 and 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 litter. After 200 days, maximum export of N and P from decaying tissues occurred 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 fertilization on nutrient export varied with pH. After 200 days, nitrogen 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 the high N treatment (as much as −2.12 mg N g−1 less at pH 8). For P, losses 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) and 8 (−0.26 mg P g−1) after 200 days. In each case the effects of acidification and N fertilization were greater after 100 days of decomposition. In summary, low pH slowed N and P export from decaying litter and N fertization seemed to retard N and P export at high pH.