inorganic nitrogen

Nitrogen Immobilization by Decomposing Woody Debris and the Recovery of Tropical Wet Forest from Hurricane Damage

Nitrogen Immobilization by Decomposing Woody Debris and the Recovery of Tropical Wet Forest from Hurricane Damage
J. K. Zimmerman, W. M. Pulliam, D. J. Lodge, V. Quiñones-Orfila, N. Fetcher, S. Guzmán-Grajales, J. A. Parrotta, C. E. Asbury, L. R. Walker and R. B. Waide
Vol. 72, No. 3 (Apr., 1995), pp. 314-322

Following damage caused by Hurricane Hugo (September 1989) we monitored inorganic nitrogen availability in soil twice in 1990, leaf area index in 1991 and 1993, and litter production from 1990 through 1992 in subtropical wet forest of eastern Puerto Rico. Experimental removal of litter and woody debris generated by the hurricane (plus any standing stocks present before the hurricane) increased soil nitrogen availability and above-ground productivity by as much as 40% compared to unmanipulated control plots. These increases were similar to those created by quarterly fertilization with inorganic nutrients. Approximately 85% of hurricane-generated debris was woody debris >5 cm diameter. Thus, it appeared that woody debris stimulated nutrient immobilization, resulting in depression of soil nitrogen availability and productivity in control plots. This was further suggested by simulations of an ecosystem model (CENTURY) calibrated for our site that indicated that only the large wood component of hurricane-generated debris was of sufficiently low quality and of great enough mass to cause the observed effects on productivity. The model predicted that nutrient immobilization by decaying wood should suppress net primary productivity for 13 yr and total live biomass for almost 30 yr following the hurricane. Our findings emphasize the substantial influence that woody debris has upon nutrient cycling and productivity in forest ecosystems through its effects on the activity of decomposers. We suggest that the manner in which woody debris regulates ecosystem function in different forests is significantly affected by disturbance regime.

Control of Nitrogen Export from Watersheds by Headwater Streams

Peterson, B.J. et al. 2001. Control of Nitrogen Export from Watersheds by Headwater Streams.
Science 6 April 2001:
Vol. 292 no. 5514 pp. 86-90
DOI: 10.1126/science.1056874

A comparative 15N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.
Syndicate content