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NITROGEN CYCLING IN TROPICAL PLANTATION FORESTS: POTENTIAL CONTROLS ON NITROGEN RETENTION
Author(s) -
Silver W. L.,
Thompson A. W.,
Reich A.,
Ewel J. J.,
Firestone M. K.
Publication year - 2005
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/04-1322
Subject(s) - nitrification , cycling , nitrogen cycle , mineralization (soil science) , nitrous oxide , environmental science , ammonium , ecosystem , nutrient cycle , nitrogen , agronomy , soil water , leaching (pedology) , ecology , chemistry , biology , forestry , soil science , geography , organic chemistry
The establishment and management of tropical plantations has the potential to significantly alter patterns in nitrogen (N) cycling relative to old‐growth tropical forests, which are generally characterized by high N availability and large fluxes of nitrous oxide (N 2 O), an important greenhouse gas. We used 15 N tracer additions to examine the effects of plantation establishment and management on gross N‐cycling rates, N retention via microbial assimilation and dissimilatory nitrate (NO 3 − ) reduction to ammonium (NH 4 + ) (DNRA), and N losses via N 2 O emissions. In general, plantations had lower rates of N cycling and increased potential for N losses compared to old‐growth forests, but there were few differences between very short (one‐year) rotation and 10‐yr‐old uncut plantations. Gross N mineralization declined by almost 50% in the plantations compared to the old‐growth forests, and much of the mineralized N was nitrified at all sites. Gross nitrification rates were more variable and did not differ between old‐growth forests and unfertilized plantations; however, fertilization increased gross nitrification by a factor of 6 in short‐rotation forests, signaling a potential mechanism for increased N losses via leaching and gaseous emissions. Old‐growth forests had significantly higher microbial biomass N and NH 4 + assimilation rates. No microbial N assimilation was measured in the plantation soils, nor was there evidence of gross NH 4 + immobilization from estimates of NH 4 + consumption and nitrification. Plantations and old‐growth forests had similar DNRA rates (0.23 μg·g −1 ·d −1 ), which retains N in the ecosystem, and plantations had lower N 2 O emissions. Nitrous oxide fluxes from plantations were highly sensitive to reducing conditions, highlighting the potential for high rates of N 2 O losses. Our results show that plantation establishment can decrease rates of N cycling, but once forests are converted to plantations, internal N‐cycling pathways and N 2 O fluxes are relatively resistant to disturbance associated with short rotation length.