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Title: Plant and microbial controls on nitrogen retention and loss in a Humid Tropical Forest

Humid tropical forests are generally characterized by the lack of nitrogen (N) limitation to net primary productivity, yet paradoxically have high potential for N loss. We conducted an intensive field experiment with {sup 15}NH{sub 4} and {sup 15}NO{sub 3} additions to highly weathered tropical forest soils to determine the relative importance of N retention and loss mechanisms. Over half of all the NH{sub 4}{sup +} produced from gross mineralization was rapidly converted to NO{sub 3}{sup -} during the process of gross nitrification. During the first 24 h plant roots took up 28 % of the N mineralized, dominantly as NH{sub 4}{sup +}, and were a greater sink for N than soil microbial biomass. Soil microbes were not a significant sink for added {sup 15}NH{sub 4}{sup +} or {sup 15}NO{sub 3}{sup -} during the first 24 hr, and only for {sup 15}NH{sub 4}{sup +} after 7 d. Patterns of microbial community composition, as determined by Terminal Restriction Fragment Length Polymorphism analysis, were weakly, but significantly correlated with nitrification and denitrification to N{sub 2}O. Rates of dissimilatory NO{sub 3}{sup -} reduction to NH{sub 4}{sup +} (DNRA) were high in this forest, accounting for up to 25 % of gross mineralization and 35more » % of gross nitrification. DNRA was a major sink for NO{sub 3}{sup -} which may have contributed to the lower rates of N{sub 2}O and leaching losses. Despite considerable N conservation via DNRA and plant NH{sub 4}{sup +} uptake, the fate of approximately 45% of the NO{sub 3}{sup -} produced and 22% of the NH{sub 4}{sup +} produced were not measured in our fluxes, suggesting that other important pathways for N retention and loss (e.g., denitrification to N{sub 2}) are important in this system. The high proportion of mineralized N that was rapidly nitrified and the fates of that NO{sub 3}{sup -} highlight the key role of gross nitrification as a proximate control on N retention and loss in humid tropical forest soils. Furthermore, our results demonstrate the importance of the coupling between DNRA and plant uptake of NH{sub 4}{sup +} as a potential N conserving mechanism within tropical forests.« less
Authors:
; ; ; ;
Publication Date:
OSTI Identifier:
951009
Report Number(s):
LBNL-1684E
Journal ID: ISSN 0012-9658; ECOLAR; TRN: US200911%%229
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Ecology; Journal Volume: 89; Journal Issue: 11; Related Information: Journal Publication Date: 2008
Research Org:
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
Sponsoring Org:
Earth Sciences Division
Country of Publication:
United States
Language:
English
Subject:
54; 58; BIOMASS; DENITRIFICATION; FORESTS; LEACHING; MINERALIZATION; NITRIFICATION; NITROGEN; PRODUCTIVITY; RETENTION; SOILS