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DTSTART:20091025T030000
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RDATE:20111030T030000
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DTSTAMP:20260609T172124Z
DESCRIPTION:Eingeladen durch Prof. Matzner. Nitrogen deposition is projecte
 d to increase rapidly in tropical ecosystems\, but few studies address how
  such environmental change affects soil N cycling\, retention\, trace gas 
 fluxes\, leaching losses and net primary production in tropical forests. W
 e used N addition experiments to achieve N-enriched conditions in mixed-sp
 ecies\, lowland and montane forests in Panama. In the lowland site\, contr
 ol and N-addition plots were laid out in a stratified random design with f
 our replicates. N addition started in June 1998. Just outside these long-t
 erm manipulation plots\, we established four additional plots in 2006 to r
 epresent the first-year N-addition treatment. In the montane site\, contro
 l and N-addition plots were set up in a paired-plots design with four repl
 icates. N addition started in February 2006. At both sites\, each treatmen
 t plot was 40x40 m and plots were separated by at least 40 m. The N-additi
 on plots received 125 kg urea-N/ha.yr split in four equal applications. In
  the old-growth lowland forest located on an Inceptisol\, with high base s
 aturation and net primary production not limited by N\, there was no immed
 iate effect of first-year N addition on gross rates of mineral N productio
 n and N-oxide emissions. Changes in soil N processes were only apparent af
 ter chronic (9-11 yr) N addition: gross N mineralization and nitrification
  rates\, NO3- leaching\, and N-oxide emissions increased while microbial b
 iomass and NH4+ immobilization rates decreased compared to the control. In
 creased mineral N production under chronic N addition was paralleled by in
 creased substrate quality (e.g.\, reduced C:N ratios of litterfall)\, whil
 e the decrease in microbial biomass was possibly due to increase in soil a
 cidity. Increase in N losses was reflected in the increase in 15N signatur
 es of litterfall under chronic N addition. Soil CO2 and CH4 fluxes were no
 t affected by chronic N addition. In contrast\, the old-growth montane for
 est located on an Andisol\, with low base saturation and aboveground net p
 rimary production limited by N\, reacted to first-year N addition with inc
 reases in gross rates of mineral N production\, microbial biomass\, NO3- l
 eaching and N-oxide emissions compared to the control. This contradicts th
 e current assumption that N-limited tropical montane forests will respond 
 to N additions with only small and delayed increases in soil N-oxide missi
 ons. We attribute this fast and large response of N-oxide emissions to the
  presence of an organic layer (a characteristic feature of this forest typ
 e) in which nitri&#64257\;cation increased substantially during the first 
 year N addition. The high NO3- availability combined with the high rainfal
 l on this sandy loam soil facilitated the instantaneous increase in NO3- l
 eaching. Soil CO2 ef&#64258\;ux was reduced after 2-3-yr N addition compar
 ed to the control. This reduction was caused by a decrease in soil CO2 ef&
 #64258\;ux during the high stem-growth period of the year\, suggesting a s
 hift in carbon partitioning from below- to aboveground in the N-addition p
 lots in which stem diameter growth was promoted. Soil CH4 fluxes were not 
 affected during 3-yr N addition. These results suggest that soil type\, pr
 esence of an organic layer\, changes in soil N cycling\, and hydrological 
 properties are more important indicators than vegetation as N sink on how 
 tropical forests respond to elevated N input.  
DTSTART;TZID=Europe/Berlin:20100506T161500
DTEND;TZID=Europe/Berlin:20100506T174500
LOCATION:H6
SUMMARY:Dr. Marife Corre\, Universität Göttingen\, Ökopedologie der Tropen:
  Impact of elevated N input on ecosystem processes in old-growth lowland a
 nd montane forests in Panama
TRANSP:TRANSPARENT
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