Tropentag, October 5 - 7, 2011 in Bonn "Development on the margin"

Aboveground Net Primary Production Response to Chronic Nitrogen Addition in a Tropical Montane Forest

Georg-August-Universität Göttingen, Institute for Soil Sciene and Forest Nutrition, Germany

Abstract

Nitrogen (N) deposition in tropical areas is projected to increase rapidly in the next decades and little is known on how tropical forest productivity will respond to increase in N availability. We used an N-addition experiment to achieve an N-enriched condition in an old-growth forest growing in an Aluandic Andosol soil at 1200-1300 m elevation in Fortuna Forest Reserve, Panama. Control and N-addition treatments (starting in 2006 at a rate of 125 kg urea-N ha^-1 yr^-1, split in four applications) were laid out in paired-plots design with four replicate plots (40mx40m each, separated by ≥40-m distance). Here, we report the changes in various components of above-ground net primary production (ANPP) during the 3-4-yr N addition: stem diameter growth (separated by diameter at breast height (DBH) classes of 10-30 cm, 30-50 cm, and >50 cm), woody biomass production (WBP) and fine litterfall. No significant differences were observed between 3-4-yr N addition and the control in stem diameter growth of any DBH classes or all classes combined (control: 1.6±0.2 mm yr^-1; N-addition plots: 1.9±0.2 mm yr^-1), in WBP (control: 4.3±0.6 Mg ha^-1 yr^-1; N-addition plots: 4.2±0.5 Mg ha^-1 yr^-1), in total fine litterfall (control: 7.3±0.4 Mg ha^-1 yr^-1; N-fertilised: 8.0±0.4 Mg ha^-1 yr^-1), and in ANPP (control: 11.6±0.8 Mg ha^-1 yr^-1; N-fertilised: 12.3±0.8 Mg ha^-1 yr^-1). The first 2 years of N addition showed significant increase in ANPP compared to the control, and this was mainly due to increased leaf-litter production. Our results showed interannual variation of ANPP response to N addition.

Keywords: Aboveground net primary production, chronic nitrogen addition, tropical forest

Contact Address: Angelica Baldos, Georg-August-Universität Göttingen, Institute for Soil Sciene and Forest Nutrition, Buesgenweg 2, 37077 Goettingen, Germany, e-mail: abaldosgwdg.de