Document: CHR-3-31-21

Effects of fertilization on patterns of carbon allocation and gross primary production in a tropical plantation forest.

GIARDINA, C.P.* ¹, M.G.RYAN ², D.BINKLEY ³ and J.H.FOWNES ¹

University of Hawaii Manoa, Honolulu, HI 96822 USA ¹
USDA Forest Service, Fort Collins, CO 80526 USA ²
Colorado State University, Fort Collins, CO 80521 USA ³

Abstract:
Nutrient inputs to forests have increased over the last 50 years, and these inputs are likely to alter ecosystem C budgets. The positive effects of increased soil nutrient supply on aboveground net primary production (ANPP) are well documented, but the effects of nutrient supply on gross primary production (GPP) and patterns of C allocation remain poorly characterized. Some evidence indicates that nutrient-related increases in ANPP are matched by decreases in total belowground C allocation (TBCA), with little change in GPP. Other evidence indicates that GPP increases with increased nutrient supply, and a greater proportion of this increase is allocated to ANPP than to TBCA. In this study, we examined 12 closed-canopy stands of Eucalyptus saligna for changes in ANPP, TBCA, and GPP following quarterly additions of 50 kg N, 25 kg P, and 25 kg K ha^-1 to half these stands. Prior to fertilization, ANPP, TBCA, and GPP did not differ among stands. After 1 year of fertilization, GPP was 28% greater in fertilized stands than in unfertilized controls (4.3 and 3.3 kg C m^-2 yr^-1, respectively); after 2 years, GPP had increased by 48% (5.1 and 3.4 kg C m^-2 yr^-1, respectively). The additional GPP was allocated primarily to ANPP, which increased by 75% in year 1 and 88% in year 2. TBCA did not change with fertilization. These results suggest that relatively small additions of limiting nutrients can dramatically increase GPP and alter C allocation patterns in forests.

Keywords: GPP, total below ground C allocation

This abstract is being presented at: 10:30 AM in session:
Oral Session #41: N Dynamics: Additions, Retention and Transformations.