PARENT SESSION
Poster Session #75: Nutrient Cycling II.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Geographic gradient in resource use efficiency in Eucalyptus plantations.

Binkley, Dan^*,1, Stape, Jose^1,2, Ryan, Michael, ¹ Colorado State University, Fort Collins, CO² Universidade de Sao Paulo, Piracicaba, Sao Paulo, Brazil

ABSTRACT- We examined the production ecology and resource use efficiency of 14 clonal plantations of Eucalyptus grandis x urophylla across an 80-km geographic gradient in Bahia, Brazil. Average annual precipitation ranged from 800 to 1700 mm/yr, with about one-third falling during the dry season, and soils were all Quartzpsaments, Ultisols, or Oxisols. At age 5.5 to 7.5 years, all plantations were near the end of the planned rotation age with tree heights among the plantations of 16 to 26 m, and stem biomasses of 6.7 to 2.0 kg/m2. Aboveground net primary production (ANPP) ranged from 9.7 to 39.1 Mg/ha annually, based on repeated measurements within plots, and site-specific regression equations. Across all sites, the trees transpired an average of 760 mm of water/year, absorbed 19.5 TJ/ha of photosynthetically active radiation (PAR) annually, and took up 52.5 kg N/ha annually. The trees produced an average of 0.92 g of ANPP per MJ of intercepted light; 2.4 kg of ANPP per cubic meter of water transpired; and 340 kg of ANPP per kg of nitrogen taken up. The use of light and water varied by +/- 40% across the plots, but the efficiencies of using these resources varied by 3-fold. Nitrogen use was more variable (+/-60%), and the range of efficiency of N use was narrower (+/- 30%). Overall, the geographic pattern of production in these Eucalyptus plantations related strongly to patterns in the supplies of water and nitrogen, but the effects of differences in resource supplies was greatly amplified by increasing efficiency of resource use in resource-richer locales.

KEY WORDS: nitrogen use efficiency, light use efficiency, water use efficiency