A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Nitrogen cycling in termite mounds in a secondary forestin Central AmazôniaIlse L. Ackerman 1 , Erick C. M. Fernandes 1 , and Elisa V. Wandelli 21 Dept. of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853 ila1@cornell.edu2 Embrapa-CPAA, AM-010 km 29, Manaus, AM BRAZILAbstractTermite mounds are a prominent feature of the post-clearing landscape in centralAmazônia. Associated with dead woody debris, their abundance increases with each cycle ofclearing. In our study site, a secondary forest which has been cleared twice, termite moundsare found at an abundance of 800 per hectare. These numerous termite-modified patcheshave different chemical, physical, and hydrological properties than the surroundinglandscape and support little vegetation. Total nitrogen is elevated in the termite mounds,b ut microbial biomass is lower, suggesting that conditions for microbial activity may beore limiting in termite mounds than in the surrounding soil. Termite mound material isrier than the surrounding soil and has a greater proportion of large aggregates. We testedhe hypotheses that (1) nitrogen mineralization is lower in termite mounds and that (2)ineralization is limited by moisture and by physical protection of organic matter.aterial from termite mounds and control soil was incubated in a factorial experiment withwo moisture and two aggregation levels.lthough the ammonification rate was not significantly lower, the nitrification and totalineralization rate were indeed significantly lower in the termite mound than in the controloils. The elevated moisture level did not affect the nitrification rate but decreased themmonification rate in both materials. The level of aggregation did not significantly affectny of the response variables.hese results confirm the hypothesis that termite mounds mineralize nitrogen at lower rateshan the surrounding soil. At the levels chosen, moisture was not a limiting factor foritrogen mineralization in thenitrogen at lower rates than the surrounding soil. At theevels chosen, moisture was not a limiting factor for nitrogen mineralization in the termiteound. Aggregate size may not have been reduced enough to expose physically-protectedrganic matter, or termite mound-building activities may chemically protect organicatter.