Document: COR-3-63-39

Linkages between the soil microbial community and biogeochemical cycling in a tropical rainforest forest of Costa Rica: The effects of soil type and land use history.

CLEVELAND, C.C.*, A.R.TOWNSEND, M.E.LEFER and B.CONSTANCE

University of Colorado, Boulder, CO, 80309, USA. ¹

Abstract:
Deforestation and conversion of land to pasture or crops in tropical rain forest ecosystems can cause wholesale alterations to ecosystem structure and function, and in particular, can lead to fundamental changes in nutrient cycling. Evidence suggests that land conversion may lead to substantial decreases in plant-available phosphorus (P), the probable limiting element in tropical ecosystems. However, the mechanism behind such losses is not well known. One strong possibility is that land transformation disrupts the structure and activity of soil microorganisms, which are the principal agents of decomposition, and play a central role in nutrient cycling. We studied the magnitude and functional composition of the soil microbial community in a matrix of forest and pasture sites on different soil types on the Osa Peninsula of Costa Rica. In sites characterized by highly weathered, nutrient-poor ultisols, microbial biomass C and N in the oldest pasture sites (20 yr.) was less than half of that in young (5 yr.) pasture sites and undisturbed forest sites. In addition, ecophysiological analyses suggested that the microbial community in both the old pasture and forest sites were not carbon limited, but were limited by some other nutrient. Conversely, the young pasture site was strongly carbon limited. We believe that land conversion may temporarily release the microbial community in young pasture sites from P limitation, and that as labile-P levels decline with pasture age, the microbial community again becomes P limited. In contrast to the ultisols, sites on nutrient-rich alluvial mollisols had relatively similar microbial biomass C and N, and were strongly carbon limited, showing no sign of P (or other nutrient) limitation. These data suggest strong linkages between the soil microbial community and biogeochemical cycling in both natural and managed ecosystems in the humid tropics.

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This abstract is being presented at: 9:30 AM in session:
Oral Session #71: Soil Microbial Biomass and Soil Respiration.