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Carbon, Nitrogen, and Phosphorus Mineralization in Northern Wetlands

Scott D. Bridgham, Karen Updegraff and John Pastor
Ecology
Vol. 79, No. 5 (Jul., 1998), pp. 1545-1561
DOI: 10.2307/176775
Stable URL: http://www.jstor.org/stable/176775
Page Count: 17
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Carbon, Nitrogen, and Phosphorus Mineralization in Northern Wetlands
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Abstract

We examined rates of C, N, and P mineralization in soils from 16 northern Minnesota wetlands that occur across an ombrotrophic-minerotrophic gradient. Soils were incubated at 30 degrees C under aerobic and anaerobic conditions for 59 wk, and the results were fit with a two-pool kinetic model. Additionally, 39 different soil quality variables were used in a principal components analysis (PCA) to predict mineralization rates. Mineralization of C, N, and P differed significantly among wetland types, aeration status (aerobic vs. anaerobic), and their interaction term. Despite low total soil N and P, there was a rapid turnover of the nutrient pools in ombrotrophic sites, particularly under aerobic conditions. On a volumetric basis, C and N mineralization increased in a predictable manner across the ombrotrophic-minerotrophic gradient, largely due to increasing soil bulk density. However, P mineralization per cubic centimeter remained relatively high in the bogs. The higher total P content of more minerotrophic soils appears to be offset by greater P immobilization due to geochemical sorption, yielding overall lower availability. Total C turnover rates were relatively similar among sites, despite large differences in soil quality. We suggest that, over time, the decay rates of organic matter in different wetland communities converge to a common rate. In contrast, CH4 production was extremely low in ombrotrophic peats. The apparent labile pools of N (N0), P (P0), and C (C0) were generally <10% of their respective total pool sizes, except for P0 in the bogs, which constituted up to 33% of total soil P. From 10% to 87% of the N, P, and C mineralized after 59 wk was derived from their respective labile pools. A simple group of variables describing the physical degree of decomposition of organic matter was often as good as, or superior to, more complicated chemical analyses in predicting C, N, and P mineralization. Because peats are classified and mapped according to these variables, it should make scaling efforts in landscape analyses much more tractable. Large differences in mineralization rates in northern wetland communities demonstrate that climate change models should not consider these areas as homogeneous entities. Our C mineralization results suggest that soil respiratory response to climate change (as CO2 and CH4) will vary considerably in different wetland communities. Our results also suggest that the common perception that more ombrotrophic sites are inherently more nutrient deficient needs to be reassessed.

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