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1 December 2007 SPATIAL HETEROGENEITY AND DEPENDENCE OF SOILS AND HERBACEOUS PLANT COMMUNITIES IN ADJACENT SEASONAL WETLAND AND PASTURE SITES
David A. Dick, Frank S. Gilliam
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Abstract

Soil processes often exhibit spatial heterogeneity that may influence plant community structure. This study was conducted to determine fine-scale spatial patterns and degrees of variability of soil nutrients and plant communities within different vegetation types in a stream floodplain in southwestern West Virginia. One 5 m × 5 m site was established in each of two vegetation/drainage types: pasture (PA) and seasonal wetland (SW). Sites were located ∼25 m apart on flat bottomland. A 10 m × 1 m transect was also established perpendicular to the visible boundary between PA and SW drainage types, but separate from the PA and SW sites. Each site was divided into 1-m2 plots (n  =  25) and the transect was divided into 0.25-m2 plots (n  =  40). Mineral soil was taken to a 5 cm depth. Soil organic matter was measured as loss-on-ignition. Extractable NH4 and NO3 were determined before and after laboratory incubation (28 days at 27°C) to determine net N mineralization and nitrification. Cations were analyzed using inductively coupled plasma emission spectrometry. Vegetation was assessed using estimated percent cover (sites) and aboveground harvested biomass (transect). Mean organic matter was significantly higher (P < 0.05) in SW than in PA (10.6% and 8.3%, respectively). Nitrification was nearly 100% of mineralization in all soils, and was significantly lower (P < 0.05) in PA than in SW (0.7 and 1.8 µg NO3-N/g soil/d, respectively). Aluminum was significantly higher (P < 0.05) in SW than in PA (202.1 and 0.5 µg Al/g soil, respectively). Calcium and pH were significantly higher (P < 0.05) in PA than in SW (768.5 µg/g soil and 4.4, respectively). Magnesium was significantly higher (P < 0.05) in SW than in PA (174.2 and 121.9 µg/g soil, respectively). Transect results were similar to PA and SW sites and an abrupt transition was found between PA and SW site types. Vegetation analysis revealed two distinct communities with SW dominated by wetland species and PA dominated by a mixture with slightly more upland species. Transect vegetation also consisted of largely wetland species within wetland and a mixture in pasture, however Arthraxon hispidus (Thunb.) Makino dominated for ∼1 m at the boundary. Spatial variability of organic matter was much lower than spatial variability of nitrification. Thus, availability of organic substrates to N-processing microbes is less variable than N processing itself, underlining the complexity of biotic factors responsible for regulating soil N processes.

David A. Dick and Frank S. Gilliam "SPATIAL HETEROGENEITY AND DEPENDENCE OF SOILS AND HERBACEOUS PLANT COMMUNITIES IN ADJACENT SEASONAL WETLAND AND PASTURE SITES," Wetlands 27(4), 951-963, (1 December 2007). https://doi.org/10.1672/0277-5212(2007)27[951:SHADOS]2.0.CO;2
Received: 14 September 2006; Accepted: 1 June 2007; Published: 1 December 2007
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KEYWORDS
Nitrification
Nitrogen mineralization
nitrogen saturation
soil cations
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