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Impacts of vegetation type on soil phosphorus availability and fractions near the alpine timberline of the Tibetan Plateau

Zhang L., Wu Y., Wu N., Luo P., Liu L., Hu H.

Polish Journal of Ecology

2011

Vol. 59, nr 2

307-316

Soil phosphorus (P) availability and fractions are influenced to a large extent by land use and cover changes. Inorganic P (IP) and organic P (OP) fractions in surface soils (0-20 cm) under typical vegetation types, including subalpine coniferous forests, alpine shrubs, and alpine shrub-meadows, near the alpine timberline of the eastern Tibetan Plateau of China, were measured by a modified Hedley fraction method. The results showed that OP is the dominant soil P fraction and the main source of available P in alpine soils near the timberline. Soil organic carbon, total nitrogen, and total P contents were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows. Concentrations of soil labile P (the sums of Resin-IP, NaHCO3-IP, and NaHCO3-OP) were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows, an observation that may be partially ascribed to the presence of deep litter layers generated by trees. Concentrations of soil labile and moderately organic P (NaHCO3-OP and NaOH-OP) in subalpine coniferous forests were also greater than in alpine shrubs and alpine shrub-meadows. Greater amounts of soil stable OP (extracted by concentrated HCl and cHCl.OP) were accumulated in alpine shrub-meadows compared to alpine shrubs or subalpine coniferous forests. The reduced availability of OP may be attributed mainly to increasing recalcitrant soil organic matter input in alpine shrub-meadows and alpine shrubs. Concentrations of IP associated with Ca minerals and parent materials (extracted by diluted HCl and HCl-IP, and extracted by concentrated HCl and cHCl-IP, respectively) were lower in subalpine coniferous forests, indicating that coniferous forests are more likely to use recalcitrant IP than alpine shrubs and alpine shrub-meadows. In this alpine region, land cover changes from subalpine coniferous forests to alpine shrubs and alpine shrub-meadows near the alpine timberline could decrease soil P conservation, availability, and supplementation.

The structure of phosphorus compounds in mid-forest humic lakes

Joniak T.

Oceanological and Hydrobiological Studies

2010

Vol. 39, No.2

105-112

This study presents the vertical distribution of phosphorus fractions in three postglacial midforest humic lakes: oligohumic, mesohumic, and polyhumic. Total phosphorus concentrations were similar in these humic lakes (mean 76 μg l^-1 P). The greatest share of phosphorus was in mineral fractions, while a lesser share was in organic, especially soluble, fractions. Concentrations of mineral forms (phosphates and polyphosphates) were the lowest at the time of maximum development of phytoplankton, especially of bacterioplankton near the bottom of the oligohumic lake. An exceptionally high participation of soluble polyphosphates was found in the polyhumiclake near the surface.