Related Experiment Video
Updated: Jun 13, 2026
06:42
Measuring Phosphorus Release in Laboratory Microcosms for Water Quality Assessment
Published on: July 22, 2019
Phosphorus and soil development: does the Walker and Syers model apply to semiarid ecosystems?
Paul C Selmants1, Stephen C Hart
1School of Forestry and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, Arizona 86011, USA. selmants@ucsc.edu
Ecology
|April 16, 2010
Summary
The Walker and Syers model accurately describes phosphorus dynamics in semiarid soils, showing age-related changes in soil phosphorus fractions and increased phosphatase activity with weathering.
Area of Science:
- Soil Science
- Ecosystem Ecology
- Biogeochemistry
Background:
- The Walker and Syers model is established for humid ecosystems, but phosphorus (P) dynamics in arid environments are less understood.
- Semiarid ecosystems present unique challenges for studying long-term soil development and nutrient cycling.
Purpose of the Study:
- To test the applicability of the Walker and Syers model in semiarid piñon-juniper woodlands.
- To investigate long-term soil phosphorus transformations along a volcanic substrate age gradient.
- To assess the influence of tree islands on soil P fractions in arid environments.
Main Methods:
- Measured soil phosphorus fractions across a 3000 ka age gradient in northern Arizona.
- Compared soil P pools under tree canopies versus intercanopy spaces.
- Analyzed phosphatase enzyme activity in relation to substrate age.
Main Results:
- Total soil P and primary mineral P decreased with substrate age.
- Labile inorganic P initially increased then decreased, while organic P consistently increased.
- Tree canopies influenced labile P pools, but this effect diminished with soil development.
- Phosphatase activity increased with substrate age, indicating higher P demand in older soils.
Conclusions:
- The Walker and Syers model's general pattern of P transformation holds for semiarid ecosystems, albeit at a slower rate.
- Pedogenic changes significantly influence labile P distribution in semiarid soils.
- Findings broaden and unify terrestrial ecosystem development theory by integrating arid ecosystem dynamics.
Related Concept Videos
01:21The Phosphorus Cycle
Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, such as phosphate ions (PO43-), found in soil, water, sediment and rocks. Phosphorus is often a limiting nutrient (i.e., in short supply). Consequently, phosphorus is added to most agricultural fertilizers, which can cause environmental problems related to runoff in aquatic ecosystems.
01:29Soil Microbial Ecology
Soil microbial ecology is defined by highly diverse, spatially structured communities that drive nutrient cycling, organic matter turnover, and overall ecosystem stability. Although a gram of soil can contain thousands of bacterial and archaeal taxa, the ecological processes they mediate are even more crucial for sustaining terrestrial life.Microhabitats and NichesSoil is a heterogeneous mixture of minerals, organic matter, water, and air. Microbes inhabit distinct microhabitats formed by...
02:23The Soil Ecosystem
Plants obtain inorganic minerals and water from the soil, which acts as a natural medium for land plants. The composition and quality of soil depend not only on the chemical constituents but also on the presence of living organisms. In general, soils contain three major components:
01:30Microbial Wastewater Treatment
Microbial communities in aquatic ecosystems play a key role in the natural breakdown of contaminants introduced through domestic and industrial effluents. Acting as biological catalysts, these microbes change and mineralize a wide range of organic and inorganic pollutants under different redox conditions.In oxygen-rich surface waters, aerobic heterotrophs lead organic matter breakdown, using oxygen as the terminal electron acceptor to efficiently oxidize substrates to carbon dioxide and water.
02:34Water and Mineral Acquisition
Specialized tissues in plant roots have evolved to capture water, minerals, and some ions from the soil. Roots exhibit a variety of branching patterns that facilitate this process. The outermost root cells have specialized structures called root hairs that increase the root surface, thus increasing soil contact. Water can passively cross into roots, as the concentration of water in the soil is higher than that of the root tissue. Minerals, in contrast, are actively transported into root cells.
02:41Responses to Drought and Flooding
Water plays a significant role in the life cycle of plants. However, insufficient or excess of water can be detrimental and pose a serious threat to plants.