The Serengeti grassland is characterized by antiparallel gradients of soil phosphorus and precipitation resulting in tall grass in the north and short grass in the south. Grasses associate with arbuscular mycorrhizal (AM) fungi to ameliorate water stress and improve nutrient acquisition. Field studies have shown that mycorrhizas also vary across the antiparallel phosphorus/precipitation gradients in the Serengeti; abundance of AM fungi is positively correlated with soil phosphorus and negatively correlated with precipitation. We hypothesized that nutrient limitation influences AM fungal abundance and both nutrient availability and water limitation partially mediate the amount of photosynthate available for symbiotic exchange. We conducted a factorial experiment to uncouple the interacting effects of soil type, phosphorus, and water availability on AM fungal abundance. Maize was grown in pots of soil collected from three locations across the natural gradients: high phosphorus and low precipitation (SOT), low phosphorus and high precipitation (KUH), and intermediate phosphorus and precipitation (SER). Full factorial treatments of +/- phosphorus fertilization and high/low water were administered for all three soils. Plant and mycorrhizal metrics were measured across treatments.
Our results support the expectation that mycorrhizal biomass increases with phosphorus fertilization when ambient phosphorus levels are low and decreases when ambient phosphorus levels are high. External hyphal abundance was reduced by fertilization in SOT soil (high phosphorus) and increased with fertilization in KUH soil (low phosphorus). Phosphorus uptake efficiency was greatest in plants grown in low phosphorus KUH while plants in the low-water treatment, especially SOT soil, allocated relatively more biomass to AM fungi soil suggesting possible functional differences and local adaptation of AM fungi. Abundance of AM fungi was also related soil pH with the greatest densities at neutral pH and less in more alkaline and more acidic soils. Interactions among soil properties, water availability and variation in the community composition of AM fungi are likely to influence the standing crop of AM hyphae in Serengeti soils.
|Advisor:||Johnson, Nancy Collins|
|Commitee:||Gehring, Catherine, Koch, George|
|School:||Northern Arizona University|
|School Location:||United States -- Arizona|
|Source:||MAI 52/02M(E), Masters Abstracts International|
|Subjects:||Plant biology, Ecology, Soil sciences|
|Keywords:||Arbuscular, Biomass allocation, Functional equilibrium, Mycorrhiza, Resource gradients, Serengeti|
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