BLACKSBURG, Va. -- Ecologists are well aware that environments are spatially variable, or patchy. However, in studies of plant competition and succession, an assumption is usually made that the soil environment is relatively homogeneous throughout the root systems of the interacting plants. Models that make this homogeneous assumption predict one species will eventually out-compete all others. Yet natural plant communities are rich in species, partly because soil properties vary dramatically across small distances.
At the 83rd annual Ecological Society of America meeting at the Baltimore Convention Center Aug, 2-6, Virginia Tech biology faculty member Robert H. Jones will report on how various forest plants respond to soil property variations. His presentation is Monday, Aug. 3, at 3:05 p.m. as part of the Consequences of Plant Response to Spatial and Temporal Heterogeneity symposium (1-5 p.m., room 310), offered jointly with the Botanical Society of America.
Virginia Tech forestry faculty member Paul Mou, Jones, and Bob Mitchell of the J.W. Jones Ecological Research Center in Newton Ga., are examining spatial variation of soil properties in southeast U.S. coastal plain forests, and how forest plants respond to that heterogeneity. "We predicted that soil would be very heterogeneous right after forests are disturbed, and most homogeneous when forests reach the middle of plant species succession, a point when one or two species are very abundant and most others are absent or scarce," Jones explains.
The researchers also believed that the type of disturbance would have important influences on spatial patterns in soil. Clearcuts and simulated bark beetle outbreaks in mid-successional pine forests confirmed these predictions, Jones says. "Clear cuts result in massive surface soil disturbance while beetle outbreaks simply add more litter to the top of an already homogeneous soil surface," he says.
Mou, Jones, and Mitchell hypothesized that plants would vary greatly in their ability to exploit rich soil patches. "In a potted plant study, we found that some species, such as sweetgum trees and pineweed, concentrated root growth within rich soil patches, while others, such as persimmon tree and horseweed, did not. More importantly, some species grew larger when the same amount of soil fertility was arranged in patches instead of spread evenly throughout the pot." Sweetgum tree and fireweed are examples of the plants with roots that seek out patches of nutrients.
However, unlike in other studies of root system behavior, few correlations among root system traits were found, Jones says, "which makes prediction of plant interactions more complex than originally thought."
Garden plots are now underway to confirm that the degree of soil heterogeneity can influence competitive outcomes in natural soil settings. Ultimately, the researchers hope to predict how and why soil patches change in time, and how such patchiness alters the course of plant succession.
In addition to the presentation by Jones, biology graduate student Juliet Einsmann will present a poster on her work with Jones, Mou, and Mitchell on the "Below ground foraging in 10 plant species." Forestry graduate student Andrew Lister will present a poster on his work with Mou, Jones and Mitchell on "Spatial patterns of soil resources in a 40-year-old South Carolina slash pine forest."