Plant competition underground

Authors: Casper, BB, RB Jackson

Belowground competition occurs when plants decrease the growth, survival or fecundity of neighbors by reducing available soil resources. Belowground competition can be stronger than aboveground competition and involve many more neighbors. Physiological ecologists and population or community ecologists have traditionally studied belowground competition from different perspectives. Physiologically-based studies often measure resource uptake without determining the integrated consequences for plant performance, while higher level studies examine plant performance but fail to identify the resource intermediary or mechanism. Belowground competitive ability is correlated with such attributes as root density, surface area, and plasticity in root growth or in the properties of enzymes involved in nutrient uptake. Unlike competition for light, where larger plants have a disproportionate advantage by shading smaller ones, competition for soil resources is apparently symmetric. Belowground competition often decreases with increases in nutrient levels, but it is premature to generalize about the relative importance of above- and belowground competition across resource gradients. Although shoot and root competition are often assumed to have additive effects on plant growth, some studies provide evidence to the contrary, and potential interactions between the two forms of competition should be considered in future investigations. Other research recommendations include the simultaneous study of root and shoot gaps, since their closures may not occur simultaneously, and improved estimates of the belowground neighborhood. Only by combining the tools and perspectives from physiological ecology and population and community biology can we fully understand how soil characteristics, neighborhood structure, and global climate change influence or are influenced by plant competition belowground.
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