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Fine root response to soil resource heterogeneity differs between grassland and forest

Pinno, B. D. and S. D.Wilson. 2013. Plant Ecology

Abstract

Soil resource heterogeneity has clear effects on plant root development and overall plant performance. Here we test whether contrasting vege- tation types have similar or different responses to soil patches of differing resource availability. We exam- ined the fine root responses of grassland and forest vegetation at the northern edge of the Great Plains to transplanted patches of resource-poor and resource- rich soils, using rhizotron imaging. Every aspect of measured root behavior, including root length, pro- duction, mortality, turnover, variability and size distribution, varied significantly between patch types, and most aspects also varied between vegetation types. Most importantly, differential responses to patches between grassland and forest were shown by signif- icant interactions between patch type and vegetation for two response variables. First, root length variabil- ity was significantly lower in resource-rich compared to resource-poor patches in forest but not grassland. Second, the proportion of very fine roots was signif- icantly greater in resource-rich than resource-poor patches in forests but not grassland. Thus, compared to grassland, forest more fully occupied resource-rich patches relative to resource-poor patches by allocating more growth to very fine roots. We report the first example of significant differences between vegetation types (grassland and forest) in root responses to soil resource heterogeneity measured in a field experiment. The relatively high ability of forest roots to more fully occupy resource-rich patches is consistent with the global expansion of woody vegetation and associated increases in soil heterogeneity.

Key Words

Fine roots Forest-grassland interface Rhizotron imaging Soil heterogeneity Soil resource availability Woody expansion