Aspen Bibliography


Root dynamics and spatial pattern in prairie and forest

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Abstract. The invasion of grasslands by woody plants is related to increased hetero- geneity in soil resources. At the northern edge of the Great Plains, the amount of hetero- geneity in soils reciprocally transplanted between prairie and aspen forest can change within a single growing season, suggesting that heterogeneity is strongly influenced by vegetation. Here we examine several mechanisms by which fine roots could influence soil resource heterogeneity. We measured the total length, spatial pattern, and turnover of fine roots in both prairie and forest using minirhizotrons installed horizontally 10 cm below the soil surface. The total length of fine roots in forest (0.7 cm/cm2) was significantly less than that in prairie (1.4 cm/cm2), which may contribute to more spatially variable resource uptake in forest. The coefficient of variation of root length was significantly higher in forest (92%) than in prairie (65%). Semivariograms showed that the scale of patchiness of root length was significantly greater in forest (8–12 cm) than in prairie (3–4 cm). Lastly, the rate of fine root turnover was significantly higher in forest (49%) than in prairie (20%). Turnover may contribute to spatial variability because a system with high rates of root turnover would appear to have high spatial variability at any given time. Root mortality was also signifi- cantly higher in forest than prairie. In summary, many aspects of root distributions and dynamics were consistent with relatively high heterogeneity in forest soil resources. The greater total root length in prairie may account for the significantly higher intensity of root competition in grasslands than forests and contribute to the exclusion of woody plants from prairies. Trees may be able to overcome this resistance by both causing and benefiting from higher levels and scales of soil resource heterogeneity.