Shifts in root dynamics along a hillslope in a mixed, mesic temperate forest

Aims Complex topography, a common feature of forested areas, generates unique environmental gradients that may shape root dynamics in unexpected ways. Nevertheless, belowground studies rarely capture the environmental gradients imposed by complex topography, such as those found along hillslopes. This begs the question: how much information is lost when complex topography is ignored? Hillslope is a common aspect of complex topography with landscape features that impact water flow, sediment transfer, and water and nutrient storage. We hypothesized that soil water content would have a nonlinear impact on fine-root production, mortality, standing crop, and turnover. Specifically, we expected increased mortality and decreased production, root standing crop, and turnover at the driest and wettest regions of the hillslope. Methods Using minirhizotron observations from 150 tubes located at 50 sites strategically placed at different hillslope positions across a first-order catchment, we examined how position along a hillslope impacts fine root dynamics. Results Contrary to our hypotheses, we found no significant hillslope effects on fine root tip production or mortality. Root tip turnover, however, was higher at drier than wetter regions of the hillslope. Additionally, fine root standing crop length was higher in wetter topographic regions. Conclusions Considering fine root tip turnover and length standing crop in combination with previous research on fine root lifespan suggest two distinct strategies of trees in root deployment along a hillslope: temporal avoidance in drier regions of a landscape (midslope planar and ridgetops) and extended survival of roots in wetter, deeper-soil regions like valley floor and swales.

Automated summary

Contrary to our hypotheses, the study found no significant hillslope effects on fine root tip production or mortality. However, root tip turnover was higher at drier regions of the hillslope, and fine root standing crop length was higher in wetter topographic regions.