Roots allow interactions between plants and their belowground environment. Such interactions are especially important in ecosystems where plant biomass is dominated by roots, such as the Arctic. In contrast, we are still lacking knowledge about roots and belowground processes in many ecological topics. These belowground processes are likely to be altered by climate change. Consequently, we need to know about basic root ecological patterns and processes before we can estimate possible effects of a changing environment on belowground processes and thus whole ecosystems. The aim of my thesis was to examine three of those basic root ecological patterns and processes: plant community composition, resource heterogeneity, and root contributions to nutrient cycling. I investigated plant species richness belowground and aboveground along an arctic elevation gradient with a great variation in vegetation types. Total plant species richness exceeded aboveground richness two-fold on average, but by as much as over seven-fold in some communities. My results indicate that conventional measurements of aboveground plant richness dramatically under-estimate actual richness in all vegetation types along an elevation gradient. Consequently, measuring total plant richness (belowground and aboveground richness) along environmental gradients should be considered in future plant community studies. Further, I examined spatial root heterogeneity at resolutions ranging from 1 to 300 mm² along an elevation gradient with great variation in vegetation types. The spatial heterogeneity of fine roots varied significantly with study resolution in all vegetation types. This result suggests that roots in different vegetation types respond to or generate very fine scales of spatial heterogeneity, including scales much smaller than those that have previously been examined. Consequently, resolutions as small as a few millimetres are relevant to studies of spatial root interactions and belowground processes. Finally, I investigated the potential input from roots and leaves to the N cycle during decomposition in contrasting vegetation types, forest and tundra. This allows examination of possible belowground plant effects on nutrient cycling of the climate change induced invasion of woody vegetation into herbaceous vegetation. The potential N input of roots and leaves was two-fold and seven-fold greater, respectively, in forest than tundra, indicating that plant-associated belowground and aboveground potential input to the N cycle in tundra is likely to be increased by the invasion of woody vegetation. In contrast, the lack of significant habitat and origin of substrate effects suggest that N contribution of roots and leaves during decomposition in tundra might not be altered by the invasion of woody vegetation. Collectively, my results suggest that roots should be included in considerations of potential plant contributions to differences between forest and tundra to the N cycle. Overall, the results of my thesis emphasize the importance of roots on several belowground ecological patterns and processes in the Arctic. Roots need to be included in considerations of plant community diversity, spatial soil and resource heterogeneity, and potential plant effects on the N cycle in general, and in the changing environment in the Arctic in particular.