Fine root production and nutrient content in wet and moist arctic tundras as influenced by chronic fertilization

We used ingrowth cores to estimate fine root production in organic soils of wet sedge and moist tundra ecosystems near Toolik Lake on Alaska's North Slope. Root-free soil cores contained in nylon mesh tubes (5 cm diameter, 20–30 cm long) were placed in control and chronically fertilized (N plus P) plots in mid-August 1994 and were retrieved 1 year later. Estimated fine root production in control plots was 75 g m−2 year−1 in wet sedge and 56 g m−2 year−1 in moist tussock tundra. Fine root production in fertilized plots was 85 g m−2 year−1 in wet sedge and 67 g m−2 year−1 in moist tussock tundra. Although our estimates of fine root production were higher on fertilized than control plots, differences were not statistically significant within either tundra type. Comparisons between our estimates of fine root production and other estimates of aboveground (plus rhizome) production on the same (wet sedge tundra) or similar (moist tussock tundra) plots suggest that fine root production was about one-third of total net primary production (NPP) under non-fertilized conditions and about one-fifth of total NPP under chronic fertilization. Fine root N and P concentrations increased with fertilization in both tundra types, but P concentrations increased more than N concentrations in wet sedge tundra, whereas relative increases in N and P concentrations in moist tundra roots were similar. These data are consistent with other studies suggesting that NPP in wet sedge tundra is often P limited and that co-limitation by N and P is more important in moist tussock tundra.