Warming chambers stimulate early season growth of an arctic sedge: results of a minirhizotron field study.

We examined the effects of passive open-top warming chambers on Eriophorum vaginatum production near Toolik Lake, Alaska, USA. During the 2002 growing season, chamber warming was consistent with the magnitude and seasonality observed in recent decades throughout northwestern North America. Leaf-growth rates were higher in late May and early June; maximum growth rates in each leaf cohort occurred earlier and peak biomass was observed 20 days earlier within the chambers. Consequently, plants within the chambers maintained more live leaf biomass during the period of highest photosynthetically active radiation. Annual leaf production within the chambers (21+/-2 mg tiller) was not significantly different than under ambient conditions (17+/-2 mg tiller) (P=0.2256) despite higher early-season growth rates. Root growth began earlier; growth rates were higher in late May and early June, and maximum growth rates occurred earlier within the chambers. Therefore, plants within the chambers maintained greater root biomass during what earlier studies have identified as a period of relatively high nutrient availability. Annual root production within the chambers (191+/-42 g m-2) was not significantly different than under ambient conditions (119+/-48 g m-2) (P=0.1979), although there was a trend toward higher production within the chambers. The tendency toward higher root production within the chambers is consistent with previous laboratory experiments and with the predictions of biomass allocation theory.