Nitrogen dynamics in arctic tundra soils of varying age: differential responses to fertilization and warming

Abstract

1In the northern foothills of the Brooks Range, Alaska, a series of glacial retreats has created a landscape that 2 varies widely in time since deglaciation (= soil age), from ~10k years to more than 2M years. Productivity of 3 the moist tundra that covers most of this landscape is generally N-limited, but varies widely, as do plant-species 4 composition and key soil properties such as pH. These differences might be altered in the future because of the 5 projected increase in N availability under a warmer climate. We hypothesized that future changes in 6 productivity and vegetation composition across soil ages might be mediated through changes in N availability. 7To test this hypothesis, we compared readily available-N (water-soluble ammonium, nitrate, and amino acids), 8 moderately-available N (soluble proteins), hydrolysable-N, and total-N pools across three tussock-tundra 9 landscapes with soil ages ranging from 11.5k to 300k years. We also compared the effects of long-term 10 fertilization and warming on these N pools for the two younger sites, in order to assess whether the impacts of 11 warming and increased N availability differ by soil age. 12Readily available N was largest at the oldest site, and amino acids (AA) accounted for 80-89 % of this 13 N. At the youngest site, however, inorganic N constituted the majority (80-97%) of total readily-available N.

Nitrate is an important nitrogen source for Arctic tundra plants

“…So far, long-term N addition experiments have revealed that elevated N inputs into Arctic tundra ecosystems change C accumulation and species diversity ( 5 , 8 , 9 ). Field observations and isotope labeling experiments provide evidence of how added N has altered the distribution, fate, biotic use, and losses of N in Arctic tundra ecosystems ( 10 – 15 ). These studies indicate that a better understanding of in situ N availability in Arctic ecosystems is important because C and N cycles are tightly coupled between the vegetation and soils, and elevated N loading can influence the Arctic’s C balance ( 5 , 16 ).…”

Can antibrowsing defense regulate the spread of woody vegetation in arctic tundra?

“…Experimental increases in soil temperature at Toolik Lake in northern Alaska caused a stimulation of N‐mineralization and increase in exchangeable ammonium of the organic horizon, (Nadelhoffer et al 1991), whereas there were only small and inconsistent changes in the soil C:N ratio and amino acids (Yano et al 2013). Experimental warming also increased the growth (Chapin et al 1995) and condensed tannin concentration (Graglia et al 2001) of B. nana subsp.…”

Arctic Plant Responses to Summer Climates and Flooding Events: A Study of Carbon and Nitrogen‐Related Larch Growth and Ecosystem Parameters in Northeastern Siberia

“…Nitrogen (N) availability is also a critical factor controlling vegetation productivity and composition in high‐latitude regions (Nasholm et al., 1998; Prager et al., 2020; Yano et al., 2013). While numerous studies have explored the relationship between N availability and vegetation growth in boreal forests and Arctic tundra (Fujiyoshi et al., 2019; Maes et al., 2019; Natali et al., 2012; Norby et al., 2019), few have focused on the boundary areas between these ecosystems.…”