Climate and species affect fine root production with long-term fertilization in acidic tussock tundra near Toolik Lake, Alaska

Abstract

Long-term fertilization of acidic tussock tundra has led to changes in plant species composition, increases in aboveground production and biomass and substantial losses of soil organic carbon (SOC). Root litter is an important input to SOC pools, though little is known about fine root demography in tussock tundra. In this study, we examined the response of fine root production and live standing fine root biomass to short-and long-term fertilization, as changes in fine root demography may contribute to observed declines in SOC. Live standing fine root biomass increased with long-term fertilization, while fine root production declined, reflecting replacement of the annual fine root system of Eriophorum vaginatum, with the longlived fine roots of Betula nana. Fine root production increased in fertilized plots during an unusually warm growing season, but remained unchanged in control plots, consistent with observations that B. nana shows a positive response to climate warming. Calculations based on a few simple assumptions suggest changes in fine root demography with long-term fertilization and species replacement could account for between 20 and 39% of observed declines in SOC stocks.

Different Root and Shoot Responses to Mowing and Fertility in Native and Invaded Grassland

“…Under conditions where plants allocate more resources above-ground under high nutrient availability, roots may respond to increased nutrient supply by absorbing and translocating more N, rather than by increasing growth (Moar and Wilson, 2006). Although changes in root length in our study may not be directly comparable to changes in root biomass, our findings are broadly consistent with previous work showing increasing aboveground as well as fine root biomass in response to fertilization in the Arctic (Chapin et al, 1995;Nadelhoffer et al, 2002;Mack et al, 2004;Sullivan et al, 2007;Gough et al, 2012). In addition to roots, rhizomes may also respond to changes in nutrient availability (Jónsdóttir and Watson, 1997), but no rhizomes were encountered in our images.…”

“…Some findings from tundra ecosystems showed increased fine root production in response to fertilization (Nadelhoffer et al, 2002;Mack et al, 2004;, while others found fertilization resulting in an increase in fine root standing crop but reduced root production (Sullivan et al, 2007). However, despite evidence that plants in high-latitude ecosystems allocate a large proportion of fixed C to roots (Shaver and Billings, 1975;Mokany et al, 2006), little is known about the collective response of above-and below-ground vegetative components to increased nutrient supply.…”

Seasonal patterns of soil nitrogen availability in moist acidic tundra

“…Soils from both sites have a well-developed organic layer of approximately 10 cm depth, underlain by a silty mineral layer, and an active layer (the layer of soil above permafrost which thaws each summer) of <50 cm. Rooting depth typically follows the thawed soil layer downward over the growing season (Chapin et al 1979), but even by the end of the growing season, >75% of root biomass for E. vaginatum (Chapin et al 1979) and the moist acidic tundra community (Sullivan et al 2007) is found within the surface 20 cm of the soil. Soils are acidic (Toolik average pH 4.3, Imnavait pH 4.4), with high soil moisture (approximately 400% dry mass soil) and a total N content of about 1% (Toolik: organic layer mean C is 43% and mean N is 1.2%; Imnavait: organic layer mean C is 45% and mean N is 0.8%).…”

Soil bacterial community and functional shifts in response to altered snowpack in moist acidic tundra of northern Alaska

“…Xylans in particular are common in woody plant tissues (Timell, 1967). The observed decrease in these genes in Deep snowpack suggests bacterial preference of readily available substrates, such as microbial biomass or root exudates Sullivan et al, 2007Sullivan et al, , 2008. Production of these substrates may have been stimulated by increased soil temperatures and NPP predicted under a climate change scenario and may require less energetic investment in exo-enzyme production (Schimel and Weintraub, 2003).…”