Abstract
AbstractGlobal change in the Arctic promotes deeper soil thaw and enhanced soil microbial activity, increasing nitrogen (N) and phosphorus (P) availability to plants and microbes in strongly nutrient‐limited ecosystems. This critical, positive climate feedback has been examined through fertilization experiments that describe short‐term (<10 yr) above‐ or belowground responses to combined NP additions, with evidence of enhanced shrub growth, nutrient availability, and soil organic matter decomposition. There has been less opportunity for long‐term comparisons of both above‐ and belowground responses with factorial N and P additions in different systems, despite broad awareness that ecosystem response can shift with time, and the potential for decoupled above‐ vs. belowground or N vs. P responses, currently and with further predicted global change. We examined the response of the plants, soil microbes, and soil nutrients, to factorial N and P additions in the moist acidic tundra (MAT; 26 yr of nutrient additions) and moist non‐acidic tundra (MNT; 16 yr). Aboveground, the MAT plant community continues to change as predicted by earlier studies: Functional groups responded independently to N and P, but NDVI‐biomass, especially of Betula nana, only increased with N addition. Unlike shorter‐term MNT studies, the MNT vegetation, which does not include B. nana, shows few new fertilization responses. Belowground responses were not predicted by aboveground responses in either MAT or MNT. In contrast to the N response aboveground, MAT microbial biomass responded positively and microbial phosphatase activity negatively to P additions, implying possible release from microbial P limitation. Critically, earlier published results of declines in soil total carbon (C) with combined NP addition in the MAT are not present in the long term. We make two conclusions: (1) Arctic ecosystems are not universally N‐limited but also exhibit complex responses to P alone or in combination with N; and (2) the presence or absence of key vegetation species can cascade from aboveground to belowground and restrict the extrapolation of responses of nutrient addition in a single arctic ecosystem to other arctic ecosystems, the short‐term to the long term, or aboveground to belowground.
Highlights
Arctic regions are warming more rapidly than other parts of the globe (Huang et al 2017) resulting in rapid ecological changes in arctic ecosystems (Post et al 2009)
The objectives of this study were fourfold: (1) to characterize the long-term response of nutrient amendments (N, P, and N and P (NP)) to arctic tundra in comparison to earlier studies; (2) to investigate similarities in response above- and belowground; (3) to compare the response in two common arctic tundra ecosystems; and (4) to understand whether these systems are responsive to P in
We had a four-part objective in this study: (1) to characterize the long-term response of factorial nutrient (N and P) amendments to arctic tundra in comparison to earlier studies; (2) to investigate similarities in response above- and belowground; (3) to compare the response in two common arctic tundra ecosystems; and (4) to understand whether these systems are responsive to P in addition to N
Summary
Arctic regions are warming more rapidly than other parts of the globe (Huang et al 2017) resulting in rapid ecological changes in arctic ecosystems (Post et al 2009). The long-term levels of nutrient additions are often unrealistic in terms of nutrient release with warming, these experiments have been extremely fruitful for characterizing responses to changing ecosystem nutrient limitations, and the effects of fertilization aboveground (Chapin et al 1995, Bret-Harte et al 2001, Campioli et al 2012), belowground (Jonasson et al 1999, Rinnan et al 2007, Deslippe et al 2011, Koyama et al 2013), and to a limited extent, above- and belowground combined (Chapin et al 1995, Gough et al 2002, Mack et al 2004, Rinnan et al 2007, Haugwitz et al 2011), are well described. Long-term fertilization experiments that more extensively explore above- and belowground responses are especially useful for helping us understand the whole-ecosystem response to changes in nutrient availability
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