Experimentally increased nutrient availability at the permafrost thaw front selectively enhances biomass production of deep-rooting subarctic peatland species
Keuper, F., E. Dorrepaal, P.M. van Bodegom, R. van Logtestijn, G. Venhuizen, J. van Hal and R. Aerts. 2017.
Abstract
Climate warming increases nitrogen (N) mineralization in superficial soil layers (the
dominant rooting zone) of subarctic peatlands. Thawing and subsequent mineralization of permafrost increases plant-available N around the thaw-front. Because plant
production in these peatlands is N-limited, such changes may substantially affect net
primary production and species composition. We aimed to identify the potential
impact of increased N-availability due to permafrost thawing on subarctic peatland
plant production and species performance, relative to the impact of increased N-availability in superficial organic layers. Therefore, we investigated whether plant roots are
present at the thaw-front (45 cm depth) and whether N-uptake (15 N-tracer) at the
thaw-front occurs during maximum thaw-depth, coinciding with the end of the growing season. Moreover, we performed a unique 3-year belowground fertilization experiment with fully factorial combinations of deep- (thaw-front) and shallow-fertilization
(10 cm depth) and controls. We found that certain species are present with roots at
the thaw-front (Rubus chamaemorus) and have the capacity (R. chamaemorus, Eriopho-
rum vaginatum) for N-uptake from the thaw-front between autumn and spring when
aboveground tissue is largely senescent. In response to 3-year shallow-belowground
fertilization (S) both shallow- (Empetrum hermaphroditum) and deep-rooting species
increased aboveground biomass and N-content, but only deep-rooting species
responded positively to enhanced nutrient supply at the thaw-front (D). Moreover, the
effects of shallow-fertilization and thaw-front fertilization on aboveground biomass production of the deep-rooting species were similar in magnitude (S: 71%; D: 111%
increase compared to control) and additive (S D: 181% increase). Our results show
that plant-available N released from thawing permafrost can form a thus far overlooked
additional N-source for deep-rooting subarctic plant species and increase their biomass
production beyond the already established impact of warming-driven enhanced shallow
N-mineralization. This may result in shifts in plant community composition and may partially counteract the increased carbon losses from thawing permafrost.
Key Words
belowground nitrogen, climate change, Empetrum hermaphroditum, fertilization, frozen soil, permafrost thaw, root uptake, Rubus chamaemorus
