Effects of warming on annual production and nutrient‐use efficiency of aquatic mosses in a high Arctic lake

Abstract

1. Primary production in Arctic and Antarctic lakes is typically dominated by benthic photosynthetic organisms. These include aquatic mosses that can be very abundant although they must be able to tolerate extreme seasonal climatic variation in irradiance and temperature. Climate change is expected to cause increased nutrient run-off and to prolong ice and snow cover on Arctic lakes. 2. Despite the substantial role that aquatic mosses play in Arctic and Antarctic lakes, our study is the first of its kind to study the in situ growth and nutrient-use efficiency of an Arctic aquatic moss, Drepanocladus trifarius, and how the net production of this species is coupled with a range of climatic factors undergoing change. Here, we verify the use of growth segments as a technique to record historic growth. We then used the method to reconstruct the growth of D. trifarius by comparing in situ measured growth with that determined from growth segments after one year's growth in a high Arctic lake. Finally, we determined nutrient-use efficiency, resorption efficiency and resorption proficiency by measuring the tissue nutrient content in different annual growth segments. 3. The observed annual mean production of D. trifarius was about 2-3 mg DW shoot À1 year À1 expressed as biomass increase and 10-30 mm shoot À1 year À1 expressed as length increase, while the age of most shoots was 7-10 years. About 90% of the variation in annual net production was explained by between-year variability in snow prolongation and net radiation in June. 4. The low tissue-N (1.05%DW) and tissue-P (0.081%DW) contents found in D. trifarius suggest that its growth in Lake Sommerfuglesø is limited by the availability of N and P during summer when the availability of light is sufficient for extensive growth of this species. P resorption was 43% in D. trifarius, whereas no N resorption was recorded, and P proficiency ranged between 0.02 and 0.04% DW, which is comparable to the concentrations measured in other plant types under P limitation, suggesting that P resorption is an advantageous trait for the existence of moss in this oligotrophic environment. 5. Our results suggest that predicted prolongation of snow cover and consequent decrease in net radiation in lakes will decrease annual net primary production. Our results also suggest that species able to exploit elevated nutrient contents have an advantage in more nutrient-rich lakes in future and indicate that dominance patterns may change. We therefore foresee that climate change will have dramatic effects on the annual net production of mosses and thus whole lake primary production in Lake Sommerfuglesø and similar lake types dominated by mosses in the high Arctic.

Mineral nitrogen and phosphorus pools affected by water table lowering and warming in a boreal forested peatland

“…Tree C:N ratio also decreased with deeper WT position, indicating that the larger TIN pools in the soils at drier sites resulted in higher N content in the overstory biomass. Our findings corroborate with those of Choi et al () and Riis et al () for strong relationships between soil TIN and vascular vegetation C:N ratios. Moss TN and C:N values also changed slightly in response to warming and short‐term drainage (very little moss was present at the longer term drained sites), but these shifts were limited.…”

“…The magnitudes of the warming‐induced increases in extractable TIN, NO 3 , and NH 4 pools were the highest at the drained hummocks at which the highest warming‐induced productivity has been reported (Munir et al, ) and in fact nutrient pools were related to the reported productivity (ANOVA, F 1, 23 = 41.69, p < .001, R 2 = .39). This study, combined with changes in carbon exchange measured at the same site, demonstrates that warming very likely increases nutrient concentrations directly by enhancing decomposition and subsequent mineralization of peat and indirectly by accelerating nutrient cycling between the peat and vegetation as reported by previous studies (Bubier, Moore, & Bledzki, ; McGrath et al, ; Riis, Christoffersen, & Baattrup‐Pedersen, ).…”

Eelgrass Zostera marina in subarctic Greenland: dense meadows with slow biomass turnover in cold waters

“…Hence, the ability of eelgrass to store carbon reserves in rhizomes during the summer period of abundant light availability is critical to meet metabolic demands during the dark winter months (Zimmerman et al 1989), and probably accounts for the fact that eelgrass indeed can survive long periods of darkness under sea ice (McRoy 1969). Prolonged periods of winter darkness may, however, affect eelgrass growth negatively, as suggested by the inverse relationship between annual net production and the duration of ice cover in arctic freshwater mosses and marine macroalgae (Krause-Jensen et al 2012, Riis et al 2014.…”

Mosses in High-Arctic lakes: in situ measurements of annual primary production and decomposition

“…Thus, only few direct quantitative measurements of moss primary production have been reported (Priddle 1980;Finlay and Bowden 1994), and these were reports on short-term measurements of primary production rates during summer without any attempt to scale up to annual production. Annual primary production of Arctic lake moss vegetation has been estimated using annual growth segments (Sand-Jensen et al 1999;Hawes et al 2002), also but this method relies on morphological distinct annual growth segments developing in certain moss species (Riis and Sand-Jensen 1997;Riis et al 2014).…”

“…Previous studies from Antarctic lakes show that moss production is strongly influenced by underwater irradiance (Priddle 1980), and Riis et al (2014) showed that annual production of Drepanocladus trifarirus [Pseudocalliergon trifarium (F. Weber & D. Mohr) Loeske] growing in a High-Arctic Greenland lake was most strongly influenced by the prolongation of snow cover in summer. Most high-latitude lakes are oligotrophic, and primary production can therefore also be nutrient-limited under saturating light and inorganic carbon conditions.…”