Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic

Abstract

Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.

Biofilm Growth in Two Streams Draining Mountainous Permafrost Catchments in NE Greenland

“…The variability in both chl a and TC on the control disks responded positively to this nutrient gradient, as evidenced by the model selection. This is in agreement with other high-latitude studies that found N as a key constraint for biofilm metabolism found in Swedish streams by Myrstener et al (2018) and the significance of algal growth in Icelandic streams recorded by Friberg et al (2009). Our study expands these previous results to the high-Arctic region.…”

“…Here, we aimed to evaluate how nutrient availability influences biofilm accrual in streams draining mountainous permafrost landscapes with contrasting geomorphological features in the High Arctic. We hypothesize that N stream concentration is one of the main drivers controlling biofilm accrual due to the low N concentrations usually found in high‐Arctic streams and following what has previously been found for the low‐Arctic region (Myrstener et al, 2018).…”

“…Most of the available data on nutrient limitation are for low‐Arctic ecosystems, although high‐Arctic region (located above 70°N on the east coast of Greenland) is distinct in various environmental, geomorphological, and biological characteristics (Olson et al, 2001). The combination of N and P additions has been shown to have the highest effects on biofilm productivity in worldwide freshwaters (Beck et al, 2017; Elser et al, 2007) and across the Arctic (Docherty, Riis, Hannah, et al, 2018; Myrstener et al, 2018; Peterson et al, 1983; Tank & Dodds, 2003). These studies have also usually found a higher effect of N than P when added alone (but see Peterson et al, 1983; Tank & Dodds, 2003).…”

Linking permafrost thaw to shifting biogeochemistry and food web resources in an arctic river

“…Watershed‐scale changes in sources of C and nutrients entering surface waters are likely to have important consequences for biofilms that serve as the primary energy base for arctic river food webs (Huryn et al, ; Myrstener et al, ; Peterson, Bahr, & Kling, ). Biofilms are important sites for metabolic and biogeochemical processes in rivers and streams (Battin, Besemer, Bengtsson, Romani, & Packmann, ), and the ultra‐oligotrophic nature of arctic rivers renders them particularly sensitive to changes in nutrient availability (Bowden, Peterson, Finlay, & Tucker, ; Kendrick & Huryn, ).…”

Changes in coupled carbon‒nitrogen dynamics in a tundra ecosystem predate post-1950 regional warming

“…Recent warming at high latitudes has resulted in deepening of the seasonal active layer and permafrost thawing with an associated increase in mineralisation of organic matter and release of CO 2 and CH 4 to the atmosphere 4 . Such warming also alters soil microbial processes, which releases nutrients (especially N 9 ) that stimulate both terrestrial 10 and aquatic productivity 11 , with potentially important consequences for regional rates of C storage.…”