P biogeochemistry in boreal forests and tundra

Information from Reiner Giesler:

Phosphorus (P) is an important nutrient in boreal forests and tundra ecosystems that may co-limit or in some cases limits primary production.
The availability of P is often driven by abiotic factors such as soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminum (Al) or iron (Fe), however, biotic factors may also play an important role. Here I will discuss the role of vegetation, elevation, herbivory and abiotic processes that affects P across different tundra vegetation types in northern Scandinavia and Alaska.

I will also present some recent results from the boreal forest that illustrates the complexity in interpreting the role of P limiting forest productivity. Our results from the Scandinavian tundra clearly suggest differences in P forms between the two most dominant vegetation types, heath and meadow.
For instance, the labile fractions of P were less abundant in meadow sites compared to heath sites. These differences are also expressed in plant N:P ratios and in the response of heterotrophic microorganism to N and P additions; both indicating a tendency towards decreased P-availability in meadow vegetation. Increasing elevation and thus declining temperature, may also affect P. Temperature can affect P availability directly via effects on microbial mineralization and soil process rates but also indirectly by influencing factors that affect soil processes such as plant and microbial community composition. Very recent results do suggest that the transition from tundra to forest is a key factor explaining previous results on elevational differences in more labile P forms. Herbivores are also known to impact nutrient availability and cycling, and can have a strong influence on tundra ecosystems.

Such effects may, however, differ across natural environmental fertility gradients. Here we show that long-term effects of reindeer can have a positive effect on soil N in the more nutrient-poor heath sites and a negative effect on soil P in the more nutrient-rich meadow type sites, suggesting that reindeer could drive the vegetation toward P-limitation. Our results indicate that predicted temperature increases in the arctic over the next century may influence P availability more strongly than N, with consequences for key ecosystem processes limited by P, such as primary productivity. The interactive effects of climate change and biotic factors such as herbivory or abiotic factors such as P sorption may on the other hand counteract climate driven effects on nutrient availability and need to be considered in future predictions of nutrient dynamics in tundra ecosystems.

All are most welcome to attend via Zoom: https://slu-se.zoom.us/j/68591669824