Phosphorus availability and microbial respiration across different tundra vegetation types

Phosphorus (P) is an important nutrient in tundra ecosystems that co-limits or in some cases limits primary production. The availability of P is largely driven by soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminium (Al) or iron (Fe). We tested how vegetation and soil properties relate to P availability across different tundra vegetation types. The different soil P fractions in the organic horizon were measured and plant foliar nitrogen (N) to P ratio and a plant bioassay was used as indicators of plant nutrient status. Microbial bioassays were used to study microbial respiration kinetics and in response to carbon, N, and P amendments. The distribution of P fractions differed significantly across vegetation types; labile fractions of P were less abundant in meadow sites compared to heath sites. Calcium-phosphates seemed to be an important P-fraction in meadows, but were only found in lower concentrations in the heath. There were only small differences in NaOH-extractable P between the vegetation types and this correlated with the distribution of oxalate-extractable Al. Plant N:P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. The microbial bioassay suggests that the heterotrophic microbial community is C-limited with N as a secondary limiting nutrient although there were indications that microbial P availability was lower in the meadow sites. Overall, we suggest that the observed variations in soil P across vegetation types are affecting both plant and microbial function although the differences seem to be relatively small.