Alleviation of phosphorus rather than nitrogen limitation driven by permafrost and landscape effects on Dahurian larch forests

Permafrost thaw is reshaping nutrient dynamics in boreal forests, but its impacts on tree nutrient limitation and functional strategies remain poorly understood. Clarifying these responses is crucial for predicting the response of boreal forests to climate change.

We investigated the stoichiometric and functional traits of Dahurian larch at the southern edge of the Eurasian permafrost zone. We compared uplands (active layer thickness, ALT >100 cm, dry) and lowland swamps (ALT <60 cm, wet) to examine variations in tree and soil nutrient status, and assessed the relative importance of climate and local soil factors in driving tree nutrient variations.

Our results showed that upland larches had higher phosphorus (P) and potassium (K) concentrations, lower carbon to phosphorus (C:P) and nitrogen to phosphorus (N:P) ratios, and similar N contents compared with lowland trees. Upland soils exhibited lower C and N contents but higher K content than swamps, whereas P levels did not differ significantly ( p  > 0.05). Climate and soil variables explained 34.2% and 26.6% of the variation in larch stoichiometry, respectively, and their interaction accounted for 4.4% of the variation. Upland larches with deeper ALT displayed more acquisitive functional traits, as they tended to have higher leaf P content, greater specific leaf area, and lower leaf dry matter content than in lowland swamps.

Our findings suggest that instead of N, deeper permafrost thaw and drier soil on uplands can increase the availability of P and K, promoting acquisitive strategies in upland larches. Our findings illustrate how permafrost and landscape factors alter nutrient limitation and boreal tree strategies in the rapidly changing climate.