Legacy effects of nitrogen and phosphorus additions on vegetation and carbon stocks of upland heaths

Abstract

‐ Soil carbon (C) pools and plant community composition are regulated by nitrogen (N) and phosphorus (P) availability. Atmospheric N deposition impacts ecosystem C storage, but the direction of response varies between systems. Phosphorus limitation may constrain C storage response to N; hence P application to increase plant productivity and thus C sequestration has been suggested. ‐ We revisited a 23‐year‐old field experiment where N and P were applied to upland heath, a widespread habitat supporting large soil C stocks. Ten years after the last nutrient application we quantified long‐term changes in vegetation composition and in soil and vegetation C and P stocks. ‐ Nitrogen addition, particularly when combined with P, strongly influenced vegetation composition, favouring grasses over Calluna vulgaris , and led to a reduction in vegetation C stocks. However, soil C stocks did not respond to nutrient treatments. We found 40% of the added P had accumulated in the soil. ‐ This study shows persistent effects of N and N+P on vegetation composition, whereas effects of P alone are small and show recovery. We found no indication that P application could mitigate the effects of N on vegetation or increase C sequestration in this system.