Soil phosphorus availability regulates ecosystem carbon dynamics during the growing season of a typical temperate grassland in inner Mongolia, China

Abstract

Human activities have resulted in increased phosphorus (P) deposition, potentially impacting the carbon (C) cycles of many ecosystems. However, the fate of the net ecosystem CO₂ exchange following phosphorus addition, which signifies the equilibrium between ecosystem C uptake and release, remains uncertain, and the underlying mechanisms involved are poorly understood. Here, an in-situ fertilization experiment (0–12.5 g P m⁻² yr⁻¹) was performed to assess ecosystem C-P interactions in a temperate grassland. The addition of P alleviated P limitation, thereby stimulating plant nutrient uptake, the leaf area index, and plant diversity, and resulting in an increase of 18.92–53.64 % in gross primary productivity via enhanced photosynthetic capacity. Phosphorus addition stimulated the allocation of photosynthate to belowground tissues, and enhanced the litter quantity and quality, with a decreased litter C: nitrogen (N) and C:P ratios. This would have a positive impact on the ecosystem C release. Because gross primary productivity was higher than ecosystem C release, the net ecosystem CO₂ exchange in the grassland was stimulated which led to the production of a net C sink over the growing season. These results highlight that soil P availability plays a critical role in regulating the trajectory of the ecosystem C cycle in temperate grassland.