Combination of nitrogen and phosphorus fertilization enhance ecosystem carbon sequestration in a nitrogen-limited temperate plantation of Northern China

• Combined N and P addition increased AR and decreased HR in N-limited ecosystems.
• Combined N and P addition increased NPP and NEP in N-limited ecosystems.
• Simultaneous addition of both N and P promoted C storage in N-limited ecosystems.

Numerous studies have shown that nitrogen (N) addition can increase net ecosystem production (NEP) in N-limited ecosystems, but it is still not clear how increasing phosphorus (P) availability affects carbon sequestration by N-limited ecosystems. A 3-year field experiment was established in May 2010 to compare the control (no fertilization), N fertilized (5 g N m−2 yr−1), P fertilized (5 g P m−2 yr−1), and N + P fertilized (5 g N m−2 yr−1 and 5 g P m−2 yr−1) treatments in N-limited Pinus sylvestris plantations of the Saihanba Forestry Center located in Hebei Province in northern China, which is the largest area of plantations in China. Net primary production (NPP), soil respiration (SR) and its autotrophic and heterotrophic components, plant tissues carbon (C) and N concentrations, soil organic carbon (SOC) and soil total nitrogen (STN), microbial biomass and community composition and the soil pH were measured. Addition of N or P alone had no significant effect on autotrophic respiration (AR) or heterotrophic respiration (HR); however, when applied in combination, AR increased and HR decreased significantly. Moreover, while N addition increased NPP by 10.16% and P addition had no significant effect on NPP, combined N and P fertilization increased NPP by 21.97%. NEP was unchanged by the addition of P, but increased significantly in response to combined N and P fertilization (510.23 g C m−2 yr−1), nearly 50% higher than that observed in response to the addition of N (339.63 g C m−2 yr−1). Taken together, our results indicate that simultaneous addition of both N and P promoted C storage in N-limited ecosystems and that simultaneously increasing in N and P availability is an effective method of expanding the C sequestration capacity of N-limited plantations.