Divergent Responses of Autotrophic and Heterotrophic Respiration to Nitrogen Application in a Pinus tabulaeformis Plantation

Abstract

Nitrogen (N) fertilization, as a plantation management technique, plays a vital role in maintaining plantation healthy development and affecting CO₂ emissions. However, the effect of N fertilization on soil respiration (Rs) in the planted forests remains debated. Distinguishing autotrophic respiration (Ra) and heterotrophic respiration (Rh) will help better understand the response of Rs to N fertilization. A 5-year field experiment with four N levels (0, 5, 10, and 20 g N m⁻² a⁻¹) was conducted in a Pinus tabulaeformis plantation in China to explore the responses of Rs and its components to N management. In the fourth and fifth years after N application, as the duration and level of N fertilization increased, its effect on Ra changed from inhibition (−28.9%) to promotion (42.5%), while the effect on Rh shifted from promotion (31.6%) to inhibition (−2.9%). This resulted in an average increase of 12.5% in Rs. This effect was due to a significant increase in fine root biomass and a decrease in microbial biomass under N fertilization. The positive effect of increased Ra due to the rise in fine root biomass on Rs outweighed the negative effect of reduced Rh caused by the decline in microbial biomass. N fertilization reduced the contribution of Rh to Rs by 5%–9%. Dissolved organic carbon and nitrogen, soil moisture, and soil temperature were key factors affecting Rs. Our findings indicate that N fertilization application promoted root growth while inhibiting soil microbial activity, ultimately promoting the growth of artificial forests and reducing the decomposition of organic matter.