Warming leads to more closed nitrogen cycling in nitrogen‐rich tropical forests.

Lie, Zhiyang; Huang, Wenjuan; Liu, Xujun; Zhou, Guoyi; Yan, Junhua; Li, Yuelin; Huang, Chumin; Wu, Ting; Fang, Xiong; Zhao, Mengdi; Liu, Shizhong; Chu, Guowei; Kadowaki, Kohmei; Pan, Xiaoping; Liu, Juxiu

Warming may have profound effects on nitrogen (N) cycling by changing plant N demand and underground N supply. However, large uncertainty exists regarding how warming affects the integrated N dynamic in tropical forests. We translocated model plant‐soil ecosystems from a high‐altitude site (600 m) to low‐altitude sites at 300 and 30 m to simulate warming by 1.0°C and 2.1°C, respectively, in tropical China. The effects of experimental warming on N components in plant, soil, leaching, and gas were studied over 6 years. Our results showed that foliar δ15N values and inorganic N (NH4‐N and NO3‐N) leaching were decreased under warming, with greater decreases under 2.1°C of warming than under 1.0°C of warming. The 2.1°C of warming enhanced plant growth, plant N uptake, N resorption, and fine root biomass, suggesting higher plant N demand. Soil total N concentrations, NO3‐N concentrations, microbial biomass N and arbuscular mycorrhizal fungal abundance were decreased under 2.1°C of warming, which probably restricted bioavailable N supply and arbuscular mycorrhizal contribution of N supply to plants. These changes in plants, soils and leaching indicated more closed N cycling under warming, the magnitude of which varied over time. The closed N cycling became pronounced during the first 3 years of warming where the sustained reductions in soil inorganic N could not meet plant N demand. Subsequently, the closed N cycling gradually mitigated, as observed by attenuated positive responses of plant growth and less negative responses of microbial biomass N to warming during the last 3 years. Overall, the more closed N cycling under warming could facilitate ecosystem N retention and affect production in these tropical forests, but these effects would be eventually mitigated with long‐term warming probably due to the restricted plant growth and microbial acclimation.

CHINA; TROPICAL forests; NITROGEN cycle; SOIL leaching; PLANT translocation; ACCLIMATIZATION (Plants); PLANT growth; MICROBIAL growth

Global Change Biology, 2021, Vol 27, Issue 3, p664

1354-1013

Academic Journal

10.1111/gcb.15432