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

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  • Published: 2020-11-16
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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.

Under the supervision of Prof. LIU Juxiu at South China Botanical Garden of Chinese Academy of Sciences, PhD student LIE Zhiyang at University of Chinese Academy of Sciences (institute: South China Botanical Garden, Chinese Academy of Sciences) translocated model plant‐soil ecosystems from a high‐altitude site (600 m) to low‐altitude sites at 300 m 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. The 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 depressed 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 the more closed N cycling would be eventually mitigated with long‐term warming probably due to the restricted plant growth and microbial acclimation. The study was published in Global Change Biology.