Nitric oxide (NO) is a major contributor to atmospheric pollution and forest soil is an important source of NO emission. However, global forest soil NO emission existed great uncertainties by the reason of the paucity in high-frequency NO emission measurements (Fig 1). During the period of augmented nitrogen deposition, forest soil NO emission has been ignored in the past few decades in Northeast China.

To quantify the NO emission from forest soils and to find out its controlling factors, Prof. Fang Yunting’s team from the Institute of Applied Ecology has been conducting a long-term and automated soil NO measurement experiment at Qingyuan Forest CERN, Northeast China.

They found the mean annual soil NO emission was 0.42 ± 0.04 kg N ha^-1 from the study forest (Fig 2). Soil temperature regulated NO emission with a significant exponential relationship, and explained more than 70% variation of daily NO emission with the apparent temperature sensitivity (Q₁₀) of 3.67 (Fig 3). NO emission was also promoted by soil moisture (WFPS) after longer drought in the growing seasons (Fig 2). By the compilation of four empirical models (Temperature model, WFPS model, Q₁₀=2 theoretical model and the interactive model of temperature and WFPS), they demonstrated temperature was most important factor in the daily emission scale (RMSE: Temp-WFPS model < Temp model < WFPS model < Q₁₀=2 model) (Fig 4).

With the global climate change, there has been a great uncertainty of gaseous nitrogen (N) in forest ecosystems. The results from this study gave a better mechanistic understanding of forest soil NO emission in Northeast China, which can help develop more accurate N biogeochemical models and improve the accuracy of soil NO emission in global estimation.

The study entitled "A strong temperature dependence of soil nitric oxide emission from a temperate forest in Northeast China" has been published in Agricultural and Forest Meteorology. The study was financially supported by the Research and Development Project of Scientific Instruments and Equipment of Chinese academy of sciences, Liaoning Vitalization Talents Program, K.C.Wong Education Foundation, and the National Natural Science Foundation of China.

Fig.1 Global site distribution for soil NO flux measurement in forest ecosystems (n = 59)(Image by HUANG Kai).

Fig.2 Seasonal variations of temperature at the 5 cm depth of the mineral soil and air temperature (a), daily precipitation and soil water-filled pore space (WFPS) (b), daily mean NO flux (c), soil available ammonium and nitrate contents (d) in the 0–10 cm soil. The shadow areas represent the growing seasons (April 15 to October 15 each year)(Image by HUANG Kai).

Fig.3 Correlations of daily NO fluxes with daily mean soil temperature at 5 cm depth during the study. Blue and black points represent the measured data in 2019 (a) and 2020 (b), and mean NO fluxes and soil temperature binned at intervals of 0.5 ℃ (c). Blue and black lines show the exponential fitting relationships between NO fluxes and soil temperatures, and the red lines represent the curves of temperature sensitivity (Q10) at 2(Image by HUANG Kai).

Fig.4 Model and observed values of daily NO flux during the study period. The gray, blue, and black line represent modeled NO flux using soil temperature, WFPS, and Temp-WFPS, respectively, the red line represents modeled NO flux predicted using the Q₁₀ value of 2. The shaded areas indicate the growing seasons (April 15 to October 15 each year)(Image by HUANG Kai). 

Contact 

YUE Qian

Institute of Applied Ecology, Chinese Academy of Sciences 

Tel: 86-24-83970324 

E-mail: yueqian@iae.ac.cn  

Web: http://english.iae.cas.cn