## 2 Materials and Methods
### Measurement of Ecosystem CO\({}_{2}\) Flux and Soil Temperature and Moisture  
The seasonal pattern of ecosystem CO\({}_{2}\) flux, including net ecosystem CO\({}_{2}\) exchange (NEE), ecosystem respiration (Re), and soil respiration (Rs), was measured 2-8 times per month between 09:00 and 11:00 during the growing season (from July 2013 to September 2015) using a revised chamber system described by [PERSON] et al. [(23)]. The diurnal pattern of CO\({}_{2}\) flux (NEE, Re, and Rs) was measured between 07:00 and 18:00 on 17 August and 25 September 2013; 15 July, 14 August, and 29 September 2014; and 28 July and 15 August 2015. NEE and Re were measured by an infrared gas analyser (LI-840, LI-COR Inc., Lincoln, NE, USA) attached to a cubic transparent chamber (50 cm \(\times\) 50 cm \(\times\) 50 cm) placed over a square PVC base (50 cm \(\times\) 50 cm and 10 cm in height) that was inserted 7 cm into the soil in each plot. Two small fans in the top of the chamber mixed the air during the measurement, and a temperature probe was inserted into the chamber to determine the air temperature. A pump (6262-04, LI-COR Inc.) transported air from the chamber to the LI-840 to measure the CO\({}_{2}\) concentration. The chamber was lifted and vented after each NEE measurement. The chamber was then replaced on the base, covered by a lightproof cloth mantle, and the CO\({}_{2}\) flux (Re) was measured. Rs was measured using the same infrared gas analyser attached to a cylindrical chamber (20 cm in diameter and 20 cm in height) placed over a PVC base (20 cm in diameter and 10 cm in height) and inserted 7 cm into the soil in each plot. The plant in the PVC base was removed by hand a week prior the start of the experiment to exclude the effects of plant respiration and photosynthesis on the Rs measurement. A small fan in  
Figure 1: Location of the study site. the top of the chamber mixed the air during the measurement, and a temperature probe was inserted into the chamber to determine the air temperature. The same pump was used to pump air from the chamber to the LI-840 for measuring the CO\({}_{2}\) concentration. The data for measurements of NEE, Re, and Rs were logged into a computer using the LI-840 data-acquisition software. The CO\({}_{2}\) concentrations inside the chamber were recorded every second for 2.5 min after the chamber was placed on the base. Our measurement showed that change in air temperature inside the chamber was less than 0.2 \({}^{\circ}\)C during the 2.5 min measurement, and thus the change in air temperature could be neglected. The attenuation of PAR by the chamber was less than 5%. There was no fog on the chamber during the measurement. Only data for the last 120 s were used to calculate NEE, Re, and Rs according to the following equation [23; 24]:  
\[\mathrm{F}=\frac{\mathrm{V}\times\mathrm{P}_{\mathrm{av}}\times(1000-\mathrm{W }_{\mathrm{av}})}{\mathrm{R}\times\mathrm{S}\times(\mathrm{T}_{\mathrm{av}}+27 3)}\times\frac{\mathrm{dc}}{\mathrm{dt}} \tag{1}\]  
where F is the CO\({}_{2}\) flux components (NEE, Re, or Rs, \(\mathrm{\mu mol}\) m\({}^{-2}\) s\({}^{-1}\)), V is the volume of the chamber (m\({}^{3}\)), Pav is the average pressure (kPa) during measurement, Wav is the average water vapor mole fraction (mmol mol\({}^{-1}\)) during measurement, R is the ideal gas constant (8.314 J mol\({}^{-1}\) K\({}^{-1}\)), S is the surface area covered by the chamber (m\({}^{2}\)), Tav is the average temperature (\({}^{\circ}\)C) during measurement, and dc/dt is the slope of the fitted equation between CO\({}_{2}\) and time. The gross ecosystem productivity (GEP) was calculated as  
\[\mathrm{GEP}=-\mathrm{NEE}+\mathrm{Re} \tag{2}\]  
Soil temperature and volumetric moisture content at a depth of 0-10 cm were measured with time-domain transmission sensors (Acclima, Meridian, ID, USA) in each plot every 10 min during the experimental period with a Campbell Scientific CR1000 data logger (Campbell Scientific, Logan, UT, USA).