Impact of the effective precipitation frequency on soil water content and annual Bowen ratio (β).

<p>The effective precipitation frequency was measured as the number of days with a precipitation amount ≥ 1.5 mm during the dry season, and soil water content was measured at 5 cm (Sw_5 cm) during the dry season.</p

Seasonal and interannual variation of environmental and physiological factors.

<p>Factors include (A) monthly mean air temperature (T_a), (B) monthly mean soil water content at 5, 20, and 50 cm (Sw_5 cm, Sw_20 cm, and Sw_50 cm) and monthly precipitation amount (P), and (C) monthly mean canopy conductance (g_c) and 8-day timescale enhanced vegetation index (EVI).</p

Long-term trends of the Bowen ratio (β), soil water content, and effective precipitation frequency.

<p>Long-term trends were marginally significant for (A) the annual Bowen ratio (p = 0.06), and significant for (B) the soil water content at 5 cm (Sw_5 cm; dashed line, p<0.001) and the effective precipitation frequency (solid line, p<0.001) during the dry season.</p

Relationships between the annual Bowen ratio (β) and dry season soil water content.

<p>Dry season (July-October) soil water content was measured at (A) 5 cm (Sw_5 cm), (B) 20 cm (Sw_20 cm), and (C) 50 cm (Sw_50 cm).</p

Interannual variation of annual net radiation (Rn, MJ m⁻² yr⁻¹), air temperature (T_a, °C), vapor pressure deficit (VPD, kPa), soil water content at 5 cm, 20 cm, and 50 cm (Sw_5 cm, Sw_20 cm, and Sw_50 cm (m³ m⁻³)), enhanced vegetation index (EVI), total precipitation amount (P, mm), latent heat flux (LE, MJ m⁻² yr⁻¹), sensible heat flux (H, MJ m⁻² yr⁻¹), and the Bowen ratio (β) during 2003–2012 at the Qianyanzhou site.

<p>SD is standard deviation. CV is the coefficient of variation (ratio of standard deviation to mean value).</p

The seasonal and interannual variation in the cumulative daily fluxes.

<p>Fluxes include net ecosystem production (NEP) (gray dots), the cumulative daily ecosystem respiration (RE) (green cross), and the cumulative daily gross ecosystem production (GEP) (blue open circle). The 10-day running mean of the NEP (red line) for Yucheng (YC) (a) and Luancheng (LC) (b) on the North China Plain is also presented.</p

The dependence of annual carbon sequestation on meteorological and biotic variables.

<p>The dependence of the net ecosystem production (NEP) and the net biome production (NBP) on (a) the mean annual air temperature (MAT) and (b) the total C uptake period (CUP) in Yucheng (YC) and Luancheng (LC) and (c) the dependence of the difference between the NBP and the NEP (△C), i.e., the annual crop yield, on the CUP in YC and LC on the North China Plain.</p

The interannual variations in annual and seasonal NEP and NBP.

<p>Interannual variations in annual NEP, annual NBP, seasonal accumulative NEP and NBP during winter wheat growing season, seasonal accumulative NEP and NBP during summer maize growing season in Yucheng (YC) (a) and Luancheng (LC) (b) on the North China Plain are presented.</p

The relationship between the mean annual air temperature (MAT) and the net ecosystem production (NEP).

<p>The data was collected from literature and the dots represent annual NEP at the different sites. The solid line is the regression line, and the dotted line is the 95% band.</p

The relationships between the CUP and the start date of the CUP (CUP_start-date).

<p>The relationships between the CUP of (a) winter wheat, (b) summer maize, (c) the whole year and the start date of the CUP (CUP_start-date) on the North China Plain. CUP is the abbreviation of C uptake period. The start date of the CUP represents the beginning of the CUP. The solid line is the regression line.</p