Fig 1.
(a) Distribution of daily precipitation (mm) and dynamics in daily mean soil water content (%) at 10 cm depth during the growing season in 2016. The inset plot represents the average soil water content in 2016. (b, c, d) The mean soil water content detected at pre- (Pre-T), during- (Dur-T) and post- (Post-T) treatment. Early-D, Mid-D and Late-D mean early-, mid- and late-growing season extreme drought, respectively. The values in parentheses mean the reduced rainfall compared to the control of the same period. *: Significant differences between extreme drought (D) and ambient treatment at P≤0.05.
Fig 2.
Variations in the average of Fv/Fm of (a-c) Stipa grandis and (d-f) Leymus chinensis during pre-, during- and post- treatment of three drought treatment. The percentage at the top of the bar represents decreased values of treatments. Data are means±se.
Fig 3.
Seasonal variations in (a) net ecosystem CO2 exchange (NEE), (b) ecosystem respiration (Re) and (c) gross primary productivity (GPP) of the treatments and ambient plots in 2016’s growing season. Each inset plot represents the average NEE, Re and GPP in 2016. The colored rectangles in (c) represent corresponding time of the three drought treatments. Data are means±se.
Fig 4.
Variations in (a-c) average NEE, (d-e) Re and (g-i) GPP of pre-, during- and post-treatment of three drought treatment. Data are means±se.
Fig 5.
(a) Effects of timing of extreme drought on aboveground net primary productivity (ANPP, g m-2) in 2016. The (b) relative ANPP and (c) relative abundance of species in each treatment. Stipa, Leymus and others represent Stipa grandis, Leymus chinensis and other species, which were only occupied a small percentage in the typical steppe. Data are means±se.
Fig 6.
Relationships between soil temperature (ST,°C) and (a) NEE (c) Re (e) GPP, and soil water content (SWC, %) and (b) NEE (d) Re (f) GPP.
Fig 7.
Path diagram illustrates the effects of abiotic factors (ST and SWC) and biotic factor (sum the Fv/Fm of L. chinensis and S. grandis as the ecosystem photosynthetic performance) on gross primary productivity (GPP).
χ2 = 0.78, df = 1, P = 0.38, RMSEA = 0.00, AGFI = 0.92, CFI = 1.00, Significance codes mean: * P < 0.10, ** P < 0.05 and *** P < 0.001.