Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP), ecosystem respiration (Reco), and their response functions. Here, we studied the variations in NEP and Reco in a grassland dominated by a perennial warm-season C4 grass, Zoysia japonica. We used the chamber method to measure NEP and Reco from August to September 2007. Biomass and leaf area index (LAI) were also measured to observe their effects on NEP and Reco. Diurnal variations in NEP and Reco were predicted well by light intensity (PPFD) and by soil temperature, respectively. Maximum NEP (NEPmax) values on days of year 221, 233, 247, and 262, were 2. 44, 2. 55, 3. 90, and 4. 17 μmol m-2 s-1, respectively. Throughout the growing period, the apparent quantum yield (α) increased with increasing NEPmax that ranged from 0. 0154 to 0. 0515, and NEP responded to the soil temperature changes by 44% and Reco changes by 48%, and Reco responded from 88 to 94% with the soil temperature diurnally. NEP's light response and Reco's temperature response were affected by soil water content; more than 27% of the variation in NEP and 67% of the variation in Reco could be explained by this parameter. NEP was strongly correlated with biomass and LAI, but Reco was not, because environmental variables affected Reco more strongly than growth parameters. Using the light response of NEP, the temperature response of Reco, and meteorological data, daily NEP and Reco were estimated at 0. 67, 0. 81, 1. 17, and 1. 56 g C m-2, and at 2. 88, 2. 50, 3. 51, and 3. 04 g C m-2, respectively, on days of year 221, 233, 247, and 262. The corresponding daily gross primary production (NEP + Reco) was 3. 5, 3. 3, 4. 6, and 4. 6 g C m-2.
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