Measurement of net ecosystem production and ecosystem respiration in a Zoysia japonica grassland, central Japan, by the chamber method

Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP), ecosystem respiration (R_eco), and their response functions. Here, we studied the variations in NEP and R_eco in a grassland dominated by a perennial warm-season C₄ grass, Zoysia japonica. We used the chamber method to measure NEP and R_eco from August to September 2007. Biomass and leaf area index (LAI) were also measured to observe their effects on NEP and R_eco. Diurnal variations in NEP and R_eco were predicted well by light intensity (PPFD) and by soil temperature, respectively. Maximum NEP (NEP_max) 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 NEP_max that ranged from 0. 0154 to 0. 0515, and NEP responded to the soil temperature changes by 44% and R_eco changes by 48%, and R_eco responded from 88 to 94% with the soil temperature diurnally. NEP's light response and R_eco's temperature response were affected by soil water content; more than 27% of the variation in NEP and 67% of the variation in R_eco could be explained by this parameter. NEP was strongly correlated with biomass and LAI, but R_eco was not, because environmental variables affected R_eco more strongly than growth parameters. Using the light response of NEP, the temperature response of R_eco, and meteorological data, daily NEP and R_eco 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 + R_eco) was 3. 5, 3. 3, 4. 6, and 4. 6 g C m^-2.