Haracteristics Of Evapotranspiration And CO₂ Exchange Under Different Canopy In Poa Pratensis Turf

As human activities affected the nature environment increasingly in the world, the water consumption and CO2 release in urban draws people's attention. For the urban green turf is one of the unreplaceable components of citialize, it's very important to reaearch its water-carbon exchange and evapotranspiration character. This paper focus on the water-carbon exchange and evapotranspiration character of urban green turf under different conapy structure, in the hope of improving the understand the water-carbon exchange in urban and guiding the turfgrass irrigation management.In order to understand the relationship between canopy structure, evapotranspiration and CO2 exchange characteristic in Poa pratensis turf, MLS and Li6400 photosynthetic measurement system with a custom chamber were used to collect data under different mowing height and coverage degree. The major issues presented in this study include:(1) There were significant differences in canopy structure, evapotranspiration and CO2 exchange under different mowing height with full water suplly. While coverage degree has no significant influence on evapotranspiration. Canopy structure, evapotranspiration and CO2 exchange characteristics in Poa pratensis turf were change significantly with the season.(2) The evapotranspiration of Poa pratensis turf increased with the increase of mowing height, the relationship bwtween ET and mowing height can be representedas:ET=103.15H+285.68 (R2=0.9361). During experiment period, the Kc of Poa pratensis turf was between 0.81 and 2.13, and there was a significant difference between different mowing height, but no significant difference under different different coverage degree.(3) There were significant correlation between LAI, SLAI, aboveground matter, aboveground biomass and ET,but no significant correlation between canopy growth, litter and ET. Among all the canopy structure parameters, ET can be most represented by LAI. The relationship between them can be represented as:ET=1.7721X0.7707(R2=0.7867,P<0.01).(4) The modle of ET forecast in Beijing was ET= a·LAI+b, and alue a and b in different seasons were defined. By compairing the observed values and predictive values, the modle was proved feasible for estimating ET of turf in Beijing.(5) NEE significantly correlated with aboveground biomass, thatch biomass, live canopy biomass, canopy growth rate and LAI under full water supply. But there is no significant correlation between NEE and SLAI. The aboveground biomass and canopy growth height are the main affecting factors and that is correlative exponentially with the NEE of Poa pratensis turf. The relationship between NEE and aboveground matter can be represented as:NEE=0.0128X+0.0455 (R2=0.7651,P< 0.01).And a significant exponential relation exist between the live canopy biomass and CO2 evolution rates. The relationship between them can be represented as:Y=0.2569X0.5084(R2= 0.799,P<0.01).(6) Air tempreture(T) and Wind speed(u2) positively correlated with ET significantly(P<0.01), while relative humidity(RH) has a significantly neigative correlation with ET(P<0.01).And solar radiation (Rn)has a significant correlation with ET(P<0.05).The relationship between ET and meteorological factors can be represented as follow:ET=-0.342T+0.085Rn-0.994RH+5.954u2-69.267 (R2=0.772,P<0.00). Among all meteorological factors, Air tempreture has the closest relationship with carbon dioxide exchange parameters, solar radiation and wind speed are fallow behind. Besides canopy respiration, there are significant linear relations between ET and CO2 exchange parameters(P<0.01).