The Temporal And Spatial Dynamics Of Photosynthetically Active Radiation, Temperature And Relative Humidity In Maize Canopy

With the rapid development of urbanization, the available land in China has been decreasing step by step and food security has become an important strategic issue for human being. Corn(maize), as a sustainable development of bio-energy, has been mentioned on the agenda of countries and also been drawn more and more attention because of its wide planting area and high-yield. The organic matter was made by photosynthesis of corn leaves, however, the interior photosynthetical active radiation (PAR), temperature and relative humidity in corn canopy can change the net production, therefore, it was urgent to know about the spatial distribution and dynamics of these factors. In terms of the environmental data from Jinzhou maize agrocultural ecosystem research station, Institute of Atmospheric Environment, China Meteorological Administration(CMA), by Li-6400R photosynthesis measurement system (Li-cor, Lincoln, NE, USA) as well as leaf ecophysiological parameters of maize and the biomass,the vertical distributions and dynamics of photosynthetical active radiation, temperature and relative humidity in maize canopy would be analyzed; and the dynamics of extinction coefficients in maize canopy would be discussed. The main conclusions were listed as follows:(1) The attenuation rates of photosynthetical active radiation in the different periods of the growth and development of maize were different, and Law of Beer could only be used around noon after the period of tasselling. The vertical distribution of photosynthetical active radiation did not change significantly at the seeding stage, and obviously at the jointing stage with about 80% of total radiation energy in the upper canopy. 70% of total radiation energy was absorbed in the upper canopy at the tasselling stage, 85% in the upper and middle canopy at the milky stage. The PAR mainly scattered above 120 cm at the mature stage. PAR in the lower canopy did not changed significantly after the stage of tasselling..(2) The vertical variation of temperature in the canopy was small at seeding stage; the upper of temperature was smaller than the lower before 7:00am, then temperature rapidly rose and reached the maximum in the upper canopy around 13:00 at the jointing stage; the temperature decreased with the decrease in canopy height except the morning and the afternoon at the tasselling stage; the canopy temperature increased slightly from the canopy to the bottom at the milky stage, and it reached the maximum in the top of the canopy and the minimum at the bottom in the morning; the canopy temperature at the mature stage was similar with that at the milky stage. The maximum of temperature appeared later than the maximum of photosynthetical active radiation, and the difference of canopy temperature between milky and mature stages could reach more than 10℃.(3) The vertical distribution of relative humidity was not apparent at the seeding stage; the relative humidity decreased from the top of the canopy to the bottom at the jointing and milky and mature stages, and increased at the tasselling stage. The diurnal dynamics of relative humidity could be expressed as"V"curve, especially at the tasselling stage.(4) Photosynthetical active radiation in the growth and development of maize mostly reached the maximum around 11:00 am, while the maximum of temperature appeared around 13:00 pm.. However, after the period of tasselling, relative humidity was affected obviously by temperature at tasselling stage, and they showed anti-phase changes.(5) The extinction coefficients of maize community showed obvious diurnal dynamics with higher values in the morning and afternoon and lower values at noon, but did not change significantly at the tasselling stage. When leaf area index was relative stable, the extinction coefficient model developed could simulate better than Norman model did. When the solar elevation angles were greater than 75°, the relationship between the extinction coefficient and leaf area index could be expressed as a parabola. New extinction coefficient K-function including the effects of the sun elevation angle and leaf area index could give the better simulations than Norman's K value.