Kiran Alapaty, UNC Chapel Hill, currently with National Science Foundation
Fitz Booker, USDA/ ARS, Air Quality-Plant Growth and Development Unit, NC
Fei Chen, National Center for Atmospheric Research, Boulder
Ken Davis, Department of Meteorology, Penn State University, University Park, PA
Lianhong Gu, Oak Ridge National Laboratory, TN
Brent Holben, GSFC, NASA, Greenbelt, MD
Teddy Holt, N. C. State Univ and Naval Research Laboratory, Monterey, CA
Tilden Meyers, ATDD/NOAA, Oak Ridge, TNWalter C. Oechel, San Diego State University
Roger A. Pielke Sr. and Toshi Matsui Colorado State UniversityRandy Wells, Department of Crop Science, N. C. State University, Raleigh, NC Kell Wilson, ATDD/NOAA, Oak Ridge, TN Yongkang Xue, Department of Geography, UCLA, Los Angeles, CA
Total solar radiation = (Diffuse + Direct) solar radiation
For increased Cloud Cover or Increased Aerosol Loading,
Diffuse Component Increases => changes the DDR (Diffuse to Direct
Increase in DDR will impact the Terrestrial Carbon and Water Cycles through Transpiration and Photosynthesis changes
(Transpiration is the most efficient means of water loss from land surface;
Photosynthesis is the dominant mechanism for terrestrial carbon cycle)
Willow Creek, WI
Lost Creek, WI
Bondville, IL (agriculture, C3 / C4, 98-02)
Walker Branch, TN (mixed forest 2000)
Barrow, AK (grassland 99)
negative values indicate CO2 sink (into the vegetation)
Does DDR Change Cause Changes in the CO2 Flux at Field Scale?
Increase in DDR appears to increase the observed CO2 flux in the field measurements.
Changes in CO2 flux Normalized for changes in global Radiation versus Diffuse Fraction
Are these results true for different landscapes?
For Forests and Croplands, aerosol loading has a positive effect on CO2 flux, where there shows a CO2 flux source at Grassland sites.
LHF is mainly due to transpiration;
with increasing aerosols,diffuse radiation increases and air / leaf temperature decreases,
=> increase in transpiration and thereby increase LHF
At low vegetation LAI:
LHF is mainly due to evaporation;
with increasing aerosols,diffuse radiation increases, and air / leaf temperature decreases,
=> reduce the evaporation and therefore LHF decreases.
(LHF values opposite in sign)
Latent heat flux appears to generally decrease with increasing Aerosol Optical Depths for most of the studied sites.
Observed data analyses:
Walker Branch (Forest site):
Low LAI case (LAI < 2.5)
LHF decrease with aerosol loading
High LAI case (LAI >3)
LHF increase with aerosol loading
However, analyzed results vary for different landscapes
Bondville(soy bean site(C3)):
Low LAI case
High LAI case
For higher LAI, the AOD –ve dependence seems to be decreasing
- High LAI: LHF increase with AOD
- Low LAI: LHF decrease with AOD
need to consider Leaf effect for the flux change.
(1) crop site: USDA Raleigh, Purdue AG Center
(2) forest site: ChEAS (?)
(1) for crops: use high/low diffuse radiation shed; change soil moisture stress and stress from temperature and humidity => need to design special chambers.
(2) for forest: repeat similar experiments for crops and need to examine vertical profiles => responses in different vertical levels may be important.
LI6400 CO2 / H2O Flux system
Analysis for AOD – LHF effects is still underway. (need to consider interaction terms such as LAI, soil moisture)
Leaf and Canopy scale measurements of CO2 and Water Vapor Flux for plants grown under different soil moisture conditions at USDA Facility in Raleigh.
Potted plants were grown in 2 sheds with different diffuse radiation screens and CO2 / H2O Exchange Measured
(with Dr. Booker and Dr. Wells)
High LAI case
LHF increase with aerosol loading up to certain level.
Low LAI case
soy bean site
Compare with previous slides, Latent heat fluxes still decrease with aerosol loading without leaf and temperature effects.
Glazing material treatment effects on average photosynthetic photon flux density (PPDF) at upper canopy height between 0800-1600 h (EST) during the experimental period. The ratio of diffuse PPFD radiation to total PPDF radiation is also shown. Values are means ± SE. Values followed by a different letter were statistically significantly different (P ≤ 0.05).
Soybean biomass and yield responses to growth under Clear and Diffusing glazing materials (mean ± SE). Plants were harvested for determination of biomass (Biomass) at 88 days after planting (DAP), and for determination of seed yield (Yield) at 153 DAP. Values in parenthesis indicate percent change from the Clear treatment. Statistics: P ≤ 0.1 (†).
Net photosynthesis (A) of upper canopy leaves and whole-plants treated with either Clear or Diffusing glazing materials (mean ± SE). Net photosynthesis of upper canopy leaves on four plants per treatment was measured weekly between 48 and 105 DAP (seven occasions). In addition, whole-plant A of three sets of three plants was measured on 56 DAP. Treatment effects on A were not statistically significant.