Folia Horticulturae

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Solar spectral irradiance in cultivated plants under cover in a submontane region. III. Sweet pepper plants in the plastic tunnels

Marian Czarnowski*, Stanisław Cebula**

**The Franciszek Górski Department of Plant Physiology
**Polish Academy of Sciences
**Sławkowska 17, 31-016 Kraków, Poland
**Department of Vegetable Crops
**Faculty of Horticulture, Agricultural University
**29 Listopada 54, 31-425 Kraków, Poland

In September (midday hours of a sunny day) the spectral quantum irradiance, measured above sweet pepper cultivated in a plastic tunnel in a submontane region, reached a maximum value of 4.2 μmol m-2 s-1 nm-1 at a wavelength of 752 nm. The irradiance (300-1100) amounted to 2340 μmol m-2 s-1, being about 24% lower than that outside the tunnel. The photosynthetically active radiation (400-700 nm, PAR) above the sweet pepper plants at that time had a value of 980 μmol m-2 s-1.

The spectral transmittance of solar irradiation thhrough the sweet pepper plant canopy depends on the value of the leaf area index (LAI). The lowest PAR transmittance through the canopy reached 4-7% (at LAI amounting to about 2.6) of the PAR value above the culture. This demonstrated a high PAR absorptance by the plants. A single leaf revealed high absorptance (about 90%), low reflectance (7-8%) and even lower transmittance (2-4%) in the PAR range. In the near infrared (over 700 nm), however, the leaves revealed very low absorptance (4-6%), and considerable reflectance (about 52%) and transmittance (about 41%). These data demonstrated that the leaves of higher plants are structurally and functionally well disposed to absorption of solar irradiation, especially in the PAR range and to reflection and transmission of irradiation of preventive character, mainly in the near infrared region.

Czarnowski M., Cebula S., 1994. Solar spectral irradiance in cultivated plants under cover in a submontane region. III. Sweet pepper plants in the plastic tunnels. Folia Horticulturae VI/2: 25-34.