SPECTRAL FILTERS INFLUENCE TRANSPIRATIONAL WATER-LOSS IN CHRYSANTHEMUM

Transpiration rates of chrysanthemum [Dendranthema x grandiflorum (Ramat.) Kitamural plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4.5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R : FR and blue (B) : R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was almost-equal-to 37% less than that of control plants. Transpiration rates were similar among plants grown under CUSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CUSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CUSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was almost-equal-to 50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.