Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2001
Publication Date: N/A
Interpretive Summary: Plants grown under reduced light intensity can experience alterations in nutrient uptake, water use, carbohydrate partitioning, plant structure, and susceptibility to plant diseases. Elevated atmospheric carbon dioxide levels can contribute indirectly to enhanced cloud formation and reduced planetary incident solar light. In order to evaluate the effects of reduced dlight on plant productivity, two snap bean cultivars were planted in the spring of 2000. Beans grown under up to 30% light reduction were as productive as beans grown under 'normal' light levels. As light levels were reduced, plants attempted to compensate by increasing their leaf area. Light reduction had little effect on pod mineral nutrients or protein content, but reduced canopy and soil temperatures, and leaf transpiration rates. There were inverse relationships between powdery mildew (a foliar leaf disease), the number of root rhizobial nodules (symbiotic bacteria) per root, and light intensity. Snap bean performance appeared to be tolerant to modest levels of reduced solar light.
Technical Abstract: Two snap bean cultivars, Strike and Carlos (Phaseolus vulgaris, L), were planted into a Hebbronville sandy loam soil on 22 February 2000, and grown under 0, 30, and 70 of ambient daily light (shade) throughout the 65-day growing season. Although the yield response was linear with respect to increased shading, first harvest and season yields were not affected by a 30% incident light reduction. Light reduction tended to decrease the larger pod sieve sizes, but increased pod dry matter content in 'Carlos'. Plant biomass was reduced by shading as was leaf greenness, but leaf area and chlorophyll content (dry wt. basis), as well as the incidence of powdery mildew late in the season, was increased by shading. Leaf, air, and soil (at 10 cm) temperatures were reduced by increased shading. The incidence of powdery mildew occurred late in the season and was linearly increased by reduced light. Leaf transpiration and stomatal conductance were generally increased by shading. Rhizobium nodulation of 'Carlos' root was greater under reduced light. Pod mineral nutrients varied between cultivars, but generally were not affected by light intensity.