Date of Award

2009

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Horticulture

Advisor

Stephanie Burnett

Second Committee Member

Donglin Zhang

Third Committee Member

Michael Day

Abstract

According to the USD A ERS, 2008 receipts from greenhouse and nursery sales ranked fourth among agricultural commodities in Maine and seventh in the nation. Greenhouse and nursery plant production relies on the availability of quality water for irrigation and, often involves the use of supplemental lighting to enhance the quality and growth of the plants being produced. Increasing energy costs and more frequent water shortages associated with changing demographics, water use legislation, and climate factors have inspired growers to consider more sustainable approaches to utilizing resources such as water and energy. Precise, crop-specific water and light recommendations are essential to help growers make more sustainable production decisions. Two investigations were conducted to determine the water and light requirements for Heuchera americana 'Dale's Strain' (heuchera), an herbaceous perennial prized for its variegated foliage. Both investigations used a capacitance sensor automated irrigation system to accurately manage substrate volumetric water content (9). In the first study, the substrate was maintained at one of eight 0 ranging from 0.15 to 0.50 L L"1 while the second experiment assessed performance under four daily light integrals (DLI) (7.5, 10.8, 14.9, and 21.8 mol'm'^d"1) with 6 remaining constant. Total leaf area in plants grown at the highest 9 was more than twice that observed in plants grown at the lowest 9. Shoot dry weight also responded positively to increasing 9, although 9 greater than 0.35 L'L"1 did not continue to yield significantly greater dry weights. DLI caused dry weight, leaf area, maximum width and leaf count to increase quadratically. Increases in dry weight and leaf area appeared to reach saturation at 10.8 molm^d"1, while width and leaf count were greatest at 14.9 molm"2d_1. Increasing DLI to 21.8 mol'm"2 d"1 negatively impacted leaf area, leaf count and width, but did not result in lower dry weights. Specific leaf area (cm2 g"1) and petiole length of the uppermost fully expanded leaf decreased with increasing DLI. Measures of fluorescence, net photosynthesis, light response curves, and carbon dioxide response curves indicated no physiological differences among plants grown under different water or light treatments. Water use efficiency (WUE) based on dry weight and water applied (g'L1) decreased with increasing 9 and DLI while WUE based on leaf gas exchange was not influenced by 9 and increased with increasing DLI. From this information, we suggest 9 be kept somewhere between 0.35 and 0.5 L L"1 and DLI in the range of 11 to 15 mol m"2 d"1 for optimal heuchera production. Solenostemon scutellarioides (coleus), another crop valued primarily for its ornamental foliage, has traditionally been used as a shade plant, but many new cultivars are suitable for full sun. Many have noted a variation in leaf coloration when coleus is grown under different light levels, but to our knowledge, no one had quantified this difference. Therefore, two cultivars of coleus were grown under four DLIs (2.9, 3.8, 5.8, and 10.0 mol-m"2-d_1) to determine how DLI influenced morphology and leaf variegation. Both cultivars coleus had optimal growth and more variegation (i.e. less green area) under lO.Omol-m^d"1.

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