Colored shadecloths are used in the production of vegetable, fruit, and ornamental crops to manipulate the light spectrum and to induce specific plant physiological responses. The influence of three colored shadecloths (red, blue, and black) with 50% shade and a no-shade control on the production of two lettuce (Lactuca sativa) cultivars [Two Star (green-leaf) and New Red Fire (red-leaf)] and snapdragon (Antirrhinum majus) was investigated. Use of shadecloth increased plant growth indices of lettuce and total length of snapdragon flower stems (at the first harvest) compared with no-shade control. Red shadecloth resulted in longer flower stems of snapdragon (at the second harvest) than black and blue shadecloths and no-shade control. However, shadecloth delayed blooming of snapdragon for 1 week compared with no-shade control. Stomatal conductance (g s) and leaf transpiration rate of both lettuce cultivars and photosynthetic rate and transpiration rate of snapdragon were decreased in response to shadecloth treatments. All shadecloths decreased health beneficial flavonoids (luteolin/quercetin glucuronide and quercetin malonyl concentrations for both lettuce cultivars and cyanidin glucoside in red-leaf lettuce). The two lettuce cultivars varied in their phenolic compounds, with the green-leaf ‘Two Star’ having higher quercetin glucoside and caftaric acid than red-leaf ‘New Red Fire’, whereas ‘New Red Fire’ had higher concentrations of chlorogenic acid, luteolin/quercetin glucuronide, and quercetin malonyl. Shadecloths reduced substrate temperature and photosynthetically active radiation (PAR) to about half of full sunlight compared with no-shade control, which may have contributed to reduced g s and leaf transpiration (for lettuce and snapdragon), decreased phenolic compounds in lettuce, and delayed flowering of snapdragon.
Tongyin Li, Guihong Bi, Judson LeCompte, T. Casey Barickman, and Bill B. Evans
Judson S. LeCompte, Amy N. Wright, Charlene M. LeBleu, and J. Raymond Kessler
Greywater is a renewable irrigation alternative to potable water; however, its use as an irrigation source is limited by the potential for salt injury to plants. Research was conducted to determine salt tolerance of three common landscape species, small anise tree (Illicium parviflorum), ‘Henry’s Garnet’ sweetspire (Itea virginica), and muhly grass (Muhlenbergia capillaris). Two experiments were performed, one with high sodium chloride (NaCl) concentrations and one with low NaCl concentrations. Plants received daily irrigation of tap water containing one of the following NaCl concentrations: 0 (tap water); 2000, 4000, 6000, 8000, or 10,000 mg·L−1 (high NaCl); or 0 (tap water), 250, 500, or 1000 mg·L−1 (low NaCl) for 15 weeks. Plants were harvested after 5, 10, or 15 weeks. Root dry weight (RDW) and shoot dry weight (SDW) were determined at each harvest; survival was determined at experiment termination. Leaf tissue was analyzed for tissue macronutrient [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and, magnesium (Mg)], sodium (Na), and chlorine (Cl) concentrations in the high NaCl concentration experiment. With high NaCl, RDW and SDW decreased with increasing NaCl for all species. Anise and sweetspire had low or no survival, respectively, at the highest NaCl concentration; muhly grass had 100% survival regardless of treatment. In general, leaf macronutrient, Na, and Cl increased with increasing NaCl concentration. With low NaCl, there was no effect of NaCl concentration on RDW or SDW for all species. All three species continued to grow between harvest dates in the lower NaCl concentration experiment, whereas only anise and muhly grass continued to grow with high NaCl. Anise and muhly grass were tolerant of saline irrigation that could be expected from greywater. Sweetspire exhibited symptoms of salt stress (necrotic leaves and leaf drop, visual observation) at all NaCl concentrations including the lowest (250 mg·L−1), and should not be irrigated with saline water.