Potassium plays a key role in plant growth and physiology, specifically in the activation of enzymes, stomata regulation, plant water relations, and mobility of ions and other solutes within the plant (Mengel and Kirkby, 2001). Potassium deficiency affects primary and secondary metabolism (Armengaud et al., 2009), leading to increased susceptibility to pest and disease (Amtmann et al., 2008), leaf edge scorching, and reduced growth and marketability of a range of ornamental species (Karimi et al., 2009; Wang, 2007; Yi Lin and Ming Yeh, 2008).
Knowledge of critical nutrient demands is of major importance for the design of sustainable horticultural production systems. Nutrient requirement is defined in terms of a critical concentration derived from growth or yield response curves over a wide range of nutrient supply (Genc et al., 2002). The response curves are usually separated into four phases: 1) a deficiency phase in which plant growth increases markedly with slight incremental increases in nutrient concentration; 2) a sufficiency phase in which growth is maximized (Salifu and Timmer, 2003); 3) an adequate phase in which further growth is not achieved despite the increase in nutrient availability as a result of luxury consumption; and 4) a toxicity phase in which nutrient concentration continues to increase but plant growth declines (Isaac and Kimaro, 2011; Marschner, 1995; Salifu and Timmer, 2003). Nutrient concentration is defined as sufficient or as the critical optimum concentration (Marschner, 1995) when plants exhibit 90% to 95% of maximum growth or yield (Ulrich and Hills, 1993), whereas the concentration at which growth declines is considered as the critical toxicity level (Marschner, 1995).
Lilium (Lilium sp.) is a widely cultivated ornamental geophyte. Studies on Lilium nutrition have been reported (Argo and Biernbaum, 1994) and tissue nutrient levels (mmol·kg−1) of high-quality lilium plants are 1700 to 2900 nitrogen (N), 32 to 226 phosphorus (P), 512 to 1279 K, 50 to 100 calcium (Ca), and 125 to 833 Mg (Dole and Wilkins, 2005). However, there is little information available on lilium cultivation for cut flower purposes in hydroponic systems. Ornamental geophytes pose a challenge for plant nutrition research because the bulb stores reserves of carbohydrates and mineral elements; thus, the response to external nutrient concentrations may not be comparable to that of non-geophytic species. The present study was conducted to determine the response of Lilium sp. L cv. Arcachon in perlite cultures to varying K levels in the nutrient solution with the objective of defining the critical internal and external K concentration. Because no reports have been published, on the present research we also assessed the relationship of K nutrition with leaf water potential (ψw), photosynthetic rate, leaf anatomy, and plant nutritional status.
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