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Tobacco (Nicotiana tabacum L.) is the primary nicotine producing plant through its root system (Steppuhn et al., 2004; Shoji et al., 2008). It produces nicotine to as high as 4% of its leaf content compared with potato, tomato, eggplant, pepper, tea, cauliflower, and wild mushrooms (Davis et al., 1991; Siegmund et al., 1999; Moldoveanu et al., 2016; Ikka et al., 2018), which produce negligible amounts ranging from 0.00001 to 0.00000038% of their leaf contents (Siegmund et al., 1999; Moldoveanu et al., 2016).
Tobacco plants transfer nicotine via the xylem to leaf vacuoles for storage (Shitan et al., 2009), where it provides defensive functions against predators (Ballaré, 2011). Previous studies have shown that some synthesized nicotine is passively released from the meristematic root regions to protect against harmful soil microorganisms, hence increasing the plant's competitive advantage for soil nutrients (Darwent et al., 2003; Walker et al., 2003). The levels of nicotine released to the rhizosphere have been reported to negatively affect the proliferation of bacteria and availability of K and P in soils (Adediran et al., 2004; Moula et al., 2018). Thus, nicotine may affect the productivity of crops planted subsequently in the same field.
Cheng et al. (2018) demonstrated that higher atmospheric temperatures resulted in the accumulation of nicotine in roots, consequently increasing the amount of nicotine released to the rhizosphere. Nicotine dynamics in the rhizosphere are also associated with soil moisture (SM) (Hsiao and Xu, 2000). The influence of SM and soil temperature (T) on nicotine concentrations in tobacco leaves has been well documented (Parups et al., 1960; Benowitz et al., 2006; Bilalis et al., 2009; Cakir and Cebu, 2010; Malik et al., 2013; Cheng et al., 2018). However, these effects are not directly linked with the dynamics of nicotine released from roots in different depth (Hsiao and Xu, 2000; Cakir and Cebu, 2010).
The main objective of the present study was to investigate the dynamics of nicotine released by tobacco roots under fertilization, and to assess the influence of rooting depth on soil parameters (pH, organic carbon (OC), SM, and T). Our findings will help tobacco growers make informed decisions on the suitability of crops for planting subsequent to tobacco based on rooting depth. |
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