Foliar Calcium Absorption by Tomato Plants: Comparing the Effects of Calcium Sources and Adjuvant Usage

Abstract

The deficiency of calcium (Ca) reduces the quality and shelf life of fruits. In this scenario, although foliar spraying of Ca2+ has been used, altogether with soil fertilization, as an alternative to prevent deficiencies, little is known regarding its absorption dynamics by plant leaves. Herein, in vivo microprobe X-ray fluorescence was employed aiming to monitor the foliar absorption of CaCl2, Ca-citrate complex, and Ca3(PO4)2 nanoparticles with and without using adjuvant. We also investigated whether Sr2+ can be employed as Ca2+ proxy in foliar absorption studies. Moreover, the impact of treatments on the cuticle structure was evaluated by scanning electron microscopy. For this study, 45-day-old tomato (Solanum lycopersicum L., cv. Micro-Tom) plants were used as a model species. After 100 h, the leaves absorbed 90, 18, and 4% of aqueous CaCl2, Ca-citrate, and Ca3(PO4)2 nanoparticles, respectively. The addition of adjuvant increased the absorption of Ca-citrate to 28%, decreased that of CaCl2 to 77%, and did not affect Ca3(PO4)2. CaCl2 displayed an exponential decay absorption profile with half-lives of 15 h and 5 h without and with adjuvant, respectively. Ca-citrate and Ca3(PO4)2 exhibited absorption profiles that were closer to a linear behavior. Sr2+ was a suitable Ca2+ tracer because of its similar absorption profiles. Furthermore, the use of adjuvant affected the epicuticular crystal structure. Our findings reveal that CaCl2 was the most efficient Ca2+ source. The effects caused by adjuvant suggest that CaCl2 and Ca-citrate were absorbed mostly through hydrophilic and lipophilic pathways.

An In-House X-ray Fluorescence Spectrometer Development for In Vivo Analysis of Plants

“…Previous studies conducted using either synchrotron or benchtop-based XRF setups revealed elemental doses of between 10 2 and 10 4 Gy. , As detailed in Figure S7C, one should notice that a minimum 50 h exposure would be required to achieve such doses in this current setup. Since in vivo XRF measurements usually encompass a few seconds up to a dozen minutes, ,,− there is no evidence that X-ray-induced radiation damage might be an issue for the SIPA setup.…”

“…Investigating the absorption and transport of minerals by roots and leaves is crucial for nutrition studies, as it provides a mechanistic understanding of the dynamics of mineral absorption and transport processes and ultimately fosters novel strategies toward higher nutrient use efficiency. ,,, Although it can also be evaluated using other analytical techniques, such as ICP OES and ICP-MS, , these do not enable in vivo studies, while the latter involves complex radiolabeled materials acquisition and safety . Hence, XRF exhibits unique features for evaluating the absorption and transport of minerals across plant tissues on a real-time basis. ,,,, Considering foliar absorption, SIPA provides an accurate in vivo assessment of the absorption and transport processes.…”

“…To verify the potential of the SIPA for in vivo studies, the transport of foliar-applied potassium (K) and calcium (Ca) was monitored in tomato plants by using rubidium (Rb) and strontium (Sr) as physiological tracers. ,− Tomato plants ( Solanum lycopersicum , variety Micro-Tom) were cultivated in the substrate and grown in a growth chamber with a 13:11 h light–dark photoperiod, 28 °C temperature, and 60–70% relative air humidity. The substrate was amended with limestone and a 4:14:8 NPK solution at 8 g L –1 , and once a day, the plants were irrigated with deionized water.…”

“…9−11 For instance, recently in vivo XRF has also been successfully employed to determine the absorption and transport rates of K and Ca fertilizers foliar applied to crop species. 11,12 Nevertheless, despite these advantages, the use of XRF in agricultural sciences meets instrumental constraints in commercial benchtop setups. This is particularly noticeable for in vivo studies of plant materials, where small analysis chambers and the positioning of the X-ray tube and detector allow only small-size specimens in vivo studies or early-stage plant life cycle investigations.…”

“…In this scenario, both in vivo and in situ XRF strategies have been explored to understand the dynamics of elements within plant tissues. − For instance, recently in vivo XRF has also been successfully employed to determine the absorption and transport rates of K and Ca fertilizers foliar applied to crop species. , …”