Abstract
Calcareous soils are characterized by low nutrient contents, high bicarbonate (HCO3−) content, and high alkalinity. The effects of HCO3− addition under zinc-sufficient (+Zn) and zinc-deficient (−Zn) conditions on the growth and photosynthetic characteristics of seedlings of two Moraceae species (Broussonetia papyrifera and Morus alba) and two Brassicaceae species (Orychophragmus violaceus and Brassica napus) were investigated. These four species were hydroponically grown in nutrient solution with 0 mM Zn (−Zn) or 0.02 mM Zn (+Zn) and 0 mM or 10 mM HCO3−. The photosynthetic response to HCO3− treatment, Zn deficiency, or both varied according to plant species. Of the four species, Broussonetia papyrifera showed the best adaptability to Zn deficiency for both the 0 mM and 10 mM HCO3− treatments due to its strong growth and minimal inhibition of photosynthesis and photosystem II (PS II). Brassica napus was sensitive to Zn deficiency, HCO3− treatment, or both as evidenced by the considerable inhibition of photosynthesis and high PS II activity. The results indicated different responses of various plant species to Zn deficiency and excess HCO3−. Broussonetia papyrifera was shown to have potential as a pioneer species in karst regions.
Highlights
Bicarbonate (HCO3−) is the product for the catalysis of carbon dioxide (CO2) hydration by carbonic anhydrase (CA)
Excess HCO3− initially appeared in all plants as chlorosis related to nutrient element deficiency [24], a considerable decrease of photosynthetic capability was associated with the lower Zn contents [25], followed by the inhibition of photosystem II (PS II) activity and decreased photosynthetic parameters, such as photosynthetic rate (PN) and water use efficiency (WUE), and Chl fluorescence parameters, such as Fo, Fv/Fm, and electron transport rate (ETR)
Excess HCO3− decreased the Zn concentration in plant tissue and the CA activity involved in photosynthetic carbon metabolism, in addition to inhibiting the HCO3−-use capacity because the substrates provided by HCO3− alleviated the CA-catalytic conversion reaction
Summary
Bicarbonate (HCO3−) is the product for the catalysis of carbon dioxide (CO2) hydration by carbonic anhydrase (CA). It can be used as an inorganic carbon source to supplement CO2 in leaf cells [1]. HCO3− is an essential constituent of the water-oxidizing complex of photosystem II (PS II). This complex is stabilized by HCO3− by binding to other components of PS II and influences the molecular processes associated with the electron acceptor and electron donor sides of PS II [1,2]. Excess HCO3− is harmful for crop growth due to the inhibition of protein synthesis and respiration and decreased nutrient absorption [4]
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