Effects of Zn Deficiency and Bicarbonate on the Growth and Photosynthetic Characteristics of Four Plant Species

Calcareous soils are characterized by low nutrient contents, high bicarbonate (HCO 3 − ) content, and high alkalinity. The effects of HCO 3 − 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 HCO 3 − . The photosynthetic response to HCO 3 − 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 HCO 3 − treatments due to its strong growth and minimal inhibition of photosynthesis and photosystem II (PS II). Brassica napus was sensitive to Zn deficiency, HCO 3 − 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 HCO 3 − . Broussonetia papyrifera was shown to have potential as a pioneer species in karst regions.