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 (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.