Oxygen stress in Salvinia natans: Interactive effects of oxygen availability and nitrogen source

Abstract

The ability of Salvinia natans (L.) All. to tolerate growth in oxic, hypoxic and anoxic nutrient solutions when supplied with either NH 4 + or NO 3 − were studied in the laboratory to test the hypothesis that inorganic N-source affects the response of the plants to O 2 deprivation. The relative growth rate (RGR) was significantly reduced in the anoxic treatment, but in the hypoxic treatment RGR was only slightly affected. The NH 4 + fed plants generally had a higher shoot to root ratio than the NO 3 − fed plants, and highest in the anoxic treatment. Plants had more roots and larger leaves when supplied with NH 4 + as compared with NO 3 −, particularly in the oxic treatment, and root length was most affected by O 2 deprivation for NO 3 − fed plants. Cell walls in the endodermis, the bundle sheath and the cortex adjacent to endodermis developed thickened sclerenchymatous walls when deprived of O 2, and more so in plants supplied with NO 3 −. Plants lost chlorophylls, had lower rates of photosynthetic electron transport (ETR max) and lower quantum yields (Fv/Fm ratios) when grown in anoxic solutions, and the negative effects were mildest for NO 3 − fed plants suggesting that NO 3 − may be used as an alternative e −-acceptor in non-cyclic electron transport in the chloroplasts. Overall S. natans grew best on NH 4 +, but it also grew well on NO 3 −, and the O 2 stress symptoms differed somewhat between NH 4 + fed and NO 3 − fed plants. However, because N-form itself significantly influenced morphology and cell metabolism, it was impossible to conclusively identify the role of N-form for the O 2 stress reactions. S. natans is not well-adapted to grow in O 2 deficient waters and will not tolerate completely anoxic conditions as will prevail in waters receiving high loadings of organic pollutants such as livestock wastewater.