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Abstract Soluble free amino acids, ammonium and nitrate ions as sources of nitrogen for plant growth were measured in soils of a coastal marsh grazed by snow geese in Manitoba, Canada. Amounts of nitrogen, primarily ammonium ions, increased in the latter half of the growing season and over winter, but fell to low values early in the growing season. Free amino acid concentrations relative to ammonium concentrations were highest during the period of rapid plant growth in early summer, especially in soils in the intertidal zone, where the median ratio of amino acid nitrogen to ammonium nitrogen was 0·36 and amino acid concentrations exceeded those of ammonium ions in 24% of samples. Amino acid profiles, which were dominated by alanine, proline and glutamic acid, were similar to goose faecal profiles. In a continuous flow hydroponic experiment conducted in the field, growth of the salt-marsh grass, Puccinellia phryganodes , on glycine was similar to growth on ammonium ions at an equivalent concentration of nitrogen. When supplies of soil inorganic nitrogen are low, amino acids represent a potentially important source of nitrogen for the re-growth of plants grazed by geese and amino acid uptake may be as high as 57% that of ammonium ions. [ABSTRACT FROM AUTHOR]

Summary: • The potential amelioration of Al (Al) toxicity by elevated dissolved inorganic carbon (DIC = CO2 + HCO3−) in the root medium was investigated in both NH4+‐ and NO3−‐fed Lycopersicon esculentum (tomato) plants.• Hydroponically grown L. esculentum seedlings were intermittently supplied with 50 µM AlCl3 and the nutrient solutions aerated with either 360 or 5000 ppm CO2. Relative growth rate (RGR), nitrogen uptake, root respiration and root incorporation of DI14C and subsequent partitioning were measured.• Al reduced the RGR of plants grown with 360 ppm root‐zone CO2. At elevated root‐zone CO2, Al had no significant effect on the RGR of NO3−‐fed plants whereas the RGR of the NH4+‐fed plants was increased by 21%. Al decreased the respiratory quotient (Rq) by 15% at 360 ppm CO2, but had no influence at 2000 ppm CO2. Exudation of organic 14C, especially of [14C]‐organic acids derived from root incorporation of DI14C, was increased by Al.• It is concluded that elevated DIC partially ameliorated Al toxicity by providing anaplerotic carbon for organic acid synthesis. [ABSTRACT FROM AUTHOR]

Summary • The potential amelioration of Al (Al) toxicity by elevated dissolved inorganic carbon (DIC = CO2 + HCO3-) in the root medium was investigated in both NH4+- and NO3--fed Lycopersicon esculentum (tomato) plants. • Hydroponically grown L. esculentum seedlings were intermittently supplied with 50 µM AlCl3 and the nutrient solutions aerated with either 360 or 5000 ppm CO2. Relative growth rate (RGR), nitrogen uptake, root respiration and root incorporation of DI14C and subsequent partitioning were measured. • Al reduced the RGR of plants grown with 360 ppm root-zone CO2. At elevated root-zone CO2, Al had no significant effect on the RGR of NO3--fed plants whereas the RGR of the NH4+-fed plants was increased by 21%. Al decreased the respiratory quotient (Rq) by 15% at 360 ppm CO2, but had no influence at 2000 ppm CO2. Exudation of organic 14C, especially of [14C]-organic acids derived from root incorporation of DI14C, was increased by Al. • It is concluded that elevated DIC partially ameliorated Al toxicity by providing anaplerotic carbon for organic acid synthesis. [ABSTRACT FROM AUTHOR]