Comparative study of nitrogen assimilation in woodland species

Pearson, Jennifer; Clough, E.C.M.; Kershaw, Joanna L.

doi:10.1051/forest:198905art0146

Cited by 5 publications

(1 citation statement)

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“…Nasholm (1991) suggested that free arginine in conifer needles does not reflect a storage function wben nitrogen is in excess, rather it indicates that other limiting factors are causing stress. Differences between species in their leaf free amino acid content may also reflect differences in their type of nitrogen nutrition (ammonia versus nitrate) (Pearson et al, 1989;Nasholm, 1991).…”

Section: Physiological Responses To Atnmoniamentioning

confidence: 99%

The deposition of atmospheric ammonia and its effects on plants

1993

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SUMMARY Across Europe, total nitrogen deposition is increasing and, of this total, atmospheric ammonia can contribute up to 50–80%. Average deposition of ammonia in the UK is likely to be around 15–20 kg ha−1 yr−1, while in The Netherlands, which has some of the highest rates of deposition, this value is likely to be between 40 and 50 kg ha−1 yr−1. It is argued that because of the processes of assimilation and nitrification this ammonia is an acidifying pollutant. Ammonia taken up by plants is most likely to be directly assimilated and this uptake can have a strong effect on the nutrient imbalances of the plant. With root uptake in particular, anions are taken up in preference to cations. However, simple soil/plant nutrient measurements are unlikely to be a definitive means of monitoring ammonia pollution. This is because the processes of ammonia metabolism and acidification affect soil ion activity, mycorrhizas, plant uptake, and foliar leaching. These effects interact with acidity per se, and are compounded by the strong correlative co‐deposition of ammonia with sulphur. Evidence for uptake of gaseous and wet deposited ammonia by leaves is presented. The exact mechanism of ammonia toxicity is still not really clear, but could be due to physiological perturbation, rather than to the direct toxicity of the ion. Assimilation of ammonia by leaves releases protons which can cause cellular acidosis, and has important implications for acid‐base regulation in cells. This regulation depends on intrinsic features of the plant's metabolism, that is in turn dependent on the ecology of root versus leaf nitrogen nutrition under normal conditions. Certain species are more acidic in a leaf physiological sense and tend to be prone to damage by pollutants. Likewise, acidic habitats are particularly prone to damage through both eutrophication and the different capacities of plants both to utilize and to buffer against this nitrogen enrichment. The current evidence from The Netherlands suggests that the part this plays in perturbing the ecosystem should not be underestimated.

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Section: Physiological Responses To Atnmoniamentioning

confidence: 99%