Foliar incorporation of gas-phase reactive nitrogen: Beneficial nutrient or phytotoxin?
Vallano, Dena *,1, Sparks, Jed1, 1 Department of Ecology and Evolutionary Biology, Ithaca, NY
ABSTRACT- Vegetation can be a significant sink for atmospheric reactive nitrogen pollutants in terrestrial ecosystems. Plants are able to assimilate this source of nitrogen through the leaves and incorporate these pollutants into organic compounds and, potentially, enhance growth. However, whether foliar uptake of reactive nitrogen is a benefit or detriment to overall plant performance has not been fully explored. To investigate this question, enriched 15N tracer experiments were conducted in custom-built hydroponic fumigation chambers where varying amounts of reactive nitrogen could be added to the leaves (as NO2) or to the roots (as NO3-). By examining changes in biomass and the isotopic composition of that biomass we quantified the direct uptake of reactive nitrogen by leaves and to what extent and at what concentrations anthropogenic sources of reactive nitrogen were beneficial (i.e., enhances growth through the addition of nutrients) or harmful (i.e., reduced growth due to the toxicity of the compound) to plant performance. The experimental protocol consisted of growing tomato plants (Lycopersicon esculentum) either under low or high (50M and 500M) root NO3- supply and exposing shoot systems to filtered or 15NO2-enriched air (0 ppb, 20 ppb, and 50 ppb) for 4 weeks within the hydroponic-fumigation system. Depending on the root availability of NO3-), NO2 derived nitrogen in leaf tissue varied between 5 and 25% at the end of the fumigation. On average, total plant biomass accumulation was lower in plants exposed to the highest levels of NO2. These results taken together imply that although gas-phase nitrogen pollution may be used as a nutritional source under nitrogen limiting conditions, the high cost of incorporation of these compounds may lead to an overall decreased growth rate. In addition, the responses to foliar uptake of reactive nitrogen appear to be very dependent on the atmospheric concentration.
Key words: Lycopersicon esculentum, nitrogen dioxide, nitrate
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