Foliar retention of 15N-nitrate and 15N-ammonium by red maple (Acer rubrum) and white oak (Quercus alba) leaves from simulated rain

Journal Article · Sun Jul 01 04:00:00 EDT 1990 · Environmental and Experimental Botany

DOI:https://doi.org/10.1016/0098-8472(90)90045-6· OSTI ID:978733

Garten, Jr, Charles T ^[1]; Hanson, Paul J ^[1]

---

1. ORNL

Studies of nitrogen cycling in forests indicate that trees assimilate atmospheric nitrate and ammonium and that differences between atmospheric deposition to the forest canopy and deposition measured in forest throughfall can be attributed to the removal of these ions from rain by tree leaves. Red maple and white oak leaves were exposed to artificial rain solutions (pH 4.1) containing {sup 15}N-labeled nitrate (3.5 {micro}g N/ml) or ammonium (2.2 {micro}g N/ml). At two time intervals after exposure (2 hr and 2 days) an exposed leaf and a control (non-exposed) leaf were removed from replicate seedlings. Based on results from {sup 15}N analysis, most of the nitrate applied to tree leaves was removed by washing with water; the mean per cent removal ({+-} standard error, N = 4) was 87 {+-} 1 and 73 {+-} 4% of the {sup 15}NO-N Applied to red maple and white oak leaves, respectively. Relative retention of {sup 15}NH{sub 4}-N by the leaves was greater than that observed for {sup 15}NO{sub 3}-N. In red maple and white oak leaves, 58 {+-} 9 and 84 {+-} 7% (mean {+-} standard error, N = 4), respectively, of the applied ammonium was not removed by washing treatments. Our results show that the foliar uptake of {sup 15}NH{sub 4}{sup +} from simulated rain by deciduous tree leaves is greater than that for {sup 15}NO{sub 3}{sup -}. Greater retention of NH{sub 4}{sup +} than NO{sub 3}{sup -} ions by red maple and white oak leaves from simulated rainfall is consistent with field observations showing a preferential retention of ammonium from rainfall by forest canopies. As nitrogen chemistry and the relative importance of nitrogen compounds in the atmosphere change in response to proposed emission reductions (and possibly climate change), an improved understanding of the fate of airborne nitrogen compounds in forest biogeochemical cycles will be necessary.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 978733
• Journal Information: Environmental and Experimental Botany, Journal Name: Environmental and Experimental Botany Journal Issue: 3 Vol. 30; ISSN 0098-8472; ISSN EEBODM
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CANOPIES
CHEMISTRY
CLIMATES
DECIDUOUS TREES
DEPOSITION
FOLIAR UPTAKE
FORESTS
MAPLES
NITRATES
NITROGEN
NITROGEN COMPOUNDS
OAKS
RAIN
REMOVAL
RETENTION
SEEDLINGS
THROUGHFALL
TREES
WASHING
WATER