Throughfall and Stemflow in the Forest Nutrient Cycle

Experimental field estimation of organic nitrogen formation in tree canopies

“…The summary data in Table 1 show some general features that have been identified before (Parker, 1983). For inorganic N, deposition in TF on average is similar to wet deposition, but with considerable scatter across sites.…”

“…'net throughfall' (NTF) = TF + SF -wet deposition, is positive. In a meta-analysis of data up to 1983, the average ratio of deposition in TF to wet deposition was 1.6 (± 1.3) for NH 4 + , 1.3 (± 0.9) for NO 3 -and 1.9 (± 1.5) for total N (including organic N) (Parker, 1983) The increase in overall N deposition below the canopy relative to wet deposition is most probably caused by dry deposition of N on the canopy, which is not measured (over annual time scales) but may be estimated using measured or modelled air concentrations and an appropriate inferential model (Butler and Likens, 1995). In such cases the measured increase in N deposition in NTF (i.e.…”

“…Although some N is retained by vegetation, and only reaches the soil when the plant dies or sheds its leaves, most passes through the canopy fairly quickly and enters the soil as throughfall (TF = canopy drip) or stem flow (SF = water running down tree stems). Canopy uptake or retention of inorganic N (ammonium or nitrate) and organic N has long been recognised as an important fate for N in forests, where it is relatively simple to measure TF and SF for comparison with wet deposition, although its dependence on dry deposition is less easily established (Parker, 1983, Schaefer and Reiners, 1990, Tukey, 1970. It is not clear, however, what happens to the N that is retained in the canopy.…”

Changes in atmospheric deposition and streamwater chemistry over 25years in undisturbed catchments in a Mediterranean mountain environment

“…While throughfall is a good estimator of dry deposition for ions with little 202 interaction with the canopy (Cl -, SO 4 2-, Na + and Ca 2+ ; Parker, 1983), for N this is not so, 203 because N is retained by leaves and the biota in the canopy (Parker, 1983). Deposition on 204 collector surfaces also may underestimate deposition for gaseous compounds, many of 205 them nitrogenated such as NO y (sum of HNO 3g , NO, NO 2 ), NH 3 We sampled a number of running-water streams and rivulets all over Montseny plus, for 230 comparison, five springs and a natural seep.…”

Kinetics of exchange of ions between artificial precipitation and maple leaf surfaces

“…While these simultaneously, including: (1) solubilization and studies leave little doubt that substances can move wash-off foliar surface materials, including exuded between plants and the external environment foliar or atmospherically deposited substances; (2) through foliage, they do not elucidate mechanisms net loss from the leaf ('foliar leaching') or uptake by which this occurs, nor do they demonstrate that ('foliar uptake') of neutral salts and weak acids and this exchange occurs at biologically significant rates. bases by diffusion and ion exchange; and (3) Laboratory and controlled field studies have also utilization or chemical transformation by leaf surface shown that increased cation leaching from foliage microflora (Cronan , & Reiners, 1983;Parker, 1983; generally occurs with increased solution acidity (Wood & Bormann, 1975;Fairfax & Lepp, 1975;Horntvedt, 1978;Scherhatskoy & Klein, 1983;Schier, 1987). Some reports, however, have shown reduced leaching of some cations -with increased solution acidity (Evans, Curry & Lewin, 1981;Evans, Santucci & Patti, 1985;Haines, Chapman & Monk, 1985;Schier, 1987), indicating that a simple mechanism does not exclusively control foliar exchange.…”