Klemm, O; Milford, C; Sutton, MA; van Putten, E; Spindler, G: A climatology of leaf surface wetness, Theoretical and Applied Climatology, 71, 107-117 (2002)
The wetness of plant leaf surfaces is an important parameter in the deposition process of atmospheric trace gases. Particularly gases with high water solubility tend to deposit faster to a wet surface, compared to a dry one. Further, drying up of a wet leaf surface may lead to revolatilization of previously deposited gases. Despite the high importance of leaf surface wetness in biosphere/atmosphere exchange, there is no quantitative description of this parameter on the ecosystem scale, quantifying its initiation, duration, dissipation, correlation with parameters such as air humidity, turbulence, vegetation type, plant physiology, and others. This contribution is a first step towards a climatology of leaf surface wetness, based on a large data basis from various ecosystems. Leaf surface wetness was monitored at two grassland and two forest research sites in NW and central Europe throughout the vegetation period of 1998. It was sensed through measurement of the electrical conductivity between two electrodes that were clipped to the living plant leaf surfaces. This yields a relative signal that responds promptly to the presence of leaf wetness. A routine is presented that combines the data from several sensors to the dimensionless leaf wetness, LW, with values between zero and one. Periods of high leaf wetness (LW>0.9) were in most cases triggered by precipitation events. After termination of rain, LW decreased quickly at the forest sites and dropped to values below 0.1 within less than 24 hours in most cases. At the grassland sites, the formation of dew led to a more complex pattern, with the occurrence of diurnal cycles of LW. Although periods of low relative air humidity (e.g., rH<50%) are normally associated with periods of low leaf wetness, the extent of correlation between these two parameters at rH>60% varies between the different sites. The grassland sites show very similar distributions of the LW data with rH, indicating a positive correlation between LW and rH, although there is much scatter in the relationship. One forest site also exhibited a positive correlation, although LW was typically lower for a given rH than at the grassland sites. At another forest site in central mountainous Europe, the correlation between LW and rH was less well established, with low leaf wetness (LW<0.001) occurring within the entire air humidity range 60% < rH < 100%. We propose that leaf wetness should be included in routine measurement programs studying biosphere-atmosphere exchange

last modified 2003-02-19