Dew is an important water input and promotes plant growth. Dew condenses on plant leaves at night, and a portion of this dew returns to the atmosphere through evaporation. The amount of dew that evaporates is not equal to the amount of condensation; however, the dew evaporation process has not received enough attention. By monitoring the dew condensation and evaporation processes associated with four typical shrubs (Syringa, Hemiptelea, Buxus, and Cornus) in northeast China, we found that dew condensation started approximately 30 min after sunset, finished approximately 30 min before sunrise, and then turned to the evaporation phase. Dew had completely depleted approximately 4 h after sunrise. The dew evaporation period was negatively correlated with the wind speed (p < 0.01) and positively correlated with temperature, solar radiation, and relative humidity (RH) (p < 0.01). The average evaporation periods of Syringa, Buxus, Cornus, and Hemiptelea were 282 ± 21 min, 255 ± 26 min, 242 ± 22 min, and 229 ± 17 min, respectively. The daily evaporation amounts in May and September reached the minimum and maximum values, respectively, and the evaporation intensity of dew was positively correlated with RH (p < 0.01). There was no significant difference in the daily evaporation amounts of Syringa, Hemiptelea, Buxus, or Cornus (p > 0.05), and the annual evaporation amounts of these four plants were 17.05 mm/y, 16.38 mm/y, 21.94 mm/y, and 16.15 mm/y, respectively. The microstructure of leaves affected both the rate and amount of evaporation. Dew evaporated faster on hydrophilic leaves, and leaves with high trichome and stomatal densities had lower proportions of the dew evaporation amount to the condensation amount. The proportions of the dew evaporation amount to the condensation amount derived for Syringa, Hemiptelea, Buxus, and Cornus were 60.38%, 46.07%, 57.24%, and 52.81%, respectively. This study supplements our understanding of dew evaporation amounts, providing information that was missing in the near-surface hydrological cycle and aiding in the assessment of the ecological significance of dew to plants.
Dew is a part of the water cycle of ecosystems and is a source of water and humidity. The climate characteristics of the frost-free period in Northeast China are suitable for dew condensation, and dew is an important factor of water balance in this area. Northeast China is among the most significant warming areas in China, with an obvious “warm and dry” climate trend, which may affect dew condensation. To determine the dew amounts in different ecosystems in Northeast China and the influence of climate change on these amounts, dew condensation in farmland (corn), wetland (Carex lasiocarpa) and urban ecosystems (Syringa oblata Lindl.) was monitored during the growing period (May to October) from 2005 to 2021. The results showed that the annual average number of dew days was 132.8 in a wetland in Fujin, 122.9 in a farmland in Lishu and 118.1 in an urban area in Changchun. The daily dew intensity in the three ecosystems was lowest in May and highest in July and August. The average daily dew intensity was higher in the wetland (0.125 ± 0.069 mm) than the farmland (0.061 ± 0.026 mm) and urban area (0.028 ± 0.009 mm). The annual dew amount was also highest in the wetland (44.09 ± 7.51 mm) compared to the farmland (34.46 ± 3.54 mm) and much higher than that in the urban ecosystem (25.32 ± 3.29 mm). The annual dew in the farmland, wetland and urban ecosystems accounted for 7.92 ± 2.76%, 14.98 ± 5.93% and 6.71 ± 2.66% of the rainfall in the same period, respectively. The results indicated that dew was an important source of water and that wetlands had greater dew deposition than farmlands and urban areas. Considering the climate data during the dew condensation period from 1957 to 2021, the annual dew amount showed a decreasing trend of −0.40 mm/10a (p < 0.05) in Changchun. However, under the joint influence of relative humidity (RH) and wind speed (V), the impact of climate change on dew condensation was not obvious. This study further clarified the impact of climate change on the near-surface water cycle.
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