Plant leaf surface moisture is a frequent meteorological phenomenon that has complicated sources. As such, the determination of whether surface moisture is the input water or only the redistribution of water in the soil–plant–atmosphere ecosystem is of great importance. In this study, δ18O and δD characteristic values of dew, guttation, and soil waters in Buxus sinica var. parvifolia M. Cheng were monitored during the frost-free period (June–September 2017) in Changchun, China, to differentiate the hydraulic relationship among atmospheric vapor, rainwater, soil, dew, and guttation waters and quantitatively distinguish the leaf surface moisture on the canopy and bottom of plants. The water vapor sources of the leaf surface moisture on plants’ canopy and bottom were quantitatively verified in accordance with isotope fractionation and mass conservation principles. Results demonstrated that leaf surface moisture, atmospheric vapor, soil water, and dew were closely related. Leaf surface moisture was mainly the condensation of dew. The sources of canopy and bottom leaf surface moisture were basically the same. The proportions of canopy moisture from plant guttation, atmospheric vapor, and soil water were 2.4%–2.5%, 79.8%–92.4%, and 5.1%–17.8%, respectively. By comparison, the proportions of bottom leaf surface moisture were 0.6%–1.4%, 80.0%–93.0%, and 6.4%–18.6%, respectively. Leaf surface moisture is an important water input in urban systems. Moreover, the characteristic values of stable hydrogen and oxygen isotopes of urban dew are supplemented, and the transformation of atmospheric vapor, rainwater, and soil and dew waters is revealed.
The dew condensation frequency is high, and the dew amount is heavy in urban ecosystems. During the condensation process, particulate matter acts as a condensation core, playing an important role in purifying the air. At night, dew mainly condenses on plant leaf surfaces, the plant leaves settle the particles in the dew, and some of the particles are resuspended into the atmosphere in the process of dew evaporation after sunrise. This paper monitored the condensation and evaporation processes of dew on four common plants in Changchun city from June to September 2020. By analyzing the mass and size of particles on different leaves after dew condensation and evaporation, the ability of different plants to retain particles in dew was analyzed. The results showed that there was no significant difference in the TSP capture ability during dew condensation between Buxus sinica (Rehd. et Wils.) Cheng subsp. sinica var. parvifolia M. Cheng, Syringa oblata Lindl., Hemiptelea davidii (Hance) Planch., and Pinus tabuliformis Carrière, with a TSP content of 0.21 ± 0.06 μg/cm2. Coarse particulate matter is the main type of deposit in the dew condensation stage. Particulate deposition varied according to species, leaf shape, and microstructure. The proportion of TSP remaining on leaves after dew evaporation from Pinus tabuliformis Carrière, Hemiptelea davidii (Hance) Planch., Buxus sinica (Rehd. et Wils.) Cheng subsp. sinica var. parvifolia M. Cheng, and Syringa oblata Lindl. tree was 89.7 ± 3.9%, 80.6 ± 3.6%, 75.9 ± 4.5%, and 71.4 ± 3.7%, respectively. The ability of the leaves to trap fine particles was significantly higher than that for coarse particles ( P < 0.05 ) after dew evaporation. The highest amount of particle captured by Syringa oblata Lindl. individual was 15.17 g/y during dew condensation, and the amount of remaining particles after dew evaporation was 10.83 g/y. This paper provides a theoretical basis for the selection of tree species for urban greening.
Dew condensation on plant leaves at night is a common and frequently occurring meteorological phenomenon. Dew generally evaporates to the atmosphere but can also be absorbed and utilized directly by plant leaves [1] or drip onto the soil surface [2]. Evidence suggests that dew formation benefits plant growth. Dew can be absorbed directly through foliar uptake and improve plant water status, which is especially relevant in plants exposed to prolonged drought [3]. In the arid region, dew is redistributed among plant organs and affects seedlings' early growth characteristics through the growth rate, plant height, stem diameter, and leaf count [4]. During the dry
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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