Dew is one of the important water resources on the earth and is beneficial to the survival, growth and development of the plants based on the arid and semiarid environment. The disputed effects of dew on plants, beneficial and harmful, were reviewed in this study. The beneficial effects mainly consist of five aspects: (1) Supplying important water resource. In the arid and semiarid regions or in the dry season, dew is the main or the only water resource because of its higher frequency and sustaining time comparing with the precipitation, which keeps the organic synthesis and metabolism, accelerates the increase of biomass in plants. (2) Regulating inner water of plants. The function of dew on regulating inner water of plants includes the following several aspects based on related studies: helping plant to rapidly activate photosynthetic activity during desiccation and rehydration; supplying a moisture environment in repairing embryo DNA of seeds, maintaining seed viability under harsh desert conditions; regulating the transpiration pressure and helping the wilting plant arrive a higher steady restoration state; etc. (3) Improving water balance of soil. There is an indirect effect of dew on plant through improving water balance of soil. On one hand, dew forms on the soil surface or drops into the soil from the nearby plants, becoming an importing water resource. On the other hand, the soil evaporation decreases along with dew event appears, leading a mitigation of soil water tension to some extent. (4) Regulating growing environment of forest plants. The regulation effect appears on canopy firstly, and then into the forest. Dew deposition increases the water resource of forest, improves its water cycle. Along with the dew deposition and evaporation, the forest micro-climate changes, especially the wind speed, moisture and heat. Dew, as a medium, is concerned with the water-heat exchange process of the forest. (5) Dew was used widely in the performing process of foliage dressing, defoliant and pesticide for its characteristics including small dew amount, long time sustaining on objects, leading an accreting of long time, extending the time of sterilization.
The harmful effects mainly consist of two aspects: (1) Inducing plant disease. The pathogen of fungus and bacteria releases spores and infects the host plant under a moisture condition, and induces plant disease easily, thus dew supplies opportunities for pathogen. The infection intensity differs from the differences of dew quantity and sustaining time. (2) Reducing output and quality of crops. The influence on the output and quality of crops is related to the quantity, sustaining time, acidification level of dew. The plant stomata movement was inhibited and the route of pollen diffusing was discouraged when the quantity and sustaining time of dew arrive at a higher level. Acid dew could lead to a degradation of vegetation for the decreasing of CO₂ assimilation efficiency. Furthermore, the black spot disease of fruit could be induced by dew.
The main problems in related researches were also pointed out in present paper. For example, the information of dew action effect on plants was absent; few documents referred to the changing environment, such as urban heat island and the polluted atmosphere etc; researches of dew on plant diversity and the use on biological control were lack.
Future studies were recommended to (1) researches of the action effect and mechanisms of dew on plants; (2) researches on the interactions of dew and plants based on the interferential factors including acid dew and the urban heat island effect; (3) researches of the influence of dew on the plant diversity; (4) applied researches on controlling harmful plants using dew.