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Dew has been recognized for its ecological significance and has also been identified as an additional source of water in arid zones. We used factorial control experiment, under dew presence in the field, to explore photosynthetic performance, water status and growth response of desert annual herbage. Bassia dasyphylla seedlings were grown in contrasting dew treatments (dew-absent and dew-present) and different watering regimes (normal and deficient). The effects of dew on the water status and photosynthetic performance of Bassia dasyphylla, grown in a desert area of the Hexi Corridor in Northwestern China, were evaluated. The results indicated the presence of dew significantly increased relative water content (RWC) of shoots and total biomass of plants in both water regimes, and enhanced the diurnal shoot water potential and stomatal conductance in the early morning, as well as photosynthetic rate, which reached its maximum only in the water-stressed regime. The presence of dew increased aboveground growth of plants and photosynthate accumulation in leaves, but decreased the root-to-shoot ratio in both water regimes. Dew may have an important role in improving plant water status and ameliorating the adverse effects of plants exposed to prolonged drought.

Abstract:Dew, as a supplementary water source, may have an important ecological role in arid and semi-arid regions. During August and September of 2007 and 2008, measurements were taken to investigate the dew accumulation and evaporation patterns in the very early morning hours, in three different habitats (dunetop, footslope, and interdune lowland) of a fixed sand dune in Northwest China. Dew quantities were measured using the cloth-plate method. The results indicated that there was a positive correlation between dew amounts and relative humidity, but a negative correlation between dew amounts and mean temperature. Clear mornings were characterized by higher dew amounts and longer dew duration, whereas less dew was recorded during cloudy and especially windy mornings. Dew continued to condense even after sunrise, although a shorter warming time after dawn is also of vital importance in dew formation. The higher average maximum dew quantities (0.06 mm) and longer average dew duration (2.3 h) occurred in the interdune lowland; the lower and shorter average dew amounts (0.048 mm) and duration (1.9 h) were obtained at the dune top. The footslope habitat exhibited intermediate values. Clearly, the differences in dew deposition can be partially attributed to the distinguishing characteristics of the microhabitats. The present study highlighted the impacts of these characteristics on near-ground dew condensation accumulation and evaporation in a fixed sand dune and may facilitate evaluation of the role of dew in arid and semi-arid environments.