Dew formation measurements
We used three methods to measure dew amount and duration:
(1) Artificial condensation surface: The daily dew production
was collected and measured using a preplaced plastic film, 20 cm × 20 cm
in size, at each plot (Vuollekoski et al. 2015). The clean plastic films
were weighed and placed at each plot at 20:00 pm (local time) the day
before each measurement. At 6:00 am the next morning, the preplaced
plastic films were weighed, and the differences in the weights were
designated as the dew production (g) for that night. The dew amount (mm)
was equal to the dew weight divided by the area of the plastic film. In
this study, the dew amounts were measured by this method on sunny and
windless days two times per week during the peak growing seasons (from
July to September) in 2012 and 2013.
(2) In situ dew formation measurements on plants : Dew
formation on plants was measured by sampling the outside plots to avoid
disturbing the plant community composition of each plot. Similar
individuals of the same species were chosen to measure dew formation.
For each species, four or five individuals were selected, weighed,
measured plant heights and placed into floral foam to prevent wilting
the day before measurement and then placed at each plot at 20:00 pm
(local time). At 6:00 am the next morning, these plants were weighed
after being brought back to the laboratory to attain the total weight.
The dew production (g) was equal to the total weight minus the plant
fresh weight. At the same time, we scanned the leaf area of plants and
finally calculated the dew amount (mm) produced per unit plant area. In
this study, the dew amounts were measured by this method on sunny and
windless days three times per week during the peak growing season (from
July to September) in 2017.
(3) Leaf wetness sensors : The dew amount and duration were
monitored hourly using leaf wetness sensors (S-LWA-M003, Onset Computer
Corporation, Bourne, MA, USA) and a HOBO data logger (H21-002, Onset
Computer Corporation, Bourne, MA, USA) at each plot from 2015 to 2017
(Chen 2015). The dew amount was calculated by the fitting relationship
between the measured leaf wetness sensor readings and the actual
condensed water amount (g). We sprayed water evenly on the leaf wetness
sensors to induce water condensation on their surface, recorded the
instrument reading, and established the relationship between the
condensation amount and the leaf wetness sensor readings. In addition,
the simulated solid condensation amount was determined using the same
method in a -20 °C refrigerator to establish a relationship curve. We
repeated the above steps multiple times to ensure a wide range of leaf
wetness sensor readings. The relationship curve between the leaf wetness
sensor readings and the condensation amount was fitted (see Appendix S1
in Supporting Information), and the relationship was as follows:
D = (0.00005 × Rl2 + 0.0001 × Rl) / S,
R2 = 0.71, p < 0.001,
where D is the dew amount (mm), Rl is the leaf wetness
sensor reading and S is the area of the leaf wetness sensor,
which was 4.7 cm × 5.1 cm.
In our study, the former two measurement methods focused on dew amount,
while only the leaf wetness sensor method measured the dew duration. The
data were automatically recorded hourly, and dew duration was calculated
as the number of days for which dew was recorded between 8:00 p.m. and
6:00 a.m. of the next morning during the measuring periods.