Measurement of assimilation branch surface area
At each site across the DGW, 10 branches were selected and labeled on
each of the five sampled plants. All foliage on each branch was
photographed using a 6 × 108 pixel digital camera (EOS550D, Canon Inc.,
Japan), at 10-d intervals, from the beginning to the end of the
experimental period. The total leaf surface area of each branch was
calculated from the images using CI-400 CIAS software (Computer Imaging
Analysis Software, CID Co., Logan, UT, USA). Seasonal changes in leaf
area per branch were recorded (H. Xu et al., 2007). The daily relative
growth rate of leaves was calculated as the change in leaf area during
the intervals between the two measurements. The calculation formula is
as follows:
, (1)
where St represents the leaf area at the time t;
St+1 represents the assimilation branch area at the next
measurement time, t+1, and Δt represent the interval time between the
two measurements.