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.