Abstract:

Objective: Constructing a multi-view plant phenotypic information collection platform, image data of seedlings under water and fertilizer stress were obtained at fixed time intervals, and phenotypic parameters were extracted from morphological changes to characterize the stress response to water and fertilizer stress of Salix suchowensis seedlings, providing reference for cultivating seedling and managing water and fertilizer accurately. Method: This paper constructed a multiple view phenotypic information collection platform and proposed a seedling phenotypic extraction method based on time sequence images by adopting the approximate stitching algorithm to realize the local image effective joining together into a complete image, phenotypic information such as plant height and major branch diameter extraction algorithm and plant height visualization algorithm were put forward based on image multiple points of view. In this paper, a water-fertilizer experiment was carried out with Salix suchowensis as the research object, and water and nitrogen factors were set up, including two levels of normal water treatment and drought stress treatment, and six levels of nitrogen concentration. The changes of plant height and main branch diameter of Salix suchowensis under time series were compared and observed. Result: 1） Compared with the traditional direct mosaic algorithm and violent mosaic algorithm, the approximate image mosaic algorithm proposed in this paper has better adaptability on the multi-perspective phenotypic information collection platform, and can eliminate the stitching traces well and realize the seamless image mosaic. 2） The deterministic coefficient R² of the plant height algorithm proposed in this paper is 0.96 under multi-view images, and that of the main branch diameter extraction algorithm under multi-perspective images is 0.74, which solves the problems of inaccurate measurement of plant height and un measurement of main branch diameter caused by plant leaf occlusion under single-perspective conditions. 3) In the time series of the whole growth cycle, the changes of average plant height and main branch diameter of Salix suchowensis seedlings with time were significantly affected by different water treatments. Under normal water treatment, the average plant height and main branch diameter of Salix suchowensis seedlings were 33.6 cm and 2.49 mm respectively. The average plant height and main branch diameter of Salix suchowensis seedlings were 22.8 cm and 2.25 mm, respectively. The average plant height and main branch diameter under normal water treatment were 47.4% and 10.7% which were higher than those under drought stress. 4） In the time series of the whole growth cycle, average plant height and main branch diameter of Salix suchowensis seedlings showed differences under gradient nitrogen fertilizer, and plant height and main branch diameter increased first and then decreased with nitrogen content. Under normal water treatment, except T5 treatment group, the average plant height and average main branch diameter of other groups were higher than CK treatment group, and T2 treatment group had the highest growth rate, which was 1.92 cm·d^?1 and 0.075 mm·d^?1. Under drought stress, the average plant height in T1 and T2 treatment groups was higher than that in CK treatment group, and the average growth rate in T2 treatment group was the highest, which was 1.05 cm·d^?1 and 0.035 mm·d^?1. Conclusion: The method based on continuous image sequence is reliable and practical in monitoring seedling phenotypic characteristics. When nitrogen content is insufficient, the plant growth rate will slow down, and when nitrogen content is excessive, the plant growth rate will be inhibited and even seedlings will be burned. Considering the two growth indexes of plant height and main branch diameter, T2 treatment group (urea 0.1 g per pot, urea 0.1 g per pot on the 40th day of cuttage planting) was the best fertilization index under normal water treatment.

Key words: phenotypic information, time series image, plant height, main branch diameter, water and fertilizer stress