Relationship between root forks and link number, branch angle of Pedicularis kansuensis under different density conditions in Gahai Wetland

The root architecture determines the root distribution and the search efficiency of water and nutrients, which is the result of the adaptability of plant roots and stress habitats. The object of this study was to examine the relationship between root forks and link number, branch angle of Pedicularis kansuensis in response to density conditions. The study site was located in Gahai Wetland, Gansu Province, China(102.08°-102.47° E, 33.97°-34.32° N). The altitude of the study site is 3430-3435 m, whereas the average annual temperature is 2.3℃. Sixty samples(1 m×1 m) were set up along the river bank to investigate the density of P. kansuensis in August 2016. Population density was categorized as low(I, 10-31 plant/m~2), medium(II, 32-53 plant/m~2), and high(III, 54-75 plant/m~2). The density, height, coverage, and above-ground biomass of the plant communities were recorded from 1 m × 1 m plots in the three densities with six replications. Thirty plants of P. kansensis were selected; the above-ground parts of those plants were cut while roots were collected by excavating the whole root system, and both were taken back to lab. Afterwards, the soil cores(30 cm × 30 cm × 50 cm) were dug from six grids(30 cm × 30 cm) in three densities. The sieve(mesh size = 0.25 mm) was used to clean the soil core in the nearby river, and the roots were taken to the lab. Afterwards, we adopted a method to stratify sampling(0-50 cm). In the laboratory, the roots were scanned with Win-RHIZO to measure the root forks and link number. The biomasses of different plots were put in an oven(at 105℃ for 30 min) for green removal, and drying(at 80℃ for 12 h), and then measured. Similarly, the soil moisture content was also measured by oven-drying(at 105℃ for 24 h). The results showed that as the population density changed from high-medium to low-medium, the coverage, height and above-ground biomass, root forks and external link number of the P. kansuensis decreased, whereas the below-ground biomass, root internal link number, and branch angle of P. kansuensis increased. The was an allometric relation between the root forks and link number, and branch angle of P. kansuensis. Additionally, the growth speed of the root internal link number and branch angle was greater than the decrease speed of root forks and external link number. The allometric slope of the root forks and external link number decreased, but that of the root forks and internal link number and branch angle increased. With a cha