Abstract:

Aims The growth relationship between twig and leaf is a strategy that plant canopy structure employs to space resources and enhance photosynthetic efficiency and competitiveness through configuration adjustments. Our objective was to examine how Stellara chamaejasme exploited twig and leaf configuration to explore the effects of slope change.
Methods In the upper reaches of Shiyang river, Gansu Province, China, 80 plots were set up at intervals of 20 m from the foot of a mountain along eight aspects. GPS was used to record latitude, longitude and altitude of each plot. Community traits were investigated and five S. chamaejasme were cut randomly on each plot for measurement of twig length, twig number, leaf area and leaf number. ArcGIS was used to set up digital elevation model (DEM) and abstract slope data of the study site. The 80 plots were divided into 0°-10°, 10°-20° and 20°-30° slope gradients. Values for twig and leaf traits were logarithmically converted, and then the standardized major axis (SMA) estimation method was used to examine the allometric relationship between twig number, twig length, leaf number and leaf length.
Important findings Twig length, twig number and leaf area of S. chamaejasme gradually decreased along the slope gradient. Significant allometric relationships between leaf number and twig length and between twig number and twig length were found to be consistent in all three slope gradients. Growing speed of twig length was greater than the speed of leaf number, and the growing speed of twig number was greater than the speed of twig length. However, there were significant differences in SMA slope in the three slope gradients, suggesting that slope constrains the leaf number and twig number that can be supported by a given twig length.

Key words: allometry, alpine grassland, leaf area, slope, Stellera chamaejasme, twig length