Comparative analysis of annual rings of perennial forbs in the Loess Plateau, China
Although recent studies have demonstrated that annual growth rings are present among perennial forbs species, little is known about whether presence of annual rings of perennial forbs, correspondingly, the age structure and life history strategy of herbs in the Loess Plateau where plant growth is strongly limited by the double stress of the severe-erosion soil and dry climate. In this study, we investigated individuals of perennial herbs (11 species) along the precipitation gradient in the Loess Plateau, and analyzed the annual growth rings in the secondary root xylem.
We found that 10 species showed distinct annual rings, and the anatomical patterns, including vessel size and vessel density, varied considerably among different families. Although the most of herbs were relatively young (3 to 4 years old), the average age is higher compared with the North American. In addition, ring widths of the forbs demonstrated a significant trend of linear decline, reflecting the deteriorating signal of growth condition with age. Our results provided a new basis for understanding the life history strategies and limits for herbaceous plants under simultaneous soil erosion, drought stress and low resource availability in the Loess Plateau.