Obstacles affecting seedling germination and reproductive success of the critically endangered species Abies beshanzuensis

Abies beshanzuensis M. H. Wu is a critically endangered plant with only three wild mother trees in the world, it has a small distribution range limited to Baishanzu National Park, and its natural regeneration has been extremely low, with fewer than three seedlings appearing from 2007 to 2017. Despite the critically endangered status in China, little is known about the obstacles affecting the natural regeneration and reproduction of this species. In our study, we investigated various factors that could influence seed germination, seedling growth, seed quality, and overall production throughout the life cycle of A. beshanzuensis. Our findings highlighted the importance of litter removal in its natural habitat. Over five years following the removal of litter, we observed the emergence of 687 new seedlings, demonstrating a significant enhancement in both germination and seedling survival. Seedling abundance and mortality were greatly influenced by litter thickness, total carbon content, NO₃^--N, and available phosphorus. Seedlings height growth rate was significantly affected by litter coverage, canopy density at 1.3 m height, total nitrogen, and litter thickness. Additionally, the insufficient energy and lower values of actual photochemical rate, electron transfer rate, and photochemical quenching coefficient support in leaves with cones in the branch and branches with cones in the branch, contributed to abnormal development of female cones, leading to endosperm and embryo abortion. Our findings underscore the significant impact of environmental factors on seedling germination and growth, and highlight that insufficient energy support and reduced photosynthetic capability during female cone reproductive development may pose significant obstacles to the success of A. beshanzuensis.