Soil available phosphorus and pH regulate the distribution of Juniperus przewalskii forest understory plant community diversity along an elevation gradient

Abstract

Plant diversity is crucial to forest ecosystem services. The Qinghai–Tibet Plateau has a rich variety of plants and high-elevation endemic species. However, variation in shrub and herb diversity along the elevational gradient in this region remains unclear. We recorded plant communities at 100-m intervals from 3000 to 3800 m asl., examining species composition, diversity, and the factors influencing plant communities. We found 128 plant species in 79 genera and 30 families in the Juniperus przewalskii community, including 110 species of herbs in 71 genera and 27 families, and 18 species of shrubs in 9 genera and 6 families. Distribution patterns of shrub and herb diversity differed. Shrub species richness was stable below 3400 m asl. and decreased linearly from 3400–3600 m asl. Herb richness increased from 3000 to 3400 m asl., with no significant change above 3400 m asl. The Jaccard index (C_j) and Sorenson index (C_s) of the β-diversity in the shrub peaked at 3400–3500 m asl. The Whittaker index (β_w) and Cody index (β_c) in the shrub and herb showed double hump shaped curve. The results indicate that 3400 m asl. is more suitable for a wide range of species, and the highest species turnover rate was at 3300–3400 m asl. Further, shrub α-diversity was positively correlated with available phosphorus, while herb α-diversity was negatively affected by soil pH. These findings broaden our understanding of the distribution of plant communities along elevation gradients and highlight the complexity of plant diversity in forest ecosystems.