Seedling survival after simulating grazing and drought for two species from the Pamirs, northwestern China

For plant populations to persist, seedling recruitment is essential, requiring seed germination, seedling survival and growth. Drought and grazing potentially reduce seedling recruitment via increased mor-tality and reduced growth. We studied these seed-related processes for two species indigenous to the Pamir Mountains of Xinjiang in northwestern China: Saussurea glacialis and Plantago lessingii. Seeds collected from Taxkorgan, Xinjiang, had a viability rate of 15.8% for S. glacialis but 100% for P. lessingii. Of the viable seeds, the highest germination rates were 62.9% for S. glacialis and 45.6% for P. lessingii. In a greenhouse experiment, we imposed a series of stressful conditions, involving a combination of simu-lated grazing and drought events. These had the most severe impact on younger seedlings. Modelling showed that 89% of S. glacialis mortality was due to early simulated grazing, whereas 80% of P. lessingii mortality was due to early simulated drought. Physiological differences could contribute to their differing resilience. S. glacialis may rely on water storage in leaves to survive drought events, but showed no shifts in biomass allocation that would improve grazing tolerance. P. lessingii appears more reliant on its root system to survive grazing, but the root reserves of younger plants could be insufficient to grow deeper in response to drought. After applying all mortality factors, 17.7 seedlings/parent of P. lessingii survived, while only <0.1 seedlings/parent of S. glacialis survived, raising concerns for its capacity to persist in the Pamirs. Inherent genetic differences may underlie the two species' contrasting grazing and drought responses. Thus, differing conservation strategies are required for their utilization and protection.Copyright (c) 2021 Kunming Institute of Botany, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY -NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigated the seed germination and seedling survival of two plant species, Saussurea glacialis and Plantago lessingii, in the Pamir Mountains of Xinjiang, China. The results showed that drought and grazing had negative effects on seedling recruitment, especially for younger seedlings. The two species also showed differences in their resilience to drought and grazing, suggesting the need for different conservation strategies.