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 mortality and reduced growth. We studied these seed-related processes for two species indigenous to the Pamir Mountains of Xinjiang in northwestern China: and Seeds collected from Taxkorgan, Xinjiang, had a viability rate of 15.8% for but 100% for . Of the viable seeds, the highest germination rates were 62.9% for and 45.6% for In a greenhouse experiment, we imposed a series of stressful conditions, involving a combination of simulated grazing and drought events. These had the most severe impact on younger seedlings. Modelling showed that 89% of mortality was due to early simulated grazing, whereas 80% of mortality was due to early simulated drought. Physiological differences could contribute to their differing resilience. may rely on water storage in leaves to survive drought events, but showed no shifts in biomass allocation that would improve grazing tolerance. 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 survived, while only <0.1 seedlings/parent of 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.