Environmental factors rather than productivity drive autumn leaf senescence: evidence from a grassland in situ simulation experiment

Leaf senescence is crucial to the land biochemical cycle. However, there are still inconsistent results regarding autumn leaf senescence; in particular, there are few studies on leaf senescence in grasslands or its key factors. This study carried out a three-year in situ simulation experiment on the Stipa krylovii steppe in Inner Mongolia, aiming to explore the drivers, critical regulation periods, and regulation pathways of leaf senescence. The results showed that precipitation significantly changed the leaf senescence of Stipa krylovii, but the effects of temperature and their interactions were not significant. An increase in precipitation of 50% (W+50%) significantly delayed leaf senescence by 5.96 d, while a reduction in precipitation of 50% (W-50%) advanced it by 2.17 d. The dry mass of Stipa krylovii at the green-up, heading, flowering, seed formation, and beginning of the withering stage was significantly fitted with a quadratic-down model with leaf senescence, which is different from most present studies. Summer soil water content (SWCsu) and spring soil temperature (STsp) were significantly correlated with leaf senescence. Including dry mass or not did not significantly influence structural equation model results, and dry mass did not drive leaf senescence significantly. Leaf senescence in both models with and without dry mass was directly regulated by precipitation and spring soil temperature. Therefore, in contrast to environmental factors, productivity was not a key driver of leaf senescence. Our results provided new evidence for the recently debatable question about the driver of leaf senescence and developed a new regression correlation between productivity and leaf senescence, which are necessary and meaningful to improve our understanding of grassland phenology.

Automated summary

Leaf senescence in grasslands is influenced by precipitation, while temperature and their interactions have no significant effects. Dry mass of leaves is significantly correlated with leaf senescence, and summer soil water content and spring soil temperature are significantly associated with leaf senescence.