Shoot senescence in perennials of seasonal habitats: Comparative analysis of a large set of species

1. Senescence in plants is a hierarchical process affecting all their body parts from cells to whole organisms. Here we aim to fill the gap between the existing knowledge on leaf senescence and rapidly accumulating evidence on whole-plant senescence by addressing patterns and drivers of shoot senescence of herbaceous plants. This is a key process that determines photosynthetic gain late in the season and economy of soil-borne nutrients in seasonal climate. 2. We present a comparative study of 231 temperate species, ranging from spring ephemeroids to species senescing in late autumn, in a common botanical garden collection, thus minimizing difference in environmental drivers affecting individual species. We assessed senescence by measuring size decline in the later part of the season. 3. There were two main directions of variation in senescence trajectories: rate-date axis, separating early and fast senescing species from late and slowly senescing species, and the shape-asynchrony axis separating species with accelerating and synchronised senescence from non-accelerating senescence asynchronous among individual shoots. While accelerating senescence late in the season can be due to environmental harshness (frost), accelerating senescence early in the season is likely to be an indication of an active process. 4. As expected, rate and shape of shoot senescence were associated both with leaf- and shoot-level traits. Species having leaves with high dry matter content senesced linearly and showed higher asynchrony among individual senescing shoots. Species with larger specific leaf area tended to senesce earlier and faster, and in synchronous and accelerating manner. Tall plants senesced later and in a more synchronous and accelerating manner. 5. Species from different habitats varied in their senescence patterns. We confirmed the hypothesis that forest species postpone their senescence relative to open-habitats species, presumably to boost their photosynthetic balance, but did not confirm the hypothesis that plants from nutrient-poor habitats senesce earlier to retain soil-borne nutrients before the advent of frost. 6. Synthesis. We show that while leaf senescence scales up to contribute to shoot senescence, shoot senescence has its additional independent drivers and is a phenomenon in its own right with clear environmental drivers.Funding provided by: Grantová Agentura České RepublikyCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001824Award Number: 19-13231