How does the longevity of Sasa kurilensis ramets respond to a light gradient? An analysis of ontogenetic changes to hydraulic resistance and carbon budget within a ramet

We investigated how Sasa kurilensis ramet longevity differs under three light conditions. Ramet longevity is an important factor affecting the abundance of ramet populations and their biomass. The objectives of this study were to clarify: (1) whether ramet longevity varies spatially along a gradient of light conditions; (2) whether physiological functions, including water transport in culms, change with ontogenesis; (3) whether ramet longevity is associated with the most effective turnover for gaining a carbon profit within a ramet following a cost‐benefit model or is affected by other factors such as death caused by a decline in physiological function. We analyzed S. kurilensis ramet longevity, hydraulic resistance, photosynthetic rate, and carbon content. We then estimated the ramet carbon budget. The longevity of S. kurilensis ramets was 2.8–4.5 years in Beneath‐patch plots, 5.8–8.7 years in Edge‐patch plots, and 1.6–2.2 years in Open‐patch plots. Although leaf photosynthetic activity was stable, the instantaneous photosynthetic rate decreased during clear days in the open area. This may have been due to increased ramet hydraulic resistance. The rotation period of the most efficient carbon budget quantified by ecophysiological measurements was consistent with ramet longevity in Open‐patch (2 years) and Edge‐patch (5 years) sites. Meanwhile, the longevity of ramets grown under canopies was inconsistent with the cost‐benefit model rules for a carbon budget because the carbon gain was low throughout the ramet life span.