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Dryad

Photosynthesis and rhizome carbohydrate concentrations of switchgrass grown from reserve-depleted rhizomes

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Sep 07, 2023 version files 97.57 KB

Abstract

A long-standing question in perennial grass breeding and physiology is whether yield improvement strategies could compromise winter survival. Perennial grasses rely on the pool of carbohydrates accumulated in storage organs from the previous growing season for winter maintenance and spring regrowth. Yield improvement strategies could reduce winter survival if they increase biomass and grain yields at the expense of carbon allocation to storage. Therefore, it is crucial to better understand the dependence of regrowth on storage reserves. We experimentally depleted switchgrass (Panicum virgatum L.) rhizome reserves by storing rhizomes for two weeks at 5 °C (control treatment) and 25 °C (reserve-depleted treatment). During the storage period rhizome respiration was 5.3x higher at 25 °C (0.010 μmol CO2 g-1 min-1 at 5 °C vs. 0.054 μmolCO2 g-1 min-1 at 25 °C; P < 0.0001) and the starch content was depleted by 30% by the end of storage. Surprisingly, reserve-depleted switchgrass had 60 % larger leaf area, and produced ~40% more aboveground biomass than control plants. In addition, it restored its rhizome starch reserves to pre-storage levels. Switchgrass showed a large plasticity amongst its source-sink components to buffer the imposed reserve depletion. It increased plant photosynthesis by increasing the photosynthetic leaf area while keeping photosynthesis constant on a leaf area basis and readjusted the timing and activity of sink organs to maintain a constant allocation of carbon to storage that was greater than the control treatment. These results suggest that switchgrass, and potentially other perennial grasses, largely over-invest in storage reserves, therefore, current breeding strategies in perennial grasses aimed to extend the growing season should not compromise crop persistence. Our study also has implications on long-term yield dynamics as it highlights sink-limitations as potential driver of the yield decline commonly observed in perennial grasses 5+ years after cultivation.