DOI: 10.5061/dryad.4b8gthtj1
title: Photosynthesis and rhizome carbohydrate concentrations of switchgrass grown from reserve-depleted rhizomes

description: 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
 &lt; 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.
description: Rhizomes used in this experiment were harvested from a
 12-year-old switchgrass stand in the Michigan State University Agronomy
 Farm (42.713 N, -84.467 W) in East Lansing, Michigan, USA. Rhizomes were
 harvested during winter, in early January, and stored at 5 °C for two
 weeks before the start of the reserve-depletion treatment.
 Reserve-depletion was imposed by storing switchgrass rhizomes at 25 °C for
 14 days, control treatment rhizomes remained at 5 °C for the same
 period. Immediately after the storage period, rhizomes
 were planted individually in 2.54 L pots filled with a peat and perlite
 mix (SureMixTM; Michigan Grower Products, Galesburg, MI, USA) and kept in
 a greenhouse at 27 °C and 16hr photoperiod supplemented with artificial
 lights for the length of the growth cycle (~180 days). Rhizome
 respiration, development, and photosynthesis were measured repeatedly over
 the course of the experiment. These non-destructive measurements were
 taken on randomly assigned rhizomes weekly or biweekly. Leaf net CO2
 assimilation rate and stomatal conductance to water were measured biweekly
 in the middle portion of the youngest fully expanded leaf with a
 Li-6800. Aboveground biomass, rhizome and root biomass,
 and total leaf area were sampled 5 times during the experiment. Rhizome
 biomass was also sampled three times during the storage period on the
 first, 8th and 14th day of storage. These destructive measurements were
 taken on 10 randomly preassigned rhizomes per treatment every 30 – 40
 days. To harvest belowground tissues, soil was rinsed
 using tap water and roots were removed from rhizomes. Roots were dried and
 weighted separately as with aboveground biomass. All rhizome samples were
 weighed fresh, placed in an aluminum pouch and flash frozen in liquid
 nitrogen for glucose, sucrose, and starch content analyses. Total
 belowground biomass was estimated as the sum of root and rhizome
 biomass. Leaf and rhizome samples were stored at -80°C
 until further processing. Leaf samples were ground to a fine powder with a
 mortar and pestle. Rhizome samples were ground with a spice mixer
 (Cuisinart; SG-10). All samples stayed in contact with liquid nitrogen
 during grinding and were then freeze-dried for at least 48 hours in a
 lyophilizer. Leaf and rhizome starch, sucrose and free glucose were
 measured at the Biomass Analytics Facility at Michigan State
 University.
description: We used R (R Core Team, 2017) for all analyses and plots. We used
 lm() to fit linear models, gnls() in the nlme package to fir nonlinear
 models (Pinherio & Bates, 2000), and emmeans() in the emmeans
 package (Lenth, Singmann, Love, Buerkner, & Herve, 2018) for mean
 and parameter comparisons. Code for data analysis and
 plotting can be found at: https://github.com/PerennialDr/SinkDepletion 
description: A 30% reduction in switchgrass rhizome reserves did not decrease biomass
 yield. --- Dataset compiles switchgrass (Panicum virgatum) carbohydrate
 (Glucose, sucrose and starch content in leaves and rhizome), development
 (tillering, leaf development flowering, and senescence), photosynthesis
 (net CO2 assimilation, stomatal conductance to water, and Photosystem II
 efficiency) and biomass data (Aboveground, root, rhizome biomass, leaf
 area) measured repeatedly over switchgrass growth cycle. Plants were grown
 from reserve-depleted and control rhizomes. Control and reserve-depleted
 rhizomes were stored at 5 C and 25 C, respectively, for 14 days. The aim
 of the study was to study the effects of switchgrass rhizome reserves on
 physiology and development. ## Description of the data and file structure
 Data are presented in a long format. Each row corresponds to an
 observation of an individual plant (RhiID). Repeated measurements were
 taken for development and photosynthesis, biomass data collection was
 destructive.Columns represent: FieldRhiHarvest: Date when rhizomes were
 harvested from the field (m/d/YYYY) ExperimentStart: Date when rhizomes
 were stored at the different temperatures (m/d/YYYY) PlantedRhi: Date when
 rhizomes were planted in the greenhouse (m/d/YYYY) RhiID: Unique rhizome
 identifier Treatment: (factor) Refers to the storage temperature at which
 rhizomes were stored for 14 days at 5 C (Control) and 25 C
 (reserve-depleted) for 14 days. RhiInitialFW\_g: Initial rhizome weight in
 grams when rhizomes were placed in storage. SamplingDate: Date when plants
 were sampled for biomass, photosynthesis, and rhizome respiration and leaf
 area data (m/d/YYYY) Phase: Refers to whether the measurement was
 collected during the storage period (Storage) or after planting (Growth)
 RhiResp\_ug.g.min: Rhizome respiration rate measured during the storage
 phase at the two different storage treatment (micro g CO2 / g rhizome /
 min) Tair: Air temperature inside the respiration chamber used to measure
 rhizome respiration (Celsius). Glucose\_Rhi: Glucose content in the
 rhizome on a mass basis (%) Glucose\_Leaf: Glucose content in the leaf on
 a mass basis (%) Sucrose\_Rhi: Sucrose content, as glucose equivalents, in
 the rhizome on a mass basis (%) Sucrose\_Leaf: Sucrose content, as glucose
 equivalents, in the leaf on a mass basis (%) Starch\_Rhi: Starch content,
 as glucose equivalents, in the rhizome on a mass basis (%) Starch\_Leaf:
 Starch content, as glucose equivalents, in the leaf on a mass basis (%)
 TotalGlu\_Rhi: Total amount of glucose equivalents in the rhizome, as the
 sum of Glucose\_Rhi, Sucrose\_Rhi and Starch\_Rhi. TotalGlu\_Leaf: Total
 amount of glucose equivalents in the leaf, as the sum of Glucose\_Rhi,
 Sucrose\_Rhi and Starch\_Rhi. Leaf.Area\_cm2: Total leaf area of the
 plant, sum of leaves and stems. AboveGround\_g: Aboveground biomass of the
 plant after material was dried for 48hr at 60 C (g). RhiSample\_g: Rhizome
 fresh weight (g) Root\_g: Root biomass after material was dried for 48hr
 at 60 C (g). Qin: Photosynthetic Photon Flux Density inside the cuvette
 used to measure photosynthesis. A: net CO2 assimilation (mol CO2 m-2 s-1)
 gsw: Stomatal conductance to water (mol H2O m-2 s-1) PhiPS2: Quantum
 efficiency of photosystem II NumberOfTiller: number of tillers per pot
 totLeaves: Number of leaves per pot Caputd: did the plant die during the
 experiment before being harvested? Yes (Dead), no (Alive) In all columns,
 NA represents not available data. Usually caused by not all variables
 measured at all sampling dates. ## Sharing/Access information Companion
 manuscript is submitted to the Global Change Biology Bioenergy for
 publication. Please direct correspondence to Mauricio Tejera-Nieves
 (mauri@msu.edu) ## Code/Software We used R (R Core Team, 2017) for all
 analyses and plots. We used lm() to fit linear models, gnls() in the nlme
 package to fir nonlinear models (Pinherio & Bates, 2000), and
 emmeans() in the emmeans package (Lenth, Singmann, Love, Buerkner,
 & Herve, 2018) for mean and parameter comparisons. Scripts are
 available at: https://github.com/PerennialDr/SinkDepletion. Please reach
 out to Mauricio Tejera-Nieves (mauri@msu.edu) for questions.