Plasticity of Sorghum Stem Biomass Accumulation in Response to Water Deficit: A Multiscale Analysis from Internode Tissue to Plant Level

Abstract

Sorghum is increasingly used as a biomass crop worldwide. Its genetic diversity provides a large range of stem biochemical composition suitable for various end-uses as bioenergy or forage. Its drought tolerance enables it to reasonably sustain biomass production under water limited conditions. However, drought effect on the accumulation of sorghum stem biomass remains poorly understood which limits progress in crop improvement and management. This study aimed at identifying the morphological, biochemical and histological traits underlying biomass accumulation in the sorghum stem and its plasticity in response to water deficit. Two hybrids (G1, G4) different in stem biochemical composition (G4, more lignified, less sweet) were evaluated during 2 years in the field in Southern France, under two water treatments differentiated during stem elongation (irrigated; 1 month dry-down until an average soil water deficit of -8.85 bars). Plant phenology was observed weekly. At the end of the water treatment and at final harvest, plant height, stem and leaf dry-weight and the size, biochemical composition and tissue histology of internodes at 2–4 positions along the stem were measured. Stem biomass accumulation was significantly reduced by drought (in average 42% at the end of the dry-down). This was due to the reduction of the length, but not diameter, of the internodes expanded during water deficit. These internodes had more soluble sugar but lower lignin and cellulose contents. This was associated with a decrease of the areal proportion of lignified cell wall in internode outer zone whereas the areal proportion of this zone was not affected. All internodes for a given genotype and environment followed a common histochemical dynamics. Hemicellulose content and the areal proportion of inner vs. outer internode tissues were set up early during internode growth and were not drought responsive. G4 exhibited a higher drought sensitivity than G1 for plant height only. At final harvest, the stem dry weight was only 18% lower in water deficit (re-watered) compared to well-watered treatment and internodes growing during re-watering were similar to those on the well-watered plants. These results are being valorized to refine the phenotyping of sorghum diversity panels and breeding populations.

Genotypic covariations of traits underlying sorghum stem biomass production and quality and their regulations by water availability: Insight from studies at organ and tissue levels

“…Previous studies reported different extents of relationships between stem size (mainly height) and lignocellulosic composition and suggested they are genetically and/or physiologically linked (Trouche et al, 2014). McKinley et al (2018) and Perrier et al (2017) reported a decrease in stem cell wall content to the benefit of nonstructural carbohydrate in biomass sorghum but they did not evaluate the genotypic variability of this response. Some studies demonstrated, however, in the case of sweet sorghum (characterized by sweet, juicy, and tall stems), that drought did not affect [postflowering stress ] or even increased [preflowering stress (Almodares, Hotjatabady, & Mirniam, 2013;Perrier et al, 2017)] stem soluble sugar content.…”

“…The quality of biomass sorghum production relies on stem biomass lignocellulosic composition, soluble sugar content, and digestibility (Trouche et al, 2014). Some studies demonstrated, however, in the case of sweet sorghum (characterized by sweet, juicy, and tall stems), that drought did not affect [postflowering stress ] or even increased [preflowering stress (Almodares, Hotjatabady, & Mirniam, 2013;Perrier et al, 2017)] stem soluble sugar content. To our knowledge, this relation was not addressed with respect to Genotype × Environment interactions (G × E) particularly in response to drought.…”

“…G. Salas Fernandez, Bao, Tang, & Schnable, 2017). Recently, Perrier et al (2017) showed on two biomass sorghum hybrids that the reduction by drought of stem biomass accumulation was associated with reduced internode length, lignin (particularly in the sclerenchyma), and cellulose contents and increased soluble sugars content. This suggests that the lignification of these tissues should not be affected to the same extent by a stress at a given time and that not only the organ but also the tissue level should be studied to understand the phenotypic plasticity of stem biomass accumulation.…”

Efeito do déficit hí­drico e CO₂ elevado sobre substâncias fenólicas e ligninas do sorgo var. 'BRS 330'

“…Sinais fenotípicos em gramíneas, como murchas antecipadas, enrolamento das folhas e diminuição do comprimento dos entrenós de colmos têm sido associados a mecanismos adaptativos ao déficit hídrico (Le Gall et al, 2015;Perrier et al, 2017).…”

“…Além disso, o conteúdo de lignina e celulose do colmo pode ser reduzido (Perrier et al, 2017). No trigo, a perda da biomassa e enrolamento das folhas foi associada ao incremento da concentração de ácidos fenólicos insolúveis em resposta ao déficit hídrico (Hura et al, 2012).…”