Miscanthus x giganteus Stem Versus Leaf-Derived Lignins Differing in Monolignol Ratio and Linkage.

Michel Bergs,Xuan Do,Ralf Pude,Georg Völkering,Yulia Monakhova,Thorsten Kraska,Margit Schulze,Christopher Konow,Peter Kusch

doi:10.3390/ijms20051200

Abstract

As a renewable, Miscanthus offers numerous advantages such as high photosynthesis activity (as a C4 plant) and an exceptional CO2 fixation rate. These properties make Miscanthus very attractive for industrial exploitation, such as lignin generation. In this paper, we present a systematic study analyzing the correlation of the lignin structure with the Miscanthus genotype and plant portion (stem versus leaf). Specifically, the ratio of the three monolignols and corresponding building blocks as well as the linkages formed between the units have been studied. The lignin amount has been determined for M. x giganteus (Gig17, Gig34, Gig35), M. nagara (NagG10), M. sinensis (Sin2), and M. robustus (Rob4) harvested at different time points (September, December, and April). The influence of the Miscanthus genotype and plant component (leaf vs. stem) has been studied to develop corresponding structure-property relationships (i.e., correlations in molecular weight, polydispersity, and decomposition temperature). Lignin isolation was performed using non-catalyzed organosolv pulping and the structure analysis includes compositional analysis, Fourier transform infradred (FTIR), ultraviolet/visible (UV-Vis), hetero-nuclear single quantum correlation nuclear magnetic resonsnce (HSQC-NMR), thermogravimetric analysis (TGA), and pyrolysis gaschromatography/mass spectrometry (GC/MS). Structural differences were found for stem and leaf-derived lignins. Compared to beech wood lignins, Miscanthus lignins possess lower molecular weight and narrow polydispersities (<1.5 Miscanthus vs. >2.5 beech) corresponding to improved homogeneity. In addition to conventional univariate analysis of FTIR spectra, multivariate chemometrics revealed distinct differences for aromatic in-plane deformations of stem versus leaf-derived lignins. These results emphasize the potential of Miscanthus as a low-input resource and a Miscanthus-derived lignin as promising agricultural feedstock.

Highlights

Miscanthus, a perennial rhizome-forming sweet grass (Poaceae), is originally cultivated in subtropical regions in Asia
There are approximately 17 species investigated in Europe for energy and material development including Miscanthus tinctorius, M. sinensis, M. sacchariflorus, and the triploid genotype M. x giganteus, which is an allotriploid hybrid of the diploid M. sinensis and the tetraploid M. sacchariflorus
This study presents comprehensive analytical data for Miscanthus x giganteus-derived lignins correlating with plant portions

Summary

Introduction

Miscanthus, a perennial rhizome-forming sweet grass (Poaceae), is originally cultivated in subtropical regions in Asia. Miscanthus field trials have been performed in Europe over the past 25 years confirming that M. x giganteus hybrids show high yields over a wide range of environmental conditions [1,2,3]. Miscanthus is one of the very few crops that is studied to serve as a CO2 sink [7,8,9,10,11,12,13] This sterile genotype does not generate fertile seeds, which avoids uncontrolled spreading [14]. The production of the perennial crop lasts for about 20 years. Within the last five years, the upscaling of Miscanthus biomass production in Europe could significantly be improved by using seed-based hybrids. Miscanthus hybrids are expected to play an increasing role in the provision of perennial lingo-cellulosic feedstock in Europe, which contributes to a lower carbon economy [1,18,19]

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Conclusion