Simultaneous Production of Cellulose Nitrates and Bacterial Cellulose from Lignocellulose of Energy Crop

This study is focused on exploring the feasibility of simultaneously producing the two products, cellulose nitrates (CNs) and bacterial cellulose (BC), from Miscanthus × giganteus. The starting cellulose for them was isolated by successive treatments of the feedstock with HNO3 and NaOH solutions. The cellulose was subjected to enzymatic hydrolysis for 2, 8, and 24 h. The cellulose samples after the hydrolysis were distinct in structure from the starting sample (degree of polymerization (DP) 1770, degree of crystallinity (DC) 64%) and between each other (DP 1510-1760, DC 72-75%). The nitration showed that these samples and the starting cellulose could successfully be nitrated to furnish acetone-soluble CNs. Extending the hydrolysis time from 2 h to 24 h led to an enhanced yield of CNs from 116 to 131%, with the nitrogen content and the viscosity of the CN samples increasing from 11.35 to 11.83% and from 94 to 119 mPa·s, respectively. The SEM analysis demonstrated that CNs retained the fiber shape. The IR spectroscopy confirmed that the synthesized material was specifically CNs, as evidenced by the characteristic frequencies of 1657-1659, 1277, 832-833, 747, and 688-690 cm-1. Nutrient media derived from the hydrolyzates obtained in 8 h and 24 h were of good quality for the synthesis of BC, with yields of 11.1% and 9.6%, respectively. The BC samples had a reticulate structure made of interlaced microfibrils with 65 and 81 nm widths and DPs of 2100 and 2300, respectively. It is for the first time that such an approach for the simultaneous production of CNs and BC has been employed.

PGPR-driven phytoremediation and physiobiochemical response of Miscanthus × giganteus to stress induced by the trace elements

The effect of inoculation of Miscanthus × giganteus Greef et Deu by the plant growth promoting rhizobacteria (PGPRs) to the phytoremediation process and physio-biochemical plant's parameters was investigated in soil contaminated with the trace elements (TEs) from the Tekeli mining complex, Kazakhstan. Yeast Trichosporon sp. CA1, strains Rhizobium sp. Zn1-1, Shinella sp. Zn5-6, and Pseudomonas sp. CHA1-4, resistant to Zn and Pb, were isolated from the rhizosphere of M × g when the plant was cultivated in the same contaminated soil. Results illustrated that inoculation improved M × g adaptability to TEs toxicity by increasing the tolerance index to 2.9. The treatment enhanced the aboveground biomass yield by up to 163%, root biomass by up to 240%, chlorophyll content by up to 30%, and Chla/b ratio by up to 21%. Through M × g active growth and development, the peak activity of antioxidant enzymes was observed: activity of superoxide dismutase and glutathione reductase was induced, while the activity of catalase and ascorbate peroxidase was inhibited. Based on bioconcentration and translocation factors it was revealed that PGPRs selectively increased the uptake of TEs or stabilised them in the M × g rhizosphere. Inoculation with PGPRs increased the stabilization of Pb, V, Cr, Co, Ni, Cu, Cd, As, and Ba in the soil and plant tissues. Further research should focus on ex situ experiments using isolated PGPRs.

Effect of Heavy-Metal-Resistant PGPR Inoculants on Growth, Rhizosphere Microbiome and Remediation Potential of Miscanthus × giganteus in Zinc-Contaminated Soil

Microbial-assisted phytoremediation is considered a more effective approach to soil rehabilitation than the sole use of plants. Mycolicibacterium sp. Pb113 and Chitinophaga sp. Zn19, heavy-metal-resistant PGPR strains originally isolated from the rhizosphere of Miscanthus × giganteus, were used as inoculants of the host plant grown in control and zinc-contaminated (1650 mg/kg) soil in a 4-month pot experiment. The diversity and taxonomic structure of the rhizosphere microbiomes, assessed with metagenomic analysis of rhizosphere samples for the 16S rRNA gene, were studied. Principal coordinate analysis showed differences in the formation of the microbiomes, which was affected by zinc rather than by the inoculants. Bacterial taxa affected by zinc and the inoculants, and the taxa potentially involved in the promotion of plant growth as well as in assisted phytoremediation, were identified. Both inoculants promoted miscanthus growth, but only Chitinophaga sp. Zn19 contributed to significant Zn accumulation in the aboveground part of the plant. In this study, the positive effect of miscanthus inoculation with Mycolicibacterium spp. and Chitinophaga spp. was demonstrated for the first time. On the basis of our data, the bacterial strains studied may be recommended to improve the efficiency of M. × giganteus phytoremediation of zinc-contaminated soil.

Species selection determines carbon allocation and turnover in Miscanthus crops: Implications for biomass production and C sequestration

Growing Miscanthus species and hybrids has received strong scientific and commercial support, with the majority of the carbon (C) modelling predictions having focused on the high-yield, sterile and noninvasive hybrid Miscanthus × giganteus. However, the potential of other species with contrasting phenotypic and physiological traits has been seldom explored. To better understand the mechanisms underlying C allocation dynamics in these bioenergy crops, we pulse-labelled (¹³CO₂) intact plant-soil systems of Miscanthus × giganteus (GIG), Miscanthus sinensis (SIN) and Miscanthus lutarioriparius (LUT) and regularly analysed soil respiration, leaves, stems, rhizomes, roots and soils for up to 190 days until leaf senescence. A rapid isotopic enrichment of all three species was observed after 4 h, with the amount of ¹³C fixed into plant biomass being inversely related to their respective standing biomass prior to pulse-labelling (i.e., GIG < SIN < LUT). However, both GIG and LUT allocated more photoassimilates in the aboveground biomass (leaves+stems = 78 % and 74 %, respectively) than SIN, which transferred 30% of fixed ¹³C in its belowground biomass (rhizomes+roots). Although less fixed ¹³C was recovered from the soils (<1 %), both rhizospheric and bulk soils were signficantly more enriched under SIN and LUT than under GIG. Importantly, the soils under SIN emitted less CO₂, which suggests it could be the best choice for reaching C neutrality. These results from this unique large-scale study indicate that careful species selection may hold the success for reaching net GHG mitigation.

Evaluation of Miscanthus × giganteus Tolerance to Trace Element Stress: Field Experiment with Soils Possessing Gradient Cd, Pb, and Zn Concentrations

Miscanthus × giganteus demonstrated good phytostabilization potentials by decreasing the trace elements (T.E.s) mobility and enhancing the degraded soil quality. Nevertheless, most of the published work was performed under controlled conditions in ex situ pot experiments and/or with soils being spiked. Hence, data about the plant's tolerance to increased T.E. concentrations in real conditions is still scarce and requires further investigation. For this sake, a field experiment was established by cultivating miscanthus plants in three different agricultural plots representing gradient trace element (Cd, Pb and Zn) concentrations. Another uncontaminated plot was also introduced. Results showed that T.E. concentrations in the leaves were tolerable to the plant. In addition, no variations were detected between the miscanthus cultivated in the contaminated and uncontaminated soils at the level of antioxidant enzymatic activities (ascorbate peroxidase and superoxide dismutase), photosynthetic pigments (chlorophyll a and b and carotenoids), and secondary metabolites (phenolic compounds, flavonoids, anthocyanins, and tannins). These outcomes validate the high capacity of miscanthus to resist and tolerate contaminated conditions. Such results may contribute to further understanding of the miscanthus tolerance mechanisms.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 2, Comparison between Two Growing Seasons

The positive impact on restoring soil functionality, decreasing toxic elements (TE) bioaccessibility, and enhancing soil physicochemical and biological parameters established a consensus on considering a Miscanthus × giganteus convenient species for phytomanaging wide TE contaminated areas. Nevertheless, information about the plant's mode of reaction to elevated soil multi-TE concentrations is still scarce. For the sake of investigating the miscanthus response to stressful TE concentrations, an ex-situ pot experiment was initiated for 18 months, with three miscanthus cultivars referred to as B, U, and A planted in soils with gradient Cd, Pb, and Zn concentrations. A non-contaminated control soil was introduced as well, and plants were cultivated within. Results revealed that the long exposure to increasing soil TE concentrations caused the number of tillers per plant to decline and the TE concentrations in the leaves to boost progressively with the soil contamination. The photosynthetic pigments (chlorophyll a, b, and carotenoids) were negatively affected as well. However, the phenolic compounds, flavonoids, tannins, and anthocyanins, along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase elevated progressively with the TE concentration and exposure duration. Conclusively, miscanthus plants demonstrated an intensified and synchronized antioxidative activity against the TE concentration.

Response of Total (DNA) and Metabolically Active (RNA) Microbial Communities in Miscanthus × Giganteus Cultivated Soil to Different Nitrogen Fertilization Rates

Miscanthus × giganteus is a promising high-yielding perennial plant to meet growing bioenergy demands; however, the degree to which the soil microbiome affects its nitrogen cycling and subsequently, biomass yield remains unclear. In this study, we hypothesize that contributions of metabolically active soil microbial membership may be underestimated with DNA-based approaches. We assessed the response of the soil microbiome to nitrogen availability in terms of both DNA and RNA soil microbial communities from the Long-term Assessment of Miscanthus Productivity and Sustainability (LAMPS) field trial. DNA and RNA were extracted from 271 samples, and 16S small subunit (SSU) rRNA amplicon sequencing was performed to characterize microbial community structure. Significant differences were observed in the resulting soil microbiomes and were best explained by the sequencing library of origin, either DNA or RNA. Similar numbers of membership were detected in DNA and RNA microbial communities, with more than 90% of membership shared. However, the profile of dominant membership within DNA and RNA differed, with varying proportions of Actinobacteria and Proteobacteria and Firmicutes and Proteobacteria. Only RNA microbial communities showed seasonal responses to nitrogen fertilization, and these differences were associated with nitrogen-cycling bacteria. The relative abundance of bacteria associated with nitrogen cycling was 7-fold higher in RNA than in DNA, and genes associated with denitrifying bacteria were significantly enriched in RNA, suggesting that these bacteria may be underestimated with DNA-only approaches. Our findings indicate that RNA-based SSU characterization can be a significant and complementing resource for understanding the role of soil microbiomes in bioenergy crop production. IMPORTANCEMiscanthus × giganteus is a promising candidate for bioeconomy cropping systems; however, it remains unclear how the soil microbiome supplies nitrogen to this low-input crop. DNA-based techniques are used to provide community characterization, but may miss important metabolically active taxa. By analyzing both DNA- and actively transcribed RNA-based microbial communities, we found that nitrogen cycling taxa in the soil microbiome may be underestimated using only DNA-based approaches. Accurately understanding the role of microbes and how they cycle nutrients is important for the development of sustainable bioenergy crops, and RNA-based approaches are recommended as a complement to DNA approaches to better understand the microbial, plant, and management interactions.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 1, Plant Defence Mechanisms

Miscanthus × giganteus demonstrated good phytostabilization potentials in toxic element (TE) contaminated soils. However, information about its tolerance to elevated concentrations is still scarce. Therefore, an ex-situ pot experiment was launched using three cultivars (termed B, U, and A) grown in soils with a gradient Cd, Pb and Zn concentrations. Control plants were also cultivated in non-contaminated soil. Results show that the number of tillers per plant, stem diameter as well as leaf photosynthetic pigments (chlorophyll a, b and carotenoids) were negatively impacted by soil contamination. On the other hand, phenolic compounds, flavonoids, tannins, and anthocyanins levels along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase increased in the plants grown on contaminated soils. Altogether, these data demonstrate that miscanthus is impacted by concentrations of toxic elements yet is able to tolerate high levels of soil contamination. These results may contribute to clarifying the miscanthus tolerance strategy against high contamination levels and its efficiency in phytoremediation.

Biorefining Potential of Wild-Grown Arundo donax, Cortaderia selloana and Phragmites australis and the Feasibility of White-Rot Fungi-Mediated Pretreatments

Arundo donax, Cortaderia selloana and Phragmites australis are high-biomass-producing perennial Poalean species that grow abundantly and spontaneously in warm temperate regions, such as in Mediterranean-type climates, like those of Southern Europe, Western United States coastal areas, or in regions of South America, South Africa and Australia. Given their vigorous and spontaneous growth, biomass from the studied grasses often accumulates excessively in unmanaged agro-forestry areas. Nonetheless, this also creates the demand and opportunity for the valorisation of these biomass sources, particularly their cell wall polymers, for biorefining applications. By contrast, a related crop, Miscanthus × giganteus, is a perennial grass that has been extensively studied for lignocellulosic biomass production, as it can grow on low-input agricultural systems in colder climates. In this study Fourier transform mid-infrared spectroscopy (FTIR), high-performance anion-exchange chromatography (HPAEC) and lignin content determinations were used for a comparative compositional characterisation of A. donax, C. selloana and P. australis harvested from the wild, in relation to a trial field-grown M. × giganteus high-yielding genotype. A high-throughput saccharification assay showed relatively high sugar release values from the wild-grown grasses, even with a 0.1M NaOH mild alkali pretreatment. In addition to this alkaline pretreatment, biomass was treated with white-rot fungi (WRF), which preferentially degrade lignin more readily than holocellulose. Three fungal species were used: Ganoderma lucidum, Pleurotus ostreatus and Trametes versicolor. Our results showed that neutral sugar contents are not significantly altered, while some lignin is lost during the pretreatments. Furthermore, sugar release upon enzymatic saccharification was enhanced, and this was dependent on the plant biomass and fungal species used in the treatment. To maximise the potential for lignocellulose valorisation, the liquid fractions from the pretreatments were analysed by high performance liquid chromatography - photodiode array detection - electrospray ionisation tandem mass spectrometry (HPLC-PDA-ESI-MS ⁿ ). This study is one of the first to report on the composition of WRF-treated grass biomass, while assessing the potential relevance of breakdown products released during the treatments, beyond more traditional sugar-for-energy applications. Ultimately, we expect that our data will help promote the valorisation of unused biomass resources, create economic value, while contributing to the implementation of sustainable biorefining systems.

Effect of Miscanthus × giganteus ash on survival, biomass, reproduction and avoidance behaviour of the endogeic earthworm Aporrectodea caliginosa

To achieve the EU's targets for reducing energy production from fossil fuels, the use of energy crops, such as Miscanthus × giganteus, is increasing resulting in a corresponding increase in waste ash from incineration. The chemical properties of Miscanthus ash (e.g. phosphorus and potassium content) may allow this waste material (currently landfilled) to be used as a fertiliser, but no information exists on the effect of the ash on the biological properties of soil. The main aim of this study was to determine the potential impact of Miscanthus ash on earthworms by assessing the effect on survival, change in biomass, reproduction and avoidance behaviour of the geophagous, soil dwelling earthworm, Aporrectodea caliginosa. Tests utilised a range of Miscanthus ash doses from 0 to 50 t ha^-1 (0, 1, 2.5, 5, 10, 25, 50). Results showed that Miscanthus ash had no significant impact on A. caliginosa survival, biomass and reproduction, but negative trends were observed for biomass from 2.5 t ha^-1 and for reproduction from 10 t ha^-1. In contrast, a significant avoidance response was observed in the 25 and 50 t ha^-1 treatment and according to ISO guideline 17512 there is a negative impact of the Miscanthus ash on soil habitat function at 25 t ha^-1 and above as more than 80% of earthworms were in the control soil. It is suggested that this negative effect on soil habitat function could be attributed to a range of factors including the presence of heavy metals in the ash and a change in substrate pH, texture and/or osmotic stress. Further laboratory-based studies conducted over extended time periods with a more refined range of ash doses and associated field-based studies are required to validate the results and determine a more precise assessment of the threshold ash value inducing a loss of soil habitat function.

Bioprospecting of a Novel Plant Growth-Promoting Bacterium Bacillus Altitudinis KP-14 for Enhancing Miscanthus × giganteus Growth in Metals Contaminated Soil

Simple Summary

Marginal land represents poor soil with low agricultural characteristics and crop productivity, which is sometimes additionally contaminated. The exploitation of marginal land for normal agriculture is not possible but it suitable for cultivation of energy crops, especially Miscanthus × giganteus (Mxg), however, the harvest biomass value in such land is lower. The produced Mxg biomass can be converted to alternative energy like biofuel and biogas, or used for production of other value-added products like insulation fibers, building materials or paper, etc. It is well known fact that plant growth-promoting bacteria are beneficial for stimulating the overall development of plants even under stress conditions. In the current study, a number of strains were isolated from the metal-contaminated post-mining land, identified, biochemically characterized, and evaluated for abiotic stress tolerance: pH, temperature, salinity, and heavy metal (lead). Among different isolates, the multiple abiotic stress-tolerant plant growth-promoting bacteria Bacillus altitudinis KP-14 showed the best properties. Its effect on the growth of Mxg under the severe stress of metal-contaminated soil was evaluated. It was found that selected bacterial strain KP-14 significantly enhanced the biomass production. The overall results suggested that B. altitudinis KP-14 can be recommended as a potent biofertilizer for marginal lands.

Abstract

Use of plant growth-promoting bacteria (PGPB) for cultivation of the biofuel crop Miscanthus × giganteus (Mxg) in post-military and post-mining sites is a promising approach for the bioremediation of soils contaminated by metals. In the present study, PGPB were isolated from contaminated soil and screened for tolerance against abiotic stresses caused by salinity, pH, temperature, and lead (Pb). Selected strains were further assessed and screened for plant growth-promoting attributes. The isolate showing the most potential, Bacillus altitudinis KP-14, was tested for enhancement of Mxg growth in contaminated soil under greenhouse conditions. It was found to be highly tolerant to diverse abiotic stresses, exhibiting tolerance to salinity (0–15%), pH (4–8), temperature (4–50 °C), and Pb (up to 1200 ppm). The association of B. altitudinis KP-14 with Mxg resulted in a significant (p ≤ 0.001) impact on biomass enhancement: the total shoot and dry root weights were significantly enhanced by 77.7% and 55.5%, respectively. The significant enhancement of Mxg biomass parameters by application of B. altitudinis KP-14 strongly supports the use of this strain as a biofertilizer for the improvement of plant growth in metal-contaminated soils.

Multiyear phytoremediation and dynamic of foliar metal(loid)s concentration during application of Miscanthus × giganteus Greef et Deu to polluted soil from Bakar, Croatia

The multiyear cultivation of Miscanthus × giganteus Greef et Deu (M.×giganteus) at the soils polluted by metal(loid)s were researched. The biomass parameters and concentrations of elements: Ti, Mn, Fe, Cu, Zn, As, Sr, and Mo were determined in the plant's organs at harvest. The same metal(loid)s were monitored in the plant's leaves throughout three vegetation seasons. The principal component analysis and general linear model approaches were applied for statistical evaluation followed by Box-Cox transformation. The difference in the distribution of elements in the plant, the content of elements in the soil, various regime of uptake to the plant tissues, and the year of vegetation were analyzed as driving factors of the phytoremediation. The results showed that the leading promoter was the factor of the zone, which was the most essential for Ti, Fe, and Cu and the smallest for Mn. The factor of differences in soil pollution was essential for Zn and Mo, much less for As, Sr, and Mn, limited for Fe, and was not seen for Ti and Cu. The factor of the interrelation effects of the zone and experiment reflected the different regime of uptake for the plant tissues was seen for two elements: more prominent for Cu and smaller for Ti. While analyzing the dynamic of foliar concentrations of the metal(loid)s during 3 years, two groups were defined. Firstly, Fe, Ni, Mn, and Sr showed stable curves with limited distribution of the plant life cycle. Secondly, As, Zn, Cu, and Mo showed different fluctuations in the curves, which can be attributed to essential influence of those elements to the plant life cycle. Further research will be focused on the application of M.×giganteus to the polluted soil in a bigger scale and comparison results of laboratory and field experiments.

Comparative assessment of using Miscanthus × giganteus for remediation of soils contaminated by heavy metals: a case of military and mining sites

Contamination of soil by heavy metals is among the important environmental problems due to their toxicity and negative impact to human health and the environment. An effective method for cleaning the soil from heavy metals is phytoremediation using the second-generation bioenergy species Miscanthus × giganteus. The purpose of this research is to study the benefits of M. × giganteus cultivation at the soils taken from the mining and former military sites contaminated by As, Pb, Zn, Co, Ni, Cr, Cu, V, Mn, Sr, and U as well as at the soil artificially contaminated by Zn and Pb, to evaluate the physiological parameters of the plant, to establish peculiarities of the phytoremediation process, and to characterize the behavior of the plant in relation to the nature and concentrations of the metals in the soils. Results showed that M. × giganteus was resistant to heavy metals (tolerance index ≥ 1) and that the greatest portion of metals accumulated in the root system. The morphological parameters of the plant while grown on different soils are influenced by soil type and the content of contaminants. The stress effect while growing M. × giganteus on soil artificially contaminated by Zn and Pb was evaluated by measuring the content of pigments (chlorophylls a, b, and carotenoids) in the plant's leaves. The decrease in the total content of chlorophylls, С_{a + b}/С_car and transpiration rate of water along with the increase in the water absorbing capacity were observed. The accumulation of heavy metals in different parts of the plant was determined; bioaccumulation coefficient and values of translocation factor were calculated. The obtained results showed that M. × giganteus was an excluder plant for nine highly toxic elements (As, Pb, Zn, Co, Ni, Cr, Cu, V, U) and an accumulator species for the moderately dangerous elements (Mn, Sr). Further research will be focused on the extraction of stable stimulated plant-growth-promoting rhizobacteria from the rhizosphere of M. × giganteus and formulation on that base the plant-bacterial associations as well as on the comparison of the plant physiological parameters, biochemical soil activity, and accumulation of heavy metals in the Miscanthus tissues between first and second vegetations.

Catalytic gasification of biomass (Miscanthus) enhanced by CO2 sorption

The main objective of this work concerns the coupling of biomass gasification reaction and CO₂ sorption. The study shows the feasibility to promote biomass steam gasification in a dense fluidized bed reactor with CO₂ sorption to enhance tar removal and hydrogen production. It also proves the efficiency of CaO-Ca₁₂Al₁₄O₃₃/olivine bi-functional materials to reduce heavy tar production. Experiments have been carried out in a fluidized bed gasifier using steam as the fluidizing medium to improve hydrogen production. Bed materials consisting of CaO-based oxide for CO₂ sorption (CaO-Ca₁₂Al₁₄O₃₃) deposited on olivine for tar reduction were synthesized, their structural and textural properties were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and temperature-programmed reduction (TPR) methods, and the determination of their sorption capacity and stability analyzed by thermogravimetric analysis (TGA). It appears that this CaO-Ca₁₂Al₁₄O₃₃/olivine sorbent/catalyst presents a good CO₂ sorption stability (for seven cycles of carbonation/decarbonation). Compared to olivine and Fe/olivine in a fixed bed reactor for steam reforming of toluene chosen as tar model compound, it shows a better hydrogen production rate and a lower CO₂ selectivity due to its sorption on the CaO phase. In the biomass steam gasification, the use of CaO-Ca₁₂Al₁₄O₃₃/olivine as bed material at 700 °C leads to a higher H₂ production than olivine at 800 °C thanks to CO₂ sorption. Similar tar concentration and lighter tar production (analyzed by HPLC/UV) are observed. At 700 °C, sorbent addition allows to halve tar content and to eliminate the heaviest tars.

In Vitro Fermentation of Xylooligosaccharides Produced from Miscanthus × giganteus by Human Fecal Microbiota

Purified xylooligosaccharides from Miscanthus × giganteus (M×G XOS) were used in an in vitro fermentation experiment inoculated with human fecal microbiota. A commercial XOS product and pectin were used as controls. Decreases in pH by 2.3, 2.4, and 2.0 units and production of short-chain fatty acids (SCFA; acetic acid, 7764.2, 6664.1, and 6387.9 μmol/g; propionic acid, 1006.7, 1089.5, and 661.5 μmol/g; and butyric acid, 955.5, 1252.9, and 917.7 μmol/g) were observed in M×G XOS, commercial XOS, and pectin medium after 12 h of fermentation, respectively. Titers of Bifidobacterium spp., Lactobacillus spp., and Escherichia coli increased when fed all three substrates as monitored by qPCR. There was no significant trend for Clostridium perfringens. During fermentation, M×G XOS was statistically equivalent in performance to the commercial XOS sample as measured by culture acidification and growth of health-promoting bacteria and resulted in the highest SCFA production among the three substrates.

Sub-zero cold tolerance of Spartina pectinata (prairie cordgrass) and Miscanthus × giganteus: candidate bioenergy crops for cool temperate climates

Miscanthus × giganteus grown in cool temperate regions of North America and Europe can exhibit severe mortality in the year after planting, and poor frost tolerance of leaves. Spartina pectinata (prairie cordgrass), a productive C4 perennial grass native to North America, has been suggested as an alternative biofuel feedstock for colder regions; however, its cold tolerance relative to M. × giganteus is uncertain. Here, we compare the cold tolerance thresholds for winter-dormant rhizomes and spring/summer leaves of M. × giganteus and three accessions of S. pectinata. All genotypes were planted at a field site in Ontario, Canada. In November and February, the temperatures corresponding to 50% rhizome mortality (LT(50)) were near -24°C for S. pectinata and -4°C for M. × giganteus. In late April, the LT50 of rhizomes rose to -10°C for S. pectinata but remained near -4°C for M. × giganteus. Twenty percent of the M. × giganteus rhizomes collected in late April were dead while S. pectinata rhizomes showed no signs of winter injury. Photosynthesis and electrolyte leakage measurements in spring and summer demonstrate that S. pectinata leaves have greater frost tolerance in the field. For example, S. pectinata leaves remained viable above -9°C while the mortality threshold was near -5°C for M. × giganteus. These results indicate M. × giganteus will be unsuitable for production in continental interiors of cool-temperate climate zones unless freezing and frost tolerance are improved. By contrast, S. pectinata has the freezing and frost tolerance required for a higher-latitude bioenergy crop.

Autumnal leaf senescence in Miscanthus × giganteus and leaf [N] differ by stand age

Poor first winter survival in Miscanthus × giganteus has been anecdotally attributed to incomplete first autumn senescence, but these assessments never paired first-year with older M. × giganteus in side-by-side trials to separate the effect of weather from stand age. Here CO2 assimilation rate (A), photosystem II efficiency (ΦPSII), and leaf N concentration ([N]) were used to directly compare senescence in first, second, and third-year stands of M. × giganteus. Three M. × giganteus fields were planted with eight plots, one field each in 2009, 2010, and 2011. To quantify autumnal leaf senescence of plants within each stand age, photosynthetic and leaf [N] measurements were made twice weekly from early September until a killing frost. Following chilling events (daily temperature averages below 10 °C), photosynthetic rates in first year plants rebounded to a greater degree than those in second- and third-year plants. By the end of the growing season, first-year M. × giganteus had A and ΦPSII rates up to 4 times greater than third-year M. × giganteus, while leaf [N] was up to 2.4 times greater. The increased photosynthetic capability and leaf N status in first-year M. × giganteus suggests that the photosynthetic apparatus was not dismantled before a killing frost, thus potentially limiting nutrient translocation, and may explain why young M. × giganteus stands do not survive winter when older stands do. Because previous senescence research has primarily focused on annual or woody species, our results suggest that M. × giganteus may be an interesting herbaceous perennial system to investigate the interactive effects of plant ageing and nutrient status on senescence and may highlight management strategies that could potentially increase winter survival rates in first-year stands.