Poplar biomass, a source of renewable energy?

The video introduces the ZOBIOPOP project, which is a regional initiative funded by the Centre-Val de Loire Region. The project aims to produce lignocellulosic biomass from woody species like poplar for renewable energy, particularly bioethanol. The project seeks to identify high-performing plant materials in terms of growth, biomass production, environmental footprint, resource efficiency, and drought tolerance.

Poplar is chosen for this project due to its high productivity, capable of producing large volumes of wood on small surfaces in under 20 years. It ranks second in French forest production after oak. Additionally, poplar is a well-understood and domesticated species, with its genome being fully sequenced, making it a model tree for genetic improvement.

The French genetic improvement program for poplar is led by the Scientific Interest Group (GIS) Poplar, a collaboration between INRAE and FCBA. The process involves creating new plant material through controlled hybridizations, followed by a 20-year evaluation period for criteria like disease tolerance, vigor, and wood quality, before releasing new varieties to the market.

The project compares two biomass production systems: Short Rotation Coppice (SRC) and Very Short Rotation Coppice (VSRC). SRC involves a harvest cycle of 8-10 years with a density of 1,000-2,000 stems per hectare, yielding small trees. VSRC is harvested every 2-4 years with a higher density of 8,000-10,000 stems per hectare, producing small woody shoots.

The study takes place on a plot established in 2010 on challenging agricultural land, featuring an experimental plantation of 60 new poplar varieties. Measurements like circumference and height are taken annually, supplemented by continuous monitoring using sensors that record growth hourly. A subset of trees is destructively sampled to establish a relationship between size and biomass, allowing for future biomass prediction from simple measurements.

The project evaluates the efficiency of water and mineral use in poplar varieties. For water, the aim is to find varieties that produce the same amount of biomass with less water consumption, often measured indirectly using stable carbon isotopes. For minerals, the goal is to identify varieties that can produce the same biomass with lower concentrations of essential minerals, reducing soil nutrient depletion upon harvest.

Mineral efficiency is assessed by measuring mineral concentration in biomass to determine export rates during harvest. Water use efficiency is indirectly estimated using stable carbon isotopes, which offer a flexible and high-throughput method compared to direct measurements. This allows for rapid screening of a large number of poplar varieties.

Drought tolerance is evaluated by comparing biomass production and growth of the same varieties across sites with contrasting pedoclimatic conditions. More detailed analysis uses automatic dendrometers to measure radial growth and daily stem contractions, providing insights into hydraulic functioning. In severe conditions, vulnerability to cavitation (embolism) is assessed, reflecting the limits of the plant's vascular system.

The process begins with finely grinding wood samples into powder. This powder is then distributed by robots into plates or vials. In the biochemistry lab, the wood quality is assessed by estimating cellulose content, which is primarily composed of glucose, a precursor for bioethanol. A high-throughput method involves a pre-treatment step where wood powder is heated under pressure, followed by enzymatic hydrolysis to break down cellulose into glucose.

After enzymatic hydrolysis, a colored reagent is added; the intensity of the pink color indicates the glucose concentration. Over 400 wood samples have been analyzed to identify the best poplars for bioethanol. Additionally, near-infrared (NIR) spectrometry is used for high-throughput analysis. NIR measures how organic matter absorbs infrared light, creating a 'fingerprint' of the sample from which glucose content can be accurately predicted using mathematical models.

Portable NIR spectrometers are used in the field to analyze wood quality directly within the tree. A small hole is drilled, and a fiber optic probe is inserted to take measurements quickly. This allows for real-time assessment of wood composition without felling the tree. The rapid and non-destructive nature of NIR spectrometry makes it highly valuable for evaluating large numbers of trees.

The video concludes by discussing the national commitment to mitigating climate change and transitioning from fossil fuels to renewable energy. Biomass, particularly from forests and cultivated land, is crucial for this transition. The ZOBIOPOP project exemplifies how research is vital to increasing biomass production under optimal environmental conditions, producing not only energy but also bio-based chemicals and materials.

FIABOIS supports research and facilitates the transfer of research results to professionals and society. The goal is to rapidly implement scientific findings to promote greater sobriety and the use of bio-sourced materials and renewable energy to achieve carbon neutrality by 2050. Researchers highlight the collaborative nature of such projects, involving diverse expertise in biology, chemistry, genetics, and forestry engineering.

The project also emphasizes integrating research into educational programs at the University of Orléans, particularly in the forestry master's program. Experimental plots and research data are used in practical work to teach concepts in genetics, genetic improvement, and global change, reinforcing the connection between research and training future professionals.