Frost stress severely affects agriculture and agroforestry worldwide. Although many studies about frost hardening and resistance have been published, most of them focused on the aboveground organs and only a minority specifically targets the roots. However, roots and aboveground tissues have different physiologies and stress response mechanisms. Climate models predict an increase in the magnitude and frequency of late-frost events, which, together with an observed loss of soil insulation, will greatly decrease plant primary production due to damage at the root level. Molecular and metabolic responses inducing root cold hardiness are complex. They involve a variety of processes related to modifications in cell wall composition, maintenance of the cellular homeostasis and the synthesis of primary and secondary metabolites. After a summary of the current climatic models, this review details the specificity of freezing stress at the root level and explores the strategies roots developed to cope with freezing stress. We then describe the level to which roots can be frost hardy, depending on their age, size category and species. After that, we compare the environmental signals inducing cold acclimation and frost hardening in the roots and aboveground organs. Subsequently, we discuss how roots sense cold at a cellular level and briefly describe the following signal transduction pathway, which leads to molecular and metabolic responses associated with frost hardening. Finally, the current options available to increase root frost tolerance are explored and promising lines of future research are discussed.

Rapid demographic growth in tropical islands can exacerbate conflicts and pressures on natural resources, as illustrated by the French island of Mayotte where resources are limited. In only 10 years, uncontrolled migration and population growth (+80% of population between 2002 and 2021) have led to a pronounced 3600% increase in deforestation rates (2010–2014) and an intensification of agricultural practices, escalating conflicts over limited land, water, and biodiversity resources. Implementing an original multi-proxy approach to sediment cores, our study reveals a staggering 300% acceleration in erosion during the first wave of migration (2011–2015), followed by a further 190% increase (2019–2021) under sustained migratory and demographic pressures. Sedimentary DNA analysis provided insights into increased connectivity and community changes. By 2050, the population of this region will increase by 74 and 103%, in Comoros and Madagascar islands, respectively. Urgent conservation measures are needed to avoid major socio-environmental crises and to protect resources for future generations.

Salix viminalis is a fast growing willow species with potential as a plant used for biomass feedstock or for phytoremediation. However, few reference genes (RGs) for quantitative real-time polymerase chain reaction (qPCR) are available in S. viminalis, thereby limiting gene expression studies. Here, we investigated the expression stability of 14 candidate reference genes (RGs) across various organs exposed to five abiotic stresses (cold, heat, drought, salt, and poly-metals). Four RGs ranking algorithms, namely geNorm^PLUS, BestKeeper, NormFinder, and GrayNorm were applied to analyze the qPCR data and the outputs were merged into consensus lists with RankAggreg, a rank aggregation algorithm. In addition, the optimal RG combinations were determined with geNorm^PLUS and GrayNorm. The genes that were the most stable in the roots were TIP41 and CDC2. In the leaves, TIP41 was the most stable, followed by EF1b and ARI8, depending on the condition tested. Conversely, GAPDH and β-TUB, two genes commonly used for qPCR data normalization were the least stable across all organs. Nevertheless, both geNorm^PLUS and GrayNorm recommended the use of a combination of genes rather than a single one. These results are valuable for research of transcriptomic responses in different S. viminalis organs.

Recent studies highlight the critical role of changes in connectivity, erosion processes and sediment sources in shaping biological communities in palaeo-environmental reconstructions (e.g., Giguet-Covex et al., 2023; Morlock et al., 2023). Such processes can lead to misinterpretations attributing shifts in biodiversity around lakes to environmental changes, when in fact they may be due to the introduction of previously unconnected sediment sources driven by human activities (e.g. land management) or extreme climate events.To assess the impact of changes in connectivity and accelerated erosion on biological communities, we analysed sediment archives from the Dzoumogné reservoir (Mayotte Island, France). This reservoir drains a small catchment (1038 ha) that underwent significant land-use changes (e.g. deforestation, agricultural intensification) during a well-documented period (2011-2021). We reconstructed land-use changes, erosion rates and sediment sources, as well as biological communities using sediment DNA (sedDNA) based on seven genetic markers targeting plants (trnL, rbcL), fungi (ITS), metazoa (16S, 18S) and vertebrates (12S).Our results show a 450% increase in operational taxonomic units (OTUs) and shifts in OTUs detected in 23 taxonomic groups following the first deforestation phase (2012-2013) and subsequent agricultural intensification resulting in landscape fragmentation. During this period, sedDNA identified an increase in forest-derived species (e.g. Streptophyta and terrestrial fungi) and agricultural species (e.g. banana, cassava, cattle). These changes coincide with accelerated sediment delivery and erosion rates (+310% between 2011 and 2015). Between 2015 and 2021, declining water levels (driven by climate and human activities) combined with high sediment and nutrient inputs continued to drive major shifts in aquatic communities. These included increases in OTUs belonging to the taxonomic groups Chlorophyta and Ciliophora - key indicators of eutrophication and water quality degradation. The high primary production associated with algae and microorganisms likely explains the observed increase in invertebrate and fish communities higher up the trophic chain within just two years of changes in sediment connectivity and sources.This study highlights how rapid shifts in biodiversity in both terrestrial and aquatic systems are driven by increased erosion and connectivity of previously isolated land use areas (e.g. forests, croplands). Understanding these connectivity dynamics is crucial to avoid misinterpretation of biodiversity change in lake sediment records. References:Giguet-Covex, C., Jelavić, S., Foucher, A., Morlock, M. A., Wood, S. A., Augustijns, F., Domaizon, I., Gielly, L., & Capo, E. (2023). The Sources and Fates of Lake Sedimentary DNA (pp. 9–52).Morlock, M. A., Rodriguez‐Martinez, S., Huang, D. Y., & Klaminder, J. (2023). Erosion regime controls sediment environmental‐based community reconstruction. Environmental DNA, 5(6), 1393–1404.