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Over the last 3,800 years, agro-pastoral activities have accelerated alpine soil erosion at a pace 4-10 times faster than their natural formation. The history of this erosion has just been revealed for the first time by a research team led by a CNRS scientist¹. The team has shown that high-altitude soil was degraded first, under the combined effect of pastoralism and forest clearing to facilitate the movement of herds. Medium- and low-altitude soil was then eroded with the development of agriculture and new techniques such as the use of ploughs, from the late Roman period to the contemporary period. The study has also revealed that the acceleration of soil erosion in mountain environments by human activities did not begin everywhere in the world in synchronous fashion.

This research, which will be published in the journal PNAS during the week of 14 July, reinforces the conclusion of a previous study by the authors². In a global context of soil degradation affecting soil fertility, biodiversity, and water and carbon cycles, the authors are calling for the implementation of global protection measures.

These conclusions were obtained by comparing the isotope signature of lithium in sediments from Lake Bourget with those sampled from the rocks and soil of today. The samples were taken from the largest catchment area in the French Alps³. The data obtained was then compared to that from other regions in the world⁴. The DNA content in the sediments was also studied to identify the mammals and plants present during each period.

Notes

1 – From the Environments, Dynamics, and Mountain Territories Laboratory (CNRS/Université Savoie Mont Blanc) and the Paris Institute of Planetary Physics (CNRS/Institut de physique du globe de Paris/Université Paris Cité). The Paris-Saclay Geosciences Laboratory (CNRS/Université Paris-Saclay) was also involved. Scientists from l’Université Paris-Saclay, l’Université Savoie Mont Blanc, and the Paris Institute of Planetary Physics also took part in the research.

2 – Human-triggered magnification of erosion rates in European Alps since the Bronze Age. Rapuc, W., Giguet-Covex, C., Bouchez, J., Sabatier, P., Gaillardet, J., Jacq, K., Genuite, K., Poulenard, J., Messager, E., Arnaud, F. Nature communications, published on 10 February 2024.

DOI : https://doi.org/10.1038/s41467-024-45123-3

3 – The catchment area in question extends from the Chambéry basin to the peak of Mont Blanc.

4 – The Andes and North America.

Article Content

A new tool allows researchers to probe the metabolic processes occurring within the leaves, stems, and roots of a key citrus crop, the clementine. The big picture goal of this research is to improve the yields, flavor and nutritional value of citrus and non-citrus crops, even in the face of increasingly harsh growing conditions and growing pest challenges. 

To build the tool, the team – led by the University of California San Diego – focused on the clementine (Citrus clementina), which is a cross between a mandarin orange and a sweet orange. 

The effort is expected to expand well beyond the clementine in order to develop actionable information for increasing the productivity and quality of a wide range of citrus and non-citrus crops. The strategy is to uncover – and then make use of – new insights on how plants respond, in terms of metabolic activities in specific parts of the plant or tree, to environmental factors like temperature, drought and disease. 

The tool, and the comprehensive genome-scale model for Citrus clementina, were published July 14, 2025 in the journal Proceedings of the National Academy of Sciences (PNAS). 

The team is led by researchers at UC San Diego, in collaboration with researchers at UC Riverside and the Universidad Autónoma de Yucatán.

“Together we created a tool that will open the door for improved crop design and sustainable farming for Citrus clementia and a wide range of citrus and non-citrus crops,” said UC San Diego professor Karsten Zengler, the corresponding author on the new paper. 

At UC San Diego, Zengler holds affiliations in the Department of Bioengineering, the Department of Pediatrics, the Center for Microbiome Innovation, and the Program in Materials Science and Engineering.  

“Our data-driven modeling approach represents a powerful tool for citrus breeding and farming and for the improvement of crop yield and quality, meeting the escalating demand for high-quality products in the global market,” said Zengler. 

The high-resolution genomic tool has been designed and built as a platform technology that can be expanded to help researchers improve a wide range of citrus and non-citrus crops. The actionable information is derived from a wide range of new mechanistic insights into how plant metabolism works within leaves, stems, roots and other tissues of key plant crops. 

The highly curated and validated model of clementine metabolism, for example, contains 2,616 genes, 8,653 metabolites and 10,654 reactions. 

“We generated seven biomass objective functions based on organ-specific metabolomics data for leaf, stem, root, and seed and experimentally validated the model – a challenge for a plant with an average lifespan of 50 years,” said Zengler. “This model represents one of the largest genome-scale models that has been built for any organism, including for humans.” 

The model is called iCitrus2616. It captures Citrus clementina’s metabolism with exceptional accuracy and enables simulating economically-relevant scenarios. 

For example, the researchers show how specific nutrients can improve the production of starch and types of cellulose, which in turn can enhance strength and rigidity of cell walls in citrus plants, which is useful for withstanding mechanical and drought stress. 

The researchers also used the new tool to demonstrate how to increase flavor-related compounds in Citrus clementina such as flavonoids. 

The team integrated organ-specific models for leaf, stem, and root into a whole plant model. Using this integrated whole-plant model, the researchers show how flavonoids and hormones are distributed through the entire plant. 

Additionally, the team constrained the clementine metabolism model with gene expression data from symptomatic and asymptomatic leaf and root tissues across four seasons during citrus greening – which is caused by a bacterial infection. Citrus greening causes millions of dollars of agricultural damage annually. 

This project has already revealed tissue-specific metabolic adaptations, including shifts in energy allocation, secondary metabolite production, and stress-response pathways under biotic stress and has provided a mechanistic understanding of disease progression. 

The researchers note that this work represents a milestone in modeling higher organisms, specifically plants. 

“I envision that these types of models will aid with crop breeding efforts in the near future. With these models, we are working to make critical plant breeding efforts more reliable and also faster,” said Zengler. “In preliminary follow-on research, we are already seeing examples of the positive impacts these models can have for data-driven strategies to optimize plant growth.” 

Paper
Unravelling Organ-specific Metabolism of Citrus clementina, published in PNAS on 14 July 2025

Funders
US Department of Agriculture, National Institute of Food and Agriculture; California Department of Food and Agriculture; UC Multicampus Research Programs and Initiatives of the University of California

Co-first authors
Anurag Passi, Diego Tec-Campos

Additional authors
Manish Kumar, Juan D. Tibocha-Bonilla, Cristal Zuñiga, Beth Peacock, Amanda Hale, Rodrigo Santibáñez-Palominos, James Borneman, Karsten Zengler

Corresponding author
Karsten Zengler

Author Affiliations

University of California San Diego
Center for Microbiome Innovation in the UC San Diego Jacobs School of Engineering; Department of Pediatrics in the UC San Diego School of Medicine; Program in Materials Science and Engineering; Shu Chien-Gene Lay Department of Bioengineering in the UC San Diego Jacobs School of Engineering

University of California, Riverside
Department of Microbiology and Plant Pathology

Universidad Autónoma de Yucatán
Facultad de Ingeniería Química 

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Climate Change

Whatever dark matter is, cosmologists are busy trying to understand the role it plays in the structure of the Universe. Our standard cosmological model, also called Lambda Cold Dark Matter (LCDM), makes a number of predictions about how galaxies form and evolve, largely focused on dark matter haloes. DM haloes are fundamental building blocks for the cosmological structure. Scientists often describe them as the scaffolding on which the Universe is built.

One of LCDM’s predictions concerns satellite galaxies. Theory says that every galaxy forms and grows within a dark matter halo, including dwarf and satellite galaxies. LCDM theory predicts more small dark matter haloes than there are observed satellite galaxies around the Milky Way. New research presented at the Royal Astronomical Society’s National Astronomy Meeting might have the answer.

The presentation is “The contribution of “orphan” galaxies to the ultrafaint population of MW satellites,” and the lead researcher is Dr. Isabel Santos-Santos, from the Institute for Computational Cosmology in Department of Physics at Durham University, UK.

“The last decade has seen a rise in the number of known Milky Way (MW) satellites, primarily thanks to the discovery of ultrafaint systems at close distances,” Santos-Santos writes. “These findings suggest a higher abundance of satellites within ~ 30kpc than predicted by cosmological simulations of MW-like halos in the CDM framework.”

Astronomers have found about 60 satellite galaxies around the Milky Way. The Large and Small Magellanic Clouds are the most well-known satellite galaxies, and there are others like the Sagittarius Dwarf Spheroidal Galaxy and the Sculptor Dwarf. Santos-Santos says there should be dozens more of them.

Some of the known satellite galaxies of the Milky Way, including the well-known Large and Small Magellanic Clouds. There could be many more of them according to simulations, and if scientists can find them, it supports the Lambda Cold Dark Matter model. Image Credit: ESA/Gaia/DPAC. CC BY-SA 3.0 IGO

“We know the Milky Way has some 60 confirmed companion satellite galaxies, but we think there should be dozens more of these faint galaxies orbiting around the Milky Way at close distances,” she said in a press release.

The problem is that these small galaxies can be extremely difficult to detect. Scientists think that these galaxies might have had their dark matter stripped away through interactions with the much more massive Milky Way. Without their dark matter, which acts as a gravitational anchor, gas, dust and even stars are more easily stripped away. That means there’s little active star formation, and only a dimmer population of older stars. This is why satellite galaxies can be so challenging to detect.

“If our predictions are right, it adds more weight to the Lambda Cold Dark Matter theory of the formation and evolution of structure in the universe. Observational astronomers are using our predictions as a benchmark with which to compare the new data they are obtaining,” Santos-Santos said. “One day soon we may be able to see these ‘missing’ galaxies, which would be hugely exciting and could tell us more about how the universe came to be as we see it today.”

The work is based on the Aquarius simulation produced by the Virgo Consortium. Aquarius simulates the evolution of the MW’s dark matter halo in the highest resolution ever. It was created to investigate the fine-scale structure around the MW.

The researchers used Aquarius and other analytic galaxy formation models to watch as dwarf galaxies formed and evolved and to “estimate the true abundance and radial distribution of MW satellites” that LCDM predicts. They determined that small dark matter haloes that could host satellite galaxies have been orbiting the Milky Way for billions of years, but since they’ve been stripped, they’re dim and hard to see. These are sometimes called ‘orphaned’ galaxies. The simulation showed that there could be up to 100 more MW satellites.

“Strikingly, orphans make up half of all satellites in our highest-resolution run, primarily occupying the central regions of the MW halo,” the researchers write.

This illustration shows galaxies forming as part of the large-scale structure of the Universe. Image Credit: Ralf Kaehler/SLAC National Accelerator Laboratory

The other piece of the puzzle concerns the approximately 30 satellite galaxies discovered recently, all small and dim. If these are stripped or orphaned galaxies, then their discovery is additional evidence in support of LCDM. They could be a subset of the dim satellite population the simulation predicts. However, they could also be globular clusters (GC).

Professor Carlos Frenk of the Institute for Computational Cosmology in the Department of Physics at Durham University is one of the co-researchers. Frenk said, “If the population of very faint satellites that we are predicting is discovered with new data, it would be a remarkable success of the LCDM theory of galaxy formation.”

“It would also provide a clear illustration of the power of physics and mathematics,” Frenk added. “Using the laws of physics, solved using a large supercomputer, and mathematical modelling we can make precise predictions that astronomers, equipped with new, powerful telescopes, can test. It doesn’t get much better than this.”

The Vera Rubin Observatory and its 10-year Legacy Survey of Space and Time might uncover the presence of these dim, orphaned satellites. “We predict that dozens of satellites should be observable within ~30 kpc of the MW, awaiting discovery through deep-imaging surveys like LSST,” the researchers explain.

Scientists have been puzzling over the connections between the Milky Way, dark matter haloes, and satellite galaxies for a long time. Some research suggests that not only does the MW have more satellites that we haven’t detected yet, but that those satellites may have had their own satellites that they dragged towards the MW with them. If that turns out to be true, then the MW may have another 150 dim satellites waiting to be found by observatories like the Rubin.

Scientists think that there are different sizes of DM haloes, some with only a few Earth masses, while some are enormously massive. They also think that they could’ve formed hierarchically, with smaller haloes merging with larger haloes, slowly building up the cosmic web that largely defines the modern Universe. If that’s true, then the MW’s orphaned galaxies might be strong evidence supporting their hierarchical nature.

Now that the Vera Rubin Observatory has achieved its long-awaited first light, we could get confirmation soon.

Maybe that will help us figure out what dark matter actually is one day .