Symbiotic relationships are everywhere in nature. Fungi enhance water and <a href="https://www.earth.com/news/water-quality-threatened-by-nutrient-pollution-in-40-u-s-states/">nutrient</a> absorption for plants by feeding on their roots. Ants find food and shelter in tree structures, while insects defend the trees from being eaten. However, not all symbiotic relationships are created equal.&nbsp;



Some interactions are specific, where one host pairs off with only one other species. Others are general and flexible. Specific relationships have advantages, allowing the two species to reap mutual benefits and co-evolve. But this type of partnership can also come with a cost, where one partner exploits the other and takes more than it offers in return.



To investigate the evolutionary dynamics of specialization, researchers at the <a href="https://www.upenn.edu/">University of Pennsylvania</a> developed a model framework using game theory.



“Each interaction has very different dynamics,” said study senior author Erol Akçay. “Generalists may evolve to work better with more partners, specialists may be specializing to be more cooperative, and other specialists may be specializing to exploit better. Ours is the first study that gets at that dialectical nature of specialization, not just looking at specialization versus generalization.”



As an undergraduate student, Chris Carlson became interested in understanding why variations in generalism and specialism might persist.&nbsp;



Working with Akçay and Bryce Morsky, a model was developed that imagines the interactions of designated “hosts” with either general or specialized preferences and “symbionts” that provide and receive different benefits and costs from their interactions with various hosts.



The experts found that a cooperative partnering strategy, where both parties benefit, could persist in populations with one specialized host and a corresponding specialized symbiont. Depending on the benefits or payoffs, a generalist partnering strategy could also persist.



On the other hand, in partnerships where the host increased benefits while the symbiont reaped less, a more dynamic outcome arose. Different hosts and symbionts rise and fall in the population over time. Generalists were driven to extinction if the payoff was lower than that of being a specialist.&nbsp;



The researchers applied a spatial layer to their models to reflect that symbiotic relationships require that the two species involved encounter one another in space.



“Neighbors are going to be more likely to interact with neighbors, so who your neighbor is and how they interact can affect the outcome,” said Morsky



The team found that cooperative specialists could develop “patches” of dominance if they could move over short distances. If the payoff was high enough, generalists could persist around the periphery of these patches. If, however, hosts and symbionts could move over greater distances, just one host-symbiont pair could completely dominate a space.



“Let’s say you have a coral reef with different types of coral and different types of algae,” said Akçay. “If a host is a cooperative specialist, and the symbiont it specializes on gets fixed, the host does better, and therefore those hosts may expand. That creates specific spatial patterns that we were able to track.”



An overall takeaway is that cooperative specialization appears to be a valuable strategy, but it comes with risks. A host’s cooperating partner could go extinct, leaving the host without a symbiont.



The researchers hope their work lends insight into the variety of patterns of mutualisms that exist in nature and contribute to biodiversity.



“When people discuss specialization, this dualism is always in the background,” said Akçay. “This work helps bring it out and clarifies the tensions that exist between mutualisms.”



The research is published in the journal <a href="http://dx.doi.org/10.1093/evolut/qpac056">Evolution</a>.



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By <a href="mailto:katherinebucko@gmail.com">Katherine Bucko</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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How do symbiotic relationships evolve between species?

Symbiotic relationships are everywhere in nature. Fungi enhance water and...

A new study led by the <a href="https://www.birmingham.ac.uk/index.aspx">University of Birmingham</a> has found that <a href="https://www.earth.com/news/ancient-trees-are-vital-to-forest-survival/">trees</a> living in conditions where carbon dioxide has been artificially elevated are likely to become more efficient in conserving water. The experts discovered that when trees are exposed to elevated levels of CO2, they increase their water use efficiency through higher carbon uptake. At the same time, the trees conserve water by adjusting the opening and closing of pores on their leaves (called “stomata”).&nbsp;



The findings will contribute to modeling and predicting plant behavior under the increased CO2 conditions that are expected to be the norm by mid-century.



Plants worldwide are characterized by a trade-off between carbon gain and water loss, as a result of their structure. While stomata open and close to allow plants to absorb CO2 for their growth, as the stomata open, water is leaving the plant through a process called “transpiration.” This means that plants must compromise between absorbing as much CO2 as possible while minimizing water loss.



The scientists analyzed data on long-term elevated CO2 experiments in trees over the past two decades, spanning 16 sites worldwide. The investigation revealed that the efficiency of water use in the trees’ leaves increased by 85 percent for a doubling of CO2 (the expected rise by 2050). Then, they used this data to compute the so-called “g1 number,” which expresses the water cost of carbon gain for each tree type, and discovered that this number did not in fact change under elevated CO2 conditions.



“The models we use to predict the responses of trees to future atmospheric CO2 levels still contain lots of uncertainties – and the behavior of stomata is one of these,” explained study lead author Anna Gardner, an expert in Tropical Tree Ecophysiology at Birmingham. 



“In elevated CO2 we might expect water consumption to reduce because stomata are taking in CO2 at a higher concentration so do not have to be open as long. But actually, we found the increased CO2 also caused an increase in photosynthesis – and this behavior was a stronger driver to increase water use efficiency. In effect, under higher CO2, the trees are getting more carbon gain for each ‘buck’ of water spent.”



“One reason trees are so important to ecosystems is because they store carbon – but water is also a valuable resource, so we need to find ways to accurately calculate the carbon cost of that water. All this data helps us build a more accurate picture of the likely behavior of these resources in the future,” she concluded.



The study is published in the journal <a href="https://doi.org/10.1111/nph.18618">New Phytologist</a>.



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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Trees respond to rising CO2 levels by conserving water

A new study led by the University of Birmingham has...

View,Of,The,Skyscrapers,Of,Manhattan,Through,The,Trees,On

According to a new study led by the <a href="https://www.isglobal.org/en">Barcelona Institute for Global Health</a> (ISGlobal), over four percent of deaths in cities during the summer months are caused by the formation of “<a href="https://www.earth.com/news/trees-are-the-best-option-to-reduce-the-urban-heat-island-effect/">urban heat islands</a>,” where cities experience higher temperatures than surrounding areas due to less vegetation, larger population density, and the presence of impermeable surfaces for buildings and roads, including asphalt. By analyzing data from 93 European cities (with a total of 57 million inhabitants), the experts determined that one third of these deaths could be prevented by reaching a tree cover of 30 percent.



Exposure to extreme heat has been associated with cardiorespiratory diseases, a higher number of hospital admissions, and premature deaths. While these problems are mainly caused by heatwaves, they also occur with moderately high temperatures in the summer. Due to the formation of urban heat islands, cities are especially vulnerable to higher temperatures, facing spikes in morbidity and mortality during summer worldwide.&nbsp;



“Predictions based on current emissions reveal that heat-related illness and death will become a bigger burden to our health services over the next decades,” warned study lead author Tamara Iungman, a biologist at ISGlobal.&nbsp;



The scientists found that, from June to August 2015, cities were on average 1.5C warmer than the surrounding countryside, a phenomenon leading to 6,700 premature deaths in the 93 cities that were examined (4.3 percent of total mortality during the summer months and 1.8 percent of year-round mortality). Cities with the highest excess heat-mortality rates were in Eastern and Southern Europe. However, projections revealed that one third of these deaths (2,644) could have been prevented by increasing tree cover by 30 percent.



These findings highlight the major benefit of planting more trees in cities, together with other interventions such as green roofs.&nbsp;



“Our results also show the need to preserve and maintain the trees that we already have because they are a valuable resource and it takes a long time to grow new trees. It is not only about increasing trees in the city, it is also about how they are distributed,” added study senior author Mark Nieuwenhuijsen, the director of the&nbsp;<a href="https://www.isglobal.org/urban-planning">Urban Planning, Environment and Health</a>&nbsp;Initiative at ISGlobal.&nbsp;



“Vulnerability to heat changes from city to city depending on several factors. Understanding the benefits of policies such as increasing tree cover can help inform action to reduce risks and prevent avoidable deaths, especially with climate change,” concluded co-author&nbsp;Antonio Gasparrini, a professor of Biostatistics and Epidemiology at the London School of Hygiene &amp; Tropical Medicine (LSHTM).



The study is published in the journal <a href="https://doi.org/10.1016/S0140-6736(22)02585-5">The Lancet</a>.&nbsp;



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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Increased tree cover could prevent heat-related deaths in cities

According to a new study led by the Barcelona Institute...

A new study led by the <a href="https://www.ncsu.edu/">North Carolina State University</a> has found that, under severe global warming scenarios, the inventory of trees used for timber in the continental United States may decline by up to 23 percent by the end of the century. The largest losses are expected to occur in two of the leading timber regions in the country, both located in the South. While these findings show relatively modest impacts on forest product prices, they suggest larger impacts in terms of carbon storage in U.S. <a href="https://www.earth.com/news/diverse-forests-are-more-resilient-and-productive/">forests</a>.



“We already see some inventory decline at baseline in our analysis, but relative to that, you could lose, additionally, as much as 23 percent of the U.S. forest inventory,” said study lead author Justin Baker, an associate professor of Forestry and Environmental Resources at NC State. “That’s a pretty dramatic change in standing forests.”



The scientists used computer modeling to estimate how 94 tree species will grow under six climate change scenarios, while also considering the impact of two different economic scenarios on demand growth for forestry products.



“Many past studies show a pretty optimistic picture for forests under climate change because they see a big boost in forest growth from additional carbon dioxide in the atmosphere,” Baker explained. “The effect that carbon dioxide has on photosynthesis in some of those models tends to outweigh the losses you see from precipitation and temperature induced changes in forest productivity and tree mortality. We have a model that is specific to individual tree species, and that allows us to better understand how climate factors influence growth rates and mortality.”



The analysis revealed that in several regions trees would grow more slowly and die faster in higher temperatures, particularly in Southeast and South-Central U.S. These regions may see tree inventories shrink by as much as 40 percent by 2095 compared to a baseline scenario. However, the researchers projected gains in tree supplies in the Rocky Mountains and Pacific Southwest regions, which will be driven by higher death rates of certain trees, leading to larger harvests initially, and followed by the growth of more heat-tolerant species (such as juniper trees). Overall, the total projected losses of U.S. tree inventory will likely range between three and 23 percent, with the value of lost carbon spiking up to $5.5 billion per year.



“We saw that the markets could be more resilient than the forests themselves. Your market effects may seem modest in terms of the effect it has on the consumers and producers, but those impacts are small compared to the carbon sequestration value that forests provide on an annual basis,” Baker warned.



“We don’t know a lot about how disturbance-related mortality or loss in tree productivity is going to bear out across the landscape as temperatures get warmer. We did our best to address a couple pieces of the puzzle with temperature and precipitation changes, and interactions between climate and market demand, but a lot more work needs to be done to get a good handle on climate change and forestry,” he concluded.



The study is published in the journal <a href="http://dx.doi.org/10.1016/j.forpol.2022.102898">Forest Policy and Economics</a>. &nbsp;



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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Forest inventory will be greatly reduced by climate change

A new study led by the North Carolina State University...

At a time when global warming is making many regions of our planet hotter and drier, <a href="https://www.earth.com/news/study-reveals-that-deserts-breathe/">deserts</a> are relatively new biomes that have grown substantially over the past 30 million years, with vast arid areas like those covering much of North America emerging only during the past five to seven million years. Thus, a better understanding of how several species of plants have invaded these harsh environments and were able to survive could help predict how ecosystems will fare in a drier, hotter future.



According to a new study led by the <a href="https://www.berkeley.edu/">University of California, Berkeley</a>, plants that invaded deserts millions of years ago, such as rock daisies, had already developed adaptations to deal with heat and water stress before. These plants adapted while living on exposed rock outcroppings within older, moist areas or even tropical forests, which made it easier for them to invade expanding deserts.



“If you think about aridity only as a stimulus to plant evolution, then in many cases people could say these plants are survivors, they are adaptable, and they will be fine. They will take advantage of these new conditions, and they will thrive,” said study lead author Isaac Lichter-Marck, plant taxonomist, biogeographer, and evolutionary ecologist at UC Berkeley.



However, the history of rock daisies shows that, when deserts emerged, “plants that had the necessary preadaptations to take advantage of new conditions were the ones that thrived. Adding more aridification to the system doesn’t necessarily mean more rapid adaptive evolution will occur. There’s a limited source of lineages that can take advantage of new levels of aridity, and that is important for understanding the effect of climate change on biodiversity.”



By collecting and analyzing hundreds of rock daisy specimens from the deserts of Arizona, California, Texas, and Mexico, and comparing them to fossilized daisies, the scientists managed to develop a timeline of the evolution of these plants’ characteristics as they eventually invaded expanded deserts. The investigation revealed that most rock daisies – particularly the genus&nbsp;Laphamia, which was the first to move into deserts — had already adapted to the multiple stresses of heat, sun, aridity, and wind by growing on cliffs before invading deserts.



“This is a clear empirical demonstration of what was originally Axelrod’s hypothesis - of a desert plant group originating in dry microclimates prior to the widespread emergence of desert habitats. What this means is that the strategies for drought tolerance that are so characteristic of desert vegetation might not actually represent responses to the dry conditions found in deserts. Instead, they could be traits that evolved earlier in association with much older and more stable dry microclimates, such as rock outcrops in tropical settings,” Lichter-Marck concluded.



The study is published in the journal <a href="http://dx.doi.org/10.1073/pnas.2214729120">Proceedings of the National Academy of Sciences</a>.



Image Credit: Isaac Lichter-Marck



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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Can plants adapt to rapid warming and drought?

At a time when global warming is making many regions...

The UK’s 14 Overseas Territories – many of them small, remote islands like St. Helena – are home to a variety of plant and animal species found nowhere else in the world. This makes them highly vulnerable to biological invasions that could lead to the extinction of their endemic species and irrevocably change their unique ecosystems.



Now, a team of researchers from the <a href="https://www.ceh.ac.uk/">UK Center for Ecology &amp; Hydrology</a> (UKCEH) and <a href="https://www.durham.ac.uk/homepage/">Durham University</a>, together with communities on the Overseas Territories, has assessed thousands of potential <a href="https://www.earth.com/news/managing-invasive-species-can-improve-climate-resilience/">invasive species</a> in order to estimate which are most likely to arrive and pose threats to the Territories within the next decade. Their findings could guide authorities, conservation ecologists, and the wider public to prevent these species from becoming established and causing ecological and economic damage.



“These Territories are exceptionally biodiverse. St Helena, for example, has over 400 invertebrates found nowhere else in world – it is simply unique. We hope that this study draws attention to these Overseas Territories and the inspiring people on them who are working so hard to protect their incredible wildlife and habitats,” said study senior author Helen Roy, an ecologist at UKCEH.



The analysis revealed that Gibraltar and St. Helena are threatened by biological invasion from the greatest number of species. While St. Helena is most at risk from invasion of plant species, the Falkland Islands and Tristan da Cunha are endangered by the most marine species. One of the species that could pose a threat to many of the Overseas Territories is the green mussel (Perna viridis), which can travel around the world on boats and ships, and form dense colonies in places where it establishes, outcompeting native species by reducing levels of phytoplankton. Other invasive species that pose a significant threat to many Territories include the little fire ant (Wasmannia auropunctata), the brown rat (Rattus norvegicus), and the mesquite tree (Prosopis juliflora).



“Preventing the introduction of invasive non-native species is key, because management of species that have established and spread is often extremely expensive and, in some cases, there are no options available. We hope that this list will help inform action, including supporting biosecurity activities, to safeguard the wildlife in these precious places,” Roy concluded.



The study is published in the journal <a href="http://dx.doi.org/10.1111/conl.12928">Conservation Letters</a>.



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer



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UK territories threatened by a variety of invasive species

The UK’s 14 Overseas Territories – many of them small,...

Plants let their <a href="https://www.earth.com/news/invisible-colors-in-sunflowers-dont-only-attract-bees/">flowers</a> fade quickly for protection from detrimental microbes, according to a study led by experts at <a href="https://www.kyoto-u.ac.jp/en">Kyoto University</a>. Using field experiments and plant microbiome analyses, the researchers discovered that microbes growing on flowers can have a negative impact on fruit yields. As a defense mechanism, plants are quick to shed their flowers before the microbes increase in abundance.



"The results suggest that old flowers harbor microbial communities different from those at anthesis, and that the microbes abundant on old flowers negatively affect plant reproduction," wrote the study authors.&nbsp;



"Although it has received little attention, antagonistic microbes that rapidly proliferate on the flowers may have affected the evolution of various flower characteristics such as flower volatiles and life span."



Previously, researchers have investigated the tradeoff between energy that plants spend on producing and maintaining their flowers. Since flowers serve as a reproductive structure, it seems that plants would benefit from keeping them longer.&nbsp;



In an earlier study, the Kyoto team had looked at the mystery of why plants invest their energy to produce fragile flowers that wither quickly, rather than investing a bit more energy to produce flowers that are more durable.



“Interestingly, flower lifespan is negatively correlated with temperature; the hotter the environment where they bloom, the shorter the period a plant retains them. The phenomenon has been known for a long time,” said study co-author Shoko Sakai.



“Then, at some point, I came up with the hypothesis that antagonistic microbes, such as bacteria and fungi growing on flowers after the flower bud opens, must be the driver that shortens the lifespan of a flower. I doubted that it was a coincidence that microbes grow faster in higher temperatures.”



The team conducted field experiments to determine what microbial communities appear on flowers that live longer. The experts transferred microbes from old flowers of wild ginger to other wild ginger plants with new flowers that had just opened.



The experimental plants ultimately produced fewer fruits, despite the fact that there were no visible signs of infection or disease. When the researchers analyzed the microbiomes of the plants, they found several groups of bacteria that were increasing with time.&nbsp;



“So far, flower characteristics have mostly been studied in the context of their interactions with pollinators," said Sakai. "Recent studies have raised the question whether we have overlooked the roles of microbes in the studies of floral characteristics. For example, flower volatiles - which are often regarded as a primary pollinator attractant - can also function to suppress antagonistic microbes."



"The impacts of microbes on plant reproductive ecology may be more deeply embedded in the evolution of angiosperms than we have considered."



The study is published in the journal <a href="https://mbmg.pensoft.net/">Metabarcoding and Metagenomics</a>.



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By <a href="http://csexton@earth.com">Chrissy Sexton</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Plants shed their flowers quickly for protection

Plants let their flowers fade quickly for protection from detrimental...

Taxonomic tree: