Category

News

Wax Helps Plants to Survive in the Desert

By | News

The leaves of date palms can heat up to temperatures around 50 degrees Celsius. They survive thanks to a unique wax mixture that is essential for the existence in the desert.

In 1956, the Würzburg botanist Otto Ludwig Lange observed an unusual phenomenon in the Mauritanian desert in West Africa: he found plants whose leaves could heat up to 56 degrees Celsius. It is astonishing that leaves can withstand such heat. At the time, the professor was unable to say which mechanisms were responsible for preventing the leaves from drying out at these temperatures. More than 50 years later, the botanists Markus Riederer and Amauri Bueno from Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, succeeded in revealing the secret.

To understand what the two scientists discovered, one must know more about the somewhat complicated structure of a plant leaf. Plant leaves, for example, have a skin that is usually invisible to the human eye. “You can see the skin in the tomato,” explains Professor Riederer, head of the JMU Chair of Botany II. Bioscientists speak of the “cuticle”. It can be imagined as a very thin plastic foil. Without this foil, the leaf of the plant would dry out within a short time: “the water permeability of a cuticle is even lower than that of a plastic foil.”

Constant trade-off: Open or close pores?

The plant skin is not a continuous layer that would extend over the whole leaf. It contains numerous pores, called stomata, which can open and close. The plant “feeds” through these stomata. Riederer: “it thereby uptakes the carbon dioxide the plant needs for photosynthesis.”

The problem is that whenever the pores open to acquire carbon dioxide, water also evaporates. Therefore, desert plants, in particular, are continually undergoing a balancing process: do they uptake carbon dioxide to grow further, or do they close the pores to retain the precious water? According to Riederer, every desert plant decides a little differently.

Colocynths are water-spenders

The plant colocynth (Citrullus colocynthis), also known as bitter cucumber, a wild relative of the watermelon, opens its pores when exposed to heat in order to cool down the leaves by transpiration cooling. It “sweats” so to speak. “This makes colocynth a water-spender,” explains the JMU professor of ecophysiology.

The plant can afford this because it has a very deep root. This enables the plant to tap water sources deep in the desert soil. As Otto Ludwig Lange found out during his experiments in the desert, the colocynth manages to make its leaf up to 15 degrees cooler than the desert air.

Date palms are water-savers

The date palm behaves quite differently. The second Würzburg experimental plant, like the colocynth, lives in oases and wadis – river valleys that dry up over long periods. “In contrast to the colocynth, it is a water-saver,” says Riederer.

Because the palm does not “sweat”, its leaves sometimes reach extremely high temperatures: they can be 11 degrees Celsius above the air temperature. How can it be that the leaves do not dry out at these high temperatures? This is what JMU biologist Amauri Bueno investigated in his doctoral thesis.

High-temperature wax for survival

His results, published in the Journal of Experimental Botany, revolve around the wax, which is embedded in the skin of plants and ensures their low permeability to water. After extensive laboratory tests, Bueno discovered that this wax differs between the colocynth and the date palm.

The date palm has a wax that can withstand high temperatures and therefore has a much more waterproof skin than the colocynth, even at extreme temperatures. Only because of this special wax the palm can survive in the desert. If the wax had a slightly different chemical composition, the leaves would dry very quickly, especially at high temperatures.

According to Riederer, these experiments were highly challenging because the wax embedded in the skin is very complicated from a chemical point of view. Not all secrets have been revealed yet. The bioscientists still do not understand why one plant skin is more permeable for water than the other.

Interesting for plant breeding

These current findings from JMU may be of importance for plant breeding. If one wants to cultivate crop plants in places where is very hot and dry or where climate change could make the surroundings hotter, one has to pay attention to the plant skin when searching for suitable plant varieties. If plants with certain cuticle waxes are selected for breeding, they have a better chance of survival in hot locations.

Read the paper: Journal of Experimental Botany

Article source: Julius-Maximilians-Universität Würzburg (JMU)

Image: Markus Riederer / Universität Würzburg

Tomato, Tomat-oh! Understanding evolution to reduce pesticide use

By | News

Although pesticides are a standard part of crop production, Michigan State University researchers believe pesticide use could be reduced by taking cues from wild plants.

The team recently identified an evolutionary function in wild tomato plants that could be used by modern plant breeders to create pest-resistant tomatoes.

The study, published in Science Advances, traced the evolution of a specific gene that produces a sticky compound in the tips of the trichomes, or hairs, on the Solanum pennellii plant found in the Atacama desert of Peru – one of the harshest environments on earth. These sticky hairs act as natural insect repellants to protect the plant, helping ensure it will survive to reproduce.

“We identified a gene that exists in this wild plant, but not in cultivated tomatoes,” said Rob Last, MSU Barnett Rosenberg Professor of plant biochemistry. “The invertase-like enzyme creates insecticidal compounds not found in the garden-variety tomato. This defensive trait could be bred into modern plants.”

Last explained that modern cultivated tomatoes make fewer of the compounds found in wild plants because – unaware of their adaptive function – breeders removed undesirable traits such as stickiness.

Bryan Leong, plant biology graduate student and co-lead author, is interested in how the wild plants evolved to be insect-resistant.

“We want to make our current tomatoes adapt to stress like this wild tomato, but we can only do that by understanding the traits that make them resistant,” said Leong. “We are using evolution to teach us how to be better breeders and biologists. For example, how can we increase crop yield by creating a pest-resistant plant and eliminate the need to spray fields with insecticides?”

Advances in technology allowed the team to apply genetic and genomic approaches, including the CRISPR gene-editing technology, to the wild tomato plant to discover the functions of specific genes, metabolites and pathways. Using these new techniques, the team identified an invertase-like enzyme specific to the cells at the tips of the sticky hairs. Invertases regulate many aspects of growth and development in plants. In the wild tomato, the enzyme evolved to facilitate the production of new insecticidal compounds.

“It is a race over evolutionary time between the consumed and the consumers,” said Leong. “Insects benefit by eating the plants. Yet, evolution favors plants that make more seeds and pass on their genes to another generation. We hope to take the defensive lessons plants already learned and apply them to existing crops.”

This discovery is a step toward understanding the natural insect resistance of Solanum pennellii plants, which could enable introduction of this trait into cultivated tomatoes using traditional breeding practices.

“Plants are amazing biochemical factories that make many unusual compounds with protective, medicinal and economically important properties,” said Cliff Weil, a program director at the National Science Foundation, which funded this study. “In this study, the authors found that a common enzyme has been repurposed for forming such compounds, giving us important insight into how life is able to bend existing tools for novel uses.”

Read the paper: Science Advances

Article source: Michigan State University

Image: Michigan State University

Risk and unnaturalness cannot justify EU’s strict policy on GMO

By | News

The EU’s policy on GMO is extremely strict and prevents new GMO crops from being authorized. The policy is based on arguments about the risk and unnaturalness of GMO plants – but these arguments cannot justify the restrictive regulation, three researchers conclude in a new study in the journal Transgenic Research. They also conclude that the use of GMO plants is consistent with the principles of organic farming.

The EU’s rules on genetically modified organisms (GMO) are so restrictive that it is virtually impossible to get an authorization for cultivating a GMO crop within the EU—which means that only one GMO crop has hitherto been authorized in the EU. And even if a GMO crop is authorized, individual member states may still ban the crop. This is untenable, argue three researchers from the University of Copenhagen and the Technical University of Denmark in a new article in the scientific journal Transgenic Research, because EU regulation may stand in the way of important agricultural innovation that could provide more sustainable and climate-friendly solutions – and because the strict regulation cannot be justified.

“If we compare the pre-authorization procedure that GMO products undergo with those for conventionally cultivated crops, it is clear that GMO’s are required to meet much stricter demands – with reference to the supposed risks that GMO crops pose. But the fact that a crop has been genetically modified does not in itself pose a risk. If there is risk involved, it is connected to the act of introducing a new variety with unfamiliar traits, which may have adverse effects on the environment or the health of humans and animals,” explains postdoc Andreas Christiansen, who has co-authored the article “Are current EU policies on GMO justified?” with Professor Klemens Kappel and Associate Professor Martin Marchman Andersen.

He continues:

“It is crucial to understand that the introduction of new varieties with compositional differences always poses a risk whether they are genetically modified or not. Our point is that GMO crops should not be treated differently than similar products when the risks they pose to the environment and people are comparable. This is the reason GMO crops have been regulated as other novel varieties in the US for years.”

When is a plant natural?

In a 2010 Eurobarometer survey, 70 per cent of Europeans agreed “that GMO food is fundamentally unnatural”. Unnaturalness is a common argument against GMO crops and foods, and it is mentioned specifically in EU legislation. What the researchers are trying to ascertain is whether the kind of “unnaturalness” which GMO’s supposedly possess can justify bans and restrictive legislation.

“Unnaturalness, firstly, has many different meanings so even though there are cogent arguments that GMO’s in some respects are more unnatural than non-GMO’s, there are also cogent arguments that many GMO’s are just as natural or unnatural as their conventional counterparts,” says Andreas Christiansen.

“One of the arguments is that the more changes human beings have made to a plant, the more unnatural it is. This makes a GMO more unnatural in the sense that it has been subjected to at least one more change than the conventionally bred plant upon which it is based. The conventionally bred plant, conversely, is much more unnatural than its wild ancestor, and has mutated so many times that it may in some cases be difficult to see any relation between to two. It is, in other words, really difficult to construct a solid argument to the effect that the distinction between natural and unnatural can warrant stricter regulation of GMO’s – even if we consider the best philosophical arguments for the value of nature and naturalness” Andreas Christiansen points out.

According to the researchers, many novel gene editing technologies, such as CRISPR/Cas9, are much more precise and cause fewer alterations in plants than traditional breeding methods, in which plant seeds e.g. are washed with chemicals in order to provoke mutations. CRISPR/Cas9 is nonetheless also included in the restrictive EU legislation whereas the chemically induced breeding is not.

GMO produces higher yields than organic farming

Naturalness and organic farming are often thought of as synonymous, and the desire to promote organic farming has been used as an argument for curbing the use of GMO’s, which is prohibited in organic farming. But can a wish to promote organic farming justify a ban on GMO’s?

“Even if we accept that organic farming is superior because it is more sustainable or environmentally friendly, it will be difficult to justify the restrictive policy on GMO, because at least some GMO’s are consistent with these aims of organic farming. And what’s more, current GMO’s are at least as good as conventional farming in terms of sustainability, so it would not make sense to impose stricter regulation on GMO’s than conventional farming as far as sustainability goes,” Andreas Christiansen explains.

“But we must also ask ourselves whether organic farming is always better than the alternatives. In one very important respect, GMO may be superior to organic farming: it can produce higher yields without putting more strain on the environment, which will make it possible to increase food production without increasing the area of land used for farming. This will be extremely important if we are to meet projected future food needs.”

Read the paper: Transgenic Research

Article source: University of Copenhagen

Image: Artverau / Pixabay

Research sheds light on genomic features that make plants good candidates for domestication

By | News

New research published identifies the genomic features that might have made domestication possible for corn and soybeans, two of the world’s most critical crop species.

The research, published in the peer-reviewed academic journal Genome Biology, has implications for how scientists understand domestication, or the process by which humans have been able to breed plants for desirable traits through centuries of cultivation. The researchers drew on vast amounts of data on the genomes of corn and soybeans and compared particular sections of the genomes of wild species and domestic varieties, noting where the genomes diverged most markedly.

Iowa State University researchers worked with scientists from the University of Georgia, Cornell University and the University of Minnesota. The researchers studied more than 100 accessions from comparisons of corn with teosinte, its progenitor species. They also looked at 302 accessions from a dataset of wild and domesticated soybeans.

“We sliced the genomes into specific sections and compared them,” said Jianming Yu, professor of agronomy and Pioneer Distinguished Chair in Maize Breeding. “It’s a fresh angle not many have looked at concerning genome evolution and domestication. We searched for ‘macro-changes,’ or major genome-wide patterns – and we found them.”

Human cultivation created a bottleneck in the genetic material associated with corn and soybeans, Yu said. As humans selected for particular traits they found desirable in their crops, they limited the genetic variation available in the plant’s genome. However, the researchers found several areas in the genomes of the species involved in the study where genome divergence seemed to concentrate.

“These patterns in genome-wide base changes offer insight into how domestication affects the genetics of species,” said Jinyu Wang, the first author of the paper and a graduate student in agronomy.

Variation in nucleotide bases between wild and domesticated species appeared more pronounced in non-genic portions of the genomes, or the parts of the genomes that do not code for proteins. The study also found greater variation in pericentromeric regions, or in areas near the centromere of chromosomes, and in areas of high methylation, or areas in which methyl groups are added to a DNA molecule. Methylation can change the activity of a DNA segment without changing its sequence.

The study looked at the occurrence of mutations in the genomes of the domesticated crops and their progenitor species.

“We now think it’s likely that good candidates for domestication, such as corn and soybeans, occupy a middle ground in their willingness to mutate,” said Xianran Li, adjunct associate professor of agronomy and a co-corresponding author of the study.

“If there’s no mutation, then everything stays the same and we don’t have evolution,” Yu said. “But too many mutations can wipe out a species.”

The study’s findings pointed to important links between UV radiation from the sun and genome evolution. UV radiation is a natural mutagen, and it leaves a special footprint when it occurs, Yu said. The study’s authors found many more of these footprints in modern corn and soybeans than their wild relatives.

Read the paper: Genome Biology

Article source: Iowa State University

Image: Sherry Flint-Garcia (teosinte) and Scott Jackson (Glycine soja)

With Flower Preferences, Bees Have a Big Gap Between the Sexes

By | News

For scores of wild bee species, females and males visit very different flowers for food – a discovery that could be important for conservation efforts, according to Rutgers-led research.

Indeed, the diets of female and male bees of the same species could be as different as the diets of different bee species, according to a study in the journal PLOS ONE.

“As we get a better sense of what makes flowers attractive to different kinds of bees, maybe we can get smarter about bee conservation,” said lead author Michael Roswell, a doctoral student in the lab of senior author Rachael Winfree, a professor in the Department of Ecology, Evolution, and Natural Resources at Rutgers University –New Brunswick.

Five years ago, when Winfree Lab members were evaluating federally funded programs to create habitat for pollinators, Roswell noticed that some flowers were very popular with male bees and others with females. That spurred a study to test, for as many wild bee species as possible, whether males and females visit different kinds of flowers.

New Jersey is home to about 400 species of wild bees – not including Apis mellifera Linnaeus, the domesticated western honeybee whose males do not forage for food, Roswell noted.

The scientists collected 18,698 bees from 152 species in New Jersey. The bees visited 109 flower species in six semi-natural meadows with highly abundant and diverse flowers. The meadows were managed to promote mostly native flowers that attract pollinators.

Female bees build, maintain, collect food for and defend nests, while male bees primarily seek mates. Both sexes drink floral nectar for food, but only females collect pollen that serves as food for young bees, so they forage at greater rates than males.

From the flowers’ standpoint, both female and male bees are important pollinators – though female bees are more prolific because they spend more time foraging at flowers.

Before mating, the males of some species travel from the area where they were born. Targeting their preferences for flowers may help maintain genetically diverse bee populations, Roswell speculated.

“We see some intriguing patterns, where certain plant families seem relatively preferred or avoided by male bees, or where males have relatively less appetite for visiting flowers that only produce pollen and not nectar,” he said. “That could help pinpoint the right mix of flowers to improve bee conservation down the road.”

Read the paper: PLOS ONE

Article source: Rutgers University

Image: Michael Roswell/Rutgers University-New Brunswick

Plant signals trigger remarkable bacterial transformation

By | News

Cycad plant roots release signals into the soil that triggers the transformation of bacteria into its motile form, helping them move to the plant roots and establish a symbiotic partnership.

The cycad Cycas revoluta is a palm-like plant that grows on rocky coastal cliffs in the sub-tropics and tropics. It has a symbiotic relationship with the Nostoc species of bacteria that can convert nitrogen from the atmosphere into ammonia, which the host plant can then use for its growth. Scientists knew that cycad roots produce a compound that can induce Nostoc species within the soil to transform into their motile form, hormogonia, and attracting them to the roots. However, nobody has determined what exactly the compound is.

In the current study published in the journal Scientific Reports, agricultural chemist Yasuyuki Hashidoko and colleagues at Hokkaido University investigated an extract made from the “coralloid roots” of C. revoluta plants. These are specialized roots that branch out from the plant’s main root system.

They found that the extract was able to trigger the transformation of Nostoc bacteria into hormogonia. Further analyses revealed the main active elements present in the extract were a mixture of diacylglycerols; typical compounds contained in plants that are composed of two fatty acid chains linked together.

The team tested each of the diacylglycerols for their abilities to act as hormogonia-inducing factors (HIF), and found that 1-palmitoyl-2-linoleoyl-sn-glycerol showed pronounced HIF-like activity on the bacteria. The investigations also enabled the researchers to theorize which specific changes to fatty acid chain segments led to the compounds having more, less, or no HIF-like activity.

“These findings appear to indicate that some common diacylglycerols act as hormogonium-inducing signal for Nostoc cyanobacteria, enabling them to move and transfer to host plants,” the researchers conclude. “Since the bacteria can provide host plants nitrogen to help them grow, better understanding of the system could someday lead to more efficient, less fertilizer-dependent agricultural production.”

Read the paper: Scientific Reports

Article source: Hokkaido University

Image: Yasuyuki Hashidoko, Hokkaido University

Targeting how fungi ‘taste’ wheat could be key to developing control

By | News

Exploring how a hazardous fungal pathogen ‘tastes’ its surroundings within a wheat plant to coordinate virulence could be the key to developing new control strategies, scientists believe.

Researchers at the University of Bath and Rothamsted Research have been examining how “fungal G-protein coupled receptors”, which are similar to taste receptors on our tongues, are involved in promoting Fusarium Head Blight (FHB) – a damaging and hazardous disease of wheat which is the number one floral disease in cereals globally.

Fusarium Head Blight targets the ear and grain of the wheat plants and is therefore a major problem for farmers of one of the world’s most important crops. The disease is economically costly, damaging wheat crops towards the end of the growing cycle, and contaminating the wheat grain with fungal toxins (mycotoxins) which are dangerous for humans and animals to eat.

In the UK we have outbreaks of FHB every few years, experiencing wheat crop losses of around 10% in 2012. In other parts of the world such as the USA, Brazil and China, the disease causes severe crop losses and mycotoxin contamination problems for farmers every harvest.

Currently there are no truly effective ways to control FHB, which is spread by airborne spores.

The research team, led by fungal biologist Dr Neil Brown from the University of Bath’s Department of Biology & Biochemistry, thinks that G-protein coupled receptors are a promising targets to develop new approaches to control fungal diseases, including the FHB causing pathogen Fusarium graminearum.

These fungal receptors ‘taste’ their environment and signal changes to the fungi cell, kicking off an appropriate biological response, including mating, mycotoxin production and virulence.

In a series of experiments the scientific team demonstrated that F. graminearum’s receptors are important in wheat infection. The team made a collection of fungal mutants lacking individual receptors. They went on to show that the absence of one type of receptor, specific to fungi, allowed the wheat plant to mount a stronger defence, which causes a traffic jam of invading filamentous fungal structures called hyphae and reducing the progression of infection.

The team also showed that the removal of this receptor meant that the virulence on wheat was reduced, because various fungal processes required for infection were disrupted and dysregulated.

The research is published in PLOS Pathogens.

Dr Brown said: “Fusarium Head Blight is the number one floral disease of cereals worldwide.

“G-protein coupled receptors have been studied extensively in humans, where around 40% of our pharmaceuticals target these human receptors, as they’re exposed on the cell surface, making them accessible to drugs, and they control important biological functions. Fungi have their own G-protein coupled receptors, but we know very little about them.

“Our results show that fungal receptors are important for Fusarium infection of wheat. By learning more about the structure and function of these fungal-specific receptors, and the compounds they detect, we may be able to develop new approaches to control FHB and other plant pathogens.”

Professor Kim Hammond-Kosack, from Rothamsted Research, said: “The options to control Fusarium floral infections in cereal crops are very limited at the moment. This is causing growers and processors in the food and feed industries a tremendous headache, and why Rothamsted has been looking to apply our considerable expertise in crop diseases to this problem. These results open up the possibility of devising novel ways to control FHB disease through either targeted drug development or by eliminating the signals these receptors perceive during a fungal attack.”

Read the paper: PLOS Pathogens

Article source: University of Bath

Image: Manfred Richter / Pixabay

Could computer games help farmers adapt to climate change?

By | News

Web-based gaming, such as simulation games, can promote innovative communication strategies that engage farmers with scientific research and help them adapt to climate change.

Methods employed to tackle climate change, such as, for example, improving drainage systems to cope with increased levels of precipitation, are known as adaptation strategies. “Maladaptation” is the implementation of poor decisions or methods that were initially considered beneficial, but which could actually increase people’s vulnerability in the future.

Researchers from Sweden and Finland have developed the interactive web-based Maladaptation Game, which can be used to better understand how Nordic farmers make decisions regarding environmental changes and how they negotiate the negative impacts of potentially damaging decisions.

Their research is presented in the article “Benefits and challenges of serious gaming – the case of “The Maladaptation Game” published in De Gruyter’s journal Open Agriculture, by author Therese Asplund and colleagues from Linköping University in Sweden and the University of Helsinki in Finland. Tested on stakeholders from the agricultural sector in Sweden and Finland, the Maladaptation Game presents the player with four agricultural challenges: precipitation, temperature increase/drought, longer growing seasons and increased risk of pests and weeds. For each challenge, the player must make a strategic decision based on the options given. At the end, the player receives a summary of the potential negative outcomes based on their decisions.

“While we observed that the conceptual thinking of the game sometimes clashes with the players’ everyday experiences and practice, we believe gaming may function as an eye-opener to new ways of thinking,” explains Asplund.

Based on recent literature on serious gaming and climate communication, the authors suggest that serious games should be designed to include elements of thinking and sharing, which will stimulate reflection and discussion among stakeholders.

“Serious games have great potential of how to address complex environmental issues. Used as a communication strategy, they illustrate, visualise and communicate research findings,” says Asplund.

Read the paper: Open Agriculture

Article source: De Gruyter

Image: Monoar Rahman Rony / Pixabay

Gene-editing technology may produce resistant virus in cassava plant

By | News

The use of gene-editing technology to create virus-resistant cassava plants could have serious negative ramifications, according to new research by plant biologists at the University of Alberta, the University of Liege in Belgium, and the Swiss Federal Institute of Technology. Their results show that attempts to genetically engineer the plants to fight off viruses, in fact resulted in the propagation of mutated viruses in controlled laboratory conditions.

“We concluded that because this technology both creates a selection pressure on the viruses to evolve more quickly, and also provides the viruses a means to evolve, it resulted in a virus mutant that is resistant to our interventions,” explained Devang Mehta, postdoctoral fellow in the Department of Biological Sciences. CRISPR-Cas9 is found in nature, where bacteria use it to defend against viruses, however the researchers found that the technology results in very different outcomes in plants—and researchers are stressing the importance of screening against these sorts of unintended results in the future.

The cassava plant, the object of the study, is a starchy root vegetable that is consumed for food throughout the tropics. Cassava is a primary staple crop grown in South America, Africa, and Asia, from which 1 billion people get most of their calories each day. Each year, cassava crops are plagued by cassava mosaic disease, which causes 20 per cent crop loss. It is the mosaic disease that Mehta and his colleagues endeavoured to engineer against.

Unsuccessful results

The researchers used a new gene-editing technology called CRISPR-Cas9 to attempt to design cassava plants that could cut the DNA of the mosaic virus and make the plants resistant to its damaging effects. Unfortunately, their results were not successful. To understand what happened, the team sequenced hundreds of viral genomes found in each plant.

“We discovered that the pressure that CRISPR-Cas9 applied to the virus probably encouraged it to evolve in a way that increased resistance to intervention,” said Mehta. Mehta hastens to add that CRISPR-Cas9 has many other applications in food and agriculture that do not pose the same risks.

The research team is keen to share their results with other scientists who are using CRISPR-Cas9 technology to engineer virus-resistant plants, and encourage these groups to test their plants to detect similar viral mutations.

“We need to do more research on these types of applications of CRISPR-Cas9 technology before we proceed with field testing” said Mehta. Mehta, a postdoctoral fellow with Professor Glen Uhrig, began this research during his PhD studies at the Swiss Federal Institute of Technology(ETH) in Zurich.

Read the paper: Genome Biology

Article source: University of Alberta

Image: Hervé Vanderschuren

Wet and dry tropical forests show opposite pathways in forest recovery

By | News

The composition of regrowing wet and dry tropical forests follow opposite pathways while these forests are growing older. This has large consequences for forest restoration initiatives. The findings of a new study published in Nature Ecology and Evolution provide insights to select the best tree species for a forest area, thus enhancing and accelerating tropical forest restoration success.

Tropical forests can regrow naturally after agricultural fields are abandoned. During this regrowing process, called succession, the vegetation gradually builds up, leading to changes in environmental conditions at the forest floor. And because species differ in their growing strategies this leads to shifts in species composition over time. Understanding how succession works is crucial to improve forest restoration initiatives and to select the best species for planting.
Soft woods have a rock-and-roll life style

A large team of ecologists from Latin America, United States, Australia and Europe followed recovery of tropical forests in fifty locations across ten Latin American countries. This 2ndFOR research team found that wet and dry forests show actually opposite successional pathways. Species with different characteristics thrive under different environmental conditions, says Prof. Lourens Poorter from Wageningen University & Research and lead author of the study. “A key characteristic of tree species is their stem wood density. Species that produce soft, and cheap, wood have the ability to grow very fast when light and water are abundant. However, this soft wood comes at the expense of a reduced survival, especially under suboptimal conditions like shade and drought. As a result, soft-wooded species have a ‘rock-and-roll’ life style; they peak early in life, live fast and die young.”

On the other hand, species that produce durable, and expensive, wood can persist for a very long time, especially under adverse conditions, the research team describes in their paper. This strategy comes at the expense of a reduced and slow growth. These results provide an important step to understand the shift in species composition during forest succession. The successional theory predicts that early in succession light and water resources are in abundant supply, which leads to the dominance of ‘fast’ pioneer species with soft wood. Later in the succession resource availability declines, leading to the dominance of ‘slow’ late-successional species with hard wood, like Maçaranduba (Manilkara bidentata) a Neotropical timber species that produces such heavy wood that it sinks in water.

“In wet forest we see a shift from soft- to hard-wooded species over time. However, in dry forest we see an opposite shift from hard- to soft-wooded species” Danaë Rozendaal.

Shift from soft to hard wood species in wet forests

To evaluate successional changes in wood density, the research team analysed forest recovery at an unprecedented spatial scale, using original data from fifty sites, 1400 plots and more than 16,000 trees from tropical forests across Latin America. Co-author Dr. Danaë Rozendaal says: “Our results show that in wet forest we indeed see a shift from soft- to hard-wooded species over time. However, in dry forest we see an opposite shift from hard- to soft-wooded species.”
Opposite trend in dry forests

This opposite trend happens because in wet forests, resources (e.g. light) decline during succession, whereas in dry forests initial conditions are very harsh, dry and hot. Only hard-wooded species can tolerate these extreme conditions. When they grow they create a milder micro environment, which paves the way for the establishment of soft-wooded species. “Intriguingly”, Danaë Rozendaal adds, “the results show that wet and dry forests start out very differently, but become more similar over time in terms of microclimate and species wood density.”

Tree species selection for forest recovery

The new ecological insights can be used to improve species selection for restoration, Wageningen Professor Frans Bongers assures. “Where possible, forest restoration should rely on natural regeneration, as it is cheaper, and leads to a more diverse and resilient vegetation. However, in degraded areas, where natural regeneration is difficult, active planting provides a good alternative. Our findings suggest that forest restoration in areas with an intense dry season, covering 16% of the Neotropical forests, should prioritize planting species with high wood density. These have higher chances of surviving the dry period. In addition, well-adapted, native tree species are preferred rather than exotic species, because they support biodiversity. This selection can also lower mortality rates among planted trees, which often exceeds more than one third of the planted trees. In wet forests, though, a mix of local soft and hard wooded species can be successfully planted at the onset. The fast soft-wooded species rapidly establish a protecting vegetation, and shelter the slower growing hard-wooded species that will form the basis of a long-term stable forest.”

Read the paper: Nature Ecology and Evolution

Article source: WUR

Image: Frans Bongers