In a study published in the Proceedings of the National Academy of Sciences, Professor Richard Thomas and alumnus Justin Mathias (BS Biology, ’13 and Ph.D. Biology, ’20) synthesized published tree ring studies. They found that increases in carbon dioxide in the atmosphere over the past century have caused an uptick in trees’ water-use efficiency, the ratio of carbon dioxide taken up by photosynthesis to the water lost by transpiration — the act of trees “breathing out” water vapor.

“This study really highlights the role of forests and their ecosystems in climate change,” said Thomas, interim associate provost for graduate academic affairs. “We think of forests as providing ecosystem services. Those services can be a lot of different things — recreation, timber, industry. We demonstrate how forests perform another important service: acting as sinks for carbon dioxide. Our research shows that forests consume large amounts of carbon dioxide globally. Without that, more carbon dioxide would go into the air and build up in the atmosphere even more than it already is, which could exacerbate climate change. Our work shows yet another important reason to preserve and maintain our forests and keep them healthy.”

Previously, scientists have thought that trees were using water more efficiently over the past century through reduced stomatal conductance — meaning trees were retaining more moisture when the pores on their leaves began closing slightly under rising levels of carbon dioxide.

However, following an analysis using carbon and oxygen isotopes in tree rings from 1901 to 2015 from 36 tree species at 84 sites around the world, the researchers found that in 83% of cases, the main driver of trees’ increased water efficiency was increased photosynthesis — they processed more carbon dioxide. Meanwhile, the stomatal conductance only drove increased efficiency 17% of the time. This reflects a major change in how trees’ water efficiency has been explained in contrast to previous research.

“We’ve shown that over the past century, photosynthesis is actually the overwhelming driver to increases in tree water use efficiency, which is a surprising result because it contradicts many earlier studies,” Mathias said. “On a global scale, this will have large implications potentially for the carbon cycle if more carbon is being transferred from the atmosphere into trees.”

Since 1901, the intrinsic water use efficiency of trees worldwide has risen by approximately 40% in conjunction with an increase of approximately 34% in atmospheric carbon dioxide. Both of these characteristics increased approximately four times faster since the 1960s compared to the previous years.

While these results show the rise in carbon dioxide is the main factor in making trees use water more efficiently, the results also vary depending on temperature, precipitation and dryness of the atmosphere. These data can help refine models used to predict the effects of climate change on global carbon and water cycles.

“Having an accurate representation of these processes is critical in making sound predictions about what may happen in the future,” Mathias said. “This helps us get a little closer to making those predictions less uncertain.”

The study is a product of the researchers’ seven-year research collaboration during Mathias’ time as a doctoral student. After graduating from WVU, Mathias joined University of California, Santa Barbara as a postdoctoral researcher.

“Since moving to California, my work has taken a turn from being in the field, collecting measurements, analyzing data and writing manuscripts,” Mathias said. “My new position is more focused on ecological theory and ecosystem modeling. Instead of measuring plants, I form hypotheses and seek out answers to questions using computer models and math.”

In the future, Mathias aspires to become a professor at a research university to continue these research pursuits.

“I would love to run my own lab at a university, mentor graduate students and pursue research questions to continue building on the work we’ve already accomplished. There’s been a lot of progress in our field. There are also an infinite number of questions that are relevant moving forward,” Mathias said. “I owe everything to my time and training from the people at WVU. My long-term goal is to be in a position where I can continue moving the field forward while giving back through teaching and mentoring students.”

“Major mental disorders, such as schizophrenia, bipolar disorder, and major depressive disorder, share common genetic roots, but each disorder presents differently in each individual,” said Francis J. McMahon, M.D., a senior author of the study and chief of the Human Genetics Branch, part of the Intramural Research Program NIMH. “We wanted to investigate why disorders present differently, despite this seeming genetic similarity.”

McMahon and colleagues suspected that the brain’s transcriptome may hold some clues. The human genome is made up of DNA that contains instructions for helping maintain and build our cells. These instructions must be read and then copied into so-called “transcripts” for them to be carried out. Importantly, many different transcripts can be copied from a single gene, yielding a variety of proteins and other outputs. The transcriptome is the full set of transcripts found within the body.

The researchers used postmortem tissue samples to examine the brain transcriptomes of 200 people who had been diagnosed with either schizophrenia, bipolar disorder, major depressive disorder, or who did not have a known mental illness. The researchers examined both genes and transcripts expressed in the subgenual anterior cingulate cortex, a brain site involved in mood disorders, reward, impulse control, and emotion regulation. The brain tissue samples came from the NIMH Human Brain Collection Core, curated by NIMH’s Barbara Lipska, Ph.D., co-senior author of the paper.

To increase the odds of detecting rare transcripts, the researchers sequenced the transcripts at a resolution about four times greater than that used in previous studies. This technique identified 1.5 times more transcripts than earlier studies using the same method at lower resolution, confirming that this sequencing method picks up many transcripts that otherwise would have been missed.

The researchers found only modest differences in gene expression between individuals with a mental disorder and individuals without a mental disorder. However, when they focused on the transcripts, they found two to three times as many differences between individuals in the two groups. The most noticeable differences emerged when the researchers compared transcripts between two groups of individuals with a mental disorder — e.g., bipolar disorder versus schizophrenia, depression versus schizophrenia, or depression versus bipolar disorder.

“When we compared disorders in our transcript-level analyses, that is when we saw the stark differences,” said Dr. McMahon. “Most transcripts that were expressed differently — produced in higher versus lower levels — turned out to be expressed in opposite directions in people with different disorders. Some transcripts were expressed in the same direction in individuals with mood disorders and the opposite direction in individuals with schizophrenia.”

For example, distinct transcripts in the gene, SMARCA2, a known risk gene for autism spectrum disorder that regulates the expression of many other genes important in neuronal development, were expressed differently in brain samples from people with schizophrenia than in samples from people with bipolar disorder.

Parts of a gene’s instructions may be kept in or left out during the transcription process. The researchers found that a common genetic variant that regulates this inclusion and exclusion, called splicing quantitative trait loci (sQTLs), may play a notable role in the inherited risk for each disorder.

“We found that subtle differences in gene expression across different disorders reflect more pronounced and diagnosis-specific changes at the level of transcripts,” said McMahon. “A cell can express many different transcripts from the same gene, resulting in different proteins — and potentially different illness processes.”

More research is needed to better understand the functions of different transcripts, the timing of alternative splicing, and the transcriptomic differences in specific brain regions and cell types. However, the current study sheds light on the importance of understanding transcript-level differences to get a full picture of why mental disorders vary in onset, progression, and symptoms.

In addition, input from the right ear reaches the left brain hemisphere first, while input from the left ear reaches the right brain hemisphere first. The two hemispheres perform different tasks during speech processing: The left side is responsible for distinguishing phonemes and syllables, whereas the right side recognizes the speech prosody and rhythm. Although each hemisphere receives the information at a different time and processes different features of speech, the brain integrates what it hears into a unified speech sound.

Brain waves establish connection

The exact mechanism behind this integration process was not known until now. In earlier studies, however, Preisig had found indications that measurable oscillations elicited by the brain — known as gamma waves — played a role. Now he has managed to demonstrate that the process of integrating what we hear is directly linked to synchronization by gamma waves. Neurolinguists from UZH worked on the project alongside researchers from the Netherlands and France.

Processing ambiguous information

The study, which took place at the Donders Center for Cognitive Neuroimaging in Nijmegen, the Netherlands, involved 28 healthy subjects who had to repeatedly solve a listening task: An ambiguous syllable (a speech sound between ga and da) was played in their right ear while a click containing a fragment of the syllables da or ga was played unnoticed in the left ear. Depending on what was played in their left ear, the participants heard either ga or da and then had to report what sound they had heard. During the process, the researchers were tracking activity in both hemispheres of the brain using functional magnetic resonance imaging (fMRI).

Electric stimulation impairs synchronization

During the experiments, the researchers disrupted the natural activity pattern of gamma waves by stimulating both hemispheres of the brain with electrodes attached to the head. This manipulation affected participants’ ability to correctly identify the syllable they heard. The fMRI analysis showed that there were also changes in the activity of the neural connections between the right and the left brain hemispheres: The strength of the connection changed depending on whether the rhythm of the gamma waves was influenced by electric stimulation in the two brain hemispheres synchronously or asynchronously. This disruption also impaired the integration process. Thus, synchronization of the gamma waves seems to serve to balance the different inputs from the two hemispheres of the brain, providing a unified auditory impression.

Possible therapy for tinnitus

“Our results suggest that gamma wave-mediated synchronization between different brain areas is a fundamental mechanism for neural integration,” says Preisig. “Moreover, this research shows for the first time, using human hearing as an example, that the connection between the two hemispheres of the brain can be successfully modulated by electric stimulation,” adds Alexis Hervais-Adelman, head of neurolinguistics at the UZH Department of Psychology, who was also involved in the study.

These findings could thus also find clinical application in the near future. “Previous studies show that disturbances in the connection between the two hemispheres of the brain are associated with auditory phantom perceptions such as tinnitus and auditory verbal hallucinations,” Preisig adds. “Thus, electric brain stimulation may present a promising avenue for the development of therapeutic interventions.”

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Materials provided by University of Zurich. Note: Content may be edited for style and length.