Why the tropical tree Clusia rosea only “breathes” at night and what scientists discovered

Tropical forests contain thousands of plant species that survive long dry periods without attracting much scientific attention outside specialist circles. Among them is Clusia rosea, a tree more often noticed for its thick leaves and ornamental appearance than for the unusual chemistry taking place inside them after sunset. While most plants absorb carbon dioxide during daylight, some tropical species reverse the pattern and do much of their gas exchange at night instead.That shift changes how water is used. In humid rainforests, the advantage may seem small, though in hotter and drier conditions it becomes far more important. Interest in the process has grown as agricultural researchers look for ways crops might cope with rising temperatures and unstable rainfall patterns. Recent work on Clusia species has added another layer to that discussion by tracing the genetic changes linked to this nocturnal form of photosynthesis. Scientists studying climate resilience are particularly interested in how these plants reduce water loss while continuing to store energy efficiently. The ability to switch or partially shift photosynthesis timing could eventually influence future research into drought-ressistant crops suites for increasingly unpredictable environmental conditions. Most plants rely on daytime photosynthesis. Their leaf pores, called stomata, open while sunlight is available, allowing carbon dioxide to enter. The drawback is that water escapes at the same time. In tropical heat, large amounts can disappear through evaporation over the course of a day.Certain plants avoid part of that loss through a process known as CAM photosynthesis, short for Crassulacean Acid Metabolism. Instead of taking in carbon dioxide during daylight hours, they open their stomata mainly at night when temperatures are lower and humidity is often higher. The stored carbon is then used for photosynthesis once the sun rises.As per the reports published through EurekAlert, titled “Unraveling the evolution of an extraordinary photosynthesis in a tropical tree species,” scientists studying several Clusia species found that the trees show different levels of dependence on this system. Some rely heavily on nighttime carbon uptake while others switch between daytime and nocturnal patterns depending on drought conditions. That flexibility has made the genus unusually valuable for plant physiologists. Many CAM plants are cacti or succulents adapted to deserts, but Clusia species are trees growing in tropical forests, cloud forests, and coastal habitats. The variation within a single plant group offers researchers a clearer view of how the mechanism evolves.The genus itself has attracted scientific attention for decades because its species do not all follow the same photosynthetic strategy. Some function much like ordinary trees, others operate almost entirely through CAM, while a few move between both systems.According to a study published in the Botanical Journal of the Linnean Society, titled “Evolutionary history of CAM photosynthesis in Neotropical Clusia: insights from genomics, anatomy, physiology and climate”, this diversity appears linked to changing environmental pressures across tropical America. Researchers examining the evolutionary history of Clusia suggested that shifts in rainfall, elevation, and habitat fragmentation may have influenced how different species adapted their metabolism over time. The group is sometimes described as one of the few tree lineages where CAM occurs on such a broad scale. That matters because it provides living examples of intermediate stages rather than a simple split between CAM and non-CAM plants.In practice, the transition is not always clean. Some species continue using ordinary daytime photosynthesis while partially activating CAM during water stress. Others maintain both systems together. The boundaries blur.Recent genomic analysis focused on three related species with differing levels of CAM activity. By comparing their DNA, researchers attempted to understand how the pathway became established and how it continues to change. As per the study published in the Botanical Journal of the Linnean Society, the genomes showed extensive rearrangements over evolutionary time. Some genes had duplicated repeatedly, while mobile DNA sequences known as transposable elements appeared to have reshaped parts of the genome structure. Certain genes linked with stress responses and carbon metabolism also showed altered activity patterns. The findings support the idea that CAM did not emerge through a single genetic switch. Instead, the process seems tied to gradual modifications affecting multiple biological systems at once, including water regulation, circadian timing, and leaf chemistry. Scientists involved in the work also pointed to gene expression patterns that differed between day and night cycles. In CAM plants, timing matters almost as much as the genes themselves because the metabolic pathway depends on separating carbon uptake from daylight photosynthesis.Agricultural interest in CAM photosynthesis has expanded steadily over the last decade, largely because the mechanism uses water more efficiently than standard photosynthesis. In dry conditions, that difference can become substantial. The idea of transferring CAM-like traits into crops remains experimental and technically difficult. Wheat, rice, and maize evolved under very different metabolic systems, and researchers are not suggesting immediate transformation into fully nocturnal plants. Still, understanding how CAM evolved in species such as Clusia may help identify genetic pathways connected to drought resistance. Part of the challenge lies in coordination. CAM is not controlled by one isolated gene but by networks that interact with environmental cues and internal biological clocks. Altering only one component would likely fail to reproduce the system properly. Even so, the long-term appeal is obvious. Crops capable of reducing water loss during extreme heat could become increasingly important in regions facing prolonged drought or unstable seasonal rainfall.Much of the scientific work surrounding rainforest plants still focuses on species with economic or medicinal value. Trees such as Clusia rosea tend to receive less public attention despite representing unusual evolutionary experiments already taking place in nature.As per the EurekAlert report, do not provide an immediate blueprint for climate-resistant agriculture, though they widen understanding of how plants adapt to difficult environments over long periods of time. In the case of Clusia, survival appears linked not to rapid growth or large root systems, but to timing. Simply changing when a tree breathes can alter how much water it loses. For now, researchers are continuing to map how different Clusia species evolved across tropical ecosystems and how flexible their photosynthetic systems remain under environmental stress. The answers may end up being useful far beyond the forests where the trees first developed them.