By demonstrating that not all plants specialize in one specific source of nitrogen, the result turns a commonly held theory on its head. It also provides a dose of optimism that tropical forests will be able to withstand environmental shifts in nutritional cycles brought on by global climate change.
Nitrogen is an essential nutrient that plants must absorb from the soil to survive. Most land plants outside the tropics appear to have evolved to rely on just one of three common sources of nitrogen: nitrate (NO3-), ammonium (NH4+), or dissolved organic nitrogen (DON). As a result of this limitation, they usually inhabit "niches" defined largely by the available nitrogen source. When that source crashes for any reason—often because of shifts in climate—the plants cannot adapt, with potentially disastrous consequences for natural ecosystems.
However, tropical species appear to be far more adaptable than their temperate kin when it comes to their nitrogen needs. A team of researchers* has found that, when confronted with shifts in nitrogen availability, these plants simply "flip a switch" and use whatever is handy.
"When it comes to nitrogen, the tropical plants we studied behave like kids at a pizza party—they may prefer pepperoni, but if only plain cheese is available, they'll still have a slice," said lead author and postdoctoral researcher Benjamin Houlton of the Carnegie Institution's Department of Global Ecology. "This result gives a glimmer of hope that tropical ecosystems may have the capacity to adjust to certain aspects of climate change."
Working in six well-known sites with variable rainfall on Hawaii's Maui Island, the researchers measured the soil content of nitrate, ammonia, and dissolved organic nitrogen. They also determined each source's relative contribution to the growth of a variety of plant species, from small floor-dwelling shrubs, to tree ferns, to tall canopy trees.
In dry areas, nitrate was most readily available, while in wetter areas, ammonium was the dominant source. The plants made use of whichever of these two sources was most common in their native soil. Dissolved organic nitrogen was plentiful, but did not make a significant contribution to plant growth at any of the sites.
To examine the plants' nutritional response to climate change, the researchers combined new measures and models of variations in the atomic masses of nitrogen compounds that occur naturally in plants and soils. By examining these different masses, known as isotopic ratios, across different rainfall climates, they discovered an abrupt shift in the nitrogen cycle and in the nutritional strategies of entire forest communities.
"It really is quite striking; once the soil gets wet and nitrate drops below a certain threshold, the tropical plants all begin using ammonium in near-perfect unison," Houlton explains. "If these diverse plant species can be flexible in their nitrogen metabolism—thought to be non-negotiable in many temperate ecosystems—then maybe they can react to other environmental stresses just as gracefully. Still, our results will need further testing in vast areas of the tropics before we will know how well they truly represent the entire ecosystem."
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Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
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Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
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For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
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