Is There Enough Phosphorus for Us? – Discovery Institute

Photo: Hunga-Tonga blast from space, by NASA

Not long ago I consideredthe element phosphorusas a test case for Michael Dentons hypothesis of prior fitness of the environment for complex beings of our size. Phosphorus is a vital element on which lifes genetic and metabolic processes depend every picosecond. And yet P is not as easily cycled through the environment as are other elements like nitrogen and carbon. Phosphorus, therefore, can be considered a limiting factor for a productive biosphere. We left the issue as a work in progress, although ample circumstantial evidence exists that P bioavailability has not been a problem throughout Earths history (consider trilobites in an ancient ocean, sauropods in a tropical rain forest, or tropical fish in a lagoon consuming phosphorus with impunity in different eras).

Phosphorus has been in the news since that article. A paper inNatureadmits that the extent to which phosphorus availability limits tropical forest productivity is highly uncertain because of intertwined effects with other limiting factors such as nitrogen. The authors experimented with adding phosphorus to a small patch of old growth rainforest in Amazonia, where soils are depleted in phosphorus. After two years, they saw increases in primary productivity, but not in stem growth. Disentangling the effects of phosphorus from other factors still seems uncertain.

At Charles University in the Czech Republic, two paleontologists investigated the phosphorus cycle over geological time by investigating the abundance of phosphatic marine shells in the fossil record as a proxy. Innews from the Faculty of Science, they ascribe a transfer of phosphorus from shelly creatures to vertebrates in the Devonian:

M. Mergl laconically remarked that phosphorus was stolen by vertebrates. This remark actually became the starting shot. The question of theradical loss of phosphorusin the environment proved so exciting that both authors set about studying in detail the various corners of the cycle of this element. [Emphasis added.]

Their tale begins with abundant phosphorus supporting the Ediacaran fauna. Then they attribute the Cambrian Explosion in part to still-plentiful phosphorus.

The Early Paleozoic was acritical era of phosphorus cycledue to the intense involvement of biota in its dynamics. At the beginning, phosphorus was easily available in great amount and therefore many groups had the opportunity to build external phosphatic shells.This very likely contributed to the story of the Cambrian explosion, a period when representatives of almost all animal phylaappeared in the fossil record within a relatively short period of time. The Cambrian was thus a golden age for organisms with external phosphatic shells.

Like theoxygen theory, this explanation transfers the explanation for the origin of genetic information to the abundances of blind elements in the periodic table hardly a logical idea. That would be like attributing the origin of books to the availability of movable type in a print shop with no Gutenberg.

In Act Two of their biological opera, phosphorus divorced the shelly creatures and married the vertebrates. Marine shells declined in size because large phosphatic shells became a luxury. This process has been accelerated by the emergence and evolutionary diversification of vertebrates, which, although they need a lot of phosphorus, are better at managing it, the paleontologists surmise. But the plot thickens when anomalies emerge:

The subsequent era from the end of the Paleozoic to the present is characterized bylimited but also selective availability of phosphorusin the seas and oceans.Geological processessuch as the Variscan (400-300 Ma) and the Alpine orogenies (80 Ma to the present)have greatly aided the supply of phosphorus to the oceans.However, the ability of phosphorus to reach the oceans from its main source in the rocks of the denuded continents washampered by the spreading of vegetation on land and other influences such as climateduring this times [sic].

Climate change should not be used as a skeleton key for incomplete answers. In combination with other influences, storytellers can make any plot work. Kraft and Mergl published their ideas in an Opinion article, Struggle for phosphorus and the Devonian overturn, last month inTrends in Ecology & Evolution.

Most instructive is their proposal that geological processes have aided the supply of phosphorus to the oceans and land. The role of volcanoes and orogenic processes in keeping phosphorus plentiful throughout Earths history deserves elaboration by design theorists. Consider what happened on January 14, when one of the most powerful volcanic eruptions ever recorded, theHunga-Tonga volcano, surprised scientists with a massive plume visible from space (see the photo above). A new paper inGeophysical Research Lettersreports a massive phytoplankton bloom that was visible from space as well following the eruption.

Two independent bio-optical approaches confirmed that the phytoplankton bloom was a robust observation and not an optical artifact due to volcanogenic material. Furthermore, the timing, size, and position of the phytoplankton bloom suggest thatplankton growth was primarily stimulated by nutrients released from volcanic ashrather than by nutrients upwelled through submarine volcanic activity. The appearance of a large region withhigh chlorophyll a concentrations less than 48 hours after the largest eruptive phase indicates a fast ecosystem response to nutrient fertilization.However, net phytoplankton growth probably initiated before the main eruption, whenweaker volcanism had already fertilized the ocean.

Although chlorophyll itself does not contain phosphorus, the availability of phosphorus in the ash may have stimulated rapid proliferation of the plankton.

Does phosphorus availability impact predator-prey relationships? In a research article inPNAS, Guilloneauet al.investigated Trade-offs of lipid remodeling in a marine predatorprey interaction in response to phosphorus limitation.

Microbial growth is oftenlimited by key nutrients like phosphorus (P)across the global ocean. A major response to P limitation is thereplacement of membrane phospholipids with non-P lipidsto reduce their cellular P quota. However, thebiological costs of lipid remodelingare largely unknown. Here, we uncover a predatorprey interaction trade-off wherebya lipid-remodeled bacterial prey cell becomes more susceptible to digestion by a protozoan predatorfacilitating its rapid growth. Thus, we highlighta complex interplaybetween adaptation to the abiotic environment and consequences for biotic interactions (grazing), whichmay have important implications for the stability and structuring of microbial communitiesand the performance of the marine food web.

Themagical thinkingin this story becomes evident when the authors opine that marine microbeshave evolved sophisticated strategiesto adapt to P limitation such as replacing phospholipids with non-P lipids. One must imagine microbes holding committee meetings, thinking out strategies as if they were business managers worried about maintaining their products under duress from shortages in the supply chain. But if we do that, one manager worries, we become susceptible to organized crime.

The low availability of key nutrients like Pin marine surface waters representsa grand challenge for microbes, particularly those inhabiting oligotrophic gyres. Although lipid remodeling enables these microbes to survive better in these potentially P-limited environments, as well as facilitating greater avoidance of ingestion by ciliate grazers, once ingested, these lipid-remodeled cells are unable to survive phagolysosomal digestion (Fig. 6). Therefore, these microbes facean unsolvable dilemma.

The managers panic; what to do? Each option is potentially disastrous. Thus, it is clear that adaptation to a specific niche can come with consequences to an organisms viability, the storytellers continue. Stay tuned for the next exciting episode! it remains to be seen what other trade-offs in predatorprey interactions exist following adaptation of cosmopolitan marine microbes to P limitation.

Speculation like this is not particularly helpful in science, especially when the story is so evidence-starved as to depend on one single example of a microbe and its predator. Global change is expected to exacerbate P limitation in the surface ocean due to water-column stratification accelerated by global warming, they say at one point. Maybe that was the motivation to ensure their story got funded and published. But what do they know from their observations? And how can they extrapolate one predator-prey interaction to the whole globe?

Moreover, given that the effects of remodeling on predatorprey interactions we report here are ultimately controlled by in situ P concentrations (which controls lipid remodeling), thensuch interaction effects are also likely to be dynamic in their nature, given the often-seasonal nature of P limitation e.g., in the Mediterranean Sea, PlcP-mediated lipid remodeling occurs across an annual cycle, whereby P limitation intensifies during spring and summer, but starts to become alleviated from September.Nonetheless, this work clearly highlights the complex interplay between the abiotic nutrient environment, microbes, and their grazers and how predatorprey dynamics aregoverned by abiotic controlof prey physiology, which hasimportant implications for how we model trophic interactionsin marine ecosystem models,particularly in a future scenariowhere nutrient-deplete gyre regions are set to expand.

Readers should note that both predator and prey have not gone extinct, which would make a stronger case for P limitation in their limited ecological case.

While agriculturalists worry about phosphorus for commercial fertilizers, none of these papers above suggest that the natural biosphere has ever suffered from a deficiency of phosphorus. The plankton bloom after the Tonga eruption shows how volcanoes can fortify marine environments with inorganic nutrients. Another paper inNature Scientific Reports suggests that terrestrial environments, too, can take advantage of volcanic phosphorus. Pioneering plants can absorb phosphorus from volcanic ash and supply it to secondary growth through their leaf litter. This is interesting because many terrestrial soils contain volcanic ash containing insoluble inorganic phosphorus that was thought unavailable to plants. Volcanic islands like Japan and Hawaii, however, seem to have thriving ecosystems.

Despite volcanic ash soil covering about 20% of the land in Japan,and phosphorus deficiency being a serious problem in Japanese agriculture,net primary productionin Japanese forests is primarily isnot lowcompared to other temperate zones of the world.This suggests that natural vegetation on the infertile volcanic ash soil obtain sufficient nutrition including phosphorus.

Geology, therefore, appears to offer a supply chain for elemental nutrients built into our planet by means of plate tectonics coupled with thermodynamics the availability of heat near the surface. Since a planets internal heat decreases over time, there may be temporal constraints on this supply chain. If so, one implication is that cold, dead worlds might not have a functioning biosphere even if they orbit in the habitable zone. Is Earth operating in a Goldilocks time as well as a Goldilocks location? These are good questions for design theorists to investigate. Meanwhile, Earths biosphere seems to be functioning tolerably with its natural phosphorus supply.

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Is There Enough Phosphorus for Us? - Discovery Institute