A warming Antarctic is changing how mosses have sex

Mosses are reacting to rising temperatures in the Antarctic in different ways. The tiny plants could cause big changes to the food web.

The Western Antarctic Peninsula, the long arm of Antarctica reaching up to South America, is one of the fastest-warming polar regions on the planet. Hannah Prather and colleagues have studied how this warming is affecting the plant life in the area, and the answer seems to depend on what species you’re looking at. Critically temperature appears to affect sexual expression on one of the dominant mosses. “Our results indicate that continued warming may impact the reproductive output of Antarctic moss species, potentially altering terrestrial ecosystems dynamics from the bottom up,” say the authors in their paper. “Understanding these effects requires clarifying the foundational, mechanistic role that individual plant species play in mediating complex interactions in Antarctica’s terrestrial food webs.”

The study was on King George Island, just to the north of the continent. Here, among the seals and penguins, you’ll also find Polytrichastrum alpinum and Sanionia georgicouncinata. The botanists say that these two species account for around two-thirds of the vegetation cover on the island. At Juan Carlos Point, they set up some open-top chambers. These acrylic boxes would heat some of the moss, a little over half a degree centigrade. They then analysed what they found, including the mosses effect on soil temperature, the moss canopy morphology and the sex ratios of the mosses.

Unlike flowering plants, mosses tend to be male or female in their largest form. They’re haploid with either male or female chromosomes. The fertilised females grow a sporophyte, a diploid plant with a pair of chromosomes. It then disperses male and female spores, with just one chromosome each, into the wind.

Polytrichum alpinum
Image: HermannSchachner / Wikipedia

The botanists found that a rising temperature increased the female sex expression, compared to the control plots. This difference has ecological consequences said the team. “Our findings also identified a correlation between the number of female moss reproductive structures and the abundance of microarthropods within the moss canopy (r2 = 0.64). Studies show that both springtails and mites prefer sexually expressing moss shoots rather than non-expressing shoots and that microarthropods prefer female over male shoots.” Some work suggests that one reason for this might be volatile chemicals that the females release.

“Microarthropods play a fundamental role in nutrient cycling within soil ecosystems, yet in the Antarctic terrestrial ecosystem, these processes have been shown to be largely governed primarily by climatic parameters.”

The team also found that P. alpinum also increased the nematode population on the soil under passive warming. However, fungal biomass dropped. Prather and colleagues said that it might not be the heat itself that was harming the moss, but that the heat was helping something else – to the fungi’s cost. “This decrease in moss-associated fungal biomass may be related to the significant increase in microarthropods associated with OTC warming, as both the moss-associated Oribatida and Collembola are known to feed on algae, dead organic material and fungi.”

With warming being so rapid around this part of Antarctica, further work is needed fast to understand what is going on. The authors conclude, “Future studies to quickly enhance our species-specific understanding of the responses of cryptogam communities to warming will be the key to develop an ecosystem scale understanding of terrestrial ecology and ecosystem function in a warming Antarctica.”