Plants and global change – PPP2019

From Plants and People we moved more on to Plants and Planet with a session that looks at how plants are coping with change on a global scale.

Katie Field has been working on wheat. Field started off by looking at the transition from water to land by plants. Looking at the Rhynie Chert you can see the root-like structures of the earliest plants. When plants were moving to land CO₂ was at 10 times the concentration than it is now. Looking at fossils from this period, there are things that look like arbuscular mycorrhizal fungi. Arbuscular mycorrhizal fungi matter because symbiosis can be highly beneficial in crops and wider agroecosystems in many ways, including improved soil structure and resistance to pests.

Forthcoming research is going to show that cultivars of wheat vary in response with mycorrhizal partners under elevated CO₂. Understanding how cultivars and fungi as a community respond to increased carbon dioxide will be hugely important to maintaining or increasing yields.

Evan DeLucia talked about farming with rocks. I remember working with my father to remove rocks from gardens and allotments. I fear I may have been wasting my time. The talk centred on carbon dioxide concentrations. DeLucia commented that reducing emissions is not enough, we need negative carbon technology. Without net emissions, we cannot meet climate targets.

There are various techniques to capture and sequester carbon dioxide. DeLucia isn’t saying there’s one solution, but that we may need to use several, depending on permanence and cost. DeLucia proposed enhanced weathering, using igneous rocks. The type of rock is important because if the rock has carbonates, it’ll be releasing carbon dioxide to the atmosphere.

If you take rock, grind it up to increase surface area and then put it in warm wet places, then you get enhanced weathering. DeLucia talked about an idealised scenario, where rock is used to fertilise tropical forests. It might work, but it’s not a realistic solution. But what about farming? Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO2-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure.

The experiments DeLucia ran were on rocks that are waste product. The experiments were at farm scale. Does it work?

DeLucia has no carbon data. That’s in progess. He does have nitrogen data. Soil pH rises and as a result nitrous oxide falls. There may be increased yields. N₂O as a greenhouse gas is nearly all from agricultural use. Cutting that might be of value in itself. However, there is the question of the emissions in getting the rock to the field.

This is desperate stuff DeLucia said, but other authors say these are desperate times.

Richard Norby noted that we usually exclude humans from experiments, as they’re a chaotic complication, but they do get everywhere. Today he was talking about
the Sphagnome Project, which incorporates genomics into a long‐running history of Sphagnum research that has documented unparalleled contributions to peatland ecology, carbon sequestration, biogeochemistry, microbiome research, niche construction, and ecosystem engineering.

The boreal region contains massive amounts of peatlands. They’re a vast carbon store. Maybe even one-third of the world’s soil carbon. Peatlands are cold, acidic waterlogged regions that retard decompostion. So warm and dry them and you have a great source of extra carbon.

Norby described Sphagnum as an ecosystem engineer. It works to keep out competitor plants. Under elevated carbon dioxide and warming productivity increases for a while, then decreases. Relative proportions of Sphagnum species will change. There’s clear evidence for a decline in coverage of land under warming. Sphagnum desiccates, and the loss appears to be irreversible, as when the land gets wet again in the spring, the Sphagnum doesn’t return.

Using two separate meta-analyses, Norby and colleagues found that a 10 °C increase in incubation temperature increased C release by a factor of two. In their paper, the authors say “These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO2 will strengthen the permafrost C feedback more than waterlogged systems releasing CO2 and CH4 for a given amount of C.”

Climate warming in peatlands promotes ancient carbon release. This will have an impact on the global carbon cycle.

Pam Diggle opened with a temperature map from Europe recently. Temperatures are going to rise. But it’s not just hotter, it’s hotter earlier. The growing season is going to be longer. This is having an effect on phenology.

Phenology is the study of the seasonal timing of life-cycle events, and Diggle spoke about flowering. There’s a lot of data now coming out based on dates from herbarium data. Diggle pointed to a recent publication that found 46% of plants are flowering earlier. Her question is, what is going on with the 54% that don’t?

Elsewhere she has written: Exceptions to the general pattern of precocious flowering are common. Many species either do not appear to respond or even delay flowering in, or following, warm growing seasons. Existing phenological models have not fully addressed such exceptions to the common association of advancing phenologies with warming temperatures.

Anthesis, the opening of a flower is just one phase of development she says. Many plants have a phase preformation, and this can be part of a two-year trajectory of flower development. We don’t know much about all the steps all along away before anthesis. If warming rushes flowers through early stages in year one, they may be left with more to do in year two before they can open.

There’s so much we don’t know you can produce several models. And any one of the models could apply depending on what species you’re looking at. There might not be just one model that will explain all things that go on. It also makes me wonder about the 46% of precious flowering plants. Are they all early for the same reason, or are they also following multiple apporaches?

Alaska, where Diggle is growing is already up 1.4 degrees. She’s using growth chambers to see how more warming will affect plants. This is work in progress so no results, but it looks like preformation warming has a different effect to warming in the year of flowering. There may also be a temperature threshold effect.

Even looking at the planetary scale, it seems we cannot escape human influence. Norby’s research into the problems facing Sphagnum look grim, but Field and DeLucia both offer solutions to forthcoming problems. Diggle, however, shows how little we understand about warming. That might be an issue if we keep our foot on the accelerator.