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Max Lloyd

Assistant Professor, Geosciences, Penn State University

Friday, October 4听

12:00 pm听

FDA 232听

How well do plants breathe in glacial climates?

Land plant photosynthesis today represents about half of global gross primary productivity. During the last glacial period, land plant productivity was reduced, potentially by a factor of two. The specific cause of the terrestrial biosphere contraction during glacial periods is uncertain, but important for understanding controls on climate in the past and near-future. One hypothesized explanation for this productivity decline is low atmospheric CO2听concentrations at the time, because when [CO2] is low, modern plants can release nearly as much carbon through photorespiration as they take in through photosynthesis. This could stress and starve plants at an individual level and perhaps at a global scale.听

However, direct evidence that high photorespiration suppressed glacial terrestrial productivity is limited. I will describe new work applying a recently developed proxy for the relative rate of photorespiration to photosynthesis based on clumped isotopes in wood methoxyl groups. We applied this proxy to samples of wood from across North America that span the last glacial period to the present. We find that photorespiration rates vary in space and time. Specifically, trees from the last glacial period below ~40掳N tended to photorespire more than those from higher latitudes and more than trees from similar locations in the more recent past. These differences can be reconciled with a single relationship between temperature, [CO2], and photorespiration. This suggests that despite environmental adaptations, trees from the glacial period experienced elevated photorespiratory stress compared to more recent counterparts. This provides direct evidence that CO2 starvation restricted land plant productivity during glacial intervals.

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