Published: Sept. 16, 2022
Trees in a forest

Bharat Rastogi
Cooperative Institute for Research in Environmental Sciences (CIRES)
University of Colorado Boulder

In Person:
GUGG 205
Sep 16, 2022, 3:35 PM

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The carbon balance of Earth’s ecosystems is a first order ecological property with wide-ranging implications for climate change, global food security, and biodiversity. Earth’s terrestrial ecosystems drive the interannual variability in the atmospheric growth rate of CO2 and act as sink, removing ~ 25% of anthropogenic carbon emissions. While this sink has so far kept pace with increasing anthropogenic emissions, the future of this climate subsidy remains unknown, due to a lack of mechanistic understanding of carbon cycle processes. There are two main reasons for this. First, we can only measure the balance between component fluxes of ecosystem photosynthesis and respiration beyond the scale of a leaf cuvette or a soil chamber. Second, measurement networks are sparse and under-sample large parts of the world, including critical regions such as the Tropics and high-latitude ecosystems. 

In this seminar, I will synthesize results from two studies that address both these issues. Our journey will begin in a moist temperate coniferous old-growth forest, where I will present measurements of a trace gas called Carbonyl Sulfide (OCS). OCS is analogous to CO2 and taken up by leaf stomata during photosynthesis. However, unlike CO2, there are no OCS emissions from photosynthesizing plants, making it a potentially excellent tracer for ecosystem processes. Co-authors and I find nocturnal uptake of this gas by epiphytes, unrelated to photosynthesis by vascular plants, and quantify co-variability of daytime OCS and CO2 flux to diffuse light and heat waves. Finally, we use these measurements to explain a puzzling response of the forest to smoke from a nearby fire. For the second half of this presentation, I will ask you to leave the forest floor for a journey with me through the atmospheric column that extends from the surface to the top of the atmosphere. Here, I will discuss the utility of atmospheric CO2 measurements to provide constraints on continental-scale NEE. Specifically, I will focus on column retrievals of CO2 from NASA’s OCO-2 satellite, the information content of these new data relative to rigorously calibrated in-situ observations made on surface-flasks, tall-towers and aircrafts, and the utility of column data in biome-wide flux estimation. We will eventually find our feet back on the ground, where I will present areas for future inquiry.


Bharat is a postdoctoral associate at the Cooperative Institute of Research in Environmental Sciences (CIRES) and NOAA’s Global Monitoring Laboratory in Boulder Colorado where he works with the Carbon Cycle Greenhouse Gasses Division. Prior to coming to Boulder, he completed his PhD in the department of Forest Ecosystems and Society at Oregon State University and an M.A. in Geography from University of California, Santa Barbara. Bharat’s research primarily asks the question:  What is the impact of anthropogenic climate change on terrestrial ecosystems, and in turn how does large-scale plant-atmosphere exchange feedback on to the climate system? Specifically, he is interested in better understanding processes that determine ecosystems’ response to climate forcing (e.g., stomatal conductance) and constrain regional-scale exchange of carbon flux between these ecosystems and the atmosphere (e.g., the response of North American Boreal forests to interannual variability in temperature). He employs a combination of ecosystem-scale and atmospheric measurements, regional-scale models, and remote sensing data to answer these questions.

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