Abstract
The role of terrestrial ecosystems as sources or sinks for carbon to the atmosphere and their contribution to inter‐annual variations in atmospheric CO2 remain hotly‐debated topics. Carbon enters terrestrial ecosystems through a single process, photosynthesis, but it is returned to the atmosphere by the combined metabolic activity of plants, animals, and microbes (Figure l). The largest uncertainties in our understanding of terrestrial carbon cycling are in these return processes, especially how CO2 losses from ecosystems are divided among respiration by living plants—termed autotrophic respiration—versus microbial and faunal decomposition of plant residues—termed heterotrophic respiration (Figure 1); and how seasonal and climatic factors that change plant physiological status and soil conditions influence that partitioning.
Highlights
The role of terrestrial ecosystems as sources or sinks for carbon to the atmosphere and their contribution to inter-annual variations in atmos pheric C02 remain hotly-debated topics
Carbon enters terrestrial ecosystems through a single process, photosynthesis, but it is returned to the atmosphere by the combined metabolic activity of plants, animals, and microbes (Figure l).The largest uncertainties in our understanding of terrestrial carbon cycling are in these return processes, especially how C 0 2 losses from ecosystems are divided among respiration by living plants—termed autotrophic respiration— versus microbial and faunal decomposition of plant residues—termed heterotrophic respira tion (Figure 1); and how seasonal and climatic factors that change plant physiological status and soil conditions influence that partitioning
In order to study ecosystem-atmosphere carbon exchange in a temperate forest, we studied a large release of radiocarbon (14C) that occurred near the Oak Ridge Reservation (ORR),Oak Ridge National Laboratory, Tennessee, in July and August of 1999.This regional,4C release was incorporated into plants as photosynthetic products, and the fate of these 14C-labeled materials is being traced over time
Summary
The rate of incorporation of this "bomb"14C provides a measure of the rate of carbon exchange among atmosphere, ocean, and terrestrial carbon reservoirs on time scales of years to centuries. During the 1960s, when rates of atmos pheric change were most rapid, only a few laboratories were measuring radiocarbon rou tinely, and observations relevant to short-term carbon cycling in ecosystems were sparse. Present investigations of short-term carbon cycling are limited to studying carbon exchange on time scales greater than ~2 years. Radiocarbon ( 1 4 C ) is a useful tool for studying the dynamics of carbon exchange between ecosystems and the atmosphere on several time scales. Radiocarbon can be used to estimate carbon exchange rates on decadal time scales
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