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A plant pathogen affects carbon dynamics in the Arctic ecosystem

Released on March 27, 2018 (in Japanese)
Posted on May 14, 2018

National Institute of Polar Research (NIPR)

A Japan–Norway international research team evaluated the effect of a plant pathogen on carbon balance of a host plant and an ecosystem in the Arctic. As the results, the pathogen strongly affect host carbon balance by the effect of carbon consumption rather than the effect of inhibiting host photosynthesis. Moreover, the carbon consumption effect also resulted in a considerable change on the carbon dynamics at the ecosystem level.

Figure 1. Left: the polar willow (Salix polaris). Right: tar spot disease caused by Rhytisma polare.

The research was conducted principally by Dr. Shota Masumoto from Yokohama National University and Dr. Masaki Uchida from the National Institute of Polar Research. Although the risks of pandemic outbreak of plant pathogens owing to global warming are increasing, knowledge about pathogenic impact on the nutrient cycling in natural ecosystems is poor. Their research team studied the effect of plant pathogens on the carbon dynamics of a host plant and an ecosystem in the Arctic, Spitsbergen Island, Norway (latitude: 79° N). Study species are the polar willow (Salix polaris), a dominant species of the Arctic region as a host plant, and Rhytisma polare which causes tar spot disease on S. polaris (Fig. 1). They measured the photosynthetic activity, respiratory activity and growth rate of the host plant and the pathogen, then simulated the annual carbon balance of the host plant and annual effect of the pathogen. By integrating those results into ecosystem carbon compartment model, the pathogenic effect on carbon dynamics at the ecosystem level was also evaluated.

From the simulation, healthy polar willow was evaluated to gain annually 5.08 mg of carbon from atmosphere per leaf. In contrast, an infected leaf by tar spot disease showed lower carbon balance than that of healthy leaf owing to the following two pathogenic effects. First, the pathogen covered the host leaf and inhibit their photosynthesis (inhibition effect), reducing carbon assimilation by 0.49 mg per leaf. Second, for their growth, the pathogen absorbed and utilized carbon from the host plant (consumption effect). From the simulation, the consumption effect was 5.50 mg of carbon per infected leaf, greater than the inhibition effect.

The pathogenic effect on the carbon dynamics at the ecosystem level was calculated based on the assumption that one-third of the leaves were infected. Compared with the non-infected ecosystem, the infected ecosystem showed a 2.9% decrease in the carbon assimilation by the plants from the atmosphere. This decrease is depending on inhibition effect on host plant productivity. On the other hand, the consumption effect resulted in the change in two carbon flow in the ecosystem, an increase in the amount of carbon release from terrestrial organisms to the atmosphere by 23.3% owing to pathogenic respiration, and an increase in the amount of carbon flow from terrestrial organisms to the ground soil by 117% because the dead pathogens’ bodies on the host leaves drop into the soil (Fig. 2).

Figure 2. The carbon balance in the ecosystem assuming that one-third of the leaves are infected.

Dr. Masumoto suggests that this study revealed the following two points. First, the tar spot pathogen have a far greater impact on the host carbon balance through their carbon consumption rather than the inhibition of host photosynthesis. The fact lead to the second point, the pathogen can change ecosystem carbon dynamics largely without reducing the host plants’ productivity. Although most previous studies have assessed only the effect on plant productivity when assessing the pathogenic effect on an ecosystem, their results suggested that such assessments could underestimate pathogenic effects on ecosystems because pathogens would affect host and ecosystem carbon dynamics by the effects which cannot captured by investigating change in the host productivity. For estimation a realistic pathogenic effect on ecosystem carbon dynamics, it is essential to consider the change in carbon flow causing pathogenic carbon consumption effects, such as their respiration or flow of organic matter from pathogens to the soil.

Published Paper

Journal: Oecologia
Title: The effect of tar spot pathogen on host plant carbon balance and its possible consequences on a tundra ecosystem
Authors: Shota Masumoto (1), Masaki Uchida (2, 3), Motoaki Tojo (4), Maria Luz Herrero (5), Akira S. Mori (1), Satoshi Imura (2, 3)
1. Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, Japan
2. National Institute of Polar Research, Tachikawa, Japan
3. School of Multidisciplinary Sciences, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Japan
4. Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Japan
5. Division of Biotechnology and Plant Health, NIBIO - Norwegian Institute of Bioeconomy Research, Ås, Norway
First online: 22 December 2017
DOI: 10.1007/s00442-017-4037-7
URL: https://link.springer.com/article/10.1007/s00442-017-4037-7

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E-mail: kofositu@nipr.ac.jp

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