The effect of tar spot pathogen on host plant carbon balance and its possible consequences on a tundra ecosystem
In Arctic tundra, plant pathogens have substantial effects on the growth and survival of hosts, and impacts on the carbon balance at the scale of ecological systems. To understand these effects on carbon dynamics across different scales including plant organ, individual, population and ecosystem, we focused on two primary factors: host productivity reduction and carbon consumption by the pathogen. We measured the effect of the pathogen on photosynthetic and respiratory activity in the host. We also measured respiration and the amount of carbon in the pathogen. We constructed a model based on these two factors, and calculated pathogenic effects on the carbon balance at different organismal and ecological scales. We found that carbon was reduced in infected leaves by 118% compared with healthy leaves; the major factor causing this loss was pathogenic carbon consumption. The carbon balance at the population and ecosystem levels decreased by 35% and 20%, respectively, at an infection rate of 30%. This case study provides the first evidence that a host plant can lose more carbon through pathogenic carbon consumption than through a reduction in productivity. Such a pathogenic effect could greatly change ecosystem carbon cycling without decreasing annual productivity.
KeywordsPlant parasite Host carbon balance Ecosystem carbon cycle Arctic tundra Rhytisma polare
We are grateful to Dr Hiroyuki Muraoka at Gifu University and Dr Yukiko Tanabe at the National Institute of Polar Research for their help with photosynthetic measurements and model estimations. This work was supported by The Graduate University for Advanced Studies (SOKENDAI), the National Institute of Polar Research (Project number KP-11), and the Green Network of Excellence (GRENE) Arctic Climate Change Research Project and Arctic Challenge for Sustainability Project (ArCS) provided by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.
Author contribution statement
SM and MU conceived and designed the experiments. SM and MU performed the experiments. SM and MU analyzed the data. SM, MU, ASM and SI wrote the manuscript; other authors provided editorial advice.
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