Date Published: February 9, 2017
Publisher: Public Library of Science
Author(s): Sangsub Cha, Hee-Myung Chae, Sang-Hoon Lee, Jae-Kuk Shim, John J. Kelly.
The atmospheric carbon dioxide (CO2) level is expected to increase substantially, which may change the global climate and carbon dynamics in ecosystems. We examined the effects of an elevated atmospheric CO2 level on the growth of Quercus acutissima and Fraxinus rhynchophylla seedlings. We investigated changes in the chemical composition of leaf litter, as well as litter decomposition. Q. acutissima and F. rhynchophylla did not show differences in dry weight between ambient CO2 and enriched CO2 treatments, but they exhibited different patterns of carbon allocation, namely, lower shoot/root ratio (S/R) and decreased specific leaf area (SLA) under CO2-enriched conditions. The elevated CO2 concentration significantly reduced the nitrogen concentration in leaf litter while increasing lignin concentrations and carbon/nitrogen (C/N) and lignin/N ratios. The microbial biomass associated with decomposing Q. acutissima leaf litter was suppressed in CO2 enrichment chambers, while that of F. rhynchophylla was not. The leaf litter of Q. acutissima from the CO2-enriched chambers, in contrast with F. rhynchophylla, contained much lower nutrient concentrations than that of the litter in the ambient air chambers. Consequently, poorer litter quality suppressed decomposition.
In terrestrial ecosystems, carbon dioxide (CO2) is absorbed or emitted through primary production and respiration processes [1–3]. The amount of carbon (C) stored in terrestrial ecosystems is approximately 2,060 Gt, which is roughly three times that in the atmosphere (735 Gt) [1, 4, 5]. In particular, temperate forests cover only 8% of the land area globally, but they account for approximately 40% of the total terrestrial C storage. These forests are important for sequestering C from atmospheric CO2 [6–8].
The objective of the present study was to investigate the effect of elevated CO2 concentration on the growth and litter quality of Q. acutissima and F. rhynchophylla, and to determine the changes in litter decomposition according to any CO2-mediated change in the litter quality. Our results did not show a statistically significant difference in plant growth, as evidenced by the total dry weight, between the ambient and elevated CO2 concentrations. The S/R ratio of the tree species was lower under elevated CO2. Changes in plant growth response to high CO2 concentrations depend on the growth conditions or growth potential of a species [16, 21, 48, 49], as well as the species’ developmental strategy, such as the creation of new sinks for extra C . Several studies have suggested that growth under elevated CO2 concentrations leads to shifts in the root system architecture, which could enhance the nutrient uptake capacity [51–53] by increasing the biomass and density of the fine roots [3, 54–56], as well as the S/R ratio . Our results are consistent with the aforementioned studies. In our experiments, the S/R ratio for Q. acutissima was clearly lower at the elevated CO2 concentration. It is evident that an elevated CO2 concentration can reduce the stem proportion and increase the root proportion, at least in young tree seedlings in some species, without changing the mass.