On the ratio of intercellular to ambient CO2 (c i/c a) derived from ecosystem flux.

The ratio of intercellular to ambient CO2 concentrations (c i/c a) plays a key role in ecophysiology, micrometeorology, and global climatic change. However, systematic investigation on c i/c a variation and its determinants are rare. Here, the c i/c a was derived from measuring ecosystem fluxes in an even-aged monoculture of rubber trees (Hevea brasiliensis). We tested whether c i/c a is constant across environmental gradients and if not, which dominant factors control c i/c a variations. Evidence indicates that c i/c a is not a constant. The c i/c a exhibits a clear "V"-shaped diurnal pattern and varies across the environmental gradient. Water vapor pressure deficit (D) is the dominant factor controls over the c i/c a variations. c i/c a consistently decreases with increasing D. c i/c a decreases with square root of D as predicted by the optimal stomatal model. The D-driving single-variable model could simulate c i/c a as well as that of sophisticated model. Many variables function on longer timescales than a daily cycle, such as soil water content, could improve c i/c a model prediction ability. Ecosystem flux can be effectively used to calculate c i/c a and use it to better understand various natural cycles.

Global terrestrial carbon fluxes of 1999-2019 estimated by upscaling eddy covariance data with a random forest.

The terrestrial biosphere is a key player in slowing the accumulation of carbon dioxide in the atmosphere. While quantification of carbon fluxes at global land scale is important for mitigation policy related to climate and carbon, measurements are only available at sites scarcely distributed in the world. This leads to using various methods to upscale site measurements to the whole terrestrial biosphere. This article reports a product obtained by using a Random Forest to upscale terrestrial net ecosystem exchange, gross primary production, and ecosystem respiration from FLUXNET 2015. Our product covers land from -60°S to 80°N with a spatial resolution of 0.1° × 0.1° every 10 days during the period 1999-2019. It was compared with four existing products. A distinguishable feature of our method is using three derived variables of leaf area index to represent plant functional type (PFT) so that measurements from different PFTs can be mixed better by the model. This product can be valuable for the carbon-cycle community to validate terrestrial biosphere models and cross check datasets.

High-resolution data on the impact of warming on soil CO2 efflux from an Asian monsoon forest.

This paper describes a project for evaluation of global warming's impacts on soil carbon dynamics in Japanese forest ecosystems. We started a soil warming experiment in late 2008 in a 55-year-old evergreen broad-leaved forest at the boundary between the subtropical and warm-temperate biomes in southern Japan. We used infrared carbon-filament heat lamps to increase soil temperature by about 2.5 °C at a depth of 5 cm and continuously recorded CO2 emission from the soil surface using a multichannel automated chamber system. Here, we present details of the experimental processes and datasets for the CO2 emission rate, soil temperature, and soil moisture from control, trenched, and warmed trenched plots. The long term of the study and its high resolution make the datasets meaningful for use in or development of coupled climate-ecosystem models to tune their dynamic behaviour as well as to provide mean parameters for decomposition of soil organic carbon to support future predictions of soil carbon sequestration.

Sustained acceleration of soil carbon decomposition observed in a 6-year warming experiment in a warm-temperate forest in southern Japan.

To examine global warming's effect on soil organic carbon (SOC) decomposition in Asian monsoon forests, we conducted a soil warming experiment with a multichannel automated chamber system in a 55-year-old warm-temperate evergreen broadleaved forest in southern Japan. We established three treatments: control chambers for total soil respiration, trenched chambers for heterotrophic respiration (Rh), and warmed trenched chambers to examine warming effect on Rh. The soil was warmed with an infrared heater above each chamber to increase soil temperature at 5 cm depth by about 2.5 °C. The warming treatment lasted from January 2009 to the end of 2014. The annual warming effect on Rh (an increase per °C) ranged from 7.1 to17.8% °C-1. Although the warming effect varied among the years, it averaged 9.4% °C-1 over 6 years, which was close to the value of 10.1 to 10.9% °C-1 that we calculated using the annual temperature-efflux response model of Lloyd and Taylor. The interannual warming effect was positively related to the total precipitation in the summer period, indicating that summer precipitation and the resulting soil moisture level also strongly influenced the soil warming effect in this forest.

Seasonal and long-term change in lead deposition in central Japan: evidence for atmospheric transport from continental Asia.

Long-range transport of air pollution from continental Asia is currently an important issue concerning the Japanese environment, especially in regions susceptible to acidification due to low buffering capacity, such as Murakami, Niigata prefecture, located on the west coast of central Japan. Evidence for long-range transport was obtained through lead and lead isotopic analysis of 84 archived precipitation filters, showing seasonal changes in lead deposition from May 1999 to May 2002. Lead deposition was highest in winter and spring (November through May) each year and lowest in summer. Computed 72-h back trajectories showed that in winter air masses were predominantly transported from the northwest, passing over northern China and eastern Russia, whilst in summer air masses predominantly originated from the southeast passing over Japan. Lead isotopic analysis showed higher (208)Pb/(206)Pb during winter, indicating that lead originated from a different source. A plot of (207)Pb/(206)Pb vs. (208)Pb/(206)Pb identified a thorogenic component, which is excess (208)Pb compared to a standard lead growth curve, indicative of certain lead ores and coals in continental Asia. The data provided evidence of long-range transport of lead from continental Asia to Japan. Bark pockets included within the trunks of two Japanese cedar trees harvested near Murakami, dating between 1972 and 1982, exhibited lead isotope ratios indicative of Japanese-sourced lead. In contrast, current (2003) bark showed thorogenic ratios, consistent with a relative decline in Japanese-sourced and increase in continental-sourced lead.