The increasing amount of measurement data on land-atmosphere flux has made it possible to assess the interannual and longer processes that are driven by environmental change and disturbance of terrestrial ecosystems. In this study, I used a global dataset of carbon dioxide (CO2) fluxes at eddy-covariance tower sites (FLUXNET2015) to investigate long-term trends of net ecosystem CO2 exchange (NEE), gross primary production (GPP), ecosystem respiration (RE), and related variables. From 118 sites with records of at least 5-years duration, I extracted 1198 site-years of data for use in my analyses. Applying moderate screening by data quality, I found that 58% of the sites showed increasing trends as net CO2 sinks, in which median slopes of annual NEE of -1.4 and -4.1 g C m-2 y-2 were obtained by linear regression and Sen’s slope estimator. Both GPP and RE showed increasing trends at different slopes; their slopes were positively correlated among sites. Across-site variation of NEE trends was analyzed by generalized linear mixed modeling; the best statistical model used temperature, stand age, and biome type as explanatory variables. The trend of increasing CO2 sinks differed among biome types, from almost none in grassland and savanna to steep slopes in deciduous broad-leaved forest sites. The flux trends derived from terrestrial model simulations showed that the increasing sink trend also prevails over the land. The global model simulations implied that the increasing land sink is primarily attributable to elevated CO2 concentration. These results demonstrate the usefulness of flux measurement datasets, especially in conjunction with models, to deepen our understanding of long-term terrestrial ecosystem processes.
Climate change may induce severe frost damage to crops, and thus a reasonable assessment of frost risk, considering both crop phenology and meteorology, is required. Here, we introduced a new index of potential frost risk (Frisk) using thermal time (minimum air temperature below the threshold value) weighted by the percentage of budburst (Pbud). Moreover, we evaluated the spatiotemporal distributions of Frisk in tea fields within a 60 km×60 km area in east Japan from 1981-2020, using 1 km2-gridded meteorological data and a newly developed model of Pbud. The Pbud model considered three phenological phases (endodormancy, ecodormancy, and progress of budburst) and successfully represented changes in the Pbud of the tea buds for 15 years, with root mean square errors of 8.5 percentage points. The spatiotemporal distributions of Frisk over the past 40 years showed that potential frost risk significantly increased at elevations ranging from 50 m to 300 m because the budburst advanced at a faster rate than the temperature warming. These elevations corresponded to areas where tea plants were mainly cultivated, which indicates that tea cultivation is becoming vulnerable to frost, and the risk of economic losses due to the frost is increasing. The proposed assessment of frost risk could contribute to predicting frost damage and developing more reliable strategies for the operation of frost protection under the effects of future climate change.
In Lao PDR (People’s Democratic Republic), rice is one of the major staple crops planted in more than 80% of the cultivated areas. We attempted to evaluate the adaptation preference of the farmers in Laos through a climate change adaptation survey approach. The eight adaptations including irrigation, nitrogen fertilizer application rates, transplanting date shifting were first assessed by the CERES‑Rice model for the two rice cultivars (TDK8 and TDK11). These adaptations with the projected rice yields were used to design the climate change adaptation survey to investigate farmers’ preference. One hundred smallholder farmers in Dongbung, Napork, Nakhaow, Hardvieng, and Parlai in Vientiane province, Laos were interviewed. For the rice yield projection, the representative concentration pathway (RCP) 4.5 and RCP 8.5 were collected from the Coordinated Regional Climate Downscaling Experiment‑South Asia. The simulation results showed that the two adaptations (irrigation and nitrogen fertilizer application rates) were beneficial to reduce the negative impacts of climate change on rice yields under the RCP 4.5 and 8.5 scenarios. On the other hand, the effects of the shifting transplanting dates were inconsistent, revealing that the transplanting date shifting may not be a sufficient adaption for this region to cope with climate change. The results from a climate change adaptation survey to investigate rice farmers’ preference in Vientiane Capital showed that the farmers preferred installing an irrigation system and applying the doubling nitrogen fertilizer application rate (120 kg‑N ha‑1). However, many farmers replied that they are still indifferent to the adverse impacts of climate change on rice yields that can be reduced by implementing adaptation technologies, suggesting a further study to raise the farmers’ awareness of climate change. It is concluded that this study can be useful to enhance food security of Lao PDR by providing efficacious agricultural managements which reflect farmers’ preference.
Methane (CH4) produced in rice-paddy soil is transported to the atmosphere either via the rice plants or by bubbling events (ebullition); however, little is known about the frequency and intensity of bubbling CH4 emissions and the factors that affect them. We developed a method to quantify ebullition using high-time-resolution (~1 Hz) CH4 concentration data obtained by closed-chamber measurements. Field measurements were conducted in a Japanese rice paddy at different rice growth stages: panicle formation (PF), booting (BT), and heading (HD). A dataset of 132 chamber measurements was used to develop and evaluate the method. A scripting file written in R programing language was used to automatically determine CH4 emissions via the two pathways. Plant-mediated CH4 emission intensity was constant during chamber deployment and was reflected as a steady linear increase in chamber [CH4] with time or as a constant baseline in a flux time series. We found that the plant-mediated emission could be determined as the peak with the lowest flux intensity in the flux frequency distribution even if bubbling events occurred during the chamber deployment. The field measurement results in combination with established data processing protocols showed that at PF, ebullition contributed only 4% of the total emission, whereas it accounted for 32% and 60% of the total emission at BT and HD, respectively. In contrast, the plant-mediated flux variation among growth stages was smaller. Both ebullition and plant-mediated emissions correlated significantly with air temperature at HD, but the magnitude of the dependency was much higher for ebullition than for rice-mediated emission. These results demonstrate that ebullition occurs more frequently than has previously been thought, and the different transport pathways show varying degrees of dependency on plant phenological and environmental factors, thus underscoring the need to separately determine CH4 emissions via each transport pathway.
Liquid crystal tunable filter (LCTF) can change the transmissible wavelength by changing the applied voltage to the filter, which enables the drastic increase in the observable wavelength resolution in a small size system and is considered to be a powerful tool for the spectral earth observation from flying units or microsatellites. However, there is limited knowledge about its season-long application for the vegetation monitoring and the prediction of the ecosystem photosynthetic capacity. We compared the seasonal variation of spectral reflectance obtained by a LCTF camera with that obtained by a popular spectral radiometer in a cool-temperate young larch plantation in northern Hokkaido, Japan. Then we tried to find the best normalized difference spectral index (NDSI) to explain the seasonal variation of the ecosystem photosynthetic capacity using all pairs of two reflectances observed in the range of wavelength between 500 and 770 nm with 10-nm intervals (28 wavelength bands) by the LCTF. The best NDSI among all combinations (28×27) of two reflectances was NDSI[770, 720] for the maximum gross primary production at light saturation and NDSI[530, 600] for the initial slope of the light-response curve, which reflect the red edge shift owing to the change in the chlorophyll content and relative strength of the light absorbance in the visible red wavelength region compared with that in the green wavelength region, respectively. Predicted daily gross primary production of the plantation using these NDSI agreed well with the observed values. NDSI[530, 600] was better to distinguish each vegetation type of the studied plantation.
In rice (Oryza sativa L.), heat-induced spikelet sterility (HISS) has long been recognized a major threat in the production, and currently the potential risk of yield reduction is likely to be increasing under global warming. However, there have been few studies on HISS conducted under field conditions. In recent years in Japan, extremely high temperatures have frequently recorded in the daytime during the summer. In 2018, heat wave lasted from mid-July to late August, which overlapped the typical rice heading period from eastern to western Honshu and raised a concern about HISS during flowering. To examine this possibility, we surveyed rice sterility in eight prefectures in the Kanto, Tokai, and Kinki regions. During surveys in 2018 and 2019, we collected field data on the sterility of ‘Koshihikari’, the most popular rice variety in Japan, and the sterility ranged from 3.7 to 15.4% in paddy fields. The sterility tended to be higher in the paddy fields where heading occurred during the heat wave. We modeled the sterility rate using the heat dose based on daytime mean panicle temperature, with a threshold for HISS at 33°C. The model estimates based on meteorological data showed that HISS can be induced even under current climatic conditions, depending on the timing of heading. Considering the projected global warming, this study raises an issue that rice plants would face a risk of HISS under the temperate climate in Japan.
A real-time monitoring system was developed and applied to monitor the time course of photosynthesis and transpiration in fully-grown tomato plants in a semi-commercial greenhouse. The system was based on an open chamber method in which the ventilator airflow rate is an important parameter affecting the environmental factors in the chamber and physiological response of plants enclosed inside the chamber. So, we assumed that the effects of this parameter on these responses should be evaluated for an agricultural production site. In this study, we investigated differences in the environmental factors in the chamber and physiological response of whole-tomato plants obtained from two chambers (0.5 m [W]×1.0 m [D]×2.2 m [H]) implemented with a single ventilator (SV, 0.36 m3 min-1) or double ventilators (DV, 0.72 m3 min-1). The relative humidity and vapor pressure deficit inside the SV chamber were about 10% higher and 0.5 kPa lower than those inside the DV chamber because of the difference in air exchange rates. However, we found no significant effect of airflow rate on net photosynthetic rate, transpiration rate and total conductance of the plants in the SV and DV chambers by analyzing with weighted Deming regression. This simultaneous monitoring method, undertaken in multiple chambers, and weighted Deming regression analysis can be used to check whether measurement conditions are appropriate for on-site monitoring.
The effects of continuous lighting (CL) before gene transfer on leaf biomass, leaf hemagglutinin (HA) content per biomass, and leaf HA content per plant in Nicotiana benthamiana after gene transfer were investigated in a transient gene expression system. A control photoperiod of 16 h d-1 and an extended photoperiod of 24 h d-1 were compared at two photosynthetic photon flux density (PPFD) levels of 200 and 400 µmol m-2 s-1. Leaf biomass was greater in the 24 h d-1 photoperiod treatments and 400 µmol m-2 s-1 PPFD treatments. The leaf HA content per biomass was smaller at 24 h d-1 than at 16 h d-1, indicating that CL before gene transfer had a negative impact on leaf HA accumulation per biomass after gene transfer. There was no significant difference in leaf HA content per biomass between 200 and 400 µmol m-2 s-1 PPFD. As a result, the leaf HA content per plant was significantly greater in the high PPFD treatments but not significantly different between photoperiod treatments. The results indicate that a simple approach of applying CL before gene transfer increases biomass but not the HA yield and is thus not necessarily cost-effective in the plant-based recombinant protein production system.