In the 21st Century, air pollution and climate change are very serious environmental problems for forest ecosystems all over the world. Therefore, many researches are needed for understanding the responses of forest ecosystems to air pollutants such as ozone (O3), a main component of photochemical oxidants, and climate change such as elevated atmospheric CO2 and air temperature. The 28th IUFRO (International Union of Forest Research Organizations) Biennial Conference of Research Group 7.01 (Impacts of Air Pollution and Climate Change on Forest Ecosystem) entitled “Actions for Sustainable Forest Ecosystems under Air Pollution and Climate Change” was held in Fuchu, Tokyo, Japan (Tokyo University of Agriculture and Technology) on 22-26 October, 2017. At this biennial conference, we had an excellent opportunity to discuss close relationships among air pollution, climate change and forest ecosystems. This special issue of Journal of Agricultural Meteorology is dedicated to the original articles derived from the organized sessions of the 28th IUFRO Biennial Conference of Research Group 7.01 as follows: (1) Asian forest ecosystem under changing environment, (2) Developing detection, monitoring and evaluation, (3) Ecophysiological and genetic understanding of plant responses, (4) Water and nutrient cycles in forest ecosystems, (5) Modelling and risk assessment, and (6) Forest ecosystems under multiple stressors. The following briefly introduces the 5 original articles in this special issue.
Current climate scenarios predict rising air temperature along with increasing frequency and intensity of summer drought in the Central and Eastern Europe. Severe drought episodes affect physiological processes in trees such as transpiration, photosynthesis and carbon allocation. Understanding gas exchange between plants and the atmosphere is important in woody plant research. The aim of this study was to evaluate differences in gas exchange characteristics and chlorophyll fluorescence of tree species prevailing in Lithuania (Scots pine, Norway spruce and Silver birch) and their physiological response to water stress. The study was conducted in Aukstaitija integrated monitoring station, Lithuania. Gas exchange parameters and chlorophyll fluorescence were measured during the vegetation season of 2016. Meteorological parameters were obtained from the monitoring station. Four weather periods with different meteorological conditions were identified. Under moderate drought conditions all investigated tree species demonstrated reduced photosynthetic rates, lower stomatal conduction transpiration rates, water use efficiency and instantaneous carboxylation efficiency. During moderate drought, intercellular CO2 concentration of Norway spruce was higher and this species demonstrated the highest decrease in instantaneous carboxylation efficiency. No significant changes of maximal chlorophyll fluorescence (Fv/Fm) among species were detected during different weather periods except Silver birch. The investigated tree species reacted differently to weather conditions. The Scots pine demonstrated the highest tolerance to different weather conditions. The study confirmed the sensitivity of Norway spruce to drought conditions. The Silver birch was the least sensitive to temperature and humidity conditions variation.
Predicted climate changings can affect hemi-boreal forests especially for soil conditions with low water-holding capacity and susceptibility to soil water deficits. In our study, species-specific sap flux, transpiration and water use efficiency of growth (WUE) were investigated at a mixed hemi-boreal forest ecosystems, especially during temporary moderate dry periods in the main growing season. Therefore, two representative forest sites with different drought susceptibility were selected in Northwest-Lithuania. The aim of our investigations was to identify the responsible factors influencing transpiration and WUE from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. H. Karst.) and birch (silver birch: Betula pendula Roth. and downy birch: B. pubescens Ehrh.) during temporary drought incidents at a water-limited, oligitrophic sand dominated forest site and at a water saturated, mesoeutrophic organic peat forest site for the whole vegetation period and two moderate short-term drought incidents in 2016. During the dry periods Norway spruce trees exhibited lowest sap flux compared to Scot pine and birch while similarly showing highest WUE. Up-scaled to a virtual pure stand none of the species were differing in species specific transpiration. Thus, we found no evidence for extended drought sensitivity of Norway spruce at the water limited site during the first investigation year. Sap flux of Scots pine trees was more or less constantly high during the main growing season and the dry periods at both plots, while WUE was quite low during the “dry periods”. Thus, we assume that Scots pine trees are less affected by temporarily drought events than Norway spruce. Birch trees exhibited significantly highest sap flux during dry periods at the water limited site whereas quite low WUE was not differing between sites. Thus, birch may compete with Scots pine trees at the study sites in terms of water consumption and growth in future.
To characterize the deposition of long-range transported particulate matter (PM) on the foliar surface of Japanese forest trees, we periodically collected the PM deposited on the needle surface of mature Japanese cypress (Chamaecyparis obtusa) grown in the mountainous area of Nagasaki located in the western region of Japan from 24 April to 30 October, 2017. Metal element compositions and concentration ratios along with the ratios of Pb isotopes in the PM were analyzed. The total amount of metal elements (Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Ni, Cu, Zn, As and Pb) on the needle surfaces was relatively low during summer and autumn but was high during the spring when there was high atmospheric concentration of PM with diameter less than 2.5 μm due to influence of outflow from Asian continent. The seasonal variations in the amounts of less-abundant metal elements (Al, V, Ni, Cu, Zn, As and Pb) exhibited similar trends. The Pb amount varied with Zn amount at a constant ratio of 0.4, which was close to the Pb/Zn ratio of PM in China. Most of the Pb isotope ratios (207Pb/206Pb and 208Pb/206Pb) in the PM were close to those observed in the Chinese coal. Therefore, Pb on the needle could have originated from the coal combustion in China. The enrichment factor (EF) of Pb ranged from 650 to 2270, and was significantly correlated with the 207Pb/206Pb ratios, suggesting that components having EFs of greater than 650 could have originated from anthropogenic source. The amount of Pb significantly correlated with that of Ni, Cu, Zn, and As, which showed EFs more than 650. These results indicate that the long-range transported PM, including Pb, Ni, Cu, Zn, and As, originated from the anthropogenic sources in China, and deposited on the needle of C. obtusa grown in Nagasaki.
Ozone (O3) is an air pollutant that negatively affect carbon budget in woody plants. In the present study, we aimed to clarify the effects of ozone on soil respiration rate of Siebold’s beech seedlings (Fagus crenata) grown under different soil-nutrient conditions. Seedlings were grown under three levels of O3 fumigation (charcoal-filtered air or O3 at 1.0 or 1.5 times ambient concentration) in combination with three levels of nutrient supplies (non-, low- or high-fertilised) for two growing seasons. We determined soil respiration rate in July, August, September, and October of the second growing season. The seedlings were harvested to determine the dry mass in October. Significant effect of O3 on soil respiration rate was not observed in all measurements. There was a significant interaction between O3 and nutrient supply for whole-root dry mass. The dry mass in non-fertilised and low-fertilised treatments was reduced by O3, whereas O3 did not affect dry mass in the high-fertilised treatment. On the other hand, neither significant effects of O3, nor a significant interaction between O3 and nutrient supply for the biomass allocations were observed. Coefficient of positive correlation in the relation of soil respiration rate with dry mass of fine-root across the all treatments was higher than that in the relation of soil respiration rate with coarse-root and whole-root dry mass. These results indicate that no significant effect of O3 on soil respiration was mainly attributable to no response of fine root dry mass to elevated O3. Soil nutrient supply decreased soil respiration rate in August. Our results emphasize the importance of fine root in the response of soil respiration to elevated O3. To clarify the response of soil respiration to elevated O3, future researches on the effect of O3 on fine root dynamics including turnover and indirect effect on soil microbial respiration are needed.
Recent studies have revealed that inland waters, such as rivers, act as an excellent source of soil-derived CO2 for the atmosphere. This flow is comparable in magnitude to that of anthropogenic CO2 release, such as fossil fuel use, playing an important part in the global carbon cycle and future climate change. Although one of the most active CO2 evasions in the world has been reported in Himalayan rivers, data on the partial pressure of CO2 (pCO2) remains sparse. In this study, we conducted a monthly sampling survey of the Ganges River in Bangladesh during 2011–2014 and measured the chemical composition of the river water. Both chemical weathering and dissolution of soil salt may affect seasonal variations in major ion composition in this river. The pCO2 values were 377–1,763 μatm, which were higher than the atmospheric level (400 μatm). Higher pCO2 values were observed during the rainy season, which was likely attributed to active respiration by soil or river biota. We also calculated approximate CO2 evasion rates from the river into the atmosphere. Our results suggest that water during the rainy season, which has high pCO2, temperature, and water current velocity, releases CO2 into the atmosphere more efficiently (150 mol m-2 yr-1) than that during the dry season (20 mol m-2 yr-1). In addition, we collected groundwater samples in Bangladesh and observed surprisingly high pCO2 values (4,926–101,610 μatm). Groundwater in this area is likely to transport abundant dissolved inorganic carbon (both HCO3- and CO2) to the ocean.