Essential Role of Symbiotic Microorganisms Supporting Forests in East Asia under Changing Environment

Regeneration success of forests is strongly dependent on symbiotic microorganisms, that is, arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM). In the northeastern part of Asia, larch and birch are used as timber resources, and in the south, fir, cedar, cypress, and oak are used as timber resources. Planted forests have reached the time of harvesting and/or thinning, and after the forestry practices, it is expected that they will become mixed forests equipped with resistance to weather damage; that is, drought, heat, typhoons, etc. On the other hand, the physical production environment has changed greatly, therefore, we investigated the growth of the major trees and the role of mycorrhizal fungi in the northeastern Asia. Elevated O3 decreased growth, colonization rates of ECM, and the biodiversity; however, elevated CO2 moderated or increased them in larch. Except for disease of rot and damping off, we discuss wise use of symbiotic microbe in far East Asia

Ecophysiological Study on the Natural Regeneration of the Two Larch Species with Special References to Soil Environment in Larch Forests

Larch plantations cover approximately 4700km2 of the island of Hokkaido and have become the principle forest ecosystem in northern Japan. This study focused on how the environmental and biological factors affect the regeneration of Japanese larch (JL: Larix kaempferi) and hybrid larches F1 (HL: Larix gmelinii x L. kaempferi) by comparing their ecophysiological characteristics of growth patterns (carbon balance, nutrient balance, the source of CO2), especially relative to their root growth. Based on the review, we could forecast which larch species will have dominancy if they co-exist under the same environmental conditions in nature. In all, under relatively good growth conditions (for example full sunlight, 15℃ soil temperature etc.), JL seedlings have a greater growth rate (allocate more biomass and nutrients) than that of HL. Thus, relative higher soil nutrient environment and above 7℃ soil temperature are necessary for the growth of JL. Otherwise, HL will be more competitive than JL for example in cold regions or higher regions since HL will be better able to grow under a low or wide variation in soil temperature, or low nutrient soil conditions. Given the slightly shade conditionsuch as at a gap in the forest, or fertile soil condition, HL may also be dominate since the growth of JL was clearly suppressed under such situation. Moreover, HL allocated more photosynthates than JL under roots inoculated by ectomycorrhizae. But the ectomycorrhizae benefited the growth of both larch species. In this perspective, we should learn more about their interactions in regard to the establishment of regenerated larch seedlings and symbiotic microorganisms

Factors controlling soil microbial respiration during the growing season in a mature larch plantation in Northern Japan

Soil microbes contribute significantly to soil respiration (SR) in boreal forests; however, there is limited knowledge on microbial contributions from long field investigations. The objective of this study was to estimate soil microbial respiration, as well as its primary controlling factors, for a period of three consecutive years. A trenching method was used to distinguish soil microbial respiration (R (Mic)) in a 55-year-old mature Japanese larch (Larix kaempferi) plantation in Northern Japan; the soil in which developed originally from volcanic soils containing pumice. We used a portable CO2 detection system to measure the soil respiration rate during the growing season. Environmental factors, soil physiochemical characteristics, and soil microbial biomass carbon and nitrogen (MBC and MBN) were analyzed to explain the seasonal variations of SR and R (Mic). The results showed that the estimated contribution of soil microbes to SR was 78, 62, and 55% during the three successive years, respectively. Respiration attributable to decomposition of aboveground litter contributed approximately 19% to SR. The major environmental factor that affected R (Mic) was soil temperature at 5 cm depth, which accounted for more than 70% of the seasonal variation in R (Mic) observed. There were close relations among MBC, MBN, and soil water content, but the soil water content showed no significant relation with R (Mic). The R (Mic) to SR varied from 78 to 55% following 3 years of trenching treatments. Our results demonstrated the important role of soil microbes on soil respiration in this larch forest. Soil temperature was the major positive factor that influenced R (Mic), while soil water content had no significant effect. Global warming will increase the loss of C into the atmosphere by increasing the R (Mic,) and could accelerate climate change

Growth and Photosynthetic Performance of Seedlings of Two Larch Species Grown in Shaded Conditions

Article

Micro-Environmental Analysis of the Natural Regeneration of Larch Forests in Northern Japan

Research Material

Meta-Analysis of Effects of Melatonin Treatment on Plant Drought Stress Alleviation

Due to the increasing frequency of extreme drought events worldwide in recent years, improving the adaptability of plants to arid environments has become an important research topic. In particular, many studies have investigated the effects of melatonin on drought stress mitigation in plants. However, most of these studies were limited in terms of the number of sampling sites or regional scale, and thus we lack a comprehensive understanding of the effects of the exogenous application of melatonin on drought stress mitigation in plants on a global scale. In this study, we integrated previous research into the physiological and growth effects of melatonin application in arid environments worldwide and analyzed the response of plants to different melatonin concentrations, application methods, and different drought degrees in order to provide a scientific basis for promoting the use of melatonin in alleviating plant drought stress. The data used in this study were obtained from the “Web of Science” database, where the keywords “drought & melatonin” were used to search the relevant literature. In total, 61 valid publications with 140 data sets were retrieved. A meta-analysis was performed using the data with no melatonin treatment as the control group and melatonin treatment as the experimental group. Melatonin application significantly increased the plant biomass, chlorophyll content, and antioxidant enzyme activity to alleviate the damage caused by drought stress. The accumulated biomass and accumulation of chlorophyll in plants varied with the melatonin concentration. The threshold value range was identified as 80–120 μmol L−1, and the effect of melatonin on the accumulation of biomass and chlorophyll decreased gradually above this range. In addition, the effects of various spraying methods on the mitigation of drought stress in plants differed significantly. Soil application had greater effects on reactive oxygen species scavengers in plants than foliar spraying. Moreover, the plant leaf membrane lipid peroxidation degree was relatively low, and the plant body chlorophyll content was higher under soil application than foliar spraying, and the cumulative biomass was lower than that with foliar spraying. The effects of melatonin on mitigating plant drought stress also varied under different drought levels when using the same melatonin concentration and application method. Soil irrigation is most effective if the main aim is to improve plant stress resistance and the below-ground root biomass, but foliar spraying is most effective for increasing photosynthesis and plant biomass