No abstract

To investigate the effects of expanding rubber (Hevea brasiliensis) cultivation on water cycling in Mainland Southeast Asia (MSEA), evapotranspiration (ET) was measured within rubber plantations at Bueng Kan, Thailand, and Kampong Cham, Cambodia. After energy closure adjustment, mean annual rubber ET was 1211 and 1459 mm yr 21 at the Thailand and Cambodia sites, respectively, higher than that of other tree-dominated land covers in the region, including tropical seasonal forest (812-1140 mm yr 21 ), and savanna (538-1060 mm yr 21 ). The mean proportion of net radiation used for ET by rubber (0.725) is similar to that of tropical rainforest (0.729) and much higher than that of tropical seasonal forest (0.595) and savanna (0.548). Plant area index (varies with leaf area changes), explains 88.2% and 73.1% of the variance in the ratio of latent energy flux (energy equivalent of ET) to potential latent energy flux (LE/LE pot ) for midday rain-free periods at the Thailand and Cambodia sites, respectively. High annual rubber ET results from high late dry season water use, associated with rapid refoliation by this brevideciduous species, facilitated by tapping of deep soil water, and by very high wet season ET, a characteristic of deciduous trees. Spatially, mean annual rubber ET increases strongly with increasing net radiation (R n ) across the three available rubber plantation observation sites, unlike nonrubber tropical ecosystems, which reduce canopy conductance at high R n sites. High water use by rubber raises concerns about potential effects of continued expansion of tree plantations on water and food security in MSEA.

Summary• Here we investigated photosynthetic traits of evergreen species under a deciduous canopy in a temperate forest and revealed the importance of CO 2 assimilation during winter for annual CO 2 assimilation.• Saplings were shaded by the canopy trees from spring through to autumn, but were less shaded during the winter months. Photosynthetic rates at light saturation ( A area ) were lower during winter than during the growing season. A area was higher in Camellia , Ilex and Photinia than in Castanopsis , Cleyera and Quercus during the winter, but differed little during summer and autumn.• Estimated daily CO 2 assimilation ( A day ) was higher during the winter than during the growing season in Camellia , Ilex and Photinia but was higher than that during the growing season only at the beginning and end of winter in Castanopsis , Cleyera and Quercus . A day was higher in Camellia , Ilex and Photinia than in Castanopsis , Cleyera and Quercus but differed little among them during the growing season.• These results reveal the importance of winter CO 2 assimilation for the growth of Camellia , Ilex and Photinia . Furthermore, differences in annual CO 2 assimilation among species are strongly modified by species-specific photosynthetic traits during the winter under deciduous canopy trees.Key words: deciduous canopy trees, the growth season, photosynthetic capacity, nitrogen content, daily CO 2 assimilation, winter CO 2 assimilation.

The rapid and widespread expansion of rubber plantations in Southeast Asia necessitates a greater understanding of tree physiology and the impacts of water consumption on local hydrology. Sap flow measurements were used to study the intra- and inter-annual variations in transpiration rate (Et) in a rubber stand in the low-elevation plain of central Cambodia. Mean stand sap flux density (JS) indicates that rubber trees actively transpire in the rainy season, but become inactive in the dry season. A sharp, brief drop in JS occurred simultaneously with leaf shedding in the middle of the dry season in January. Although the annual maxima of JS were approximately the same in the two study years, the maximum daily stand Et of ∼2.0 mm day(-1) in 2010 increased to ∼2.4 mm day(-1) in 2011. Canopy-level stomatal response was well explained by changes in solar radiation, vapor pressure deficit, soil moisture availability, leaf area, and stem diameter. Rubber trees had a relatively small potential to transpire at the beginning of the study period, compared with average diffuse-porous species. After 2 years of growth in stem diameter, transpiration potential was comparable to other species. The sensitivity of canopy conductance (gc) to atmospheric drought indicates isohydric behavior of rubber trees. Modeling also predicted a relatively small sensitivity of gc to the soil moisture deficit and a rapid decrease in gc under extreme drought conditions. However, annual observations suggest the possibility of a change in leaf characteristics with tree maturity and/or initiation of latex tapping. The estimated annual stand Et was 469 mm year(-1) in 2010, increasing to 658 mm year(-1) in 2011. Diagnostic analysis using the derived gc model showed that inter-annual change in stand Et in the rapidly growing young rubber stand was determined mainly by tree growth rate, not by differences in air and soil variables in the surrounding environment. Future research should focus on the potentially broad applicability of the relationship between Et and tree size as well as environmental factors at stands different in terms of clonal type and age.

No abstract

In nature, spatiotemporally dynamic coevolutionary processes play major roles in the foundation and maintenance of biodiversity. Here, we examined the arms race coevolution involving a seed-eating weevil with a long snout and its camellia plant host with a thick fruit coat (pericarp) throughout the marked climatic gradient observed across the Japanese islands. Results demonstrated that female weevils, which bored holes through camellia pericarps to lay eggs into seeds, had evolved much longer snouts than males, especially in areas in which Japanese camellia pericarps were very thick. The thickness of the plant pericarp was heritable, and the camellia plant evolved a significantly thicker pericarp on islands with the weevil than on islands without it. Across populations with weevils, resource allocation to plant defense increased with increasing annual mean temperature or annual precipitation, thereby geographically differentiating the evolutionary and ecological interactions between the two species. Given that the coevolutionary relationship exhibited appreciable variation across a relatively small range of annual mean temperatures, ongoing global climatic change can dramatically alter the coevolutionary process, thereby changing the ecological interaction between these species.

Understanding water use characteristics of C3 and C4 crops is important for food security under climate change. Here, we aimed to clarify how stomatal dynamics and water use efficiency (WUE) differ in fluctuating environments in major C3 and C4 crops. Under high and low nitrogen conditions, we evaluated stomatal morphology and kinetics of stomatal conductance (gs) at leaf and whole-plant levels in controlled fluctuating light environments in four C3 and five C4 Poaceae species. We developed a dynamic photosynthesis model, which incorporates C3 and C4 photosynthesis models that consider stomatal dynamics, to evaluate the contribution of rapid stomatal opening and closing to photosynthesis and WUE. C4 crops showed more rapid stomatal opening and closure than C3 crops, which could be explained by smaller stomatal size and higher stomatal density in plants grown at high nitrogen conditions. Our model analysis indicated that accelerating the speed of stomatal closure in C3 crops to the level of C4 crops could enhance WUE up to 16% by reducing unnecessary water loss during low light periods, whereas accelerating stomatal opening only minimally enhanced photosynthesis. The present results suggest that accelerating the speed of stomatal closure in major C3 crops to the level of major C4 crops is a potential breeding target for the realization of water-saving agriculture.

Differences in the incidence and mortality rate of prostate cancer between the USA and Japan have been decreasing over time, and were only twofold in 2017. Therefore, countermeasures against prostate cancer could be very important not only in Western countries, but also in developed Asian countries. Screening for prostate cancer in the general population using transrectal ultrasonography, digital rectal examination and/or prostate acid phosphatase began in Japan in the early 1980s, and screening with prostate‐specific antigen and digital rectal examination has been widespread in the USA since the late 1980s. Large‐ and mid‐scale randomized controlled trials on screening for prostate cancer began around 1990 in the USA, Canada and Europe. However, most of these studies failed as randomized controlled trials because of high contamination in the control arm, low compliance in the screening arm or insufficient screening setting about screening frequency and/or biopsy indication. The best available level 1 evidence is data from the European Randomized Study of Screening for Prostate Cancer and the Göteborg screening study. However, several non‐urological organizations and lay media around the world have mischaracterized the efficacy of prostate‐specific antigen screening. To avoid long‐term confusion about screening for prostate cancer, leading professional urological organizations, including the Japanese Urological Association, are moving toward the establishment of an optimal screening system that minimizes the drawbacks of overdetection, overtreatment and loss of quality of life due to treatment, and maximizes reductions in the risk of death as a result of prostate cancer and the development of metastatic prostate cancer.