Megumi Yamashita

Variation in pollen dispersal between years with different pollination conditions in a tropical emergent tree

We examined differences in pollen dispersal efficiency between 2 years in terms of both spatial dispersal range and genetic relatedness of pollen in a tropical emergent tree, Dipterocarpus tempehes. The species was pollinated by the giant honeybee (Apis dorsata) in a year of intensive community‐level mass‐flowering or general flowering (1996), but by several species of moths in a year of less‐intensive general flowering (1998). We carried out paternity analysis based on six DNA microsatellite markers on a total of 277 mature trees forming four spatially distinct subpopulations in a 70 ha area, and 147 and 188 2‐year‐old seedlings originating from seeds produced in 1996 and 1998 (cohorts 96 and 98, respectively). Outcrossing rates (0.93 and 0.96 for cohorts 96 and 98, respectively) did not differ between years. Mean dispersal distances (222 and 192 m) were not significantly different between the 2 years but marginally more biased to long distance in 1996. The mean relatedness among cross‐pollinated seedlings sharing the same mothers in cohort 96 was lower than that in cohort 98. This can be attributed to the two facts that the proportion of intersubpopulations pollen flow among cross‐pollination events was marginally higher in cohort 96 (44%) than in cohort 98 (33%), and that mature trees within the same subpopulations are genetically more related to each other than those between different subpopulations. We conclude that D. tempehes maintained effective pollen dispersal in terms of outcrossing rate and pollen dispersal distance in spite of the large difference in foraging characteristics between two types of pollinators. In terms of pollen relatedness, however, a slight difference was suggested between years in the level of biparental inbreeding.

Modeling CO2 exchange over a Bornean tropical rain forest using measured vertical and horizontal variations in leaf‐level physiological parameters and leaf area densities

Southeast Asian tropical rain forests are among the worlds most important biomes in terms of global carbon cycling; nevertheless, the impact of environmental factors on the ecosystem CO 2 flux remains poorly understood. One-dimensional multilayer biosphere-atmosphere models such as soil-vegetation-atmosphere transfer (SVAT) models are promising tools for understanding how interactions between environmental factors and leaf-level physiological parameters might impact canopy-level CO 2 exchange. To examine application of the SVAT model in tropical rain forests, which is expected to be difficult partly because of the complex canopy structure and large number of tree species, we measured vertical and horizontal variations in leaf-level physiological parameters and leaf area densities together with eddy covariance measurements using a canopy crane in a tropical rain forest in Sarawak, Malaysia. Despite differences in species and canopy positions, leaf nitrogen per unit area (N a ) within the canopy could be one-dimensionally described as a linear function of height. N a also clearly explained the other leaf-level physiological parameters across species and canopy positions. Even though the leaf area density profile likely varies in this tropical forest, the SVAT model satisfactorily reproduced the eddy covariance measurements. Furthermore, the CO 2 flux calculated on the assumption that N a measured in the upper canopy was distributed evenly throughout was almost the same as that taking the vertical gradient into consideration. These findings suggest that when reproducing the CO 2 flux in tropical rain forests using the SVAT model, the leaf area density profile obtained from the leaf area index (LAI) measured at one point and leaf-level physiological properties measured across species in the upper canopy are sufficient.

Height-related changes in leaf photosynthetic traits in diverse Bornean tropical rain forest trees

Knowledge of variations in morphophysiological leaf traits with forest height is essential for quantifying carbon and water fluxes from forest ecosystems. Here, we examined changes in leaf traits with forest height in diverse tree species and their role in environmental acclimation in a tropical rain forest in Borneo that does not experience dry spells. Height-related changes in leaf physiological and morphological traits [e.g., maximum photosynthetic rate (Amax), stomatal conductance (gs), dark respiration rate (Rd), carbon isotope ratio (δ13C), nitrogen (N) content, and leaf mass per area (LMA)] from understory to emergent trees were investigated in 104 species in 29 families. We found that many leaf area-based physiological traits (e.g., Amax-area, Rd, gs), N, δ13C, and LMA increased linearly with tree height, while leaf mass-based physiological traits (e.g., Amax-mass) only increased slightly. These patterns differed from other biomes such as temperate and tropical dry forests, where trees usually show decreased photosynthetic capacity (e.g., Amax-area, Amax-mass) with height. Increases in photosynthetic capacity, LMA, and δ13C are favored under bright and dry upper canopy conditions with higher photosynthetic productivity and drought tolerance, whereas lower Rd and LMA may improve shade tolerance in lower canopy trees. Rapid recovery of leaf midday water potential to theoretical gravity potential during the night supports the idea that the majority of trees do not suffer from strong drought stress. Overall, leaf area-based photosynthetic traits were associated with tree height and the degree of leaf drought stress, even in diverse tropical rain forest trees.

Measurement of tropical rainforest three-dimensional light environment and its diurnal change

A key link to understand the relationship between tropical forest canopy physiology and remote-sensing technology is forest light distribution. Accordingly, we conducted three-dimensional light environment measurements to acquire a quantitative and qualitative understanding of tropical rainforests at Lambir Hills National Park, Sarawak, Borneo, Malaysia, as a typical tropical rainforest region. The aim of this study was to elucidate links between canopy physiological studies and remote-sensing technology, and to investigate the up-scaling capability of canopy processes and mechanisms. Measurements were conducted using a ground-based laser profiler system and terrestrial survey instrument. For understanding qualitative forest characteristics, both reflective and transmissive light measurements were conducted, using photon and quantum sensors and a spectroradiometer. Our results suggest there is no great difference in canopy height, when all trees are mature, are interdependent and are employing the same growth strategies. Photosynthetic active radiation attenuation showed no changes over time.

8 million phenological and sky images from 29 ecosystems from the Arctic to the tropics: the Phenological Eyes Network

We report long-term continuous phenological and sky images taken by time-lapse cameras through the Phenological Eyes Network (http://www.pheno-eye.org. Accessed 29 May 2018) in various ecosystems from the Arctic to the tropics. Phenological images are useful in recording the year-to-year variability in the timing of flowering, leaf-flush, leaf-coloring, and leaf-fall and detecting the characteristics of phenological patterns and timing sensitivity among species and ecosystems. They can also help interpret variations in carbon, water, and heat cycling in terrestrial ecosystems, and be used to obtain ground-truth data for the validation of satellite-observed products. Sky images are useful in continuously recording atmospheric conditions and obtaining ground-truth data for the validation of cloud contamination and atmospheric noise present in satellite remote-sensing data. We have taken sky, forest canopy, forest floor, and shoot images of a range of tree species and landscapes, using time-lapse cameras installed on forest floors, towers, and rooftops. In total, 84 time-lapse cameras at 29 sites have taken 8 million images since 1999. Our images provide (1) long-term, continuous detailed records of plant phenology that are more quantitative than in situ visual phenological observations of index trees; (2) basic information to explain the responsiveness, vulnerability, and resilience of ecosystem canopies and their functions and services to changes in climate; and (3) ground-truthing for the validation of satellite remote-sensing observations.

Effect of climatic elements on Campylobacter colonization in broiler flocks reared in southern Japan from 2008 to 2012

&NA; To demonstrate the effect of climatic elements on Campylobacter colonization in broiler chickens reared in Japan, the correlation between Campylobacter isolated from chickens (191 of 236 flocks, 80.9%) between 2008 and 2012 and climatic elements was analyzed by logistic regression. We divided the rearing process into 13 terms of 5 d each (total: 65 d). Terms were numbered backwards, wherein a 0‐term lag was considered as the sampling day plus 4 d before sampling; 1‐term lag was the 5‐d term before the 0‐term lag, and so on, until the 12‐term lag. We obtained climatic data tracing back from the 0‐term to the 12‐term lags. For evaluation in each season, we divided chickens reared during periods of rising temperature (spring, summer) and decreasing temperature (autumn, winter). Air temperature showed a positive correlation with Campylobacter colonization from the 0‐ to 12‐term lags in chickens reared during the period of rising temperature (odds ratio [OR], 1.069 to 1.104), and from the 0‐ to 4‐ and 6‐term lags (OR, 1.079 to 1.105) in chickens reared during the period of decreasing temperature. The strong positive effect of air temperature on Campylobacter colonization, particularly during the period of rising temperature, may be associated with the effect on the Campylobacter environmental sources and/or vectors. A positive correlation was observed between Campylobacter colonization and humidity when chicken houses were empty and new chicks were introduced (from the 9‐ to 12‐term lags) during the period of decreasing temperature (OR, 1.076 to 1.141). Thus, high humidity would be an important factor causing carry‐over of Campylobacter infection during the period of decreasing temperature. We also found that solar radiation increased Campylobacter colonization during the period of decreasing temperature, from the 2‐ to 8‐term lags, except for the 4‐ and 5‐term lags, in Japan. The results of this study demonstrate the effects of air temperature, humidity, and solar radiation on Campylobacter colonization in broiler chickens, and are potentially important for developing strategies to reduce the risk of Campylobacter contamination in broiler chickens.