The environmental DNA (eDNA) technique is expected to become a powerful, non-invasive tool for estimating the distribution and biomass of organisms. This technique was recently shown to be applicable to aquatic vertebrates by collecting extraorganismal DNA floating in the water or absorbed onto suspended particles. However, basic information on eDNA release rate is lacking, despite it being essential for practical applications. In this series of experiments with bluegill sunfish (Lepomis macrochirus), we examined the effect of fish developmental stage on eDNA release rate. eDNA concentration reached equilibrium 3 days after the individual fish were introduced into the separate containers, enabling calculation of the eDNA release rate (copies h−1) from individual fish on the assumption that the number of eDNA released from the fish per unit time equals total degradation in the container (copies h−1). The eDNA release rate was 3–4 times higher in the adult (body weight: 30–75 g) than in the juvenile group (0.5–2.0 g). Such positive relationship between fish size and eDNA release rate support the possibility of biomass rather than density estimation using eDNA techniques. However, the eDNA release rate per fish body weight (copies h−1 g−1) was slightly higher in the juvenile than the adult group, which is likely because of the ontogenetic reduction in metabolic activity. Therefore, quantitative eDNA data should be carefully interpreted to avoid overestimating biomass when the population is dominated by juveniles, because the age structure of the focal population is often variable and unseen in the field. eDNA degradation rates (copies l−1 h−1), calculated by curve fitting of time-dependent changes in eDNA concentrations after fish removal, were 5.1–15.9% per hour (half-life: 6.3 h). This suggests that quantitative eDNA data should be corrected using a degradation curve attained in the target field.

High temperature‐induced grain sterility in rice is becoming a serious problem in tropical rice‐growing ecosystems. We studied the mechanism of high temperature‐induced grain sterility of different rice (Oryza sativa L) cultivars at two relative humidity (RH) levels. Four varieties of Indica and Japonica rice were exposed to over 85 % RH and 60 % RH at 36/30 °C, 34/30 °C, 32/24 °C and 30/24 °C day/night air temperatures from late booting to maturity inside sunlit phytotrons. Increasing both air temperature and RH significantly increased spikelet sterility while high temperature‐induced sterility decreased significantly with decreasing RH. Neither Indica nor Japonica rice types were superior to the other in the response of their spikelets to increased air temperature and RH. Increased spikelet sterility was due to increased pollen grain sterility which reduced deposition of viable pollen grains on stigma. Reduction in sterility with decreased RH was more due to decreased spikelet temperature than to air temperature. Thus the impact of RH should be considered when interpreting the effect of high temperature on grain sterility. Spikelet fertility was curvilinearly related to spikelet temperature. Grain sterility increased when spikelet temperature increased over 30 °C while it became completely sterile at 36 °C. The ability of a variety to decrease its spikelet temperature with decreasing RH could be considered as avoidance while the variability in spikelet sterility among varieties at a given spikelet temperature could be considered as true tolerance.

Time lags associated with changes in stable isotope ratios are essential information for quantitatively analyzing shifts of food habits and habitats. To investigate time lags associated with fish growth in a natural setting, we monitored the change in δ15N in the muscle tissue of a fluvial–lacustrine amphidromous goby, Rhinogobius sp. (the orange form), in the Lake Biwa water system. Because δ15N is distinct between lacustrine and fluvial ecosystems, the δ15N of age-0+ fish drastically decreased after their upstream migration from the lake. About 80% of the change in δ15N was attributed to growth. Nitrogen was replaced at the rate of 5–20%·month–1 by metabolic turnover. The half-change period for δ15N was estimated as being longer than 1 month with the contribution of growth and metabolic turnover in the field. These results from the field show that growth is primarily responsible for isotopic changes in fish muscle and highlight the need to examine the role of metabolic turnover using slow-growing fish.

No abstract

Foehn-induced dry wind during grain filling increased ring-shaped chalky kernels in rice {Oryza sativa L.) plants. The objective of this study was to determine physiological mechanisms of the occurrence of ring-shaped chalky kernels. Rice plants were subjected to water deficit in a paddy field after shade by applying dry high-speed wind. Additionally, a growth chamber experiment was conducted with plants in pots to measure the water status under the dry wind condition for 24 h by combining in situ turgor {^'^) assay in developing endosperms with the water potential measurements. The dry (high vapor pressure deficit [VPD]) wind treatment produced the largest number of ring-shaped chalky kernels due to poor starch accumulation, compared with shade or low-VPD wind treatment. The inner endosperm cells, where a high frequency of chalkiness was observed, spatially maintained y by osmotic adjustment before the chalky formation with no decline of grain weight. Dry wind reduced photosynthesis due to a partial stomatal closure after water deficit developed. However, these responses, including those related to the plant water status, returned to a level similar to those of the control plants in a day after the dry wind was stopped. We conclude that (i) H'^ maintenance by osmotic adjustment contributes to grain development under water deficit under foehn conditions and (ii) osmotic adjustment has a role in temporally inhibiting starch accumulation in endosperms, resulting in ring-shaped chalky kernels under foehn-induced water deficit conditions.

Achieving higher canopy photosynthesis rates is one of the keys to increasing future crop production; however, this typically requires additional water inputs because of increased water loss through the stomata. Lowland rice canopies presently consume a large amount of water, and any further increase in water usage may significantly impact local water resources. This situation is further complicated by changing the environmental conditions such as rising atmospheric CO concentration ([CO ]). Here, we modeled and compared evapotranspiration of fully developed rice canopies of a high-yielding rice cultivar (Oryza sativa L. cv. Takanari) with a common cultivar (cv. Koshihikari) under ambient and elevated [CO ] (A-CO and E-CO , respectively) via leaf ecophysiological parameters derived from a free-air CO enrichment (FACE) experiment. Takanari had 4%-5% higher evapotranspiration than Koshihikari under both A-CO and E-CO , and E-CO decreased evapotranspiration of both varieties by 4%-6%. Therefore, if Takanari was cultivated under future [CO ] conditions, the cost for water could be maintained at the same level as for cultivating Koshihikari at current [CO ] with an increase in canopy photosynthesis by 36%. Sensitivity analyses determined that stomatal conductance was a significant physiological factor responsible for the greater canopy photosynthesis in Takanari over Koshihikari. Takanari had 30%-40% higher stomatal conductance than Koshihikari; however, the presence of high aerodynamic resistance in the natural field and lower canopy temperature of Takanari than Koshihikari resulted in the small difference in evapotranspiration. Despite the small difference in evapotranspiration between varieties, the model simulations showed that Takanari clearly decreased canopy and air temperatures within the planetary boundary layer compared to Koshihikari. Our results indicate that lowland rice varieties characterized by high-stomatal conductance can play a key role in enhancing productivity and moderating heat-induced damage to grain quality in the coming decades, without significantly increasing crop water use.

Spikelet sterility in rice (Oryza sativa L.) induced by high temperatures is a major concern given global warming predictions. We studied differences among eight rice cultivars in spikelet fertility at five different temperature levels in temperature gradient chamber (TGC) experiments. Six japonica and two indica cultivars were exposed to high-temperature gradients in TGCs during the 2005 flowering season. Spikelet sterility increased with temperature in TGCs and differed among cultivars because of both variations in temperature tolerance and timing of heading. The correlation between spikelet fertility of individual panicles and both air temperature and panicle temperature during flowering was analyzed to compare tolerances among cultivars. The temperature (T 75 ) at which spikelet fertility was 75 % of maximum ranged from 34 to 39°C air temperature and differed significantly among cultivars. Indica varieties had higher T 75 values than japonica varieties. The T 75 values based on panicle temperature also differed among cultivars, but the difference between indica and japonica varieties were less significant. We concluded that the higher temperature tolerances of indica cultivars in our experiments could be attributed to lower spikelet temperatures, and cultivars with similar spikelet temperatures still had different heat tolerances due to differences in pollination ability.

Modeling stomatal behavior is critical in research on land-atmosphere interactions and climate change. The most common model uses an existing relationship between photosynthesis and stomatal conductance. However, its parameters have been determined using infrequent and leaf-scale gas-exchange measurements and may not be representative of the whole canopy in time and space. In this study, we used a top-down approach based on a double-source canopy model and eddy flux measurements throughout the growing season. Using this approach, we quantified the canopy-scale relationship between gross photosynthesis and stomatal conductance for 3 years and their relationships with leaf nitrogen content throughout each growing season above a paddy rice canopy in Japan. The canopy-averaged stomatal conductance (gsc ) increased with increasing gross photosynthesis per unit green leaf area (Ag ), as was the case with leaf-scale measurements, and 41-90% of its variation was explained by variations in Ag adjusted to account for the leaf-to-air vapor-pressure deficit and CO2 concentration using the Leuning model. The slope (m) in this model (gsc versus the adjusted Ag ) was almost constant within a 15-day period, but changed seasonally. The m values determined using an ensemble dataset for two mid-growing-season 15-day periods were 30.8 (SE = 0.5), 29.9 (SE = 0.7), and 29.9 (SE = 0.6) in 2004, 2005, and 2006, respectively; the overall mid-season value was 30.3 and did not greatly differ among the 3 years. However, m appeared to be higher during the early and late growing seasons. The ontogenic changes in leaf nitrogen content strongly affected Ag and thus gsc . In addition, we have discussed the agronomic impacts of the interactions between leaf nitrogen content and gsc . Despite limitations in the observations and modeling, our canopy-scale results emphasize the importance of continuous, season-long estimates of stomatal model parameters for crops using top-down approaches.