Optimum Temperature Threshold Research Articles

Improving temperature‐based predictions of the timing of flowering in cotton

AbstractKey management recommendations for cotton (Gossypium hirsutum L.) management require estimates of the timing of crop phenology. Most commonly growing day degree (DD) (thermal time) approaches are used. Currently, across many cotton production regions, there is no consistent approach to predicting first square and flower timing. Day degree approaches vary considerably, with base thresholds different (12.0–15.6 °C) with no consistency using an optimum temperature threshold (i.e., temperature where development ceases to increase). As cotton is grown in variable and changing climates, and cultivars change, there is a need to ensure the accuracy of this approach for predicting timing of flowering for assisting cotton management. In this study new functions to predict first square and first flower were developed and validated using data collected in multiple seasons and regions (Australia and the United States). Earlier controlled environment studies that monitored crop development were used to assess in more detail how temperatures were affecting early cotton development. New DD functions developed predicted first square and first flower better than the existing Australian and U.S. approaches. The best performing functions had base temperatures like those of existing U.S. functions (15.6 °C) and an optimum threshold temperature of 32.0 °C. New universal DD targets for first square (343 DD [°C]) and first flower (584 DD) were developed. Controlled environment studies supported this base temperature outcome; however, it was less clear that 32.0 °C was the optimum threshold temperature from these data. Precise predictions of cotton development will facilitate accurate growth stage assessments and hence better cotton management decisions.

Emerging Strategies Mold Plasticity of Vegetable Plants in Response to High Temperature Stress.

As a result of energy consumption and human activities, a large amount of carbon dioxide emissions has led to global warming, which seriously affects the growth and development of plants. Vegetables are an indispensable part of people’s diet. In the plant kingdom, a variety of vegetables are highly sensitive to climate change. For them, an increase of just a few degrees above their optimum temperature threshold can result in a loss of yield and quality. Emerging strategies such as practice management and breeding varieties in response to above-optimal temperatures are critical for abiotic stress resistance of vegetable crops. In this study, the function and application of multiple strategies, including breeding improvement, epigenetic modification directed generation of alleles, gene editing techniques, and accumulation of mutations in multigenerational adaptation to abiotic stress, were discussed in vegetable crops. It is believed to be meaningful for plants to build plasticity under high temperature stress, thus generating more genetic structures for heat resistant traits in vegetable products.

Arctic has been going through a transition from solid precipitation to liquid precipitation in spring

The changes of precipitation form have important impacts on mass balance and energy flux of the underlying Cryosphere that closely related to hydrological cycles and the health of the ecosystem over the Arctic. So far, most of land stations around Arctic record the total precipitation amount only, except for dozens of stations in Alaska and northern Canada, where the solid and liquid precipitation are recorded respectively. Based on these different precipitation form records and daily mean air temperature observations during 1961–2015, we developed a special standard of optimum temperature threshold to separate rainfall from the total precipitation. That is, if the air temperature is greater than the temperature threshold, the probability of precipitation occurring as rain is larger than 0.5, then we assume the precipitation falls in liquid form. We derived the seasonal optimum temperature threshold of 2.01°C (spring), 0.54°C (summer), 1.14°C (fall) and 1.17°C (mean annual), respectively. We did not discuss the situation in winter because of rare liquid precipitation observations. By using these temperature thresholds, we distinguished the solid and liquid phase from total precipitation archived at 253 stations over the northern Eurasia region and investigated their variation trend during 1961–2010. Results showed that the proportion of rainfall in total precipitation decreased with latitudes in the region north of 60°N. In general, we found the maximum and minimum of the rainfall to total precipitation ratio (RPR) in summer and winter. Further analysis demonstrated that the precipitation forms showed obvious seasonal and interannual variability. Specially, the spring RPR increased over most of the terrestrial Arctic (82.46% stations), 22.37% of which passed 95% statistical significance test, indicating that there was a general transition trend from solid precipitation to liquid precipitation in the spring Arctic continents over the past decades. In summer and autumn, there was obvious regional variability in the south of the research area, but in the arctic coastal stations the increasing trend appeared uniform. The RPR trends, respectively derived from the lower and upper limits of 95% confidence interval of temperature threshold, were highly consistent with the trend in the spatial distribution that derived from the optimum temperature threshold. Additionally, more precipitation had fallen as rainfall instead of snowfall in Alaska, Siberia and Northern Europe during the ablation season (March-July), which would make profound impacts on the Arctic land-atmosphere interaction.

Unexpected warming‐induced growth decline in Thuja occidentalis at its northern limits in North America

AbstractAimTowards the cold margins of the Northern Hemisphere boreal zone, continuing warming should theoretically provide a longer vegetative season, favouring growth and a northward shift in tree species distribution. The northern distribution of Thuja occidentalis L. (eastern white cedar) is marked by the presence of isolated marginal populations distant from the continuous distribution. If those populations proved to be well adapted to their future local climatic conditions, their expansion could accelerate cedar poleward migration. We tested the hypotheses that (1) there will be a growth increase in cedar northern marginal populations as a result of global warming, and (2) the edaphic conditions and regional precipitation regimes will modulate their response to warming.LocationCanadian boreal forest, western Québec (47–50° N, 74–80° W).MethodsWe investigated radial growth using tree‐ring measurements from dominant and co‐dominant eastern white cedar trees (n = 723) distributed along a latitudinal gradient from the species' northern margin to the centre of its natural range. First, low‐frequency growth variations were analysed on whole chronologies (ad 1720–2010). Second, inter‐annual growth variations were tested against ad 1953–2010 monthly temperature and precipitation time series with a bootstrapped correlation function. Finally, the impact of environmental variables on the growth–climate relationships was assessed.ResultsUnexpectedly, a growth decline was observed starting in 1980 in marginal sites. Dendroclimatic analyses revealed that radial growth was not only limited by short growing seasons but also by summer droughts in the marginal zone. This response was exacerbated in sites that received less summer precipitation. Counterintuitively, autumn and spring precipitation negatively impacted on growth, especially in wet soil stands.Main conclusionsNorthern marginal populations of cedar may have already reached their optimum temperature threshold for radial growth. Our results suggest that they will probably be facing increasing hydric stress selection pressure under the assumptions of climate change. Their responses to future warming will be highly dependent on the seasonality and magnitude of variation in precipitation regimes.

Life Table Study ofAnagyrussp. nr.pseudococci(Girault) (Hymenoptera: Encyrtidae) on Its Host,Planococcus ficus(Signoret) (Hemiptera: Pseudococcidae)

Anagyrus spp. are well-known primary parasitoids of Pseudococcidae employed in augmentative release programmes. Anagyrus sp. nr. pseudococci was found to be the dominant Anagyrus sp. present in vineyards around the Stellenbosch area, during scouting in 2006 and 2007. Given the lack of sufficient life table data on this species, a life table study was conducted at constant temperatures, 11, 17, 22, 27, 30, 32 and 34 °C, at a humidity of approximately 53 % and daylight regime of 16L:8D. The maximum values for the intrinsic rates of increase and net reproduction rate were 4.305 and 152.7, respectively, and were obtained at 27 °C. The lower temperature threshold (T0), upper lethal limit (TL) and optimum temperature threshold (Topt), were estimated at 16.32 °C, 35.66 °C and 30.75 °C, respectively. Given these developmental parameters, A. sp. nr. pseudococci is well adapted to outperform its host, Planococcus ficus, at higher temperatures.

Thermal tolerance of two seagrass species at contrasting light levels: Implications for future distribution in the Great Barrier Reef

This study assessed metabolism, growth, and survival of two seagrass species at three different seawater temperatures (27°C, 30°C, and 33°C) under saturating (400 µmol photons m‐2 s‐1) and limiting (40 µmol photons m‐2 s‐1) light over 1 month. Halodule uninervis grown at 33°C was within its physiological optimum temperature range, exhibiting 2.3× higher photosynthetic rates than at 27°C, and increased net shoot carbon (C) production (up to 10× higher) at saturating light levels. In contrast, 33°C exceeded the optimum temperature threshold for Zostera muelleri, resulting in critical metabolic imbalances with large reductions in photosynthesis and increases in leaf respiration. This led to substantially lower growth rates (0‐2% of those at 27°C) and lower final biomass (only 10% of that at 27°C) in the 33°C treatment after 1 month. This decline at higher temperatures occurred at both light levels, but it was more severe in limiting light, where the C balance went into deficit. H. uninervis in the Great Barrier Reef (GBR) exists well within its optimal temperature range and should continue to thrive at projected future temperatures, at least under saturating light levels. In contrast, Z. muelleri currently exists near its upper thermal threshold, and future temperature increases of the magnitude investigated here would likely lead to the contraction of the range of this species from the northern GBR ‐ potentially by more than 1000 km. This could have ecologically significant ramifications, because Z. muelleri is often the only GBR species that currently inhabits muddy estuarine areas, which are critical fisheries habitats.

Cloud fraction and cloud shadow property retrievals from coregistered TIMS and AVIRIS imagery: the use of cloud morphology for registration

The Thermal Infrared Multispectral Scanner (TIMS) and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) were operated simultaneously from the ER2 aircraft during a March 1990 test over the Rio Bravo region, Belize. Coregistration of the imagery obtained by these two instruments is necessary to utilize the data effectively. A technique for registering the TIMS imagery to AVIRIS imagery is presented. It takes advantage of the morphology of the fair weather cumulus (FWC) clouds present in the imagery for estimating inter-sensor distortions. It relies on an iterative process in which skew, nearest neighbor sampling, and cross-correlation (1D and 2D) are applied. Comparison between the AVIRIS three-band ratio (3BR) imagery and the coregistered TIMS imagery shows that TIMS is superior in detecting thin cloud and cloud edge pixels, especially over shadowed background. Although the seven scenes analyzed in the study were obtained within the same one-hour time period and over the same geographical region, the optimum temperature threshold for cloud detection, with respect to the background temperature, varies significantly from 2.1 to 3.3/spl deg/C. These values agree with the AVIRIS 3BR cloud fraction equivalent temperature thresholds to within 0.5/spl deg/C. When applying a cloud shadow mask from the AVIRIS near infrared imagery to the coregistered TIMS background imagery, a 1/spl deg/C temperature differential is found between the shadowed and nonshadowed background. This significant radiative cooling by Fair Weather Cumulus cloud shadows could introduce errors in surface emissivity retrievals by other Earth Observing System (EOS) investigators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>