Use of thermal imaging and the photochemical reflectance index (PRI) to detect wheat response to elevated CO2 and drought

The spectral-based photochemical reflectance index (PRI) and leaf surface temperature (T_leaf) derived from thermal imaging are two indicative metrics of plant functioning. The relationship of PRI with radiation-use efficiency (RUE) and T_leaf with leaf transpiration could be leveraged to monitor crop photosynthesis and water use from space. Yet, it is unclear how such relationships will change under future high carbon dioxide concentrations ([CO₂]) and drought. Here we established an [CO₂] enrichment experiment in which three wheat genotypes were grown at ambient (400 ppm) and elevated (550 ppm) [CO₂] and exposed to well-watered and drought conditions in two glasshouse rooms in two replicates. Leaf transpiration (T_r) and latent heat flux (LE) were derived to assess evaporative cooling, and RUE was calculated from assimilation and radiation measurements on several dates along the season. Simultaneous hyperspectral and thermal images were taken at $~$1.5 m from the plants to derive PRI and the temperature difference between the leaf and its surrounding air ($∆$T_leaf−air). We found significant PRI and RUE and $∆$T_leaf−air and T_r correlations, with no significant differences among the genotypes. A PRI–RUE decoupling was observed under drought at ambient [CO₂] but not at elevated [CO₂], likely due to changes in photorespiration. For a LE range of 350 W m^–2, the ΔT_leaf−air range was $~$10°C at ambient [CO₂] and only $~$4°C at elevated [CO₂]. Thicker leaves in plants grown at elevated [CO₂] suggest higher leaf water content and consequently more efficient thermoregulation at high [CO₂] conditions. In general, T_leaf was maintained closer to the ambient temperature at elevated [CO₂], even under drought. PRI, RUE, ΔT_leaf−air, and T_r decreased linearly with canopy depth, displaying a single PRI-RUE and ΔT_leaf−air T_r model through the canopy layers. Our study shows the utility of these sensing metrics in detecting wheat responses to future environmental changes.     

Dryness limits vegetation pace to cope with temperature change in warm regions

Climate change leads to increasing temperature and more extreme hot and drought events. Ecosystem capability to cope with climate warming depends on vegetation's adjusting pace with temperature change. How environmental stresses impair such a vegetation pace has not been carefully investigated. Here we show that dryness substantially dampens vegetation pace in warm regions to adjust the optimal temperature of gross primary production (GPP) ($T_{\mathrm{opt}}^{\mathrm{GPP}}$) in response to change in temperature over space and time. $T_{\mathrm{opt}}^{\mathrm{GPP}}$ spatially converges to an increase of 1.01°C (95% CI: 0.97, 1.05) per 1°C increase in the yearly maximum temperature (T_max) across humid or cold sites worldwide (37^oS–79^oN) but only 0.59°C (95% CI: 0.46, 0.74) per 1°C increase in T_max across dry and warm sites. $T_{\mathrm{opt}}^{\mathrm{GPP}}$ temporally changes by 0.81°C (95% CI: 0.75, 0.87) per 1°C interannual variation in T_max at humid or cold sites and 0.42°C (95% CI: 0.17, 0.66) at dry and warm sites. Regardless of the water limitation, the maximum GPP (GPP_max) similarly increases by 0.23 g C m⁻² day⁻¹ per 1°C increase in $T_{\mathrm{opt}}^{\mathrm{GPP}}$ in either humid or dry areas. Our results indicate that the future climate warming likely stimulates vegetation productivity more substantially in humid than water-limited regions.     

Diurnal change in psychological and physiological responses to consistent relative humidity

Diurnal changes in physiological and psychological responses to consistent relative humidity (RH) conditions were investigated in the present study. Lightly clothed six male and six female subjects participated in the first experiment at 40% and 50% RH, and seven male and seven female subjects participated in the second experiment at 60%, 70%, and 80% RH. Both experiments were conducted at 28 °C air temperature (T_a) from 9:00–18:30. Skin temperatures, local heat flux rates and tympanic temperature (T_ty) were monitored at 2-min intervals throughout the experimental period. Body weight loss and oxygen consumption rate were measured during the 9:30–10:30, 13:30–14:30, and 17:30–18:30 periods. Thermal sensation and thermal comfort responses were recorded at the same periods. The amount of heat loss was greater than metabolic heat production (M) in the male subjects but was well balanced with M in the female subjects. A morning increase in T_ty at 50%–80% RH was observed, and mean skin temperature (${\bar{\text{T}}}_{\text{sk}}$) at 70% and 80% RH was significantly higher (p < 0.05) than T_sk at 40% and 50% RH in both subject groups. Although difference in the relationship between thermal sensation and ${\bar{\text{T}}}_{\text{sk}}$ based on sex was confirmed, diurnal changes in thermal sensation were observed in both subject groups based on the responses of “warm” in the morning but “neutral” or “slightly warm” in the evening at 70% and 80% RH. This result demonstrates that high RH may be acceptable in the late afternoon and evening at 28 °C and indicates that dynamic control of RH during the daytime (e.g., low RH in the morning and high RH in late afternoon) may be beneficial to save energy when using air-conditioning.     

Coherence of terrestrial vertebrate species richness with external drivers across scales and taxonomic groups

Aim

Understanding connections between environment and biodiversity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining biodiversity requires an understanding of how species richness and environment covary across scales. Here, we identify scales and locations at which biodiversity is generated and correlates with environment.

Location

Full latitudinal range per continent.

Time Period

Present day.

Major Taxa Studied

Terrestrial vertebrates: all mammals, carnivorans, bats, songbirds, hummingbirds, amphibians.

Methods

We describe the use of wavelet power spectra, cross-power and coherence for identifying scale-dependent trends across Earth's surface. Spectra reveal scale- and location-dependent coherence between species richness and topography (E), mean annual precipitation (Pn), temperature (Tm) and annual temperature range (ΔT).

Results

>97% of species richness of taxa studied is generated at large scales, that is, wavelengths $\gtrsim {10}^3$ km, with 30%–69% generated at scales $\gtrsim {10}^4$ km. At these scales, richness tends to be highly coherent and anti-correlated with E and ΔT, and positively correlated with Pn and Tm. Coherence between carnivoran richness and ΔT is low across scales, implying insensitivity to seasonal temperature variations. Conversely, amphibian richness is strongly anti-correlated with ΔT at large scales. At scales $\lesssim {10}^3$ km, examined taxa, except carnivorans, show highest richness within the tropics. Terrestrial plateaux exhibit high coherence between carnivorans and E at scales $\sim {10}^3$ km, consistent with contribution of large-scale tectonic processes to biodiversity. Results are similar across different continents and for global latitudinal averages. Spectral admittance permits derivation of rules-of-thumb relating long-wavelength environmental and species richness trends.

Main Conclusions

Sensitivities of mammal, bird and amphibian populations to environment are highly scale dependent. At large scales, carnivoran richness is largely independent of temperature and precipitation, whereas amphibian richness correlates strongly with precipitation and temperature, and anti-correlates with temperature range. These results pave the way for spectral-based calibration of models that predict biodiversity response to climate change scenarios.     

Crowding-induced protein destabilization in the absence of soft attractions

It is generally assumed that volume exclusion by macromolecular crowders universally stabilizes the native states of proteins and destabilization suggests soft attractions between crowders and protein. Here we show that proteins can be destabilized even by crowders that are purely repulsive. With a coarse-grained sequence-based model, we study the folding thermodynamics of two sequences with different native folds, a helical hairpin and a β-barrel, in a range of crowder volume fractions, ${\phi }_{\text{c}}$. We find that the native state, N, remains structurally unchanged under crowded conditions, while the size of the unfolded state, U, decreases monotonically with ${\phi }_{\text{c}}$. Hence, for all ${\phi }_{\text{c}}>0$, U is entropically disfavored relative to N. This entropy-centric view holds for the helical hairpin protein, which is stabilized under all crowded conditions as quantified by changes in either the folding midpoint temperature, $T_{\text{m}}$, or the free energy of folding. We find, however, that the β-barrel protein is destabilized under low-T, low-${\phi }_{\text{c}}$ conditions. This destabilization can be understood from two characteristics of its folding: 1) a relatively compact U at $T<T_{\text{m}}$, such that U is only weakly disfavored entropically by the crowders; and 2) a transient, compact, and relatively low-energy nonnative state that has a maximum population of only a few percent at ${\phi }_{\text{c}}=0$, but increasing monotonically with ${\phi }_{\text{c}}$. Overall, protein destabilization driven by hard-core effects appears possible when a compaction of U leads to even a modest population of compact nonnative states that are energetically competitive with N.     

Ion temperature profiles along a hydrogen diagnostic beam in a TORE SUPRA tokamak plasma

The active particle diagnostic technique is used to study the ion temperature at five spatial points along the path of a hydrogen diagnostic beam. The temperature of the main ion plasma component (deuterium ions) measured by this diagnostic technique along the beam path is compared with the temperature of carbon ions (C⁺⁵). A study is made of the following characteristic features of the behavior of the ion temperature profiles T_i in various TORE SUPRA operating modes: the formation of flat and even hollow T_i profiles in ohmic discharges with q ～3 at the plasma edge, the change in T_i profiles in ergodic divertor discharges, and the difference between the temperature of the bulk ions measured by the active particle diagnostic technique and the temperature of C⁺⁵ ions in the plasma region r/a>0.5. The features revealed are explained at a qualitative level.