Response of wheat canopy CO2 and water gas-exchange to soil water content under ambient and elevated CO2

The nature of the interaction between drought and elevated CO₂ partial pressure (pC_a) is critically important for the effects of global change on crops. Some crop models assume that the relative responses of transpiration and photosynthesis to soil water deficit are unaltered by elevated pC_a, while others predict decreased sensitivity to drought at elevated pC_a. These assumptions were tested by measuring canopy photosynthesis and transpiration in spring wheat (cv. Minaret) stands grown in boxes with 100 L rooting volume. Plants were grown under controlled environments with constant light (300 µmol m^?2 s^?1) at ambient (36 Pa) or elevated (68 Pa) pC_a and were well watered throughout growth or had a controlled decline in soil water starting at ear emergence. Drought decreased final aboveground biomass (?15%) and grain yield (?19%) while elevated pC_a increased biomass (+24%) and grain yield (+29%) and there was no significant interaction. Elevated pC_a increased canopy photosynthesis by 15% on average for both water regimes and increased dark respiration per unit ground area in well‐watered plants, but not drought‐grown ones. Canopy transpiration and photosynthesis were decreased in drought‐grown plants relative to well‐watered plants after about 20–25 days from the start of the drought. Elevated pC_a decreased transpiration only slightly during drought, but canopy photosynthesis continued to be stimulated so that net growth per unit water transpired increased by 21%. The effect of drought on canopy photosynthesis was not the consequence of a loss of photosynthetic capacity initially, as photosynthesis continued to be stimulated proportionately by a fixed increase in irradiance. Drought began to decrease canopy transpiration below a relative plant‐available soil water content of 0.6 and canopy photosynthesis and growth below 0.4. The shape of these responses were unaffected by pC_a, supporting the simple assumption used in some models that they are independent of pC_a.     

Zooxanthellae of the Montastraea annularis species complex: patterns of distribution of four taxa of Symbiodinium on different reefs and across depths.

Corals of the Montastraea annularis complex host several different dinoflagellates in the genus Symbiodinium. Here we address two questions arising from our previous studies of these associations on an offshore reef. First, do the same taxa and patterns of association (Symbiodinium A and B found in higher irradiance habitats than Symbiodinium C) occur on an inshore reef? Second, does M. franksi at the limits of its depth range host only Symbiodinium C, as it does at intermediate depths? In both surveys, a new Symbiodinium taxon and different patterns of distribution (assayed by analyses of small ribosomal subunit RNA genes [srDNA]) were observed. Inshore, a taxon we name Symbiodinium E predominated in higher irradiance habitats in M. franksi and its two sibling species; the only other zooxanthella observed was Symbiodinium C. Offshore, M. franksi mainly hosted Symbiodinium C, but hosted Symbiodinium A, B, C, and E in shallow water and Symbiodinium E and C in very deep water. Symbiodinium E may be stress-tolerant. Observed srDNA heterogeneity within samples of Symbiodinium B, C, and E is interpreted as variation across copies within this multigene family. Experimental bleaching of Symbiodinium C supported this interpretation. Thus sequences from natural samples should be interpreted cautiously.     

Regulation of salt respiration in carrot root slices

In slices of carrot-phloem parenchyma washed for 7 days in water at 20 C, 50 mm KCl stimulates respiration by up to 100% of the ground respiration within 4 minutes of application. The data presented imply that ADP liberated in the cytoplasm as a consequence of KCl accumulation first stimulates a regulator reaction requiring ADP (phosphoglycerate kinase). Thereafter, the point of control alternates between this reaction and the phosphofructokinase reaction, forming a sequence of enzyme stimulations which continue after the new steady state of increased respiration is established. KCl induces a similar sequence in slices washed for 3 days, but it is completed within 3 minutes, and metabolite oscillations are not so marked. In slices washed for 2 days, KCl stimulates respiration by less than 10%, and the sequence of regulator reactions does not occur. Phosphoglycerate kinase is the only enzyme stimulated within 3 minutes of applying KCl to these slices. Contrary to previous reports, KCl frequently stimulates the respiration of freshly prepared slices by 10 to 30%.     

Some like it hot: the physiological ecology of C4 plant evolution

Oecologia - The evolution of C4 photosynthesis requires an intermediate phase where photorespiratory glycine produced in the mesophyll cells must flow to the vascular sheath cells for metabolism by...     

The genetic consequences of selection in natural populations

The selection coefficient, s, quantifies the strength of selection acting on a genetic variant. Despite this parameter's central importance to population genetic models, until recently we have known relatively little about the value of s in natural populations. With the development of molecular genetic techniques in the late 20th century and the sequencing technologies that followed, biologists are now able to identify genetic variants and directly relate them to organismal fitness. We reviewed the literature for published estimates of natural selection acting at the genetic level and found over 3000 estimates of selection coefficients from 79 studies. Selection coefficients were roughly exponentially distributed, suggesting that the impact of selection at the genetic level is generally weak but can occasionally be quite strong. We used both nonparametric statistics and formal random‐effects meta‐analysis to determine how selection varies across biological and methodological categories. Selection was stronger when measured over shorter timescales, with the mean magnitude of s greatest for studies that measured selection within a single generation. Our analyses found conflicting trends when considering how selection varies with the genetic scale (e.g., SNPs or haplotypes) at which it is measured, suggesting a need for further research. Besides these quantitative conclusions, we highlight key issues in the calculation, interpretation, and reporting of selection coefficients and provide recommendations for future research.     

An intervention to improve teacher well-being support and training to support students in UK high schools (the WISE study): A cluster randomised controlled trial

BackgroundTeachers are at heightened risk of poor mental health and well-being, which is likely to impact on the support they provide to students, and student outcomes. We conducted a cluster randomised controlled trial, to test whether an intervention to improve mental health support and training for high school teachers led to improved mental health and well-being for teachers and students, compared to usual practice. We also conducted a cost evaluation of the intervention.Methods and findingsThe intervention comprised (i) Mental Health First Aid training for teachers to support students; (ii) a mental health awareness session; and (iii) a confidential staff peer support service. In total 25 mainstream, non-fee-paying secondary schools stratified by geographical area and free school meal entitlement were randomly allocated to intervention (n = 12) or control group (n = 13) after collection of baseline measures. We analysed data using mixed-effects repeated measures models in the intention-to-treat population, adjusted for stratification variables, sex, and years of experience. The primary outcome was teacher well-being (Warwick-Edinburgh Mental Well-being Scale). Secondary outcomes were teacher depression, absence, and presenteeism, and student well-being, mental health difficulties, attendance, and attainment. Follow-up was at months 12 (T1) and 24 (T2). We collected process data to test the logic model underpinning the intervention, to aid interpretation of the findings. A total of 1,722 teachers were included in the primary analysis. Teacher well-being did not differ between groups at T2 (intervention mean well-being score 47.5, control group mean well-being score 48.4, adjusted mean difference −0.90, 95% CI –2.07 to 0.27, p = 0.130). The only effect on secondary outcomes was higher teacher-reported absence among the intervention group at T2 (intervention group median number of days absent 0, control group median number of days absent 0, ratio of geometric means 1.04, 95% CI 1.00 to 1.09, p = 0.042). Process measures indicated little change in perceived mental health support, quality of relationships, and work-related stress. The average cost of the intervention was £9,103 per school. The study’s main limitations were a lack of blinding of research participants and the self-report nature of the outcome measures.ConclusionsIn this study, we observed no improvements to teacher or student mental health following the intervention, possibly due to a lack of impact on key drivers of poor mental health within the school environment. Future research should focus on structural and cultural changes to the school environment, which may be more effective at improving teacher and student mental health and well-being.Trial registrationwww.isrctn.com ISRCTN95909211.

Using a cluster randomized study, Judi Kidger and colleagues study an intervention to improve teacher wellbeing support and training to support students in UK high schools (the WISE study).     

Organoselenides from Nicotiana tabacum genetically modified to accumulate selenium

Nicotiana tabacum L. (tobacco) plants were transformed to overexpress a selenocysteine methyltransferase gene from the selenium hyperaccumulator Astragalus bisulcatus (Hook.) A. Gray (two-grooved milkvetch), and an ATP-sulfurylase gene from Brassica oleracea L. var. italica (broccoli). Solvent extraction of leaves harvested from plants treated with selenate revealed five selenium-containing compounds, of which four were identified by chemical synthesis as 2-(methylseleno)acetaldehyde, 2,2-bis(methylseleno)acetaldehyde, 4-(methylseleno)-(2E)-nonenal, and 4-(methylseleno)-(2E,6Z)-nonadienal. These four compounds have not previously been reported in nature.