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IntroductionC4 photosynthesis is an adaptation that has independently evolved at least 66 times in angiosperms. C4 plants, unlike their C3 ancestral, have a carbon concentrating mechanism which suppresses photorespiration, often resulting in faster photosynthetic rates, higher yields, and enhanced water use efficiency. Moreover, the presence of C4 photosynthesis greatly alters the relation between CO2 assimilation and stomatal conductance. Previous papers have suggested that the adjustment involves a decrease in stomatal density. Here, we tested if C4 species also have differing stomatal responses to environmental cues, to accommodate the modified CO2 assimilation patterns compared to C3 species.MethodsTo test this hypothesis, stomatal responses to blue and red-light were analysed in three phylogenetically linked pairs of C3 and C4 species from the Cleomaceae (Gynandropsis and Tarenaya), Flaveria, and Alloteropsis, that use either C3 or C4 photosynthesis.ResultsThe results showed strongly decreased stomatal sensitivity to blue light in C4 dicots, compared to their C3 counterparts, which exhibited significant blue light responses. In contrast, in C3 and C4 subspecies of the monocot A. semialata, the blue light response was observed regardless of photosynthetic type. Further, the quantitative red-light response varied across species, but the presence or absence of a significant stomatal red-light response was not directly associated with differences in photosynthetic pathway. Interestingly, stomatal density and morphology patterns observed across the three comparisons were also not consistent with patterns commonly asserted for C3 and C4 species.DiscussionThe strongly diminished blue-light sensitivity of stomatal responses in C4 species across two of the comparisons suggests a common C4 feature that may have functional implications. Altogether, the strong prevalence of species-specific effects clearly emphasizes the importance of phylogenetic controls in comparisons between C3 and C4 photosynthetic pathways.

Gas exchange measurements enable mechanistic insights into the processes that underpin carbon and water fluxes in plant leaves which in turn inform understanding of related processes at a range of scales from individual cells to entire ecosytems. Given the importance of photosynthesis for the global climate discussion it is important to (a) foster a basic understanding of the fundamental principles underpinning the experimental methods used by the broad community, and (b) ensure best practice and correct data interpretation within the research community. In this review, we outline the biochemical and biophysical parameters of photosynthesis that can be investigated with gas exchange measurements and we provide step‐by‐step guidance on how to reliably measure them. We advise on best practices for using gas exchange equipment and highlight potential pitfalls in experimental design and data interpretation. The Supporting Information contains exemplary data sets, experimental protocols and data‐modelling routines. This review is a community effort to equip both the experimental researcher and the data modeller with a solid understanding of the theoretical basis of gas‐exchange measurements, the rationale behind different experimental protocols and the approaches to data interpretation. Summary statement: This review outlines the fundamental principles underpinning photosynthetic gas exchange and gives guidance on best practice for obtaining and correctly interpreting measurements. It is meant to provide a solid foundation in gas exchange techniques to the novice and act as a point of reference for the experienced researcher. [ABSTRACT FROM AUTHOR]

IntroductionDespite their importance for the global carbon cycle and crop production, species with C4 photosynthesis are still somewhat understudied relative to C3 species. Although the benefits of the C4 carbon concentrating mechanism are readily observable under optimal steady state conditions, it is less clear how the presence of C4 affects activation of CO2 assimilation during photosynthetic induction.MethodsIn this study we aimed to characterise differences between C4 and C3 photosynthetic induction responses by analysing steady state photosynthesis and photosynthetic induction in three phylogenetically linked pairs of C3 and C4 species from Alloteropsis, Flaveria, and Cleome genera. Experiments were conducted both at 21% and 2% O2 to evaluate the role of photorespiration during photosynthetic induction.ResultsOur results confirm C4 species have slower activation of CO2 assimilation during photosynthetic induction than C3 species, but the apparent mechanism behind these differences varied between genera. Incomplete suppression of photorespiration was found to impact photosynthetic induction significantly in C4Flaveria bidentis, whereas in the Cleome and Alloteropsis C4 species, delayed activation of the C3 cycle appeared to limit induction and a potentially supporting role for photorespiration was also identified.DiscussionThe sheer variation in photosynthetic induction responses observed in our limited sample of species highlights the importance of controlling for evolutionary distance when comparing C3 and C4 photosynthetic pathways.

Abstract Background Old-growth and primeval forests are passing through a natural development cycle with recurring stages of forest development. Several methods for assigning patches of different structure and size to forest development stages or phases do exist. All currently existing classification methods have in common that a priori assumptions about the characteristics of certain stand structural attributes such as deadwood amount are made. We tested the hypothesis that multivariate datasets of primeval beech forest stand structure possess an inherent, aggregated configuration of data points with individual clusters representing forest development stages. From two completely mapped primeval beech forests in Albania, seven ecologically important stand structural attributes characterizing stand density, regeneration, stem diameter variation and amount of deadwood are derived at 8216 and 9666 virtual sampling points (moving window, focal filtering). K-means clustering is used to detect clusters in the datasets (number of clusters (k) between 2 and 5). The quality of the single clustering solutions is analyzed with average silhouette width as a measure for clustering quality. In a sensitivity analysis, clustering is done with datasets of four different spatial scales of observation (200, 500, 1000 and 1500 m2, circular virtual plot area around sampling points) and with two different kernels (equal weighting of all objects within a plot vs. weighting by distance to the virtual plot center). Results The clustering solutions succeeded in detecting and mapping areas with homogeneous stand structure. The areas had extensions of more than 200 m2, but differences between clusters were very small with average silhouette widths of less than 0.28. The obtained datasets had a homogeneous configuration with only very weak trends for clustering. Conclusions Our results imply that forest development takes place on a continuous scale and that discrimination between development stages in primeval beech forests is splitting continuous datasets at selected thresholds. For the analysis of the forest development cycle, direct quantification of relevant structural features or processes might be more appropriate than classification. If, however, the study design demands classification, our results can justify the application of conventional forest development stage classification schemes rather than clustering.

Online teacher professional development has become an alternative to face-to-face professional development. Such a shift from face-to-face to online professional development, however, brings new challenges for professional development facilitators, whose roles are crucial in orchestrating teacher learning. This paper is motivated by the need to address the current gap in our understanding of what is entailed in the roles of facilitators, and how those roles might vary by context (i.e., face-to-face or asynchronous online). We drew on Anderson et al.'s (2001) "teaching presence" framework to lay the groundwork for characterizing the role of online and face-to-face facilitators. Qualitative analysis revealed that although professional development facilitators attended to similar issues irrespective of the context, the actions they engaged in to attend to these issues varied by context. Further exploration and synthesis of the findings suggests that shifting from traditional face-to-face to online professional development presents several design and instructional tensions that can impact how facilitators carry out their roles to support teacher learning. We conclude by using the findings from this study to present potential design tensions or pedagogical challenges that might arise when facilitators shift from face-to-face to online professional development contexts. (Contains 5 tables.)

As teacher professional development research includes more experimental designs, new challenges arise. We examine the threat of participant attrition as an example of the types of problems researchers face. Counter-intuitively, higher levels of recruitment effort were related to higher dropout rates among teachers. We also found that teachers left because of changes in teaching assignments, institutional challenges, and personal challenges. Finally, the majority of teachers in urban schools dropped out, while the majority of teachers in rural or suburban schools remained. We conclude with recommendations for future teacher learning experiments. (Contains 3 tables.)

We were pleased to read the response to our Journal of Teacher Education (JTE) article (Fishman et al., 2013) by Moon, Passmore, Reiser, and Michaels (2013). We believe that Moon [...]