CONTENTS: Summary 674 I. Introduction 675 II. The case for low‐CO₂ studies 675 III. Experimental approaches for reducing CO₂ 677 IV. Early low‐CO₂ studies 679 V. Low‐CO₂ effects on the individual ...plant 680 VI. Low CO₂ and plant evolution 683 VII. Interactions of low CO₂ with other factors 687 VIII. Low‐CO₂ effects on community composition 689 IX. Low‐CO₂ effects on the ecosystem 689 X. Low‐CO₂ effects on early human societies 690 XI. Conclusions 691 Acknowledgemnts 692 References 692 SUMMARY: During the Last Glacial Maximum (LGM; 18 000-20 000 yr ago) and previous glacial periods, atmospheric CO₂ dropped to 180-190 ppm, which is among the lowest concentrations that occurred during the evolution of land plants. Modern atmospheric CO₂ concentrations (CO₂) are more than twice those of the LGM and 45% higher than pre‐industrial concentrations. Since CO₂ is the carbon source for photosynthesis, lower carbon availability during glacial periods likely had a major impact on plant productivity and evolution. From the studies highlighted here, it is clear that the influence of low CO₂ transcends several scales, ranging from physiological effects on individual plants to changes in ecosystem functioning, and may have even influenced the development of early human cultures (via the timing of agriculture). Through low‐CO₂ studies, we have determined a baseline for plant response to minimal CO₂ that occurred during the evolution of land plants. Moreover, an increased understanding of plant responses to low CO₂ contributes to our knowledge of how natural global change factors in the past may continue to influence plant responses to future anthropogenic changes. Future work, however, should focus more on the evolutionary responses of plants to changing CO₂ in order to account for the potentially large effects of genetic change.
Rising atmospheric CO₂, cₐ, is expected to affect stomatal regulation of leaf gas‐exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of ...forests. Researchers have proposed various strategies for stomatal regulation of leaf gas‐exchange that include maintaining a constant leaf internal CO₂, cᵢ, a constant drawdown in CO₂ (cₐ − cᵢ), and a constant cᵢ/cₐ. These strategies can result in drastically different consequences for leaf gas‐exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas‐exchange responses to varying cₐ. The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas‐exchange responses to cₐ. To assess leaf gas‐exchange regulation strategies, we analyzed patterns in cᵢ inferred from studies reporting C stable isotope ratios (δ¹³C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of cₐ spanning at least 100 ppm. Our results suggest that much of the cₐ‐induced changes in cᵢ/cₐ occurred across cₐ spanning 200 to 400 ppm. These patterns imply that cₐ − cᵢ will eventually approach a constant level at high cₐ because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant cᵢ. Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low cₐ, when additional water loss is small for each unit of C gain, and increasingly water‐conservative at high cₐ, when photosystems are saturated and water loss is large for each unit C gain.
Characterizing plant responses to past, present and future changes in atmospheric carbon dioxide concentration (CO2) is critical for understanding and predicting the consequences of global change ...over evolutionary and ecological timescales. Previous CO2 studies have provided great insights into the effects of rising CO2 on leaf-level gas exchange, carbohydrate dynamics and plant growth. However, scaling CO2 effects across biological levels, especially in field settings, has proved challenging. Moreover, many questions remain about the fundamental molecular mechanisms driving plant responses to CO2 and other global change factors. Here we discuss three examples of topics in which significant questions in CO2 research remain unresolved: (1) mechanisms of CO2 effects on plant developmental transitions; (2) implications of rising CO2 for integrated plant–water dynamics and drought tolerance; and (3) CO2 effects on symbiotic interactions and eco-evolutionary feedbacks. Addressing these and other key questions in CO2 research will require collaborations across scientific disciplines and new approaches that link molecular mechanisms to complex physiological and ecological interactions across spatiotemporal scales.
Conservative flowering behaviours, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures ...which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to 10 winter-annual Arabidopsis thaliana populations from a wide climactic gradient in Norway. We used a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their flowering behaviours when tested for responsiveness to photoperiod after saturation of vernalization; then, assessed sequence variation of 19 known environmental-response flowering genes. Photoperiod responsiveness inversely correlated with interannual variation in timing of growing season onset. Time to flowering appeared driven by growing season length, curtailed by cold fall temperatures. The distribution of FLM, TFL2 and HOS1 haplotypes, genes involved in ambient temperature response, correlated with growing-season climate. We show that long-day responsiveness and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length, perhaps to opportunistically maximize growth.
Since industrialization began, atmospheric CO2 (CO2) has increased from 270 to 415 ppm and is projected to reach 800-1000 ppm this century. Some Arabidopsis thaliana (Arabidopsis) genotypes delayed ...flowering in elevated CO2 relative to current CO2, while others showed no change or accelerations. To predict genotype-specific flowering behaviors, we must understand the mechanisms driving flowering response to rising CO2. CO2 changes alter photosynthesis and carbohydrates in plants. Plants sense carbohydrate levels, and exogenous carbohydrate application influences flowering time and flowering transcript levels. We asked how organismal changes in carbohydrates and transcription correlate with changes in flowering time under elevated CO2. We used a genotype (SG) of Arabidopsis that was selected for high fitness at elevated CO2 (700 ppm). SG delays flowering under elevated CO2 (700 ppm) relative to current CO2 (400 ppm). We compared SG to a closely related control genotype (CG) that shows no CO2-induced flowering change. We compared metabolomic and transcriptomic profiles in these genotypes at current and elevated CO2 to assess correlations with flowering in these conditions. While both genotypes altered carbohydrates in response to elevated CO2, SG had higher levels of sucrose than CG and showed a stronger increase in glucose and fructose in elevated CO2. Both genotypes demonstrated transcriptional changes, with CG increasing genes related to fructose 1,6-bisphosphate breakdown, amino acid synthesis, and secondary metabolites; and SG decreasing genes related to starch and sugar metabolism, but increasing genes involved in oligosaccharide production and sugar modifications. Genes associated with flowering regulation within the photoperiod, vernalization, and meristem identity pathways were altered in these genotypes. Elevated CO2 may alter carbohydrates to influence transcription in both genotypes and delayed flowering in SG. Changes in the oligosaccharide pool may contribute to delayed flowering in SG. This work extends the literature exploring genotypic-specific flowering responses to elevated CO2.
Temperate species often require or flower most rapidly in the long daylengths, or photoperiods, experienced in summer or after prolonged periods of cold temperatures, referred to as vernalization. ...Yet, even within species, plants vary in the degree of responsiveness to these cues. In
,
(
) and
(
) genes are key to photoperiod and vernalization perception and antagonistically regulate
(
) to influence the flowering time of the plants. However, it is still an open question as to how these genes vary in their interactions among wild accessions with different flowering behaviors and adapted to different microclimates, yet this knowledge could improve our ability to predict plant responses in variable natural conditions. To assess the relationships among these genes and to flowering time, we exposed 10 winter-annual
accessions from throughout Norway, ranging from early to late flowering, along with two summer-annual accessions to 14 weeks of vernalization and either 8- or 19-h photoperiods to mimic Norwegian climate conditions, then assessed gene expression levels 3-, 5-, and 8-days post vernalization.
and
explained both
levels and flowering time (days) but not rosette leaf number at flowering. The correlation between
and flowering time increased over time. Although vernalization suppresses
,
was high in the late-flowering accessions. Across accessions,
was expressed only at low
levels and did not respond to
in the late-flowering accessions. We proposed that
may only be expressed below a threshold value of
and demonstrated that these three genes correlated to flowering times across genetically distinct accessions of
.
Summary
Flowering is a critical milestone in the life cycle of plants, and changes in the timing of flowering may alter processes at the species, community and ecosystem levels. Therefore ...understanding flowering‐time responses to global change drivers, such as elevated atmospheric carbon dioxide concentrations, CO2, is necessary to predict the impacts of global change on natural and agricultural ecosystems. Here we summarize the results of 60 studies reporting flowering‐time responses (defined as the time to first visible flower) of both crop and wild species at elevated CO2. These studies suggest that elevated CO2 will influence flowering time in the future. In addition, interactions between elevated CO2 and other global change factors may further complicate our ability to predict changes in flowering time. One approach to overcoming this problem is to elucidate the primary mechanisms that control flowering‐time responses to elevated CO2. Unfortunately, the mechanisms controlling these responses are not known. However, past work has indicated that carbon metabolism exerts partial control on flowering time, and therefore may be involved in elevated CO2‐induced changes in flowering time. This review also indicates the need for more studies addressing the effects of global change drivers on developmental processes in plants.
Contents
Summary
243
I.
Introduction
244
II.
Effects of elevated CO2 on flowering time
245
III.
Mechanisms for altered flowering time in response to elevated CO2
250
IV.
Conclusion
252
Acknowledgements
253
References
253
We introduce a cheminformatics approach that combines highly selective and orthogonal structure elucidation parameters; accurate mass, MS/MS (MS²), and NMR into a single analysis platform to ...accurately identify unknown metabolites in untargeted studies. The approach starts with an unknown LC-MS feature, and then combines the experimental MS/MS and NMR information of the unknown to effectively filter out the false positive candidate structures based on their predicted MS/MS and NMR spectra. We demonstrate the approach on a model mixture, and then we identify an uncatalogued secondary metabolite in
. The NMR/MS² approach is well suited to the discovery of new metabolites in plant extracts, microbes, soils, dissolved organic matter, food extracts, biofuels, and biomedical samples, facilitating the identification of metabolites that are not present in experimental NMR and MS metabolomics databases.
Past studies have shown that flowering times have accelerated over the last century. These responses are often attributed to rising temperature, although short-term field experiments with warming ...treatments have under-estimated accelerations in flowering time that have been observed in long-term field surveys. Thus, there appears to be a missing factor(s) for explaining accelerated flowering over the last century. Rising atmospheric CO₂ concentration (CO₂) is a possible candidate, and its contributions to affecting flowering time over historic periods are not well understood. This is likely because rising CO₂ is confounded with temperature in the field and preindustrial CO₂ studies are relatively rare. To address this, we tested the individual and interactive effects of rising CO₂ and temperature between preindustrial and modern periods on flowering time in the model system, Arabidopsis thaliana. We used a variety of genotypes originating from diverse locations, allowing us to test intraspecific responses to last-century climate change. We found that accelerated flowering time between the full-preindustrial and full-modern treatments was mainly driven by an interaction between rising CO₂ and temperature, rather than through the individual effects of either factor in isolation. Furthermore, accelerated flowering time was driven by enhanced plant growth rates and not through changes in plant size at flowering. Thus, the interaction between rising CO₂ and temperature may be key for explaining large accelerations in flowering times that have been observed over the last century and that could not be explained by rising temperature alone.
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