Impact of future elevated carbon dioxide on C3 plant resistance to biotic stresses

Before the end of the century, atmospheric carbon dioxide (CO2) levels are predicted to increase to ~900 ppm. This will dramatically affect plant physiology and influence environmental interactions and, in particular, plant resistance to biotic stresses. This review is a broad survey of the current research on the effects of elevated CO2 (eCO2) on phytohormone-mediated resistance of C3 agricultural crops and related model species to pathogens and insect herbivores. In general, while plants grown in eCO2 often have increased constitutive and induced salicylic acid levels and suppressed induced jasmonate levels, there are exceptions that implicate other environmental factors, such as light and nitrogen fertilization in modulating these responses. Therefore, this review sets the stage for future studies to delve into understanding the mechanistic basis behind how eCO2 will affect plant defensive phytohormone signaling pathways under future predicted environmental conditions that could threaten global food security to inform the best agricultural management practices.

The Physiological Responses of Zea Mays L. and Cucumis Sativus L. on Drought Stress and Re-Watering

Drought leads to deficit water availability and its detrimental effects seriously threaten plant growth. This study assessed the physiological, biochemical, and antioxidant adjustments in different types of photosynthetic plants between Zea mays L. (C4) and Cucumis sativus L. (C3 plant) under response to short-term drought stress. Analyses of relative water content (RWC), proline, and ascorbic acid (AsA) were performed to explore how these plants react to drought. Fifteen-day-old plants were subjected to full irrigation or gradual drought periods for 2-d, 4-d, 6-d, and 8-d following by recovery for 7-d. The results revealed that drought significantly reduces leaf RCW in both plants. Re-watered Z. mays after 8-d drought was higher than C. sativus and reestablished RCW by 23% of stressed plant although remained lower by 9% of the well-watered plant. While, proline and AsA contents in Z. mays were higher than those in C. sativus in drought treatment at 8-d (2.05 µmol/g FW) and 6-d (3174.60 AsA/100 g FW), respectively, that could demonstrate osmotic adjustment ability in this C4 species. The increased proline in both plants also indicates a good strategy for plants to recover. Rewatering gave a decrease AsA and could be expected that plants restore cellular activity after oxidative injury. Based on our study, proline is the most informative biochemical marker to differentiate plant response to drought and Z. mays adjusted defense mechanism to drought rather than C. sativus due to higher accumulation of proline, better antioxidant activity, and improved RCW after recovery.

Stable Isotope Geochemistry of Paleocene to Early Eocene Strata around Southern New Zealand

<p>The Late Teurian (Paleocene) Tartan Formation is an organic-rich mudstone that has been identified in five of the eight exploration wells drilled in the Great South Basin, and three of four exploration wells drilled in the Canterbury Basin. In this study, the geochemistry of two wells from the Great South Basin (Pukaki-1 and Rakiura-1) and four wells from the Canterbury Basin in southern New Zealand (Resolution-1, Clipper-1, Galleon-1, and Endeavour-1) have been investigated using elemental analyser isotope ratio mass spectrometric (EA-IRMS) analyses on selected sidewall core and cuttings samples. This study builds on previous geochemical work by the author from five other wells from the Great South Basin (Takapu-1A, Toroa-1, Pakaha-1, Kawau-1A, and Hoiho-1C). All wells except Rakiura-1, Takapu-1A, and Resolution-1 showed geochemical characteristics that allowed recognition of the Tartan Formation. The formation is characterised by enrichments in TOC (typically above 3%) and 13C (generally delta13C ratios are between -21 and -17 per 1000), indicating a significant marine contribution. C/N ratios recorded within the Tartan Formation are all above 20, which suggest that the organic matter contains a significant contribution from terrestrial and/or altered marine material. Geochemical evidence of samples within the Tartan Formation suggests that it contains a mixture of marine bacterial/plant/algal and C3 terrestrial plant source components. This is consistent with the findings of Killops et al. (2000), who reported from biomarker studies that the organic matter of some Great South Basin samples contained organic matter derived from a marine source with varying degrees of terrestrial contribution. The Tartan Formation is distinct from enclosing formations which are characterised by low organic contents (generally below 2%), isotopically light delta13C values (typically around -26 per 1000), which is indicative of terrestrial C3 plant matter, and a wide range of C/N ratios (ranging from 4 to 64). The latter suggests that there were varying degrees of preservation of the deposited organic matter within these formations. Organic matter within enclosing formations appears to be derived from a combination of C3 land plants and marine material. The high TOC content of Tartan Formation sediments compared to the underlying formation suggests that it represents a profound change in depositional conditions. Conditions for the preservation and accumulation of organic matter were more favorable prior to deposition of the Tartan Formation than following it. The enrichment of 13C and the high TOC contents within the Tartan Formation are similar to those for the mid to Late Teurian Waipawa Formation that has been identified throughout many of New Zealand's major sedimentary basins; however, TOC and delta13C values for the Tartan Formation exceed those previously reported for the Waipawa Formation. Geochemical changes characteristic of the Tartan Formation are recognised below the lithological base of the formation in some wells, contemporaneous with the onset of the Paleocene Carbon Isotope Maximum (PCIM), and represent different lithostratigraphic expressions of that event. Termination of the environmental effects associated with the PCIM around New Zealand appears to have been diachronous and differences between the exact ages and stratigraphic positions of the Tartan and Waipawa formations are attributed to local environmental variations during deposition. TOC and delta13C enrichments associated with the Tartan Formation are not ubiquitous, and the formation has variable thickness throughout the Great South and Canterbury basins. It is concluded that the Tartan and Waipawa formations are correlatives.</p>

Stable Isotope Geochemistry of Paleocene to Early Eocene Strata around Southern New Zealand

<p>The Late Teurian (Paleocene) Tartan Formation is an organic-rich mudstone that has been identified in five of the eight exploration wells drilled in the Great South Basin, and three of four exploration wells drilled in the Canterbury Basin. In this study, the geochemistry of two wells from the Great South Basin (Pukaki-1 and Rakiura-1) and four wells from the Canterbury Basin in southern New Zealand (Resolution-1, Clipper-1, Galleon-1, and Endeavour-1) have been investigated using elemental analyser isotope ratio mass spectrometric (EA-IRMS) analyses on selected sidewall core and cuttings samples. This study builds on previous geochemical work by the author from five other wells from the Great South Basin (Takapu-1A, Toroa-1, Pakaha-1, Kawau-1A, and Hoiho-1C). All wells except Rakiura-1, Takapu-1A, and Resolution-1 showed geochemical characteristics that allowed recognition of the Tartan Formation. The formation is characterised by enrichments in TOC (typically above 3%) and 13C (generally delta13C ratios are between -21 and -17 per 1000), indicating a significant marine contribution. C/N ratios recorded within the Tartan Formation are all above 20, which suggest that the organic matter contains a significant contribution from terrestrial and/or altered marine material. Geochemical evidence of samples within the Tartan Formation suggests that it contains a mixture of marine bacterial/plant/algal and C3 terrestrial plant source components. This is consistent with the findings of Killops et al. (2000), who reported from biomarker studies that the organic matter of some Great South Basin samples contained organic matter derived from a marine source with varying degrees of terrestrial contribution. The Tartan Formation is distinct from enclosing formations which are characterised by low organic contents (generally below 2%), isotopically light delta13C values (typically around -26 per 1000), which is indicative of terrestrial C3 plant matter, and a wide range of C/N ratios (ranging from 4 to 64). The latter suggests that there were varying degrees of preservation of the deposited organic matter within these formations. Organic matter within enclosing formations appears to be derived from a combination of C3 land plants and marine material. The high TOC content of Tartan Formation sediments compared to the underlying formation suggests that it represents a profound change in depositional conditions. Conditions for the preservation and accumulation of organic matter were more favorable prior to deposition of the Tartan Formation than following it. The enrichment of 13C and the high TOC contents within the Tartan Formation are similar to those for the mid to Late Teurian Waipawa Formation that has been identified throughout many of New Zealand's major sedimentary basins; however, TOC and delta13C values for the Tartan Formation exceed those previously reported for the Waipawa Formation. Geochemical changes characteristic of the Tartan Formation are recognised below the lithological base of the formation in some wells, contemporaneous with the onset of the Paleocene Carbon Isotope Maximum (PCIM), and represent different lithostratigraphic expressions of that event. Termination of the environmental effects associated with the PCIM around New Zealand appears to have been diachronous and differences between the exact ages and stratigraphic positions of the Tartan and Waipawa formations are attributed to local environmental variations during deposition. TOC and delta13C enrichments associated with the Tartan Formation are not ubiquitous, and the formation has variable thickness throughout the Great South and Canterbury basins. It is concluded that the Tartan and Waipawa formations are correlatives.</p>

Reconstructing the childhood diet of the individuals from the Middle Late Bronze Age Bezdanjača Cave, Croatia (ca. 1430 1290 BCE) using stable C and N isotope analysis of dentin collagen

This paper investigates the childhood diet of 16 individuals from the Middle Late Bronze Age (1430 1290 BCE) Bezdanjača Cave (Lika region, Croatia) using stable isotope analysis of dentin collagen from permanent first molars. Results from the analysis reveal that the individuals from Bezdanjača consumed notable quantities of C4 plants during their childhood. The most common C4 plant is millet, whose spread throughout Southern Europe was recently dated to the second half of the 2nd millennium BCE, which agrees with the results obtained in this research. Comparisons between the data collected for the individuals from Bezdanjača and other Middle and Late Bronze Age sites in Croatia suggest that only the individuals from the site of Veliki Vital (Middle Bronze Age, inland Croatia) exhibit similar isotopic values to those from Bezdanjača. Human isotopic values from coastal sites, however, reveal that during the Middle and Late Bronze Age people from the coast had diet that still predominantly contained C3 plant-based foods, which appears to suggest that the dispersion of this crop in Croatia during the Bronze Age followed an east-west trajectory, appearing earlier (Middle and Late Bronze Age) in inland settlements such as Veliki Vital and Bezdanjača and only later (Late Bronze Age and mostly Iron Age) in coastal sites.

C3 plant isotopic variability in a boreal mixed woodland: implications for bison and other herbivores

Plant isotopic baselines are critical for accurately reconstructing ancient diets and environments and for using stable isotopes to monitor ecosystem conservation. This study examines the stable carbon and nitrogen isotope compositions (δ13C, δ15N) of terrestrial C3 plants in Elk Island National Park (EINP), Alberta, Canada, with a focus on plants consumed by grazers. EINP is located in a boreal mixed woodland ecozone close to the transition area between historic wood and plains bison habitats, and is currently home to separate herds of wood and plains bison. For this study, 165 C3 plant samples (grasses, sedges, forbs, shrubs, and horsetail) were collected from three habitat types (open, closed, and wet) during two seasons (summer and fall). There were no statistically significant differences in the δ13C or δ15N values of grasses, sedges, shrubs and forbs. On the other hand, plant δ13C and δ15N values varied among habitats and plant parts, and the values increased from summer to fall. These results have several implications for interpreting herbivore tissue isotopic compositions: (1) consuming different proportions of grasses, sedges, shrubs, and forbs might not result in isotopic niche partitioning, (2) feeding in different microhabitats or selecting different parts of the same types of plants could result in isotopic niche partitioning, and (3) seasonal isotopic changes in herbivore tissues could reflect seasonal isotopic changes in dietary plants rather than (or in addition to) changes in animal diet or physiology. In addition, the positively skewed plant δ15N distributions highlight the need for researchers to carefully evaluate the characteristics of their distributions prior to reporting data (e.g., means, standard deviations) or applying statistical models (e.g., parametric tests that assume normality). Overall, this study reiterates the importance of accessing ecosystem-specific isotopic baselines for addressing research questions in archaeology, paleontology, and ecology.

CO2 Responses of Winter Wheat, Barley and Oat Cultivars under Optimum and Limited Irrigation

Field crop production must adapt to the challenges generated by the negative consequences of climate change. Yield loss caused by abiotic stresses could be counterbalanced by increasing atmospheric CO2 concentration, but C3 plant species and varieties have significantly different reactions to CO2. To examine the responses of wheat, barley and oat varieties to CO2 enrichment in combination with simulated drought, a model experiment was conducted under controlled environmental conditions. The plants were grown in climate-controlled greenhouse chambers under ambient and enriched (700 ppm and 1000 ppm) CO2 concentrations. Water shortage was induced by discontinuing the irrigation at BBCH stages 21 and 55. Positive CO2 responses were determined in barley, but the CO2-sink ability was low in oats. Reactions of winter wheat to enriched CO2 concentration varied greatly in terms of the yield parameters (spike number and grain yield). The water uptake of all wheat cultivars decreased significantly; however at the same time, water-use efficiency improved under 1000 ppm CO2. Mv Ikva was not susceptible to CO2 fertilization, while no consequent CO2 reactions were observed for Mv Nádor and Mv Nemere. Positive CO2 responses were determined in Mv Kolompos.

Absence of carbonic anhydrase in chloroplasts affects C3 plant development but not photosynthesis

The enzyme carbonic anhydrase (CA), which catalyzes the interconversion of bicarbonate with carbon dioxide (CO2) and water, has been hypothesized to play a role in C3 photosynthesis. We identified two tobacco stromal CAs, β-CA1 and β-CA5, and produced CRISPR/Cas9 mutants affecting their encoding genes. While single knockout lines Δβ-ca1 and Δβ-ca5 had no striking phenotypic differences compared to wild type (WT) plants, Δβ-ca1ca5 leaves developed abnormally and exhibited large necrotic lesions even when supplied with sucrose. Leaf development of Δβ-ca1ca5 plants normalized at 9,000 ppm CO2. Leaves of Δβ-ca1ca5 mutants and WT that had matured in high CO2 had identical CO2 fixation rates and photosystem II efficiency. Fatty acids, which are formed through reactions with bicarbonate substrates, exhibited abnormal profiles in the chloroplast CA-less mutant. Emerging Δβ-ca1ca5 leaves produce reactive oxygen species in chloroplasts, perhaps due to lower nonphotochemical quenching efficiency compared to WT. Δβ-ca1ca5 seedling germination and development is negatively affected at ambient CO2. Transgenes expressing full-length β-CA1 and β-CA5 proteins complemented the Δβ-ca1ca5 mutation but inactivated (ΔZn-βCA1) and cytoplasm-localized (Δ62-βCA1) forms of β-CA1 did not reverse the growth phenotype. Nevertheless, expression of the inactivated ΔZn-βCA1 protein was able to restore the hypersensitive response to tobacco mosaic virus, while Δβ-ca1 and Δβ-ca1ca5 plants failed to show a hypersensitive response. We conclude that stromal CA plays a role in plant development, likely through providing bicarbonate for biosynthetic reactions, but stromal CA is not needed for maximal rates of photosynthesis in the C3 plant tobacco.