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Colin P. Osborne - One of the best experts on this subject based on the ideXlab platform.
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water relations traits of C4 Grasses depend on phylogenetic lineage photosynthetic pathway and habitat water availability
Journal of Experimental Botany, 2015Co-Authors: Colin P. OsborneAbstract:The repeated evolution of C4 photosynthesis in independent lineages has resulted in distinct biogeographical distributions in different phylogenetic lineages and the variants of C4 photosynthesis. However, most previous studies have only considered C3/C4 differences without considering phylogeny, C4 subtype, or habitat characteristics. We hypothesized that independent lineages of C4 Grasses have structural and physiological traits that adapt them to environments with differing water availability. We measured 40 traits of 33 species from two major C4 Grass lineages in a common glasshouse environment. Chloridoideae species were shorter, with narrower and longer leaves, smaller but denser stomata, and faster curling leaves than Panicoideae species, but overall differences in leaf hydraulic and gas exchange traits between the two lineages were weak. Chloridoideae species had two different ways to reach higher drought resistance potential than Panicoideae; NAD-ME species used water saving, whereas PCK species used osmotic adjustment. These patterns could be explained by the interactions of lineage×C4 subtype and lineage×habitat water availability in affected traits. Specifically, phylogeny tended to have a stronger influence on structural traits, and C4 subtype had more important effects on physiological traits. Although hydraulic traits did not differ consistently between lineages, they showed strong covariation and relationships with leaf structure. Thus, phylogenetic lineage, photosynthetic pathway, and adaptation to habitat water availability act together to influence the leaf water relations traits of C4 Grasses. This work expands our understanding of ecophysiology in major C4 Grass lineages, with implications for explaining their regional and global distributions in relation to climate.
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Biogeographically distinct controls on C3 and C4 Grass distributions: merging community and physiological ecology
Global Ecology and Biogeography, 2014Co-Authors: Daniel M. Griffith, Colin P. Osborne, T. Michael Anderson, Caroline A.e. Strömberg, Elisabeth J. Forrestel, Christopher J. StillAbstract:Aim C4 photosynthesis is an adaptation that maintains efficient carbon assimilation in high-light, high-temperature conditions. Due to the importance of C4 Grasses for carbon and surface energy fluxes, numerous models have been proposed to describe their spatial distribution and forecast their responses to climate change. These models often rely on broad climatic predictors (e.g. temperature and precipitation) but fail to integrate other ecologically relevant factors like disturbance and competition, which may modify realized C3/C4 Grass distributions. Here, we present a combined evaluation of the contribution of ecological factors and climatic predictors to realized C3/C4 Grass distributions. We consider multiple biogeographic regions of North America using a multisource database of over 40,000 vegetation plots. Location The conterminous United States of America (USA). Methods We identified a comprehensive pool of climatic models in the literature and used information theoretic criteria to select a primary climatic predictor of C3 and C4 Grass distributions. Subsequently, the best model was combined with ecological predictors (e.g. fire, tree cover) using a multiple regression framework and tested within eight regions. Results Surprisingly, Grass-dominated communities across the USA exist largely in C3- or C4-dominated states. Transitions between C3/C4 dominance were best explained by models that integrated temperature and precipitation with ecological factors that varied according to region. For some regions, like Eastern Temperate Forests, local ecological factors were comparable in strength to broad-scale climatic predictors of C3/C4 abundance. Main conclusion Local ecological factors modify C3/C4 Grass responses to broad-scale climatic drivers in ways that manifest at regional scales. In Eastern Temperate Forests, for example, C4 Grass abundances are maintained below climatic expectations where tree cover creates light limitation but above expectations where frequent fires reduce tree cover. Thus, local ecological factors, which vary among biogeographic regions, contribute to large-scale climate disequilibrium.
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Phylogenetic niche conservatism in C4 Grasses.
Oecologia, 2012Co-Authors: Hui Liu, Erika J. Edwards, Robert P. Freckleton, Colin P. OsborneAbstract:Photosynthetic pathway is used widely to discriminate plant functional types in studies of global change. However, independent evolutionary lineages of C4 Grasses with different variants of C4 photosynthesis show different biogeographical relationships with mean annual precipitation, suggesting phylogenetic niche conservatism (PNC). To investigate how phylogeny and photosynthetic type differentiate C4 Grasses, we compiled a dataset of morphological and habitat information of 185 genera belonging to two monophyletic subfamilies, Chloridoideae and Panicoideae, which together account for 90 % of the world’s C4 Grass species. We evaluated evolutionary variance and covariance of morphological and habitat traits. Strong phylogenetic signals were found in both morphological and habitat traits, arising mainly from the divergence of the two subfamilies. Genera in Chloridoideae had significantly smaller culm heights, leaf widths, 1,000-seed weights and stomata; they also appeared more in dry, open or saline habitats than those of Panicoideae. Controlling for phylogenetic structure showed significant covariation among morphological traits, supporting the hypothesis of phylogenetically independent scaling effects. However, associations between morphological and habitat traits showed limited phylogenetic covariance. Subfamily was a better explanation than photosynthetic type for the variance in most morphological traits. Morphology, habitat water availability, shading, and productivity are therefore all involved in the PNC of C4 Grass lineages. This study emphasized the importance of phylogenetic history in the ecology and biogeography of C4 Grasses, suggesting that divergent lineages need to be considered to fully understand the impacts of global change on plant distributions.
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environmental factors determining the phylogenetic structure of C4 Grass communities
Journal of Biogeography, 2012Co-Authors: Vernon Visser, Robert P. Freckleton, Ian F Woodward, Colin P. OsborneAbstract:Aim To determine how the distribution of species richness is associated with environmental factors for the four major C4 Grass lineages in South Africa, as a means to explore the mechanisms responsible. Location South Africa, Lesotho and Swaziland. Methods The geographical distributions of species richness for four major C4 Grass lineages (Aristidoideae, Chloridoideae, Andropogoneae and Paniceae) were sourced from a recently published flora that divided the study region into different vegetation types. Mean values of potential environmental correlates were calculated for each vegetation type, and the relative importances of these were determined using single- and multiple-predictor generalized linear models, with and without control for spatial autocorrelation. Model selection of the multiple-predictor generalized linear models was conducted using an Akaike’s information criterion–information theoretic approach. Association with wet, intermediate or dry, shady or open, and disturbed or undisturbed habitats was also determined for each C4 Grass clade using habitat data for all the Grass species, and analysed using chi-square tests of independence. Results Andropogoneae and Paniceae are most species-rich in areas of high precipitation and in mesic habitats. Andropogoneae are associated with high fire frequencies. Species richness in Andropogoneae decreases and in Paniceae increases in relation to livestock density. Chloridoideae species richness is relatively constant across South Africa, but is highest where there are infrequent fires, high temperatures and basic soils, and in mesic and disturbed habitats. Aristidoideae are most species-rich in arid regions and in habitats with high temperatures, and are associated with disturbed habitats. Main conclusions Environmental variables other than precipitation, including temperature, fire frequency and grazing pressure, are strongly associated with the contrasting distributions of species richness for the various C4 Grass clades in South Africa. Our results suggest that ecological sorting is an important determinant of phylogenetic patterns in the species richness of these C4 Grass lineages.
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drought limitation of photosynthesis differs between c3 and C4 Grass species in a comparative experiment
Plant Cell and Environment, 2011Co-Authors: Samuel H. Taylor, Brad S Ripley, F I Woodward, Colin P. OsborneAbstract:Phylogenetic analyses show that C4 Grasses typically occupy drier habitats than their C3 relatives, but recent experiments comparing the physiology of closely related C3 and C4 species have shown that advantages of C4 photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in Grass species representing the known evolutionary diversity of C4 NADP-me and C3 photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C4 Grasses in control treatments were characterized by higher CO2 assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C3 than C4 species, and photosynthetic water-use and nitrogen-use efficiency advantages held by C4 species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C4 than C3 Grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic-type. This phylogenetically controlled experiment suggested that a drought-induced reduction in the photosynthetic performance advantages of C4 NADP-me relative to C3 Grasses is a general phenomenon.
Onisimo Mutanga - One of the best experts on this subject based on the ideXlab platform.
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Optimal season for discriminating C3 and C4 Grass functional types using multi-date Sentinel 2 data
GIScience & Remote Sensing, 2019Co-Authors: Cletah Shoko, Onisimo Mutanga, Timothy DubeAbstract:The ability of remote sensing systems to optimally discriminate and map C3 and C4 Grass species varies over time, due to environmental changes, which influence their phenological, physiological and...
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Examining the strength of the newly-launched Sentinel 2 MSI sensor in detecting and discriminating subtle differences between C3 and C4 Grass species
ISPRS Journal of Photogrammetry and Remote Sensing, 2017Co-Authors: Cletah Shoko, Onisimo MutangaAbstract:C3 and C4 Grass species discrimination has increasingly become relevant in understanding their response to environmental changes and to monitor their integrity in providing goods and services. While remotely-sensed data provide robust, cost-effective and repeatable monitoring tools for C3 and C4 Grasses, this has been largely limited by the scarcity of sensors with better earth imaging characteristics. The recent launch of the advanced Sentinel 2 MultiSpectral Instrument (MSI) presents a new prospect for discriminating C3 and C4 Grasses. The present study tested the potential of Sentinel 2, characterized by refined spatial resolution and more unique spectral bands in discriminating between Festuca (C3) and Themeda (C4) Grasses. To evaluate the performance of Sentinel 2 MSI; spectral bands, vegetation indices and spectral bands plus indices were used. Findings from Sentinel 2 were compared with those derived from the widely-used Worldview 2 commercial sensor and the Landsat 8 Operational Land Imager (OLI). Overall classification accuracies have shown that Sentinel 2 bands have potential (90.36%), than indices (85.54%) and combined variables (88.61%). The results were comparable to Worldview 2 sensor, which produced slightly higher accuracies using spectral bands (95.69%), indices (86.02%) and combined variables (87.09%), and better than Landsat 8 OLI spectral bands (75.26%), indices (82.79%) and combined variables (86.02%). Sentinel 2 bands produced lower errors of commission and omission (between 4.76 and 14.63%), comparable to Worldview 2 (between 1.96 and 7.14%), than Landsat 8 (between 18.18 and 30.61%), when classifying the two species. The classification accuracy from Sentinel 2 also did not differ significantly (z = 1.34) from Worldview 2, using standard bands; it was significantly (z > 1.96) different using indices and combined variables, whereas when compared to Landsat 8, Sentinel 2 accuracies were significantly different (z > 1.96) using all variables. These results demonstrated that key vegetation species discrimination could be improved by the use of the freely and improved Sentinel 2 MSI data.
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Progress in the remote sensing of C3 and C4 Grass species aboveground biomass over time and space
ISPRS Journal of Photogrammetry and Remote Sensing, 2016Co-Authors: Cletah Shoko, Onisimo Mutanga, Timothy DubeAbstract:Abstract The remote sensing of Grass aboveground biomass (AGB) has gained considerable attention, with substantial research being conducted in the past decades. Of significant importance is their photosynthetic pathways (C3 and C4), which epitomizes a fundamental eco-physiological distinction of Grasses functional types. With advances in technology and the availability of remotely sensed data at different spatial, spectral, radiometric and temporal resolutions, coupled with the need for detailed information on vegetation condition, the monitoring of C3 and C4 Grasses AGB has received renewed attention, especially in the light of global climate change, biodiversity and, most importantly, food security. This paper provides a detailed survey on the progress of remote sensing application in determining C3 and C4 Grass species AGB. Importantly, the importance of species functional type is highlighted in conjunction with the availability and applicability of different remote sensing datasets, with refined resolutions, which provide an opportunity to monitor C3 and C4 Grasses AGB. While some progress has been made, this review has revealed the need for further remote sensing studies to model the seasonal (cyclical) variability, as well as long-term AGB changes in C3 and C4 Grasses, in the face of climate change and food security. Moreover, the findings of this study have shown the significance of shifting towards the application of advanced statistical models, to further improve C3 and C4 Grasses AGB estimation accuracy.
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predicting c3 and C4 Grass nutrient variability using in situ canopy reflectance and partial least squares regression
Journal of remote sensing, 2015Co-Authors: Clement Adjorlolo, Onisimo Mutanga, Moses Azong ChoAbstract:The use of hyperspectral data to estimate forage nutrient content can be a challenging task, considering the multicollinearity problem, which is often caused by high data dimensionality. We predicted some variability in the concentration of limiting nutrients such as nitrogen N, crude protein CP, moisture, and non-digestible fibres that constrain the intake rate of herbivores. Insitu hyperspectral reflectance measurements were performed at full canopy cover for C3 and C4 Grass species in a montane Grassland environment. The recorded spectra were resampled to 13 selected band centres of known absorption and/or reflectance features, WorldView-2 band settings, and to 10 nm-wide bandwidths across the 400–2500 nm optical region. The predictive accuracy of the resultant wavebands was assessed using partial least squares regression PLSR and an accompanying variable importance VIP projection. The results indicated that prediction accuracies ranging from 66% to 32% of the variance in N, CP, moisture, and fibre concentrations can be achieved using the spectral-only information. The red, red-edge, and shortwave infrared SWIR wavelength regions were the most sensitive to all nutrient variables, with higher VIP values. Moreover, the PLSR model constructed based on spectra resampled around the 13 preselected band centres yielded the highest sensitivity to the predicted nutrient variables. The results of this study thus suggest that the use of the spectral resampling technique that uses only a few but strategically selected band centres of known absorption or reflectance features is sufficient for forage nutrient estimation.
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spectral resampling based on user defined inter band correlation filter c3 and C4 Grass species classification
International Journal of Applied Earth Observation and Geoinformation, 2013Co-Authors: Clement Adjorlolo, Onisimo Mutanga, Riyad IsmailAbstract:Abstract In this paper, a user-defined inter-band correlation filter function was used to resample hyperspectral data and thereby mitigate the problem of multicollinearity in classification analysis. The proposed resampling technique convolves the spectral dependence information between a chosen band-centre and its shorter and longer wavelength neighbours. Weighting threshold of inter-band correlation (WTC, Pearson's r ) was calculated, whereby r = 1 at the band-centre. Various WTC ( r = 0.99, r = 0.95 and r = 0.90) were assessed, and bands with coefficients beyond a chosen threshold were assigned r = 0. The resultant data were used in the random forest analysis to classify in situ C 3 and C 4 Grass canopy reflectance. The respective WTC datasets yielded improved classification accuracies (kappa = 0.82, 0.79 and 0.76) with less correlated wavebands when compared to resampled Hyperion bands (kappa = 0.76). Overall, the results obtained from this study suggested that resampling of hyperspectral data should account for the spectral dependence information to improve overall classification accuracy as well as reducing the problem of multicollinearity.
Melinda D Smith - One of the best experts on this subject based on the ideXlab platform.
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photosynthetic responses of a dominant C4 Grass to an experimental heat wave are mediated by soil moisture
Oecologia, 2017Co-Authors: David L Hoover, Alan K Knapp, Melinda D SmithAbstract:Extreme heat waves and drought are predicted to increase in frequency and magnitude with climate change. These extreme events often co-occur, making it difficult to separate their direct and indirect effects on important ecophysiological and carbon cycling processes such as photosynthesis. Here, we assessed the independent and interactive effects of experimental heat waves and drought on photosynthesis in Andropogon gerardii, a dominant C4 Grass in a native mesic Grassland. We experimentally imposed a two-week heat wave at four intensity levels under two contrasting soil moisture regimes: a well-watered control and an extreme drought. There were three main findings from this study. First, the soil moisture regimes had large effects on canopy temperature, leading to extremely high temperatures under drought and low temperatures under well-watered conditions. Second, soil moisture mediated the photosynthetic response to heat; heat reduced photosynthesis under the well-watered control, but not under the extreme drought treatment. Third, the effects of heat on photosynthesis appeared to be driven by a direct thermal effect, not indirectly through other environmental or ecophysiological variables. These results suggest that while photosynthesis in this dominant C4 Grass is sensitive to heat stress, this sensitivity can be overwhelmed by extreme drought stress.
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The effect of timing of growing season drought on flowering of a dominant C4 Grass.
Oecologia, 2016Co-Authors: John D. Dietrich, Melinda D SmithAbstract:Timing of precipitation is equally important as amount for determining ecosystem function, especially aboveground net primary productivity (ANPP), in a number of ecosystems. In tallGrass prairie of the Central Plains of North America, Grass flowering stalks of dominant C4 Grasses, such as Andropogon gerardii, can account for more than 70 % of ANPP, or almost none of it, as the number of flowering stalks produced is highly variable. Although growing season precipitation amount is important for driving variation in flowering stalk production, it remains unknown whether there are critical periods within the growing season in which sufficient rainfall must occur to allow for flowering. The effect of timing of rainfall deficit (drought) on flowering of A. gerardii, was tested by excluding rainfall during three periods within the growing season (starting in mid-April, mid-May and mid-June). Mid-summer drought (starting in mid-June) strongly reduced the flowering rate (e.g., density and biomass) of A. gerardii (e.g., as high as 94 % compared to the control), suggesting flowering is highly sensitive to precipitation at this time. This effect appeared to be related to plant water status at the time of flowering stalk initiation, rather than an indirect consequence of reduced C assimilation. Our results suggest that increased frequency of growing season drought forecast with climate change could reduce sexual reproduction in this dominant Grass species, particularly if it coincides with timing of flowering stalk initiation, with important implications for ecosystem functioning.
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resource availability modulates above and below ground competitive interactions between genotypes of a dominant C4 Grass
Functional Ecology, 2014Co-Authors: Cynthia C Chang, Melinda D SmithAbstract:Summary The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking. We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 Grass species, Andropogon gerardii, in tallGrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse. We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values (RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity. Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial Grass. Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes.
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genotypic diversity of a dominant C4 Grass across a long term fire frequency gradient
Journal of Plant Ecology, 2013Co-Authors: Cynthia C Chang, Melinda D SmithAbstract:Aims and Methods Diversity-disturbance research has focused on community diver sity, but disturbance frequency could impact diversity within species as well, with important consequences for community diversity and ecosystem function. We examined patterns of genetic diver sity of a dominant Grass species, Andropogon gerardii, in native North American tallGrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments (burned every 1, 2, 4 or 20 years) since the 1970s. In addition, we were able to assess the relationships between genetic diversity of A. gerardii, species diversity and productivity across this range of fire frequencies. Important Findings We found no significant relationships between genetic diversity of A. gerardii at the local scale (1 m 2 plot level) and disturbance frequency (burned 2 to 32 times over a 38-year period). However, at the site level (i.e. across all plots sampled within a site, ~100 m 2 ) there were differences in genotype richness and composition, as well as genomic dissimilarity among individuals of A. gerardii. Genotype richness was greatest for the site burned at an inter mediate (4-year) frequency and lowest for the infrequently (20year) burned site. In addition, genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites. Genotype composition of A. gerardii was not significantly different between the frequently burned sites (annual vs. 2 year) but did differ between frequently burned and infrequently burned sites (1 and 2 year vs. 4 and 20 year, etc.). Together, these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies, likely driven by alterations in environmental conditions. Frequent fire promotes the abundance of dominant Grass species, reduces plant community diversity and impacts ecosystem processes such as productivity. Our study suggests that genetic diversity within dominant Grass species also may be affected by disturbance frequency, which could have important implications for how species are able to respond to disturbance.
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intra specific responses of a dominant C4 Grass to altered precipitation patterns
Plant Ecology, 2013Co-Authors: Melinda D Smith, Meghan L AvolioAbstract:The mechanisms by which global change alters the genotypic structure of populations by selection remain unclear. Key to this understanding is elucidating genotype–phenotype relationships under different environmental conditions as genotypes could differ in their plasticity or in their tolerance to changing environmental conditions. We have previously observed selection of certain genotypes of the dominant C4 Grass Andropogon gerardii L. within the on-going Rainfall Manipulation Plots (RaMPs) experiment at Konza Prairie Biological Station in Kansas. The RaMPs experiment has been experimentally imposing ambient and more variable (altered) precipitation patterns since 1998. Here, we studied phenotypic differences among six genotypes to gain insight into what drove the pattern of selection previously observed and assess potential genotype × environmental interactions. In 2008 and 2009 we sampled individuals of genotypes in the RaMPs and within unmanipulated reference plots located adjacent to the RaMPs experiment. For each individual, we measured both leaf-level (specific leaf area, stomatal conductance) and whole-plant growth (height, biomass) traits. We consistently detected differences among genotypes in the reference plots. Additionally, when focusing on two genotypes found in the altered and ambient RaMPs we observed no genotype × environment interactions. Overall, we found in an intact population of A. gerardii there exists phenotypic variability among genotypes, but no genotype × environment interactions. Thus our results demonstrate that differences in plasticity of genotypes do no explain the pattern of selection we observed.
Oula Ghannoum - One of the best experts on this subject based on the ideXlab platform.
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CO2 availability influences hydraulic function of C3 and C4 Grass leaves.
Journal of experimental botany, 2018Co-Authors: Samuel H. Taylor, David T. Tissue, Michael J. Aspinwall, Chris J. Blackman, Brendan Choat, Oula GhannoumAbstract:Atmospheric CO2 (ca) has increased since the last glacial period, increasing photosynthetic water use efficiency and improving plant productivity. Evolution of C4 photosynthesis at low ca led to decreased stomatal conductance (gs), which provided an advantage over C3 plants that may be reduced by rising ca. Using controlled environments, we determined how increasing ca affects C4 water use relative to C3 plants. Leaf gas exchange and mass per area (LMA) were measured for four C3 and four C4 annual, crop-related Grasses at glacial (200 µmol mol-1), ambient (400 µmol mol-1), and super-ambient (640 µmol mol-1) ca. C4 plants had lower gs, which resulted in a water use efficiency advantage at all ca and was broadly consistent with slower stomatal responses to shade, indicating less pressure on leaf water status. At glacial ca, net CO2 assimilation and LMA were lower for C3 than for C4 leaves, and C3 and C4 Grasses decreased leaf hydraulic conductance (Kleaf) similarly, but only C4 leaves decreased osmotic potential at turgor loss. Greater carbon availability in C4 leaves at glacial ca generated a different hydraulic adjustment relative to C3 plants. At current and future ca, C4 Grasses have advantages over C3 Grasses due to lower gs, lower stomatal sensitivity, and higher absolute water use efficiency.
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Photosynthesis of C3, C3–C4, and C4 Grasses at glacial CO2
Journal of experimental botany, 2014Co-Authors: Harshini Pinto, Robert E. Sharwood, David T. Tissue, Oula GhannoumAbstract:Most physiology comparisons of C3 and C4 plants are made under current or elevated concentrations of atmospheric CO2 which do not reflect the low CO2 environment under which C4 photosynthesis has evolved. Accordingly, photosynthetic nitrogen (PNUE) and water (PWUE) use efficiency, and the activity of the photosynthetic carboxylases [Rubisco and phosphoenolpyruvate carboxylase (PEPC)] and decarboxylases [NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PEP-CK)] were compared in eight C4 Grasses with NAD-ME, PCK, and NADP-ME subtypes, one C3 Grass, and one C3-C4 Grass grown under ambient (400 μl l(-1)) and glacial (180 μl l(-1)) CO2. Glacial CO2 caused a smaller reduction of photosynthesis and a greater increase of stomatal conductance in C4 relative to C3 and C3-C4 species. Panicum bisulcatum (C3) acclimated to glacial [CO2] by doubling Rubisco activity, while Rubisco was unchanged in Panicum milioides (C3-C4), possibly due to its high leaf N and Rubisco contents. Glacial CO2 up-regulated Rubisco and PEPC activities in concert for several C4 Grasses, while NADP-ME and PEP-CK activities were unchanged, reflecting the high control exerted by the carboxylases relative to the decarboxylases on the efficiency of C4 metabolism. Despite having larger stomatal conductance at glacial CO2, C4 species maintained greater PWUE and PNUE relative to C3-C4 and C3 species due to higher photosynthetic rates. Relative to other C4 subtypes, NAD-ME and PEP-CK Grasses had the highest PWUE and PNUE, respectively; relative to C3, the C3-C4 Grass had higher PWUE and similar PNUE at glacial CO2. Biomass accumulation was reduced by glacial CO2 in the C3 Grass relative to the C3-C4 Grass, while biomass was less reduced in NAD-ME Grasses compared with NADP-ME and PCK Grasses. Under glacial CO2, high resource use efficiency offers a key evolutionary advantage for the transition from C3 to C4 photosynthesis in water- and nutrient-limited environments.
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High vapour pressure deficit and low soil water availability enhance shoot growth responses of a C4 Grass (Panicum coloratum cv. Bambatsi) to CO2 enrichment
Functional Plant Biology, 1998Co-Authors: Saman Seneweera, Oula Ghannoum, Jann P. ConroyAbstract:The hypothesis that shoot growth responses of C4 Grasses to elevated CO2 are dependent on shoot water relations was tested using a C4 Grass, Panicum coloratum (NAD-ME subtype). Plants were grown for 35 days at CO2 concentrations of 350 or 1000 µL CO2 L-1. Shoot water relations were altered by growing plants in soil which was brought daily to 65, 80 or 100% field capacity (FC) and by maintaining the vapour pressure deficit (VPD) at 0.9 or 2.1 kPa. At 350 µL CO2 L-1, high VPD and lower soil water content depressed shoot dry mass, which declined in parallel at each VPD with decreasing soil water content. The growth depression at high VPD was associated with increased shoot transpiration, whereas at low soil water, leaf water potential was reduced. Elevated CO2 ameliorated the impact of both stresses by decreasing transpiration rates and raising leaf water potential. Consequently, high CO2 approximately doubled shoot mass and leaf length at a VPD of 2.1 kPa and soil water contents of 65 and 80% FC but had no effect on unstressed plants. Water use efficiency was enhanced by elevated CO2 under conditions of stress but this was primarily due to increases in shoot mass. High CO2 had a greater effect on leaf growth parameters than on stem mass. Elevated CO2 increased specific leaf area and leaf area ratio, the latter at high VPD only. We conclude that high CO2 increases shoot growth of C4 Grasses by ameliorating the effects of stress induced by either high VPD or low soil moisture. Since these factors limit growth of field-grown C4 Grasses, it is likely that their biomass will be enhanced by rising atmospheric CO2 concentrations.
Cletah Shoko - One of the best experts on this subject based on the ideXlab platform.
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Optimal season for discriminating C3 and C4 Grass functional types using multi-date Sentinel 2 data
GIScience & Remote Sensing, 2019Co-Authors: Cletah Shoko, Onisimo Mutanga, Timothy DubeAbstract:The ability of remote sensing systems to optimally discriminate and map C3 and C4 Grass species varies over time, due to environmental changes, which influence their phenological, physiological and...
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Examining the strength of the newly-launched Sentinel 2 MSI sensor in detecting and discriminating subtle differences between C3 and C4 Grass species
ISPRS Journal of Photogrammetry and Remote Sensing, 2017Co-Authors: Cletah Shoko, Onisimo MutangaAbstract:C3 and C4 Grass species discrimination has increasingly become relevant in understanding their response to environmental changes and to monitor their integrity in providing goods and services. While remotely-sensed data provide robust, cost-effective and repeatable monitoring tools for C3 and C4 Grasses, this has been largely limited by the scarcity of sensors with better earth imaging characteristics. The recent launch of the advanced Sentinel 2 MultiSpectral Instrument (MSI) presents a new prospect for discriminating C3 and C4 Grasses. The present study tested the potential of Sentinel 2, characterized by refined spatial resolution and more unique spectral bands in discriminating between Festuca (C3) and Themeda (C4) Grasses. To evaluate the performance of Sentinel 2 MSI; spectral bands, vegetation indices and spectral bands plus indices were used. Findings from Sentinel 2 were compared with those derived from the widely-used Worldview 2 commercial sensor and the Landsat 8 Operational Land Imager (OLI). Overall classification accuracies have shown that Sentinel 2 bands have potential (90.36%), than indices (85.54%) and combined variables (88.61%). The results were comparable to Worldview 2 sensor, which produced slightly higher accuracies using spectral bands (95.69%), indices (86.02%) and combined variables (87.09%), and better than Landsat 8 OLI spectral bands (75.26%), indices (82.79%) and combined variables (86.02%). Sentinel 2 bands produced lower errors of commission and omission (between 4.76 and 14.63%), comparable to Worldview 2 (between 1.96 and 7.14%), than Landsat 8 (between 18.18 and 30.61%), when classifying the two species. The classification accuracy from Sentinel 2 also did not differ significantly (z = 1.34) from Worldview 2, using standard bands; it was significantly (z > 1.96) different using indices and combined variables, whereas when compared to Landsat 8, Sentinel 2 accuracies were significantly different (z > 1.96) using all variables. These results demonstrated that key vegetation species discrimination could be improved by the use of the freely and improved Sentinel 2 MSI data.
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Progress in the remote sensing of C3 and C4 Grass species aboveground biomass over time and space
ISPRS Journal of Photogrammetry and Remote Sensing, 2016Co-Authors: Cletah Shoko, Onisimo Mutanga, Timothy DubeAbstract:Abstract The remote sensing of Grass aboveground biomass (AGB) has gained considerable attention, with substantial research being conducted in the past decades. Of significant importance is their photosynthetic pathways (C3 and C4), which epitomizes a fundamental eco-physiological distinction of Grasses functional types. With advances in technology and the availability of remotely sensed data at different spatial, spectral, radiometric and temporal resolutions, coupled with the need for detailed information on vegetation condition, the monitoring of C3 and C4 Grasses AGB has received renewed attention, especially in the light of global climate change, biodiversity and, most importantly, food security. This paper provides a detailed survey on the progress of remote sensing application in determining C3 and C4 Grass species AGB. Importantly, the importance of species functional type is highlighted in conjunction with the availability and applicability of different remote sensing datasets, with refined resolutions, which provide an opportunity to monitor C3 and C4 Grasses AGB. While some progress has been made, this review has revealed the need for further remote sensing studies to model the seasonal (cyclical) variability, as well as long-term AGB changes in C3 and C4 Grasses, in the face of climate change and food security. Moreover, the findings of this study have shown the significance of shifting towards the application of advanced statistical models, to further improve C3 and C4 Grasses AGB estimation accuracy.