Guy F. Midgley

Bio: Guy F. Midgley is an academic researcher from Stellenbosch University. The author has contributed to research in topics: Climate change & Biodiversity. The author has an hindex of 66, co-authored 217 publications receiving 30649 citations. Previous affiliations of Guy F. Midgley include University of Cape Town & International Union for Conservation of Nature and Natural Resources.

Interactive effects of photon fluence rates and drought on CAM‐cycling in Delosperma tradescantioides (Mesembryanthemaceae)

Abstract: The ability of photosynthesis and CAM to acclimate to low (220 μmol m -2 s -1 ; LL) and relatively high (550 μmol m -2 s HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of C0 2 gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (A-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO 2 uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (F V /F m ). Non-photochemical quenching (q N ) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in q N resulted mainly from the change in its fast-relaxing component (q NF ), while the slow component (q Ns ) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO 2 .

Photosynthetic responses to CO2 concentration and photon fluence rates in the CAM-cycling plant Delosperma tradescantioides (Mesembryanthemaceae)

Abstract: summary Responses of gas exchange and photosynthesis to changes in CO # concentration and PPFD were examined in well watered plants of Delosperma tradescantioides Bgr to establish the relative importance of these environmental changes on the photosynthetic machinery in this CAM-cycling species which grows naturally in both exposed and partly shaded environments Plants were grown at two PPFDs (220 [LL] and 550 [HL] lmol m’# s’") HL plants had larger leaves with higher specific weight, water content and diurnal malic acid fluctuation Photosynthetic PPFD responses were typically those of sun and shade species for HL and LL plants, both under 21% O # and non-photorespiratory (2% O # ) conditions The CO # compensation point in the absence of non-photorespirational CO # evolution in the light (Ck) was c 3 0 lmol mol’" Irradiation reduced mitochondrial respiration by " 50% Comparison of the PPFD responses of linear electron flow rates derived from gas exchange measurements and from fluorescence analysis (J F ) indicated eective photosynthetic control J F was always larger than electron flow rates calculated from gas exchange, indicating that processes other than carboxylation and oxygenation were consistently important in energy consumption under all sampled environmental conditions Regardless of PPFD during growth, electron flow to carboxylation and J F were linearly correlated, demonstrating that the photosynthetic apparatus was well adapted to PPFD during growth In HL plants, non-photochemical quenching increased, and photochemical quenching and the quantum yield of linear electron transport through PS II decreased more slowly with increasing PPFD than in LL plants In plants of both treatments non-photochemical energy dissipation seemed to be exhausted when the proportion of photons not utilizable by photochemistry exceeded 0‐7 Results illustrate a pronounced ability of D tradescantioides to acclimate to a 100% change in the prevailing PPFD and lend support to the hypothesis that CAM cycling might act as a photoprotective process

Ecosystem Response to Elevated CO2: Nutrient Availability and Nutrient Cycling

Abstract: Atmospheric CO2 levels have risen from an estimated preindustrial concentration of 280µLL-1 (Friedli et al., 1986; Neftel et al., 1985) to 350µLL-1 today (Boden et al., 1990) and, even using conservative assumptions regarding future energy sources, could increase to 600 µLL-1 by the end of the next century (Ausubel et al., 1988). The increase in agricultural crop yield which could result from a doubling of preindustrial CO2 levels has been suggested to be in the range of 30–40% (Kimball, 1983; Cure and Acock, 1986). However, natural ecosystem responses to increasing atmospheric CO2 levels are more difficult to predict, as their mechanistic basis remains poorly understood (Bazzaz, 1990), especially in terms of system processes and interactions between system components (Morison, 1990). Such an understanding depends heavily on the elucidation of the linkages between plant carbon uptake, carbon allocation, and nutrient cycling. Because these processes interact, disruption of any one often induces changes in others, which then leads to either positive reinforcement or negative feedback at the ecosystem level. This interaction is critical for the ultimate structural, functional, and floristic nature of the altered ecosystem. Natural ecosystems of certain Mediterranean climate regions have been shown to be altered substantially by changes in nutrient availability (Specht, 1963) in terms of species composition and system functioning, and it appears that rising atmospheric C02 levels may hold a similar threat, but at a global scale.

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Abstract: Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides, a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (≅ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C3 gas exchanges when well-watered to water-conserving CAM-idling during drought.

Food Security: The Challenge of Feeding 9 Billion People

Abstract: Continuing population and consumption growth will mean that the global demand for food will increase for at least another 40 years. Growing competition for land, water, and energy, in addition to the overexploitation of fisheries, will affect our ability to produce food, as will the urgent requirement to reduce the impact of the food system on the environment. The effects of climate change are a further threat. But the world can produce more food and can ensure that it is used more efficiently and equitably. A multifaceted and linked global strategy is needed to ensure sustainable and equitable food security, different components of which are explored here.

Novel methods improve prediction of species' distributions from occurrence data

Abstract: Prediction of species' distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species' distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species' occurrence data. Presence-only data were effective for modelling species' distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.

Extinction risk from climate change

Abstract: Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.