6 research outputs found
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Climate change impacts on cacao: genotypic variation in responses of mature cacao to elevated CO2 and water deficit
Climate change poses a significant threat to agricultural production in the tropics, yet
relatively little research has been carried out to understand its impact on mature tropical tree
crops. This research aims to understand the genotypic variation in growth and photosynthesis
in mature cacao trees in response to elevated CO2 and water deficit. Six genotypes were grown
under greenhouse conditions at ambient (ca. 437 ppm) and elevated CO2
(ca. 724 ppm) and under
well-watered and water deficit conditions for 23 months. Leaf- and canopy-level photosynthesis,
water-use efficiency, and vegetative growth increased significantly in response to elevated CO2
. Water
deficit had a significant negative effect on many photosynthetic parameters and significantly reduced
biomass production. The negative effect of water deficit on quantum efficiency was alleviated
by elevated CO2
. Genotypic variation was observed in several parameters including stomatal
conductance, stomatal density and index, quantum efficiency, and biomass production, indicating
the potential to develop more climate-change-resilient genotypes that can cope with predicted future
climate change conditions. Elevated CO2 reduced some of the negative effects of water deficit through
changes in water-use efficiency and light utilisation and reduced the negative impact of water deficit
on biomass accumulation, but this was genotype-specific
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Cocoa plant productivity in West Africa under climate change: a modelling and experimental study
The potential effect of climate change on regional suitability for cocoa cultivation is a serious economic concern for West Africa - especially for Ghana and CoÌte dâIvoire, whose cocoa cultivation accounts for respectively ~19% and ~45% of world production. Here, we present a modelling and observational study of cocoa net primary productivity (NPP) in present day and future West African climates. Our analysis uses a data assimilation technique to parameterise a process-based land-surface model. The parameterisation is based on laboratory observations of cocoa, grown under both ambient and elevated CO . Present day and end of 21st century cocoa
2
cultivation scenarios are produced by driving the parameterised land-surface model with output
from a high-resolution climate model. This represents a significant advance on previous work, because unlike the CMIP5 models, the high-resolution model used in this study accurately captures the observed precipitation seasonality in the cocoa-growing regions of West Africa - a key sensitivity for perennials like cocoa. We find that temperature is projected to increase significantly and precipitation is projected to increase slightly, although not in all parts of the region of interest. We find, furthermore, that the physiological effect of higher atmospheric CO2 concentration ameliorates the impacts of high temperature and variation in precipitation thereby reducing some of the negative impacts of climate change and maintaining net primary productivity in West Africa, for the whole 21st Century, even under a high emissions scenario. Although NPP is an indicator of general vegetation condition, it is not equivalent to yield or bean quality. The study presented here is, nevertheless, a strong basis for further field and modelling studies of cultivation under elevated CO2 conditions
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The physiological responses of cacao to the environment and the implications for climate change resilience. A review
Cacao (Theobroma cacao L.) is a tropical perennial crop which is of great economic importance to the confectionary industry and to the economies of many countries of the humid tropics where it is grown. Some recent studies have suggested climate change could severely impact cacao production in West Africa. It is essential to incorporate our understanding of the physiology and genetic variation within cacao germplasm when discussing the implications of climate change on cacao productivity and developing strategies for climate resilience in cacao production.
Here we review the current research on the physiological responses of cacao to various climate factors. Our main findings are 1) water limitation causes significant yield reduction in cacao but genotypic variation in sensitivity is evident, 2) in the field cacao experiences higher temperatures than is often reported in the literature, 3) the complexity of the cacao/ shade tree interaction can lead to contradictory results, 4) elevated CO2 may alleviate some negative effects of climate change 5) implementation of mitigation strategies can help reduce environmental stress, 6) significant gaps in the research need addressing to accelerate the development of climate resilience. Harnessing the significant genetic variation apparent within cacao germplasm is essential to develop modern varieties capable of high yields in non-optimal conditions. Mitigation strategies will also be essential but to use shading to best effect shade tree selection is crucial to avoid resource competition. Cacao is often described as being sensitive to climate change but genetic variation, adaptive responses, appropriate mitigation strategies and interactive climate effects should all be considered when predicting the future of cacao production. Incorporating these physiological responses to various environmental conditions and developing a deeper understanding of the processes underlying these responses will help to accelerate the development of a more resource use efficient tree ensuring sustainable production into the future
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A physiological model to quantify impacts of climate change variables on cocoa productivity
Climate change has the potential to alter cocoa production through, for example, changes in rainfall patterns (more intense droughts and/or more intense wet seasons), higher temperatures and increased carbon dioxide concentrations. A crop modelling approach allows prediction of yield changes in relation to climate events and quantification of interventions designed to ameliorate such changes (e.g. use of overhead shade or planting of different cocoa varieties more adapted to climate change).
A physiological model is described that is parameterised using experimental data collected under controlled environment conditions. The model is compartmentalised into interacting modules that include assimilation of carbohydrates through canopy photosynthesis, respiration, partitioning of assimilates between vegetative and reproductive growth, partitioning of assimilates within the pod and the dynamics of pod-setting and wilting. Canopy photosynthesis is calculated from the parameters of photosynthetic light response curves of genotypes, specified by the user, and the properties of the canopy (leaf area index and light attenuation through the canopy, quantified as the extinction coefficient). Environmental parameters that can be modulated in the model include carbon dioxide concentration, soil water content, air temperature, vapour pressure deficit and solar radiation. These parameters then influence the outputs of the different modules, for example temperature impacts on photosynthetic rate and also on the amount of cherelle wilt.
A range of model simulations are presented on the impacts of elevated CO2 concentration, increases in temperature, water deficit and their interaction on productivity and yield. The potential impact of interventions such as changing variety and use of overhead shade in ameliorating the effects of climate change is also discussed
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Combined effects of elevated [CO2] and increased temperatures on cacao reproductive development
Climate change is leading to increased temperature worldwide, however the impact of this on crops needs to be considered in conjunction with accompanied increases in CO2 concentration ([CO2]). This study examined the combined effects of elevated [CO2] and increased temperature on pollen viability, pod set, pod growth and bean yield in cacao. All pods were established by hand pollination. Mature cacao trees of three genotypes (CCN 51, SCA 6, and T 85/799) were grown in a six compartment, controlled environment glasshouse adapted for cacao studies under non-limiting water and nutrient supply. Trees were exposed to three day/night temperatures; 31/22°C (Tc), 33.5/24.5°C (Tc+2.5°C) and 36/27°C (Tc+5.0°C) combined with two [CO2] treatments; ambient (ca. 437 ppm) and elevated (ca. 693 ppm) in a factorial design for 553 days. The control temperature regime (Tc) was based on temperatures that are common for West African cacao regions.
Pollen germination and pollen tube length were negatively affected by a 5°C increase in temperature; this was particularly evident for SCA 6 and T 85/799. However, elevated [CO2] largely compensated the negative effect of high temperature in all three genotypes. The percentage of pods set decreased with an increase in temperature, and the highest percentage of wilted pods was observed at 33.5/24.5°C. However, elevated [CO2] enhanced pollination success and pod set, and reduced the percentage of pods wilted across all temperatures. At ambient [CO2], pod size declined with increases in temperatures, whereas at elevated [CO2] an increase in temperature resulted in larger pods in CCN 51 and little change for SCA 6. A similar trend was observed for pod dry weight. A positive effect of elevated [CO2] on individual bean dry weight was observed at the higher temperatures for CCN 51, whereas little effect was seen in SCA 6.
For most of the reproductive components studied here, it can be concluded that elevated [CO2] mitigates to a greater or lesser extent the negative effect of elevated temperatures. Pod growth and bean yield were more responsive to elevated [CO2] under warm conditions in CCN 51 than SCA 6 suggesting there is some scope for selecting genotypes better suited to a changing climate
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Effects of simulated climate change conditions of increased temperature and [CO2] on the early growth and physiology of the tropical tree crop, Theobroma cacao L.
Despite multiple studies of the impact of climate change on temperate tree species, experiments on tropical and economically important tree crops such as cacao (Theobroma cacao L.) are still limited. Here, we investigated the combined effects of increased temperature and [CO2] on the growth, photosynthesis, and development of juvenile plants of two contrasting cacao genotypes: SCA 6 and PA 107. The factorial growth chamber experiment combined two [CO2] treatments (410 and 700 ppm) and three day/night temperature regimes (control: 31/22°C, control+2.5°C: 33.5/24.5°C, and control+5.0°C: 36/27°C) at a constant vapour pressure deficit of 0.9 kPa. At elevated [CO2], final dry weight, total and individual leaf area increased in both genotypes, whilst duration for individual leaf expansion declined in PA 107. For both genotypes, elevated [CO2] also improved light-saturated net photosynthesis (Pn) and intrinsic water-use efficiency (iWUE), whereas leaf transpiration (E) and stomatal conductance (gs) decreased. Under a constant low vapour pressure deficit, increasing temperatures above 31/22°C enhanced rates of Pn, E, gs, in both genotypes suggesting that photosynthesis responds positively to higher temperatures than previously reported for cacao. However, dry weight, total and individual leaf area declined with increases in temperature being more evident in SCA 6 than PA 107, suggesting the latter genotype was more tolerant to elevated temperature. Our results suggest that the combined effect of elevated [CO2] and temperature is likely to improve the early growth of high temperature-tolerant genotypes, while elevated [CO2] appeared to ameliorate the negative effects of increased temperatures on growth parameters on more sensitive material. The evident genotypic variation observed in this study, demonstrates scope to select and breed cacao varieties capable of adapting to future climate change scenarios