Farming systems adaptations to climate change and extreme climatic events
Creators: name: Liu, K
Publisher: name: University Of Tasmania
Year: 2023

description: Securing global food supply under increasingly variable climates will be one of the grandest challenges facing humanity in the 21st century. Increased frequencies and intensities of extreme temperature and rainfall will have ramifications for the production environments of most crops, including barley, which globally is the fourth most prevalent cereal crop. There is thus an urgent need to develop adaptations that reverse adverse climate change effects on the productivity of barley crops. This is particularly so in Australia, where the rate of genetic yield gain of cereals is amongst the lowest in the world, primarily due to challenging climatic conditions. <br> This thesis investigated strategies for mitigating detrimental effects of current and future climate change on barley production at a global scale, with special attention on Australia. Adaptation strategies included systemic changes in agronomy (e.g. altering flowering time through sowing time or genotypic duration) and improving genetic tolerance by breeding to allow successful cultivation under likely future environmental conditions. Field experiments were conducted at representative sites in Western Australia and Tasmania, where summer conditions are forecast to become hotter during the 21st century. <br> A modelling study (Chapter 3) identified optimal sowing and flowering times for rainfed barley in water limited environments throughout the Australian barley growing regions. A genotype × environment × management (G×E×M) factorial analysis showed that optimal flowering periods (OFP) were driven by environmental conditions more so than the genotype such that the relative importance of solar radiation, frost, heat and water stresses varied significantly with location. The OFP was earlier (mid-August to late-September) in Western Australia and South Australia, while OFPs were generally later (mid-October to mid-November) in Tasmania and Victoria. Knowledge of OFPs based on long-term abiotic stresses will allow breeders to develop genotypes with phenological durations that are pertinent to each location. Better knowledge of OFPs will also allow growers to match genotype with sowing time for their location/s, minimising the combined risk of frost, heat and water stresses. Collectively, these adaptations would be expected to be conducive to increased maximum yield potential. <br> A little explored area associated with impacts of extreme climatic events on cropping systems is that related to waterlogging. To address this knowledge deficit while also quantifying OFPs in waterlogging-prone regions, controlled-environment experiments (Chapter 4) were conducted with a range of modern barley genotypes differing in their waterlogging tolerance. In these experiments, the extent to which yield was dictated by the timing and duration of waterlogging stress relative to crop phenology was examined. It was found that crop heading was the most susceptible period to waterlogging, with yield losses during this period primarily attributed to reductions in spikelet fertility and grain weight. At earlier stages, yield loss caused by waterlogging were primarily caused by reduced spike number and to a lesser extent kernels per spike. Phenology was delayed 1-8 Zadok stages at the end of waterlogging treatments, with the waterlogging-susceptible cultivar Franklin showing the greatest delays in crop development. <br> Chapter 4 provided a solid foundation for the derivation and improvement of the internationally-renowned systems model APSIM in Chapter 5. To account for physiological effects of waterlogging on phenology and photosynthesis, new algorithms were developed for commercial Australian barley genotypes and coded within APSIM. The improved version of the model was used to conduct a genotype by environment by management analysis (G×E×M) that was used to examine the effects of soil type, phenology and genotypic tolerance to waterlogging on crop development and yield under current and future climates. It was shown that climate change will reduce waterlogging stress and shift forward OFPs significantly (26 days earlier on average across locations) under the emissions scenario RCP8.5 at 2090. While waterlogging stresses diminished, alleviation of this stress was unable to prevent yield reduction due to severe high temperature stress exposure (−35% average reduction in yield across locations, genotypes and sowing dates). Chapter 5 also showed that seasonal waterlogging stress patterns under future conditions will be similar to those occurring historically. Earlier sowing and adoption of waterlogging tolerant genotypes alleviated yield penalty caused by waterlogging by up to 26% and 24% under historical and future climates. <br> To understand how climate changes affect global barley production and the timing and magnitude of waterlogging stresses (Chapter 6), rainfed barley cropping systems were simulated on a global scale using the improved version of APSIM to investigate the risk posed by soil waterlogging on crop production. A new paradigm was used to classify the typology and frequency of waterlogging-stress across environments using statistical clustering. This process was conducted using 4,104 global simulations from 27 global climate models, 38 sites, 2 genetic traits, and 2 management inputs of sowing date for RCP8.5 at mid- and end-century. Using the new paradigm it was shown that extreme waterlogging stress will cause large reductions in barley yields at the global scale, even though typologies of waterlogging stress under future climates were relatively similar to those occurring historically. Application of our new paradigm reveals that averaged yield penalty caused by waterlogging ranged by up to 3-11% across GCMs, sites and climate horizons. Holistic systems adaptations such as altering sowing time and planting waterlogging tolerant genotypes mitigate yield penalty caused by future waterlogging up to 14%. We uncover a dangerous shift of waterlogging typologies under future climates towards flowering time. This may have serious implications, because cereals are highly sensitive to waterlogging during their reproductive phase. We highlight the serendipitous outcome wherein future waterlogging typologies will be similar to those occurring in the recent past, suggesting that adaptations designed today will also suited future agricultural systems, provided adaptations are applied within the same typology.