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• W3043985696 abstract "Climate variability and extreme climate events such as heat waves, droughts, extreme precipitation and frost occurrences are increasingly challenging the agricultural systems in Australia and globally. Despite this, the majority of the previous climate change studies have focused on the influence of average climate change on agricultural systems, which risks underestimating the impacts of climatic changes. In south eastern (SE) Australia, climate variability has increased in recent decades accompanying an increased frequency and severity of extreme climate events such as heat waves and droughts. The objective of this research was to investigate the impacts of changing climate variability and extreme climate events on pasture systems in SE Australia using biophysical modelling and controlled experimental approaches.Year to year variability in pasture yields has many consequences on the key management decisions such as stocking rates and the timing of the reproductive cycle. Changes to the pasture growth patterns were investigated at five sites in SE Australia ranging from medium rainfall, warm temperate climate at Wagga Wagga in southern New South Wales to high rainfall, cool temperate climate at Elliott in Tasmania using DairyMod biophysical software over the period 1960-2015. Across the sites, winter production has increased, spring pasture growth has decreased and year to year yield variability during autumn and spring seasons has increased in the most recent period (2002-2015) compared to 1988-2001. Increased number of days with water and temperature limitation together with increased spring and summer soil moisture deficit are in line with the simulated changes in pasture growth patterns, suggesting that adaptations such as incorporating deep rooting and heat tolerant species should be prioritized to stabilize pasture production.The year to year variability in pasture yield was better explained when extreme climate indices were used in combination with climate averages, as compared with climate average alone. Extreme climate indices together with the average climate variables explained more yield variability at the medium rainfall sites (eg. Wagga Wagga R2=0.89) than high rainfall sites (eg. Elliott R2=0.70) indicating that medium rainfall sites are more sensitive to the changes in rainfall distribution and high temperatures. Increased occurrences of dry months, wet months during the winter and spring, number of hot days above 30 C and the duration of hot days in a year decreased pasture yields highlighting the importance of considering extreme climate events in future climate change studies on agricultural systems.El-Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are two major rainfall drivers that influence rainfall variability in Australia and their phases reach the peak during the spring season which is the major pasture growing season in SE Australia. Each driver has a dry and hot phase (El-Nino and IOD(+)) and a cool and wet phase (La-Nina and IOD(-)). The influence of these phases individually and in combination were investigated on simulated annual pasture production from 1950-2015 in five sites in SE Australia. In dry and hot phases of both of ENSO and IOD (El-Nino and IOD(+)), lower pasture production was simulated, while the phases responsible for the wet and cool climate increased the yield. When combined ENSO-IOD phases were examined, the highest yields resulted when the La-Nina phases coincided with IOD(-) or neutral, whilst the El-Nino with IOD(+) phases led to the lowest yields. Forecast analysis revealed that the effects of climate driver phases emerge at the end of winter, but this is not a sufficient lead time for making important pasture management decisions. Therefore, further studies are warranted to increase the forecast ability of each climate driver phase to use them in agriculture decision making.Climate models project increased frequency of extreme climate events in SE Australia in the future. A controlled environmental experiment was conducted to investigate growth and physiological responses of four summer active temperate perennial pasture species to consecutive 7-day heat and drought stresses. Exposure of perennial ryegrass, tall fescue, cocksfoot and chicory to consecutive moderate (30/20 C, day/night) and severe (35/25 C, day/night) heat and drought stress revealed that all the species can acclimate to moderate combined heat and drought stress by maintaining the physiological functions such as photosynthesis, maximum photochemical efficiency of photosystemII, cell membrane permeability and relative leaf water content. However, chicory was the only species that maintained the above physiological processes under consecutive severe heat and drought stresses while all grass species decline to the minimum values. Plants that were irrigated showed cooler canopies than non-irrigated plants during high temperature treatments and this transpirational cooling mitigated the impacts of heat stress in all species.Leaf temperature data measured using infrared images during the experiment were used to validate the leaf energy budget equation and the calculated leaf temperatures (using the energy budget) were used to model heat stress impacts on perennial ryegrass in DairyMod model. The leaf temperature calculation incorporates the interaction of air temperature and soil water through the feedback effects of transpiration through stomata. The simulations run with calculated leaf temperatures predicted the observed reduction of photosynthesis accurately while air temperature simulations overestimatedthe actual impacts under moderate temperature, indicating that leaf temperature more accurately represents the environment under which plants are grown under heat stress rather than air temperature. Further, the DairyMod high temperature stress recovery function (T sum) for perennial ryegrass was parameterized using measured data of the experiment. The findings demonstrated that simulations of DairyMod can be improved using leaf temperature and parameterizing heat stress recovery functions.In conclusion, this research highlighted that the climate variability and extreme events have changed the pasture growth patterns in SE Australia in the recent period (2002-2015) therefore, climate variability and extreme climate events need to be fully considered in the future climate change studies. Chicory may be a more adapted pasture species in temperate livestock areas where extreme summer heat and moisture stresses limit summer feed supply. Leaf temperature modelling improves the heat stress simulations in the DairyMod model and this approach can also be used in other cropsimulation models to improve high temperature stress modelling. Future research should aim to identify the plant traits and key metabolic processes in Chicory that confer greater heat stress tolerance and what other species would have similar traits. Future research on climate change impacts should also aim to determine critical combinations of extreme events that would result in tipping points for farming systems." @default.
• W3043985696 created "2020-07-29" @default.
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• W3043985696 date "2020-01-01" @default.
• W3043985696 modified "2023-09-27" @default.
• W3043985696 title "Impacts of changing climate variability and extremes on pasture systems in south eastern Australia" @default.
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