Sunlight is essential to plants as the main energy source for photosynthesis, yet excess light that cannot be processed in photosynthesis can be damaging. Australian plants are regularly exposed to very intense light, enriched in ultraviolet (UV) radiation, placing them at direct risk of photodamage. Low inorganic phosphate (Pi) availability, characteristic of Australian soils, can reduce the energy threshold of photosynthesis and exacerbate photodamage. Whilst intense light and low Pi are common in Australian ecosystems, relatively little is known about the strategies generalist plant species use to overcome these stressful conditions. This thesis addresses this gap in scientific knowledge, increases general understanding of plant stress responses and identifies traits associated with stress tolerance that could be exploited in future crops.
This thesis investigates the individual and combined impacts of solar UV, light intensity and Pi availability on plant physiology, development and biochemistry in native and domesticated Australian plants. Spectral screens allowed assessment of plant responses to solar UV components; short-term responses to changes in Pi availability were investigated by adding exogenous P, and biochemical strategies to tolerate long-term Pi limitation were ascertained by using paired sub-alpine ecosystems with naturally contrasting availability of Pi.
Throughout the studies reported in this thesis, it was clear that both native and agricultural plants have evolved strategies to cope with intense light and soils lacking in phosphorus. The biggest distinction was that these adaptive responses were adequate to alleviate potential reductions in photosynthetic rate for crop species, yet in native plants these responses reduced rates of photosynthesis. From an agricultural perspective, this suggests that genetically inherited traits from native plants could increase tolerance to environmental stress in crop species but at a cost to plant productivity.