The place of C4grasses in temperate pastures in Australia

Abstract

This paper explores the potential role of summer-active C 4 grasses in temperate areas in Australia from an ecological perspective. The main functional differences between C3 and C4 plants are briefly outlined. Taken together, the characteristics and environmental requirements of introduced C3 perennial pasture cultivars lessen their natural competitive ability except in well-watered and cool habitats. C4 plants are more competitive under conditions of high temperature and solar radiation. Within the C4 group, grasses belonging to the subfamily Panicoideae usually prefer humid, wet environments and generally decline in importance with increasing grazing pressure and increased soil nitrogen (N) levels. Genera of Eragrostoideae generally prefer hot, dry habitats; they increase in dominance with increased grazing pressure and N availability. These responses give the C4 group as a whole a wider adaptive range and at the community level provide versatility in responses to changed conditions such as grazing. Based on their preferred zones of natural distribution, it appears that introduced C3 pasture species are sown widely outside the area where they would be favoured to persist. The ecological impacts of grazing by domestic livestock and pasture improvement are briefly outlined with particular emphasis on changes in botanical composition. There are similarities between changes in Australian grasslands and those reported in South Africa. It is concluded that species which naturally increase in A96012 Received 15 January 1996; accepted 10 July 1996 abundance in grazed pastures (such as some genera of Eragrostoideae) would offer considerable advantages for the development of naturally sustainable pastures. Such pasture species would offer a number of side-benefits including reduced rates of pH decline and deep drainage of excess water to water tables. These two problems represent major threats to agricultural sustainability in the temperate zone and both result from the inability of C 3 grass-based pastures to grow actively in summer.

Climate profiles of temperate C3and subtropical C4species in New Zealand pastures

“…The distinction between temperate and subtropical biology is clearly a primary functional basis for the separation of clusters, confirming the findings of previous research by indicating that the distinction between C3 and C4 photosynthesis types can be broadly used to predict the responses of plants to climate (Hattersley & Watson 1992;Johnston 1996). The cluster analysis confirmed that a large proportion of the variance in species climate envelopes can be accounted for by a division into two groupings: (i) the C3 species, and (ii) the C4 species plus R. racemosum.…”

The role of C4grasses in New Zealand pastoral systems

“…The potential for summer-active C 4 grasses to contribute to pasture production in temperate areas of Australia has been explored (Johnston & Sutherland 1996) from the ecological perspective. Given the relatively wide adaptive range of C 4 grasses, the authors concluded that they would provide versatility in responses to changed conditions such as grazing.…”

“…Extra benefits included reduced rates of both soil pH decline and deep drainage of excess water to water tables. Both occur when C 3 grasses are unable to grow in summer conditions, and they represent a major threat to the sustainability of agriculture in some areas of Australia (Johnston & Sutherland 1996).…”

Tropical Grasslands-Forrajes Tropicales Vol.5 No.1 [January 2017]

“…In temperate and subtropical areas, tropical (C4) grasses have the potential to increase forage production during summer, when growing conditions are not ideal for C3 temperate grasses (Davies and McNaughton 1980;Johnston 1996;Crush and Rowarth 2007). As well as having better growth potential, some tropical grasses have shown good adaptation to saline soils (Loch et al 2004), drought conditions (Pitman 2001), soils with low or high pH (Robinson et al 1993), infertile soils (Loch 1980), seasonal flooding (Baruch 1994;Imaz et al 2015a) and other environmental stresses, whereas temperate grasses showed poor persistence (Crush and Rowarth 2007).…”