Since the late Miocene, plants using the C4 photosynthetic pathway have increased to become major components of many tropical and subtropical ecosystems. However, the drivers for this expansion remain under debate, in part because of the varied histories of C4 vegetation on different continents. Australia hosts the highest dominance of C4 vegetation of all continents, but little is known about the history of C4 vegetation there. Carbon isotope ratios of plant waxes from scientific ocean drilling sediments off north‐western Australia reveal the onset of Australian C4 expansion at ~3.5 Ma, later than in many other regions. Pollen analysis from the same sediments reveals increasingly open C3‐dominated biomes preceding the shift to open C4‐dominated biomes by several million years. We hypothesize that the development of a summer monsoon climate beginning in the late Pliocene promoted a highly seasonal precipitation regime favorable to the expansion of C4 vegetation.
The photosynthetic pathway of plants is a fundamental trait that influences terrestrial environments from the local to global level. The abundance of different photosynthetic pathways in Australia is expected to undergo a substantial shift due to climate change and rising atmospheric CO2; however, tracking change is hindered by a lack of data on the pathways of species, as well as their distribution and relative cover within plant communities. Here we present the photosynthetic pathways for 2428 species recorded across 541 plots surveyed by Australia’s Terrestrial Ecosystem Research Network (TERN) between 2011 and 2017. This dataset was created to facilitate research exploring trends in vegetation change across Australia. Species were assigned a photosynthetic pathway using published literature and stable carbon isotope analysis of bulk tissue. The photosynthetic pathway of species can be extracted from the dataset individually, or used in conjunction with vegetation surveys to study the occurrence and abundance of pathways across the continent. This dataset will be updated as TERN’s plot network expands and new information becomes available. This manuscript is currently in review with the journal "Scientific Data" and was submitted on 17/11/2020
Numerous studies have analysed the relationship between C4 plant cover and climate. However, few have examined how different C4 taxa vary in their response to climate, or how environmental factors alter C4:C3 abundance. Here we investigate (a) how proportional C4 plant cover and richness (relative to C3) responds to changes in climate and local environmental factors, and (b) if this response is consistent among families. Proportional cover and richness of C4 species were determined at 541 one-hectare plots across Australia for 14 families. C4 cover and richness of the most common and abundant families were regressed against climate and local parameters. C4 cover and richness in Poaceae and Cyperaceae were strongly positively correlated with January temperatures, however C4 Cyperaceae occupied a more restricted temperature range. C4 Poaceae cover was also correlated with seasonal rainfall, but no such trends were identified in Cyperaceae. Soil pH and tree cover modified relative C4 cover in these families. Proportional C4 Euphorbiaceae and Chenopodiaceae cover and richness were weakly correlated with climate, but were more strongly influenced by local environmental factors, including tree cover and soil texture. However, the explanatory power of C4 Euphorbiaceae and Chenopodiaceae models were poor. Results demonstrate the unique relationships between different C4 taxa and climate, and the significant modifying effects of environmental factors on C4 distribution. Our work also reveals C4 families will not exhibit consistent responses to perturbations in climate or local conditions. These results have substantial implications for predicting C4 cover over global, continental and regional areas. This preprint is current under review following revisions with the journal Oecologia.
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