Ecophysiological responses of Brazilian cerrado invasive grasses to increases in CO2 concentration and temperature

Global climate changes and biological invasions are environmental disturbances that may interact synergistically, causing loss of biodiversity. The Brazilian Cerrado is a fragile environment which is greatly affected by anthropic actions. Much of its natural biodiversity has been lost because of spreading African grasses that have gradually replaced its landscapes and this problem is likely to be compounded by climate change. Since most invasive plant species have C4 photosynthetic pathway, many studies focused on understanding how these species respond to elevated CO2 and temperature. This study aimed to evaluate ecophysiological responses of three invasive African grasses that are more threatening to Brazilian Cerrado biodiversity: Urochloa brizantha, Urochloa decumbens and Megathyrsus maximus. For this purpose, the early stages of development, growth, photosynthetic and biochemical responses to increasing CO2 and temperature, and the protoplasmatic tolerance of plants grown under these conditions to acute thermal and water stress were investigated. The results obtained indicate that climate changes affect these species in all developmental stages investigated and in all levels, from protoplasm to whole plant. U. brizantha and U. decumbens were affected from the moment of emergence but only M. maximus was affected after seedlings establishment. All the three species had improved water use efficiency under elevated CO2 and this increase also enhanced photosynthetic assimilation of U. brizantha and M. maximus and growth of M. maximus. Carbohydrate content of M. maximus plants was also affected, non-structural carbohydrates being more sensitive to climate changes than cellulose. Lignin content was affected by all environmental treatments, but only for U. brizantha plants. Despite the little positive responses during growth, increase in CO2 and temperature improved U. decumbens protoplasmic responses to water deficit, and increase in CO2 improved its acute heat shock tolerance. Taken together, the results indicate that the effects of increased CO2 and temperature are speciesspecific and highlight that all of the three species could benefit in some way by the climate changes foreseen for 2100. It is imperative to investigate native species responses as well as other invasive species co-occurring in the same environment to assess whether the invasive potential of these species could increase, and to what extent this could be an even greater threat to the biodiversity of the Cerrado.

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