Primarily as a result of fossil fuel burning, the amount of CO2 in the atmosphere continues to rise far above pre-industrial concentrations of 280 parts per million (ppm)– it is currently around 422 ppm and increasing by about 2.5 ppm per year. Increasing CO2 concentrations influences plant growth and water use, with potential important and wide- reaching consequences for ecosystem function including carbon storage.
Work involving Manaaki Whenua’s scientists has been underway since the 1990s to quantify the effects of rising CO2 on plant growth. At a field site near Bulls in the Rangitikei, established in 1997 by AgResearch, pasture productivity under elevated CO2 levels (via free-air CO2 enrichment) has been consistently monitored and measurements of soil carbon were also made. This was the longest-running study of CO2 enrichment in a grazed pasture system (23 years) making it unique. Measurements revealed that elevated CO2 increased pasture
production by about 10% but there was no detectable effect on soil carbon stocks. Aligned modelling also showed increased pasture production but minimal changes in soil carbon stocks.
Our researchers have also recently completed a wide-ranging review and modelling study for the Ministry for Primary Industries (MPI) on the potential effects of rising CO2 concentrations on forest growth (Pinus radiata) in New Zealand. Simulated responses to CO2 concentrations of 800 ppm at 25°C were translated into minor growth stimulations and minor increases in future carbon storage potential, notably in currently wetter and colder parts of the country. However, limiting factors brought about by climate change, such as acute water limitation and nutrient availability, would act to reduce these gains.
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