Vertical and Diurnal Profiles of Atmospheric Carbon Dioxide Concentrations in Manawatu, New Zealand

Carbon dioxide concentrations were monitored at 2 heights above pasture, at Flock House, New Zealand using an infrared gas analyzer attached to a multiport sampler, Characteristic profiles for a calm day and a windy day are presented. At low wind speeds there was a marked diurnal cycle in CO2 concentration with a maximum difference of 336 ppm between day and night concentrations. An elevated CO2 concentration· was evident for some hours after sunrise. At higher wind speeds the CO2 cycle was less marked, with only a 20 ppm difference between day and night levels. At times, plants are exposed to much higher levels of CO2 than the mean ambient level; much more information is needed on the effects of vertical and diurnal gradients of CO2 on plant growth and how these gradients may change as the mean ambient concentration increases.