text: Factors which influence this include the atmospheric abundance of the two gases, the supply of the gases to the site of fixation (i.e. in land plants: whether the stomata are open or closed), the length of the liquid phase (how far these gases have to diffuse through water in order to reach the reaction site). For example, when the stomata are closed to prevent water loss during drought: this limits the  supply, while  production within the leaf will continue. In algae (and plants which photosynthesise underwater); gases have to diffuse significant distances through water, which results in a decrease in the availability of  relative to . It has been predicted that the increase in ambient  concentrations predicted over the next 100 years may lower the rate of photorespiration in most plants by around 50%. However, at temperatures higher than the photosynthetic thermal optimum, the increases in turnover rate are not translated into increased  assimilation because of the decreased affinity of Rubisco for .