Physiology of plants and climate change

I thought it would be interesting to look at plants at a physiological level to see what impact climate change is having on them. This is of great importance for farmers and scientists to assess how crops may adapt to climate change and this is likely to have implications for crop yields and the management of farms into the future. Climate change brings about changes in temperature, atmospheric carbon dioxide levels and rainfall levels and frequency. These have impacts on the physiology of plants in a variety of different ways.

C₃ and C₄ crops

Below shows the two different forms of uptake of carbon dioxide by plants. The majority of plants fix the atmospheric carbon dioxide with the C₃ pathway such as wheat, rice and soybean. The C₄ pathway is where carbon dioxide is concentrated internally. There are fewer plants that use the C₄ pathway, these include maize, sorghum and sugarcane. The process of photorespiration, which occurs alongside photosynthesis, is where plants take up some oxygen and release some CO₂ back to the atmosphere. Photorespiration occurs more in C₃ plants as the rate of photorespiration in C₄ plants is almost zero. The impact of climate change is therefore more likely to be on C₃ crops with increased photosynthesis due to higher CO₂ levels as well as a suppressed oxygenation process. The C₄ crops are less likely to respond to changes in CO₂ because ‘these plants have an internal mechanism that concentrates CO₂ internally.'

Figure 1: C₃ and C₄ plants

Energy balance

Under the influence of climate change, the net energy balance of plant leaves will change. Increases in temperature will lead to a greater loss of water because of a vapour pressure deficit. This will increase the amount of water lost by plants and the amount of water the plant consumes to meet these losses. Despite this, rises in atmospheric carbon dioxide would actually decrease the amount of water lost by leaves because stomatal conductance would decrease as a result of these stomata remaining openfor a shorter period of time. The actual amount of water used by the plant will still be reliant on the amount of water supplied to the leaf through precipitation and irrigation. This means that the frequency of rainfalls and the availability of irrigation are still very important to crop growth.

Soil surface wetness

In areas where there is low canopy cover, such as large crop fields, soil surface wetness determines the amount of water used. If the surface of the soil is dry, this increases water consumption as there is a higher vapour pressure deficit. This subjects crops to harsher conditions which negatively impacts growth. In hot African regions such as the Sahel, this is likely to be a key issue and with the impacts of climate change into the future, the demand for water for crops is expected to increase. With rainfall also becoming more sporadic and intense, the need for irrigation techniques is greater than ever.

Impacts for farmers and the provision of food in Africa

A study in southern Africa investigated the response of crops to climate change. The paper suggested that the positive effects of carbon dioxide may be able to offset the potential negative impacts on crops of climate change. These feedbacks are important to consider and because they are highly spatial variable, it is very difficult to predict the impacts. This study also suggested that by the time we reach the latter half of the 21^st century, the fertilising effects of carbon dioxide may not be able to make up for the other negative effects. Therefore climate change may have a more long term impact on crop yields and the system may actually be able to adapt in the short term.

I believe this post has emphasised the importance of effective irrigation in Africa. There are a variety of physiological changes to plants caused by climate change and these are more likely to affect future food scarcity than existing scarcity. To adapt to increasing water loss, crops will need to be irrigated more intensively but this requires access to sufficient water resources and the technology to extract it.