The role of plants in the ecosystem has been known from time immemorial. Being the primary producers in any food chain, all the animals within an ecosystem depend directly or indirectly on the energy from plants. This enormous task of generating food nutrients for energy supply in an ecosystem is made possible by the process, of photosynthesis (seen in green plants that contain the green pigment, chlorophyll) or chemosynthesis (in plants that do not contain chlorophyll). Photosynthesis by definition is the process by which green plants manufacture their food by using atmospheric carbon dioxide and water in the presence of sunlight.
From the definition above, one could summarize that for the photosynthetic process to occur, there must be an availability of carbon dioxide, water, and energy from the sun. This definition is however limiting as it does not bring to bear all the key players in the process including nitrogen. So, acknowledging the role of plants in the continuity of life and the dependence of the photosynthetic process on climatic variables begs the question, how has climate change affected plant productivity?
Effects of rising carbon dioxide level
Research carried out at Berkeley Lab and UC Berkeley suggests that increasing atmospheric levels of CO2 is accompanied by an almost proportionate increase in plant photosynthesis through an effect referred to as carbon fertilization. According to the findings in the research, between 1982 and 2020, worldwide photosynthesis rose 12% with an accompanying 17% rise in CO2 level. This averages an increased plant growth of 21% to 28% and an increased yield of 12% to 14%. There is an associated reduction in plant water loss of about 5% to 20% owing to the partial closure of the stomata in plants during accelerated photosynthesis.
Deficient nitrogen trapping
Every living thing contains nitrogen. It makes up about 80% of the atmosphere and is an essential component of the building blocks of life – DNA and RNA. For plants to be able to utilize the atmospheric nitrogen, it has to be fixed in the soil by certain bacteria found in the root nodules of leguminous plants in a symbiotic relationship. Research has it that the ratio of CO2 to nitrogen is fixed and an increase in atmospheric CO2 without a corresponding increase in nitrogen will in the long decrease plant productivity. Nitrogen fixation works at an optimum temperature of 25⁰C. Temperatures above this reduce the rate of fixation.
Rubisco, an enzyme required in the fixation process is denatured at high temperatures. Rising temperatures also cancel out the benefits of water conservation that accompanies increased photosynthesis from elevated CO2 levels resulting in drier soils and fewer runoffs that contribute to rivers.
Warmer seasons also lead to increased pest and pathogen activity as warm temperatures are known to speed up their lifecycle. In addition to these, elevated temperature increases the growth of weeds which already account for about 34% of food crop losses.
Plant migration is also an important cause of concern with rising temperatures. Plants with specific temperature needs are migrating to elevated lands which tend to be cooler. This migration may make the new environment less hospitable due to competition and nutrient depletion.
Harsh changes in weather
The climate change that is ushering in extremes of weather variables will come with their attendant negative consequences including heatwaves and drought (whose combined effect may cause a 20% to 40% drop in maize yield), extreme precipitation, and wind disturbance. All these will result in a significant drop in productivity that offsets the positive carbon fertilization.
The accelerated change in the climate factors that regulate plant productivity paints an uncertain picture of the future of plants. This is speculated to result in drops in the global food output and possibly tip the world into another stone age. There are however still a lot of gaps in our knowledge of the process behind plant productivity.
Climate change is a real thing and its effects are especially felt by the primary fuel source of the ecosystems. Concerted efforts should be geared towards controlling or arresting these changes if world hunger and environmental destruction are to be averted.