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Climate Change – Are Plants at Stake?
BIOL 3P91
Friday April 8th, 2022
In this comprehensive review, we will be discussing the phenomenon of climate change
on the everlasting effects of plant physiology and metabolism. Through analysis of the various
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factors of plant structure, physiology, and function, this review will give a knowledgeable
approach to the impact of climate change. While also discussing the faults of climate change on
plant livelihood, there are however, benefits to climate change that will also be reviewed.
As stated by the United Nations, climate change refers to long-term shifts in temperature
and weather patterns (UN, n.a.). The drive for these changes in temperature and weather have
been long attributed since the 1800’s due to anthropogenic effects such as the burning of fossil
fuels, oil, and gas. As a result, through accumulated burning, this has given rise to greenhouse
gas emissions surrounding the Earth’s surface, trapping in heat, and raising temperatures. Within
the last decade (2011-2020), greenhouse gas emissions have been at their highest levels in 2
million years posing many challenges and risks to our ecosystems. Carbon dioxide is the primary
greenhouse gas emitted through anthropogenic means with the highest emittance rate.
The consequences of climate change should be noted, especially when it has led to the
disruption of many ecosystems and wildlife habitats through evidence of droughts, wildfires,
invasive species, losses of plant species, and much more. In this review, the emphasis will be on
climate change effects on plant physiology and metabolism through evidence of stresses on soil,
water, temperature, and other functional processes. With rising temperatures from climate
change, this adds detrimental effects to plants with lowered productivity, spread of invasive
species, vulnerability to pests, saltwater intrusion, and ultimately altered ecosystem structures.
With drought stress, plants have become susceptible to heat stress causing less productivity and
affecting the support of wildlife and many continuous food chains. In the case of changes in
environmental conditions, native species of plants have lost their advantages causing an increase
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of invasive species taking over landscape. Alongside losing the advantage of landscape, native
species have become susceptible and vulnerable to invasive insect species causing ultimate
damage to the plant species through accumulated insect numbers. With rising temperatures, sea
levels will also continue to rise intruding low-lying plant species, damaging plants and disrupting
wetland ecosystems. Ultimately, rising temperatures will continue to cause soil moisture
changes, affecting vegetative and plant responses due to migration of species to find more
suitable climates and habitats (NPS, 2021). Also to be considered is the number of nutrients and
microbes that can be found within soil niches that will be impacted as well as a result of climate
change and other anthropogenic effects.
In attempt to understand the effects of climate change on plants, the physiology,
metabolic actions/responses, and biochemistry of plants must also be reviewed. Beginning with
the structures found within the plant, besides the photosynthetic tissues and cells, the main
structures can be split up into 3 compartments – the roots, stems, and leaves. The roots of a plant
act as an anchor to the soil allowing uptake of water and transportation throughout the plant with
the help of specialized structures such as xylem and phloem, root hairs, root tips and caps. The
stems are long and cylindrical providing strength and support to the plant with assisted
transportation of water, minerals, and sugars to different regions. Lastly, the leaves contain cells
with chlorophyll and chloroplasts of large surface area aiding in gas diffusion and opportunities
for photosynthesis (RSC, n.a.). The types of physiological processes plants go through can be
defined by photosynthesis, respiration, photorespiration, transpiration, growth and development.
Photosynthesis is a very important physiological process in order to obtain chemical energy for
the plant through given sunlight in addition to water and carbon dioxide. The mechanisms of
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photosynthesis can be categorized into 3 pathways – C3, C4, and CAM. The respiration process
involves 2 processes, one being physical and the other being chemical using the pathways of
glycolysis and the electron transport chain to create energy or ATP for the plant.
Photorespiration refers to the light-dependent oxygen uptake and carbon dioxide production in
which only occurs in chlorophyll cells. Finally, the transpiration process within a plant involves
the loss of water in the form of vapour transpired from the leaves (Khandewal, n.a.). All these
processes are beneficial to the physiology and metabolism of a plant with emphasis on specific
functions per plant structure.
From research it has been concluded through past experiments that root decomposition is
significant with climatic and environmental variables. In particular, temperature is a key
component to influencing decomposition of several structures (Silver & Miya, 2001). As
previously mentioned, climate change can cause heat stress for plants, overall impacting their
structures such as the repression of roots in response to water deficit (Babe et al., 2012). This
however, contradicts against evidence of increased root biomass and increased root length with
elevated carbon dioxide levels found in many selective crop species (Gray & Brady, 2016;
Madhu & Hatfield, 2013). Carbon dioxide is one of the many prominent greenhouse gases that
are on the rise causing a great shift in climate and temperature globally. In response to carbon
dioxide, many studies have confirmed increased root: shoot ratios through observations of
controlled environmental conditions and field experiments. The root component of nodules and
branches have increased with the addition of carbon dioxide and reduced precipitation (Gray &
Brady, 2016). Several studies have conducted increased plant responses to elevated carbon
dioxide coinciding with other influences such as water uptake efficiency and nutrient resource
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gathering (Gray & Brady, 2016). With carbon dioxide influence, roots have been increasing their
branching and expansion in a way to facilitate to the amount of carbon dioxide available. Within
plants, the interior structures of stele and cortex diameters and root diameters have also been
observed to increase in response to exposed and elevated carbon dioxide levels (Rogers et al.,
1992).
Surface temperatures rising is a big issue with global climate change, affecting many
ecosystems and precious soil that is needed for plant growth. The increasing global surface
temperatures in the last century are putting much harm to the soil temperatures of plants overall
affecting root development (Gray & Brady, 2016). Specifically within soil niches, microbial
organisms are a very beneficial component to the plant-soil feedbacks (PSFs). This however, is
becoming an issue due to climate change being able to modify the direction and intensity of
microbial-mediated PSFs in conjunction with drought stress changing soil bacterial and fungal
communities (Pugnaire et al., 2019; Kaisermann et al., 2017). Elevated temperatures are also
putting significant effects on other root functions such as respiration and nutrient uptake (Atkin
et al., 2000; Awal et al., 2003). Specific studies have conducted observations on increased root
growth and length in response to elevated temperatures, some plants that have been studied are
maize, oilseed rape, sunflowers, and cotton. Although there has been increased root growth and
length, a common theme throughout several studies is to consider the optimal temperatures at
which the roots will plateau which is normally at temperatures higher than 30º C (Gray & Brady,
2016). Some plants are already accustomed to higher temperatures however optimal temperature
can change with increased elevation of carbon dioxide and increased temperature.
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Higher global temperatures will cause many more droughts affecting the water resources
for animals and plants. In field experiments, it has been found that increased drought stress has
allowed plants to expand their root systems and reorient their root tips to make up for water
deficit. In response to the expansion and reorientation of roots, one study looked at the role of
auxin for its purpose of redirecting root growth angles downward in response to drought stress
(Rellan-Alvarez et al., 2015). Another theory predicted by Wu et al. (1994) states that the root
expansion is maintained through changes in cell wall properties when roots are experiencing
drought stress and low water potential (Wu et al., 1994). To combat the issues of drought stress,
plants will change their root cellular anatomy, forming aerenchyma, reduced surface area, or
reduced number of cortical cells to facilitate optimal root growth during water scarcity (Lynch,
2015). Plants are accustomed to adjusting to different environmental conditions when in stress
thus they have natural mechanisms to cope with losses and bring in the best efficiency.
Similar to effects in roots with increased root biomass in response to increased carbon
dioxide levels, shoot biomass of plants have also significantly increased bringing in higher yields
for soybean, wheat, rice, peanut, and bean (Gray & Brady, 2016; Hatfield et al., 2011). In
addition to shoot biomass, other structures such as nodes and axillary meristems have also
increased in plants such of soybean and wheat through elevated carbon dioxide levels in the
atmosphere. The relationship between root and shoot ratios among a plant can be quite
interlinked, as evidence has showed with drought stress, there is increased amounts of sugar,
amino acids, and nucleosides within the roots while simultaneously decreasing the same
metabolites in the shoot tissues. Therefore, root elongation is often maintained at the expense of
shoot growth ceasing (Gray & Brady, 2016).
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The leaves play a very functional role for a plant, as they are the main contributor of
photosynthesis and energy production throughout the plant. At the response of elevated carbon
dioxide levels however, increased leaf sizes are a result of increased cell proliferation and cell
expansion (Gray & Brady, 2016). A unique study by Taylor et al. (2003) found that elevated
carbon dioxide levels increased the size of epidermal cells in developing leaves, but not in
mature leaves, with predictions that this may be due to increased cell wall extensibility once
development starts for a leaf (Gray & Brady, 2016). Through studies of soybean plants, it is
common for leaf nodes to increase through elevated carbon dioxide levels, where the growing
season of the soybean plant is also lengthened however, the longevity of the individual leaves
remain the same (Dermody et al., 2006). In response to elevated temperatures, leaf development
is highly regulated with temperature as with evidence found with the plant species, Arabidopsis.
As a result of increased temperatures, leaf initiation, leaf expansion, and duration of expansion
changes linearly with temperature increases. The addition of new leaves is also influenced by
higher temperatures while the leaf morphology is yet still sensitive to temperatures rising.
However, it is yet still unknown by which molecular mechanisms that keep elevated
temperatures regulated to affect leaf morphology and the rate of lead initiation (Gray & Brady,
2016).
In response to drought stress, the cell division and cell expansion of leaves is
significantly affected across many plant species. Dependent on the leaf development stage,
drought stress can have different effects on leaf expansion however, the result is often an act of
reduction of expansion. In plant species such as Arabidopsis, even with mild drought stress,
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individual leaf size and cell area and number is reduced (Gray & Brady, 2016; Clauw et al.,
2015). However, all is not lost as some species of plants can rejuvenate the loss of water by
rehydration depending on leaf length size such as 12 centimetres in the plant species – Ricinus
communis (Schurr et al., 2000). Other forms of dealing with water stress is to aid in transpiration
through stomal closure, minimizing water loss.
Within plants and soil niches, the composition of several minerals and nutrients is
important to maintain a nutritional and viable source of energy and food for the plant. This is
purposeful through soil-plant interactions as the soil contains many minerals and microbes that
aid in the energy output for the plants. The main minerals that are rich in nutrients found in
plants are specifically nitrogen (N), phosphorus (P), and potassium (K). It has been found that
with increasing carbon dioxide levels in the atmosphere, seed yields of some plant species such
as wheat have generally reduced due to reduced mineral content such as zinc and iron (Myers et
al., 2014). The protein content of non-legume seeds has also been observed to find reduced levels
of nitrogen through elevated carbon dioxide levels (Gray & Brady, 2016). This however
contradicts against the benefits of elevated carbon dioxide levels increasing the number of fruits,
flowers, and seeds on average in some species (Jablonski et al., 2002). With increasing
temperatures, there are many risks to many plant species such as soybean, projected with 2.4%
yield losses due to elevated temperatures. Much is still yet unknown for future projections of
losses of plant and seed yields however, it is stated that global surface temperatures are to
increase by 1.0 – 3.7ºC by the end of the century (Gray & Brady, 2016; Hartmann et al., 2013).
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Plant development and physiology are also at risk in response to elevated temperatures,
such as the variability of photosynthetic assimilation that will come in effect due to speciesspecific reactions. As a result of drought stress and climate change, global plants will be
experiencing increased water stress with the frequency of droughts also increasing by the end of
the 21st century (IPCC, 2014). Plant growth and development will be the ultimate consequence of
such water stresses due to varying degrees of intensity and duration of droughts causing
hydrologic imbalances. To fix this issue of growth and developmental stress on plants, plants
will perform what is known as the functional equilibrium theory, meaning they will shift their
allocation among other tissues to optimize the acquisition of the most limiting resource (Gray &
Brady, 2016; Brouwer, 1983). In this case, drought and water stress can be relieved through
investment into other areas of the plant such as the root and shoot tissues over leaf tissues
reducing the area of water loss through transpiration.
In regards to specific physiological functions of the plant affected by climate change,
many studies have been conducted to understand these effects of increased climate. Starting with
photosynthesis, through increased carbon dioxide levels and climate change, altercations of
photosynthesis may lead to shifts in plant growth rates, reduced productivity, and reduced
resource use (Becklin et al., 2016). This however, contradicts against evidence of increased
photosynthesis and increased carbohydrate production due to stimulation by carbon dioxide.
With rising carbon dioxide levels among photosynthesis, the Rubisco biochemistry, stomatal
conductance, morphogenesis, membrane lipid fluidity, and composition of plants in highly
affected. With rising surface temperatures, leaf temperatures are increasing ultimately increasing
photorespiration in plants and at a larger rate than photosynthesis. When grown in elevated
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temperatures, photosynthesis and respiration of plants will usually adjust to conditions as both
act in an interlinked manner (Dusenge et al., 2019). Through field experiments studying the rate
of photosynthesis of plants in response to elevated carbon dioxide levels, research found that at
longer durations (approximately 3 or 4 weeks to months), there was inhibition of photosynthetic
capacity (Irioyen et al., 2014). The dependency on temperature and carbon dioxide availability
by photosynthesis can be attributed toward species-specific interactions as some species may be
accustomed to hotter and drier climates however, with rising climate changes, the temperature
optimums may change thus affecting the plants energy input and output. The difference between
C3, C4, and CAM plants for photosynthesis rates can also explain the different thermal
optimums at which plants will regulate at. In response to higher temperatures, photosynthesis
will decrease due to changes in key enzymes however reversibility is possible dependent on the
duration and intensity at high temperature exposure. Most of the time, plant species can
acclimate to the photosynthetic responses of changing temperature suggesting that with
continuous global climate change, some plants may be able to sustain these harmful effects.
Dealing with transpiration of plants involves the vapour pressure that consists between
the inner leaf surfaces and the humidity of surrounding air. In respect to climate change,
increasing temperatures during the daytime and nighttime will lead to increases in vapour
pressure deficit (VPD). The differences within the VPD will be used to compute the changes in
transpiration rates dependent on the environment and temperature being accessed. Such as the
example with forest canopies versus grassland canopies, due to the more open space provided,
transpiration will most likely be controlled (Kirschbaum, 2004). Through higher carbon dioxide
levels, plants may reduce their water loss through stomatal closures with transpiration rates
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almost decreasing by 30% in effect to climate change (Mahato, 2014). Specifically in C3 plants,
it has been found that increased carbon dioxide levels normally reduce leaf level transpiration,
followed by reduced transpiration in annual crops (Lynch & Clair, 2004). Through literature,
Kirschbaum & McMillian (2018) express how climate change has two opposing effects on
transpiration rates – the first being increasing temperature causing enhanced biophysical force of
transpiration contributing toward increased transpiration rates. The second effect being partial
stomatal closure as discussed previously, restricting the diffusion of water vapour out of leaves
under elevated carbon dioxide levels.
In conclusion, climate change can be very detrimental but also beneficial to a plants
structure and physiological functioning. There is not much to say which outcome is better in the
long run for plant physiology and metabolism, however, climate effects will not only be affecting
plants, but also wildlife, aquatic life, and humans too. Through the literature discussed today,
there is still yet so much to discover in the future in terms of climatic changes to plant
sustainability and function on different aspects of temperature, carbon dioxide, nutrient uptake,
and much more. What we hope to take away from this review is to protect and care for our plant
life as it most important during this crucial period of continuous climate change.
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