Plant Ecology Research: Plant Ecology in Desert Biome Context

This report delves into the intricacies of plant ecology within the context of desert biomes, focusing on the impact of environmental factors such as drought, temperature, and nutrient availability on plant growth and survival. The study begins with an overview of biome classifications, emphasizing the unique characteristics of desert ecosystems. It then examines the photosynthetic process, highlighting the role of water and nutrients in plant growth and discussing the potential effects of water scarcity and nutrient deficiency. The report further investigates the effects of climate change, discussing the differences between C3 and C4 photosynthetic pathways and their adaptation to varying environmental conditions. Finally, the report proposes an experimental approach to study the responses of vegetation to drought and nitrogen deposition in a cool desert ecosystem, considering the expected increase in drought intensity and frequency due to climate change. The report uses APA citations throughout the document. The research discusses the effects of drought and nitrogen on plant growth and the importance of understanding plant adaptations in a changing climate, especially on the Colorado Plateau.

Running head: PLANT ECOLOGY RESEARCH
Discussion on Plant Ecology in Context to Desert Biome
Name of the Student
Name of the University
Author Note

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Part 1
Geological and ecological areas based community on a large global scale is known as
a biome. The environmental condition of a biome is determined by several abiotic factors
such as geology, soil type, relief, climate, temperature and vegetation. The primary type of
biomes recognized are grasslands, aquatic, forest and desert. Within the same prefixed
ecological area distribution, several ecosystems can be observed forming a biome. The global
distribution of biomes is determined by the annual measure of two variables, precipitation
and temperature. The biome type can be adjudged by the annual temperature measures based
on the proximity to the equatorial region of the globe, greater the distance, lower the
temperature. Classification of biomes based on a measure of annual precipitation is important
to get an indication of the vegetation level, higher the precipitation, and greater would be the
vegetation. However, desert, a type of terrestrial biome, tends to have extreme levels of both
the variables, that is, high levels of temperature, with very low levels of precipitation. This
tends to the development of few characteristic features of desert including drought, aridity,
extremely low precipitation, low humidity and extremely high temperatures. Such extremities
result in an associated threat of high evaporation rate of water in plants and the absence of
biologically nutrient soil.
A critical process in the plant systems which enables them to produce organic
molecules is photosynthesis. The photosynthetic process helps the plants to harness the solar
radiation from the sun to convert into chemical energy. Sugar is one of the byproducts formed
by further exploitation of this chemical energy. The harnessing of solar radiation is performed
by the photosynthetic system comprising of absorbing pigments and other complexes which
helps in the conversion of solar energy to the chemical. The primary absorbing pigments,
chlorophyll ‘a’ and chlorophyll ‘b’ absorb photons of radiation one at a time, which is
transferred to a single photon receptor chlorophyll a molecule at the reaction center. This

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photon displaces an electron from the receptor and the void is fulfilled by electron received
from the breaking down of water molecules, leading to the formation of O2 molecules and
[H+] ions. The increasing concentration of hydrogen ions passes through ATP synthase to
form ATP (energy molecule). On the other hand, the free electron passes through several
complexes in the electron transport chain leading to the generation of NADPH energy carrier
molecule. This generated chemical energy is used in the Calvin cycle for the formation of
sugar molecules. In the mesophyll of the cell, RuBisCO enzyme initiates carbon fixation by
hydrolyzing a 6-carbon molecule of 3-phosphoglycerate.
This 6-carbon molecule is reduced in the initial steps of carbon fixation in the Calvin
cycle. The final product formed with the reduction is glyceraldehyde-3-phosphate (G3P),
which is synthesized to starch and sugar, post leaving the Calvin cycle. Completion of three
turns of Calvin cycle results in the formation of one molecule of G3P. This photosynthetic
process is considered important for plant growth. However, the realized efficiency levels of
the process are very low, with the conversion rate of solar to the chemical energy of only 2-
4%. The correlation of photosynthetic rate with the overall plant growth rate is quite
insignificant. The lower efficiency levels of the photosynthetic process are affected by
nutrient and water limitations.
For most of the plant’s metabolic and other biological activity, water plays a crucial
role as it is one of the most significant solvents for biochemical reactants to dissolve.
Carbohydrate synthesis during the photosynthetic process is aided by carbon dioxide and
water. For the movement of nutrients throughout the plant body, water plays the role of the
transport medium. Transpiration is the evaporation process in plants in which the water
absorbed from the roots of a plant are transported through xylem tissues to the leaf surfaces,
from where it is diffused to air via the stomatal opening. In desert biome, where there is
limited availability of water, a significant impact on the overall plant growth is observed,

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with the limited growth rate. Tradeoffs between carbon dioxide uptake and water loss are
adjusted in plants from such conditions by the adjustment of the stomatal pore openings. In
the situation of water deficit, reduced photosynthetic activity, restrained carbon dioxide
uptake and negatively influenced metabolic activities can be observed (Tomeo & Rosenthal,
2017).
In addition to water, nutrients are another crucial element that influences the plant’s
overall growth. The primary source of mineral for the plants is soil, from which it gets most
of the macro and micro-nutrients. These nutrient elements help the proper functioning of
physiological and biochemical processes in the plant body. Essential macronutrients include
nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and iron and micro-nutrients
include manganese, copper, boron, molybdenum, chlorine and zinc (Ru et al., 2017). There
are three major pathways in which the plants ensure nutrient acquisition, which includes
direct uptake from the soil, symbioses with soil-based microorganisms and mycorrhizal
interactions with plants. In direct uptake, the plant roots absorb nutrients such as potassium
and iron from the soil. In symbioses type of nutrient acquisition, symbiotic relationship with
soil-based bacteria such as Rhizobia is ensured, which helps in fixing the atmospheric
nitrogen to a usable form of ammonia. Mycorrhizal interactions are the establishment of a
symbiotic association of the plant with fungal organisms.
From the above discussion on the photosynthetic process and importance of water and
nutrient availability in the plant’s overall growth, it is conclusive that water scarcity and
nutrient deficiency will hinder the plant’s ability to grow. Thus, in conditions of water
scarcity, which is common in terrestrial biomes of cold desert, it can be hypothesized that
limited availability of water will result in a reduction of the plant’s growth rate. However,
with the addition of nutrient such as nitrogen, it is hypothesized that a compensatory result in
context to water scarcity led hindered plant growth, can be observed. Increase in the net

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photosynthetic rate is expected with the addition of nitrogen (Tang et al., 2017). The
experimental approach would be to take two plants and let them survive in four induced
conditions, one with water deficit, second with the addition of nitrogen, third with water
deficit plus the addition of nitrogen and the last one would be control, with the plant growing
in natural conditions. The morphological characteristics such as total biomass, average leaf
area, shoot-to-root ratio, leaf number and root weight will be measured to evaluate the results.
Part 2
The current global situation is concerned with the steady increase in the average
surface temperature of the world. With climate change, the incidence of the abnormally low
and high level of temperatures is indicated. It is predicted that in the upcoming 100 years, the
average global surface temperature would increase to about 1.8-4.0°C, which is a significant
increase in temperature. It is known that temperature and precipitation are the primary
influencers for the distribution of biomes and vegetation within it and increasing temperature
limits plant growth.
The two major photosynthetic pathways, that is, C3 and C4 pathways are determined
by their first byproduct, which is 3-carbon and 4-carbon respectively. In C3 plants, the
photosynthetic efficiency is heavily compromised due to oxygenase activity of the enzyme
RuBisCO, or photorespiration. On the contrary, the C4 plants show highly reduced
photorespiration, which increases the net photosynthetic efficiency rate and also enabling the
plant to survive in hot and drier conditions or environment.
The evolutionary phase of the two photosynthetic pathways can be determined by
placing the evolution of C3 pathways way ahead of C4 pathway in the timeline. The C3
pathway is more evolutionary ancient and C4 plants speciated after them. The presence of
high concentrations of carbon dioxide and low concentrations of oxygen in the atmosphere
favored the growth of C3 pathway. The C4 plants are highly effective in conditions of low

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carbon dioxide. Evolution of C4 plants was significantly in response to the conditions
involving an increase in oxygen concentration, humid and hot weather. Moreover, the C4
plants have very low levels of stomatal conductance, which helps them to mitigate the water
deficiency problem in the plant. Thus, it is evident that the need of effective water
conservation mechanism with low stomatal conductance in conditions of low carbon dioxide,
increased temperature and high light intensity led to the evolution of more advanced
photosynthetic pathway that is C4 pathway. The prime differences between the two pathways
are the carbon fixation cycle initiation enzyme of RuBisCO in C3 and Phospho-enol-pyruvate
(PEP) carboxylase in C4 pathway, which leads to formation of 3-carbon (3-Phospho Glyceric
Acid) and 4-carbon (Oxalo Acetic Acid) compounds in the respective pathways as the first
stable products (Shen et al., 2017). Moreover, the first step of carbon fixation occurs in
mesophyll cells, from where the 4-carbon product is transported to specialized bundle sheath
cells (absent in C3 pathways) and decarboxylation occurs to form 3-caron sugar and a carbon
dioxide molecule. The enzyme RuBisCO reduces the sugars via the Calvin cycle. This
activity indicates that how C4 plants can perform their photosynthetic process in low carbon
dioxide and even with the stomatal opening being closed. Thus carbon dioxide fixation in C4
plants, which is resistant to heat and drought, and greater water efficiency are two major
advantage of C4 pathways over C3 pathways in plants (Jansson et al., 2019).
However, the understanding of the global distribution of C3 and C4 plants depicts a
contrary story. Even with such advantages over C3 plants, the global prevalence of C4 plants
is just 3 per cent (Trammell et al., 2019). All the major species of plants, including the ones
that the humans are highly reliant upon, are C3. Majority of the C4 plants are found in extreme
conditions and especially the desert regions of the water, where water availability is highly
limited. These regions include warm temperate zones, tropical grasslands and subtropics. The

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C4 plants are not marked suitable for human consumption, except few plants such as soya
beans, maize and sugarcane.
Considering the prediction of the dramatic increase in the average global surface
temperatures, it can be predicted that the plants with C3 photosynthetic pathway will struggle
to survive in the upcoming decades (Kumar et al., 2017). High light intensities and increasing
temperature are most likely to favor the growth of C4 plants (Bordignon et al., 2019).
However, the prediction is deterred with an important property of C3 plants concerned with
the greater capability of using nitrogen in arid conditions, which favors their growth (Luo et
al., 2018).

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References
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membrane level and photosystem II activity in two C4 plants after growth in elevated
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Brutnell, T. (2019). A Perspective on a Paradigm Shift in Plant Photosynthesis:
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Tomeo, N. J., & Rosenthal, D. M. (2017). Variable mesophyll conductance among soybean
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