Soil and Plant Nutrition by Design by Owen Borville December 13, 2024 Biology 31
Plants absorb nutrients and water through their roots and carbon dioxide in the atmosphere. Soil quality and climate are the major determinants of plant distribution and growth.
The majority of the volume in a plant cell is water (89-90 percent of plant weight). Soil is the water source for land plants, absorbed through the root hairs of the roots and through the xylem tissue to the rest of the plant. Plants need water to support cell structure, for metabolic functions, to carry nutrients, and for photosynthesis.
Plants need essential nutrients and these are organic compounds or inorganic compounds.
Organic compounds are chemical compounds that contain carbon, such as carbohydrates, lipids, proteins, and nucleic acids that are made by living organisms. Carbon obtained from atmospheric CO2 becomes part of organic molecules of plants.
Inorganic compounds in plants do not contain carbon except CO2 and is not produced by plants or a living organism. Inorganic substances form the majority of the soil solution, and are mostly minerals needed by plants containing nitrogen and potassium.
Plants need about 20 essential nutrients in addition to light and water. For an element to be classified as essential, three requirements are needed: 1) a plant cannot complete its life cycle without the element. 2) no other element can perform the function of the element. 3) the element is directly involved in plant nutrition.
Macronutrients are nutrients that plants require in larger amounts and include: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S). Reduced presence of these elements can affect plant growth and health.
Carbon is required to form carbohydrates, proteins, nucleic acids, and many other compounds. Carbon is present in all macromolecules and biomolecules. Almost half of the weight of a cell minus water is carbon.
Cellulose is the main structural component of the cell wall of plants and makes up over 30 percent of plant matter. Cellulose is the most abundant organic compound on earth and its structure is a linear polymer made of linked units of glucose.
The third most abundant element in plant cells is nitrogen and is part of proteins and nucleic acids. Hydrogen and oxygen form water in addition to being part of many organic compounds. Oxygen is necessary for cellular respiration. Plants use oxygen to store energy in the form of ATP. Phosphorus is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Light energy is converted to chemical energy during phosphorylation in photosynthesis, and into chemical energy to be extracted during respiration. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain, where hydrogen gradients play a key role in the conversion of light energy in to ATP. Potassium (K) is important because of its role in regulating stomatal opening and closing with an ion pump. Calcium regulates nutrient transport and supports many enzyme functions. Magnesium is important to the photosynthetic process. Macronutrients and micronutrients contribute to the plant's ionic balance.
Micronutrients include: Iron (Fe), Manganese (Mn), Boron (B), Molybdenum (Mo), Copper (Cu), Zinc (Zn), Chlorine (Cl), Nickel (Ni), Cobalt (Co), Sodium (Na), Silicon (Si)
Soil is the outer loose layer that covers the surface of the Earth and where plants obtain inorganic elements from the soil. Soil quality and climate are major factors of plant growth and distribution. Soil quality depends on the chemical composition of the soil, surface topography, and the presence of living organisms. In agriculture, the history of the soil, such as the cultivating practices and previous crops modify the characteristics and fertility of the soil.
Soil develops over time from natural and environmental processes acting minerals, rocks, and organic compounds. Organic soils are those formed from sedimentation and composed primarily of organic matter. Mineral soils are formed from the weathering of rock are primarily composed of inorganic material. Mineral soils exist in terrestrial ecosystems, where soils can be covered by water part of the year or exposed to the atmosphere.
Soil composition contains inorganic mineral matter (40-45 percent volume), organic matter (5 percent of volume), and water and air (50 percent of volume). The amount of each of these in the soil depends on the amount of vegetation, soil compaction, and water present in the soil. A healthy soil has a sufficient amount of water, air, minerals, and organic matter to support life.
Organic material of soil is called humus, made of microorganisms dead and alive along with various dead animals and plants at different stages of decay. Humus improves soil structure and provides plants with water and minerals. The inorganic material of soil consists of rock, broken down into smaller pieces of various sizes: sand (0.1-2 mm), silt (0.002-0.1), clay (less than o.002 mm). Loam is a mixture of sand, silt, and humus soil particles.
Soil formation is the result of biological, chemical, and physical processes. Soil should ideally be half solid material and half pore space. One half of the pore spaces should be water, and the other half should be air. Organic material is a cementing agent, returns nutrients to the plant, allows soil to store moisture, makes soil tillable for farming, and provides energy for soil microorganisms. Most soil microorganisms (bacteria, algae, fungi) are dormant in dry soil, but are active in wet soil.
Soil formation results in layers of different composition, and the vertical section of a soil is called the soil profile. The soil profile is divided into horizons, which are soil layers with distinct physical and chemical properties that differ from those of other layers. Five factors affect soil formation: parent material, climate, topography, biological factors, and time.
Parent material is the organic and inorganic material in which soil forms from. Mineral soils form directly from the weathering of bedrock, the rock beneath the soil, and have a composition similar to the original rock. Other soils form in materials that came from sand and glacial drift. Materials in the depth of the soil are relatively unchanged from the deposited material. Sediments in rivers can vary in composition depending on the speed of the water flow. A fast flowing river can have sediments of rock and sand, while a slow moving river could have fine-textured material such as clay.
Climate affects soil formation as temperature, moisture, and wind cause different patterns of weathering and therefore affect soil characteristics. Moisture and nutrients from weathering will promote biological activity, which is a key component of quality soil.
Topography affects soil formation as surface features affect water runoff, which strip away parent material and affects plant growth and soil fertility. Steep soils are more prone to erosion and may be thinner than soils that are relatively flat or level.
Living organisms in the soil affect its formation and development. Microorganisms and animals can produce pores and crevices, and plant roots can penetrate these crevices and produce more fragmentation. Plant secretions promote development of microorganisms around the root, in the area known as the rhizosphere. Also, leaves and other materials fall into the soil, decompose, and contribute to soil formation.
Time is an important factor in soil formation because soils develop over long periods of time as materials are deposited, decompose, and transform into other materials that can be used by living organisms or deposited onto the surface of the soil.
Physical properties of the soil include the horizon layers and the soil profile has four distinct layers: the O horizon, A horizon, B horizon, or subsoil, and C horizon, or soil base.
The O horizon has freshly decomposing organic matter or humus at its surface, with decomposed vegetation at its base. Humus enriches the soil with nutrients and enhances soil moisture retention. Topsoil, the top layer of the soil, is rich in organic material, microbes, and plants.
The A horizon has a mixture of organic material and inorganic products of weathering, where mineral soil begins. The A horizon is dark colored because of organic material where rainwater percolates and carries materials downward.
The B horizon is an accumulation of mostly fine material that has moved downward, resulting in a dense layer of the soil. In some soils, the B horizon contains nodules or layers of calcium carbonate.
The C horizon, or soil base, includes the parent material, plus the organic and inorganic material that is broken down to form soil. The parent material may be either created in its natural place, or transported from other places. Beneath the C horizon is the bedrock.
Some soils may have more of these layers or fewer layers and the thickness of each layer can vary depending on the factors of soil formation. Less developed soils may not have a B horizon. Very developed soils can have O, A, B, C horizon layers plus more layers.
Nutritional Design Adaptations of Plants
Plants can obtain their own food by photosynthesis, carbon dioxide, water, and sunlight (autotrophic). Some plants are parasitic and don't have chlorophyll, and cannot make their own food, so they obtain some or all of their nutrients from a host plant (heterotrophic).
Some plants use microbial partners to obtain food, particularly in symbiotic relationships with bacteria and fungi to the plant roots.
Nitrogen Fixation with Root and Bacteria Interactions
Nitrogen is an important macronutrient part of nucleic acids and proteins, and the atmosphere. Plants cannot use nitrogen unless it is fixed by a process called nitrogen fixation, where nitrogen is converted to ammonia through biochemical or physical processes.
Biological Nitrogen Fixation BNF is the conversion of atmospheric nitrogen (N2) into ammonia (NH3), performed by prokaryotes like soil bacteria or cyanobacteria. Most nitrogen used in agriculture is made by biological processes.
N2 + 16ATP + 8e- + 8H+ => 2NH3 + 16ADP + 16Pi + H2
The main source of BNF is the symbiotic interaction of soil bacteria and legume plants. NH3 produced by BNF can be transported to plant tissue and incorporated into amino acids and plant proteins. Soybeans and peanuts have high protein levels and are very important to agriculture.
Soil bacteria (rhizobia) symbiotically interact with legume roots to form specialized structures called nodules, in which nitrogen fixation takes place. Atmospheric nitrogen is reduced to ammonia by the enzyme nitrogenase. Rhizobia is the natural and environmentally friendly method of plant fertilization, in contrast to chemical fertilization that uses nonrenewable resources like natural gas. Symbiotic nitrogen fixation allows for an endless source of nitrogen from the atmosphere for the plants' benefit. Soil fertility is also increased as the plant root system leaves behind some nitrogen in the soil. In the symbiosis, both organisms benefit, as the plant obtains ammonia, and bacteria obtain carbon compounds generated through photosynthesis and a protected niche in which to grow.
Fungi form symbiotic associations called mycorrhizae with plant roots, where the fungi are integrated into the physical structure of the root. The fungi colonize the living root tissue during active plant growth. Most plants rely on fungi to facilitate the uptake of minerals from the soil.
During mycorrhizae, plants obtain phosphate and other minerals like zinc and copper from the soil. The fungus obtains nutrients such as sugars from the plant root. Mycorrhizae help increase the surface area of the plant root system because hyphae, which are narrow, can spread beyond the nutrient depletion zone. Hyphae can grow into small soil pores that allow access to phosphorus that would otherwise be unavailable to the plant. Plants benefit when there are poor soils. Fungi benefit by gaining up to 20 percent of the total carbon accessed by plants. Mycorrhizae acts as a physical barrier to pathogens and provides induction of a generalized host defense mechanisms, and sometimes involves the production of antibiotic compounds by the fungi.
There are two types of mycorrhizae: Ectomycorrhizae is an extensive dense sheath around the roots called a mantle. Hyphae from the fungi extend from the mantle into the soil, which increases the surface area for water and mineral absorption. Ectomycorrhizae is found in forest trees. Endomycorrhizae (arbuscular mycorrhizae) do not form a dense sheath over the root, but rather the fungal mycelium is embedded in the root tissue. Endomycorrhizae are found in the roots of more than 80 percent of terrestrial plants.
Plant parasites and saprophytes cannot produce their own food and must obtain food elsewhere through mutual symbiosis or as an epiphyte, or an insectivore.
Parasitic plants depend on their hosts for survival. Some parasitic plants have no leaves, such as the dodder which has a weak, cylindrical stem that coils around the host and forms suckers. From the suckers, cells invade the host stem and grow to connect with the vascular bundles of the host. The parasitic plant obtains water and nutrients through these connections. This plant is a holoparasite and is totally dependent on the host. Some parasitic plants are hemiparasites and are fully photosynthetic, and only use the host for water and minerals.
Saprophytes are plants that do not have chlorophyll and obtain their food from dead matter (as bacteria and fungi do). These plants use enzymes to convert organic food materials into simpler forms from which they can absorb nutrients. Most saprophytes don't directly ingest dead matter, but rather they parasite fungi that digest dead matter, or are mycorrhizal and ultimately obtain photosynthate from a fungus that derived photosynthate from its host. Saprophytic plants are uncommon.
Symbionts are plants in a symbiotic relationship, by way of mycorrhizae or nodule formation.
Epiphytes are plants that grow on other plants, but are not dependent on the other plants for nutrition. Epiphytes have two types of roots: clinging aerial roots, which absorb nutrients from humus that accumulate in the crevices of trees, and aerial roots, which absorb moisture from the atmosphere.
Insectivorous plants have specialized leaves that attract and digest plants. The Venus Fly Trap is an insectivorous plant that has leaves that work as traps of flies and other organisms. The minerals that it obtains from prey compensate for the lack of nutrients in the boggy soil of North Carolina coastal plains where it lives. Sensory hairs are included inside each leaf and the edges of each leaf have spines that help capture prey. Nectar secreted by the plant attracts flies to the leaf. As a fly touches a sensory hair, the leaf immediately closes. Fluids and enzymes help break down the prey and minerals are absorbed by the leaf.
Plants absorb nutrients and water through their roots and carbon dioxide in the atmosphere. Soil quality and climate are the major determinants of plant distribution and growth.
The majority of the volume in a plant cell is water (89-90 percent of plant weight). Soil is the water source for land plants, absorbed through the root hairs of the roots and through the xylem tissue to the rest of the plant. Plants need water to support cell structure, for metabolic functions, to carry nutrients, and for photosynthesis.
Plants need essential nutrients and these are organic compounds or inorganic compounds.
Organic compounds are chemical compounds that contain carbon, such as carbohydrates, lipids, proteins, and nucleic acids that are made by living organisms. Carbon obtained from atmospheric CO2 becomes part of organic molecules of plants.
Inorganic compounds in plants do not contain carbon except CO2 and is not produced by plants or a living organism. Inorganic substances form the majority of the soil solution, and are mostly minerals needed by plants containing nitrogen and potassium.
Plants need about 20 essential nutrients in addition to light and water. For an element to be classified as essential, three requirements are needed: 1) a plant cannot complete its life cycle without the element. 2) no other element can perform the function of the element. 3) the element is directly involved in plant nutrition.
Macronutrients are nutrients that plants require in larger amounts and include: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S). Reduced presence of these elements can affect plant growth and health.
Carbon is required to form carbohydrates, proteins, nucleic acids, and many other compounds. Carbon is present in all macromolecules and biomolecules. Almost half of the weight of a cell minus water is carbon.
Cellulose is the main structural component of the cell wall of plants and makes up over 30 percent of plant matter. Cellulose is the most abundant organic compound on earth and its structure is a linear polymer made of linked units of glucose.
The third most abundant element in plant cells is nitrogen and is part of proteins and nucleic acids. Hydrogen and oxygen form water in addition to being part of many organic compounds. Oxygen is necessary for cellular respiration. Plants use oxygen to store energy in the form of ATP. Phosphorus is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Light energy is converted to chemical energy during phosphorylation in photosynthesis, and into chemical energy to be extracted during respiration. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain, where hydrogen gradients play a key role in the conversion of light energy in to ATP. Potassium (K) is important because of its role in regulating stomatal opening and closing with an ion pump. Calcium regulates nutrient transport and supports many enzyme functions. Magnesium is important to the photosynthetic process. Macronutrients and micronutrients contribute to the plant's ionic balance.
Micronutrients include: Iron (Fe), Manganese (Mn), Boron (B), Molybdenum (Mo), Copper (Cu), Zinc (Zn), Chlorine (Cl), Nickel (Ni), Cobalt (Co), Sodium (Na), Silicon (Si)
Soil is the outer loose layer that covers the surface of the Earth and where plants obtain inorganic elements from the soil. Soil quality and climate are major factors of plant growth and distribution. Soil quality depends on the chemical composition of the soil, surface topography, and the presence of living organisms. In agriculture, the history of the soil, such as the cultivating practices and previous crops modify the characteristics and fertility of the soil.
Soil develops over time from natural and environmental processes acting minerals, rocks, and organic compounds. Organic soils are those formed from sedimentation and composed primarily of organic matter. Mineral soils are formed from the weathering of rock are primarily composed of inorganic material. Mineral soils exist in terrestrial ecosystems, where soils can be covered by water part of the year or exposed to the atmosphere.
Soil composition contains inorganic mineral matter (40-45 percent volume), organic matter (5 percent of volume), and water and air (50 percent of volume). The amount of each of these in the soil depends on the amount of vegetation, soil compaction, and water present in the soil. A healthy soil has a sufficient amount of water, air, minerals, and organic matter to support life.
Organic material of soil is called humus, made of microorganisms dead and alive along with various dead animals and plants at different stages of decay. Humus improves soil structure and provides plants with water and minerals. The inorganic material of soil consists of rock, broken down into smaller pieces of various sizes: sand (0.1-2 mm), silt (0.002-0.1), clay (less than o.002 mm). Loam is a mixture of sand, silt, and humus soil particles.
Soil formation is the result of biological, chemical, and physical processes. Soil should ideally be half solid material and half pore space. One half of the pore spaces should be water, and the other half should be air. Organic material is a cementing agent, returns nutrients to the plant, allows soil to store moisture, makes soil tillable for farming, and provides energy for soil microorganisms. Most soil microorganisms (bacteria, algae, fungi) are dormant in dry soil, but are active in wet soil.
Soil formation results in layers of different composition, and the vertical section of a soil is called the soil profile. The soil profile is divided into horizons, which are soil layers with distinct physical and chemical properties that differ from those of other layers. Five factors affect soil formation: parent material, climate, topography, biological factors, and time.
Parent material is the organic and inorganic material in which soil forms from. Mineral soils form directly from the weathering of bedrock, the rock beneath the soil, and have a composition similar to the original rock. Other soils form in materials that came from sand and glacial drift. Materials in the depth of the soil are relatively unchanged from the deposited material. Sediments in rivers can vary in composition depending on the speed of the water flow. A fast flowing river can have sediments of rock and sand, while a slow moving river could have fine-textured material such as clay.
Climate affects soil formation as temperature, moisture, and wind cause different patterns of weathering and therefore affect soil characteristics. Moisture and nutrients from weathering will promote biological activity, which is a key component of quality soil.
Topography affects soil formation as surface features affect water runoff, which strip away parent material and affects plant growth and soil fertility. Steep soils are more prone to erosion and may be thinner than soils that are relatively flat or level.
Living organisms in the soil affect its formation and development. Microorganisms and animals can produce pores and crevices, and plant roots can penetrate these crevices and produce more fragmentation. Plant secretions promote development of microorganisms around the root, in the area known as the rhizosphere. Also, leaves and other materials fall into the soil, decompose, and contribute to soil formation.
Time is an important factor in soil formation because soils develop over long periods of time as materials are deposited, decompose, and transform into other materials that can be used by living organisms or deposited onto the surface of the soil.
Physical properties of the soil include the horizon layers and the soil profile has four distinct layers: the O horizon, A horizon, B horizon, or subsoil, and C horizon, or soil base.
The O horizon has freshly decomposing organic matter or humus at its surface, with decomposed vegetation at its base. Humus enriches the soil with nutrients and enhances soil moisture retention. Topsoil, the top layer of the soil, is rich in organic material, microbes, and plants.
The A horizon has a mixture of organic material and inorganic products of weathering, where mineral soil begins. The A horizon is dark colored because of organic material where rainwater percolates and carries materials downward.
The B horizon is an accumulation of mostly fine material that has moved downward, resulting in a dense layer of the soil. In some soils, the B horizon contains nodules or layers of calcium carbonate.
The C horizon, or soil base, includes the parent material, plus the organic and inorganic material that is broken down to form soil. The parent material may be either created in its natural place, or transported from other places. Beneath the C horizon is the bedrock.
Some soils may have more of these layers or fewer layers and the thickness of each layer can vary depending on the factors of soil formation. Less developed soils may not have a B horizon. Very developed soils can have O, A, B, C horizon layers plus more layers.
Nutritional Design Adaptations of Plants
Plants can obtain their own food by photosynthesis, carbon dioxide, water, and sunlight (autotrophic). Some plants are parasitic and don't have chlorophyll, and cannot make their own food, so they obtain some or all of their nutrients from a host plant (heterotrophic).
Some plants use microbial partners to obtain food, particularly in symbiotic relationships with bacteria and fungi to the plant roots.
Nitrogen Fixation with Root and Bacteria Interactions
Nitrogen is an important macronutrient part of nucleic acids and proteins, and the atmosphere. Plants cannot use nitrogen unless it is fixed by a process called nitrogen fixation, where nitrogen is converted to ammonia through biochemical or physical processes.
Biological Nitrogen Fixation BNF is the conversion of atmospheric nitrogen (N2) into ammonia (NH3), performed by prokaryotes like soil bacteria or cyanobacteria. Most nitrogen used in agriculture is made by biological processes.
N2 + 16ATP + 8e- + 8H+ => 2NH3 + 16ADP + 16Pi + H2
The main source of BNF is the symbiotic interaction of soil bacteria and legume plants. NH3 produced by BNF can be transported to plant tissue and incorporated into amino acids and plant proteins. Soybeans and peanuts have high protein levels and are very important to agriculture.
Soil bacteria (rhizobia) symbiotically interact with legume roots to form specialized structures called nodules, in which nitrogen fixation takes place. Atmospheric nitrogen is reduced to ammonia by the enzyme nitrogenase. Rhizobia is the natural and environmentally friendly method of plant fertilization, in contrast to chemical fertilization that uses nonrenewable resources like natural gas. Symbiotic nitrogen fixation allows for an endless source of nitrogen from the atmosphere for the plants' benefit. Soil fertility is also increased as the plant root system leaves behind some nitrogen in the soil. In the symbiosis, both organisms benefit, as the plant obtains ammonia, and bacteria obtain carbon compounds generated through photosynthesis and a protected niche in which to grow.
Fungi form symbiotic associations called mycorrhizae with plant roots, where the fungi are integrated into the physical structure of the root. The fungi colonize the living root tissue during active plant growth. Most plants rely on fungi to facilitate the uptake of minerals from the soil.
During mycorrhizae, plants obtain phosphate and other minerals like zinc and copper from the soil. The fungus obtains nutrients such as sugars from the plant root. Mycorrhizae help increase the surface area of the plant root system because hyphae, which are narrow, can spread beyond the nutrient depletion zone. Hyphae can grow into small soil pores that allow access to phosphorus that would otherwise be unavailable to the plant. Plants benefit when there are poor soils. Fungi benefit by gaining up to 20 percent of the total carbon accessed by plants. Mycorrhizae acts as a physical barrier to pathogens and provides induction of a generalized host defense mechanisms, and sometimes involves the production of antibiotic compounds by the fungi.
There are two types of mycorrhizae: Ectomycorrhizae is an extensive dense sheath around the roots called a mantle. Hyphae from the fungi extend from the mantle into the soil, which increases the surface area for water and mineral absorption. Ectomycorrhizae is found in forest trees. Endomycorrhizae (arbuscular mycorrhizae) do not form a dense sheath over the root, but rather the fungal mycelium is embedded in the root tissue. Endomycorrhizae are found in the roots of more than 80 percent of terrestrial plants.
Plant parasites and saprophytes cannot produce their own food and must obtain food elsewhere through mutual symbiosis or as an epiphyte, or an insectivore.
Parasitic plants depend on their hosts for survival. Some parasitic plants have no leaves, such as the dodder which has a weak, cylindrical stem that coils around the host and forms suckers. From the suckers, cells invade the host stem and grow to connect with the vascular bundles of the host. The parasitic plant obtains water and nutrients through these connections. This plant is a holoparasite and is totally dependent on the host. Some parasitic plants are hemiparasites and are fully photosynthetic, and only use the host for water and minerals.
Saprophytes are plants that do not have chlorophyll and obtain their food from dead matter (as bacteria and fungi do). These plants use enzymes to convert organic food materials into simpler forms from which they can absorb nutrients. Most saprophytes don't directly ingest dead matter, but rather they parasite fungi that digest dead matter, or are mycorrhizal and ultimately obtain photosynthate from a fungus that derived photosynthate from its host. Saprophytic plants are uncommon.
Symbionts are plants in a symbiotic relationship, by way of mycorrhizae or nodule formation.
Epiphytes are plants that grow on other plants, but are not dependent on the other plants for nutrition. Epiphytes have two types of roots: clinging aerial roots, which absorb nutrients from humus that accumulate in the crevices of trees, and aerial roots, which absorb moisture from the atmosphere.
Insectivorous plants have specialized leaves that attract and digest plants. The Venus Fly Trap is an insectivorous plant that has leaves that work as traps of flies and other organisms. The minerals that it obtains from prey compensate for the lack of nutrients in the boggy soil of North Carolina coastal plains where it lives. Sensory hairs are included inside each leaf and the edges of each leaf have spines that help capture prey. Nectar secreted by the plant attracts flies to the leaf. As a fly touches a sensory hair, the leaf immediately closes. Fluids and enzymes help break down the prey and minerals are absorbed by the leaf.