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Chapter 37
Plant Nutrition
植物營養
A Nutritional Network (營養網路)
Every organism is an open system connected to its environment by a continuous exchange of energy and materials.
In the energy flow and chemical cycling that keep an ecosystem alive, plants and other photosynthetic autotrophs perform the key step of transforming inorganic compounds into organic ones.
Plants need sunlight as the energy source for photosynthesis. And to synthesize organic matter, plants also require raw materials in the form of inorganic substances: carbon dioxide, water, and a variety of minerals present as inorganic ions in the soil.
With its ramifying root system and shoot system, a plant is extensively networked with its environment----the soil and air, which are the reservoirs of the plants inorganic nutrients.
For a typical plant water and minerals come from the soil, while carbon dioxide (CO2) comes from the air
Key Concepts
Concept 37.1: Plants require certain chemical elements to complete their life cycle
Concept 37.2: Soil quality is a major determinant of plant distribution and growth
Concept 37.3: Nitrogen (N) is often the mineral that has the greatest effect on plant growth
Concept 37.4: Plant nutritional adaptations (營養適應) often involve relationships with other organisms
The branching root system and shoot system of a vascular plant
Ensure extensive networking with both reservoirs of inorganic nutrients (無機營養)
Concept 37.1: Plants require certain chemical elements to complete their life cycle
Plants derive most of their organic mass from the CO2 of air, but they also depend on soil nutrients such as water and minerals
Mineral nutrients
Figure 37.2
CO2, the source of carbon for photosynthesis, diffuses into leaves from the air through stomata.
Through stomata, leaves
expel H2O and O2.
H2O
O2
CO2
Roots take in O2 and expel CO2.
The plant uses O2 for cellular
respiration but is a net O2 producer.
O2
CO2
H2O
Roots absorb H2O and
minerals from the soil.
Minerals
Functions of water in plants
Solvent in the cell
Photosynthetic reactant
Metabolic reactant or product
Respiration
Vacuolar content for cell elongation and extension
Turgor pressure
Others
Macronutrients and Micronutrients
巨量營養素與微量營養素
More than 50 chemical elements
Have been identified among the inorganic substances in plants, but not all of these are essential (必需的/必要的)
Essential elements (必需元素)
A chemical element is considered essential If it is required for a plant to complete a life cycle
Hydroponic culture and essential elements(水耕法與必需元素)
Researchers use hydroponic culture (水耕法) to determine which chemicals elements are essential
Figure 37.3
TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential.
RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral deficiencies in soil.
Control: Solution containing all minerals
Experimental: Solution
without potassium (K+)
APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants.
17 essential elements=9 macro- and 8 micrnutrients
Nine of the essential elements are called macronutrients (巨量營養素), because plants require them in relatively large amounts
C, O, H, N, S, P, K, Ca
The remaining eight essential elements are known as micronutrients (微量營養素)
Because plants need them in very small amounts
Cl, Fe, B, Mn, Zn, Cu, Mo, Ni
Essential elements in plants
Symptoms of Mineral Deficiency (礦物質缺乏的症狀)
The symptoms of mineral deficiency
Depend partly on the nutrient’s function
Depend on the mobility of a nutrient within the plant
Chlorosis (黃化現象)
Deficiency of a mobile nutrient (移動力強的元素)
Mg
Usually affects older organs more than young ones
Drawing power (汲取力) is stronger in young organs
Deficiency of a less mobile nutrient (移動力弱的元素)
Fe
Usually affects younger organs more than older ones
The most common deficiencies
Are those of nitrogen (N), potassium (K), and phosphorus (P)
Figure 37.4
磷缺乏
鉀缺乏
氮缺乏
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Concept 37.2: Soil quality (土壤質地) is a major determinant of plant distribution and growth
Along with climate (氣候)
The major factors determining whether particular plants can grow well in a certain location are the texture and composition of the soil (土壤質地與組成)
Texture (質地)
Is the soil’s general structure
Composition (組成)
Refers to the soil’s organic and inorganic chemical components
Texture and Composition of Soils(土壤質地與組成)
Various sizes of particles derived from the breakdown of rock (岩石) are found in soil
Along with organic material (humus腐植質) in various stages of decomposition (分解)
The eventual result of this activity is topsoil (頂層土壤)
A mixture of particles of rock and organic material
The topsoil (表土/頂層土壤) and other distinct soil layers or horizons (土壤分層)
Are often visible in vertical profile (垂直剖面/斷面) where there is a road cut or deep hole
The availability (可利用性) of soil water and minerals
After a heavy rainfall, water drains away from the larger spaces of soil. But smaller spaces retain water because of its attraction to surfaces of clay and other particles
The film of loosely bound water is usually available to plants (與土壤結合不緊密的薄水層的水才能被根吸收)
Figure 37.6a
(a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root.
親水性土壤粒子
土壤結合不緊密
親水性
土壤粒子
土壤結合
不緊密

Acids (???) derived from roots contribute to a plant’s uptake of minerals when H+ displaces (排擠/取代) mineral cations from clay particles (粘土粒子)
Cation exchange in oil (土壤中的陽離子交換)
Soil Conservation and Sustainable Agriculture
土壤保育與永續(可持續)農業
In contrast to natural ecosystems (自然生態系統)
Agriculture (1) depletes the mineral content of the soil, (2) taxes water reserves, and (3) encourages erosion
The goal of soil conservation strategies (土壤保育策略的目標)
Is to minimize this damage
Fertilizers (肥料)
Commercially produced fertilizers
Contain minerals that are either mined or prepared by industrial processes
“Organic” fertilizers (有機肥料)
Are composed of manure (糞便), fishmeal (魚肉), or compost (堆肥)
Deficiency warnings from “smart” plants
Agricultural researchers are developing ways to maintain crop yields while reducing fertilizer use
Genetically engineered “smart” plants (遺傳工程智慧植物) inform the grower when a nutrient deficiency is imminent (急迫性營養缺失)
Figure 37.7
Irrigation (灌溉)
Irrigation, which is a huge drain on water resources when used for farming in arid regions (乾旱地區)
Can change the chemical makeup of soil
Topsoil from thousands of acres of farmland
Is lost to water and wind erosion (水與風的侵蝕) each year in the United States
等高線耕地
Certain precautions (預警)
Can prevent the loss of topsoil
The goal of soil management (土壤管理的目標)
Is sustainable agriculture (永續農業), a commitment embracing (using) a variety of farming methods that are conservation-minded (保育理念)
Soil Reclamation (土壤復育)
Some areas are unfit for agriculture
Because of contamination of soil or groundwater with toxic pollutants
A new method known as phytoremediation (植物復育)
Is a biological, nondestructive (非破壞性) technology that seeks to reclaim contaminated areas
A part of bioremediation (生物復育)
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Concept 37.3: Nitrogen is often the mineral that has the greatest effect on plant growth
Plants require nitrogen (N) as a component of
Proteins
nucleic acids
chlorophyll
other organic molecules
Soil Bacteria and Nitrogen Availability (氮的利用)
Nitrogen-fixing bacteria (固氮細菌) convert atmospheric N2 to nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis
N2+8e-+8H++16ATP 2NH3+H2+16ADP+16Pi
Figure 37.9. The role of soil bacteria in the nitrogen nutrition of plants.
nitrogenase
Improving the Protein Yield of Crops
Agriculture research in plant breeding
Has resulted in new varieties of maize, wheat, and rice that are enriched in protein
Such research
Addresses the most widespread form of human malnutrition (營養不良): protein deficiency
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Concept 37.4: Plant nutritional adaptations often involve relationships with other organisms
植物營養適應通常包括其與其它微生物的關係
Two types of relationships plants have with other organisms are mutualistic (相互的)
Symbiotic nitrogen fixation (共生的固氮作用)
Mycorrhizae (菌根)
The Role of Bacteria in Symbiotic Nitrogen Fixation (共生固氮作用細菌的角色)
Symbiotic relationships with nitrogen-fixing bacteria (固氮細菌) by coevolution (共同演化)
Provide some plant species with a built-in source of fixed nitrogen
From an agricultural standpoint
The most important and efficient symbioses (共生) between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)
Along a legumes possessive roots are swellings (膨脹物/隆起物) called nodules (根瘤), plant cells
Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria
Figure 37.10a
Nodules
Roots
(a) Pea plant root. The bumps (腫塊) on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant.
根瘤
Inside the nodule (根瘤), which a plant cell
Rhizobium bacteria assume a form called bacteroids (類菌體), which are contained within vesicles (囊泡) formed by the root cell
Figure 37.10b
5 m
(b) Bacteroids in a soybean root nodule. In this TEM, a cell from a root nodule of soybean is filled with bacteroids in vesicles. The cells on the left are uninfected.
大豆根瘤中的類菌體
vesicle
Infected root
cell of nodule
Bacteroids within vesicle
囊泡中的
類菌體
Uninfected cell of root
The bacteria of a nodule (根瘤中的細菌)
Obtain sugar from the plant and supply the plant with fixed nitrogen
Each legume (豆科)
Is associated with a particular strain (菌株) of Rhizobium
Development of a soybean root nodule
(大豆根瘤的發育)
2.
The Molecular Biology of Root Nodule Formation
The development of a nitrogen-fixing root nodule depends on chemical dialogue (化學對話) between Rhizobium bacteria and root cells of their specific plant hosts
Symbiotic Nitrogen Fixation and Agriculture
共生的固氮作用與農業
The agriculture benefits of symbiotic nitrogen fixation
Underlie crop rotation (作物輪作/輪耕)
In this practice
A non-legume such as maize is planted one year, and the following year a legume is planted to restore the concentration of nitrogen in the soil (恢復土壤氮濃度)
Mycorrhizae and Plant Nutrition (菌根與植物營養)
Mycorrhizae (菌根), may be an evolutionary adaptation
Are modified roots (變形根) consisting of mutualistic (相互的) associations of fungi and roots
The fungus (真菌)
Benefits from a steady supply of sugar donated by the host plant (寄主植物穩定地供給糖類給真菌)
In return, the fungus
Increases the surface area of water uptake and mineral absorption and supplies water and minerals to the host plant (真菌回報以增加寄主植物根的表面績，以增加水份與礦物質的吸收)
Produce growth factor and antibiotics for host plants
The Two Main Types of Mycorrhizae (菌根)
In ectomycorrhizae (外根菌), no formation of root hair
The mycelium (菌絲體) of the fungus forms a dense sheath (濃密的鞘) over the surface of the root
Figure 37.12a
a
(a) Ectomycorrhizae. The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant.
皮層
表皮
內皮
The Two Main Types of Mycorrhizae (菌根)
In endomycorrhizae (內根菌), formation of root hair
Microscopic fungal hyphae extend into the root
Figure 37.12b
Epidermis
Cortex
Fungal hyphae
菌絲
Root hair
10 m
(LM, stained specimen)
Cortical cells
Endodermis
Vesicle
Casparian
strip
Arbuscules
枝狀瘤
2
(b) Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex.
皮層
表皮
內皮
Agricultural Importance of Mycorrhizae
(菌根在農業上的重要性)
Farmers and foresters
Often inoculate (接種) seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae
Green manure and crop rotation (綠肥與輪作)
Epiphytes, Parasitic Plants, and Carnivorous Plants
Some plants have nutritional adaptations (營養適應) that use other organisms in nonmutualistic ways (非互利共生)
Epiphytes (附生植物)
Parasitic Plants (寄生植物)
Carnivorous Plants (食蟲植物)
Exploring unusual nutritional adaptations in plants
Figure 37.13
Staghorn fern,
an epiphyte
EPIPHYTES
PARASITIC PLANTS
CARNIVOROUS PLANTS
Mistletoe,
a photosynthetic
parasite
Dodder, a
nonphotosynthetic
parasite (菟絲子)
Host’s
phloem
Haustoria
Indian pipe, a
Nonphotosynthetic
parasite (水晶蘭)
Venus’ flytrap
Pitcher plants
Sundews
Dodder
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The Molecular Biology of Root Nodule Formation