Agricultural Ecology Exam 1 Flashcards from WYM UF

The energy accumulated by plants via photosynthesis is referred to as primary production.

Primary producers are plants. Plants harvest the energy of the sun. They are also referred to as autotrophs (auto means self, troph means food). Heterotrophs (hetero meaning other) are consumers (they get their food from others, these are things that eat plants).

Plants typically only use 2% of incoming solar radiation.

Agriculture uses solar energy to produce the biomass that we harvest. Biomass is the total amount of energy in an ecosystem at a given point in time.

Carbon fixation occurs during photosynthesis. Plants harvest CO2 from the atmosphere to do this. Oxidation also occurs during photosynthesis. Water is oxidized as it loses electrons, but it is considered inorganic.

The end products of respiration are carbon dioxide and water (which are the inputs for photosynthesis).

There is no nitrogen fixation as part of photosynthesis. Nitrogen fixation occurs in a variety of processes as part of the nitrogen cycle.

Trophic pyramids represent the transfer of energy between trophic levels. So, the shape in the form of the pyramid is reflective of the inefficiency of energy transfer between trophic levels.. The percentage of energy that is transferred between trophic levels is typically only around 10%.

Gross primary production is  all  the energy captured by plants GPP=P+R. P is production. R is respiration. It does not account for the energy lost to respiration (R)- when you take that into account you are talking about NET primary productivity (NPP=P-R).

Assimilated energy accounts for both production and energy lost to respiration. In terms of energetics, anything that is not assimilated refers to waste that is excreted.

A food web is more accurate than a food chain because most relationships are not just simple linear relationships in our agricultural and natural systems. You have organisms that feed at multiple trophic levels or on multiple organisms, etc.

Review the principles of production: you must understand assimilation efficiency to understand why birds have the lowest Production to Assimilation efficiency. The P/A ratio refers to the proportion of energy that an organism can use to produce new biomass. How efficient are different organisms at converting consumed food into body mass. A higher ratio means more energy can be used for growth and reproduction. Mammals, as warm-blooded animals, have a pretty low P/A ratio because they utilize a significant portion of the energy derived from food consumed to maintain their body temperature (homeostasis). This means of all the energy they take in, they are using up a lot of it and not converting it to tissue/biomass. The P/A is even lower for birds because they maintain body temperature AND expend huge amounts of energy in flight.

Phototropism is plants growing towards or away from a light source (from book readings).

Water vapor, methane, and carbon dioxide are major contributors to the build-up of greenhouse gases. Nitrite is not a major contributor.

Please review the sequence of events leading to ocean acidification. How will climate change contribute to the acidification of the oceans?  What is the hypothesized impact on marine ecosystems? If there is increased carbon dioxide in the atmosphere, this will lead to increased carbon dioxide dissolving into the oceans. This increase in carbon dioxide will lead to decreased ocean pH (acidification).

Trees are carbon sinks. Trees store carbon, they take up carbon dioxide and convert it to tissue. So, if we are removing forests, we are removing carbon sinks (places we can store carbon). Carbon dioxide (and other gases) in the atmosphere traps heats and warms the atmosphere (this is referred to as the “greenhouse effect” as the atmosphere is acting like a greenhouse).

Carbon and energy leave the agricultural ecosystem via respiration, burning in shifting cultivation (slash and burn) agricultural practices, or harvest. Photosynthesis is how carbon enters the agricultural system.

***Be able to draw the carbon and nitrogen cycle including all inputs and outputs and various forms.***

In terms of climate change, we can mitigate the potential effects by lessening the amount of heat-trapping gases like carbon dioxide and methane in the atmosphere through a reduction in their production/release or recapture.

Cultural energy is a type of indirect energy. Cultural energy includes human labor, nitrogen fertilizer, animal labor, etc.

Applying forms of indirect energy like pesticides will allow a plant to invest less in defense against insects by producing less of things like secondary plant compounds.

When we invest indirect energy like fertilizers or pesticides into an agricultural ecosystem, the plants can frequently change how they allocate energy. Instead of investing in producing secondary plant compounds in defense of insect pests, if we apply pesticides and there aren't pressures exerted by pests, they can allocate that energy to reproduction. Organisms are typically not going to forego reproduction. For example, when we apply fertilizer, plants actually get more nutrients and allocate MORE energy in reproduction (producing fruit). Anything we add to the agriculture system is typically to get plants to produce more fruits (or grow larger) to maximize yield.

Fertilizer is a type of indirect energy. It is something we add to the agricultural system and requires a lot of fossil fuels (energy) to make it as part of the Haber-Bosch process.

Heavy synthetic fertilizer use can destroy soil structure. Fertilizers typically contain nitrogen and phosphorus in the form of salts (N salts are more problematic). Salts are considered an environmental pollutant. In large quantities or applied inappropriately, salts can build up and damage soil structure!

When we overuse fertilizers, they leave behind salt and this destroys the structure of the soil making it difficult for the soil to hold nutrients and water.

Conventional agriculture does require intensive energy inputs - fertilizer, pesticides, and irrigation are all heavily reliant on fossil fuels to produce and/or deliver.

One benefit of intensive cultivation (tilling) is the control of weeds. Tilling the soil doesn’t necessarily help control most insect pests.  In fact, if it is a non-mobile soil pest, tilling could help spread them to different parts of the field or between fields.

Conventional agriculture does typically involve a reset of the successional process. Remember, we remove biomass in harvest and then typically disc the land to replant (starting over). That is a reset of the succession process.

Monoculture is the cornerstone of conventional agriculture.

CAFO= factory farming (Concentrated Animal Feeding Operation). These operations typically ADD huge amounts of nutrients to the environment because of the intense production of animal waste.

The ways that nutrients are lost from agricultural ecosystems includes leaching, harvest, and erosion.

Genetic engineering has decreased the diversity of crops grown. For example, we grow a handful of genetically-engineered corn and soybean cultivars on much of the agricultural land in the U.S.  Historically, there were many regional cultivars of each crop type grown, GE crops have really decreased that.

And, genetic diversity of plants and animals has decreased in the last century. In agriculture, we tend to grow or raise the fastest, largest, disease resistance varieties over growing a diversity of different types.

Plants that have been genetically modified to contain vaccines are NOT currently available on the market.

Cellulosic ethanol is more environmentally friendly than grain ethanol because it uses the entire plant, not just the grain (corn kernels). Also, you could utilize crops other than corn if you could use the whole plant. This would allow you to potentially use a plant that grows faster, accumulates more biomass and that doesn’t require a lot of water or fertilizer.

However, cellulosic ethanol that can utilize the entire plant requires the use of enzymes to break down the cellulose and those enzymes are fairly expensive. This makes cellulosic ethanol production on a whole less cost effective. Also, the waste product of cellulosic ethanol can be used to create nanotubles (see assigned video on topic).

C4 plants like sugarcane (and other grasses) are very efficient at converting solar energy to biomass, much more efficient than C3 crops (which include things like soybeans, most vegetables, etc.)

Synthetic pesticides ARE quick acting and effective.

Common criticisms associated with use of synthetic pesticides include high cost, environmental toxicity, and the potential for increased resistance.

The pesticide treadmill refers to the reliance of agriculture on increasing amounts and types of pesticides. We use something to kill insects, they evolve resistance, we formulate something new, they evolve resistance, etc.

Resilience is straight from the book. It is a property of communities.

Natural systems do not require nutrient inputs like agricultural systems. We don't have to fertilize forests.

Agricultural systems are not closed systems; things outside the agricultural system influence them. We add fertilizer, for example.  Diseases of native plants can impact closely-related agricultural plants, etc.

Both natural and agricultural systems have impacts on surrounding habitats (because they aren’t closed systems).

Agricultural ecosystems are NOT more complex than natural ecosystems. In fact, you could argue the opposite because we usually invest a lot of energy in simplifying conventional agricultural systems to monocultures. Because agricultural ecosystems are not inherently more complex, you would not expect them to have more complex trophic interactions.

Natural ecosystems typically do have lower net productivity, but higher species diversity when compared to agroecosystems.

Natural systems are not less stable than agricultural ecosystems.

ALL inorganic fertilizers (meaning we make them from nitrogen gas and phosphorus mined from rock) require a massive input of fossil fuels to make an inorganic form of nitrogen through the Haber Bosch process. The other major element of inorganic fertilizers is mined.

Yield can be increased by intercropping (it is a dependent on the specific scenario).

When you are considering a polyculture, which contains multiple different crops grown at the same time together along with other organisms, that is an example of a community because you have multiple populations of different species. An ecosystem would also include non-living things (abiotic) factors.

An off-target effect is when an agricultural practice has an unintended negative consequence. Examples would include spraying a pesticide to kill a pest of a crop that also kills pollinators or applying fertilizers that move outside the agricultural system and cause toxic algal blooms in nearby waterways.

Hardpan is a negative development in agricultural fields that is associated with intensive tillage or cultivation (when we churn up the soil).

Soil degradation also occurs when we overuse synthetic fertilizers. Often salts are left behind and act as an environmental pollutant.

Agriculture does account for almost half of the water used in the U.S. (eek!)

Make sure you are clear on the difference between a population, community, and ecosystem. A population is a group of individuals of one species that are living in a given area. Community refers to all living organisms in the area. If you expand that to include the non-living things that affect those organisms, then you are talking about an ecosystem.

 Some of you are making mistakes regarding the concepts of mineralization/ mobilization/immobilization/organic/inorganic.

Mineralization is when a nutrient is changed from an ORGANIC form where it is immobilized (unavailable to plants) because it is incorporated within tissues to an INORGANIC form where it is mobile in the sense that it is in a form that can be utilized and taken up by plants.

So, manure and compost are both organic fertilizers. The nitrogen and phosphorus in manure and compost is still IMMOBILIZED. It is not in a form plants can use until bacterial and fungal decomposers work their magic to MINERALIZE it so that the nutrients are in an INORGANIC form that plants can use. This is why organic fertilizers are considered slow-release fertilizers.

Synthetic (also called chemical or inorganic) frtilizers that we manufacture are sold in the INORGANIC forms of those nutrients.  Remember, plants take up nutrients in the INORGANIC forms. Those nutrients are in their  “mineralized” forms already and can be immediately used by plants, no microbes needed! That is why these fertilizers are often referred to as quick-acting or fast-release fertilizers.

Phosphate, nitrate, and ammonium are INORGANIC forms of those nutrients that can be taken up immediately by plants.

Inorganic forms of nutrients are SOLUBLE. They dissolve in water and can be taken up by plants.

Organic forms of nutrients are immobilized and NOT SOLUBLE, they cannot be dissolved in water and taken up by plants. They need help from microbes to be mineralized into their inorganic form.

Know the difference between macro and micronutrients and be able to identify them.

Biological nitrogen fixation

Generally refers to the mineralization of organic forms of nitrogen in the soil to inorganic forms of nitrogen that can be utilized by plants.

There are all sorts of bacteria and fungi that participate in this process.

In addition to the nitrogen fixation that occurs in the soil, there is also a very important mutualism between certain plants (legumes like soybeans) and certain bacteria (like Rhizobia). You should know the benefits that each partner receives in this association. You also understand how these associations may change the nutrient needs for a plant. For example, if a plant has these bacteria and is being provided with nitrogen it can use, it would likely not require as much nitrogen-based fertilizer.

Phosphorus in Ag

P does not have an atmospheric component. We mine it from rock…and we do a lot of that here in Florida!

Be familiar with the role these fungal organisms play in the association with plants.

Nitrogen in Ag

Have a complete picture of the N cycle in your head with all inputs and outputs and forms. If you can draw that and know which forms are usable by plants, you can answer almost any question I ask about nitrogen.

What is Haber Bosch process? What does it do with respect to agriculture? What are the inputs and outputs? Remember that the Haber Bosch process is also referred to as industrial nitrogen fixation.

Nitrogen enters the ag system through mineralization- it has to start with mineralization to make that nutrient available to plants. Nitrogen typically becomes immobilized in plant tissues.

Of the options presented to you in the question regarding the path of nitrogen through the ag system, only one scenario started with mineralization and ended with immobilization. That’s the correct one.

Be able to explain denitrification and where it happens in the N cycle? Denitrification is prevalent in anaerobic environments and results in releasing nitrogen back as a gas to the atmosphere. It is performed by denitrifying bacteria. Nitrate is reduced to nitrite that is then reduced in nitrogen gas.

Be able to identify all the chemical forms of nitrogen that are important in agriculture and their names. For example, nitrogen gas, nitrite, nitrate, ammonia, and ammonium.

I have very many versions of this question so make sure you know the nitrogen cycle backwards and forwards!

In agricultural systems, the biggest removal of nitrogen is from harvest!

Potassium in Ag

Understand the importance of potassium and how it behaves and cycles through the agricultural system.

C3 vs. C4

Be able to pick out examples of pants utilizing each of these pathways based on information from lecture and the book.

Understand the general difference between the two pathways and the benefits/limitations of plants that utilize them.

Understand how these two different photosynthetic pathways can be utilized in strategic light management in agricultural systems.

Key terms associated with C3/C4 are rubisco and photorespiration. 

What is photorespiration and in what plants (and under what conditions) would it occur?

Light

The leaf surface does have its own sunblock compounds to keep out a lot of the UV (mostly B) radiation.

Understand all the potential paths incoming solar radiation takes as it travels to Earth’s surface. Light is NOT adsorbed.  It can be re-radiated from the land surface (feel that heat coming off the asphalt) or absorbed or reflected by the atmosphere (or we would all be crispy nuggets!).

Remember, most plants reflect green/yellow wavelengths.  That is why they appear green!

Review the saturation point AND compensation point- know what happens to plants if light levels are above and below both of those points.  Above the compensation point, light levels are damaging to plants.

Infrared radiation influences germination hormones. (A lot of this light stuff was from the book so reread that if you missed a lot of these questions).

Temperature

What is a chill hour in the context of agriculture?

What crops do we associate with chill hour requirements?

Hint- Think about where things are grown. There are no chill hour requirements for avocados…remember those are grown in subtropical and tropical regions! Some of the crops that we are starting to grow in North Central Florida like peaches are cultivars that have been developed here at UF for this region and have a low number of chill hours required when compared to those grown further north.

Understand how heat units are employed in agriculture. How can they inform a farmer about the growth of pest insects?

Hardening involves short-term exposure to variable temperature environments and increased irrigation.

Know the difference between photoperiod and phototropism.

Remember that photoperiodism is based on the uninterrupted hours of DARKNESS.

Understand what is meant by short-day, long-day, and day-neutral plants. Be familiar with examples of those provided in lecture or the book (pg. 49-50).  Know which season short and long day plants would flower.

If it a long day plant, it flowers when it has a short night (shorter than some critical value).

If it is a short day plant, it flowers when the nights are long (longer than some critical value).

Day neutral does not flower in response to light as the main cue.

Be able to describe structural vs. physiological adaptations that crop plants may have in response to temperature or light.

 Ex: waxy leaves are considered a structural adaptation in plants grown in high temperature and/or low moisture situations.

 Windbreaks decrease erosion. Remember, windbreaks are just planting that help deflect the wind moving across an agricultural field. If you diminish the wind, you will diminish erosion of soil by the action of the wind on the surface. 

Atmospheric mixing can increase the amount of CO2 at the leaf's surface. 

Volatilization of certain nutrients is an abiotic effect of fire. Go back and look at the definitions of biotic (living) vs. abiotic (nonliving). 

The are many ways to minimize lodging, but practicing minimal tillage is not one of them. The book talks about several ways to minimize lodging if you want to review that. Things like windbreaks, mounding soil around plants, etc.  

Sustainability of swidden agriculture does require a long fallow period. When you slash and burn, you need provide a substantial amount of time for recolonization of plants after harvest so that nutrients can naturally be added back into the system. If you slash and burn and continue to utilize that piece of land, the nutrients are rapidly depleted and the soil is damaged.  

Fire does not add large amounts of nitrogen to the soil because much of the nitrogen is volatilized into the air during fires (this is an abiotic effect of fire). With this in mind, nitrogen would not be found in higher quantities after a fire in the soil environment. Calcium and potassium are two nutrients that you would find in higher concentrations.  

In the book, it discusses the use of fire to prepare sugarcane for harvest.  This chapter of the book is important to read in preparation for the test based on the questions I see that were missed regarding fire.  

A decrease in soil aggregates means you have damaged soil structure. This is a negative outcome of some agricultural practices including shifting cultivation.  

Other questions people tend to miss involve direct vs. indirect effects so revisit those examples from the lectures. Desiccation or drying out is a direct physical effect of wind on crops.  The action of desiccation decreases the boundary layer. 

In contrast, Wind DOES NOT have a direct physical effect on crops via soil erosion. That is an example of an INDIRECT effect because the wind acts on the soil and the removal of soil is what impacts the plant. In the desiccation example, the wind is acting DIRECTLY on the plant.  

When fire is used in swidden or slash/burn agricultural practices, one of the NEGATIVE consequences is increased leaching of nutrients from the soil. This is discussed in the fire chapter in the book. This type of agriculture is often in tropical systems that experience heavy rains and the fire has acted to mineralize many of the nutrients. This means they are soluble in water and can be carried away (along with the soil) during heavy rain events.  

Serotinous cones are those that require fire to open and release seeds. These types of trees are associated with catastrophic crown fires.