Soil and Plant Nutrition

Note three ways the properties of water contribute to soil formation.

Explain how the phrase “too much of a good thing” can apply to watering and fertilizing plants.

Some lawn mowers collect clippings. What is a drawback of this practice with respect to plant nutrition?

How would adding clay to loamy soil affect capacity to exchange cations and retain water? Explain.

How do the young leaves differ in appearance from the older leaves?

In three words, what is the most prominent mineral deficiency symptom seen in this photo? List the three nutrients whose deficiencies give rise to this symptom. Based on the symptom’s location, which one of these three nutrients can be ruled out, and why? What does the location suggest about the other two nutrients?

How would your hypothesis about the cause of this deficiency be influenced if tests showed that the soil was low in humus?

Are some essential elements more important than others? Explain.

If an element increases the growth rate of a plant, can it be defined as an essential element?

Based on Figure 9.17, explain why hydroponically grown plants would grow much more slowly if they were not sufficiently aerated.

Why is the study of the rhizosphere critical to understanding plant nutrition?

How do soil bacteria and mycorrhizae contribute to plant nutrition?

What is a general term that is used to describe the strategy of using photosynthesis and heterotrophy for nutrition (see Concept 28.1)? What is a well-known class of protists that uses this strategy?

A peanut farmer finds that the older leaves of his plants are turning yellow following a long period of wet weather. Suggest a reason why.

The inorganic nutrient most often lacking in crops is 

(A) carbon. 

(B) nitrogen. 

(C) phosphorus. 

(D) potassium

Micronutrients are needed in very small amounts because 

(A) most of them are mobile in the plant. 

(B) most serve mainly as cofactors of enzymes. 

(C) most are supplied in large enough quantities in seeds. 

(D) they play only a minor role in the growth and health of the plant.

Mycorrhizae enhance plant nutrition mainly by 

(A) absorbing water and minerals through the fungal hyphae. 

(B) providing sugar to root cells, which have no chloroplasts.

(C) converting atmospheric nitrogen to ammonia. 

(D) enabling the roots to parasitize neighboring plants.

Epiphytes are 

(A) fungi that attack plants. 

(B) fungi that form mutualistic associations with roots. 

(C) non photosynthetic parasitic plants. 

(D) plants that grow on other plants.

Some of the problems associated with intensive irrigation include all of the following except 

(A) soil salinization. 

(B) overfertilization. 

(C) land subsidence.

(D) aquifer depletion

A mineral deficiency is likely to affect older leaves more than younger leaves if 

(A) the mineral is a micronutrient. 

(B) the mineral is very mobile within the plant. 

(C) the mineral is required for chlorophyll synthesis. 

(D) the mineral is a macronutrient.

The greatest difference in health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, would be in an environment

(A) where nitrogen-fixing bacteria are abundant.

(B) that has soil with poor drainage.

(C) that has hot summers and cold winters. 

(D) in which the soil is relatively deficient in mineral nutrients. 

Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil and one a control without humus. The leaves of the plants grown without humus were yellowish (less green) compared with those of the plants grown in humus-enriched soil. The best explanation is that 

(A) the healthy plants used the food in the decomposing leaves of the humus for energy to make chlorophyll. 

(B) the humus made the soil more loosely packed, so water penetrated more easily to the roots.

(C) the humus contained minerals such as magnesium and iron needed for the synthesis of chlorophyll. 

(D) the heat released by the decomposing leaves of the humus caused more rapid growth and chlorophyll synthesis.

The specific relationship between a legume and its mutualistic Rhizobium strain probably depends on 

(A) each legume having a chemical dialogue with a fungus. 

(B) each Rhizobium strain having a form of nitrogenase that works only in the appropriate legume host. 

(C) each legume being found where the soil has only the Rhizobium specific to that legume. 

(D) specific recognition between chemical signals and signal receptors of the Rhizobium strain and legume species.

Draw a simple sketch of cation exchange, showing a root hair, a soil particle with anions, and a hydrogen ion displacing a mineral cation.

Imagine taking the plant out of the picture in Figure 37.12. Write a paragraph explaining how soil bacteria could sustain the recycling of nitrogen before land plants evolved.

Acid precipitation has an abnormally high concentration of hydrogen ions (H+). One effect of acid precipitation is to deplete the soil of nutrients such as calcium (Ca2+), potassium (K+), and magnesium (Mg2+). Suggest a hypothesis to explain how acid precipitation washes these nutrients from the soil. How might you test your hypothesis?

In many countries, irrigation is depleting aquifers to such an extent that land is subsiding, harvests are decreasing, and it is becoming necessary to drill wells deeper. In many cases, the withdrawal of groundwater has now greatly surpassed the aquifers’ rates of natural recharge. Discuss the possible consequences of this trend. What can society and science do to help alleviate this growing problem?

The soil in which plants grow teems with organisms from every taxonomic kingdom. In a short essay (100–150 words), discuss examples of how the mutualistic interactions of plants with bacteria, fungi, and animals improve plant nutrition.

Making a footprint in the soil seems like an insignificant event. In a short essay (100–150 words), explain how a footprint would affect the properties of the soil and how these changes would affect soil organisms and the emergence of seedlings.