PP4: soil moisture and niche

why is soil moisture considered a critical factor in determining plant distribution and growth?

Soil moisture determines whether plants can obtain enough water to maintain cell activity, avoid desiccation, and support growth

how does water availability change throughout the soil profile during drought?

plants initially absorb water from upper soil horizons; as the surface dries, they increasingly absorb water from lower horizons

why are upper soil horizons especially important for water absorption

most roots are concentrated near the soil surface, so water is absorbed where root density is highest

What happens to soil moisture during small rainfall events?

Small rainfall events periodically recharge the surface soil horizons.

what is the largest source of soil-water recharge according to the lecture

snow during the winter

how does soil moisture change after trees break bud and begin flushing

water availability begins to decrease as trees use water for growth and transpiration increases

why does soil moisture continue to decrease during early summer

Tree and plant transpiration is high during early summer, causing continued water loss from the soil

why is water essential for plants

Water keeps plants turgid, maintains cell activity, and helps move nutrients through the plant

what two processes can cause plant death late in the summer

Desiccation and using more photosynthate than the plant produces

where are most tree roots located in the soil profile

Most roots are concentrated in the upper 20 cm of soil

where does a plant absorb the most soil water

It absorbs water where water is most available and where root density is highest

how does root distribution affect water absorption during drought

As upper soil layers dry, plants increasingly rely on roots in deeper soil layers where water remains available

how does oak rooting depth compare with pine rooting depth

Oaks generally have deeper rooting systems than pines

what percentage of roots can occur in the upper 50 cm of soil

The lecture gives very high percentages, including 94% in 35-year-old loblolly pine, 95% in 50-year-old shortleaf pine, and 96–97% in several oak populations

why are roots concentration near the soil surface

Several factors favor the upper soil layers, including precipitation, organic matter, nutrient availability, and soil temperature

how does precipitation affect root distribution

Precipitation enters primarily through upper soil horizons, making surface soil an important source of water

how does decomposition of organic matter affect root distribution

Decomposed organic matter is mixed into the A horizon and helps the soil hold water

how does soil fertility affect root distribution

Nitrogen availability is higher near the surface, encouraging root growth there

how does winter soil temperature affect root distribution

Upper soil layers freeze first but also thaw first

what additional factors affect root distribution in michigan

The water table and impermeable/hardpan layers can affect where roots can grow.

how do trees primarily deal with drought

They primarily use avoidance mechanisms that help them obtain or conserve water

how does root water-extraction ability help trees avoid drought

Efficient roots can extract large amounts of available water from the soil

how does a high root-to-shoot ratio help a tree during drought?

more root capacity relative to leaf/shoot area helps the plant obtain water and reduces water demand

how does reducing leaf surface area help a plant survive drought

less leaf area reduces water loss through transpiration

how does stomatal control help plants during drought

plants can regulate stomata to reduce water loss

how does a thick cuticle help plants during drought

a thick cuticle reduces water loss from leaf surfaces

how does the ratio of water-conducting to non-water-conducting tissue help drought tolerance

A higher proportion of conducting tissue improves the plant's ability to move water through active tissues

what is a niche in terrestrial ecology

A niche is a theoretical space describing all the needs, abilities, and specializations of a species

how is a niche sometimes represented conceptually

As an “n-dimensional hypervolume,” where each important environmental factor or resource is an axis

what is the fundamental niche

The range of conditions and resources under which a species could potentially maintain a viable population, based on site factors alone

what is a realized niche

The conditions and locations where a species actually exists after biological interactions with other organisms are considered

what is the key difference between the fundamental and realized niche

The fundamental niche describes where a species could exist; the realized niche describes where it actually exists

how do competitors, predators, and parasites affect a species’ realized niche

biological interactions can restrict the species from occupying its entire fundamental niche

what is the principle of competitive exclusion

no two species can occupy the same realized niche

why can two species occur across a broad area when they are separated but occupy different niches when they occur together

competition can force species into different positions of their potential niche

how can competition eventually contribute to niche differentiation

competition and mutualisms can contribute to genetic differentation, which leads to niche differentitation

what are the three components of a plant’s niche

spatial, temporal, and functional

what is the spatial component of a plant’s niche?

the physical site or microsite where a plant occurs and competes with other species

how can two species differ in their spatial niches?

they may occupy different physical environments, such as dry uplands versus swamps

what are examples of species occupying different spatial niches?

black oak occurs in dry uplands, while black ash and buttonbush occur in swamps

what is the temporal component of a plant’s niche

the relative time during ecological succession when a species occurs

how can two species differ in their temporal niches

one species may occur early in succession while another occurs later

what are examples of species with different temporal niches

aspen occurs early; red oak occurs early-to-mid; sugar maple and american beech occur late

what is the functional component of a plant’s niche

the physiological adaptations and natural-history traits that determine how a species functions

how can two species differ in their functional niches

their physiological adaptations can use them to respond differently to environmental conditions