The leaves coming out on the trees is a response to temperature change. Warming in the spring causes a hormonal release in the tree (plant) and therefore triggers the sprouting of leaves. This hormonal reaction is very similar to the response of a plant growing toward the light. This response is triggered by the hormone auxin. Auxin is stopped when exposed to light. This causes plant growth to stop as well. Since only one side of the
plant is exposed to light, the side where auxin
release is not stopped, will continue to grow. This is what causes the "tilting" of the plant toward the light source.
Many plants are able to survive the freezing temperatures of winter because of metabolic changes that occur in the plant between
summer and winter. When plants are damaged by the
cold you see browning of the leaves, injury or
death of flower buds, splitting of bark, or death
of roots. Ice crystals can actually form within
the plant cells if the temperature decreases
really quickly. Luckily this is rare!
Some plants stop growing in July or August and others continue to grow into autumn. These differences are due to hormonal balances in the plants controlled by day length and modified by temperature.
Plant growth can be greatly affected by the
habitat and climate in which it grows. Factors like temperature, sunlight, precipitation, soil moisture, soil nutrients, and length of growing season can all affect plant growth.
There are some factors necessary for all
plant growth: All plants need water, light, air
and minerals but some plants need more water than
others. Different plants require different
environments. This means that what might be
considered warm conditions for some plants will be
considered cold conditions for others. So you
would have to check different environments and
temperatures to answer this question specifically for different plants.
Generally though, temperature influences a wide variety of plant functions, so it is not surprising that soil
temperature affects root growth in many ways.
Root system expansion is a function of three
temperature dependent processes: growth,
development, and orientation. Roots are
responsible for anchoring the plant to the ground
and extracting water and minerals from the soil.
They can also store food. Temperature affects root growth through its influence on root weight, root length, and root diameter. Root development is affected by temperature's effect on root initiation and root turnover.
Lastly, temperature controls root orientation through its impact on the direction of root growth. Stems are responsible for supporting leaves and flowers physically, holding the leaves and flowers in the best position for food gathering and reproduction and storing nutrients for future use. Leaves are
responsible for absorbing the suns rays, the
majority of the photosynthetic production, taking
in carbon dioxide and releasing oxygen and water
vapor (breathing), and removing waste products
from the plant. At moderate temperatures most
plants show stem elongation and leaf growth
because of an increase in photosynthesis. The plant acquires more carbon through this process and therefore is able to make bigger leaves or grow in general.
In extreme temperatures theses growing processes slow down. For example, desert plants usually grow smaller leaves minimizing water loss. In their effort to survive in a rather hostile environment, desert plants may have this feature to help them deal with the harsh
climate and hot temperatures: small or thick
leaves, hairy leaf surface, shiny or waxy leaves
and deep tap roots or extensive surface
In cold environments, plants may use
other mechanisms for surviving. Evergreen plants, such as many conifers, often have narrow,
needle-like leaves and a thick waxy coating, and
these adaptations help them to conserve water
during winter. Deciduous plants, such as oak, shed
their leaves in the autumn, shutting down almost
completely, relying on the food stored in their
underground roots to get them through the winter.
Apart from the problem of a shortage of available
water during the winter, photosynthesis in the
leaves would also be difficult because there are
only a few hours of very weak sunlight.
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