Saturday, November 19, 2016

Ramble Report November 17 2016



Today's Ramble was conducted by our guest leaders: Dr. Chelsea Cunard and Carly Phillips.
Here's the link to Don's Facebook album for today's Ramble. (All the photos in this post are compliments of Don.)
Today's post was written by Dale Hoyt.

A message from Linda to all the Ramblers:
"What a great year of rambling, poetry, fellowship, art, and learning it has been. I am awed by being a part of this group. Thanks to all of you! L."

Attendees:42, another new record!

Announcements:

Cafe au Libris; ACC Library, Mon., Nov. 28 @ 7PM. J. Drew Lanham will be speaking about his book, The Home Place: Memoirs of a Colored Man's Love Affair with Nature.
Today's Ramble is the last for the year. We will resume regular Rambles on March 3, 2017.
We will probably have a few informal rambles during the hiatus. They will be announced in advance by email. (You'll be notified when or if Frost Flowers appear.)
When the snack bar in the Visitor's Center opens we will meet for coffee and talk at 10:00 AM. on Thursdays. This will just be a chance to continue our friendships and, weather permitting, enjoy a short walk in the woods.
Visit this page to see the current Announcements.

Today's reading: Bob Ambrose celebrated the last Ramble of the year with another of his original poems, this one inspired by frost flowers. (If you're a new Rambler you probably don't know what frost flowers are. This post will help put Bob's poem in context.


To Make a Frost Flower

You could go a whole life
scarcely aware of ephemera.
How frost flowers grace

the morning hours in unkempt
ditches, ragged shoulders,
borders and abandoned fields

that first hard freeze of fall.
Consider the White Crownbeard
how it grows. It flourishes

in heat of summer, flowers
ugly early autumn, leaves
a stick carcass standing

barren to the bitter wind
that rattles down the winter.
But come the quiet dawn

when cold envelops open
fields and seeps inside
the hardened earth —

when morning crackles
frostweed blooms. Up
from old roots, sap bleeds

through breached stems,
oozing into open air
as frozen locks of cotton

candy, silver swirls
of crystal clouds leaven
its now broken body.

Translucent grace is born
to morning, gone by noon.
Wounded by winter the weed

turns guts to ghostly flowers
and waits for the inconceivable
spring to rise again from roots.

You can find more of Bob's poems at Reflections in Poetry and his book of poems, Journey to Embarkation, at Avid Books or one of the online booksellers.

Today's route: We walked to the bottom of the Dunson Native Flora Garden where we sampled soil cores from two locations. From there we walked to the flood plain and into the woods east of the power line where we looked at more soil cores and some of us got our hands dirty participating in soil texture analysis. Then back to the Visitor's Center where several people shared their homemade cookies and breads with all the Ramblers.

Show & Tell: Richard Saunders brought two "hedge balls" or "hedge apples", the fruits of the Osage Orange (Maclura pomifera) tree. Before European settlement the distribution of this species was confined to S. Oklahoma and Texas, but it subsequently became widely used as a hedge row and is now naturalized in almost every state. The fruit is suspected to be a "ghost of evolution" or anachronistic fruit – fruits that appear to have no modern day dispersal agents. It has been suggested that some of the large, now extinct Pleistocene mammals, like giant ground sloths may have fed on the fruits and disseminated the seeds. Another common name for the tree is "bodark" an English corruption of French bois d'arc, meaning bow wood. The Native Americans preferred the tree for the manufacture of bows and the Osage tribes in the area where it grew controlled the trade.

Our guest leaders today were Dr. Chelsea Cunard and Carly Phillips. Chelsea recently received her Ph.D. from UGA studying the relationship between the soil microbial community and Microstegium. Carly is currently a student in the Odum School of Ecology and works in Northern Alaska on plant-microbial interactions in soils that remain frozen for much of the year.

Soil classification. Soils, like plants and animals, are classified in a hierarchy of levels. In animals the highest level under the kingdom is the phylum and there are about 25-30 animal phyla. By comparison, in soils the highest level of classification is called the order and there are 12 orders currently recognized. The typical soils of our area are called Ultisols and are frequently red in color because they contain large amount of iron oxides (rust). You can find a more exhaustive description of Ultisols here. Ultisols are typically not very fertile. The relatively high rainfall in the southeast produces extensive leaching of the soils. As a result, they are low in the mineral nutrients needed by plants. This doesn't mean they are not productive, as trees and other kinds of vegetation have ways to extract what they need from the nutrient poor soil. (See mycorrhizal fungi later in this post.)

Soil Horizons
By Wilsonbiggs - derived work from File:SOIL PROFILE.png by Hridith Sudev Nambiar at English Wikipedia., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=46207693 
Soil profiles. Soils are like a fancy cake – a stack of layers with frosting on the top. Unlike a cake, the layers of soils are created by biological, physical and chemical forces which, acting together, produce a discontinuous gradient in appearance and texture from the surface to the bedrock. In soils these visible layers, including the frosting, are called horizons and are identified by letters, e.g., O, A, and B. (There are many more recognized soil horizons; for a list and further details see this Wikipedia article.) Different kinds of soils vary in the numbers of identifiable layers. The vertical extent of each layer and its presence or absence varies with the climate, local conditions and many other factors. Never the less, the idea of the soil horizon is useful because it is caused by the factors that influence the development of the soil.

In a forest leaves and other organic debris fall and lay on top of the uppermost soil layer, the O (for Organic) horizon. They have not yet been incorporated into the soil. This will happen when the soil organisms begin to breakdown the leaves. Insects will shred them and fungal spores will germinate and begin to rot them. Worms will carry them into the soil and they will be further degraded. Gradually they will cease to be recognizable as leaves as they become incorporated into the O horizon. Our southeastern soils typically have a very poorly developed O horizon because much of this layer has been lost through erosion caused by 300 years of poor agricultural practices. In much of the south the O horizon of former agricultural fields is a fraction of an inch in thick. (Prior to European settlement the O horizon was over a foot in thickness. )

Further activity by the soil fauna mixes the material in the O horizon with the material below. In addition, rain water dissolves material in the organic layer and transports it downward. This region where the material in the O horizon is incorporated into the soil below is called the A horizon. It is the area in which plant roots and soil microorganisms are most abundant.

Beneath the A horizon and often grading into it is the mineral subsoil, the B horizon. The change in texture and appearance between the A and B horizons is often gradual. Deciding on the boundary is like trying to determine the exact point in a rainbow where the red color stops and the orange color begins. The sharpness of the boundary varies, depending on the local conditions. Where there is a lot of rainfall or soil animal activity the upper horizons may broadly merge into the lower horizon.

To demonstrate these soil horizons Chelsea and Carly selected the lower part of the Dunson Native Flora Garden. This area has a sloping hillside subject to erosion (if it ever rains) and, at the base of the hill, a intermittently wet area. Some areas higher up the hill are devoid of fallen leaves but lower down a leaf layer is present. Leaves tend to accumulate in the wetland at the bottom of the hill.

The profile of a soil can be seen by removing a column of soil, a core, using a coring tool. The coring device is a stout stainless steel tube, about 3/4 inch in diameter and a T-handle at the top. The tube is pushed into the soil with a twisting motion and, when it can't be pushed any further it is carefully removed. A column of soil remains in the tube as it is withdrawn. There is a slot in one side of the tube that permits examination of the soil core brought up.

First core; tiny O horizon on top;
followed by A horizon; B horizon on bottom

Soil cores taken from the hillside showed very little organic layer (the O horizon). Below this very shallow O layer was a broader orange layer, the A horizon, and, below that, a darker orange layer, the B horizon.

(Sometimes there is a thin white layer, called the E horizon, between the A and B horizons, where all the minerals have been leached out of the soil, leaving behind sand and other light colored material. The E refers to the process of eluviation, or the leaching of minerals from the soil layer by downward movement of infiltrating water. We did not see an E horizon in the cores we took today.)

Core with no O or A horizon
Emily and Carly collected a core at a bare spot higher on the hill. It lacked an O horizon and consisted only of reddish colored soils of the B horizon. Apparently the A horizon had been removed by erosion.

Wetland core (L to R: O, A, B horizons)
In the wetter depression a core had a much thicker O horizon followed by a black stained A horizon and a red B horizon.

Carly, who works in the very cold Alaskan environment, told us that there the O horizon may be over a meter thick. The climate is so cold for so much of the year that decomposition is extremely slow, leading to a lot of accumulation in the O horizon.

Coring has limitations and is not the only method to study soils. A better approach is to dig a test pit a meter or two deep to expose the soil horizons down to the bedrock. A book of color chips called the Munsell soil color chart, similar to what you find in a paint store, but standardized, is used to describe the color of the different horizons. Then the texture of the soils in each horizon is determined (see soil texture, later in this post).

Finished with the Dunson Garden, we moved across the power line to the upper flood plain where the original privet removal project had been. A soil core in this area had a thin, dark O horizon followed by a reddish orange A horizon.

Here we learned how to determine the soil texture and find mycorrhiza on the roots of a pine seedling.

Hand soil texture analysis
Cora shows us how it's done
Soil texture. The texture of a soil is determined by the proportions of three common soil ingredients: sand, silt and clay. Chelsea and Carly brought copies of a flow chart that gave "hands on" instructions for determining, by feel, the texture of a soil sample. If you would like a copy of these instructions they can be downloaded from here. A bunch of Ramblers got their hands dirty and discovered that the soil in this area is a sandy clay loam.

Chelsea really digs her work!
The white coverings are the ectomycorrhizal roots
Chelsea carefully dug up a small pine seedling with a trowel, being careful not to disturb its root system. Using a squeeze bottle filled with water she gently washed the dirt away from the root system and, viola!, she had exposed the roots, some of which had tiny white sheaths on their tips. These light colored structures are created by the fungus. They consist of a dense network of microscopic threads, called hyphae (singular: hypha), that make up the body (the mycelium) of the fungus. The mycelium extends out into the surrounding soil and it is so delicate that it almost impossible to remove it intact. Only the part wrapped about the root tips is seen. The fine connections to the rest of the mycelium are broken by removing the plant from the soil. The hyphae that wrap around the root send out a network of more hyphae that penetrates the outer layer of the root, branching and ramifying until they form a net that surrounds the outer root cells. It is at this dense interface that the plant root exchanges carbohydrates for minerals and water from the fungus. Because the fungus never penetrates the root cells, but just surrounds them, it is called an ectomycorrhizal fungus. Fungi of this type form the familiar "toadstool" mushrooms we often see after a rain. (But not all such mushrooms are mycorrhizal. Some are parasitic on living plants, other are saprobic, meaning they subsist on dead organic matter and in the process they rot it.) 

Ectomycorrhizal fungi are commonly associated with conifers and broad-leafed trees in temperate zone forests as well as the evergreen boreal forest trees. When deprived of an ectomycorrhizal connection the tree does not do well. It struggles to obtain the minerals required for growth and frequently suffers water deprivation. You were probably taught that plants absorb water and minerals from the soil through tiny root hairs. This is true, as far as it goes. The fungal hyphae are much smaller in diameter than even the finest root hairs. This smaller diameter means they can explore the microscopically small spaces between soil particles, spaces that root hairs are too large to penetrate. The mycorrhizal network acts like a super-root and acquires more water and minerals than the tree could by itself.

There is a second kind of mycorrhiza associated with even more plant species: Endomycorrhizal fungi. About 80% of the terrestrial plant species form associations with such fungi. In fact, this association dates back to the earliest land plants. Fossils from the Devonian era, approximately 400 million years ago, have structures that resemble those of modern day endomycorrhizal fungi. These fungi are everywhere but are never noticed because they do not produce mushrooms. Their association with their hosts roots is even more intimate – they actually penetrate the cells of the outer layer of the root. Each point of entry branches inside the host cell, forming a tiny hyphal tree called an arbuscule (literally: "tiny tree"). It is through the arbuscule that the fungus exchanges water and minerals for carbohydrates. For this reason these fungi are often called arbuscular mycorrhizal fungi.

Within the last 20 years research has shown that both ecto- and endo- mycorrhizal fungi can form connections with multiple host plants. This means that one fungus it sharing its water and minerals with two or more plants and, in return, receiving carbohydrates from them. And, even more mind-boggling, carbohydrate can be transferred from one plant to another plant via the mycorrhizal fungus. The implications of this are profound. Ecologists have usually portrayed plants as competing with one another for nutrients and sunlight. But if each plant is connected by a fungal associate to multiple other plants couldn't they be sharing nutrients and carbohydrates with one another? Even more exciting, it has recently been shown that plants can send chemical signals to other plants via their mycorrhizal connections. The implications of this discovery have yet to be fully explored.

All the people who made todays Ramble such fun!
Linda and Don and I want to thank all of you for being so curious and asking such stimulating questions during our Rambles this year. We hope you have enjoyed them as much as we have. And we wish you all a happy Thanksgiving.

1 comment:

  1. Nice work, Ramblers. Have a joyous holiday season, and let's home for a mile winter. Spring will be here before we know it!

    ReplyDelete

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