Tuesday, November 25, 2014

Fall Colors

Most would say that autumn's splendid array of colors comes from the leaves turning (especially those on the east coast). However, there is another often overlooked emergence of color from another organism. After the first fall rains, fungi begin to come out of the woodwork (and soil)! Hiking through wooded and even grassy areas one begins to notice these little guys everywhere. Fungi can come in a variety of colors, shapes, and sizes*. We may immediately think of the traditional mushroom with a cap and stipe (stem). However, there are others that have many branching limbs or just resemble a large blob.

Hygrophorus spp.

Ramaria formosa

Pseudohydnum gelatinosum

So why do we have to wait for a change in weather for these guys to come out of hiding? Furthermore how do mushrooms or fruiting body of the fungus form? 

Well as stated, mushrooms are the fruiting body of the fungus. The mushroom is not the organism itself, it is part of the organism, just as an apple is part of the tree. Not all fungi form these structures. Think of a bread mold. It would be pretty crazy to pull a moldy loaf of bread out of the cupboard and see a mushroom trying to break out of the bag. When are are talking about mushrooms we are talking about basidiomycetes and acsomycetes. These fungal phylum differ in how they product their spores. Basidiomycetes have their spores on the outside of a cell known as a basidium, This looks like a club with small roundish microscopic objects attached at the end. Ascomycetes produce spores that are encased inside of an ascus or long microscopic sack. This is where our story begins - the fungal spore. The spore is released from the basidium or ascus to a new substrate (soil, wood, plant material). The spore germinates or begins to grow by sending out a germ tube. This "tube" begins to form hyphae (thin threads). Fungi can undergo sexual reproduction where DNA from these hyphae are brought into one hypha (there are lots of steps I am skipping here. If you want a few more details you can check out this diagram Basidiomycete Life Cycle). These hyphae grow and grow forming mycelia (many hyphae together) through out the soil, duff layer, or wood gathering nutrients via excretion of enzymes. After enough nutrients are gathered and the environment is damp (but not flooded) and cool (not cold) the fungus can bring hyphae together into larger bunches, to form what we know as the mushroom. First a "button" is formed where the cap and stalk are inside an "egg." As the stalk grows it pushes the cap through the egg. This egg is known as the universal veil. The remnants of this veil can be seen on Amanitas.

Button stage with universal veil breaking a part. 

Veil remnants or "scales" 

     Mature fruiting body or mushroom

Mushrooms can be found on growing a various different substrates: wood, soil, duff, or even dung! This is due to the fact that fungi have different feeding strategies that all boil down to how they acquire carbon. Some are more adapted to being able to digest complex carbohydrates from dead woody materials such as cellulose and lignin. These guys produce enzymes that allow them to break down these compounds for energy. We will typically find them growing on logs. These guys are known as saprotrophic fungi. 

                              Hygrophorus russula                                    

Other fungi can obtain carbon from trees via a symbiotic relationship (see earlier post of mycorrhizae). Specifically, those associated with trees like the one shown below are ectomycorrhizal fungi (EMF). They have hyphae (see explanation above) that grow from the base of the fruiting body into tree root tips where the exchange of carbon for nutrients occurs. However, some EMF's have been shown saprotrophic capabilities when carbon from a host is limited.

 Suillus spp. (One of the Slippery Jacks)

Finally, a third type of feeding strategy are the pathogenic fungi. These fungi cause disease for living plants and animals.  These absorb nutrients directly from the cells of the host, but unlike EMF's do not give back to the plant. Pathogenic fungi typically weaken and eventually will kill the plant they colonize. 

        Tramella mesenerica

As Thanksgiving is approaching, I will leave you with well wishes and Turkey Tails (Trametes spp.). Take a look around while hiking (or walking very slowly) post gorge-fest this Thursday. You may notice a whole other world of fall colors you might have normally missed in the past!

*Although I have had a lot of classes/training in mycology, I am not a mycologist. Fungal identification is based on my best educated guess from books/web resources. All fungi were observed at Big Basin Redwood State Park in California. If you have any additions or corrections, please feel free to add them in the comments section. Thanks!

Thursday, November 13, 2014

Playing in the Mud!

After a precipitation event (i.e. rain), there are recommendations to avoid contact with the soil. We are advised in both recreation and business to restrict personal and mechanical activity during this time as tractors, construction or logging equipment, and even our own feet can impact soil negatively leading to compaction and erosion. However, getting muddy brings us back to our childhood. As an adult, activities that bring us in contact with soil often elicit feelings of joy and maybe even a bit of mischievousness at the thought of bringing home a little dirt on our shoes to a house where mom and dad won't yell at us. So why, despite these youthful urges to go out and play, do we need to give the soil a break for a few hours to days before we head out to plow the fields or ride our mountain bikes?

Sarah P. fellow mountain biker with her muddy bike (2012). 

In order to answer this, we have to start with some basics. Soil particle size! Soil particles are split into various size classes. Basically the diameter of the particle determines what size class it falls into. The two groups are coarse fragments (the big stuff - gravel cobbles,and boulders) and fine earth fraction (sand, silt, and clay). Particles that are 2 mm and smaller fall into the fine earth fraction (per USDA classification). Sand is the largest ranging from 2-0.05 mm with various subdivisions within this, ranging from very coarse to very fine. Silt ranges from 0.05-0.002 mm and clay is 0.002 mm and smaller.  The range from boulders to clay is separated by 6 orders of magnitude. This means a clay particle is 1 millionth the size of a boulder!  So how do these sizes compare in a more visual sense?


We can see that at the current scale, clay doesn't even show up it is so tiny! So how do these particles influence soil's reaction to water and the pressure we put on it? The combination of these particles (percentages) determine the soil texture. Some of the soil textures you may have heard of are sand, clay, and loam. There are 12 textural classes in total. For example, if soil to has a "clay" texture, it has at least 40% clay sized particles within it. These textures can have an added "modifier" if a certain percent of the sample by volume contains particles in the gravel, cobble, or boulder categories. You could have a soil that is a "gravelly loam" (pictured below). For this blog post I won't go into specifics about how these coarse fraction particles can affect soil, but know their presence can change soils in various areas. 


Ok, we have learned about particles and how particle combinations result in different textures. How does this play a role in soil compaction after it has rained? Picture your self the size of a sand particle and you are hanging out between the particles. This area between the particles is known as pore space. Most of the spaces between the particles right after a good rain will be filled with water (you can have scuba gear for this imagery if being immersed in water terrifies you!). Now there is pressure exerted from the soil surface, which pushes the soil particles together and fills in the pores (gaps) in between the particles. 

Strawberry fields with reduced infiltration.

Why is compaction bad? Compacted soils have higher bulk densities. Bulk density is the mass per volume a soil takes up. Soils with higher bulk densities have reduced infiltration rates. When irrigating, if the rate at which water enters the soil is reduced you can have more runoff and evaporation (lost water). Another problem is reduced air permeability. Reduction in air affects the plant roots and microbes, which can reduce nutrient cycling and over all plant growth. The increase in bulk density means that the soil has to change shape or "structure" is altered and/or reduced. Briefly, structure of the soil is determined by the particles that make up the soil. Generally speaking, soils with more clay (material that can bind particles), will have more structure than those with more sand. Think of the beach. The soil is just one big "massive" accumulation of sand sized material. Where as in your garden you will see small round/crumbles or blocky shapes resulting from clay as well as other constituents in the soil. The presence of water in the soil allows the particles to move more easily over and around each other. This results in loss of soil shape and settling of particles into the pore spaces. 


In areas where farming, construction, or logging occur pausing the work so that plant growth is not impacted makes sense. However, what about trails? There isn't vegetation on the path when you are hiking, mountain biking, or trail riding, so why should we care? As mentioned when soils become compacted soil structure is lost. When soil loses its shape the particles no longer stick together and can become subject to erosion via wind and water (Remember that reduced infiltration concept? Water not entering a soil will travel elsewhere, such as running over a slope. When this happens, it  can carry soil particles with it). With soil loss you begin to expose roots. For mountain bikers this adds obstacles, which is fun. However, it can affect the plant life present. The larger roots may be more resistant, but the fine roots holding the soil together can become impacted resulting in further soil loss. Soil loss essentially leads to trail loss and no more fun for you and me. 


Compacting soil reduces overall soil quality and plant growth and can result in erosion and and soil loss. Although we would love to be able to get out and hike, ride, even get work done on occasion, it is necessary after a precipitation event to allow for the soil to dry out somewhat before we jump back in the saddle.