Showing posts with label Water. Show all posts
Showing posts with label Water. Show all posts

Thursday, November 10, 2011

Guttation


Fig. 1   Droplets of water suspended on the tip of leaf blades.


Water is a key component of any life form. In every organism, water is constantly moving within the system as the transport vehicle for essential elements. Water molecules move around in response to both environmental and internal conditions.  In the case of plants when water is lacking, cells lose their turgor pressure and they behave in an austere mode - functioning to the minimum in order try to conserve all the remaining water within. On the contrary, when there is excess of water within and around the roots zone, plants behave in such a way that water is used up or released as fast as physiological processes allow. The plant system opens all water exits to the maximum because plant cells can only hold up to a certain amount of water before damage can occur. 

Fig. 2    Guttation:  Water is pushed out through hydathodes.


Excess Water. This topic is about a condition of excess water both in the soil and in the air.  Water gets absorbed by the roots and released through the leaves.  When the release-process is hindered by both sides of the system (by being saturated), the plant has to do something beyond ordinary. 

When you see your lawn in the morning glistening with drops of water suspended at the tip of every grass blade (Fig. 1 and Fig. 2),  you are seeing a case of guttation.  Guttation is simply the process when water from within the plant accumulates on the tips of the leaves.  However, in order to fully understand guttation, we need to contrast and compare aspects of this phenomenon with similar but not related occurrences.   

1.  The water droplet:  Is it the same as dew? 

During guttation, water droplets form at the apical margins of some grasses (Fig.1) or along the leaf margins of some dicots species (Fig. 3).   These droplets of water are different from dew.  Dew is the result of condensation of atmospheric moisture.  The whole surface of the leaves would be all wet.  As the temperature cools down at night and evaporation of molecules outside the leaf slows down or completely stops, root pressure builds up causing water to be pushed violently upwards in search of an exit. Guttation droplet (fluid) originates from within the plant.  Sometimes it is considered a xylem sap.  It is not pure water since it contains some amounts of minerals and sugars.

Guttation droplets form only around the leaf margin.  Dew forms on the leaf surface. 

Fig. 3  Guttation on young leaves of  a rose.


2.  The Passage Way:  Is it the Stomata? 

Some plant species are equipped with hydathodes.   Hydathodes are pore-like structures along the leaf margins that allow the exit of water from the plant in liquid form (Fig.3).  During photosynthesis, stomata open not only to allow carbon dioxide to get into the plant but it also allows the passage of water molecules.  The stomata allow the exit of water in gas form.  For that reason, although water is continuously exiting through the stomata, water is not visible on the leaf surface.  The water molecules join the atmospheric air immediately.   When the temperature is low (at night in particular), transpiration is dramatically decreased resulting in excess water in the plant system.  However this does not mean that water stops getting into the plant. 
Through osmosis, water moves from an area of weaker concentration to stronger concentration.   Because of the higher salt content of the plant sap, (difference in the salt content of the plant sap and soil moisture) water diffuses into the root xylem.   As a result, root pressure builds up - water rushes into the plant but with low temperatures, a traffic jam occurs at the stomata exit.  Fluids are then forced through the hydathodes and fluid comes out are tears along the leaf margins of some plants (Fig. 3). 

Guttation happens through a specialized structure called hydathodes.


3.  The Process:  Is it the same as transpiration? 

Transpiration is the process when the water molecules from the roots are lost into the surface of the leaves.   Imagine that inside the plant there are tiny capillary tubes, called xylem, that stretch from the roots to the leaves.  Then imagine that the tubes are filled with a single line of water molecules starting from right outside the root hair all the way up to the opening of the stomata by way of cohesion (the property of water molecules to attract the same molecules).  As the outer-most molecule escapes the stomata into the air, the next molecule takes its position and the rest follow leaving a new vacant position at the tip of the root.  So another  molecule gets in.  It's a cycle that goes on and on. There are two processes involved here:  transpiration (exit of water molecule from the stomata) and water absorption (entrance of water molecule into the plant).  Depending on the condition of the surrounding environment (temperature, relative humidity, wind velocity, light intensity) these stomata open and close to regulate transpiration.  For the plant, transpiration is an on-going process.

Guttation on the other hand is special-occasion process.  Certain uncommon conditions have to be met for guttation to occur.  Saturated soil and high soil temperature combined with high atmospheric humidity and low air temperature are the optimum conditions for guttation. This is  usually happens at night that is why we see the beads of water only in the morning.   Guttation happens only in specific plant species.  The process is only possible in plants that are equipped with enlarged specialized stomata called hydathodes.  I found an excellent picture of hydathodes in action - one can almost feel the movement of water through those openings.  The image is very helpful in understanding the process of guttation.


Guttation happens when there is excessive water in the soil and there is an absence of water loss through transpiration


Guttation is likely to occur during the night, hence the guttation droplets are seen in the mornings.


Thursday, January 13, 2011

One Reason Not to Over Water Succulents

Echeveria spp.
The leaves crack.  Too much water in the plant tissues result in increased turgor pressure; eventually the pressure breaks the cell wall.  Normally, transpiration (loss of water through the leaves) alleviates the pressure coming from the contents of the cells.  The leaves of most succulents, however, are designed to hold water. Transpiration, which is a constant event in most plants, balances the water level in the cells.  In the case of succulents this process is set to very low level or even none at all. Sometimes they have leathery or waxy leaves from a thick layer of epidermis that keep the water inside.  This is how they adapt to dry environments.  However, when they are exposed to conditions of excessive water their defensive virtues work against them. 

Not all succulents respond to excess water in the same way.  Some of them rot starting from the parts that are directly in contact with the excess moisture. 

Tuesday, July 27, 2010

Colorful Basket

Cherry Tomatoes (Lycopersicon esculentum 'Super Sweet 100')

I'm back in the garden! Last week my family went on a road tour of universities in California (which explains my inconsistency on my blog posts recently). Now we are back and happy to find out that my garden is in great condition. Thanks to my sixteen-year-old daughter who made sure that the drip system was working well before we left and my neighbor who came during the week and gave the plants a cool-treat by watering during those triple-digit-days.

When the temperatures are high and water is not limiting plants usually grow very fast.  My youngest child noted that the fig tree in the corner of the yard grew almost a foot while we were gone.   Same thing is true for the bottle gourd.
A colorful basket of vegetables from my kitchen garden.

Although I asked my friend to harvest from my garden, there was still a lot of food that needed to be brought in.  They need to be harvested so that the plants can continue producing.   Those tomatoes are very sweet.  This afternoon we grilled some summer squash and they were great.  The basil plants are still green and growing with some flowers every now and then but I keep pinching them off.  

Cracked tomatoes.

Have you ever wondered why some tomatoes are cracked?  It is not caused by a disease.  Instead, it happens when the amount of water available to the plant is inconsistent.  When the soil is allowed to get close to dry followed by over-watering can cause the plants to absorb more water than the cells can contain.  As a result the tissues break like this one in the picture.  This happens to potatoes also.  In any case, the vegetables are still edible.  The only negative effect is on the appearance.  In commercial scale farming, this would be detrimental on the marketability of the produce.  Solution - Consistent watering schedule.

The sweetest tomatoes are those that ripened under the sun.

Saturday, July 17, 2010

Beating the Heat

Daylily (Hemerocallis L.)

Yesterday
Maximum Temp:  102 ºF 
Minimum  Temp:    66 ºF
Realtive Humidity:   20%

Today
Maximum Temp: 99 ºF
Minimum Temp:  64 ºF
Relative Humidity: 17%

It is that time of the year again when being in the garden is almost like being in a furnace. 
Plants love the sun.  Plants are plants because of the sun and the heat energy they derive from it.  To most plants summer is heaven.  In addition to the abundance of sunshine, temperature also increases the rate of photosynthesis or production.  That's what plants love to do.  But anything good especially in excess always comes with a price.  Intense sunlight which is accompanied by high temperatures jeopardizes the availability of water to the plant.

Ground water dissipates from the ground through evaporation while absorbed water escapes the plants through transpiration at a high rate.  Ideally, natural weather conditions would provide replacement of lost water through precipitation.  My garden is not so ideally located when it comes to rainfall.  Affected by the Mediterranean climate, California's subtropical environment is characterized by a dry summer.   The example of weather condition above shows how dry it is here by the relative humidity of lower than 20%.  Gardening here requires some techniques to beat the heat during the dry months.

Adjust watering schedule. 
1.  Water less frequently but deeply to encourage the roots to grow deeper. 
2.  Water during the cooler times of the day/night to avoid loss by evaporation.
3.  Drip irrigate to avoid runoff especially where the soil is on a slope.
4.  Check irrigation pipes for leaks and breakage.

Mulch.
Mulching is the simply the process of spreading a protective layer of material on top of the soil.  It is an effective way to conserve soil moisture, reduce soil temperature, and prevent weed growth.  There are several materials available at your local nursery or home improvement center.  When using organic materials (those that are derived from plant and animal by-products) mulching eventually improves the water-holding capacity of the soil.

Use what is available and free.  In my garden I use dried grass clippings for mulching instead of throwing them away.  It has to be dry before they are used to mulch shallow rooted plants but you can directly use fresh clippings to mulch around trees or in opens spaces.   Coffee grounds also make a good mulch material; I use them for mulching potted plants.  Coffee shops such as Starbucks and Peets Coffee offer coffee grounds for free.   Sometimes they already in bags ready for anyone interested. 

Protect potted plants. 
Potted plants are "caged" and they have limited space to hunt for resources particularly water.  During the hot months of summer, it is best to move them to a place where they can get some shade.  This will reduce water loss through excessive transpiration and evaporation. 

And then fertilize...
Frequent watering depletes the soil from the essential nutrients especially those in pots.  Applying fertilizer on a regular basis benefits the plants.  It is not enough to provide water for the plants.  The nutrients they need have to be available also for continued growth and development.  The potted orange trees in my yard are great examples. After a couple of months into the warmer months, the leaves show signs of yellowing which is a symptom of nitrogen deficiency.  A little bit of complete fertilizer quickly restores the nice green coloration of the leaves. 

Summer gardening is fun as long as we beat the effects of high temperatures.

Friday, March 19, 2010

Volunteer mushrooms


Beautiful and healthy mushrooms were all over our neighbors' yard last month.  They were concentrated on the mulched areas of their garden.  This leads me to believe that spores were carried with the mulch.  For the gardener, mushrooms are not considered pest, they only grow when the soil is moist.   When the season change and the rainfall is less or down to nothing, mushrooms will not grow.  Having said so, some gardeners still find mushrooms on their lawns even in the spring or summer.  The reason for this has something to do with management practices and it is avoidable.   When an area in the yard is over-watered at a frequent interval, the soil remains moist providing a favorable growing media for mushrooms.   To solve the problem, irrigate deeply at lesser intervals.  It is alright to allow the soil to get close to dry before the next watering schedule. 

If you have small curious children in the home, teach them that some types of mushrooms are poisonous.  As a kid growing up in the Philippines, I played with all sorts of mushrooms (different shapes and colors) in the wild.  Since we never ate mushrooms raw, it was not inviting for a little girls to taste them.  There was one rule that my grandmother told me which I still remember and apply even up to this time:  Avoid all mushrooms with rings on their stem; they are poisonous.  However, this is not the only indicator that a mushroom is toxic or not.  MykoWeb provides an expansive reference about the different mushrooms in California. 

Thursday, December 31, 2009

Caged Plants



At this time of year, gardening is at the bottom of my to-do-list.   It is cold outside.  Other than shedding leaves, the plants are not doing anything visible that would inspire me to go work outside.  The truth is the plants are alive.  Just like any other form of life plants, even when they are not actively growing, are physiologically active.  If the needs of these living forms are neglected they will show it but usually, it will be too late.  The damage will already have been done.

Water. The one thing that I need to remind myself is to water my potted plants on a regular basis.  The roots of the plants are limited within the soil in the pot and when that soil is dry they have no other source.  Plants grown in the ground can grow their roots further just to reach the source of moisture but plants in pots are like animals in cages.  Everything they need has to be provided.   Water also helps the plants withstand freezing temperatures.

Shelter.  Plants that are sensitive to freezing temperatures need protection during the winter months.  Plants in pots are easier to move around than their in-ground counterparts.  Move them closer to the buildings or position them in such a way that they will get exposed to the southern sun.  The days are very short, it is important to allow the plants to get as much sunlight as possible.

Stroll in your garden...it's good for you and your plants. 
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