ENVS 162: Physiological Ecology Laboratory
Microclimate & Energy Budgets
Microclimate refers to the physical conditions in the immediate vicinity of an organism. Factors included within the realm of microclimate include precipitation (rain, snow and fog inputs), light intensity and quality, infrared radiation (heat), temperature, wind speed (and sometimes direction and fetch (the distance travelled without changing direction)), humidity (and more properly, vapor pressure deficit), gas concentrations, soil nutrient content, soil salinity, soil pH, soil O2, CO2 content, and others
Microclimate is important because it impacts the survival of plants from day to day and year to year. Microclimate also determines the ability of plants to conduct photosynthesis to produce the compounds neccessary for growth, development, and reproduction. Clearly, microclimate will vary from species to species as scale dictates; wind speed at 50 m height is a relevant part of the microclimate for a redwood tree but not so much for a redwood sorrel (Oxalis sp.) growing in the shade of the redwood tree. Certain factors are more important in some habitats than in others. For example, drought and extremes of temperature are important in deserts, whereas competition for light may be a limiting factor for plants in tropical ecosystems. The importance of a particular microclimatic factor may change over the seasons, such as in alpine ecosystems where freezing temperatures, the mass of snow (due to its depth), and scouring by wind-blown ice and snow particles is important for certain months.
In today's lab, we will examine some of the techniques for measuring certain microclimatic parameters. We will measure air and soil temperature, relative humidity, wind speed, solar radiation, and light intensity.
We will make these measurements as part of the comparison of Broom and Coyote Bush at the north end of the Arboretum. Our overall experiment will be comparing watered and nonwatered Broom (Genista sp., a non-native species that is quite invasive) and Coyote Bush (Baccharis pilularis, a Califronia native species and member of the sunflower family) which are two common shrub species of coastal California. Nick watered them to simulate an extra 25% precipitation based on this winter's rainfall for Santa Cruz (which has been 30 cm so far) recorded by the National Weather Service. An increase in precipitation of this magnitude due to climate change has been predicted for the west coast by 2050, and could have important effects on plants, such as by extending the length of the growing season or increasing the amount of stomatal opening and CO2 uptake. This in turn could impact the invasiveness of non-native species such as Broom and allow them to take over more habitat to the exclusion of ecologically similar species such as Coyote Bush.
We will combine our microclimate measurements with photosynthetic gas exchange, water relations and chlorophyll fluorescence measurements of control and +H2O treatments for Broom and Coyote Bush. Remember that you have a paper due at the end of the quarter; data from today's lab would be ideal for this particular assignment.
At the beginning of today's lab, we will give a brief introduction to each of the microclimate sensors.
Wind
speed
We will measure wind speed with an anemometer. Wind turns the propeller and this is turned into an electrical current. Circuitry turns the current into a calibrated speed displayed on the LCD screen. Wind can be tricky: it obviously sppeds up and slows down, so you will need to decide how often to make measurements. Compare measurements made at 2 m height, immediately adjacent to a plant canopy, and immediately adjacent to the soil surface.
Temperature
We will measure temperature with a thermocouple and thermocouple meter. Temperature alters the flow of current through the junction of two dissimilar metals in the thermocouple junction. Circuitry turns the current into a calibrated temperature displayed on the LCD screen. Temperature measurements need to be shaded to avoid excessive heating from direct and reflected solar shortwave radiation; temperatures reported on tv, radio, newspapers and the internet are shaded temperatures.. Compare shaded measurements made at 2 m height, immediately adjacent to a plant canopy, and immediately adjacent to the soil surface.
Relative humidity
We have three ways to measure RH:
1. We have "sling pshycrhomters". The work by comparing the temperature of a wet thermometer bulb and a dry thermometer bulb after they have been allowed to evaporate some water. Obviously, the wet thermometer bulb will evaportae more water, so it will be cooler than the dry bulb. By comparing the temperature difference, RH can be calculated. We facilitate the evaporation by slinging the psychrometer (to be demonstrated).
2. We have a RH meter. It works much like that described for #3 below.
3. We can measure RH with a Vaisala Humitter humidity sensor (ours is not gold-plated like the one in the above picture, though!). Humidity alters the flow of current through a chip (a humidity-resistance chip) in the tip of the sensor; temperature is also measured by this device. The current is sent into one of our Li-Cor dataloggers and software converts it into RH which is displayed on the LCD screen.
Compare measurements made at 2 m height, immediately adjacent to a plant canopy, and immediately adjacent to the soil surface.
All-wave Radiation
These sensors measure all-wave (400 to 1100 nm) radiation. Current flowing through the sensor is altered by energy from the sun through the little white circle on the top of the sensor. The current is sent into one of our Li-Cor dataloggers and software converts it into radiation (W m-2) which is displayed on the LCD screen.
Compare measurements out in open sunlight with under the canopy of Broom and Coyote Bush.
Net Radiation
Generally, it is difficult to point a radiometer like the all-wave radiometer in all directions to get a measurement of the total direct plus reflected solar radiation. The net radiometer (the long sensor at the top of this photo) measures the total amount of incoming radiation from above and below the location where the sensor head is being held. Current flowing through the sensor is altered by energy from the sun as well as reflected energy from the ground and surrounding objects. The current is sent into one of our Li-Cor dataloggers (or read by a digital voltmeter) and software converts it into radiation (W m-2) which is displayed on the LCD screen.
This instrument is pretty delicate, so we will set it up and leave it in one place for the entire lab.