DEVELOPMENTAL ECOLOGY OF PLANTS IN NATURAL SHADE

Earlier research on natural light climates in tropical forest understory made possible the investigation of the influences of reduced intensity and shifts in spectral quality on plant development.  This research began in the early 1980’s with Selaginella uncinata and continued in India in the mid 1980’s on tropical vines, and in Miami with Jenny Richards and Eichhornia crassipes.  This research effort intensified in the 1990’s with NSF support to conduct research on Malaysian tropical rainforest tree seedlings. with a novel factorial design that separated the influences of  irradiance (photosynthetically active radiation, or PAR) and spectral quality (red to far-red or R:FR) on plant development.  This researches uses energy films (generously supplied by the 3M Corporation).  This research was conducted at the Forest Research Institute of Malaysia, near Kuala Lumpur.  In this research I collaborated with a team of Malaysian researchers led by Dr. Marzalina Mansor.  Metallic films reduce irradiance without altering spectral quality, and dye-impregnated films reduce the red to far-red quanta.  By using both films with 20 % transmission and R:FR of sunlight (1.25) or understory shade (0.25), and using neutral shade fabric for reduced light levels, we created experiments that allowed us to determine the effects of reduced PAR independent of shifts in R:FR, in a factorial design

            The Malaysian experiments have shown that (1) reduced R:FR – and thus phytochrome – is an important environmental factor in controlling early seedling development, these characters presumably under the control of phytochrome; (2) effects of R:FR are less important than reduced PAR; (3) the influences of PAR and R:FR varied among species dramatically; (4) shade responses were not correlated with ecological site preferences or systematic relationships among the tree species.  This research has established the importance of spectral quality in influencing the development of a number of seedling characters in these tropical rainforest trees.

We are using this experimental system to conduct research on plants in south Florida.   Some small projects have been completed here (with Steve Smith on Rhizophora mangle and Martin Roberts on Psychotria), and I am working with Jennifer Richards and Adrienne Edwards on the influence of light on shoot growth in the spike rush (Eleocharis cellulose) an important component of the long hydroperiod Everglades marshes.

To increase the ecological and taxonomic diversity of tree seedlings studied in Malaysia, I undertook a second NSF-funded project at Madurai Kamaraj University in South India.  I am working with Prof. Kailash Paliwal, and we have established a system of shadehouses with experimental conditions similar to those in Malaysia.  We are finishing experiments examining the effects of PAR and R:FR on the development of seedlings of five tree species of the Combretaceae as well as races within the pigeon pea (Cajanus cajan).    That project will be completed in 2001.

 

Experimental shadehouses constructed at the Forest Research Institute of Malaysia (FRIM), in 1991.

 

Interior of FRIM shadehouses, showing the random arrangements of seedlings of different species inside,
the blind ventilation vents, and the location of the energy films inside of the greenhouse film and shade fabric on the outside.

Spectral distribution of radiation in two of the shade treatments,
showing the effects of the two shade films on the shadehouse light environments.

 

Representative examples of the effects of the light conditions on the growth of seedlings of Shorea singkawang (Dipterocarpaceae).

Plasticity of shade responses (both to irradiance and spectral quality) of the ten species analyzed in the Malaysian results, showing the dramatically different responses of different characters to R:FR and PAR among seedlings of these species.

Shadehouses constructed for current research at Madurai Kamaraj University in India.