Launching experiment “FAHM” (Free air humidity manipulation) Presented by Anu Sõber Authors: whole group of Plant Ecophysiology, University of Tartu, Estonia Kupper, P.; Sõber, J.; Sellin, A.; Lõhmus, K.; Tullus, A.; Räim, O.; Lubenets, K.; Tulva, I.; Uri, V.; Zobel, M.; Kull, O.; Sõber, A. (2010). An experimental facility for Free Air Humidity Manipulation (FAHM) can alter water flux through deciduous tree canopy. Environmental and Experimental Botany "The Special Issue on Responses, Acclimations and Adaptations of Northern Plants to Global Change". (accepted, DOI information: 10.1016/j.envexpbot.2010.09.003).
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Launching experiment “FAHM”(Free air humidity manipulation)
Presented by Anu Sõber
Authors: whole group of Plant Ecophysiology, University of Tartu, Estonia
Kupper, P.; Sõber, J.; Sellin, A.; Lõhmus, K.; Tullus, A.; Räim, O.; Lubenets, K.; Tulva, I.; Uri, V.; Zobel, M.; Kull, O.; Sõber, A. (2010).An experimental facility for Free Air Humidity Manipulation (FAHM) can alter water flux through deciduous tree canopy.Environmental and Experimental Botany "The Special Issue on Responses, Acclimations and Adaptations of Northern Plants to Global Change".(accepted, DOI information: 10.1016/j.envexpbot.2010.09.003).
How “the first in the world” free air humidity manipulationexperiment was started.Aims: 1.To manipulate evapotranspiration in forest ecosystem via increasing air humidity.2. To investigate the changes in different parts of ecosystem at diffferent level of organization.
Design 1: Vent-pipe system (as at FACE), 9 experimental rings (diameter 14 m): one half of each – Silver birch, another half - Hybrid aspen. Three treatments were planned: C – control, H - elevated air humidity, D – decreased air humidity.Weather station and sensors in rings logging from 2007.Conclusion in autumn 2007:
We can not produce signifficant increase in air humidity via adding humidified air by ventilators and vent-pipe system (amount of added moist air was not sufficient to compete with the wind).2008: New approach: Design 2 - Misting.To rise the air humidity inside of H-plots, liquid water (from the pond) was atomised by moving through thin jets (0.15 mm) under high pressure (8 atm). The size of generated water particles about 20 -50 µm. Thereafter the vaporised water was carried into experimental plots by the wind and/or by the airflow, generated by ventilator through the pipe system. (Air outlets located behind each vapor-generating jet). Jets and airflow are usually working up-wind but all directions are covered in still air.
Conclusion: We were able to decrease transpiration in free air experiment What we must take into account:
1. Leaf temperature decreases. 2. Young, growing leaves can be damaged by misting.
New approaches: 1, Decrease in humidity generated in rings, surrounded with plastic to increase transpiration (+ rise in leaf temperature and decrease in wind impact + need for control and misted ring rurrounded with plastic). 2. Higher (60 bar) pressure used for misting – water particles ca 10 microns,
leaves are not wet.
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