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Title: Growth and Physiological Response of Two Coffea arabica L. Populations under High and Low Irradiance
Authors: Hiwot, Hailu
Advisors: Masresha Fetene(Prof.)
Keywords: Coffee
Net CO2 assimilation
Stomatal conductance
Internal CO2 concentration,
Irradiance Photosynthetic active radiation
Copyright: Jan-2011
Date Added: 4-Jul-2012
Publisher: Addis Ababa University
Abstract: The objective of this study was to evaluate the effects of varying irradiance on the growth and physiology of Coffea arabica. Growth measurements such as stem height (SH), number of branches (NB), stem girth (SG), internode length (IL) and specific leaf area (SLA) were measured, whereas, net assimilation rate, transpiration rate and water use efficiency were measured for gas exchange measurements. Two Coffea arabica populations (Bale and Sheko) were grown in pots placed in the greenhouse of Addis Ababa University under two irradiance regimes, high irradiance (HI)/direct sunlight and 20% of shade (20% HI) for six months. The result of this study shows that stem height, number of branches and stem girth was found higher for exposed coffee plants than the shaded in both populations. However, the Bale coffee population achieved higher growth rate than Sheko coffee population under their respective irradiance level with respect to the three parameters. Specific leaf area in shaded coffee plants was found to be higher than exposed in both populations. But under shade environment, Sheko coffee plants attained lower value than Bale, where, under high irradiance the reverse is achieved. Internode length was also higher in shaded coffee plants of Bale populations, whereas, it showed the same growth with exposed ones in Sheko populations. For internode length, Shaded Bale coffee plants showed higher growth rate than shaded Sheko coffee plants. But under high irradiance Sheko coffees achieved higher value than Bale. As stated for gas exchange measurements, net assimilation rate (Anet) and stomatal conductance (gs) for exposed coffee plants was higher in both populations than shaded. But transpiration rate (E) for both coffee populations under direct sunlight was found lower than under shade. Compared to Sheko coffee plants, Bale coffees showed higher value for daily integrated net assimilation rate and transpiration rate under their respective irradiance level. Moreover, as a result of higher net assimilation rate and lower transpiration rate in exposed coffee plants, it was expressed that integrated daily water use efficiency (WUE) was found higher in exposed coffee trees in both populations. And comparing the two populations, under high irradiance Bale coffees exhibited higher daily integrated water use efficiency than Sheko, while both populations showed similar value under shade. Exposed Bale coffee plants had higher light saturated rates of photosynthesis than the shaded one, which shifted from 200 μ mol Photons m-2 s-1 to 600 μ mol Photons m-2 s-1. ix But leaves of Sheko coffee trees under high and low irradiance levels were saturated between 800 μ mol Photons m-2 s- and 900 μ mol Photons m-2 s- respectively. Furthermore, it is observed from the result that the coffee plants exhibited substantial phenotypic plasticity for most of growth and physiological traits in response to varying irradiance level; thereby the magnitude of plasticity differed markedly among the populations. In particular, plants originating from drier climate (Bale region) showed the highest amount of plasticity suggesting fast adaptation to changing irradiance. These results suggest that this species performs well under high irradiance light though it has been grouped under shade adapted plants .It provides the growth and physiological response and reveal the difference among the two coffee populations in morpho-physiological characteristics. This differential response to light conditions may contribute to its ability to succeed in natural and agricultural environments or to endure control strategies. Moreover, this study contributes as baseline information for further research on the management and use of coffee production.
URI: http://hdl.handle.net/123456789/3265
Appears in:Thesis - Biology

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