Journal Article

Comparing Morphological Plasticity of Root Orders in Slow- and Fast-growing Citrus Rootstocks Supplied with Different Nitrate Levels

Agostino Sorgonà', Maria Rosa Abenavoli, Pietro Giorgio Gringeri and Giovanni Cacco

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 100, issue 6, pages 1287-1296
Published in print November 2007 | ISSN: 0305-7364
Published online September 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm207
Comparing Morphological Plasticity of Root Orders in Slow- and Fast-growing Citrus Rootstocks Supplied with Different Nitrate Levels

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Studies of the plasticity of functional root traits involved in resource acquisition have focused mainly on root length without considering such ‘morphological components’ as biomass allocation, specific root length, root fineness, and tissue density that affect root length. The plasticity of the above components in response to nitrate supply was studied in each root order of two co-generic citrus rootstocks, namely the fast-growing Citrus jambhiri ‘Rough Lemon’ (RL) and the slow-growing Citrus reshni ‘Cleopatra Mandarin’ (CM).

Methods

Morphological traits of individual root orders of CM and RL, grown at different nitrate levels (NO3-N at 0·1, 0·5, 1 and 10 mm) were examined by using an image-specific analysis system.

Key Results

At high nitrate levels, the root length ratio, root mass ratio and, to a lesser degree, specific root length, root fineness and tissue density of tap and 1st-order laterals in both CM and RL were reduced. In 2nd-order laterals, however, the same treatment led to increased values of each morphological trait in CM but decreased values of the same traits in RL. At low nitrate supply, CM exhibited longer tap roots whereas RL developed longer 2nd-order laterals. These effects were due to root mass ratio and, to a lesser extent, specific root length.

Conclusions

Biomass allocation was the main component of nitrate-induced changes in root length ratio. The 2nd-order laterals were more sensitive to nitrate availability than the tap root and 1st-order laterals. At low nitrate availability, RL displayed longer 2nd-order lateral roots and lower root plasticity than CM. This suggests a different root growth strategy among citrus rootstocks for adapting to nitrate availability: RL invests in 2nd-order laterals, the preferred zone for acquiring the nutrient, whereas CM responds with longer tap roots.

Keywords: Root morphology; root orders; phenotypic plasticity; nitrate; Citrus jambhiri; Citrus reshni

Journal Article.  6409 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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