Effects of Shading on Chlorophyll Content, Chlorophyll Fluorescence and Photosynthesis of Subterranean Clover

• Published in: Journal of agronomy and crop science (1986) 2011-02, Vol.197 (1), p.57-66
• Main Authors: Mauro, R.P, Occhipinti, A, Longo, A.M.G, Mauromicale, G
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; carbon dioxide; chlorophyll; cover cropping; cultivars; early development; ecotypes; field experimentation; fluorescence; forage legumes; Fundamental and applied biological sciences. Psychology; gas exchange; leaf area; leaf conductance; light intensity; photosynthesis; photosynthetically active radiation; plant dry weight; seasonal variation; shade; shading; T. subterraneum; Trifolium brachycalycinum; Trifolium subterraneum; Trifolium subterraneum subsp. brachycalycinum
• ISSN: 0931-2250; 1439-037X
• DOI: 10.1111/j.1439-037X.2010.00436.x

A field-experiment (2004/2005 and 2005/2006 seasons) was conducted in the coastal plain of south-eastern Sicily (37°03′N, 15°18′E, 15 m a.s.l.), on a Calcixerollic Xerochrepts soil, aimed at quantifying the effect of shading on chlorophyll (Chl) content, Chl fluorescence, photosynthesis and growth of subterranean clover. Four levels of photosynthetically active radiation reduction (from 0 % to 90 %) were tested on Trifolium brachycalycinum cv. ‘Clare' and Trifolium subterraneum ecotype ‘Ragalna'. In both species shading progressively increased Fv/Fm, internal CO₂ concentration, diffusive leaf resistance and specific leaf area (up to 8 %, 34 %, 18 % and 68 %, respectively), and decreased Chl content, Tmax, photosynthetic rate and plant dry weight (up to 9 %, 24 %, 79 % and 39 %, respectively). As plants aged, characteristic bell-shaped trends were evident for photosynthetic parameters, with Fv/Fm increasing up until the onset of flowering, and thereafter declining. This implies that Fv/Fm may be a useful indicator of earliness in subterranean clover genotypes. The aboveground dry biomass response to shading was both genotype- and season-dependent, but was predictable from the measurement of relative leaf Chl content. Moreover, our results suggest that an improvement in the interaction between host-rhizobium may represent a major potential breeding target for enhancing subterranean clover tolerance to shading.