Abstract, Wu Zuoli

Instituttt for plante- og miljøvitenskap

Abstract

Wu, Z. 2004. Quantification of Photoperiodic Effects on Growth of Phleum pratense (Funksjonelle sammenhenger mellom daglengde og vekst hos timotei) Doctor Scientiarum Thesis 2004: 6, Agricultural University of Norway, ISSN 0802-3220, ISBN 82-575-0591-9

Paper 1: Quantification of Photoperiodic Effects on Growth of Phleum pratense
(Submitted to Annals of Botany)
Paper 2: Photoperiodic Effects on Leaf Growth of Phleum pratense
(Submitted to Australian Journal of Botany)
Paper 3: Photoperiodic Effects on Morphological Development of Phleum pratense
(Submitted to Journal of Experimental Botany)
Paper 4: Dry Matter Production Response to Photoperiod in Phleum pratense
(Submitted to Canadian Journal of Botany)

Seedlings of two Norwegian latitudinal ecotypes of Phleum pratense L., Engmo (69.5oN) and Grindstad (59oN) were grown in pots for 70 days in growth chambers with 9 hours of 155-170 &#956;mol m-2s-1 photosynthetic light, and 1.5-1.6 &#956;mol m-2s-1 photoperiodic extension light to obtain six photoperiods: 9, 12, 15, 18, 21, and 24 h. Main tiller leaf tip heights were recorded every other day. Area and dry weight of leaf blades and stems + leaf sheaths and dry weight of roots were determined by harvests of samples at the start and at day 35, 49, 62, and 70 during the experiment. The reactions to photoperiod (PP) were described by a photoperiodic response term (formula1) where PPc is PP at the inflection point of the response curve, and c describes its slope and the width of the main response PP interval. The course of the responses curve to PP beyond this interval, described by d, may be: levelling off (d &#8776; 0), increase (d < 0), or decrease (d > 0) implying an optimum PP (OPP). The size variation among individual leaves (Yi) on the main tiller, identified by their sequential number (LN), was described with high precision by the function:(formula2) . The variations in leaf size and dry matter growth with time were described by a similar function replacing LN with day (t) of experimental exposure to different photoperiods.

For all morphological traits and growth characteristics investigated an overall positive effect of daylength extension was observed, but the reaction patterns varied strongly. In main tiller leaf blade size the major increase of both cultivars occurred between 12 and 15 h. In leaf tip elongation rate, cv. Grindstad showed the main increase in the same interval, in contrast to Engmo, which responded more continuously within the whole PP range from 9 to 24 h. The photoperiodic effect and the cultivar response differences were strongly related to phonological development, especially the transition to and progress of generative development, manifested in growth of stems and leaf sheaths. Whereas cv. Grindstad showed a main response within a relatively narrow PP-interval, 12 to 15 h, in DM partitioning to these plant parts, Engmo responded more slowly, but continuously throughout the whole range from 9 to 24 h.

The PPc values for leaf blade growth varied between 12.6 and 14.7 h, with minor cultivar differences. Only in stem+sheaths dry matter and area the PPc values and the cultivar differences, 19.1 and 19.2 h vs. 12.5 and 12.2 h for Engmo and Grindstad, respectively, are indicative of the differences in seasonal daylength of their region of origin (6-8 h). The OPP values, most frequently occurring in Engmo varied between 16.1 and 23.9 h for different plant parts in this cultivar. The differences vs. Grindstad, when occurring also in this cultivar, were relatively small, 1.4-3.2 h.

According to a classical growth analysis, the two cultivars were rather similar as to relative growth rate, RGR, increase of RGR with daylength up to 15 h, and a slight decrease during the last part of the experiment. An increase of net assimilation rate, NAR, with time during the last part of the experiment, could be ascribed to increased leaf thickness during vegetative growth, and throughout generative development mainly to an increase of photosynthetic efficiency by phase change.

The characteristics of the descriptive functions are discussed with respect to precision, efficiency, and applicability in indicating mechanisms for plant daylength reactions and latitudinal adaptation of perennial species. The interpretation of the results in terms of possible utilization in crop growth models of perennial grasses is also considered.
Keywords: Timothy (Phleum pratense L.); Photoperiodic response function; Daylength; Modelling; Leaf growth; Morphological development; Dry matter production; Partitioning

Oppdatert: 14.04.04
Utskriftsvennlig versjon : Arkiv : Tips en venn