caa a22 4500 477109535 CHVBK 20180405111604.0 cr unu---uuuuu 170330e19960601xx s 000 0 eng 10.1007/BF00010462 doi (NATIONALLICENCE)springer-10.1007/BF00010462 Effects of leaf position and nitrogen supply on the expansion of leaves of field grown sunflower ( Helianthus annuus L.) [Elektronische Daten] [N. Trápani, A. Hall] Leaf growth responses to N supply and leaf position were studied using widely-spaced sunflower plants growing under field conditions. Both N supply (range 0.25 to 11.25 g added N per plant) and leaf position significantly (p=0.001) affected maximum leaf area (LAmax) of target leaves through variations in leaf expansion rate (LER); effects on duration of expansion were small. Specific leaf nitrogen (SLN, g N m-2) fell quite rapidly during the initial leaf expansion phase (LA < 35% LAmax) but leveled off during the final 65% increase of leaf area. This pattern held across leaf positions and N supply levels. Leaf nitrogen accumulation after 35% LAmax continued up to achievement of LAmax; reductions in the higher SLN characteristic of the initial phase were insufficient to cover the nitrogen requirements for expansion during the final phase. LER in the quasi-linear expansion phase (35 to 100% of LAmax) was strongly associated with SLN above a threshold that varied with leaf position (mean 1.79±0.225 g N m-2). This contrasts with the response of photosynthesis at high irradiance to SLN, which has previously been shown to have a threshold of 0.3 g N m-2; in the present work saturation of photosynthetic rate was evident when SLN reached 1.97 g N m-2. Thus, once the area of a leaf exceeds 35% of LAmax, expansion proceeds provided SLN values are close to the levels required for maximum photosynthesis. However, growth of leaves during the initial expansion phase ensures a minimum production of leaf area even at low N supply levels. Kluwer Academic Publishers, 1996 Helianthus annuus nationallicence leaf expansion nationallicence leaf photosynthesis nationallicence specific leaf nitrogen nationallicence sunflower nationallicence DAA : days after leaf appearance nationallicence DAE : days after plant emergence nationallicence H plants : plants used to monitor the dynamics of SLN nationallicence LA : leaf area nationallicence LA plants : plants used to monitor LA changes of target leaves nationallicence LAmax : maximum leaf area nationallicence LED : leaf expansion duration nationallicence LER : leaf expansion rate nationallicence LERlg : leaf expansion rate during the linear growth phase nationallicence LERmax : maximum LER nationallicence LN plants : plants used to determine the SLN at LERlg nationallicence Pmax : leaf potential photosynthetic capacity nationallicence Pmax : leaf photosynthetic rate under irradiances > 1600 μmol PAR m-2 s-1 nationallicence SLA : specific leaf area nationallicence SLN : specific leaf nitrogen nationallicence SLNth : threshold SLN nationallicence Trápani N. F.E.V.A., Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417, Buenos Aires, Argentina aut Hall A. F.E.V.A., Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417, Buenos Aires, Argentina aut Plant and Soil Kluwer Academic Publishers; gopher://gopher:wkap.nl 184/2(1996-06-01), 331-340 0032-079X 184:2<331 1996 184 11104 https://doi.org/10.1007/BF00010462 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00010462 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Trápani N. F.E.V.A., Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417, Buenos Aires, Argentina aut NATIONALLICENCE 700 1- Hall A. F.E.V.A., Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417, Buenos Aires, Argentina aut NATIONALLICENCE 773 0- Plant and Soil Kluwer Academic Publishers; gopher://gopher:wkap.nl/ 184/2(1996-06-01), 331-340 0032-079X 184:2<331 1996 184 11104 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer