Are Seedlings From Small Seeds Always

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    New Phytol. (1991), 119, 299-305

    Are seedlings from small seeds alwaysinferior to seedlings from large seeds?

    Effects of seed b iomass on seedl ing growthin Pastinaca sativa L.

    BY STEPHEN D. HENDRIX\ ERIC NIELSEN TODD NIELSEN ANDMARK SCHUTT^

    ^Department of Botany., University of Iowa, Iowa City, IA 52242^Department of Biology, University of Iowa, Iowa City, I A 52242

    {Received 16 August 1990; accepted 30 June 1991)

    S U M M A R Y

    Previous field studies of recruitment in Pastinaca sativa L. indicate that more seedlings from small seeds than fromlarge seeds survive short-term droughts. ' I'o explore this phenomenon, the effects of variation in seed biomass inPastinaca sativa on embryo size and seedling characteristics 10, 20, 30 and 40 days after emergence wereinvestigated. On the basis of nnost characteristics;, seedhngs from large seeds should be superior to seedlings fromsmall seeds. Embryo length and cotyledon area were positively related to seed biomass, as were above groundbiomass, total leaf area, and root biomass in all harvests. Total seedling biomass was positively related to seedbiomass in the 10, 20, and 30 day harvests, but not the 40 day har\'est. However, the ratio of maximum rootlength/total leaf area was negatively related to seed biomass in the 10 and 20 day harvests, suggesting that, underdrought conditions, seedlings from small seeds may transpire less water than those from large seeds relative to theirability to reach water supplies. Although seedhngs from larger seeds had greater root biomass, this may be of littleadvantage under drought conditions since approximately 90 '' of the root biomass is in the upper 10 cm of soilwhich dries out quickly. The advantage that seedlings from small seeds have under drought conditions is short-Iiyed, lasting about 20 days in the glasshouse and an estimated 60-90 days in the field. This advantage is short-term because the relationship between seed biomass and resource allocation patterns changes during early seedlingdevelopment.

    Key words: Seed biomass, seedling growth, drought tolerance, Pastinaca sativa.

    germination (Black, 1959; Cidecivan & Malloch,INTRODl-CTION !^ _ . . , . .,nci\ ' -J1982; Weis, 1982), greateror more rapid emergence

    The importance of interspecific variation in seed from deeper dep ths of sowing (Black, 1956; Harperbiomass in the critical processes of dispersal and & Oheid, 1967; Haskins & Gorz, 1975; Wulff, 1986;population recruitment is well know n (Salisbury , W eller, 1989),and less stringent requirementsfor1942; Ha rpe r, Lovell & M oo re, 1970; Baker, 1972; emerge nce with respectto litter and herbaceousHarper, 1977; Fenner, 1983; M arshall, 1986). cover (W inn, 1985).As a consequence of theseIntraspecific variation in seed biom ass, w hich com - effects, large seeds may give rise to better co mp etitomonly occurs in the range of two to sixfold (An ders on, 1971; Wulff, 1986).(Salisbury, 1942; Twamley, 1967; Janzen, 1977, Far few^er advantages of small seeds over larg1978; Gross & Soule, 198 1; Ho we & Rich ter, 1982; seeds have been suggested. Small seeds may gaiaWeis, 1982 ; Hen drix, 1984; Stanton , 1984; Th om p- competit ive advantage over large seeds due to earlson, 1984; W inn , 1985 ; He nd rix & Sun , 1989), may germ ination (Black& Wilkinson, 1963) and whenb ll i t t ll d di d f th th l d

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    30 0 S. D. Hendrix and others

    1-25

    1-00

    0 7 5

    0-50 -I

    025

    = 0.245, P =

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    Seed mass and seedling growth in Pastinaca sativa

    30 10 days: r = 0-438, P =

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    30 2 S. D. Hendrix and others

    Table 1. Regression equations, associatedregression coefficients, and m eanvalues {SD) for the effects of seed bioma ss on growth characteristics ofseedlings of Pastinaca sativa 10, 20, 30, and 40 days after emergence. Nvalues for each harvest are 50, 50, 49 and 30 seedlings, respectively

    Age at harvesting Regression equation Mean +SD

    {a ) Above ground biomass (mg)10 days Y =20 days Y =30 days F ^ 99-62 + 20-43 A40 days F = 324-48 + 39-68A'

    (6) Total leaf area (mm'')10 days F = 0-38 + 0-63A"20 days F = 3-51+2-28A'30 days Y= 30-64+ 4'93X40 days F - 52-02+1 1-27X

    (c) Root biomass (mg)10 days F = 0-02+ 0-63A20 days F = 0-79+3-81 A'

    30 days F = 11-74+24-41 A'40 days F = 149-4] +61-64A:

    {d ) Maximum root length (mm)10 days F 102-04 + 4'96A'20 days F = 163-69+ 4-00A'30 days F = 223-80 + 7-25A'40 davs F = 131 -80 + 43-44A'

    0-436***0-179***0-150**0-069 n.s.

    0 - 3 4 6 * * *0 - 2 0 5 * * *0 - 1 7 1 * *0 - 1 9 1 * *

    0-352***0-173***

    0-290***0-316***

    0-000 n.s.0-000 n.s.0-000 n.s.0-232**

    6-9512-7738-28 15 -68

    183-60+54-08489-66 + 138-55

    2 - 9 0 l - l l12-57 + 4-965O-9O12-3298-92 26 -75

    2-53 1-1015-94 8-88

    112-07 47-96406-01 117 -46

    121'7836-84179-58 + 52-84253-61+71-26312-67 + 94-87

    * P < 0 - 0 5 ; * * P < 0-01; ***P

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    Seed mass and seedling growth in Pastinaca sativa 303

    D9

    oo

    cc

    120 1

    100-

    8 0 -

    60 -

    40 -

    2 0 -

    0

    10 days: r = 0-207, P =

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    304 S. D. Hendrix and others

    1-20 -,

    1-00-

    S 0-80 -

    4DD

    a:

    0-60

    0-40

    0-20

    days

    days

    days

    10 days

    Seed biomass {mg)

    Figure 4. Regression lines for the relationship betweeninitial seed biomass and the ratio of root to shoot biomassof Pastinaca sativa. Regression equations, regressioncoefficients, and P values are: F - O-38-O-O1 A", r ^ -O'OOO, n.s. (10 days); F = 0-28 + 0-03^, /-^ = 0-091, P