Reproductive Allometry in Soybean, Maize and Sunflower

We compared the relationship between grain yield per plant ( Y P ) and shoot biomass per plant ( S P ) in three annual crops with contrasting reproductive strategies: sunflower, a determinate species with a single inflorescence; maize, a determinate species with a limited capacity to adjust the number of ears in response to resource availability; and indeterminate soybean, a species with a large capacity to adjust the number of inflorescences. Our working hypotheses were: H 1 —the relationship between Y P and S P is linear; H 2 —the intercept of the model is zero, i.e. there is not a threshold plant mass for reproduction. A wide range of Y P and S P was generated by manipulation of plant density; S P varied between 0.3 and 196 g per plant in soybean, between 6 and 873 g per plant in sunflower and between 23 and 697 g per plant in maize. Within these broad ranges of plant size, both hypotheses were rejected in five out of six experiments, i.e. the relationship between Y P and S P departed from linearity and there was a threshold for S P below which no grain set occurred. The S P threshold for grain set varied widely among species; it was close to 2 g per plant for soybean, 27 g per plant for sunflower and 43–71 g per plant for maize. Because of this size threshold and non-linearity, harvest index (HI = Y P S P −1 ) was stable for mid-size plants, diminished slightly for large plants, and diminished sharply for smaller plants in all three crops. Harvest index stability was highest in soybean, intermediate in sunflower and lowest in maize. Differential stability of reproductive partitioning partially derived from contrasting patterns of meristem allocation. Keywords Helianthus annuus L., Zea mays L., Glycine max (L.) Merrill, grain yield, harvest index, plant density, reproductive allocation, meristem allocation, plasticity References LITERATURE CITED 1 FH Andrade C RC Vega SA Uhart AG Cirilo M Cantarero O Valentinuz Kernel number determination in maize Crop Science 39 1999 453 459 2 SP Bonser LW Aarssen Meristem allocation: a new classification theory for adaptive strategies in herbaceous plants Oikos 77 1996 347 352 3 DA Charles-Edwards Physiological determinants of crop growth 1982 Academic Press North Ryde 4 WJ Cox Whole-plant physiological and yield responses of maize to plant density Agronomy Journal 88 1996 489 496 5 J Doebley A Stec L Hubbard The evolution of apical dominance in maize Nature 386 1997 485 488 6 CM Donald J Hamblin The biological yield and harvest index of cereals as agronomic and plant breeding criteria Advances in Agronomy 28 1976 361 405 7 GO Edmeades TB Daynard The relationship between final yield and photosynthesis at flowering in individual maize plants Canadian Journal of Plant Science 89 1979 585 601 8 LT Evans Crop physiology: prospects for the retrospective science KJ Boote JM Bennett TR Sinclair GM Paulsen Physiology and determination of crop yield 1994 ASA, CSSA, SSSA Madison 19 35 9 WR Fehr CE Caviness Stages of soybean development Special Report 1977 929 931 10 KS Fischer A FE Palmer Tropical maize PR Goldsworthy NM Fisher The physiology of tropical field crops 1984 J. Wiley & Sons Ltd Bath 213 248 11 WR Gardner HR Gardner Principles of water management under drought conditions Agricultural Water Management 7 1983 143 155 12 RM Gifford JH Thorne WD Hitz RT Giaquinta Crop productivity and photoassimilate partitioning Science 225 1984 801 808 13 DC Hartnett Size dependent allocation to sexual and vegetative reproduction in four clonal composites Oecologia 84 1990 254 259 14 R KM Hay Harvest index: a review of its use in plant breeding and crop physiology Annals of Applied Biology 126 1995 197 216 15 EC Johnson KS Fischer GO Edmeades A FE Palmer Recurrent selection for reduced plant height in lowland tropical Maize Crop Science 26 1985 253 260 16 TA Kiesselbach The structure and reproduction of corn Nebraska Agricultural Research Bulletin No 161 1949 University of Nebraska Lincoln 17 P GL Klinkhamer TJ De Jong E Meelis How to test for proportionality in the reproductive effort of plants American Naturalist 135 1990 291 300 18 P GL Klinkhamer E Meelis TJ de Jong J Weiner On the analysis of size-dependent reproductive output in plants Functional Ecology 6 1992 308 316 19 RS Loomis DJ Connor Crop ecology. Productivity and management in agricultural systems 1996 Cambridge University Press Cambridge 20 C Marshall MA Watson Ecological and physiological aspects of reproductive allocation C Marshall J Grace Fruit and seed production. Aspects of development, environmental physiology and ecology 1992 Cambridge University Press Cambridge 173 202 21 DJ Moot DR Wilson DL McNeil Validation of the principal axis model (PAM) and its application to genotype selection in field pea ( Pisum sativum L.) crops Annals of Botany 79 1997 651 656 22 M Motto RH Moll Prolificacy in maize: a review Maydica 28 1983 53 76 23 ME Otegui Prolificacy and grain yield components in modern Argentinian maize hybrids Maydica 40 1995 371 376 24 E Paterniani Influence of tassel size on ear placement Maydica 26 1981 85 91 25 SS Prihar BA Stewart Sorghum harvest index in relation to plant size, environment, and cultivar Agronomy Journal 83 1991 603 608 26 CL Prior WA Russell Yield performance in non prolific and prolific maize hybrids at six plant densities Crop Science 15 1975 482 486 27 EG Reekie FA Bazzaz Reproductive effort in plants. 1. Carbon allocation to reproduction American Naturalist 129 1987 876 896 28 M Rees MJ Crawley Growth, reproduction and population dynamics Functional Ecology 3 1989 645 653 29 SW Ritchie JJ Hanway How a corn plant develops Special Report 1982 30 VO Sadras Variation in apical dominance and its implications for herbivory resistance, competitive ability and biomass partitioning ME Otegui GA Slafer Proceedings of the international workshop on physiological bases for maize improvement 1998 71 81 31 VO Sadras DJ Connor Physiological basis of the response of harvest index to the fraction of water transpired after anthesis. A simple model to estimate harvest index for determinate species Field Crops Research 26 1991 227 239 32 VO Sadras MP Bange SP Milroy Reproductive allocation of cotton in response to plant and environmental factors Annals of Botany 80 1997 75 81 33 DA Samson KS Werk Size-dependent effects in the analysis of reproductive effort in plants American Naturalist 127 1986 667 680 42 B Schmid W Polasek J Weiner A Krause P Stoll Modeling of discontinuous relationships in biology with censored regression American Naturalist 143 1994 494 507 34 AA Schneiter JF Miller Description of sunflower growth stages Crop Science 21 1981 901 903 35 TR Sinclair Historical changes in harvest index and crop nitrogen accumulation Crop Science 38 1998 638 643 36 TR Sinclair JM Bennett RC Muchow Relative sensitivity of grain yield and biomass accumulation to drought in field-grown maize Crop Science 30 1990 690 693 37 O Solbrig DJ Solbrig Size inequalities and fitness in plant populations Topics in Evolutionary Biology 1 1985 141 159 38 SC Spaeth HC Randall TR Sinclair JS Vendeland Stability of soybean harvest index Agronomy Journal 76 1984 482 486 39 BK Thompson J Weiner SI Warwick Size-dependent reproductive output in agricultural weeds Canadian Journal of Botany 69 1991 442 446 40 M Tollenaar E McCullough LM Dwyer Physiological basis of the genetic improvement of corn GA Slafer Genetic improvement of field crops 1994 Marcel Dekker New York 183 236 41 J Weiner The influence of competition on plant reproduction J Lovett Doust L Lovett Doust Plant reproductive ecology: patterns and strategies 1988 Oxford University Press New York 228 245 43 J Weiner SC Thomas Competition and allometry in three species of annual plants Ecology 73 1992 648 656