Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. GROWTH STUDIES ON DEFOL IATED LOTUS PEDUNCULATUS CV . I GRASs LANDS HAKU I • A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University Palmers ton North New Zealand GAVIN WILLIAM SHEATH April , 1973 ABSTRACT This thesis reports on a series of experiments designeG to study the response of 'Grasslands Maku' to defoliation and thereby extend the understanding of growth and production of Lotus peduncuZatus . Morphol­ ogical s tructuring , production and nonstructural carbohydrate status of 'Grasslands Maku' were assessed for different defoliation regimes in two separate field experiments . The relative importance of several residual plant factors and assimilate partitioning in early shoot regrowth, was studied in controlled environmental conditions . i In the first field experiment, seasonal differences in the partitioning of growth were recorded , with the spring to mid-summer period being dominated by aerial shoot growth and the late-summer , autumri period by underground growth. Of the underground components, rhizome growth was the most responsiv� to seasonal and defoliation changes and it was this horizontal stem system that formed the basis of basal shoot initiation . Canopy growth became increasingly dominated by rhizome shoots as cutting height and frequency decreased and stubble shoots, stubble and dead matt r declined . Following defoliation, regrowth was consistently slow during the first two to three weeks; thus production increases were achieved where regrowth intervals were extended and subsequent, higher growth rates were allowed to be ex�res��d. Higher cutting improved shoot regrowth, particularly in the stubble shoot pool, but increased within-canopy dry matter losses that were related to death and decomposition processes, resulted in little, if any improvement in net productivity . Shoot regrowth responses resulting from highet cutting were primarily , related to increa�es in the size of the residual shoot pools from which regrowth commenced . Residual shoot number and individual size were therefore important determinants of early regrowth . Any direct influence of residual nonstructural carbohydrate status on regrowth appeared to be principally confined to the rhizome shoot pool for the first few days of regrowth . The importance of accumul.ated starch would appear to be related to the provision of metabolic substrate for underground respiration during late autumn to early spring . ii Where defoliation is incomplete, residual stubble would appear to be an important source of current and redistributed assimilates du�ing early regrowth. Following defoliation, redistribution of carbon compounds to shoot growth was principally confined to the rhizome shoot pool . Total shoot growth increasingly dominated the partitioning of current assimilates as plants recovered from de1oliation . Where defoliation is incomplete it is proposed that assimilate ucilization is a more important l imitation to early shoot regrowth than assimilate supply. The defoliation responses recorded with 'Grasslands Maku' in these ex�eriments are finally considered with regard to the role of L. pedunculatus in agriculture . Management guidelines are proposed and improved re�·Jwth characteristics , necessary for any further extension of L. pedunculatus into grasslands farming, are suggested. TABLE OF CONTENTS Chapter 1: Introduction and Objectives Chapter 2: Literature Review 2.1 Lotus pedunculatus (syn . Lotus u liginosus . ) 2.2 Plant component growth pat terns and iii Page 1 4 4 relationships . 10 2.2.1 Growth of shoo ts . 11 2.2.1.1 Lotus corniculatus 11 2.2.1.2 Medicago sativa 12 2.2.1.3 Coronil la varia 14 2.2.2 Growth of underground organs 15 2.2.2.1 Seasonal effects on underground organs 15 2.2.2.2 Defoliation effects on underground organs 16 2.3 Defoliation management and herbage dry matter production 17 2.3.1 General concepts 17 2.3.2 Lotus corniculatus 18 2.3.3 Medicago sativa 20 2.3.4 Coronil la varia 22 2.4 Nonstructural carbohydrates 22 2.4.1 Seasonal changes in nonstructural carbohydrates 2.4.2 Defoliation effects on nonstructural carbohydrates 2.4.3 Nonstructural carbohydrates and plant regrowth 2.5 Carbon partitioning in plants 2.5.1 Carbon distribution 2.5.2 Carbon redistribution Chapter 3: Morphological characteristics of Lotus pedunculatus cv . 'Grasslands Maku' 3.1 Introduction 3.2 Experimental 3.3 Results 23 24 25 27 27 29 31 31 32 37 3.3.1 Underground plant components 3.3.1.1 Primary crown and taproot 3.3 .1.2 Rhizome 3.3.1.3 Fibrous root 3.3.2 Final canopy components 3.3.2.1 Final shoot growth Page 37 39 42 45 46 46 3.3.2.2 Final stubble and \.L!ad matter 48 3.3.3 Final shoot numbers and characteristics 50 3.3.3.1 Stubble shoots 3.3.3.2 Rhizome shoots 3.3.3.3 Rhizome shoot initials 3.3.3.4 Crown shoots and crown shoot initials 3.3.4 Residual shoot numbers 50 52 55 56 56 3.3.4.1 Residual stubble shoot numbers 60 3.3.4.2 Residual rhizome shoot numbers 60 3.3.4.3 Residual crown shoot numbers 61 3.4 Discussion 3.4.1 Underground plant components 3.4.2 Crown and taproot 3.4.3 Rhizome 3.4.4 Fibrous root 3.4.5 Stubble shoots 3.4.6 Rhizome shoots Chapter 4: Defoliation management and herbage dry matter production of Lotus pedunculatus cv . 'Grasslands �1aku' 4.1 Introduction 4.2 Experimental 4.2.1 Experiment 1 4.2.2 Experiment 2 4.3 Results 4.3.1 Experiment 1 61 61 63 64 64 6 7 6 8 71 71 72 72 72 75 75 4.3.1.1 Net herbage production 75 4.3.1.2 Regrowth cycles: (i) spring regrowth cycle; (ii) summer regrowth cycle 7 6 iv 4 .3 .2 Experiment 2 4 .3 .2 . 1 4 .3 .2 .2 4 .3 .2 .3 4 .3 .2 . 4 4 .3 .2 .5 4 .3 .2 .6 Treatment Treatment Treatment Treatment Treatment Treatment RS SAS 6S 61 SAL LS 4 .3 .3 Winter production of 4 . 4 Discussion 4 . 4 . 1 Stubble shoots 4 . 4 .2 Rhizome shoots Experiment 4 . 4 .3 Secondary axillary shoots 4 . 4 . 4 Stubble and dead matter 4 . 4 .5 Leaf area 4 . 4 .6 Net canopy growth 4 . 4 .7 Proposed management 1 and 2 Chapter 5: Nonstructural carbohydrate levels in Lotus peduna- ulatus cv . 'Grasslands Maku' 5. 1 Introduction 5 .2 Experimental 5 .3 Results 5 .3 . 1 Experiment 1 5 .3. 1. 1 Central system total nonstruct­ ural carbohydrates 5 .3 . 1 .2 Peripheral system total non­ structural carbohydrates 5 .3 .2 Experiment 2 5 .3 .2 . 1 Spring sampling 5 .3 .2.2 Autumn sampling 5 . 4 Discussion Chapter 6: The importance of several residual plant factors in determining early regrowth in Lotus pedunaulatus cv . 'Grasslands Maku' 6 . 1 Introduction Page 77 82 86 87 9 1 92 96 97 9 8 99 1 0 1 102 103 1 04 105 1 07 109 109 1 10 1 12 112 1 14 1 16 1 19 1 1 9 12 1 125 125 V 6 .2 Experimental 6 .3 Results 6 . 3 .1 Shoot regrowth 6.3 .2 Shoot ntnnbers 6 .3 .3 Residual leaf area, stubble weight and underground weight 6 .3 . 4 Nonstructural carbohydrate status 6 . 4 Discussion Chapter 7 The partitioning of c14 labelled assimilates in def- oliated Lotus pedunculatus 'Grasslands ��ku' 7 .1 Introduction 7 .2 Experimental 7 .3 Results 7 .3 .1 c14 Distribution experiment 7 .3 .2 c14 Redistribution experiment 7 . 4 Discussion 7 . 4 .1 c14 Distribution experiment 7 . 4 .2 c14 Redistribution experiment Chapter 8: General Discussion Acknowledgements Bibliography Appendices Page 126 128 128 133 137 139 144 1 50 1 50 151 154 1 54 160 168 168 171 174 1 82 1 83 1 97 vi Table 1 2 3 4 5 6 7 8 9 10 11 12 1 3 14 15 16 17 18 1 9 20 . 21 22 23 24 25 vii LIST or TABLES Page Plant densities for pre-autumn and post- winter samplings . 40 Total underground dry weight . 40 Crown plus tapro t dry weight . 43 Rhizome dry weight· 4 3 Fibrous root dry weight . 45 Percentage contribution of stubble and rhizome shoots to final canopy weight . 47 Percentage contribution of stubble and dead matter to final canopy weight . 49 Number of final stubble shoots . 51 Number of final rhizome shoots . 51 Number of rhizome shoot initials . 55 Number of final crown shoots and crown shoot initials . 58 Residual shoot numbers . 59 Net herbage production in Experiment 1 . 76 Leaf area indices during a spring and summer regrowth cycle of Experiment 1 . 79 Total and component dry matter production in Experiment 2 . 81 Net dry matter production during winter in Experiment 1 and 2. 97 Nonstructural carbohydrate status of the central plant system in Experiment 1 . 115 Nonstructural carbohydrate status of the peripheral plant system in Experiment 1 . 117 Nonstructural carbohydrate status of the rhizome and above-ground fractions of the peripheral system sampled on 6/4/76 . 11 8 TNC concentrations and dry weights of underground organs during late spring and autumn in Experiment 2. 120 Total, stubble and rhizome shoot dry weights . 129 Shoot dry weight relationships with regrowth time. 132 Individual stubble and rhizome shoot dry weights . 134 Stubble and rhizome shoot numbers . 136 Leaf area of stubble, stubble shoots and rhizome shoots . 138 Table 26 27 28 29 30 31 32 33 34 35 Stubble and total underground dry weights Dry weights of plant components during regrowth in the c14 Distributition experiment Specific activities of plant components in the c14 Distribution experiment Absolute activity of plant components in the cl4 Distribution experiment Percentage distribution of total plant activity between components in the c14 Distribution experiment Dry weights of plant components during regrowth in the c14 Redistribution experiment Specific activity of plant components in the c14 Redistribution experiment Absolutle activity of plant components in the c14 Redistribution experiment Percentage distribution of total plant activity between components in the c14 Redistribution experiment Activity levels of plant components, as a percentage of their original activity on day 0, viii page 139 155 1 56 1 57 1 58 161 162 164 165 in the c14 Redistribution experiment 167 LIST OF FIGURES Figure 1 A diagramatic representation of the morphology of 'Grasslands Maku', Lotus peduncuZatus . 2 Total underground weight per plant a t six-weekly · harvest dates . 3 Net herbage production during a six week spring period in Experiment 1 . 4 Net herbage production during a six week summer period in Experiment 1 . 5 Component dry matter yields for treatments RS (A) and SAS (B) . 6 Shoot numbers and LAI for treatments RS (h) and SAS (B) • 7 Component dry mat ter yields for treatments 6S (A) and 61 (B) . 8 Shoot numbers and LAI for treatments 6S (A) and 61 (B) . 9 Component dry matter yields for treatments SAL (A) and LS (B) . 10 Shoot numbers and LAI for treatments SAL (A) and LS (B) . 11 TNC status of residual plants following cutting. 1 2 RGR uf collective to tal (A) , stubble (B) and rhizome (C) shoo t pools . 13 RGR of individual stubble (A) and rhizome (B) shoots . 14 Nonstructural carbohydrate levels in stubble shoo ts (A) ; rhizome shoots (B) ; stubble (C) ; rhizome (D) ; ix Page 35 38 78 80 84 85 89 90 94 95 113 131 135 and crown plus taproot (E) . 142 & 143 1 5 Percentage distribution of total plant activity in collective components of high and low cut plants in the cl4 Distribution experiment 16 Percentage distribution of to tal plant activity in collective components of high and low cut plants in 159 the c14 Redistribution experiment . 166 Plate 1 . 2 . 3 and 4 . 5 . 6 . 7 . 8 . 9 . 10 . 1 1 . 1 2 . 1 3 . 1 4 . LIST OF PLATES A multicrown and taprooted plant linked by woody rhizome growth; considered as one plant Page unit. 41 Primary crown and forked taproot; pink crown shoot initials are also evident . 4 1 Rhizome components: non-woody rhizume; woody rhizome with a swollen nodal region and concentrated shoot locii; basal portion of a terminal rhizome shoot. 44 A stubble node possessing three axillary shoots at different stages of development. Contrasting leaf and stem complements in rhizome shoots and stubble shoots during early regrowth . A rhizome shoot characteristically dominating two stubble shoots and a rhizome shoot with a basal underground portion. Two rhizome shoots and several rhizome shoot initials at different stages of development. Early rhizome shoot development ranging from a leafy orthotropic rhizom� shoot to an underground rhizome shoot initial . Stages of abnormal rhizome shoot initials; apical death; subtended axillary bud development; resumed rhizome shoot initial growth . A spreading, open plant habit, typical of 9 .5 cm cutting (LF) where underground growth was extensive . Intermediate plant habit of 5 . 0 cm cutting (MF). A compact plant habit resulting from 1 .5 cm cutting and reduced rhizome expansion (SF) . A dorsal view indicating concentrated shoot locii at swollen rhizome nodes distant from the crown. 53 5 3 54 54 5 7 5 7 65 65 66 66 X L I S T OF APPENDICES Appendix Page 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 Percen tage soil mo is ture during 1 9 7 5 / 7 6 for 0-5 cm , 5- 1 5 cm and 1 5-30 cm depths Met eorological measurements , D . S . I . R , Palmers ton North Res idual and f inal dry mat ter levels o f Experiment 1. Res idual and f inal leaf area indices o f Experiment 1 . Growth rates in treatment RS Growth rates in t reatment SAS Growth rat es in trea tment 6S G rowth rates in treatment 61 Growth rates in treatment SAL Growth rates in trea tment LS Environmental de tails of the controlled c l imates in Experiment 3 and 4 . Leaf to stem dry weigh t ratios of s tubb l e , s tubb le shoots and rhizome shoots . Experimental details of the c14 Red i s t r ibution and 1 9 7 1 9 8 199 200 20 1 W 2 2 0 3 204 205 206 207 208 D i s t r ibut ion experiment s . 209 14 To tal plant l eaf area in the c14 Dis tribution experiment 2 10 1 5 Rhizome and c rown plus taproot TNC in the c14 Redis tribut ion exper iment 2 10 x i