Below-ground reserves are thought to provide an indication of a forage potential for shoot regrowth after defoliation. The aim of this work was to re-evaluate the causal relationships existing between organic reserves (non-structural carbohydrates and N reserves) and shoot regrowth of alfalfa. The variations brought about by cultivar differences (cv Lodi or Europe), length of the previous regrowth period (30 or 45 d), or by intraspecific competition for light within a dense canopy, were studied. Field grown plants were harvested at weekly intervals, and separated as dominant, intermediate and suppressed plants. Shoot regrowth yield was determined and taproot were analyzed for starch, N, soluble proteins and vegetative storage proteins. Results showed that taproot starch and N contents were modified by the length of the previous regrowth but not by the position of the plant within the canopy. Soluble protein or VSP concentrations increased with the length of the previous regrowth, and with a higher position of the plant within the canopy. Shoot regrowth yield was linearly related to taproot soluble protein and VSP contents on day of defoliation, but relationships were not found with initial starch or N contents. These results suggest that root protein and VSP are key organic nutrient for alfalfa shoot regrowth after harvest

Avice, Jean Christophe

Boucaud, Jean

Lemaire, Gilles

Ourry, Alain

Volenec, Jeffrey J

English

University of Kentucky

University of Kentucky UKnowledge IGC Proceedings (1997-2023) XVIII IGC (1997) Manitoba & Saskatchewan Intraspecific Competition in Lucerne and Relationships with Reserve Availability Jean Christophe Avice INRA, I.R.B.A, France Alain Ourry INRA, I.R.B.A, France Gilles Lemaire INRA, France Jeffrey J. Volenec Purdue University Jean Boucaud INRA, I.R.B.A, France Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, and the Weed Science Commons This document is available at https://uknowledge.uky.edu/igc/1997/session7/45 <>Grasslands 2000</> This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in IGC Proceedings (1997-2023) by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. Session 7 - Plant Physiology and Growth 7-91ID NO. 1413INTRASPECIFIC COMPETITION IN LUCERNE AND RELATIONSHIPS WITHRESERVE AVAILABILITYJean Christophe Avice1, Alain Ourry1, Gilles Lemaire2, Jeffrey J. Volenec3, and Jean Boucaud11 U.A. INRA Physiologie et Biochimie Végétales, I.R.B.A., Université, 14032 Caen Cedex, France2 I.N.R.A., Station d’écophysiologie des plantes fourragères, INRA, Centre de Poitou Charentes, 86600 Lusignan, France3 Department of Agronomy, Purdue University, West Lafayette, IN 47907-1150, USAABSTRACTBelow-ground reserves are thought to provide an indication of aforage potential for shoot regrowth after defoliation. The aim of thiswork was to re-evaluate the causal relationships existing betweenorganic reserves (non-structural carbohydrates and N reserves) andshoot regrowth of alfalfa. The variations brought about by cultivardifferences (cv Lodi or Europe), length of the previous regrowthperiod (30 or 45 d), or by intraspecific competition for light within adense canopy, were studied. Field grown plants were harvested atweekly intervals, and separated as dominant, intermediate andsuppressed plants. Shoot regrowth yield was determined and taprootwere analyzed for starch, N, soluble proteins and vegetative storageproteins. Results showed that taproot starch and N contents weremodified by the length of the previous regrowth but not by theposition of the plant within the canopy. Soluble protein or VSPconcentrations increased with the length of the previous regrowth,and with a higher position of the plant within the canopy. Shootregrowth yield was linearly related to taproot soluble protein andVSP contents on day of defoliation, but relationships were not foundwith initial starch or N contents. These results suggest that root proteinand VSP are key organic nutrient for alfalfa shoot regrowthafter harvest.KEY WORDSDefoliation, Lucerne, Medicago sativa, Nitrogen, Reserve, Starch,Tap roots, Vegetative storage proteins.INTRODUCTIONAlthough it is well admitted that carbon reserves are needed to sustainregrowth after defoliation of forage species, numerous experimentalevidences show that the role of N reserves may be more importantthan often believed (see Richards, 1993 for a review). Nitrogen flowsfrom source tissues remaining after defoliation to regrowing sinktissues of lucerne have been quantified using 15N labelling,demonstrating that a significant amount of N in regrowing shoot oflucerne may be derived from reserve mobilization (Kim et al., 1993).Furthermore, it has been shown that N reserve availability ratherthan starch may limit regrowth potential of isolated, hydroponic-grown lucerne plants (Ourry et al., 1994), and this can be explainedby the fact that root carbohydrates are predominantly used for rootrespiration (61% of the stored C) while only a small proportion (5%)was recovered in regrowing shoots (Avice et al., 1996a). Similarly,for Lolium temulentum L. (Ourry et al., 1996), greater storage of Nprior to defoliation significantly increased leaf regrowth rate.Protein-N constitutes the largest reserve pool, and amino acid-N themost readily mobilized from source to sink tissues (Hendershot andVolenec, 1993a,b ; Volenec et al., 1996). In Medicago sativa taproots,specific proteins of molecular masses of 15, 19 and 32 kD are believedto act as vegetative storage proteins. These abundant proteins exhibita cyclic pattern of synthesis/mobilization induced either bydefoliation (Hendershot and Volenec, 1993b) or spring growth(Hendershot and Volenec, 1993a), are localized primarily in vacuoles,with smaller amounts found associated with amyloplasts (Avice etal., 1996c) and their degradation during regrowth is concomitant withN mobilization from source to sink tissues (Kim et al., 1993).These previously cited studies were conducted with isolated plantsgrown under controlled conditions without resource (light, water,nutrients) limitation. Competition for such resources in a densecanopy affects growth of individual plants, and consequently plantsurvival. It can be hypothetized that differential C and N storageduring regrowth under light competition is a factor contributing todifferences in shoot yield and plant mortality. Therefore, the aim ofthis work was to study intraspecific competition within a lucernecanopy in order to evaluate the causal implication of root organicreserves, i.e. nonstructural carbohydrates or N reserves as N, solubleprotein and vegetative storage protein (VSP) contents on regrowthpotential of plants situated at different depth in the canopy.MATERIAL AND METHODSAlfalfa stands (cv. Europe, or cv. Lodi) were sown (16.5 cm betweenrows) in April 1993 at Lusignan (46.26°N ; 0.07°E) and harvestedthree times (July, August and November) in 1993. In February 1994,they received 80 kg P.ha-1 and 90 kg K ha-1. Plants were then subjectedto a frequent defoliation regime (first cut on 5 May 1994 and thenharvested at 30 day intervals) or an infrequent defoliation regime(first cut on 24 May 1994 followed by a 45 days regrowth interval).All plants allowed to regrow for 30 or 45 days were defoliated on 6July 1994. Regrowth of the different plants was then followed bysuccessive weekly samplings for 35 days.In order to sample plants whose shoots have been located in differentpositions (from suppressed to dominant) in the canopy during theprevious regrowth, a preliminary study was conducted to relatetaproot diameter to the position of plants within the canopy. Taprootdiameter was found to be highly significantly and linearly correlatedwith the length of the longest stem. After defoliation, plants werethen sampled according to their taproot diameter, in order to separateplants which were either dominant, intermediate and suppressedduring the previous regrowth. Plants were harvested firstly byremoving the taproots of all plants from the first 20 cm of soil along2 m of row and then sorted according to taproot diameter. The taprootfresh weights were determined and the sample was immediatelyfrozen in liquid N2. After freeze-drying, samples were analyzed forN, starch, protein and VSP concentrations (Avice et al., 1996b).Shoots were harvested and separated into stem, leaves, and crown.RESULTS AND DISCUSSIONLengthening the previous regrowth from 30 to 45 d increased shootyield during the following regrowth (Table 1), as well as taproot andcrown dry weight. Similarly, N, starch, soluble proteins andvegetative storage protein concentrations of taproots were positivelyaffected. Shoot yield after 35 d of regrowth was similar for the twocultivars Lodi and Europe, but it should be pointed out that initialregrowth rates were faster for Lodi than for Europe during the first 3weeks of regrowth (data not shown), while N, starch, soluble protein(significant only for suppressed plants) concentrations were higherin Lodi than in Europe cultivar. Shoot regrowth yield, taproot andcrown dry weights (Table 1) were affected according to plant positionwithin the canopy (dominant, intermediate or suppressed). Moresurprisingly, the position of the plant within the canopy had no effecton N or little on starch concentrations in taproots : only plants witha suppressed position had a lower starch concentration than dominantor intermediate plants (Table 1). Taproot soluble protein and VSPconcentrations in taproots were significantly decreased with the depthof the plant within the canopy, being the lowest for suppressed plants,and higher for dominant than for intermediate plants.Session 7 - Plant Physiology and Growth 7-92When data from both cultivars, defoliation frequencies, and all plantsirrespective of position in the canopy, were pooled and regressedtogether against shoot dry matter production after 35 days ofregrowth, there was no relationship to either N or starchconcentrations of taproots measured on the day of defoliation (Fig.1A and 1B). In contrast, highly significant linear relationships werefound between shoot dry matter production and soluble protein orVSP concentrations in taproots on day of defoliation (Fig. 1C and1D). Increased VSP levels or soluble protein concentrations werefound in plants with a larger root biomass which correspond todominant plants, i.e. to plants having a greater access to highresources as they also produced greater shoot dry matter duringregrowth. Soluble protein concentrations were significantly relatedto VSP concentrations while, more surprisingly, root N concentrationwas independent of soluble protein and VSP concentrations(regressions not shown).Results showed that taproot starch was not affected markedly bygenotypic effects, harvest frequency, and more surprisingly, by plantsize resulting from its position within the canopy (Table 1). Shootregrowth was not associated with initial starch accumulation intaproots (Fig. 1B), a conclusion  supported by other studies (see forexample, Volenec, 1988; Boyce and Volenec, 1992; Ourry et al.,1994). The functional role of non-structural carbohydrates duringregrowth was assessed in labeling experiments which demonstratedthat most root C was used for root respiration and therefore, is anenergy source rather than a source of C skeletons for regrowth ofshoot tissues (Ta et al., 1990 ; Avice et al., 1996a).The rapidity of alfalfa shoot regrowth is largely determined byavailability of the taproot N reserves, so that the survival of anindividual plant within a dense canopy may heavily rely on itscapacity for a more rapid shoot regrowth than nearby competitors.Multiple cuttings within a season would amplify the importance ofpossessing a faster ability to store/mobilize and store again, Nreserves in taproots. Taproot soluble protein or VSP rather than N orstarch, may provide reliable estimates of shoot regrowth potentialalthough these contents are subjected to variations resulting fromnumerous biotic (cultivar, competition effects) and abiotic factors(harvest frequency, availability of resources).REFERENCESAvice, J.C., A. Ourry, G. Lemaire and J. Boucaud. 1996a. Nitrogenand carbon flows estimated by 15N and 13C pulse chase labelingduring regrowth of Medicago sativa L. Plant Physiol., submitted.Avice, J.C., A. Ourry, G. Lemaire, J.J. Volenec and J. Boucaud.1996b. Alfalfa intraspecific competition and the involvement ofreserve availability. Crop Science, submitted.Avice, J.C., A. Ourry, J.J. Volenec, G. Lemaire and J. Boucaud.1996c. Defoliation-induced changes in abundance and immuno-localization of vegetative storage proteins in taproots of Medicagosativa L. J. Plant Physiol. Biochem., in press.Boyce, P.J. and J.J. Volenec. 1992. Taproot carbohydrateconcentrations and stress tolerance of contrasting alfalfa genotypes.Crop Sci. 32: 757-761.Hendershot, K.L. and J.J. Volenec. 1993a. Taproot nitrogenaccumulation and use in overwintering alfalfa (Medicago sativa L.).J. Plant Physiol. 141: 68-74.Hendershot, K.L. and J.J. Volenec. 1993b. Nitrogen pools intaproots of Medicago sativa L. after defoliation. J. Plant Physiol.141: 129-135.Kim, T.H., A. Ourry, J. Boucaud and G. Lemaire. 1993.Partitioning of nitrogen derived from N2 fixation and reserves innodulated Medicago sativa L. during regrowth. J. Exp. Bot. 266:555-562.Ourry, A., T.H. Kim and J. Boucaud. 1994. Nitrogen reservemobilization during regrowth of Medicago sativa L. : relationshipsbetween their availability and regrowth yield. Plant Physiol. 105:831-837.Ourry, A., J.H. Macduff and H. Ougham. 1996. The relationshipbetween mobilization of N reserves and changes in translatablemessages following defoliation in Lolium temulentum L. and Loliumperenne L. J. Exp. Bot. in press.Richards, J.H. 1993. Physiology of plants recovering fromdefoliation. Proc. XVII Int. Grassld. Cong., Palmerston, NewZealand, pp 85-94.Ta, T.C., F.D.H. MacDowall and M.A. Faris. 1990. Utilization ofcarbon and nitrogen reserves of alfalfa roots in supporting N2-fixationand shoot regrowth. Plant Soil 127: 231-236.Volenec, J.J. 1988. Herbage growth and carbohydrate metabolismof diploid and tetraploid alfalfa. Crop Sci. 28: 128-132.Volenec, J.J., A. Ourry and B.C. Joern. 1996. A role for nitrogenreserves in forage regrowth and stress tolerance. Physiol. Plant.,in press.Figure 1Relationships between lucerne shoot dry matter production after 35d of regrowth and initial (Day 0) nitrogen (A), starch (B), solubleprotein (C) and VSP (D) concentrations in taproots, the day ofdefoliation in two Medicago sativa L. cultivars (Europe or Lodi)previously subjected to a harvest frequency of 30 or 45 d and fordominant (D), intermediate (I) and suppressed (S) plants. Regressionswere highly significant at P < 0.01 (**) or not significant (NS) atP > 0.05.Table 1Effects of the length of the previous regrowth period (30 or 45 d), the cultivarused (Lodi or Europe) and the position of the plant within the canopy (D:dominant, I: intermediate, and S: suppressed position) on shoot, crown andtaproots dry weight and taproot N, starch, soluble proteins and vegetativestorage proteins (VSP) concentration. Data obtained from weekly harvestsduring 35 days of regrowth were averaged and pooled together forcomparisons. Significantly higher (>) or not significantly different (=) forP=0.05.on dry matter of:on taproot concentration of:Effects of: Taproots Crown Shoot N Starch Soluble VSPproteinsLength of the previous 45d>30d 45d>30d 45d>30d 45d>30d 45d>30d 45d>30d 45d>30dregrowth (45d>30d)Cultivars L=EL=E L=E L>E L>E L>E for S L>E (Lodi or Europe) plants onlyPlant position within D>I>S D>I>S D>I>S D=I=S D=I>S D>I>S D>I>Sthe canopy (D, I or S)

Intraspecific Competition in Lucerne and Relationships with Reserve Availability

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Intraspecific Competition in Lucerne and Relationships with Reserve Availability

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