AOBPreview originally published online on May 22, 2008
Annals of Botany 2008 102(2):247-254; doi:10.1093/aob/mcn083
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Flooding Effects on Plants Recovering from Defoliation in Paspalum dilatatum and Lotus tenuis
IFEVA-CONICET, Facultad de Agronomía, Universidad de Buenos Aires, Avenida San Martín 4453. CPA 1417 DSE Buenos Aires, Argentina
* For correspondence. E-mail: striker{at}ifeva.edu.ar
Received: 6 March 2008 Returned for revision: 15 April 2008 Accepted: 24 April 2008 Published electronically: 22 May 2008
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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Background and Aims: Flooding and grazing are major disturbances that simultaneously affect plant performance in many humid grassland ecosystems. The effects of flooding on plant recovery from defoliation were studied in two species: the grass Paspalum dilatatum, regrowing primarily from current assimilation; and the legume, Lotus tenuis, which can use crown reserves during regrowth.
Methods: Plants of both species were subjected to intense defoliation in combination with 15 d of flooding at 6 cm water depth. Plant recovery was evaluated during a subsequent 30-d growth period under well-watered conditions. Plant responses in tissue porosity, height, tiller or shoot number and biomass of the different organs were assessed.
Key Results: Flooding increased porosity in both P. dilatatum and L. tenuis, as expected in flood-tolerant species. In P. dilatatum, defoliation of flooded plants induced a reduction in plant height, thus encouraging the prostrated-growth response typical of defoliated plants rather than the restoration of contact with atmospheric oxygen, and most tillers remained submerged until the end of the flooding period. In contrast, in L. tenuis, plant height was not reduced when defoliated and flooded, a high proportion of shoots being presented emerging above water (72 %). In consequence, flooding plus defoliation did not depress plant recovery from defoliation in the legume species, which showed high sprouting and use of crown biomass during regrowth, whereas in the grass species it negatively affected plant recovery, achieving 32 % lower biomass than plants subjected to flooding or defoliation as single treatments.
Conclusions: The interactive effect of flooding and defoliation determines a reduction in the regrowth of P. dilatatum that was not detected in L. tenuis. In the legume, the use of crown reserves seems to be a key factor in plant recovery from defoliation under flooding conditions.
Key words: Allocation, defoliation, flooding, Lotus tenuis, Paspalum dilatatum, submergence
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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Flooding and defoliation are major disturbance factors affecting plant performance in many grassland ecosystems of the world (McNaughton, 1983; Soriano, 1991). Defoliation triggers a series of morpho-physiological adjustments in order to cope with tissue removal, including mobilization and utilization of reserves, priority allocation of carbon and nutrients to leaf production and decreased plant height by shifting toward more prostrate growth forms (Richards, 1993; Gautier et al., 1999). This way, defoliated plants present a higher number of smaller shoots, and biomass located in the lower layers of the canopy (Gibson et al., 1992; Gautier et al., 1999), helping them to ameliorate subsequent defoliation events (McNaughton, 1983). In contrast, plants normally respond to flooding by increasing plant height and placing a higher proportion of shoot biomass on the upper layers of the canopy (Van der Sman et al., 1991; Insausti et al., 1999, 2001; Striker et al., 2005) to restore contact with the atmosphere to allow oxygen capture for submerged tissues (Laan et al., 1990; Grimoldi et al., 1999). It could be stated that defoliation and flooding trigger opposite conflicting morphological responses in plant height, which can affect proportions of submerged/emergent shoots and thus plant biomass accumulation. The paper explores this issue in plants recovering from defoliation under flooding conditions by comparing a grass and a legume species with potentially different types of regrowth.
A factor that may influence the capacity of plants to tolerate the combined action of defoliation and flooding is the relative use of reserves during regrowth. A higher use of reserves would minimize the consequences of lower/submerged remnant leaf area. Grasses and legumes differ in the significance of reserves to supply plant regrowth after defoliation. Grass regrowth depends mainly on current carbon assimilation (Schnyder and de Visser 1999; Lattanzi et al., 2005). In contrast, legumes can support carbon requirements during regrowth by using crown reserves (Ourry et al., 1994), mainly to supply root respiration (Avice et al., 1996). Pre-defoliation carbon supports shoot regrowth of grasses only for 2–5 d after cutting (Schnyder and de Visser 1999; Lattanzi et al., 2005), while in alfalfa it can last >10 d (Ourry et al., 1994; Avice et al., 1996). The grass Paspalum dilatatum and the legume Lotus tenuis (syn. Lotus glaber) are important forage species of increasing agricultural interest for pastures and natural grasslands, especially in soils suffering from extremely wet conditions (Blumenthal and McGraw, 1999). Both species are tolerant of soil flooding (Insausti et al., 2001; Striker et al., 2005, 2006). Also, morphological differences between the grass and the legume may influence their regrowth under flooding conditions. The higher position of the meristems in axillary buds of the legume with respect to the grass (with meristems near the soil surface; see Briske, 1991) could favour a more rapid emergence of their shoots from water. The few available reports on the interaction between flooding and defoliation mostly cover grasses and describe detrimental effects on plant performance (Oesterheld and McNaughton, 1991b; Merril and Colberg, 2003; Hayball and Pearce, 2004). As far as is known, there is only one study of the effects of root anoxia and partial shoot removal on legume species (Barta, 1988). Such a work found a lower shoot regrowth in seedlings of 4- to 5-week-old Medicago sativa and Lotus corniculatus in response to defoliation followed by 5 d of root anoxia (Barta, 1988). However, for adult legume plants, which can regrow by using crown reserves, the effects of flooding on plant recovery from defoliation have never been addressed.
The objective of this work was to study the effects of flooding on plant recovery from defoliation on two species: the grass Paspalum dilatatum, whose regrowth mainly depends on current assimilation; and the legume Lotus tenuis, which can use crown reserves during regrowth. For this purpose, plants of these species were subjected to defoliation in combination with 15 d of flooding, and their performance evaluated during a subsequent 30-d growth period under well-watered conditions. Plant responses in tissue porosity, height, tiller or shoot number and biomass of the different organs were assessed. As far as is known, this is the first study on the effect of flooding on plant recovery from defoliation on a long-term basis, and the first one performed with a legume species capable of regrowth by using crown reserves.
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MATERIALS AND METHODS |
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Plant material and study site
Paspalum dilatatum Poir. is a highly productive C4 grass and a conspicuous component of the temperate humid Pampa grasslands of Argentina. It is widely distributed along topographical gradients and its growing season ranges from late spring to end of the summer. Plants are leafy, tufted perennials with clustered stems rising from short creeping rhizomes. Lotus tenuis Waldst. & Kit. (syn. Lotus glaber Mill.) is a warm-season perennial legume naturalized in Pampa grasslands subjected to periodic flooding events. Its growing season ranges from spring to autumn. It usually presents a well-developed crown and taproot with extensive lateral root branching. Stems present pentafoliate leaves with two of the leaflets at the petiole base resembling stipules. Both species are able to alter their growth habit in response to environmental conditions: they grow prostrated (plagiotropic orientation of their shoots) under full sunlight in grazed environments, and become erect by shifting their shoots towards an orthotropic position under closed canopies (Gibson et al., 1992; Clúa et al., 1996).
For the experiment, adult plants of similar size of P. dilatatum and L. tenuis were extracted in grassland soil blocks with natural vegetation (0·3 x 0·3 x 0·25 m depth), taking the target individual as the centre of the block. Plants were taken from an extensive stand of a lowland grassland located in the Department of Pila, Province of Buenos Aires, Argentina (36°30'S, 58°30'W), defined phytosociologically as the community of Piptochaetium montevidensis, Ambrosia tenuifolia, Eclipta bellidioides and Mentha pulegium (Burkart et al., 1990). This plant community is found in flat areas associated with typical Natraquoll soils (Soriano, 1991). Such grasslands are grazed throughout the year and regularly exposed to flooding of varying intensity and duration (Soriano, 1991). The grassland was not flooded at the time of block extraction. Immediately after extraction, soil blocks containing the plants were put into plastic containers and positioned in the experimental garden at the University of Buenos Aires.
Flooding and defoliation treatments
After a 3-month acclimation period, plants of each species were subjected to flooding and defoliation treatments following a completely randomized design (2 x 2: non-defoliation and defoliation x non-flooding and flooding) with five replicates. Defoliation treatment was applied once at the beginning of the experiment by clipping plant biomass above 6 cm height. Approximately 50 % of total leaf biomass was removed in both species. Biomass removal was checked to be similar between defoliated plants assigned to non-flooding (i.e. watered to field capacity) and flooding treatments (P > 0·5, based on Student's t-test). Flooding treatment was applied for 15 d by maintaining a water level 6 cm above the soil surface. Non-flooded soil blocks were watered daily to field capacity and allowed to drain freely. After flooding, plants were allowed to grow for 30 d under drained conditions to evaluate their recovery. The experiment ran during early summer, when the air vapour pressure deficit was on average 2·6 kPa. Soil anoxia by flooding was characterized by measuring the oxygen diffusion rate (ODR) at a soil depth of 5 cm with platinum microelectrodes (Letey and Stolzy, 1964). The ODR decreased quickly during flooding treatment from 60 ± 1 to 6 ± 1 x 10–8 g cm–2 min–1 in the first 3 d, and to 0·6 ± 0·3 x 10–8 g cm–2 min–1 at the end of the flooding period. When flooding was discontinued, the ODR recovered its original values during the first 5 d of the recovery phase.
Tissue porosity
Fractional porosity of roots and sheaths in P. dilatatum, and roots and stems in L. tenuis were quantified at the end of the flooding period (day 15) using the pycnometer method (Jensen et al., 1969), based on the weight increase which occurs when air spaces of plant tissues are replaced by water after maceration.
Biomass responses
Plant harvests were carried out at the beginning of the treatments (initial) in additional randomly chosen individuals (n = 5), and at the end of the recovery phase (day 45). Plant biomass was separated into tiller, rhizome and root for P. dilatatum, and into shoot, crown and root for L. tenuis. The portion of biomass removed by defoliation was weighed, and later included in the shoot fraction of the corresponding plants at the end of the recovery phase. By dissecting the plants it was possible to study how treatments affected plant biomass compartmentalization and to infer the use of reserves for plant recovery from defoliation. Harvested material was weighed after oven drying for 72 h at 70 °C.
Plant height and shoot number
Plant height, the number of tillers of P. dilatatum and the number of shoots of L. tenuis were quantified three times: at the beginning of the treatments (initial); at the end of the flooding period (day 15); and at the end of the recovery phase (day 45). Tillers of P. dilatatum and shoots of L. tenuis were classified in two categories: above and below 6 cm height, in accordance with the imposed water level during the flooding treatment. The proportion of organs located above 6 cm was calculated in all treatments. It is important to note that the fraction of aerial organs below 6 cm corresponded to fully submerged tillers or shoots under flooding conditions.
Statistical analyses
All variables were analysed separately for each species through two-way ANOVAs with flooding and defoliation as the main factors. Analyses were performed separately for flooding and recovery periods. When significant interactions were detected, Tukey's test was applied subsequently to determine the treatment effects. Normality and the homogeneity of variances were previously verified. Variables involving percentages were arcsine 
x transformed before analysis. Statistical analyses were performed using the package STATISTICA for Windows (StatSoft, Tulsa, OK, USA). All results are presented as non-transformed means of five replicates ± s.e.
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RESULTS |
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Effects on plant tissue porosity
Flooding increased tissue porosity both in Paspalum dilatatum (P < 0·001) and Lotus tenuis (P < 0·01) as expected in flood-tolerant species (Table 1). Defoliation did not affect this parameter (P > 0·5; flooding x defoliation: P > 0·55 in both species). Flooded plants of P. dilatatum presented 42 % higher root porosity and twice the sheath porosity as plants growing under non-flooding conditions (Table 1). Similarly, flooded plants of L. tenuis attained 61 % higher root porosity and duplicated their stem porosity in relation to non-flooded plants (Table 1).
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Biomass responses
The combination of flooding and defoliation negatively affected recovery from defoliation in P. dilatatum (Table 2 and Fig. 1). In the grass species, total biomass accumulation was 32 % lower in plants subjected to the combination of flooding and defoliation than in all other treatments (P < 0·05). In those plants, the lower growth rate was associated with reductions in shoot and root biomass, while rhizome biomass was not affected by treatments (Table 2 and Fig. 1). The proportion of rhizome biomass (with respect to total biomass) was higher in flooded x defoliated (F–D) plants than in the non-flooded and non-defoliated (NF–ND) ones (21·5 ± 1·6 % versus 15·0 ± 1·1 %, P < 0·01; Fig. 1). Remarkably, the combination of flooding and defoliation did not affect plant recovery in the legume L. tenuis (Table 2 and Fig. 1). In this species, flooded x defoliated plants attained biomass accumulation similar to that of plants subject to single treatments (P > 0·3), although it was lower in non-flooded and non-defoliated plants (NF–ND; P < 0·05). Interestingly, shoot biomass was not affected by the combination of treatments (Table 2), while flooded x defoliated plants presented a major reduction in crown dry weight (Table 2 and Fig. 1). Accordingly, the proportion of crown biomass (with respect to total biomass) was lower in flooded x defoliated (F–D) plants than in non-flooded and non-defoliated (NF–ND) ones (5 ± 2·4 % versus 17 ± 1·0 %, P < 0·005; Fig. 1).
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Plant height
At the beginning of the experiment, plants assigned to different treatments presented similar plant height (P > 0·7; Fig. 2). After 15 d of treatment, defoliation induced a shift toward a prostrate growth form in both species (Fig. 2). Defoliated (NF–D) plants of P. dilatatum and L. tenuis presented a lower stature than non-flooded and non-defoliated (NF–ND) plants (Table 2), even though shoot and total biomass (i.e. plant size) were in the same range for all treatments (compare Figs 1 and 2). Defoliated (NF–D) plants of P. dilatatum and L. tenuis presented 52 % and 48 % of their tillers/shoots, respectively, below 6 cm height, a much higher proportion than other treatments (P < 0·05; Fig. 3). As expected, flooding (F–ND) greatly enhanced the shoot height of P. dilatatum (Fig. 2), resulting in a large fraction of leaf area emerging above the water level (approx. 80 % of the tillers; Fig. 3). But surprisingly, flooded and defoliated (F–D) plants of P. dilatatum were mostly submerged until the end of the flooding period (Figs 2 and 3), presenting more than half of their tillers totally below the water level (P < 0·05; Fig. 3). In contrast, L. tenuis plants subjected simultaneously to both disturbances (F–D) showed a height similar to the plants growing under non-defoliated conditions (NF–ND and F–ND; Table 2 and Fig. 2), presenting only 28 % of their shoots in the layer below 6 cm height (F x D: P < 0·025), a much lower fraction with respect to all other treatments (Fig. 3).
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After a 1-month recovery period, in which plants were grown under well-watered conditions, differences in plant height were not particularly apparent in either species (Table 2 and Fig. 2). However, the proportion of tillers of P. dilatatum located below 6 cm height was still higher in flooded x defoliated plants (F–D: 47 %) with respect to the other treatments (NF–ND: 20 %, F–ND: 21 % and NF–D: 23 %; P < 0·05; Fig. 3). At that time, previously flooded plants of L. tenuis showed a high proportion of shoots in the lower layer (compare day 15 with day 45; Fig. 3), in accordance with the high level of sprouting of such plants during the recovery period.
Tiller and shoot number
At the beginning of the experiment, P. dilatatum and L. tenuis plants assigned to different treatments presented similar tiller and shoot numbers (P > 0·8 and P > 0·9, respectively; Fig. 3). After 15 d of treatment, defoliation increased the tiller number of P. dilatatum, while flooding did not modify this parameter (Table 2 and Fig. 3). In L. tenuis, defoliation greatly increased the number of shoots per plant, while flooding conditions determined a pronounced reduction in this parameter (Table 2 and Fig. 3). Interestingly, when both disturbances were combined, L. tenuis plants attained approximately double the number of shoots as plants only subjected to flooded conditions (Fig. 3).
During the recovery period, tillering promotion was not more apparent as the result of defoliation on P. dilatatum flooded plants (Table 2 and Fig. 3). Thus, flooded x defoliated (F–D) plants of Paspalum achieved a lower tiller number in comparison to defoliated (NF–D) plants (P < 0·05; Fig. 3). In contrast, previously flooded plants of L. tenuis showed high sprouting during this period, duplicating their shoot number in relation to the end of the flooding period (P < 0·001; compare day 15 with day 45; Fig. 3). Thus, flooded x defoliated (F–D) plants of L. tenuis attained the same number of shoots as non-flooded and non-defoliated (NF–ND) plants at the end of experiment (P > 0·3; Fig. 3).
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DISCUSSION |
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Recovery from defoliation of Paspalum dilatatum and Lotus tenuis under flooding conditions
The results show a negative effect of the flooding and defoliation combination affecting regrowth of the grass Paspalum dilatatum, which was not detected in the legume Lotus tenuis. Defoliated plants could partially or fully compensate or overcompensate leaf removal depending on their intrinsic tolerance to defoliation conditions (McNaugthon, 1983; Richards, 1993). In the present study, leaf removal did not affect compensatory growth in non-flooded plants of the grass P. dilatatum (Fig. 1), a finding that concurs with the general similarity in terms of above-ground biomass for non-defoliated and defoliated grasses (Loreti et al., 2001; Ferraro and Oesterheld, 2002, and references therein). However, it is known that environmental stresses can alter the ability of plants to recover from defoliation (Davidson and Milthorpe, 1965; Oesterheld and McNaughton, 1991a). Here, it is demonstrated that flooding, as a stress factor, affected the compensatory growth of defoliated plants of P. dilatatum, which maintained a great proportion of leaf area below the water level without contact with atmospheric oxygen. In contrast, defoliated plants of the legume L. tenuis showed the capacity to emerge from the water, with crown reserves a main support during recovery from defoliation under flooding conditions.
In grasses, Oesterheld and McNaughton (1991b) have proposed that the synergistic negative effects on plant growth caused by the combination of flooding and defoliation is based on opposing allocation responses: the replacement of leaves removed by cutting and the costly maintenance of the new adventitious root system developed under anaerobic conditions (see also Merril and Colberg, 2003; Hayball and Pearce, 2004). The present results suggest an additional morphological component associated with the decreased plant height of defoliated plants under flooding conditions. This was the morphological response of prostrate plants that remained submerged with presumably diminished carbon assimilation during the flooding period. Therefore, the growth of those plants is dependent on the less efficient underwater photosynthesis (Mommer and Visser, 2005). As a reference, underwater photosynthesis is lower than 5 % with respect to aerial leaves (Mommer et al., 2006). On that note, a number of physiological mechanisms have been proposed to favour compensatory growth, such as incremental photosynthesis and stomatal conductance rates, decrease of self-shading and delayed leaf senescence (McNaughton, 1983; Richards, 1993). All of these mechanisms seem to be compromised in submerged conditions. Decreased plant height appears to be an important component of the depressed recovery from defoliation under flooding conditions in the grass, as its regrowth mainly depends on current carbon assimilation (Lattanzi et al., 2005), while rhizome reserves (Fig. 1) seem not to be a primary source of nutrients for plant regrowth (Kavanová and Gloser, 2005).
Unlike the grass, L. tenuis successfully recovered from defoliation under flooding conditions, in biomass terms, when it is compared with plants subjected to single stress factors (Fig. 1). Two attributes appear to explain the higher recovery of flooded x defoliated plants. First, most of the shoots in the legume species were located above water, contributing to rapid aerial carbon fixation and oxygen capture for plant internal aeration (Figs 2 and 3). Besides, the highest oxygen consumption occurs in meristems with high metabolic activity (Bidel et al., 2000), so that the highest position of the meristems of defoliated plants of Lotus tenuis (that rapidly emerged from water) could help to explain the better performance of this species in comparison to the grass P. dilatatum with meristems located near the soil surface (Briske, 1991). Secondly, crown reserves supported plant recovery from defoliation to a great extent when plants were subjected to the combination of stress factors. This last result contrasts with the common response of this species when subjected to intermediate defoliation intensities, which is to regrow by assimilation of residual leaves (Smith, 1962; Kallenbach et al., 2001). Otherwise, flooding seems to simulate a very intense defoliation by partially submerging the plants, greatly reducing carbon fixation, and compelling plants to use reserves for regrowth (Meuriot et al., 2004). Although this response resulted in partial compensation in relation to the non-flooded and non-defoliated plants, flooded x defoliated plants were not affected by the combination of treatments. However, it is important to note that if successive defoliation events are applied to those taller plants, leaf removal will be more intensive and the regrowth capacity will be lower as crown reserves have not yet been recovered. The need for a longer recovery period after flooding to build up reserves should be taken into account when determining grazing management.
Morphological responses associated with tolerance to flooding and defoliation
Oxygen capture and its transport to submerged tissues are crucial to define plant internal aeration under flooding conditions (Armstrong, 1979; Colmer, 2003). The present results showed that flooded plants of P. dilatatum developed a suite of morphological and anatomical responses that facilitate both processes. First, the grass grew taller under flooding conditions, positioning a higher proportion of tillers above the water level (Fig. 3); this increases the possibility of oxygen capture (Laan et al., 1990; Grimoldi et al., 1999). Secondly, P. dilatatum presented sheaths and roots with higher porosity (Table 1), which is known to provide a continuous pathway of lower resistance for oxygen transport from aerial leaves to submerged tissues (Armstrong, 1979; Colmer, 2003). These results matched previous reports on the higher desubmergence capacity of P. dilatatum due to rapid increases in the tiller insertion angle and the length of aerial organs, as well as important increases in tissue porosity under flooding conditions (Insausti et al., 2001; Grimoldi et al., 2005; Striker et al., 2006). As expected for a flood-tolerant legume, L. tenuis greatly increases tissue porosity in stems and roots (Table 1), and presents a high proportion of shoots emerging from the water under flooding conditions (Fig. 3). In this legume species, the development of aerenchyma and the positioning of leaves towards the upper layers of the canopy had already been found to increase tolerance to soil flooding conditions (Striker et al., 2005, 2006; Teakle et al., 2006).
Interestingly, defoliation altered the potential for tissue aeration in flooded plants of these species in a contrasting way. In P. dilatatum, flooded x defoliated plants presented 71 % of their tillers fully submerged until the end of the flooding period, which hindered their oxygen capture besides reducing aerial carbon fixation. By contrast, L. tenuis presented 72 % of its shoots emerging from the water (Fig. 3), facilitating both oxygen and carbon capture. It is important to note that root aeration of defoliated plants appeared to be more limited by oxygen capture than by oxygen transportation, since tissue porosity was similarly increased by flooding in both non-defoliated and defoliated plants (Table 1). It is well documented that both species can have plastic morphological responses to environmental signals. On one hand, L. tenuis shoots grew erect in response to shade (Clúa et al., 1996) and flooding (Striker et al., 2005), while remaining prostrated under full sunlight (Clúa et al., 1996) and/or defoliation conditions (Fig. 2). In the present study, it was demonstrated that defoliation did not alter the response pattern of L. tenuis under flooding conditions, as plant height increased rapidly and most of the shoots were positioned above the water level (Fig. 2). On the other hand, P. dilatatum plants grew prostrated in response to a photomorphogenic signal as a high red to far-red ratio which simulated grazed environments (Casal et al., 1987; Gibson et al., 1992), while growing taller under flooding conditions (Insausti et al., 2001) possibly induced by the accumulation of ethylene in submerged tissues (Voesenek et al., 1989, 2006; Blom et al., 1994). Remarkably, in contrast to the legume species, P. dilatatum remained prostrated under flooding x defoliation conditions, suggesting that the light environment associated with defoliation (high red to far-red ratio) predominates over flooding signals (presumably ethylene-mediated; Colmer, 2003). Current reports on the trade-off between environmental signals in response to different stresses have already showed a predominance of light signals over others as inducible defences against herbivores (Cipollini, 2004; Izaguirre et al., 2006). The mechanisms associated with the predominance of light environment over flooding signals in grasses have yet to be clarified.
Concluding remarks
The interactive effect of flooding and defoliation causes a depression in the regrowth of the grass P. dilatatum, which is not detected in the legume L. tenuis. Defoliation even under flooding conditions led to a reduction in plant height of P. dilatatum, with prostrated growth prevailing over restoration of contact with atmospheric oxygen. Therefore, flooding x defoliation negatively affected compensatory growth after cutting, leading to lower biomass accumulation than in the other plants. Plant height of L. tenuis was always promoted by flooded conditions, and biomass accumulation was not reduced by the combination of stress factors. In the legume species, the use of crown reserves seems to support plant recovery from defoliation to a great extent under flooding conditions. The way in which these relationships could be affected by repeated cutting events and the physiological mechanisms controlling plant height under flooding x defoliation conditions deserves further experimental investigation.
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ACKNOWLEDGEMENTS |
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We specially thank Fernando A. Lattanzi (Technische Universität München, Germany) for his critical review of this manuscript. We thank Rolando J. C. León (University of Buenos Aires, Argentina), Federico Mollard (University of Buenos Aires, Argentina) and two anonymous reviewers for their suggestions on this manuscript. We also thank the Bordeau family, owners of Estancia Las Chilcas, who facilitated our work on their land. The study was funded by grants of University of Buenos Aires (UBA G 057) and Academia Nacional de Agronomía y Veterinaria (ANAV 48). G.G.S. was supported by a fellowship from University of Buenos Aires and ‘Consejo Nacional de Investigaciones Científicas y Técnicas’ (Argentina).
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LITERATURE CITED |
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