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Anatomy and Morphology |
Departamento de Botánica, Universidad Nacional del Comahue, Quintral 1250, 8400, Bariloche, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina; INRA, Unité Mixte de Recherche (UMR) Cirad-Cnrs-Inra-Ird-Université Montpellier 2, "botAnique et bioinforMatique de l'Architecture des Plantes" (AMAP), UMR T51 (CIRAD), UMR 5120 (CNRS), UMR 931 (INRA), M123 (IRD), UM27 (UMII) TA A-51/PS2, Boulevard de la Lironde, 34398 Montpellier, Cedex 5, France
Received for publication October 18, 2006. Accepted for publication June 26, 2007.
ABSTRACT
In temperate trees, axis length growth generally results from the differentiation of organs at the end of a growing season and the extension of such "preformed organs" in the next growing season. Neoformation, i.e., the simultaneous differentiation and extension of organs, has been studied for only a few species. Here we evaluated bud composition and growth unit (GU) size for seedlings and saplings of Nothofagus alpina, a valuable South American forest tree. Trunk GUs of seedlings and saplings included preformed and neoformed organs, whereas main-branch GUs of saplings were entirely preformed. The size of a GU was more closely related to the number of preformed green leaves than to the number of cataphylls of its preceding bud. Proximal buds of a trunk GU had more cataphylls and less green-leaf primordia than distal buds. Individual leaf area increased from proximal to distal positions on trunk GUs. For trunk and main-branch GUs, the length/width ratio was maximum for leaves in intermediate positions. The development of large neoformed leaves at the end of the growing season could increase the photosynthetic capacity of this species in late summer, when the activity of preformed organs is likely to be decreasing.
Key Words: bud structure • growth unit • leaf size • neoformation • Nothofagaceae • Nothofagus alpina • Patagonia • preformation
Plants growth involves the differentiation of organ primordia from meristematic cells and the extension of such primordia into fully grown organs. For a particular organ, differentiation and extension may take place simultaneously or at different times (Hallé et al., 1978
). The period or periods of the year when differentiation and extension occur are major determinants of a species capacity to inhabit specific world regions and sites (Oldeman, 1989
). Organs differentiated as primordia in one growing season and extended in the following growing season, after an autumn–winter resting period, are described as preformed organs. The entirely preformed character of shoots seems to be the regular growth pattern in tree species from temperate to cold regions (Kozlowski, 1971
; Diggle, 1997
). Nonetheless, the simultaneous differentiation and extension of organs, termed neoformed organs, after preformation extension has been documented (Critchfield, 1960
; Hallé et al., 1978
; Sabatier et al., 1998
). Neoformation is considered to be relatively uncommon among tree species from temperate to cold regions of the northern hemisphere, sometimes occurring only in vigorous axes such as the trunks of young trees, trunk-base sprouts, and root suckers (Kozlowski, 1971
; Barthélémy et al., 1997
; Guédon et al., 2006
). For some tree species, the neoformation contributes more to axis growth than preformation does (Snowball, 1997
; Costes, 2003
; Gordon et al., 2006
). For further discussion of preformation and neoformation, see Barthélémy and Caraglio (2007)
.
There is evidence that preformed and neoformed leaves of a growth unit (GU, i.e., an axis portion developed in one uninterrupted extension event) may differ both morphologically and physiologically (Critchfield, 1960
; Carles et al., 1964
; Steeves and Sussex, 1989
; Koike et al., 1990
). Intraspecific variations in the extent of neoformation among tree provenances, clones, ages, and pruning treatments have been reported (Davidson and Remphrey, 1994
; Guédon et al., 2006
). The capacity of a particular tree to develop preformed and neoformed organs may be of adaptive value under particular conditions. For instance, the development of entirely preformed GUs would benefit trees growing in temperate regions where unfavorable conditions for GU extension are likely in late spring and summer. In contrast, the development of neoformed organs after preformation extension would be advantageous wherever favorable conditions are likely to persist late in the growing season.
Many of the tree species inhabiting the temperate to cold forests of South America (southern Chile and Argentina, along the Andes mountains) are evolutionarily close to species from the northern hemisphere. Among them are those belonging to the genus Nothofagus, whose family, Nothofagaceae, forms the "fagalean complex" together with Fagaceae and Betulaceae (Jones, 1986
). The relevance of these species lies in their broad distribution area, abundance, timber production, and phylogenetic relationships (Steenis, 1971
; Stewart, 1979
; Tuley, 1980
; Hill, 1992
; Donoso, 1993
; Hill and Dettmann, 1996
; Veblen et al., 1996
). Studies on young trees of the South American species N. dombeyi and N. pumilio indicate that most GUs are exclusively preformed, whereas the largest GUs include preformed and neoformed organs (Puntieri et al., 2000
; Souza et al., 2000
). In contrast, N. antarctica shrubs may produce neoformed organs in GUs of intermediate size (Puntieri et al., 2002b
).
The species N. alpina (Poepp et Endl.) Oersted (= N. nervosa (Phil.) Dim. et Mil.), locally known as "raulí," is the most valuable species of this genus in terms of quality timber production and height growth rate (Lebedeff, 1942
; Stewart, 1979
; Tuley, 1980
; Destremau, 1988
; Dimitri et al., 1997
; INFOR-CONAF, 1998
). Its natural range along the Andes mountains (35° S to 41° S in Chile and 39°25' S to 40°35' S in Argentina; 100 to 1200 m a.s.l.) is highly fragmented because of biogeographical factors, overexploitation, and land reassignment to pastures and exotic tree cultivation (Marchelli et al., 1998
; Gallo et al., 2004
). Like other Nothofagus species, it regenerates from seeds mostly in large forest gaps (Donoso, 1993
; Veblen et al., 1996
). Significant progress has been made concerning ecological, reproductive, and molecular aspects of the biology of this species (Manos, 1997
; Calderón-Baltierra et al., 1998
; Marchelli et al., 1998
; Denne et al., 1999
; Marchelli and Gallo, 1999
; Weinberger and Ramírez, 1999
; Martínez-Pastur et al., 2003
). Nevertheless, much remains to be known about the morphological and architectural features of N. alpina. Several traits seem to distinguish N. alpina from other South American Nothofagus species. For instance, N. alpina trees tend to develop thicker axes and a better-defined vertical trunk at early stages of development than other Nothofagus species (Stewart, 1979
; Tuley, 1980
; Deans et al., 1992
). It also seems to have higher probabilities of regenerating under the canopy of adult trees than other Nothofagus (Donoso, 1993
). The aim of the present study was to assess the extent to which these morpho-architectural traits may relate to preformation and neoformation at seedling and sapling stages of development and/or to differences in preformation and neoformation between the trunk and main branches of saplings.
MATERIALS AND METHODS
Data set 1: seedlings
To evaluate preformation and neoformation in N. alpina seedlings, seeds were collected from natural populations at five localities within the Lanín National Park, Argentina: Lácar, Huechulafquen, Quillén, Tromen, and Hermoso, ranging from 39°26' S to 40°21' S, from 71°25' W to 71°30' W, and from 750 to 1200 m a.s.l. In October 1999, the seeds were sparsely sown on a 15 m2 area in a forest nursery belonging to the Unidad de Genética Forestal of Instituto Nacional de Tecnología Agropecuaria, Bariloche (Argentina; 41°04' S, 71°10' W; 770 m a.s.l.). First emergences were registered in November 1999. The area was regularly weeded. About 1900 N. alpina seedlings emerged but only 25% survived to the end of the first growing season; presumably, mortality was caused by late frosts. Two samples of seedlings (hereafter referred to as year-1 and year-2 seedlings) were taken after the end of two successive annual growth periods. In both cases, plants with signs of severe damage by insects or frost were avoided.
Year 1
In April 2000, after the 1999–2000 growth season, 176 healthy seedlings were cut at soil level so as to avoid damaging the roots of the remaining seedlings. At that time, all plants consisted of a main vertical axis with axillary buds and, often, a terminal bud. The size of the trunk GU was assessed in terms of stem length from the cotyledonary node to the base of the most distal bud, stem diameter at the cotyledonary node (measured with digital calipers), and number of nodes (assessed either by the presence of leaves or their scars on the stem). The terminal bud or the most distal axillary bud (in case the terminal bud had abscised) of each harvested seedling was fixed in 70% ethanol for 2 wk and dissected using an Olympus SZH-10 stereomicroscope (Olympus Optical Co. Ltd., Tokyo, Japan) at up to 70x magnification (Fig. 1). The numbers of leaves were recorded for each bud. In some buds, two sets of green-leaf primordia could be distinguished: a proximal set of large primordia (2–4 mm long) and a distal set of small primordia (<1 mm long).
|
). For other Nothofagus species, GUs extending from terminal buds do not differ greatly in their morphology and growth dynamics from relay GUs of axillary origin (Puntieri et al., 1998
). Consequently, both types of GUs were considered equivalent for the purpose of the present study. The size of the year-2 trunk GU was assessed as in the case of year-1 GUs. Year-2 trunk GUs were fixed in 70% ethanol for 2 wk. Their buds were numbered consecutively starting at one for the most proximal bud (Fig. 1) and were dissected as detailed for year-1 seedlings. For this data set, year-2 trunk GUs will be referred to, hereafter, as year-2 GUs.
Data set 2: saplings
To assess the developmental pattern of GUs in saplings, we labelled two samples of 20 10- to 15-yr-old N. alpina trees in a 10-ha area at Pucará, Parque Nacional Lanín, Argentina (40°05' S, 71°41' W). These trees had a vertical trunk 2–3 m high and 4–10 cm in basal diameter, from which slanted or horizontal branches were derived. These trees belong to the regeneration cohort naturally established in a managed mixed forest of N. alpina, N. obliqua, and N. dombeyi. Growth units were measured in two successive years from different sets of saplings (sample-1 and sample-2 GUs).
Sample 1
In April 2003 (early autumn), after GU extension and bud set, a random sample of 20 labelled trees was selected. The GU from the 2002–2003 growth season was cut from the trunk and from one of the main branches (between 1 and 2 m high on the trunk) of each tree. The size of each of these GUs was measured in terms of stem length, stem diameter, and number of cataphylls and green leaves as was done for seedlings. The most distal bud of each GU was dissected following the procedure described for seedlings.
Sample 2
In March 2004 (early autumn), the GU from growth season 2003–2004 was collected from the trunk and from one of the main branches of each of the 20 labelled trees not included among year-1 saplings. Stem length and diameter and the numbers of cataphylls and green leaves were registered for each GU. Leaf blades of each GU were numbered consecutively starting from the most basal green leaf, as in previous studies on Nothofagus (Puntieri et al., 2003
). Each blade was digitally scanned, and its length, maximum width, and area (on one side) were measured using the program Scion Image 4.0 (Scion Corporation, Maryland, USA). Blade shape was assessed by the length to maximum width ratio. The outline of barely damaged blades was reconstructed digitally. When more than 50% of a leaf blade was missing or damaged so as to make outline reconstruction impossible, the leaf was excluded from the analyses. Variations in leaf size and shape with position of the leaf on its bearing stem were assessed separately for trunk and main branch GUs by averaging these variables among GUs for each position. The buds of all GUs were numbered and dissected following the procedure described for the second sample of seedlings.
Data analyses
For seedlings and saplings, we separately evaluated the entirely preformed or partially preformed/partially neoformed nature of GUs by comparing the number of primordia in distal buds of GUs in the first sample (year-1 seedlings and sample-1 saplings) with the number of extended organs of GUs in the second sample (year-2 seedlings and sample-2 saplings) through one-way analysis of variance (ANOVA; Sokal and Rohlf, 1981
). In the case of saplings, data from trunk and main-branch GUs were analyzed separately.
For each data set, we assessed the variation in the numbers of cataphylls, small and large green-leaf primordia, and the total number of organs per bud, with position of the bud counted from the proximal end of GUs of year-2 seedlings and sample-2 saplings. To compare the numbers of leaves per bud between seedlings and saplings concerning we used an ANCOVA that included plant developmental stage (seedling or sapling) as a fixed factor, leaf type (cataphylls, small, and large green leaf primordia) as a random factor, and bud position (between positions 1 and 7, represented in both seedlings and saplings) as a covariable. The areas and length to width ratios of sapling blades were plotted against leaf position on the parent GU.
Pearson's correlation coefficients relating the total number of organs or the number of green-leaf primordia per bud with the length, diameter, and number of leaves of the bearing GU were calculated for the most distal bud for both data sets combined.
RESULTS
Growth-unit size
Seedlings
Year-1 GUs were, on average, longer and thinner than those of year 2; the GUs of both samples had fewer leaves (Table 1). The most distal bud of year-1 GUs included 0.3 ± 0.53 (mean ± 1 SD) cataphylls, 4.0 ± 0.93 large green-leaf primordia, and 1.9 ± 0.66 small green-leaf primordia. Year-2 GUs had 1.4 ± 0.21 cataphylls and 8.5 ± 2.01 green leaves. The most distal bud of these GUs consisted, on average, of 0.2 ± 0.36 cataphylls, 6.4 ± 1.58 large green-leaf primordia, and 1.7 ± 0.49 small green-leaf primordia.
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Number of organs in distal buds and growth units
Seedlings
The distributions of the number of organs in the most distal bud of year-1 GUs and the number of leaves of year-2 GUs were unimodal (Fig. 2A). The number of organs in the most distal buds of year-1 GUs was less than the number of leaves of year-2 GUs (F = 185, P < 0.001).
|
Variation in bud composition along growth units
Buds of year-2 seedlings and sample-2 saplings varied in structure depending on their position on the parent GU. The number of cataphylls per bud decreased linearly from the proximal to the distal end of the parent GU (Fig. 3). On the contrary, the number of large green-leaf primordia per bud increased as bud position approached the distal end of the parent GU. Numbers of small green-leaf primordia per bud were relatively steady along parent GUs. The total number of organs per bud increased between proximal and distal buds in the case of seedlings and was steady in the case of saplings.
|
Blade size along growth units
The mean area of individual leaf blades of trunk GUs increased from proximal to distal positions (Fig. 4). The most notable variations were those between green leaves in positions 1 and 2, 10 and 11, and 15 and 16. In the case of main-branch GUs, mean blade surface increased in the first four proximal positions and decreased to approximately constant values up to position 10. Leaf size for main branches fluctuated sharply for more distal positions, as the number of leaves averaged for each of these positions decreased (N = 14 for the 10th leaf; 8 for the 11th leaf; and 5 for the 12th, 13th, and 14th leaves). The length to width ratio increased from the most proximal green leaf up to the leaf in position 7 for trunks and 9 for main branches. The leaves in subsequently more distal positions had a notably lower length to width ratio for both axis types.
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Preformation in N. alpina
Buds of N. alpina seedlings and saplings include up to about 16 internodes and nodes. At this stage, cataphylls and green-leaf primordia are identifiable. In Nothofagus, the differentiation of a leaf primordium as a green leaf or a cataphyll depends on whether or not a petioled blade primordium develops between a pair of stipules (Puntieri et al., 2000
, 2002b
; Souza et al., 2000
). The one to four most basal nodes of a bud bear cataphylls, although terminal buds may lack cataphylls, like in other Nothofagus species (Barthélémy et al., 1999
). A feature observed in many N. alpina buds is the size difference between the large proximal blade primordia (except for the most proximal one, which may be very small) and the one or two (rarely up to five) small primordia closest to the bud's apical meristem (Fig. 1D). Size differences between proximal and distal primordia have also been observed in buds of N. pumilio (Souza et al., 2000
). For short shoots of Betula papyrifera, the size of a particular primordium is linked to its times of initiation and extension: whereas large, proximal primordia would extend in the growing season following that of their initiation, small, distal ones would extend two growing seasons after their initiation (Macdonald and Mothersill, 1983
). On the contrary, for all Nothofagus species so far studied, including N. alpina, all leaf primordia in a bud either extend in the first growing season after their inception or dry out together with the GUs apex during that season (Puntieri et al., 2000
, 2002b
; Souza et al., 2000
; present study).
The decrease in the number of green-leaf primordia from distal to proximal buds on the same GU of N. alpina is consistent with the gradient of GU size observed for this and other tree species (Macdonald et al., 1983
; Remphrey and Powell, 1984
; Remphrey and Davidson, 1994
; Thorp et al., 1994
; Stecconi, 2006
). The total number of organs per bud of N. alpina varies less than the numbers of cataphylls and green-leaf primordia with bud position because variations in the numbers of cataphylls and green-leaf primordia tend to compensate for each other (as found for Juglans regia; Sabatier and Barthélémy, 2000
). In other Nothofagus species, in contrast, the number of cataphylls does not vary with bud position, and the total number of organs per bud increases from proximal to distal buds, paralleling the increase in the number of green-leaf primordia (Puntieri et al., 2000
, 2002a
, b; Souza et al., 2000
). This indicates two possible processes by which the number of preformed green leaves of a GU is set in Nothofagus. The first process would involve the inception of more green-leaf primordia from the bud's apical meristem in distal than in proximal buds (as found for N. dombeyi, N. pumilio, and N. antarctica; Puntieri et al., 2000
, 2002b
; Sabatier and Barthélémy, 2000
; Souza et al., 2000
). The second process would be the inception of more green-leaf primordia per bud at the expense of the number of basal cataphylls in distal than in proximal buds (as shown here for N. alpina and observed for other tree species; Rivals, 1965
; Thorp et al., 1994
). There is evidence that the differentiation of the stipules at a bud node in Nothofagus may precede that of the corresponding blade primordium (García et al., 2006
). Therefore, physiological mechanisms acting at specific times could affect the differentiation of a blade but not that of its stipules, thus modifying the expression of heteroblasty at the GU level in species with cataphylls of stipular origin. Hormonal interactions and resource availability could well be among such mechanisms (Zilkah et al., 1987
; Kozlowski and Pallardy, 1997
; Flore and Layne, 1999
).
The comparison of trunk buds between seedlings and saplings of N. alpina supports the idea that the developmental stage of the tree affects bud composition and therefore the number of preformed leaves per GU of a particular axis type (Figs. 2 and 3). As the seedlings and saplings developed under different environmental conditions, quantitative differences must be considered cautiously. Nonetheless, the higher number of primordia in buds of saplings than in those of seedlings is an expected outcome following the idea of morphogenetic gradients in plants (Barthélémy and Caraglio, 2007
).
For seedlings and saplings of N. alpina, GU length, diameter, and number of leaves are significantly correlated to both the total number of organs and the number of green-leaf primordia of the GU's most distal bud (Fig. 5). The higher correlations for the diameter than for the length and number of nodes of the parent GU would show the relevance, for the differentiation of organs in the buds, of a stem's cross section area (as shown for Fagus sylvatica; Cochard et al.,
2005), probably linked to the income of water and nutrients to the GU. Each of the measures of GU size was more correlated with the number of green-leaf primordia than with the total number of organs per bud, indicating the involvement of GU vigor in the differentiation of green leaves. On the other hand, the relationship between the total number of organs of a distal bud and the size of its bearing GU seems to be affected by both axis type and plant age. Sharper changes in bud composition with GU size occur in seedling trunks and sapling main branches than in sapling trunks. Our results suggest that the clear differentiation between the main branches and the more vigorous vertical trunk observed for saplings of this species would not be related to differences in preformation, unlike what appears to be the case in other Nothofagus species (Puntieri et al., 2000
, 2002b
; Souza et al., 2000
). This idea would require verification from more samples of shoots from trees growing in different locations.
Neoformation in N. alpina
Previous studies on Nothofagus species suggested that neoformation may be relatively common in long and even intermediate-size GUs of this genus (Puntieri et al., 2000
, 2002b
; Souza et al., 2000
; Guédon et al., 2006
). In the case of N. alpina, neoformation likelihood would depend on the type of axis to which the GU belongs: whereas trunk GUs of both seedlings and saplings may include neoformed organs, those of main branches of saplings (thicker and longer than trunk GUs of seedlings) consist, entirely or nearly so, of preformed organs. A low probability of neoformation development in main-branch GUs was calculated, for the same data set, through a deconvolution method (Guédon et al., 2006
). The difference in neoformation capacity between the trunk and the main branches seems to be higher for N. alpina than for other Nothofagus species so far studied (Puntieri et al., 2000
, 2002b
; Souza et al., 2000
) and is one reason for the better definition of the vertical trunk in saplings of N. alpina (Stewart, 1979
; Tuley, 1980
; Deans et al., 1992
).
The results of the present study suggest that height growth in N. alpina may be related with neoformation in the trunk. Neoformation is usually linked with favorable growth conditions (Puntieri et al., 2002b
; Guédon et al., 2006
). The sites within the distribution area of N. alpina with the tallest trees are those with the longest frost-free vegetative period (but not the highest mean temperatures; Gallo et al., 2004
). This would suggest that high minimum temperatures affect the development of neoformation in this species.
Leaf size and form in N. alpina growth units
Several factors may be involved in the relationships between leaf size and form and leaf position on its GU. Size differences between the most proximal leaves of trunk GUs seem to be related to size differences between primordia in buds (Fig. 1), a feature already observed in other Nothofagus species (e.g., Souza et al., 2000
). Because the average number of preformed leaves of trunk GUs was 12.6, the transition between preformed and neoformed leaves could be related with the sharp size difference between the 10th and the 11th leaves. The other sharp variation in leaf size, between positions 15 and 16, could only be due to growth differences, perhaps environmentally induced, among neoformed leaves. In the case of main-branch shoots, the irregular fluctuations in mean leaf size between positions 11 to 14 of main branches seem more likely to be linked with the low numbers of averaged leaves (five) than to other factors. The largest variations in the length to width ratio of the blade occurred at more proximal nodes than did the largest variations in leaf size both for trunk and main branches (Fig. 4B). This would indicate that factors determining the area of a leaf blade may not be the same as those determining its shape.
Some studies have pointed at the morphological differences between preformed and neoformed leaves of the same GUs (Critchfield, 1960
; Kozlowski and Pallardy, 1997
). The expression heterophyllous shoots has been used to refer such GUs (Kozlowski and Clausen, 1966
; Kozlowski, 1971
; Kozlowski and Pallardy, 1997
), which stresses the relevance of the time of leaf differentiation on leaf morphology. Because, as shown here, systematic variations in leaf size may be found within the sets of preformed and neoformed leaves, we consider the expression heterophyllous shoot in reference to GUs with preformed and neoformed portions to be ambiguous and we suggest that it be avoided.
Nothofagus alpina develops the largest leaves among South American Nothofagus (Hoffmann, 1982
). Differences in leaf area between this and other Nothofagus species so far studied are far more striking when expressed on a per-GU basis: whereas the mean leaf area per trunk GU for N. alpina saplings reached 1011 cm2 (for GUs with up to 27 leaves), those for trunk GUs of N. dombeyi and N. pumilio saplings were about 86 cm2 and 57 cm2, respectively (Puntieri et al., 2001
; C. Calabria and J. Puntieri, unpublished data). In addition, leaves in the distal half of trunk GUs of N. alpina are larger than more proximal leaves of the same GUs, in contrast with the more uniform distribution of leaf sizes along GU of N. dombeyi and N. pumilio (Puntieri et al., 2001
). This difference may affect light-capture efficiency, carbohydrate accumulation, and competitive ability. As the age and photosynthetic capacity of fully expanded leaves are inversely related (Rawson et al., 1983
; Flore and Layne, 1999
; Xie and Luo, 2003
), the differentiation and extension of neoformed leaves in the summer, several months after the extension of the majority of preformed leaves, could significantly increase the summer biomass production of a plant. This benefit would be more notable in N. alpina than in N. dombeyi and N. pumilio because of the large surface of the distal leaves of N. alpina trunk GUs.
Axis differentiation in N. alpina saplings involves gradients of increasing numbers of neoformed leaves and leaf size towards distal positions of each GU. The combination of these traits would provide the vertical axis an advantage compared to lower axes in terms of light capture ability and thickening and set the scene for the formation of a dominant vertical trunk. The higher capacity of young N. alpina trees, as compared to other Nothofagus species, to develop under the canopy of larger trees would be related to these developmental features (Donoso, 1993
). Additional data on how preformed and neoformed leaves contribute to the biomass accumulation and stem thickening in different axes of Nothofagus species would help in the evaluation of this hypothesis.
Conclusions
From early developmental stages, GUs of N. alpina may consist either entirely of organs preformed in the previous growing season or of both preformed and neoformed organs. Differences in preformation among buds developed along a GU are determined mainly by the proportion of leaves initiated as cataphylls or green leaf primordia. Neoformation development is more likely in GUs corresponding to the vertical axis of a tree than in horizontal axes, irrespective of GU size. Because of their size and time of development, neoformed leaves may substantially increase GU leaf area and photosynthesis late in the growing season.
FOOTNOTES
1 The authors thank L. Gallo for providing the seeds of N. alpina for the seedling population, A. Passo and L. Oudkerk for help in establishing and maintaining seedlings, and the Intendencia del Parque Nacional Lanín for the permit for sampling in the Pucará area. This study was funded by the Secretaría de Investigación, Universidad Nacional del Comahue and CONICET, Argentina. 
5 Author for correspondence (jpuntier{at}crub.uncoma.edu.ar
)
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