nutrient conservation strategies in native andean-patagonian forests

- Nutrient conservation strategies in native Andean-Patagonian forests - 63

Journal of Vegetation Science 14: 63-70, 2003© IAVS; Opulus Press Uppsala.

Abstract. Nutrient conservation in vegetation affects rates oflitter decomposition and soil nutrient availability. Althoughresorption has been traditionally considered one of the mostimportant plant strategies to conserve nutrients in temperateforests, long leaf life-span and low nutrient requirements havebeen postulated as better indicators. We aimed at identifyingnutrient conservation strategies within characteristic functionalgroups of NW Patagonian forests on Andisols. We analysedC-, N-, P-, K- and lignin-concentrations in mature and senes-cent leaves of ten native woody species within the functionalgroups: broad-leaved deciduous species, broad-leaved ever-greens and conifers. We also examined mycorrhizal associa-tions in all species. Nutrient concentration in mature leaves andN- resorption were higher in broad-leaved deciduous speciesthan in the other two functional groups. Conifers had lowmature leaf nutrient concentrations, low N-resorption and highlignin/N ratios in senescent leaves. P- and K-resorptions did notdiffer among functional groups. Broad-leaved evergreens ex-hibited a species-dependent response. Nitrogen in mature leaveswas positively correlated with both N resorption and soil N-fertility. Despite the high P-retention capacity of Andisols, Nappeared to be the more limiting nutrient, with most speciesbeing proficient in resorbing N but not P. The presence ofendomycorrhizae in all conifers and the broad-leaved evergreenMaytenus boaria, ectomycorrhizae in all Nothofagus species(four deciduous, one evergreen), and cluster roots in the broad-leaved evergreen Lomatia hirsuta, would be possibly explain-ing why P is less limiting than N in these forests.

Keywords: Andisol; Leaf nutrient concentration; Mycorrhiza;Nutrient proficiency; Nutrient resorption; Patagonian forest.

Nomenclature: Zuloaga & Morone (1996, 1999).

Nutrient conservation strategies in native Andean-Patagonian forests

Diehl, P.1*; Mazzarino, M.J.1,2; Funes, F.1; Fontenla, S.1; Gobbi, M.1 & Ferrari, J.1

1CRUB, Universidad Nacional del Comahue, Quintral 1250, 8400 Bariloche, Argentina; 2CONICET Researcher;*Corresponding author; Fax +542944422111; E-mail [email protected]

Introduction

Net primary production in temperate forest ecosys-tems is considered to be strongly dependent on internalnutrient cycling, with plant litter fall being the dominantpathway for nutrient return to the soil, especially for Nand P (Schlesinger 1991). It can be therefore expectedthat nutrient conservation mechanisms in vegetationwill affect soil nutrient availability.

Resorption before senescence (Vitousek et al. 1982;Adams & Attiwill 1986; Killingbeck 1986; Vitousek &Sanford 1986; Schlesinger et al. 1989), and low nutrientrequirements (Escudero et al. 1992; Enright & Ogden1995; Aerts 1996) have been suggested to be among themost important plant strategies to conserve nutrients.However, there is still much controversy about theirrelative importance as a function of soil fertility andplant functional groups. Contrary to traditional expecta-tions (Vitousek 1982; Waring & Running 1998), there isevidence that resorption increases with soil nutrient avail-ability (Fisher & Binkley 2000), and is higher in decidu-ous species than in evergreens (Perry 1994); within thelatter group, low nutrient requirements and long leaf lifespan appear to be more important mechanisms of nutrientconservation than resorption (Aerts 1996). An importantdrawback in the analysis of resorption is temporal varia-tion in measured or realized resorption; thus, measuredresorption is not always the same as potential resorptioncapacity of a given species (Killingbeck et al. 1990). Inorder to estimate the degree to which realized resorptionapproaches potential resorption, Killingbeck (1996) hasestablished threshold values for the nutrient concentra-tion in senescent leaves as indicators of resorption ca-pacity. By analysing a large data set of deciduous andevergreen woody species, this author defined ‘profi-ciency’ as the ability of a species to reduce nutrientconcentrations (N and P) below these benchmark levels.

N is considered more limiting than P in most temper-ate and boreal forests, although changes of this patternare currently suggested in the Northern Hemisphere asa consequence of anthropogenic N-deposition (Perry1994; Waring & Running 1998; Fisher & Binkley 2000;

64 Diehl, P. et al.

Matson et al. 2002). An important difference betweenthe soil cycles of N and P is that the available forms of N,especially nitrates, are easily lost by leaching and deni-trification, while P tends to be retained in soils, i.e. asCa-, Fe- and Al-phosphates and/or by specific anionadsorption in variable charge soil colloids (amorphousoxides and allophanes). Despite the low general capac-ity of the soils to release plant-available P, organicacids and enzymes exuded from plant roots and micro-organisms contribute to P-release by decomposing soilorganic matter and weathering soil minerals. In thissense, mycorrhizal associations play an essential role inthe acquisition of P and other nutrients because of theircapacity to release enzymes and organic acids, to en-large the absorption area of plant roots, and to increaseabsorption efficiency (Fox et al. 1990; Sylvia 1990;Varma & Hock 1995; Lambers et al. 1998).

Native forests occupy the western, most humid re-gion of Patagonia along the Andean Mountains. Theseforests are dominated by the genus Nothofagus and theconifer species Austrocedrus chilensis, but other de-ciduous and evergreen species of high ecological andcommercial value are also present (Veblen et al. 1996).Soils are predominantly derived from volcanic ash(Andisols), and are characterized by a high capacity tostabilize organic matter, store water, buffer pH, andretain P. Except for A. chilensis (Buamscha et al. 1998),knowledge of nutrient cycling in this ecosystem is scarce.After examining a limited number of sites and woodyspecies, Mazzarino et al. (1998) suggested some trendsin N-conservation, namely higher N-use efficiency inthe order conifers > broad-leaved evergreens > decidu-ous species. Despite regional soil P-deficiency, somestudies on Nothofagus pumilio forests suggest that P isnot limiting, possibly because of high mycorrhizal in-fection (Gutierrez et al. 1991; Richter & Frangi 1992).

In the present work, our objective was to identifynutrient conservation strategies in the most representa-tive woody conifer, broad-leaved evergreen and broad-leaved deciduous species of the northwestern Andean-Patagonian forests. Based on the analysis of lignin-, C-, N-, P-, and K-concentrations in mature and senescentleaves, we assessed indicators of C-rich compound in-vestment, and nutrient concentrations, resorption andproficiency. We also identified mycorrhizal associa-tions, and examined the relationships among nutrientconservation indicators, plant functional groups and soilfertility. Based on existing information on nutrient limi-tation and conservation strategies in temperate forests,we hypothesized that in the Andean-Patagonian forests:(1) plant functional groups have different strategies,deciduous species being associated with high nutrientresorption, and conifers with low nutrient concentrationin mature leaves; (2) sites of low soil fertility are more

associated with low nutrient concentration in matureleaves than with high resorption; (3) N is the limitingnutrient and (4) P is not limiting due to infection withectomycorrhizae in Nothofagus species, as commonlydescribed for this genus in other parts of the world, andwith arbuscular mycorrhizae in most other species.

Methods

Study sites

The study was conducted in the NW Andean-Patagonian Region of Argentina, dominated by nativeforests growing mainly on allophanic soils (Andisols).Precipitation is concentrated mostly in autumn-winteras both rain and snow. The study comprised 29 siteslocated in Nahuel Huapi and Lanín National Parks,within the provinces of Neuquén and Río Negro (ca.39∞36'- 41∞22' S, 71∞ 02'- 71∞42' W). Sites were distrib-uted along a range of mean annual precipitation varyingfrom 800 to 2500 mm (increasing from E to W), withmean annual temperatures between 10 and 12 ∞C (in-creasing from S to N), and elevation varying from 560 to1320 m a.s.l.

Ten species were chosen from three functionalgroups:

(1) broad-leaved deciduous: Nothofagus1 pumilio, N. antarctica, N.obliqua and N. nervosa; 1Fagaceae;(2) broad-leaved evergreen: N. dombeyi, Lomatia2 hirsuta andMaytenus3 boaria; 2Proteaceae; 3Celastraceae;(3) coniferous: Austrocedrus4 chilensis, Araucaria5 araucana andFitzroya4 cupressoides; 4Cupressaceae; 5Araucariaceae.

N. pumilio, N. antarctica, N. dombeyi and A. chilensisare widely distributed throughout the study area. N.obliqua, N. nervosa, and A. araucana are found in thenorthern limit, while F. cupressoides, L. hirsuta, and M.boaria are located in the southern and central part of thestudy area. M. boaria is found in humid islands withinthe driest areas.

Experimental design

Three sites were selected for each species, except forF. cupressoides (two sites). At each site ten trees ofsimilar DBH (diameter at breast height) and canopycover were chosen. Five trees from the ten were ran-domly selected for foliar tissue analysis. During latespring-early summer (December 1999), correspondingto the vegetative growth peak (Puntieri et al. 1998), fullyexpanded leaves were collected. In the same period,soils (at 0 - 15 cm depth, and ca. 50 cm from the stem)were sampled to characterize soil fertility (three repli-cates per site). In autumn (April-May 2000), senescent


leaves were taken directly from five trees, and threesamples of fine roots (< 2 mm diameter) were taken toidentify mycorrhizal associations.

Analytical methods

Air-dried soil samples passed through a 2 mm sievewere analysed according to Page et al. (1982): pH inwater (1:2.5), P extracted in 0.5-N NaHCO3 by themolybdate ascorbic acid method, and exchangeable cati-ons extracted in 1-N NH4OAc by flame emissionspectrometry (K) and EDTA titration (Ca+Mg). As arapid test of allophane presence, pH was also deter-mined in 1-N NaF (1:50) (Fieldes & Perrot 1966).Samples passed through a 0.5 mm sieve were analyzedfor total N by semi-micro Kjeldahl and organic C byWalkley-Black wet digestion.

Foliar tissue analyses were conducted on samplesdried at 60 ∞C and ground to pass through a 1-mm sieve:total N by semi-micro Kjeldahl; C by dry digestion at550 ∞C (Schlesinger & Hasey 1981); lignin by the VanSoest (1963) procedure; P and K by dry digestion at 550 ∞Cand HCl extraction (Richards 1993), followed bycolorimetric (P) and flame emission spectrometric (K)determinations.

The following nutrient conservation indicators wereestimated: (1) nutrient concentration in mature leaves ornutrient concentration in photosynthetically active leaves(Lambers et al. 1998); (2) nutrient resorption as thepercentage of nutrient reduction between mature andsenescent leaves (Vitousek et al. 1982; Adams & Attiwill1986; Vitousek & Sanford 1986); (3) resorption profi-ciency as the concentration of N and P in senescentleaves compared to the following benchmark levels: <0.7 % N in all species, < 0.05 % P in deciduous speciesand < 0.04 % P in evergreens (Killingbeck 1996); (4)investment in C-rich compounds as the concentration oflignin and C/N and lignin/N ratios in mature and senes-cent leaves (Lambers et al. 1998).

Fine root samples were washed and preserved in therefrigerator or in alcohol (70 %). Presence/absence andtype of mycorrhizal association were recorded follow-ing Harley & Smith (1983) and Smith & Read (1997).To recognize endomycorrhizal structures, roots werepreviously clarified and dyed (Phillips & Hayman 1970).The characteristic structures of each type of mycorrhizawere identified by stereoscopic and optic microscopy(Schenk 1982; Agerer 1998a, b). Species without thesestructures were considered as non-mycorrhizal (Vier-heiling et al. 1998).

Statistical analyses

Significant differences in nutrient conservation indi-cators among species were determined using one-wayanalysis of variance (ANOVA). Main effect means wereseparated by tests of least significant differences (LSD).Spearman rank correlation (rs) was employed to analysethe relationships between mature leaf nutrient concen-tration vs. soil nutrient concentration and nutrientresorption. Null hypotheses were rejected at the P < 0.05level. The program Statgraphics Plus for Windows (1994-1997) was used for all analysis.

Results

The presence of allophanes in the volcanic-derivedsoils of this study was confirmed by pH values in NaF ≥9.2, and the formation of very stable allophane-organicmatter complexes resulting in high concentrations oforganic C and N (Table 1). The sum of exchangeablecations (mostly between 12 and 34 cmol.kg–1) and theslightly acid pH in water (6-7) indicated a moderatesupply of cations, characteristic of Andisols with lowdegree of development. Extractable P values were low,ranging from 4 to 14 mg.kg–1 except under Nothofagusobliqua (24.6 mg.kg–1).

Table 1. Soil characteristics of ten woody species dominant in NW Patagonia. Values are means of three replicates per site and threesites per species (except Fc: two sites). Standard deviations are in parentheses.

Functional Species Symbol pHH2O pH(NaF) C(%) N(%) P K Ca + Mggroup (mg.kg–1) (cmol.kg–1) (cmol.kg–1)

Broad-leaved Nothofagus antarctica Na 6.1 (0.4) 10.0 (0.6) 7.6 (3.2) 0.34 (0.13) 12.6 (9.6) 0.59 (0.16) 14.1 (8.4)deciduous Nothofagus nervosa Nn 5.7 (0.3) 10.0 (0.6) 8.9 (2.6) 0.40 (0.16) 11.2 (7.4) 0.51 (0.24) 14.5 (7.1)species Nothofagus obliqua No 6.4 (0.2) 9.5 (0.4) 13.6 (4.8) 0.80 (0.23) 24.6(14.4) 0.67 (0.14) 33.5 (10.8)

Nothofagus pumilio Np 6.0 (0.4) 9.6 (0.8) 14.2 (5.6) 0.65 (0.20) 14.1 (9.8) 1.06 (0.37) 25.3 (8.3)

Broad-leaved Nothofagus dombeyi Nd 6.2 (0.4) 9.9 (1.2) 10.8 (3.7) 0.48 (0.15) 7.3 (4.6) 0.49 (0.17) 19.4 (8.4)evergreen Lomatia hirsuta Lh 6.1 (0.4) 10.2 (0.5) 7.3 (3.2) 0.37 (0.16) 10.5 (5.1) 0.46 (0.22) 13.3 (6.6)species Maytenus boaria Mb 6.9 (0.4) 9.2 (0.2) 6.9 (2.0) 0.44 (0.11) 14.7 (9.3) 1.92 (0.90) 27.4 (5.4)

Conifers Araucaria araucana Aa 6.1 (0.2) 10.5 (0.2) 4.0 (2.0) 0.24 (0.10) 4.0 (1.6) 0.27 (0.07) 4.7 (2.5)Austrocedrus chilensis Ac 7.1 (0.2) 9.9 (0.3) 7.5 (2.2) 0.42 (0.09) 12.6 (3.5) 0.85 (0.40) 23.3 (4.7)Fitzroya cupressoides Fc 6.2 (0.3) 10.0 (0.9) 6.9 (4.8) 0.31 (0.16) 5.8 (3.8) 0.26 (0.12) 10.4 (4.1)

66 Diehl, P. et al.

Nitrogen concentration in mature leaves was higherin broad-leaved deciduous species (2.13 - 2.52 %) thanin broad-leaved evergreens (1.16 - 1.21%), while coni-fers showed the lowest values (0.53 - 0.85%) (Fig. 1A).All species, except Nothofagus obliqua, N. nervosa, andLomatia hirsuta, were N proficient (N in senescentleaves < 0.7 %). Resorption in broad-leaved deciduousspecies and Maytenus boaria was higher than 60 %. Inconifers and N. dombeyi mean resorption ranged from

Fig. 1. Nutrient concentrations in leaves of woody dominantspecies in NW Patagonian forests: mature leaves (open bars),senescent leaves (shaded bars); nitrogen (A), phosphorus (B)and potassium (C). The horizontal lines in parts A and Bindicate benchmark levels of resorption proficiency (Killing-beck 1996). Symbols for species are as in Table 1. Symbols forfunctional groups are: BLD = Broad-leaf deciduous; BLE =Broad-leaf evergreens; C = conifers. Means were calculatedfor five replicates per site and three sites per species, except F.cupressoides (two sites). Different lower case letters, abovethe bars, indicate significant differences (P < 0.05) amongspecies for the same leaf compartment (bold = mature; italicbold = senescent).

Fig. 2. Nutrient resorption in mature and senescent leaves ofwoody dominant species in NW Patagonia forests: nitrogen(A), phosphorus (B) and potassium (C). Symbols for speciesare as in Table 1, and for functional groups as in Fig. 1. Meanswere calculated as in Fig. 1. Error bars represent standarddeviation (±1 SD).


(Fig. 1C). As in the case of P, K-resorption was highlyvariable within species, and L. hirsuta showed the low-est values (Fig. 2C).

For the indicators of C-rich compound investment(Fig. 3), the most significant difference among func-tional groups was found for the lignin/N ratio in senes-cent leaves (Fig. 3B), which was markedly lower inbroad-leaved species, both deciduous and evergreens(23-28) than in conifers (40 - 94). A similar trend, butwith lower values (3 - 12 in broad-leaved species and 14- 39 in conifers), was observed in mature leaves (datanot shown).

A significant positive correlation was found be-tween mature leaf N- and soil N-concentration (rs =0.82; P = 0.014) (Fig. 4A). Non significant correlationswere found between mature leaf P and soil P (rs = 0.39;P = 0.236), and between mature leaf K and soil K (rs =0.59; P = 0.078). Nitrogen in mature leaves was also

Fig. 4. Relationships between N in mature leaves and soil N(A), and between N in mature leaves and N resorption (B).Symbols for species are as in Table 1. Means were calculatedas in Fig. 1.

Fig. 3. Indicators of C-rich compounds investment in senes-cent leaves: lignin concentration (A), lignin/N ratio (B) and C/N ratio (C). Different lower case letters, above the bars,indicate significant differences (P < 0.05) among species.

40 to 50 %, while the lowest values (< 20 %) corre-sponded to L. hirsuta (Fig. 2A).

P-concentration in mature leaves was higher in broad-leaved deciduous species (0.15 - 0.20 %) than in coni-fers (0.08 - 0.10 %) (Fig. 1B). In broad-leaved evergreens,mature leaf P (0.06 - 0.16 %) was dependent on thespecies, with M. boaria being more similar to the decidu-ous species, and N. dombeyi and L. hirsuta being moresimilar to the conifers. Most species were not P proficient(P in senescent leaves > 0.05 % in deciduous species and> 0.04 % in evergreens); the conifers A. araucana and F.cupressoides (0.038 %) were the exception. P-resorptionwas extremely variable within each species, with thelowest values observed in L. hirsuta (Fig. 2B).

K-concentration in mature leaves showed a similarpattern to N and P, with values ranging from 0.68 to 1.0% in broad-leaved deciduous species, 0.38 to 0.54 % inconifers, and 0.45 to 0.82 % in broad-leaved evergreens

68 Diehl, P. et al.

positively correlated with N-resorption (rs = 0.79; P =0.017) (Fig. 4B). The correlations between mature leafP and P resorption, and between mature leaf K and Kresorption (rs = – 0.05 and 0.32, P = 0.884 and 0.335,respectively) were not significant.

The characteristic structures of ectomycorrhizalsymbioses (mantle, rizomorphs, and Harting net) werepresent in all individuals of the five species of Notho-fagus, while arbuscular mycorrhizal infection (arbusculesand coils) characterized all conifers and M. boaria. L.hirsuta had no mycorrhizal structures, but it did haveabundant cluster roots, i.e., clusters of longitudinal rowsof extremely hairy rootlets located near the root tip.

Discussion

Our results confirmed that nutrient conservation strat-egies, especially for N, differed between broad-leaveddeciduous and conifer species, while broad-leaved ever-greens were intermediate varying by species. Nitrogenconcentration in mature leaves and N-resorption were highin deciduous broad-leaved species (> 2 % and > 60 %,respectively) and low in conifers (< 1 % and < 50 %,respectively). Phosphorus and K concentrations in ma-ture leaves showed similar patterns as N, while P and Kresorptions were not clearly associated with functionalgroups.

These results are in agreement with evidence indi-cating that resorption and nutrient concentration inmature leaves are lower for evergreens than for de-ciduous species (Chapin 1980; Aerts 1990, 1996; DelArco et al. 1991; Knops et al. 1997). It has beensuggested that lower N-resorption in plants with lowN-requirements may be due to the fact that most leaf Nis structurally bound, being less accessible to hydroly-sis and retranslocation (Lajtha 1987). Chapin &Kedrowski (1983) have also suggested that the pres-ence of high concentrations of phenolic compoundssuch as lignin may lead to precipitation of proteinsprior to protein hydrolysis. Long-lived leaves are be-lieved to invest much more carbon in this type ofcompounds than do short-lived ones. On the otherhand, the production of high levels of lignin is associ-ated with low nutrient availability, especially N (Larcher1995; Lambers et al. 1998). In our case, all coniferswere strongly associated with high lignin/N ratios and,to a lesser extent, with high lignin concentrations andC/N ratios in senescent leaves.

Although a negative relationship between N-re-sorption and soil N-fertility seems logical, severalauthors have reported either weak or no relationshipsbetween these two variables (Aerts 1996; Knops et al.1997), and even an increase of resorption with soil

fertility (Fisher & Binkley 2000). In the temperateforests of the present study, we found a significantpositive correlation between N in mature leaves, N-resorption, and soil N, confirming our second hypoth-esis, i.e., that, at least for N, sites of low soil fertilityare more associated with low nutrient concentration inmature leaves than with high resorption.

In agreement with results reported by several au-thors for temperate and Mediterranean forests (Pugnaire& Chapin 1993; Aerts 1996; Knops et al. 1997), wefound high variability of P-resorption within the samespecies, and no relationship between P-resorption, func-tional groups, and soil P-fertility. Since the pattern ofnutrient conservation was stronger for N than for P, weinfer that, as in other temperate forests, N is the morelimiting factor in NW Patagonia. Data on nutrientresorption proficiency support this inference. Consid-ering the benchmark levels stated by Killingbeck(1996), most species behaved as N-proficient, i.e. N-concentration in senescent leaves was < 0.7 %. Despitethe high capacity of Andisols to retain P and thegenerally low values of soil available P found in thepresent study, most species behaved as P-non-profi-cient (P in senescent leaves > 0.05% in deciduousspecies and > 0.04 % in evergreens).

The presence of cluster roots in Lomatia hirsutaand mycorrhizae in all other species would possiblyexplain why P is less limiting than N in these forests.Maytenus boaria and all conifers exhibited arbuscularmycorrhizal associations, as described for otherMaytenus species of South America (Godoy et al.1994) and most conifers of the Southern Hemisphere(Baylis et al. 1963; Reddell & Milnes 1992; Godoy etal. 1994; Mc Gee et al. 1999; Breuninger et al. 2000),while all species of Nothofagus were associated withectomycorrhizae. In reviews from New Zealand, Aus-tralia, New Guinea, New Caledonia and Argentina (seeVeblen et al. 1996), ectomycorrhizal associations areconsidered to be a very effective adaptation mecha-nism of Nothofagus to P-deficient soils.

In conclusion, our results indicate that in thesetemperate forests mechanisms of nutrient conservationare strongly related to plant functional group. Conifershave low nutrient concentration in leaves and highinvestment in C-rich compounds, especially high lignin/N ratios. In contrast, broad-leaved deciduous speciesare characterized by high N-, P- and K-concentrationsin mature leaves and high N-resorption. Broad-leavedevergreens behave as a broad transitional group be-tween conifers and deciduous species. Nitrogen ap-pears to be the limiting nutrient, and N concentrationin mature leaves is positively related to soil N-fertilityand N-resorption. Despite the endemic P-deficiency ofAndisols, the non-proficient P-behaviour of most spe-


cies was probably associated to facilitation mecha-nisms provided by mycorrhizal infection and clusterroots.

In the light of high anthropogenic N-deposition inbroad areas of the Northern Hemisphere, currently ex-ceeding the N acquired through natural processes, itseems logical to expect increases in plant growth andover-enrichment with N in most temperate forests ofthat hemisphere (Matson et al. 2002). On the contrary,under the very low N- deposition characteristic of SouthAmerican temperate forests (Holland et al. 1999), wehypothesize that N will continue to be the limitingnutrient. Thus, these forests could represent a worldcontrol of what might have happened under minimalpollution.

Acknowledgements. We thank S. Moyano, S. Varela, V.Flores and M. Fernández for field and laboratory support, andG. Buamscha, J. Donnegan, J. Puntieri, P. Harcombe and ananonymous reviewer for useful comments. We are also grate-ful to the National Park authorities for sampling permission,and to P. Laclau for site selection support. This research wasfunded by the Agencia Nacional de Promoción Científica yTecnológica (PICT98-ANPCyT 08-03944) and UniversidadNacional del Comahue (B-100/99).

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Received 27 December 2001;Revision received 12 August 2002;

Accepted 2 October 2002.Coordinating Editor: P. Harcombe.

nutrient conservation strategies in native andean-patagonian forests

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