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Variation in Carbon Isotope Ratios of Euphorbia Species from Different Habitats of Teneriffe in the Spring
Flora (1983) 173: 363- 370
Variation in Carbon Isotope Ratios of Euphorbia Species from Different Habitats of Teneriffe in the Spring J. D. TENHUNEN, L . C. TENHUNEN, H . ZIEGLER, W. STICHLER and O. L . LANGE L e hrstuhl fiir Botanik II del' Un ivers itat Wiirzbul'g (BH,D) ; Inst itut fiir Botanik und Mikrob iolog ie d el' T ec hni sch on Un ive rs itiit MtIDchen (BRD); Instit ut fiir R a diohydrometrie del' Gesellsch aft flir StrahLen- und Umwolt [o l's hung Mi:lD ch n (BRD)
Summary A ccording to carbon isotop e ratios, Euphorbia aphylla, E. atl'Opw'pUI'W, E. balsamifera, E . bourgaeana, E. pal'alias, a nd E. regis-jubae fi x carbon v ia t h e C3 p athway on TonorifTo in tho s pring. Euphorbia canariensis p erforms CAM. Among the C3 spocies, li tt Le differonco is fo und in ,513C values obtained from leaf mate ri a l a nd su cc ulen t stem material. Th o variation in ,513C vaLues which occ urs geographically is sm a ll, a l though amon g t he C3 s p ec ies, ,513C values of sampLes f rom the so uth of t h e isla nd t end to be slightly less negat ive, p e rhaps due to changc in in tercell ular CO 2 concentrat ion as t h e pla n ts adapt to drier, less humid conditions.
Indroduction The carbon isotope composition or b13C value1 ) of plant material can be u sed to distinguish which photosynthetic pathway h as been used in CO 2 fixation (cf. OsMOND & ZIEGLER 1975; ZIEGLER 1979 ; TROUGHTON 1979 ; FARQUHAR et al. 1981). Plants showing net CO 2 fixation only in the light via RuBP carboxylase (C 3 metabolism) have b13 C values varying between - 20 and - 35%0 (FARQUHAR et al. 1981) while those exhibiting CAM and fixing additional CO 2 in the dark have b13C values between - 14 and - 30% 0 (OSMOND & ZIEGLER 1975). In the case of carbon fixation via the C4 pathway, the r esulting plant material has b13C values between - 8 and -180/00' Further information in addition to b13C values is needed to distinguish between C4 and CAM carbon fixation . The b13C value of plant material is further affected by environmental conditions which change internal a ir space CO 2 concentration prevailing during fixation. Factors such as water stress (WINTER 1981) , low air humidity (FARQUHAR et al. 1981; WINTER et al. 1982), or high salinity in the case of ma ngrove species (FARQUHAR et al. 1981) r educe intercellular CO 2 concentration, alter the fraction ation of isotopes occurring during diffusion from the external air to the fixation sites , and result in less negative b13C values. In the family Euphorbiaceae, C3 , CAM a nd C4 species have been d ocumented (WEBSTER et al. 1975; EDER et al. 1979). The Euph01'bia species of T eneriffe are 1) OT'h ' (J13CO/ 00 -.L evaI ue'I S expresse d as.
(
13C/12C sample 13C/12C standard -
1
)
. 1000
,T. D. 'I'ENH NE
36../.
et a1.
found in h ab itatfl which differ greatly in temperature , humidity, and soil moisturo avai lab iliLy. Th PI' R nt fl tudy wa oonducted to determine the type ofphotosynthetio c!1l'bon. fixat i n xhibit d by flpeeie of Euphorbia from Teneriffe and whether type of fi atio n ifl m difi d in r eflponfl to habit!1t environmental conditions. Samples of FlL rn and 1 af mat rial were coll ected from soven Euphorbia, pecies at different altitud A and al ng nvironmental gradients in the , pring of 1980 and were analyzed for al'b n. iROL p rati .
Methods L av s aA woll It~ HUC ul ollt stom p iecos of sovo ml Euph01'bia species werc collccted during a t,\Yo wook p o r' iod in Apr' il I!) 0 f'!'om locations in Tonel·iffo. Plant material was coll ected along altitudinal g r'"di ont~ wlr or'o pOH8 ibi and in such a pattern th a t eac h species was reprosentatively Hr unpl od tilr' ug il out its rang of di s tribution (soo OBEIWORl!'El~ 1965). The plant samplos wero ma intain d opon to til o a ir' and w or o oven dei d at 100 °C upon r e turn to the laboratory inWurzbU I'g (FRO). Th o dr'y matot·.ial was frozon in liquid nitrogen and puLverized. The combustion of t.lr o s(,mpl s and th o d otormin ation of th e 613 C vaLu e wero p orformed according to the methods of'S "",GL & Vo o rr,r. (1!)70; cf. OSMOND e t al. 1!l75). The 613 C m eas urements were done with a MAT HPO'tt'om tor fr m Varian, Brom en (FRO), aga inst tho PDB s tandard (CRAIG 1957).
Results and Discussion Th topography, t emperature, and humidity gradients on T en eriffe are charact I'iz d in Figs. 1 and 2 and in Table 1 (see also TENHUNEN et a1. 1982). As previously Aummarized by CEBALLOS & ORTUNO (1951) and FERNANDOPULLE (1976), the volcanic m untain fl running from east to west on Teneriffe (Fig. 1) strongly determine local climate. Large grad ient in moisture availability occur from north to south and tcmperatur fl depcnd strongly on elevation. On the northel'll slopes , cloud banks T able 1. Monthly m ••ximum (tnd minimum mean ail' temperatw'es for t en weather stations on Te· J1ol'iff (loCl.tions shown in Fig. 1). D a t a shown for January and August when temperatures are lowest a nd highest respec tivel y Numbe r: in Fig.
1 2 3 4 5 6 7 8 !l 10
Station location
Pue l'to de la Cl'lI7La OUl1l1cha Aguamal1sa Izaii.a VilE,flor Omnac1illa La Laguna Santa Cruz cle T ene r'iffe San A ncl r'es Los Oigltntes
E le vlttion (meters)
Monthly Mea n Ail' Temperatures J a nuary
August
Maximum
Minimum
M a ximum
Minimum
50 550 1,075 2,365 1,400 650 550 40
19.5 18.2 10.5 6.9 13.1 17. 15.7 20.4
13.1 8.5 13.7 0.8 4.8 8.4 8.7 14.4
25.8 23.6 23.8 21.7 27.7 27.7 25.2 28.8
19.3 14.2 14.5 13.1 17.8 16.4 16. 20.7
50 150
20.6 21.5
14.7 15.9
27.7 26.7
21.2 21.1
Carbon I sotopo Rat ios
365
Fig. 1. Contours of equal elevation at sea level, 1,000,2,000,3,000 and 4,000m on Tonoriffo and location of weather stations for temperature data given in Table 1. Te mperature data fL'om ADlWU (1977) . -
liB ~
EZl D
alpine hum i d moderate dry
Fig. 2. Humidity zones of Te n eriffe according to ABREU (1977). Climate in the a lpino zono chan ges rapidly and is further not r elevant s ince Euphorbia sp ecies do not occ ur in this r og ion.
form daily in the pine forest zone between 1,200 and 2,000 m and the greatest precipitation occurs. The air masses sink in the south, warm up, and dry the slopes . Xerophytes, including Euphorbia species, occur her e at high er elevation than in the north (see OBERDORFER 1965). Mean maximum and minimum air temperatures for J anuary and August are given in Table 1 for ten weather stations (locations in Fig. 1) distributed from north to south and on the east and west sides of the island. Changes in humidity from north to south and with change in elevation are indica t ed in Fig. 2 (see ABREU 1977).
J.D.TENHuNENet~.
:lG(j Euphorb.a aphylla :
aph
otropurpurea :
olr
balsamifera :
bol
bourgaeano : .
bau
poralias :
por
bal -27. 6(2 ' 0) aph - 254(100) oph -24 51 .00)
01,-24. 318001 0Ir-23.914101 bau-24 .7(400)
\ \ - 0Ir-25.4(920)
" \ 0Ir-25.61.020) ~ 0Ir -25.7IS30)
bal·-25.lIS)
0Ir-30.31300)
bal-25.6ISIJl
bal-25. 513S0' bol-24.21l00' bol-25.2(430) 01,-28.21430'
F ig. 3. Th <513 valu es (lurge negative numbers) a nd loeation a ltitude in m et ers (sm a ll numbers in parenLheses) obtained for indi v idual samples of Euphorbia aphylla, Euphorbia atropurpurea, Eupho1'bia bal8omijem, Euph01'bict bourgaea,na, a nd Euphorbia paralias (sp ecies names abbreviated O.H s hown in k y in figure ) co llected during April 1980. Sample is located e ither at the center of t he text s t"ing s hown or when ind icated at the end of the s olid line away from the text string.
The sp ccics investigated were of three different growth forms. Euphorbia paralias L. is ~Ln h rb lcs. t han 50 cm in height having st em s with a woody base. E . atropurpurea (BROLTSS.) W EBB & BERTH., E . balsamifera AlT ., E. bou1'gaeana GAY, and E. regis-jubae WEBB & BERTH. are shrubs of up to three meters in height with thick, su cuI nt stems a nd branches and non-fleshy spathulate to lanceolate leaves which are shed at least partly during the dry season . E . aphylla BROUSS. ex WlLLD . is a compact stem-succulent shrub less than 50 cm in height with slender pencil-like leafl es. branches. E. canariensis L . is a tall leafless stem- succulent shrub which branches from t he base and h as a candelabra-like growth form. Its branches are four or five sided with short curved spines. The (j13C values obtained from st em samples of Euphorbia canariensis and E. aphylla and from leaves of all other Euphorbia species studied, are plotted according to collection in Figs. 3 through 5. Collection locations are either at the center of the text string hown on the maps or at the end of the solid line away from the text
Carbon I sotop e Ratios
367
Euphorbia regis - jubae
- 27.512151 - 27.51351
-26.512001
-24 .615701 -26.814001 -2 3.211451
-26,.615501 -27.71750)
-26.91510) . -25.61340)\ \
-23.911220) -26.419001 -24.516201
a
Fig. 4. The 13 C v alues, collection altitudes, and locations as described for Fig. 3 of ind ividual samples of Euphorbia regis-jubae .
string . As seen in Figs . 3 and 4 , the euphorbias of Teneriffe showed almo. t exclusively C3 -type t5 13 C values, ranging between - 30.3 and -23 .20/00' Less negative values were obtained only with samples from Euphorbia canariensis (Fig. 5). The pattern in t5 13C values obtained with leaves of Euphorbia aphyUa, E. atropurpurea, E. balsamifera, E. bourgaeana, E . paralias, and E. regis-jubae are in general the sanIe . Slightly nIore negative t5 13C values are obtained for plants from the cool moist north side of the island than for plants sampled from the dry southern areas. This is particularly evident in the data obtained for E . regis-jubae (Fig. 4) which is widely distributed on the island and was collected at 29 locations. The small change in t5 13 C value occurring from north to south may b e due to differences in humidity and water availability which affect stomatal conductance, intercellular CO 2 concentration and fractionation of isotopes during the diffusion to the fixation sites as suggested by FARQUHAR et a l. (1981; see also WINTER 1981 ; WINTER et al. 1982). The t5 13 C value of stem material was slightly less n egative than that obtained for leaf nIaterial of E . regis-jubae (average for leaf nIaterial - 26.4; for stenI material - 25.2), E . balsamifera (leaf -25.8; st em - 24.9) , and E. atropurpurea (leaf - 26.2; stem -25.7). Based on only two sanIples, the average t5 13 C value for leaves of E . bourgaeana was - 25.7 and for stems was -26.0. These differences again may be due to
J. D.
36
TENHU NEN
ot at.
Euphorbia canariensis
_12.911301-13.717201
-12.814201
-13.314001
Fig. 5. ' I' lto Il 13 C va lu os , colloc tion altitudes , and locations as described for Fig. 3 of individual s £\rnpl 8 o f EuphOl'bia c(I,!wl·'i en sis.
diffoi' nee. ' in fractionation of isotopes during diffusion to the fixation sites in leaves vel' 'us At om .. They may also be caused by a different chemical composition of leaves and st m s, especially by a different lipid content. Euphorbia canarien is inhabits rocky cliffs in dry areas. The 013C values obtained with material from T eneriffe varied between -12.3 and -14.6%0 (Fig. 5), which suggest the participation of PEP-carboxylase in total CO 2 fixation. Since we found E. canariensis to lack " Kranz-anatomy" , it is without doubt a CAM rather than a 04. sp ecie and relies h eavily on dark fixation in its natural habitat. Glasshouse E. canariensis plants had a 013C value of - 20.6 0/ 00 , much more negative than the value obtained for plants from T en eriffe (ZIEGLER, unpublished). Thus, this species appears to have the potential to regulate the degree of dark fixation occurring. The a sh content of the leaves in the analyzed Euphorbia spp. varied between 6.6 and 18.1 % of dry weight with an average value of 11.2 % of dry weight (n = 53). A h content ofthe stems varied between 4.7 and 14.5 % of dry weight (average 10.8 %; n = 72). The higher ash content of leaves may indicate a higher transpiration rate in the l eaves than in the stems, combined with an incomplete redistribution of the transpiration residues.
369
Carbon Isotope Ratios
Conclusion Except for Euphorbia canariensis, the Euphorbia specie of Teneriffe which were investigated fix carbon via the C3 pathway in the spring. This is somewhat surprising in the cases of E. balsamifera, E. atropurpurea, E. bou1'gaeana, and E. ngisjubae which all have thick succulent stems and branches and which are in. gencral found at warm dry sites. Apparently the stem functions as a water rcservoir in thcse species. Even the leafless, stem-succulent Euphorbia aphylla, which occur' with oth r succulent species on the coastal platform at Punta de Teno , show' 13 C valueR whi ch suggest that it is a C3 species or that at least any CAM ability i upprcssed und r springtime conditions. Euphorbia canariensis, which occurs at many sites along with other Euphorbia species, is a true CAM species. In contrast to pecies of the Sempervivoideae (TENHuNEN et al. 1982), the euphorbias of Teneriffe show little variation in photosynthetic metabolism geographically or with habitat conditions.
a
Acknowledgement W e wish to thank Ms. G. BEYSCHLAG, Ms. W. SAMFASS, and Ms. "V. ANGEHEH [01' toohni al assistance. This work was supported in part by the D e utsch e Forsc hungsgomo insc haft.
Zusammenfassung Blatt- und Stamm-Material von EuphOl·bia.Arten aus T enel'iffa, die 3 untorsc hi od li chon Lebensformen angehoren, wurden auf ihr Kohlenstoffi sotop en-Verhaltni s hin untel's uc ht. Aus den Ergebnissen lii13t s ich schlie13en, da13 die krautige Staude E. paralias, die Strauchel' mit dicken, sukkulenten Stammen und mesophytischen Blattern E. atl'OpUrpU1'ea, E. balsamije1'Ct, E. bou"gaeana und E. regis-jubae und die Stammsukkulente E. aphylla (zumindest wah rend del' Untol's uc hungszeit im Fruhjahr) ihr Kohlendioxid ausschlie13lich uber den C 3- W eg fixieI'en. Nul' gel'ingo Diffol'enzen tl'eten in den <513C-Wel'ten zwischen BlatteI'n und s ukkulenten Sta mmen a uf. Auch die Variation des Isotopenverhaltnisses b e i Proben d el' gleichen Art, die an unterse hi edli ch on Standorton gesammelt wurden, sind nul' unbede utend. Allerdings zeigt s ieh hier di e T end en z zu weniger' nogativen <513C-\Verten bei Exemplaren aus d em sudlichen T eil del' Insel; das mag mit UntoI'seh iod en im inte l'zellularen CO 2 -Gehalt del' Pflanzen zusammenhangen, d ie dort untoI' warmel'on und trockeneren B edingungen wach sen als Exemplare im kuhl -fe uchteren Norden. Nul' di o ka nd olabol'al'tige stammsukkulente E. canariensis erweist sioh aufgl'und ihres wenig nogativen I otopon. vel'haltnisses als einde utige CAM-Pflanze.
References AB;REU, J. M. H. (1977): Estudio agroclimatico de l a isla d e Teneriffe. An. Inst. Nac. Inv. Agr. Ser. General No.5: 113- 181. CEBALLOS, L., & O;RTUNO, F. (1951): Estudio Sobre la Vegetacion y Flora Forestal d o las Canarias Occidentales. 465 pp. Madrid. C;RAlG, H. (1957): Isotopic standards for carbon and oxygen and correction fac tors for mass spectroscopic analysis of carbon dioxide. Geochim. Cosmochim. Acta 12: 133- 149_ EDE;R, A., STICHLE;R, W ., & ZIE GLER, H. (1979): Typen d el' photosynthetischen CO 2 -Fixierung bei mitteleuropaischen Euphorbia-Arten. Flora 168: 227- 2 40. FAHQUHA;R, G. D., BALL, M. C., VON CAEMME;RE;R, S., & ROKSANDIC, Z. (1981): Effect of salini ty and humidity on <513C value of halophytes-evidence for diffusional isotope fractionation de25 Flora, Bd. 173
370
.J . D . TI~NHtJN(1;N tal., Carbon Isotope Ratios
LOt'm ined by t he "atio
I' in w reeliul al' jtLtmosphel'i e partial pressure of CO 2 under different
on v ir' nm onto.l on
:32:1
:32. STl IIL En, W ., & TJtlMBOJ~N , P. (1975): Carbon isotope discr imination in alpine succulent pI.lnt.!; s uppos d to be capabl e 01' C,'assu lacean Acid Me tabolism (CAM), Oecologia 18: 209- 2l7. , III II0L, W" & VOOI;;L, .J. (1970): D e ute rium content of organi c matter. Earth and planet. Sc. LeLL ,'s 7: 307- :313. ' I'EN II EN, J. D. , TJ~NJl. UNJ~N, L. C., ZIEGLE;R, H., STICHLER, W., & LANGE, O. L. (1982): Va"illLion in c(wbon iso tope ratios of Sompe rvivoideae species from different habitats of 'l'eneJ'iff' in t h spring. Oeco logia 55: 217- 224. Tn tJO 1[1'0 , .J. H . (1979) : 15 '3 C as an indi cator of carboxylation reactions. In : GIBBS, M ., LATZKO, I~. (
Variation in Carbon Isotope Ratios of Euphorbia Species from Different Habitats of Teneriffe in the Spring J. D. TENHUNEN, L . C. TENHUNEN, H . ZIEGLER, W. STICHLER and O. L . LANGE L e hrstuhl fiir Botanik II del' Un ivers itat Wiirzbul'g (BH,D) ; Inst itut fiir Botanik und Mikrob iolog ie d el' T ec hni sch on Un ive rs itiit MtIDchen (BRD); Instit ut fiir R a diohydrometrie del' Gesellsch aft flir StrahLen- und Umwolt [o l's hung Mi:lD ch n (BRD)
Summary A ccording to carbon isotop e ratios, Euphorbia aphylla, E. atl'Opw'pUI'W, E. balsamifera, E . bourgaeana, E. pal'alias, a nd E. regis-jubae fi x carbon v ia t h e C3 p athway on TonorifTo in tho s pring. Euphorbia canariensis p erforms CAM. Among the C3 spocies, li tt Le differonco is fo und in ,513C values obtained from leaf mate ri a l a nd su cc ulen t stem material. Th o variation in ,513C vaLues which occ urs geographically is sm a ll, a l though amon g t he C3 s p ec ies, ,513C values of sampLes f rom the so uth of t h e isla nd t end to be slightly less negat ive, p e rhaps due to changc in in tercell ular CO 2 concentrat ion as t h e pla n ts adapt to drier, less humid conditions.
Indroduction The carbon isotope composition or b13C value1 ) of plant material can be u sed to distinguish which photosynthetic pathway h as been used in CO 2 fixation (cf. OsMOND & ZIEGLER 1975; ZIEGLER 1979 ; TROUGHTON 1979 ; FARQUHAR et al. 1981). Plants showing net CO 2 fixation only in the light via RuBP carboxylase (C 3 metabolism) have b13 C values varying between - 20 and - 35%0 (FARQUHAR et al. 1981) while those exhibiting CAM and fixing additional CO 2 in the dark have b13C values between - 14 and - 30% 0 (OSMOND & ZIEGLER 1975). In the case of carbon fixation via the C4 pathway, the r esulting plant material has b13C values between - 8 and -180/00' Further information in addition to b13C values is needed to distinguish between C4 and CAM carbon fixation . The b13C value of plant material is further affected by environmental conditions which change internal a ir space CO 2 concentration prevailing during fixation. Factors such as water stress (WINTER 1981) , low air humidity (FARQUHAR et al. 1981; WINTER et al. 1982), or high salinity in the case of ma ngrove species (FARQUHAR et al. 1981) r educe intercellular CO 2 concentration, alter the fraction ation of isotopes occurring during diffusion from the external air to the fixation sites , and result in less negative b13C values. In the family Euphorbiaceae, C3 , CAM a nd C4 species have been d ocumented (WEBSTER et al. 1975; EDER et al. 1979). The Euph01'bia species of T eneriffe are 1) OT'h ' (J13CO/ 00 -.L evaI ue'I S expresse d as.
(
13C/12C sample 13C/12C standard -
1
)
. 1000
,T. D. 'I'ENH NE
36../.
et a1.
found in h ab itatfl which differ greatly in temperature , humidity, and soil moisturo avai lab iliLy. Th PI' R nt fl tudy wa oonducted to determine the type ofphotosynthetio c!1l'bon. fixat i n xhibit d by flpeeie of Euphorbia from Teneriffe and whether type of fi atio n ifl m difi d in r eflponfl to habit!1t environmental conditions. Samples of FlL rn and 1 af mat rial were coll ected from soven Euphorbia, pecies at different altitud A and al ng nvironmental gradients in the , pring of 1980 and were analyzed for al'b n. iROL p rati .
Methods L av s aA woll It~ HUC ul ollt stom p iecos of sovo ml Euph01'bia species werc collccted during a t,\Yo wook p o r' iod in Apr' il I!) 0 f'!'om locations in Tonel·iffo. Plant material was coll ected along altitudinal g r'"di ont~ wlr or'o pOH8 ibi and in such a pattern th a t eac h species was reprosentatively Hr unpl od tilr' ug il out its rang of di s tribution (soo OBEIWORl!'El~ 1965). The plant samplos wero ma intain d opon to til o a ir' and w or o oven dei d at 100 °C upon r e turn to the laboratory inWurzbU I'g (FRO). Th o dr'y matot·.ial was frozon in liquid nitrogen and puLverized. The combustion of t.lr o s(,mpl s and th o d otormin ation of th e 613 C vaLu e wero p orformed according to the methods of'S "",GL & Vo o rr,r. (1!)70; cf. OSMOND e t al. 1!l75). The 613 C m eas urements were done with a MAT HPO'tt'om tor fr m Varian, Brom en (FRO), aga inst tho PDB s tandard (CRAIG 1957).
Results and Discussion Th topography, t emperature, and humidity gradients on T en eriffe are charact I'iz d in Figs. 1 and 2 and in Table 1 (see also TENHUNEN et a1. 1982). As previously Aummarized by CEBALLOS & ORTUNO (1951) and FERNANDOPULLE (1976), the volcanic m untain fl running from east to west on Teneriffe (Fig. 1) strongly determine local climate. Large grad ient in moisture availability occur from north to south and tcmperatur fl depcnd strongly on elevation. On the northel'll slopes , cloud banks T able 1. Monthly m ••ximum (tnd minimum mean ail' temperatw'es for t en weather stations on Te· J1ol'iff (loCl.tions shown in Fig. 1). D a t a shown for January and August when temperatures are lowest a nd highest respec tivel y Numbe r: in Fig.
1 2 3 4 5 6 7 8 !l 10
Station location
Pue l'to de la Cl'lI7La OUl1l1cha Aguamal1sa Izaii.a VilE,flor Omnac1illa La Laguna Santa Cruz cle T ene r'iffe San A ncl r'es Los Oigltntes
E le vlttion (meters)
Monthly Mea n Ail' Temperatures J a nuary
August
Maximum
Minimum
M a ximum
Minimum
50 550 1,075 2,365 1,400 650 550 40
19.5 18.2 10.5 6.9 13.1 17. 15.7 20.4
13.1 8.5 13.7 0.8 4.8 8.4 8.7 14.4
25.8 23.6 23.8 21.7 27.7 27.7 25.2 28.8
19.3 14.2 14.5 13.1 17.8 16.4 16. 20.7
50 150
20.6 21.5
14.7 15.9
27.7 26.7
21.2 21.1
Carbon I sotopo Rat ios
365
Fig. 1. Contours of equal elevation at sea level, 1,000,2,000,3,000 and 4,000m on Tonoriffo and location of weather stations for temperature data given in Table 1. Te mperature data fL'om ADlWU (1977) . -
liB ~
EZl D
alpine hum i d moderate dry
Fig. 2. Humidity zones of Te n eriffe according to ABREU (1977). Climate in the a lpino zono chan ges rapidly and is further not r elevant s ince Euphorbia sp ecies do not occ ur in this r og ion.
form daily in the pine forest zone between 1,200 and 2,000 m and the greatest precipitation occurs. The air masses sink in the south, warm up, and dry the slopes . Xerophytes, including Euphorbia species, occur her e at high er elevation than in the north (see OBERDORFER 1965). Mean maximum and minimum air temperatures for J anuary and August are given in Table 1 for ten weather stations (locations in Fig. 1) distributed from north to south and on the east and west sides of the island. Changes in humidity from north to south and with change in elevation are indica t ed in Fig. 2 (see ABREU 1977).
J.D.TENHuNENet~.
:lG(j Euphorb.a aphylla :
aph
otropurpurea :
olr
balsamifera :
bol
bourgaeano : .
bau
poralias :
por
bal -27. 6(2 ' 0) aph - 254(100) oph -24 51 .00)
01,-24. 318001 0Ir-23.914101 bau-24 .7(400)
\ \ - 0Ir-25.4(920)
" \ 0Ir-25.61.020) ~ 0Ir -25.7IS30)
bal·-25.lIS)
0Ir-30.31300)
bal-25.6ISIJl
bal-25. 513S0' bol-24.21l00' bol-25.2(430) 01,-28.21430'
F ig. 3. Th <513 valu es (lurge negative numbers) a nd loeation a ltitude in m et ers (sm a ll numbers in parenLheses) obtained for indi v idual samples of Euphorbia aphylla, Euphorbia atropurpurea, Eupho1'bia bal8omijem, Euph01'bict bourgaea,na, a nd Euphorbia paralias (sp ecies names abbreviated O.H s hown in k y in figure ) co llected during April 1980. Sample is located e ither at the center of t he text s t"ing s hown or when ind icated at the end of the s olid line away from the text string.
The sp ccics investigated were of three different growth forms. Euphorbia paralias L. is ~Ln h rb lcs. t han 50 cm in height having st em s with a woody base. E . atropurpurea (BROLTSS.) W EBB & BERTH., E . balsamifera AlT ., E. bou1'gaeana GAY, and E. regis-jubae WEBB & BERTH. are shrubs of up to three meters in height with thick, su cuI nt stems a nd branches and non-fleshy spathulate to lanceolate leaves which are shed at least partly during the dry season . E . aphylla BROUSS. ex WlLLD . is a compact stem-succulent shrub less than 50 cm in height with slender pencil-like leafl es. branches. E. canariensis L . is a tall leafless stem- succulent shrub which branches from t he base and h as a candelabra-like growth form. Its branches are four or five sided with short curved spines. The (j13C values obtained from st em samples of Euphorbia canariensis and E. aphylla and from leaves of all other Euphorbia species studied, are plotted according to collection in Figs. 3 through 5. Collection locations are either at the center of the text string hown on the maps or at the end of the solid line away from the text
Carbon I sotop e Ratios
367
Euphorbia regis - jubae
- 27.512151 - 27.51351
-26.512001
-24 .615701 -26.814001 -2 3.211451
-26,.615501 -27.71750)
-26.91510) . -25.61340)\ \
-23.911220) -26.419001 -24.516201
a
Fig. 4. The 13 C v alues, collection altitudes, and locations as described for Fig. 3 of ind ividual samples of Euphorbia regis-jubae .
string . As seen in Figs . 3 and 4 , the euphorbias of Teneriffe showed almo. t exclusively C3 -type t5 13 C values, ranging between - 30.3 and -23 .20/00' Less negative values were obtained only with samples from Euphorbia canariensis (Fig. 5). The pattern in t5 13C values obtained with leaves of Euphorbia aphyUa, E. atropurpurea, E. balsamifera, E. bourgaeana, E . paralias, and E. regis-jubae are in general the sanIe . Slightly nIore negative t5 13C values are obtained for plants from the cool moist north side of the island than for plants sampled from the dry southern areas. This is particularly evident in the data obtained for E . regis-jubae (Fig. 4) which is widely distributed on the island and was collected at 29 locations. The small change in t5 13 C value occurring from north to south may b e due to differences in humidity and water availability which affect stomatal conductance, intercellular CO 2 concentration and fractionation of isotopes during the diffusion to the fixation sites as suggested by FARQUHAR et a l. (1981; see also WINTER 1981 ; WINTER et al. 1982). The t5 13 C value of stem material was slightly less n egative than that obtained for leaf nIaterial of E . regis-jubae (average for leaf nIaterial - 26.4; for stenI material - 25.2), E . balsamifera (leaf -25.8; st em - 24.9) , and E. atropurpurea (leaf - 26.2; stem -25.7). Based on only two sanIples, the average t5 13 C value for leaves of E . bourgaeana was - 25.7 and for stems was -26.0. These differences again may be due to
J. D.
36
TENHU NEN
ot at.
Euphorbia canariensis
_12.911301-13.717201
-12.814201
-13.314001
Fig. 5. ' I' lto Il 13 C va lu os , colloc tion altitudes , and locations as described for Fig. 3 of individual s £\rnpl 8 o f EuphOl'bia c(I,!wl·'i en sis.
diffoi' nee. ' in fractionation of isotopes during diffusion to the fixation sites in leaves vel' 'us At om .. They may also be caused by a different chemical composition of leaves and st m s, especially by a different lipid content. Euphorbia canarien is inhabits rocky cliffs in dry areas. The 013C values obtained with material from T eneriffe varied between -12.3 and -14.6%0 (Fig. 5), which suggest the participation of PEP-carboxylase in total CO 2 fixation. Since we found E. canariensis to lack " Kranz-anatomy" , it is without doubt a CAM rather than a 04. sp ecie and relies h eavily on dark fixation in its natural habitat. Glasshouse E. canariensis plants had a 013C value of - 20.6 0/ 00 , much more negative than the value obtained for plants from T en eriffe (ZIEGLER, unpublished). Thus, this species appears to have the potential to regulate the degree of dark fixation occurring. The a sh content of the leaves in the analyzed Euphorbia spp. varied between 6.6 and 18.1 % of dry weight with an average value of 11.2 % of dry weight (n = 53). A h content ofthe stems varied between 4.7 and 14.5 % of dry weight (average 10.8 %; n = 72). The higher ash content of leaves may indicate a higher transpiration rate in the l eaves than in the stems, combined with an incomplete redistribution of the transpiration residues.
369
Carbon Isotope Ratios
Conclusion Except for Euphorbia canariensis, the Euphorbia specie of Teneriffe which were investigated fix carbon via the C3 pathway in the spring. This is somewhat surprising in the cases of E. balsamifera, E. atropurpurea, E. bou1'gaeana, and E. ngisjubae which all have thick succulent stems and branches and which are in. gencral found at warm dry sites. Apparently the stem functions as a water rcservoir in thcse species. Even the leafless, stem-succulent Euphorbia aphylla, which occur' with oth r succulent species on the coastal platform at Punta de Teno , show' 13 C valueR whi ch suggest that it is a C3 species or that at least any CAM ability i upprcssed und r springtime conditions. Euphorbia canariensis, which occurs at many sites along with other Euphorbia species, is a true CAM species. In contrast to pecies of the Sempervivoideae (TENHuNEN et al. 1982), the euphorbias of Teneriffe show little variation in photosynthetic metabolism geographically or with habitat conditions.
a
Acknowledgement W e wish to thank Ms. G. BEYSCHLAG, Ms. W. SAMFASS, and Ms. "V. ANGEHEH [01' toohni al assistance. This work was supported in part by the D e utsch e Forsc hungsgomo insc haft.
Zusammenfassung Blatt- und Stamm-Material von EuphOl·bia.Arten aus T enel'iffa, die 3 untorsc hi od li chon Lebensformen angehoren, wurden auf ihr Kohlenstoffi sotop en-Verhaltni s hin untel's uc ht. Aus den Ergebnissen lii13t s ich schlie13en, da13 die krautige Staude E. paralias, die Strauchel' mit dicken, sukkulenten Stammen und mesophytischen Blattern E. atl'OpUrpU1'ea, E. balsamije1'Ct, E. bou"gaeana und E. regis-jubae und die Stammsukkulente E. aphylla (zumindest wah rend del' Untol's uc hungszeit im Fruhjahr) ihr Kohlendioxid ausschlie13lich uber den C 3- W eg fixieI'en. Nul' gel'ingo Diffol'enzen tl'eten in den <513C-Wel'ten zwischen BlatteI'n und s ukkulenten Sta mmen a uf. Auch die Variation des Isotopenverhaltnisses b e i Proben d el' gleichen Art, die an unterse hi edli ch on Standorton gesammelt wurden, sind nul' unbede utend. Allerdings zeigt s ieh hier di e T end en z zu weniger' nogativen <513C-\Verten bei Exemplaren aus d em sudlichen T eil del' Insel; das mag mit UntoI'seh iod en im inte l'zellularen CO 2 -Gehalt del' Pflanzen zusammenhangen, d ie dort untoI' warmel'on und trockeneren B edingungen wach sen als Exemplare im kuhl -fe uchteren Norden. Nul' di o ka nd olabol'al'tige stammsukkulente E. canariensis erweist sioh aufgl'und ihres wenig nogativen I otopon. vel'haltnisses als einde utige CAM-Pflanze.
References AB;REU, J. M. H. (1977): Estudio agroclimatico de l a isla d e Teneriffe. An. Inst. Nac. Inv. Agr. Ser. General No.5: 113- 181. CEBALLOS, L., & O;RTUNO, F. (1951): Estudio Sobre la Vegetacion y Flora Forestal d o las Canarias Occidentales. 465 pp. Madrid. C;RAlG, H. (1957): Isotopic standards for carbon and oxygen and correction fac tors for mass spectroscopic analysis of carbon dioxide. Geochim. Cosmochim. Acta 12: 133- 149_ EDE;R, A., STICHLE;R, W ., & ZIE GLER, H. (1979): Typen d el' photosynthetischen CO 2 -Fixierung bei mitteleuropaischen Euphorbia-Arten. Flora 168: 227- 2 40. FAHQUHA;R, G. D., BALL, M. C., VON CAEMME;RE;R, S., & ROKSANDIC, Z. (1981): Effect of salini ty and humidity on <513C value of halophytes-evidence for diffusional isotope fractionation de25 Flora, Bd. 173
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.J . D . TI~NHtJN(1;N tal., Carbon Isotope Ratios
LOt'm ined by t he "atio
I' in w reeliul al' jtLtmosphel'i e partial pressure of CO 2 under different
on v ir' nm onto.l on
:32:1
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