NaCl salinity-induced changes in water status, ion contents and photosynthetic properties of Shepherdia argentea (Pursh) Nutt.

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1 NCl slinity-induced chnges in wter sttus, ion contents nd photosynthetic properties of Shepherdi rgente (Pursh) Nutt. seedlings J. Qin 1, W.Y. Dong 2, K.N. He 1, Y. Yu 3, G.D. Tn 1, L. Hn 1, M. Dong 1, Y.Y. Zhng 1, D. Zhng 1, A.Z. Li 1, Z.L. Wng 4 1 College of Soil nd Wter Conservtion, Beijing Forestry University, Beijing, P.R. Chin 2 College of Forestry, Beijing Forestry University, Beijing, P.R. Chin 3 College of Resource nd Environment, Centrl South University of Forest nd Technology, Chngsh, P.R. Chin 4 Qinghi Acdemy of Agriculture nd Forestry, Xining, P.R. Chin ABSTRACT Two-yer old seedlings of Silver buffloberry (Shepherdi rgente (Pursh) Nutt.) were exposed to NCl slinity (, 2, 4 nd 6 mmol/l) for 3 dys. Lef wter potentil (Ψ w ), chlorophyll contents (Chl, b, nd + b) nd K + content decresed with n increse in slinity. Reltive wter content (RWC) declined significntly with 4 nd 6 mmol/l NCl. However, slinity induced n excessive ccumultion of N + in the leves of plnts. Light responses of photosynthesis showed tht net photosynthetic rte (P N ) vlues were continuously rised with the increse of photosynthetic photon flux density (PPFD) t ll slinity levels nd plnts treted with 6 mmol/l slinity suffered from photoinhibition with the lowest P N vlues. The reduction of P N nd stomtl conductnce (g s ) ssocited with shrp increse of intercellulr CO 2 ) in the leves t 6 mmol/l slt-treted plnts showed tht non-stomtl limittions might hve previled over stomtl limittions under severe sline conditions, due to severe cellulr dehydrtion, inhibited synthesis of chlorophyll nd ionic imblnce nd toxicity. It is concluded tht S. rgente possesses high slt tolernce cpcity nd cn be widely cultivted in slt-ffected res. Keywords: lef wter potentil; ion ccumultion; chlorophyll contents; net photosynthetic rte; non-stomtl limittions; slinity High slinity is the most widespred biotic stress nd constitutes the most stringent fctor in limiting plnt distribution nd productivity (Iqbl nd Ashrf 25, Yildirim et l. 29). The min negtive effects of high slinity tht influence plnt growth nd development re photosynthesis inhibition (Shrm et l. 25), wter deficit (Suárez nd Medin 28), ion toxicity ssocited with excessive Cl nd N + (Afzl et l. 28, Ptel nd Pndey 28), interference with nutrition leding to nutrient imblnce (Misr et l. 1997). Bstís et l. (24) hve reported tht high concentrtions of slt disrupt homeostsis in wter reltions nd chnge the ion distribution t both cellulr nd whole plnt levels. Lter, ltered wter homeostsis leds to moleculr dmge, growth rrest nd even deth. The reduction in growth under sline conditions is consequence of severl physiologicl responses nd photosynthesis is thought to be the most importnt process (Stępień nd Kłbus 26). Slinity-induced limittion of photosynthesis under slinity is not only ttributed to stomtl closure leding to reduction of intercellulr CO 2 ), but lso to non-stomtl fctors. There re incresing evidences tht slt ffects photosynthetic Supported by the Doctorl Progrm Foundtion of Institutions of Higher Eduction of Chin, Project No , nd by the 11 th Five Scientific nd Technologicl Sustining Reserch Progrm of Chin, Project No. 26BAD3A123. PLANT SOIL ENVIRON., 56, 21 (7):

2 enzymes, chlorophylls nd crotenoids (Misr et l. 1997, Youssef nd Awd 28). It hs lso been observed by Biswl et l. (22) tht NCl slinity ffects photosystem 2 (PS 2) photochemicl efficiency, chrge seprtion of primry chrge pirs in PSII nd pigment-protein complexes of thylkoid membrnes. However, plnts seem to lck unique mechnism of resistnce to slt stress nd, despite n incresing number of studies, the dt concerning effects of slt stress on photosynthesis re still frgmentry. Utiliztion of slt-tolernt plnts is expected to be n effective method to improve sline soil. Hence, better understnding of the mechnisms tht enble plnts to dpt to slt stress is necessry for exploiting sline soil (Ptel nd Pndey 28). Silver buffloberry (Shepherdi rgente (Pursh) Nutt.) is considered to be ble to ber cold, drought, lenness nd slinity (Geng nd Wng 27, Qin et l. 29). It ws introduced from Americ to Chin in 22 nd hs been successfully plnted in lrge scle in Chin s Loess Plteu nd costl re. Drought stress studies conducted by Geng nd Wng (27) showed tht the soil-wter compenstion point for hydrtion of S. rgente ws 4.4% nd the optimum soil moisture to mintin the mximum net photosynthetic rte (P N ) ws 18.5% with the highest wter use efficiency (WUE) compred to Zygophyllum xnthoxylum nd Atrphxis mndshuric. Qin et l. (29) hs nlyzed the comprison of physiology responses to slt stress in S. rgente nd Hippophe rhmnoides, s ntive tree species widely distributed in the northwest of Chin. It hs been reported tht S. rgente possesses higher slt tolernce thn H. rhmnoides nd cn ber the stress of 6 mmol/l NCl for bove 3 dys. Nevertheless, studies on the tolernce of S. rgente to slt stress re still incomplete nd preliminry. In the present study, to understnd the dptive fetures of S. rgente tht llow it to grow nd survive in sline regions, we nlyzed chnges of lef wter potentil, reltive wter content, ion nd chlorophyll contents nd photosynthesis in S. rgente in four slinity tretments. MATERIAL AND METHODS Experimentl design. S. rgente seedlings were obtined from the experimentl bse (ltitude 36 39'N, longitude 11 46'E nd ltitude 239 m) of Reserch Institute of Forestry, Qinghi Acdemy of Agriculture nd Forestry, Chin. In April 27, the seedlings of S. rgente were plnted in plstic pots (one per pot), filled with 11 kg ntive chernozem soil nd irrigted every three dys, in order to mintin soil wter t field cpcity. In July 28, the experiment ws crried out for 3 dys under ntive condition in the open ir. Twenty two-yer old seedlings, uniform in size, were subjected to slt stress by dding NCl solutions of four concentrtions: (control), 2, 4 nd 6 mmol/l, with the clculted mount of NCl dissolved in wter. The finl slt concentrtion ws progressively djusted with incresing NCl solutions (5 mmol/l per dy). At the sme time, the plnts were irrigted with fresh wter every three dys to mintin soil wter t field cpcity nd void drought stress. Five replictes of ech tretment were used to mesure lef wter sttus, ion ccumultion nd chlorophyll contents of S. rgente t the end of the experiment before hrvest, while three replictes were used to mesure lef photosynthetic prmeters t 25 dys fter the slt tretments. Lef wter sttus. Predwn lef wter potentil (Ψ w ) ws mesured on medil leves of ech plnt, using HR-33T Dew Point Mikrovolt-meter (Wescor Inc., Logn, UT, USA). Reltive wter content (RWC) ws determined on medil leves of ech plnt nd clculted from the eqution: RWC (%) = 1% (FW DW)/(TW DW), where FW, DW, nd TW denote lef fresh, dry or turgid weight, respectively (Yildirim et l. 29). Ion contents. The contents of N + nd K + in leves were determined from dry mtter nd were quntified by n inductively coupled plsm opticl emission spectrometry (ICP-OES, Leemn Lbs Inc., NH, USA) fter nitric-perchloric cid (1%) digestion (Bstís et l. 24). Chlorophyll contents. Chlorophyll (Chl) ws extrcted from dry leves fter hrvest t the end of experiment with 8% cetone nd bsorbnce vlues were determined on spectrophotometer (SP-756, Beijing, Chin) t 663 nd 645 nm, respectively. Chl, Chl b nd totl Chl (Chl + b) contents were clculted s described by Arnon (1949). Photosynthetic prmeters. Mesurements of net photosynthetic rte (P N ), stomtl conductnce (g s ), trnspirtion rte (E) nd intercellulr CO 2 ) were crried out on the third fully expnded lef (from top) of ech plnt (3 plnts for ech tretment), using Li-64 portble photosynthesis system (Li-Cor Inc., Lincoln, NE, USA). The photosynthetic photon flux density (PPFD) sequence for generting light response curves ws set s, 5, 1, 15, 2, 4, 6, 8, 1, 12, 15, 18, 2, 22 nd 326 PLANT SOIL ENVIRON., 56, 21 (7):

3 Ψw ( MP) d c b RWC (%) b c Slinity (mmol/l) Slinity (mmol/l) Figure 1. Effects of slt stress on lef wter potentil (Ψ w ) nd reltive wter content (RWC) in leves of S. rgente seedlings. Vlues re mens of five replictes ± SE. Brs with different letters re significntly different t P <.5 level, s determined by DMRT 25 µmol/mol with the LI-64-2B LED light source (Qin et l. 29b). The mximum P N (P Nmx ), light sturtion point (LSP), light compenste point (LCP) nd pprent quntum yield (AQY) were clculted from the regression eqution of light response curves. All mesurements were mde between 9: 11:.m. in the ntive environment, with the following specifictions nd djustments: mbient CO 2 concentrtion ± 4.4 µmol/mol, ir temperture 22.7 ± 1.9 C nd reltive humidity 39.4 ± 4.3%. Sttisticl nlysis. One wy nlysis of vrince (ANOVA) t significnce level P <.5 ws performed using the SPSS softwre (version 15.). Duncn s Multiple Rnge Test (DMRT) ws used when significnt differences were found mong slt tretments. Reltionships between PPFD nd P N were exmined with liner regression models. RESULTS Slinity effects on lef wter sttus. There ws mrked nd progressive decline in lef wter potentil (Ψ w ) in leves of seedlings with incresing slinity (Figure 1). The decrements of 2 2 N + content (mg/g DW) b c d K + content (mg/g DW) b c d Slinity (mmol/l) Slinity (mmol/l) Figure 2. Effects of slt stress on N + nd K + contents in leves of S. rgente seedlings. Vlues re mens of five replictes ± SE. Brs with different letters re significntly different t P <.5 level, s determined by DMRT PLANT SOIL ENVIRON., 56, 21 (7):

4 Tble 1. Slinity effects on chlorophyll (Chl ), chlorophyll b (Chl b) nd totl chlorophyll (Chl + b) contents in leves of S. rgente seedlings Slinity (mmol/l) Chl Chl b Chl + b (mg/g DW) Chl /b 2.25 ±.6.43 ± ± ± ±.5 b.41 ±.1 b 2.46 ±.5 b 4.93 ± ±.7 c.38 ±.3 bc 2.1 ±.1 c 4.62 ± ±.4 d.35 ±.1 c 1.72 ±.4 d 3.93 ±.25 b Vlues re mens of five replictes ± SE. Different letters in the sme column re significntly different t P <.5 level, s determined by DMRT Ψ w were 11.8%, 24.9% nd 37.% t 2, 4 nd 6 mmol/l, respectively, when compred with the control. Slinity lso significntly reduced RWC in leves of plnts treted with 4 nd 6 mmol/l (Figure 1). The decrement of RWC in slt-treted plnts ws 1.2%, nd tht in 6 mmol/l slt-treted plnts ws 15.5%. Slinity effects on ion contents. Sline conditions significntly ltered the tissue concentrtion of N + nd K + (Figure 2). N + content in the leves of plnts shrply incresed with incresing slinity nd ws 4.6, 9.8 nd 15.6 times higher thn the control t 2, 4 nd 6 mmol/l slt tretments, respectively. In contrst, K + content ws significntly decresed with the increse of slinity (Figure 2) nd hd lower chnging rnge thn N + (only decresed by 7.3%, 14.4% nd 29.5% of the control). Slinity effects on chlorophyll contents. A continuous nd significnt decrese in Chl, Chl b nd Chl + b contents in leves of S. rgente seedlings due to slt stress ws detected (Tble 1). The rte of decrese in these prmeters ws greter t the higher slinity. Compred with the controls, Chl content declined by 9.%, 23.4% nd 39.2%, Chl b content declined by 4.5%, 12.9% nd 19.2%, nd Chl + b content ws reduced by 8.3%, 21.7% nd 35.9%, t 2, 4 nd 6 mmol/l NCl concentrtions, respectively. Chl b ws less sensitive or better protected ginst slt stress thn Chl under the sme slinity level, which resulted in the drop in the Chl /b rtio, especilly for 6 mmol/l slt-treted plnts (75.9% of the controls; Tble 1). Slinity effects on photosynthetic properties. Net photosynthetic rte (P N ) vlues were continuously rised with the increse of photosynthetic photon flux density (PPFD) t ll slinity levels; however, there ws significnt difference in the increse mplitude of P N vlues under different NCl concentrtions (Figure 3). P N vlues of plnts grown under non-sline conditions were the highest nd did not decline when PPFD exceeded 25 µmol/ mol, wheres those of 2 nd slttreted plnts were reltively low nd mintined constnt bove 2 µmol/mol PPFD. However, plnts treted with 6 mmol/l slinity seriously suffered from photoinhibition nd hd the lowest P N vlues compred to others. The chnges of stomtl conductnce (g s ) nd trnspirtion rte (E) in the leves of S. rgente seedlings subjected to vrying slinity hd the sme tendency s P N under different PPFD (Figure 3). Non-obvious difference in intercellulr CO 2 ) vlues in the plnts were observed when slinity ws below, wheres C i vlues in 6 mmol/l slttreted plnts ws significntly higher when PPFD exceeded 1 µmol/mol (Figure 3). To nlyze the effects of NCl slinity on the mximum P N (P Nmx ), light sturtion point (LSP) nd pprent quntum yield (AQY), regression of light response curves nd the initil slope of the curves between P N nd PPFD were mde (Figure 4, Tble 2). Compred with the control, P Nmx ws decresed by 29.2%, 43.7% nd 87.1%, nd AQY decresed by 9.8%, 26.8% nd 82.9% t 2, 4 nd 6 mmol/l NCl concentrtions, respectively (Tble 2). Slinity lso reduced LSP vlues to certin extent but there ws no obvious difference mong sline conditions (Tble 2). DISCUSSION Wter sttus is the min fctor ffecting the plnts growth nd development. Decresing externl wter potentil produces net ccumultion of solutes in cells, which lowers the cell osmotic potentil neces- 328 PLANT SOIL ENVIRON., 56, 21 (7):

5 25 2 mmol/l 2 mmol/l 6 mmol/l.4.3 mmol/l 2 mmol/l 6 mmol/l P PN N (µmol/m (μmol/m 2 2 /s) /s) g gs s (mol/m 2 2 /s) /s) PPFD (μmol/m 2 /s) PPFD (μmol/m 2 /s) E (mmol/m 2 /s) mmol/l 2 mmol/l 6 mmol/l C i i (µmol/mol) (μmol/mol) mmol/l 2 mmol/l 6 mmol/l PPFD (μmol/m 2 /s) PPFD (μmol/m 2 /s) Figure 3. Light responses of net photosynthetic rte (P N ), stomtl conductnce (g s ), trnspirtion rte (E) nd intercellulr CO 2 ) in the leves of S. rgente seedlings grown under different NCl concentrtions. Vlues re mens of three replictes ± SE nd SE is not shown when smller thn symbol sry for mintining the turgor pressure (Nvrro et l. 23). Through the nlysis of wter reltions in the leves of S. rgente, we observed tht plnts djusted their Ψ w to more negtive levels s slinity incresed (Figure 1), which is common rection to slinity similr to those reported for other species (Nvrro et l. 23, Suárez nd Medin 28). Significnt reduction of RWC in leves of plnts treted with 4 nd 6 mmol/l (Figure 1) indicted tht slinity lso resulted in dehydrtion t cellulr level nd dehydrtion symptoms were greter in higher NCl concentrtion tretment becuse of the incresing cellulr wter loss. Ion uptke is the chepest form of osmotic djustment under soil sline conditions, but it could lso led to problems of decline in lef function nd ionic imblnce nd toxicity (Bstís et l. 24, Yildirim et l. 29). In prticulr, slinity lters uptke nd bsorption rtes of ll minerl nutrients resulting in deficiency symptoms. Bonill et l. (24) found tht most toxic effects of NCl cn be ttributed to N + toxicity. Excessive ccumultion of N + cn cuse rnge of osmotic nd metbolic problems for plnts (Hoi et l. 23). In the present study, N + content in the leves of plnts ws 4.6, 9.8 nd 15.6 times of the controls t 2, 4 nd 6 mmol/l, respectively (Figure 2), which indicted tht S. rgente seedlings hd no efficient cpcity to restrict sodium movement to the photosynthetic prts of the plnt. Potssium is mjor plnt mcro-nutrient tht plys importnt roles relted to stomtl behvior, osmoregultion, enzyme ctivity, cell expnsion, neutrliztion of non-diffusible negtively chrged PLANT SOIL ENVIRON., 56, 21 (7):

6 P PN (μmol/m 2 N (µmol/m 2 /s) /s) mmol/l 2 mmol/l 6 mmol/l PN P (μmol/m N (µmol/m 2 /s) mmol/l 2 mmol/l 6 mmol/l PPPFD PFD (µmol/m (μmol/m 2 /s) 2 /s) PPPFD PFD (µmol/m (μmol/m 2 /s) 2 /s) Figure 4. Reltionship between photosynthetic photon flux density (P PFD ) nd net photosynthetic rte (P N ) in the leves of S. rgente seedlings grown under different NCl concentrtions. The expressions of y = x 2 + bx + c for light response curves is shown in Tble 4 ions nd membrne polriztion. Moreover, it is known tht toxic effects of N + re lrgely due to its bility to compete with K + for binding site essentil for cellulr function (Yildirim et l. 29). We found tht the slt tretments decresed K + content with incresing NCl level (Figure 2). However, our results might disgree with the view of Blumwld et l. (2) tht mny K + trnsport systems hve significnt ffinity for N + nd thus reduction in K + uptke is minly cused by N +, since the decrement of K + content ws much lower when N + content shrply incresed with vrying slinity (Figure 2). Concentrtions of chlorophyll components of the photosynthetic pprtus re normlly used to quntify lef senescence in slt-stressed plnts. Most studies show tht slinity dversely ffects Chl content (Meloni et l. 23). The observed decrese in Chl contents in the leves of S. rgente seedlings grown under sline conditions (Tble 1) my be ttributed to both n inhibited synthesis of tht pigment nd dmged PS ntenn system (Youssef nd Awd 28). The higher Chl /b rtio in 6 mmol/l slt-treted plnts compred to tht in other tretments obtined in this study (Tble 1) indictes tht the rtio of PS 2/PS 1 content ws chnged in stressed leves under severe slinity level (Stępień nd Kłbus 26). Photosynthesis is often reduced by slt stress, irrespective of the type of slts used (Misr et l. 1997). In the present study, when compred to the control, P N vlues of 2 nd slttreted plnts were reltively low, wheres plnts treted with 6 mmol/l slinity seriously suffered from photoinhibition nd hd the lowest P N vlues (Figure 3). In ddition, P N mx nd AQY declined Tble 2. Effects of slt stress on the mximum P N (P N mx ), light sturtion point (LSP) nd pprent quntum yield (AQY) in the leves of S. rgente seedlings s determined by regression eqution: y = P N, x = P PFD Slinity (mmol/l) Regression eqution R 2 P N mx LSP (µmol/m 2 /s) y = x x ** y = x x ** y = x x ** y = x x ** **indicte extremely significnt difference in the regression eqution t P <.1 level AQY 33 PLANT SOIL ENVIRON., 56, 21 (7):

7 progressively with the increse of slinity (Tble 2, Figure 4), especilly in 6 mmol/l slinity level (only 12.9% nd 17.1% of the control, respectively). Menwhile, LSP vlues were lso reduced to certin extent under sline conditions (Tble 2). Our results re in greement with the findings of Kruss nd Allen (23), suggesting tht slinity negtively ffects the efficiency of solr energy utiliztion in S. rgente seedlings. The close reltionship between P N nd N + concentrtion in lef tissue ws reported by Iqbl nd Ashrf (25), indicting tht P N ws ffected by N + in the lef mesophyll. Slinity-induced excessive ccumultion of N + in the leves of plnts which ws lso obtined in the present study (Figure 2); it is in greement with the opinion tht high ccumultion of N + in the cytoplsmor chloroplst cn ffect the integrity nd function of photosynthetic membrnes, when the vcuole cn no longer sequester toxic ions (Bstís et l. 24). Moreover, the reduced photosynthesis t high slinity could be lso ttributed, in prt, to the reduced content of K + (Figure 2) which is indispensble in mintining the stedy-stte photosynthetic rte nd contributes to better regultion of stomt opening (Stępień nd Kłbus 26). Stomtl closure is well known to be n effective mechnism for economicl wter utiliztion under slinity nd limittion of the hrmful slt ions uptke (Hsegw et l. 2). However, the decrese in g s lso cused simultneous decrese in both P N nd E (Figure 3). According to our study, the chnges of g s nd E in the leves of S. rgente seedlings subjected to vrying slinity hd the sme tendency s P N under different PPFD. On the contrry, C i vlues in 6 mmol/l slt-treted plnts were significntly higher thn those in other tretments when PPFD exceeded 1 µmol/mol (Figure 3). The high slinity-induced increse of C i vlues ws lso observed by Yng et l. (26) nd supported the hypothesis tht the inhibition of photosynthesis cused by slt ccumultion in the mesophyll produces n increse in C i, which reduces the stomtl perture (Mnsfield et l. 199). It ws reported tht both stomtl nd non-stomtl limittions ccount for reduction of photosynthesis (Frquhr nd Shrkey 1982). According to our results, the gret reduction of P N nd g s ssocited with shrp increse of C i in the leves of S. rgente seedlings subjected to 6 mmol/l concentrtion showed tht nonstomtl limittions (chloroplst cpcity to fix CO 2 ) t the biochemicl level might hve previled over stomtl or mesophyll limittions under severe sline conditions, which ws minly due to serious cellulr dehydrtion, inhibited synthesis of chlorophyll nd ionic imblnce nd toxicity. Thus, we cn conclude tht S. rgente introduced from brod possesses high slt tolernce cpcity which cn help to dpt to moderte slinity levels (2 nd NCl), nd cn be widely cultivted in slt-ffected res. REFERENCES Afzl I., Ruf S., Bsr S.M.A., Murtz G. (28): Hlopriming improves vigor, metbolism of reserves nd ionic contents in whet seedlings under slt stress. Plnt, Soil nd Environment, 54: Arnon D.I. (1949): Copper enzymes in isolted chloroplsts. Polyphenoloxidse in Bet vulgris. Plnt Physiology, 24: Bstís E.I., González-Moro M.B., González-Muru C. (24): Ze mys L. mylce from the Llut Vlley (Aric-Chile) tolertes slinity stress when high levels of boron re vilble. Plnt nd Soil, 267: Biswl A.K., Dilnwz F., Rmswmy N.K., Dvid K.A.V., Misr A.N. (22): Thermoluminescence chrcteristics of sodium chloride slt-stressed Indin mustrd seedlings. Luminescence, 17: Blumwld E., Ahron G.S., Apse M.P. (2): Sodium trnsport in plnt cells. Biochimic et Biophysic Act (BBA) Biomembrnes, 1465: Bonill I., El-Hmdoui A., Bolńos L. (24): Boron nd clcium increse Pisum stivum seed germintion nd seedling development under slt stress. Plnt nd Soil, 267: Frquhr G., Shrkey T. (1982): Stomtl conductnce nd photosynthesis. Annul Review of Plnt Physiology, 33: Geng S.L., Wng Z.L. (27): Study on physiologicl chrcteristics of Zygophyllum xnthoxylum, Atrphxis mndshuric, Shepherdi rgente species under different soil wter. Shnxi Forestry Science nd Technology, (In Chinese) Hsegw P.M., Bressn R.A., Zhu J.K., Bohnert H.J. (2): Plnt cellulr nd moleculr responses to high slinity. Annul Review of Plnt Physiology nd Plnt Moleculr Biology, 51: Hoi N.T.T., Shim I.S., Kobyshi K., Kenji U. (23): Accumultion of some nitrogen compounds in response to slt stress nd their reltionships with slt tolernce in rice (Oryz stiv L.) seedlings. Plnt Growth Regultion, 41: Iqbl M., Ashrf M. (25): Chnges in growth, photosynthetic cpcity nd ionic reltions in spring whet (Triticum estivum L.) due to pre-sowing seed tretment with polymines. Plnt Growth Regultion, 46: Kruss K.W., Allen J.A. (23): Influences of slinity nd shde on seedling photosynthesis nd growth of two mngrove species, Rhizophor mngle nd Bruguier sexngul, introduced to Hwii. Aqutic Botny, 77: PLANT SOIL ENVIRON., 56, 21 (7):

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