Introduction
Experimental ecology in the su b litto ra l marine environment har Involved the use of growth station s to in vestigate the e ffe c ts o f lig h t, and temperature on the growth o f macrophytio algae. These have eitner been set up 'in situ* using SCUBA (Heushul & KaxjQ,1963i Neushul & rov/el.l ^
1964; Luning; 1969a, 1970a; John, 1968; H.T,Powell pers, comm) or have been s e t up from the surface (Sargent & Lan trip , 1952; Jones 1959; Sun dene, 1962, 1964; Nicholson 1968}♦
Liin.ing (1969a) mounted plants of L. hyperborea on rVO plates
and outgrowths of haptera fixed the plants to these p la te s whten were actached to iron frames. The experimental treatm ents consisted of amputating the oxd Jami'nB, amputating both th e s tip e and old Imaina, and submerging these plants with control^ in th e same region the plan ts were talc en from, Other p lan ts were grown in complete darkness, The plants were brougjit to the surface c-n the
frames at frequent in te rv a l a and the lamina areas measured. These experiments showed th a t p la n ts grown in dark-rioss could s t i l l produce a small new lamina. The is o la te d new laminae produced 'in situ ' were the same s i ye as cho dark- grown plan ts, and amputation of the old lamina reduced tne si.zo o f \hd new
lamina produced compared to the control p la n t.
In a second series o f experiments, Luning (l97Ga) grow the sim ilar four experimental groups in complete darkness, l,e , control; new lamina with o ld lamina but no stip e; new lamina with stip e but no old lamina; isolated new lamina. The r e s u lts showed t h a t the growth ra te s o f the new iam1na kepI in darkness from Fouruary untxl May are considerao'y reduced ii'th o old lamina is amputated but th e new lamina was la rg e r than the c o n tro l when
the s tip e was removed,
Luning (1969a; 197Ga) concluded that the new lamina depends on reserve materials in th e old lamina and tliat 'in s i t u' the stip e taay provide
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some roserves but in darkness the stip e exhibits a 'p arasitic behaviour’ and appears to act as a 'sink' for m aterials from the old and ne^
Liinijig also calculated that about o f the new lamina area produced during the period o f rapid growth is due to reserve m aterials stored nainly in the o ld lamina, Luning (1971b) has shown the existence o f a tra n slo ca tio n of CI4
la b elled assim ilates from the old lamina to Uxe developing base of the new lamina and, to a smaller axtent, the stip e and holdfast in L, saccharina and
This chapter describes an ‘in situ ' growth experiment bo in vestigate further th e importance of th-x 9Id lamina to the development of th e new lamina and the effe c t o f canopy shading on the subsequent developmwt of the new lamina,
A permanent quadrat was s e t up in February in the I,, hyperDorea fo re s t at F ife Ness, The quadrat was made o f ^jjnch souare section mild s te e l with
inolde length of 141cm rind to ta l area of 2 square rat res, A central bar divided the quadrat into two areas, each of 1 n",
Tlie quadrat was placed over a dense region o f L. hyperborea on a rock pinnacle at 3,1m H^LWS, The quadrat was manoeuvred to taicompasc as vany
0
plant hoIdfaotB as possible, In \.-no h a lf of the quadrat (.1 nL) the area was cleared of older, canopy forming p la n ts, w hilst i,he canopy wa- maintained in the other ' -■ If ,
The in i t ia l now Laraina area was measured by placing the Lamina f l a t on a formica board and tracing around the lamina edge with a p en cil, The now lamina was very small then (O .l to 14,8 cm'^) and could e a sily be drawn around, incli plant was tagged a t the base of tlic stip e, There were» a t o t a l o f 9 plants in the cleared hal.f o f th e quadrat ; 2 of these had the old lannna amputated in February and 7 were le f t as controls, ''liere Mere 10 plants
analysed jij the other h a lf and 5 of thesc haa th e ir old lamina removed in -Februaï-y and the remaining 5 were l e f t in tact. The experiment was re t up on 26, 2,71 and a l l the tagged plants were removed from the quadrat on 20,8.71.
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Each p lan t lamina was photographed and th e lamina was cut up into small lengths which were la id f la t in a polythene bag and #iotooopied; the lamina am as matohed up on the photooo^y and th ese were out out and weighed. The
lamina area was oaloulatsd from th e weight of a known area of paper.
o ld lamina
2
old lamina
L
Figure. Ef.fg.ct. of, rempyal, of. thé-, old lamina and, the canopy, on..the growth, of. the, new lamina.
R esults
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Table 4--1
The i l n a l lamijia a rea of p lan ts in th e Krovrbh experiment
CLbARSD HALF CANOFY HALF
9 p la n ts ; 7+3 2-01 j 10 p la n ts: 5+'T-'f OLD LAMINA 12,0 3,4 (0,25) (0,25) OLD LAMINA JK 5,8 - 2,3 i (0 . 25) 4- 9 9
1, Mean lamina areas are given in dm" (100cm") with SKM, The p ro b a b ility le v els for 't ' te s ts o f d ifferen ces between means is given :ln brackets betweon each treatm ent,
2, The average age of plants in the cleared h alf was B years, stip e length 40cm 3, The average age o f p lan ts under the canopy was 7 years, s tip e length 28cm,
4, Representative p lan ts are shown in Figure 4-1
None of the differences are very sig n ific a n t due t o the small number o f plants in each tr e a t mm t The poorest .growth, shown was that o f plants
under th e canopy without the old lamina, The best growth was th a t of plants in the cleared h a lf with the old lamina retain ed Trom February,
* Thus only the difference between f i n a l lamina area of p lan ts in the cleared h a lf with old lamina re ta in ed and plants under the canopy with the o ld lamina amputated was s ig n ific a n t at the u su ally accepted le v e l of p ro b a b ility of t ,
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J& scussjm
This experiment confirms the findings of Luning lloc c i c ) , th a t th?
removal o f the old lamina a t the beginning o f the growing season reduces the vsubsequent new lamina area given at the end o f the season, This suggestr th a t the new lamina r e l ie s on reserv es which are tra n slo ca te d from the old lamina. Expel Iments to demonstrate th is tra n s local ion are described in Chapter 9,
The rigorous shading e ffe c t of the canopy on the growth of under- storey pl'mt-s is in d icated ;ln th is experiment. Thus the new lamina o f control plants under the canopy is reduced compared to the control value in the cleared h alf, md, in fa ct, the new lamina pm duced under the canopy by control pJans.s i s the sams area as the lamina of p la n ts in th e cleared h a lf which had the o ld lamina amputated in February.
Amputated plan ts in the cleared and canopy halves had approxîpïat.f?3y the same lamina area, This suggests th a t the absence o f the old lamina, during the fir s t few months of the year, when lig h t conditions are frequently poor, has a c r i t i c a l e ffe c t on th e subsequent lamina growth pattern. Thus, even when the amputated new lamina had as goud llg lit conditions as c o n tro l plants in the cleared h alf, the photosynthesis of th e new lamina could not make up for the i n i t i a l absence of support from the old lamina. It is suggeotedthat the supply of m etabolites from the old lamina i s c r i t i c a l for the establishm ent of an
active meristem; the ir r e tr ie v a b le loss had 9 compound inte.rcFt e ffe c t and n-'vt. evan improved ll^ h t could make up for the in it ia l lo s s.
I t must also be borno in mind, however, that the amputation of the old uamina may cause rorne d ir e c t, physical damage to the meristem and the resu lts may be explained in terms of a wounding roaction, h.icholson (1968) could not elim inate a possib le wounding e ffe c t as an explanati.on of data in fie ld experhnmts after deblading plan to of Nereocystis luetkana.
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üHAPTüR 9 The 'in s i t u ' raeasuremcnt of chotosynthes'i-?
Introduction
The importance of the me a sûrement of the I'hoto synthesis of ma ri ne algaa under n a tu ra l conditions must oe stressed i f any attempt i s being made an analysing the e ffe c t of 'key' environmental facto rs on these ra te s and assessing the iiTiportar,ce of photosynthesis during the growth of the plant , without th is data there i s danger of a p ro life ra tio n of hypotheses such as the probably )indue emphasis placed on heterotrophy by Wilce (1967), as a means o f supporting the growth of macrophytic algae under low lig h t regimes in the Artie sublittx>rai. Jackson (lv71) has reappraised d i l c e 's data and found l i t t l e evidence to supyort the th e s i s th a t heterotrophy could support gi'owth but found th a t exogenously : supplied glucose may reduce tlga light requirement for photosynthesis. I t was
f e l t unnecessary to p o stu late heterotrophic supplement and Artie s u b litto r a l p la n ts, although slow gmwing, may survive purely by th e ir own photosyntnosis. Zaneveld (1966) found th at 1.41 of incident lig h t, i . e . a calcu lated 13 f t- c , penetrates a 2m thick ice cover to a depth o f 2‘^m u.d refu ted the pr vlous
suggestioîi of heushul (1963) th a t aphotic conditions e x is t under th ic k ice cover. The measurement of phot ('synthesis 'in s i t u ' and long term production studios vr- u hi ' be able to assess the importance of lig h t and itiotorynthori s under these coritr t i u.s .
Ga i l (1922) measu.red - he photosynthesis of sunlit t o r s i red and iu\)%r algae 'in s i t u ' and c o rre la te d the maximum amount of photosynthesis with thr normal depth h a b ita t of these algae; the maximum amount of photosyntheri s by brown
algae occurred a t a depth of l-8m w hilst the maximum photosynthesis in red algae occurred at 10-2 5m. F rin tz (1939), lav ring (1947, 1966, 196?), -ind Drew
(1969) liave c a rrie d out ‘in s i t u ' measurenonts of photosynthesis in ss'fôral genera of marine algae in t h e i r studies of the zonation of s u b l it t o r a l algae, Sargent & Lantrip (1952) shov/ed, with th e aid of 'in s i t u ' measurements of photosynthesis, th at tra n slo c a tio n was necessary to supply organic compounds
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to the growing tip s of i'4acrocys t is py I’i fei'a, which wore found to do bo low the
compensation point. Ti?<hovskaya (194)) cLowou th a t photosynthesis of 1. sacohar ina changed markedly with season and depth a/jd tn a t growth s t i l l took place dur i ng the polar night in Decembor and oanr-iry when no photonynthosio occurred. Blinks
(1955) and Kanwirher 11966) report photosynthesis rates of l i t t o r a l and
sub l i t to r a] a.igae in various-, ecological s itu a tio n s . There have been extensive stu d ie s on the pro d u ctiv ity of marine phytoplankton using 'in s i t u ' tociinl ucs such as the Winkler oxygen method, and th e CI4 technique introduced by
Eteeman-l'.ielseri (1952). The information on primary p roductivity of marine phytoplankton has been reviewed by Strickland (1965).
A c ritiq u e of the 'in s i t u ' measurement o f photosynthesis fo llo w s., Advantages
1, The a lg al tis s u e is disturbed as l i t t l e as possiole from i t s n a tu ra l
environment. I t i s very lik e ly th a t the re..,oval of plani.s to the laboratory for measuring met"holism markedly a ffe c ts the physiology of the p lan t, Kanwishor
(1966) found th a t m a te ria l kept in the lab o rate r y for some time before use showed decreased oxygen uptake even thouch the sansples were not in the dark .
2. Photosynthesis of tis s u e under various ecological s itu a tio n s c,an be measured, such as at ^vai’ious depths and undi’.r th e fo re st canopy,
3- I t is d if f ic u l t to simulate th e complex marine environment in the laboratory. The many variables, such as lig h t in te n s ity apd q u a lity , and the almost
continual flux o f th ese variaoles, are di ftd c u lt to reproduce and >2 ri.cklan<i 1196 5 ) has reviewed the problems associated with Incubators attem pting to sii-LÜ-iat un '.r- water lig h t.
4 , A wide range of experiments can be c arrie d out 'in s i t u ' such as i.ransplant stu d ies, the e ffe c t of n u trie n t eia’ichmant and p o llu ta n ts on photosynthesis, and the method can be used for estim ating productivity in algae th a t are not e a s ily aged or are not su ita b le su b jects fo r the increment cropping teenniq u e, Pi sadvantages.
i . I t is d i f f i c u l t to correlate, changes in photosynthesis 'in s i t u ' in anything more than a q u a lita tiv e o r sem i-q u an titativ e w,ay with the more im portait
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• nv^ronmentai v a ria b les, crcept perhaps th'; hraster ' fa c to r of lig h t (T ailing, 1961),
2. Where large tis s u e : volume ra tio s are used in studying photosynt.nesi s of tis s u e discs the p o s s ib ility o f stagnation may occur, Whit ford & : chumacher
(lV6l) have emphasised the impor*tance of fa s t currents around a lg a l tis s u e which . prevent a s t r a ti f i c a ti o n of boundary layers.
3, The metnod i s generally more inconvenient for obtaining adequate re p lic a te d measurements of photosynthesis than in the laboratory,
In the 'in s i t u ' experiments no mechanical s t i r r i n g of th e medium in th e incubation ja rs was c a rrie d out but the low tis s u e :volume r a tio and the a g ita tio n of the ja rs on the buoyant platforms in currents meant i t unlikely th a t much stagnation occurred in the ja rs ,
Before presenting th e data the in te rp re ta tio n of r e s u lts from the 014 experiments is discussed and an example calcu latio n set out.
I n te rp re ta tio n of 'in s i t u ' 014 experiments
The C14 technique for measuring primary p ro d u ctiv ity , introduced by St e eman-N i e Is en (1952), has bo-jn extensively used in marine pro dm t i v i t y stu d ie s. I t has much increased s e n s itiv ity over oxygen exchange technioues, e sp e c ially in oligotrophic w aters. k t th e same time an often acrimonious debate seems to have sprung up aoout the in te rp re ta tio n of r e s u lts from C14 experiments, and in p a rtic u la r, disagreement has arisen as to whether uptake of CL4 measu res net
photosynthesis, as favoured by Ryther (1954, 1956), or somewhere between net