Numbers of mycorrhizas and the growth of Picea sitchensis — What is the relationship?

293

Agriculture, Ecosystems and Elsevier Soienoe Publishers Printed in Czechoslovakia

Environment, 28 B.V., Amsterdam

(1989)

293-298

NL~IBERS OF NYCORRHIZAS ~ THE GROWTH OF PICEA SITCHENSIS - WHAT IS THE RELATIONSHIP? F.T. Last I, J. Wilson 2 and P.A. Mason 2 I. Department of Forestry and Natural Resources, University of Edinburgh, Edinburgh, Scotland EH9 3JU 2. Institute of Terrestrial Ecology, Bush Estate, Penlcuik, Midlothian, Scotland EH26 OQB ABSTRACT Irrespective of the types of mycorrhlzas that developed, the heights (Y nun) of Sitka spruce seedlings inoculated with Laccarla ~roxlma or isolates of Paxillus involutus were related exponentially to total numbers (n) of mycorrhizas Y = 26.40 ÷ 4.90 e

+0.97x

m where x = logl0(n+l). INTRODUCTION

Cline and Reid (1982) found, when examining the effects of Pisollthus tlnctoriue (Pere.) Coker and Couch. on Pinue contorta var. istifolia Engelm. grown in axenlc condlt~ons, that seedling dry weights were related exponentially to the abundance of Nycorrhizas. Alexander (1981) and Bolden et al.

Because observations made by

(1983) suggest that the early growth of

Sitka spruce (Picea sitchensis (Bong.)Carr.), a species of major importance in the UK, might be similarly related to the occurrence of mycorrhizas a detailed investigation was made of ranges of mycorrhizal fungi and forest soils. MATERIALS AND METHODS A multifactorial (4x4x4) experiment with four randomly arranged replicate blocks was done in an unheated glasshouse to assess the effects of combinations of three series of factors: A.Inoculation, during propagation in axenic conditions, with vermiculite/ peat cultures of Paxillus Involutus (Batsch: Ft.) Fr. isolates A and B or Laccaria ~roxima (Boud.) Pat.: there was a fourth uninoculated 'control' series. B.Seedllngs were transplanted after propagation into 4 forest soils (2 peats and 2 brown earths) of Scottish origin, which were not sterilised. C.4 provenances of Sitka spruce. Seeds, surface sterilised with hydrogen peroxide, were germinated on water agar at room temperatures and 20 days later (30 April 1981) transplanted, for

294

propagation, into polystyrene open-ended tubes containing vermiculite/peat supplemented with nutrients and appropriate inoculum.

After 64 days'propaga-

tion in an unheated glasshouse, seedlings were individually transferred on 3 July to pots containing test soils mixed 3:1 by volume with coarse washed gravel.

With the application of Ingestad's

(1971) nutrient solution in June

1982, growth was maintained for two seasons. Many aspects of fungus and seedling develolmnent were recorded but this report is restricted to heights and numbers of mycorrhizas per seedling (Last etal., 1985) recorded at the end of the first and second growing seasons.

Because

standard errors and means were directly proportional, instead of independent, numbers (n) of mycorrhizas and seedlings heights (h) were transorrmed to lOgl0 (n+l) or lOgl0(h+1)

for statistical analysis. ~ESULTS

1.1noculating with L. proxima and isolates A and B of P. involutus consistently and significantly increased mean numbers o f mycorrhizas per plant(Table I). 2.1solate B of P. involutus increased mean numbers of mycorrhizas more than isolate A, but less than L. ~roxima.

The differences between L. ~roxima and

P. involutus isolate B were not statistically significant. 3.On average fewer mycorrhizas developed on seedlings grown in peats than in brown earths, the differences

(340-720, peats; 1300-3700, brown earths) being

strongly significant at the end of the second season.

However in some treat-

merit combinations, there were more mycorrhizas on seedlings in peat than in brown earth.

In peats~seedlings inoculated with L. proxima had more mycorr-

hizas than uninoculated seedlings in Glentress brown earth. 4 . A t the end of the first season most mycorrhizas on seedlihgs grown in peats were attributable to inoculant fungi but L. ~roxima was significantly more successful than P. involutus in brown earths.

The mean proportions of

mycorrhizas on seedlings grown in brown earths attributable to inoculant fungi were 7%, 61% and 100% following inoculation with isolates A and B of P. involutus and L. ~roxima respectively. At the end of the the second year 77% of mycorrhizas on seedlings inoculated with L. proxima continued to be attributable to that fungus, but only 4% and 3% of those on seedlings inoculated with P. involutus could be attributed to isolates of this inoculant fungus.

The other mycorrhizas are thought to

have been formed by species of Thelephora, Cenococcum and Inoc~be. 5.Seedling heights and total dry weights, the attributes favoured by foresters and tree physiologists respectively, were consistently and directly related (r2=0.86-0.93).

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6.By the end of the second year, seedlings grown in brown earths were usually taller than those in peats. 7.Inoculatlon with L. ~roxima and P. involutus significantly increased seedling heights.

P. involutus isolate B increased mean heights more than isolate A

but less than L. ~roxima. 8.Irrespective of treatments, seedlings with similar numbers of mycorrhizas .. tended to be the same size.

At the end of the second season seedlings

inoculated with L. proxima and grown in Glentress peat had 2300 zycorrhlzas and were 128mm tall; seedlings inoculated with P. involutus isolate B had 2000 mycorrhizas and were 121mm tall. DISCUSSION

1.Although inoculation with P. involutus continued to enhance numbers of mycorrhizas very few of them could be attributed, in the second season, to the inoculant fungus.

Instead the activities of this fungi increased numbers

of mycorrhizas attributable to naturally occurring inocula of Thelephora, Cenococcum and Inoc~be.

This enhancement may reflect the increased search

capability of rootsystems which were enlarged by P. involutus during the first season of growth, or a change in the responsiveness of seedling roots to colonization or an effect, direct or indirect, of one mycorrhizal fungus upon another. 2.In this. experiment done with seedlings in conditions nearer to those in nurseries than established forests, it was noted that seedlings with similar numbers of mycorrhizas were, irrespective of soil type, of similar heights.

To examine this apparently overriding importance of numbers,

regardless of the occurrence of extramatrical mycelium and the presence/ absence of strands,parallel curve analyses were made of the relation between numbers (n) of mycorrhizas and seedling heights (Y). significant terms for 'parallelism' and Uisplacement'

In the absence of it was found that

Y = 26.40 + 4.90 ÷0.97x : where x = lOgl0(n+l) (Figure I). e This equation implies that a ten-fold increase in numbers of mycorrhizas from 10 to 102 per plant is unlikely to increase heights appreciably, whereas a comparable ten-fold increase from 103 to 104 mycorrhizas per plant is likely to result in very substantial increases. is similar to that found by Cline and Reid (1982).

This relationship

It may provide the

basis of a bioassay to judge if the artificial inoculation of seedlings may give a profitable growth increase.

To increase numbers to 102 per plant is

unlikely to be rewarding: to increase them to 103 or more is likely to prove profitable, but is there sufficient natural inoculum to make this unnecessary?

297

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Figure i. Relationship between height (mm) and numbers of mycorrhizas per plant after growing Sitka spruce seedlings, inoculated d~ring pzopagation with Paxillus involutus isolates A (A) and B ( ~ or Laccaria ~roxima (0), in four forest soils whlch were not sterilised. (@, uninoculated controls).

298

REFERENCES ALEXANDER,

I.J.: The Picea sitchensis + Lactarius rufus mycorrhizal

association and its effects on seedling growth and development. Transactions of the British Mycological Society 76:417-423,

1981.

CLINE, M.L., REID, C.P.P.: Seed source and mycorrhizal fungus effects on growth of containerized Pinus contorta and Pinus ~onderosa seedlings. Forest Science 28:237-250,

1982.

HOLDEN, J.M., THOMAS, G.W., JACKSON, R.M.: Effect of mycorrhizal inocula on the growth of Sitka spruce seedlings in different soils. Plant and Soil 71:313-317,

1983.

INGESTAD, T.: A definition of optimum nutrient requirements in birch seedlings II. Physiologia plantarum 24:118-125,

1971.

LAST, F.T., MASON, P.A., WILSON, J., INGLEBY, K., MUNRO, R.C., FLEMING, L°V., DEACON, J.W.:

'Epidemiology' of sheathing

(ecto-)mycorrhizas

in unsterile soils: a case study of Betula pendula. the Royal Society of Edinburgh 85B:299-315,

Last,

F.T.,

wilson,

myoorrhizas and the relationship?

J.

and

Manson,

Proceedings of

1985.

P.,

1989: Numbers of

the growth of Picea sitchensis Agric., Ecosystems Environ., 28:

- w h a t is 293-298.