Roots and mycorrhiza in plantation ecosystem

Contents 1. Introduction

2. Role of roots and mycorrhizas in forest ecosystem1. Root characteristics2. Mycorrhiza association characteristics3. Tree productivity, carbon allocation, and abiotic control4. Stand development and succession5. Nutrient cycles, roots and mycorrhizal association

3. Roots and mycorrhiza in management1. Fungal pathogen and insect pest2. Heavy metal toxicity3. Management activity

4. Conclusion

Introduction: Below ground component – roots and mycorrhizas are an integral part of the ecosystem – helps

in acquiring nutrients and water – affects plant carbon allocation between the shoots and roots

in short and long term

Mycorrhizal fungi : - a specialized root like organs – present in soil – as a symbiotic association

with roots – receive carbon from host plants – helps the plant in receiving nutrients from soil.

Role of roots and mycorrhizas in forest ecosystem

1. Root characteristics

2. Mycorrhiza association characteristics

3. Tree productivity, carbon allocation, and abiotic control

4. Stand development and succession

5. Nutrient cycles, roots and mycorrhizal association

1. Root characteristicsa. Root diameter and function

◦ Fine roots <2 mm dia – nutrient uptake

◦ Small to medium roots >2mm dia – transport and storage of carbohydrates and nutrients

◦ Coarse and primary tap roots – anchorage for plant- resist from wind damage – take up water

from deeper sources.

b. Root density and nutrient uptake

• Useful indication of plant ability to access soil nutrients

• Barley (1970) – soil nutrient depletion curves that related rooting density to

the mobility of soil nutrients ( highly, poorly or non mobile)

• For highly mobile elements (nitrates & sulfate) >2cm/cm³

• For poorly mobile elements > 4cm/cm³

mycorrhizae helps in facilitating nutrient uptake in poorly mobile and non mobile

elements ( ammonium, phosphate, copper and zinc)

c. Rooting depth

d. Fine root seasonality• Cold temperate zone – high root growth occur immediately before or after of

high shoot growth

• Tropical wet forest – dry period duration has strong influence on high fine root growth

• Tropical dry forest – misture availability controls the timing of fine root growth

e. Root adaptation• Soil chemical

• Physical environment

• Root grafting

2. Mycorrhiza association characteristics

a. Types and distribution of mycorrhizal association

i. Ecto-mycorrhiza – change morphology of

roots – increase the surface area

◦ Fagaceae

◦ Dipterocarpaceae

◦ Pinaceae

◦ Myrtaeae

◦ betulaceae

ii. Endo-mycorrhiza – do not modify the structure of root – present inside the root cortical cells.

• Found in all non-ectomycorrhizal plants

b. Mycorrhizal attributes

Fungi help in – uptake of nutrients, protect plants against pathogens

Plant - supplies the growth and maintenance requirements of fungus

c. Variability in host plant and fungus relationship

Obligatory mycotrophs

Facultative mycotrophs

Non-mycorrhizal

3. Tree productivity, carbon allocation, and abiotic control

a. Roots

◦ Cold temperate conifers – show a decrease in carbon allocation to fine roots when water and/or

nutrient availability is increased

◦ In tropics – same pattern of carbon allocation ( Gonclaves, 1994)

b. Symbiotic association

◦ Ecto-mycorrhiza – having greater biomasses and more extensive sheath and hyphal network – requires

greater carbohydrate investment by the host plant than VA mycorrhizas.

4. Stand development and succession

a. Fine roots◦ Fine root biomass – peaking at canopy closure & levelling off after this time

b. Symbiotic association

◦ VA mycorrhiza dominate during early stages – ectomycorrhizal fungi dominate in later stage (Eucalyptus

plantation)

◦ No. of mycorrhizal species is greater for the younger trees than older trees (Termorshulzen and

Schaffers, 1989 )

◦ Management activities that effect surface organic horizons or the soil may influence mycorrhizal fungal

succession.

5. Nutrient cycles, roots and mycorrhizal association

a. Nutrients and plant carbon allocation

◦ N availability increases – plant decreases carbon allocation to root biomass, to mycorrhizal fungi –

increases allocation to above ground tissues

◦ Decrease in fine root biomass due to excessive addition of one nutrient with strong effects on carbon

allocation – result in deficiency in other nutrients

b. Roots, mycorrhiza and nutrient availability

Fine roots and mycorrhizas – affect soil nutrient availability through

secretion of organic acids, soluble sugars and carbon dioxide,

upon senescence of fine roots and mycorrhizal tissues

P. menziesii Mycorrhizal roots comprised of 6% of living biomass – contributing 48% of

the organic matter to soil

Roots and mycorrhiza in management

1. Fungal pathogen and insect pest

2. Heavy metal toxicity

3. Management activity

1. Fungal pathogen and insect pest

Tropical plantations may be highly susceptible to fungal pathogens and insect pests – capable of eliminating young trees planted after harvesting - Seedlings may have been planted out with an introduced mycorrhizal fungus

Mycorrhizal fungi have been studied to be very effective at preventing the infection of plant roots by pathogenic fungi (Marx, 1973)

Enhanced resistance of mycorrhizal plants to disease may be largely due to indirect effects of improving plant nutrition and health

2. Heavy metal toxicity Some Plants are able to tolerate and accumulate heavy metals with mycorrhizal associations on their roots – either exclude metals or – accumulate them within their mental sheaths (Vogt e al, 1987; wilkins, 1991)

3. Management activity Fertilizers

◦ Excessive application of P and N fertilizer alter mycorrhizal relationships – due to high conc – results in change in species composition

Pesticide and herbicide◦ Excess pesticide and herbicide application causes deleterious effect on VAM fungi

Thinning◦ Thinning reduces fine root longevity.

Soil disturbance

Conclusion Fine roots and mycorrhiza association constitute an interface between plants and soils and thus play a crucial role in forest carbon, nutrient and water cycles. Their continuous growth and dieback, often termed turnover of fine roots, may constitute a major carbon input to soils and significantly contribute to belowground carbon cycle.

As most of plantation species are exotic – focus on testing exotic symbiotic fungi is obvious.

Most studies have concentrated on determining the effect of single symbiont on seedling establishment in pot house/ nursery condition – study need for effect in field condition.

Thank you