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Phytophthora and Oak Decline - Impact on Seedlings and Mature Trees in Forest Soils

Jönsson Belyazid, Ulrika LU (2004)
Abstract (Swedish)
Popular Abstract in Swedish

Under de senaste decennierna har många ekar i Sverige och i övriga Europa uppvisat en klart försämrad hälsa och på många ställen har omfattande ekdöd förekommit. Forskning för att klarlägga orsakerna bakom ekskadorna pågår och ett flertal möjliga förklaringar har lagts fram, men ännu finns ingen lösning på gåtan. De flesta forskare anser dock att skadorna beror på komplexa interaktioner mellan ett flertal olika faktorer, såsom ogynnsamt klimat, luftföroreningar, växtskadegörare och utebliven eller felaktig skogsskötsel. Denna avhandling behandlar en av dessa faktorer, nämligen en grupp av svampliknande växtskadegörare som kallas Phytophthora. Phytophthora kan angripa och förstöra rötter, stam och... (More)
Popular Abstract in Swedish

Under de senaste decennierna har många ekar i Sverige och i övriga Europa uppvisat en klart försämrad hälsa och på många ställen har omfattande ekdöd förekommit. Forskning för att klarlägga orsakerna bakom ekskadorna pågår och ett flertal möjliga förklaringar har lagts fram, men ännu finns ingen lösning på gåtan. De flesta forskare anser dock att skadorna beror på komplexa interaktioner mellan ett flertal olika faktorer, såsom ogynnsamt klimat, luftföroreningar, växtskadegörare och utebliven eller felaktig skogsskötsel. Denna avhandling behandlar en av dessa faktorer, nämligen en grupp av svampliknande växtskadegörare som kallas Phytophthora. Phytophthora kan angripa och förstöra rötter, stam och blad hos unga plantor såväl som vuxna träd. Jag ville därför undersöka om jordburna arter av Phytophthora förekommer i ekbestånd i södra Sverige, och om de isåfall är inblandade i de skador på träden som vi idag kan se i många ekbestånd. Resultaten visade att det finns åtminstone tre olika jordburna arter av Phytophthora i sydsvenska ekbestånd. Den art som hittades i flest bestånd (10 av 32 undersökta bestånd) var den för ek specifika patogenen P. quercina. Phytophthora visades förekomma på mycket varierande marktyper med olika markkemiska förhållanden. För att utröna om Phytophthora hade någon negativ effekt på ekens rotsystem och därmed kunde påverka trädens hälsa utfördes växthusförsök där unga ekplantor planterades i skogsjord som infekterats med P. quercina och en annan art av Phytophthora, P. cactorum. Båda arterna infekterade och förstörde en stor andel av plantornas rotsystem trots att förhållandena inte var optimala för skadegörarna (skogsjorden var sur, vattentillgången var begränsad och andra mikroorganismer var närvarande i jorden). Fältstudier visade senare att P. quercina även kunde orsaka omfattande skador på rotsystem hos vuxna träd. Omfattningen av skadorna verkade variera beroende på trädens vitalitet, markförhållandena och det rådande klimatet. Trots de omfattande skadorna på rotsystemen kunde få effekter på de unga plantornas ovanjordiska tillväxt eller på näringsstatusen hos plantor eller vuxna träd ses. Detta är dock inte ovanligt, eftersom Phytophthora ofta infekterar rotsystemen hos vuxna träd många år innan effekter i kronan kan upptäckas. Upprepade och omfattande infektioner av rotsystemet, där trädet måste ersätta de rötter som förstörts som en följd av infektionerna, tär dock på trädets reserver av kolhydrater. Detta kan leda till reduktioner i tillväxt av rötter och krona, samt även påverka produktionen av försvarsämnen negativt. Trädens känslighet mot ytterligare rotinfektioner av Phytophthora och mot andra stressfaktorer kan därför öka och trädens hälsa försämras. (Less)
Abstract
This thesis investigated the occurrence of soilborne species of the plant pathogenic genus Phytophthora in southern Swedish oak forests and their possible involvement in southern Swedish oak decline. The emphasis was on the impact of P. quercina on Quercus robur in acid forest soils. Several different methods, including screening for Phytophthora in oak forest soils, greenhouse experiments with seedlings grown in soils inoculated with Phytophthora, and field studies of mature oaks growing in Phytophthora-infested stands, were used. The results showed that Phytophthora species occur in southern Swedish oak forests. The most frequently recovered species was P. quercina, which was found in 10 of 32 investigated oak stands. In addition, P.... (More)
This thesis investigated the occurrence of soilborne species of the plant pathogenic genus Phytophthora in southern Swedish oak forests and their possible involvement in southern Swedish oak decline. The emphasis was on the impact of P. quercina on Quercus robur in acid forest soils. Several different methods, including screening for Phytophthora in oak forest soils, greenhouse experiments with seedlings grown in soils inoculated with Phytophthora, and field studies of mature oaks growing in Phytophthora-infested stands, were used. The results showed that Phytophthora species occur in southern Swedish oak forests. The most frequently recovered species was P. quercina, which was found in 10 of 32 investigated oak stands. In addition, P. cactorum and P. cambivora (mating type A2) were recovered from one stand each. The soil conditions at the sites from which Phytophthoras were recovered ranged from mesic sediments to moraines, with clayey to silty textures and with pH(BaCl2) in the rhizosphere soil between 3.5 and 5.0. In greenhouse studies, P. quercina and P. cactorum were found to infect and cause substantial damage to roots of Q. robur seedlings grown in acid forest soils under a mesic water regime. The presence of the natural soil microflora did not hinder the pathogens from infecting and damaging the roots. In addition, significant differences in live fine-root length were found between healthy mature oaks and declining mature oaks growing in stands infested with P. quercina. No such difference was found between trees growing in non-infested stands. The impact of the pathogen on mature oaks seemed to depend on tree vitality, site and climatic conditions. Despite the significant reductions in live fine-root length of both seedlings and mature oaks, few differences in above-ground growth (measured only in seedlings) and leaf nutrient concentrations were detected. However, it seems likely that continuous root infections, with subsequent replacement of roots, will deplete the carbohydrate stores in the plant and cause reductions in the production of new root and shoot tissue as well as in the production of secondary metabolites. This may result in an increased susceptibility of the tree to further pathogen infections as well as to other stress factors. A weak association was found between the occurrence of P. quercina and the vitality of oak stands (determined from estimates of crown defoliation). The impact of soil type on carbon allocation patterns in plants and its consequences for the extent of root damage caused by P. quercina is discussed, as well as the influence of abiotic and biotic factors on the aggressiveness of Phytophthora, susceptibility of oak and subsequent disease development. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Press, Malcolm, Department of Animal and Plant Sciences, Univeristy of Sheffield, UK
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Växtekologi, Plant ecology, microbial competition, carbon allocation, nutrients, water availability, soil chemistry, mature oaks, seedlings, acid soils, Phytophthora quercina, Quercus robur
pages
126 pages
publisher
Ulrika Jönsson, Department of Ecology (Plant Ecology and Systematics), Ecology Building, Lund University, 223 62 Lund,
defense location
Blå Hallen, Department of Ecology, Ecology Building, Lund
defense date
2004-11-19 10:00
ISBN
91-7105-214-3
language
English
LU publication?
yes
id
f6f617ed-59f9-448d-aba2-4bd5b44d4980 (old id 467479)
date added to LUP
2007-09-05 09:44:40
date last changed
2016-09-19 08:45:14
@phdthesis{f6f617ed-59f9-448d-aba2-4bd5b44d4980,
  abstract     = {This thesis investigated the occurrence of soilborne species of the plant pathogenic genus Phytophthora in southern Swedish oak forests and their possible involvement in southern Swedish oak decline. The emphasis was on the impact of P. quercina on Quercus robur in acid forest soils. Several different methods, including screening for Phytophthora in oak forest soils, greenhouse experiments with seedlings grown in soils inoculated with Phytophthora, and field studies of mature oaks growing in Phytophthora-infested stands, were used. The results showed that Phytophthora species occur in southern Swedish oak forests. The most frequently recovered species was P. quercina, which was found in 10 of 32 investigated oak stands. In addition, P. cactorum and P. cambivora (mating type A2) were recovered from one stand each. The soil conditions at the sites from which Phytophthoras were recovered ranged from mesic sediments to moraines, with clayey to silty textures and with pH(BaCl2) in the rhizosphere soil between 3.5 and 5.0. In greenhouse studies, P. quercina and P. cactorum were found to infect and cause substantial damage to roots of Q. robur seedlings grown in acid forest soils under a mesic water regime. The presence of the natural soil microflora did not hinder the pathogens from infecting and damaging the roots. In addition, significant differences in live fine-root length were found between healthy mature oaks and declining mature oaks growing in stands infested with P. quercina. No such difference was found between trees growing in non-infested stands. The impact of the pathogen on mature oaks seemed to depend on tree vitality, site and climatic conditions. Despite the significant reductions in live fine-root length of both seedlings and mature oaks, few differences in above-ground growth (measured only in seedlings) and leaf nutrient concentrations were detected. However, it seems likely that continuous root infections, with subsequent replacement of roots, will deplete the carbohydrate stores in the plant and cause reductions in the production of new root and shoot tissue as well as in the production of secondary metabolites. This may result in an increased susceptibility of the tree to further pathogen infections as well as to other stress factors. A weak association was found between the occurrence of P. quercina and the vitality of oak stands (determined from estimates of crown defoliation). The impact of soil type on carbon allocation patterns in plants and its consequences for the extent of root damage caused by P. quercina is discussed, as well as the influence of abiotic and biotic factors on the aggressiveness of Phytophthora, susceptibility of oak and subsequent disease development.},
  author       = {Jönsson Belyazid, Ulrika},
  isbn         = {91-7105-214-3},
  keyword      = {Växtekologi,Plant ecology,microbial competition,carbon allocation,nutrients,water availability,soil chemistry,mature oaks,seedlings,acid soils,Phytophthora quercina,Quercus robur},
  language     = {eng},
  pages        = {126},
  publisher    = {Ulrika Jönsson, Department of Ecology (Plant Ecology and Systematics), Ecology Building, Lund University, 223 62 Lund,},
  school       = {Lund University},
  title        = {Phytophthora and Oak Decline - Impact on Seedlings and Mature Trees in Forest Soils},
  year         = {2004},
}