Factors affecting ectomycorrhizal roots and rhizosphere in silver birch stands
Date
2011-05-23
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Abstract
Mineraaltoitainete, eelkõige lämmastiku kättesaadavus on peamine metsaökosüsteemi produktiivsust ja süsiniku salvestumist limiteeriv tegur. Doktoritöö põhieesmärk oli (I) analüüsida arukase (Betula pendula Roth.) imijuurte morfoloogilisi adaptatsioone ja risosfääriefekti erinevates kasvukohatingimustes; (II) välja selgitada puude vanuse mõju imijuurte morfoloogiale ja risosfääriefekti avaldumisele seoses puu mineraalse toitumusega.
Kaasiku kasvukoht (jänesekapsa kasvukohatüüp, endine põllumaa ja rekultiveeritud karjäär) ning puu vanus avaldasid olulist mõju nii imijuurte morfoloogiale kui ka risosfääriefekti avaldumisele. Imijuurte eripind ja eripikkus olid suuremad väiksema lehelämmastiku, seega halvema lämmastikutoitumuse korral nii endistel põllumaadel kui ka metsamaal kasvavates kaasikutes. Kase imijuurte morfoloogia dünaamika oli sarnane nii happelisel metsamaal kui ka lubjakivirikkal karjääripuistangul kasvavate puistute vanuseridades, kusjuures muutused imijuurte morfoloogias toimusid kiiremini nooremas eas. Puu vanusega kahanesid imijuurte eripind ja eripikkus, samuti lehtede eripind ja lämmastikukontsentratsioon. Seega olid kiiret kasvu, kõrget efektiivsust ja füsioloogilist aktiivsust näitavad lehe- ja juureparameetrid suuremad nooremates puistutes ning võib järeldada, et lehtede ja imijuurte morfoloogia dünaamika puistu arengu vältel on kooskõlas. Mükoriisa seenpartneri mütseelitüüp (exploration type) mõjutas imijuurte morfoloogiat oluliselt.
Risosfääriefekt oli seda suurem (risosfääribaktereid toetati seda enam), mida happelisem (bakteritele ebasoodsam) oli kasvukoha muld ja mida suurem oli imijuurte endi lämmastikusisaldus. Risosfääri hapestamine toimus, kui kasvukoha mulla pH(KCl)>5.
Antud doktoritöös hinnati esmakordselt arukase ektomükoriissete imijuurte morfoloogiliste parameetrite varieeruvuse piire ning analüüsiti ektomükoriissete imijuurte morfoloogiliste adaptatsioonide funktsionaalset rolli erinevates kasvukohtades ja seoses puistute vanusega. Käesoleva töö tulemused aitavad püstitada uusi hüpoteese juurte ja risosfääri adaptatsioonimehhanismide edasiseks analüüsiks ja on kasutatavad erinevate keskkonnamõjude, sealhulgas muutuva maakasutuse tagajärgede prognoosimisel arukaasikutes.
Limited nutrient acquisition from soil is a key process limiting productivity in boreal forest, and nutrition strategies change during stand development. The overall objective of the doctoral thesis was (i) to find and quantify the response of ectomycorrhizal (EcM) root morphology and rhizosphere effect of silver birch (Betula pendula) to different site conditions, (ii) to ascertain tree-age-related changes in EcM root morphology and rhizosphere effect in relation to nutrient status of silver birch. EcM morphology and rhizosphere effect were influenced by site properties, especially by previous land use (natural forest, forest on previous agricultural land, and forest in reclaimed opencast oil shale mine area) as well as tree age. High EcM root SRL and SRA can be considered as root N nutrition stress indicators for silver birch – both increased in case of low leaf N%. Ontogenetic changes in EcM root morphology were similar in natural forest and reclaimed oil shale mine area chronosequence despite the very different site conditions. Age-related changes in EcM root morphology occurred faster in younger age, before the age of 5–10 years. The functional balance between physiology and morphology of leaves and roots appeared during stand development in natural forest – the specific leaf area and specific EcM root area as well as leaf N decreased simultaneously with tree age, probably as a result of down-regulation of growth. Molecular analyses revealed 33 EcM fungal species among the dominant morphotypes in three age classes of natural forest chronosequence. The exploration type of EcM fungi affected EcM root morphology significantly. The rhizosphere effect was higher by lower pH and higher root N% on agricultural land. Rhizosphere acidification occurred in the studied stands when bulk soil pH(KCl) > 5. The results of the thesis pro¬vide a cognitive basis for formulating new hypotheses concerning fine root and rhizosphere processes under changing environmental conditions.
Limited nutrient acquisition from soil is a key process limiting productivity in boreal forest, and nutrition strategies change during stand development. The overall objective of the doctoral thesis was (i) to find and quantify the response of ectomycorrhizal (EcM) root morphology and rhizosphere effect of silver birch (Betula pendula) to different site conditions, (ii) to ascertain tree-age-related changes in EcM root morphology and rhizosphere effect in relation to nutrient status of silver birch. EcM morphology and rhizosphere effect were influenced by site properties, especially by previous land use (natural forest, forest on previous agricultural land, and forest in reclaimed opencast oil shale mine area) as well as tree age. High EcM root SRL and SRA can be considered as root N nutrition stress indicators for silver birch – both increased in case of low leaf N%. Ontogenetic changes in EcM root morphology were similar in natural forest and reclaimed oil shale mine area chronosequence despite the very different site conditions. Age-related changes in EcM root morphology occurred faster in younger age, before the age of 5–10 years. The functional balance between physiology and morphology of leaves and roots appeared during stand development in natural forest – the specific leaf area and specific EcM root area as well as leaf N decreased simultaneously with tree age, probably as a result of down-regulation of growth. Molecular analyses revealed 33 EcM fungal species among the dominant morphotypes in three age classes of natural forest chronosequence. The exploration type of EcM fungi affected EcM root morphology significantly. The rhizosphere effect was higher by lower pH and higher root N% on agricultural land. Rhizosphere acidification occurred in the studied stands when bulk soil pH(KCl) > 5. The results of the thesis pro¬vide a cognitive basis for formulating new hypotheses concerning fine root and rhizosphere processes under changing environmental conditions.
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Keywords
dissertatsioonid, arukask, risosfäär, imijuured, morfoloogia (biol.), kasvukohad, silver birch, risosphere, sucking roots, morphology, growth sites