Adaptive root foraging strategies along a boreal–temperate forest gradient

The tree root–mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C) : N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root–mycorrhiza–bacteria continuum along climate and soil C : N gradients.Peer reviewe

Süsiniku vood ja varud erivanuselistes arukaasikutes

Võimalike kliimamuutuste tõttu on muutunud tänapäeval aktuaalseks teemaks süsihappegaasi kontsentratsiooni tõus atmosfääris, seejuures pööratakse tähelepanu nii CO2 emissiooni vähendamisele kui ka selle ulatuslikumale sidumisele. Käesolevas doktoritöös hinnati erinevate süsinikuvoogude ja -varude dünaamikat jänesekapsa kasvukohatüübi arukaasikute vanusereas (6-60 a.). Jänesekapsa kasvukohatüübi puistud valiti, kuna need on Eesti metsades väga levinud ja arukaasikud moodustavad selles kasvukohas kasvavatest puistutest veerandi. Töö põhieesmärgid: 1. hinnata puistu maapealset ja maa-alust biomassi ja -produktsiooni, lehestiku parameetreid, ning süsiniku sidumist puude biomassi arukaasikute aegreas; 2. hinnata süsiniku sisendvoogu mulda läbi maapealse varise ; 3. hinnata peenjuurte produktsiooni arukaasikute aegreas ning süsiniku sisendvoogu mulda läbi juurevarise; 4. hinnata mulla süsinikuvaru ning aastast süsiniku emissiooni mullast läbi heterotroofse hingamise; 5. koostada süsiniku bilansid erinevate arenguklasside arukaasikutele. Uuritud jänesekapsa kasvukohatüübi arukaasikute kasvudünaamika oli heas kooskõlas varasemate kasvukäigutabelitega. Mitmes puistus aga ületas aastane jooksev juurdekasv O. Henno (1980) kasvukäigutabeli väärtusi, mis näitab nende metsade kõrget produktsioonivõimet. Töö ühe põhitulemusena selgus, et arukaasikud viljakal kasvukohal on metsaökosüsteemid, mis talletavad süsinikku peamiselt puitunud biomassis, kuna mulla süsinikuvaru vanemates arukaasikutes usaldusväärselt ei suurenenud, st. süsinikku mulda ei akumuleerunud. Vanemates arukaasikutes suurenes puitunud biomassis akumuleerunud süsiniku suhteline osakaal, seda võrreldes mullasüsinikuga. Jämedad juured moodustasid ligikaudu viiendiku puude biomassist ja samas proportsioonis toimus ka süsiniku talletumine juurtesse. Kogu puistu süsinikuvarust oli puude maa-alusesse biomassi seotud märkimisväärne osa (3-28%), see suurenes puistu vanuse suurenedes. Viljakatel muldadel kasvavates arukaasikutes oli peenjuurte osa puistu netoproduktsioonis tagasihoidlik, jäädes kõigil juhtudel alla 10%. Läbi peenjuure varise lisandus aasta jooksul mulda 0,46-0,74 t C ha-1 a-1 süsinikku. Uuritud arukaasikute vanusereas moodustas peenjuurtesse akumuleerunud süsinik 11-25% puude maa-alusesse biomassi seotud süsinikust. Puistu vananedes suurenes süsinikuvoog mulda läbi peenjuurte varise. Aasta jooksul jõudis arukaasikutes läbi maapealse ja maa-aluse varise mulda arvestatavas koguses süsinikku (2,8-3,6 t C ha-1 a-1), kuid mulla orgaanilise süsiniku varu puistu vananedes ei suurenenud. Stabiilne mullasüsiniku sisaldus on seletatav intensiivse heterotroofse mullahingamisega , mis oli samas suurusjärgus, kui aastane süsiniku sisendvoog mulda. Kahe aasta jooksul uurimisaladel läbiviidud mõõtmised näitasid, et aastane heterotroofne mullahingamise voog jäi erivanuselistes puistutes vahemikku 2,9-4,2 t C ha-1 a-1, mis kattis või ületas aastast süsiniku sisendvoogu mulda. Kõikide uuritud puistute süsinikubilansid olid positiivsed, st metsaökosüsteem sidus aasta jooksul oluliselt rohkem süsinikku, kui seda emiteeris. Reeglina vanemates puistutes kasvukiirus väheneb ning sellega ka süsiniku salvestumine biomassi. Uuritud arukaasikute puhul oli aga produktsioon veel ka 45-aastases puistus kõrge ning ainuüksi puude maapealse osa biomassi aastases produktsioonis seoti süsinikku ligikaudu 4 t C ha-1 a-1. Erivanuselised arukaasikud on viljakas kasvukohatüübis süsinikku siduvad metsaökosüsteemid. Aastane seotud süsinikukogus uuritud kaasikutes jäi vahemikku 3,7-4,9 t C ha-1 a-1 , mis seoti valdavalt puude biomassis. Kõik uuritud arukaasikud osutusid efektiivseteks süsiniku akumuleerijateks, sidudes süsinikku peamiselt puude puitunud biomassi. Viljakate kasvukohtade arukaasikutes oli aastas seotud süsiniku kogus samas suurusjärgus puidu aastase juurdekasvuga. Seega peegeldab puistu juurdekasv nendes arukaasikutes ligikaudset aastast süsiniku akumulatsiooni.Owing to the increased anthropogenic emissions of CO2 in world ecosystems and their predicted effects on global climate, carbon (C) cycling is very actual topic around the world. In the present thesis the cycling and accumulation of C was studied in silver birch forest ecosystems. All data presented in the current thesis are based on eight silver birch stands aged between 6 and 60 years. The dynamics of the growth and biomass production of silver birch chronosequence stands was estimated and analysed in consistence with empirical data from earlier yield tables. New knowledge was gained about belowground biomass, fine root production and soil C efflux in birch stands. Carbon accumulation in biomass (above- and belowground biomass of both trees and the undergrowth) as well as in the soil was estimated. The overall aims of the doctoral thesis were: 1. To estimate the biomass and production of silver birch chronosequence stands and carbon accumulation in aboveground and belowground biomass of trees; 2. To estimate annual C input into the soil through aboveground litter; 3. To estimate fine root production in silver birch stands as well as the C flux into the soil through root litter; 4. To estimate soil C storages and the annual C flux from the soil through soil heterotrophic respiration; 5. To sum up all estimated C storages and fluxes in order to compile carbon budgets for silver birch stands of different developmental stages. Carbon budgets were compiled for silver birch chronosequence stands by synthesizing the above- and belowground C pools and fluxes. Total annual net primary production (NPP) of the ecosystems of 7.4, 7.9 and 8.5 t C ha-1 yr-1 was estimated in the young, middle-aged and premature silver birch stands. Net ecosystem production (NEP) was 4.4, 3.7 and 4.9 t C ha-1yr-1 in the young, middle-aged and premature stands, respectively. The C pool in tree biomass increased with increasing stand age, whereas the soil C pool did not depend on stand age; nor did C accumulate in the soil during stand succession. The share of C accumulated in the belowground part in the total stand C storage increased with increasing stand age. As the biomass of the trees was the main carbon sink, a significant share (3-28%) of the total forest carbon pool was accumulated in the belowground part of the stand. Also the C flow through the fine-root litter into the soil increased with increasing stand age. The C accumulation in the fine roots made up 11 to 25% of the total C accumulated in the belowground biomass of the studied birch stands. The annual C efflux from the soil through soil heterotrophic respiration was of the same magnitude as the annual C input into the soil through aboveground and belowground litter. The balance between the soil organic C input and soil heterotrophic respiration is main reason why the soil organic C pool remained stable in the silver birch chronosequence stands. All investigated silver birch stands were acting as effective C sinks and the main C sink was the woody biomass of the trees. In the case of fertile silver birch stands NEP and annual C accumulation in woody biomass were roughly equal. Thus, the woody biomass increment of fertile silver birch stands reflects annual C sequestration in the ecosystem. The topic is relevant since chronosequence studies in birch stands are still rare despite the broad distribution of birches. The novelty of the study is its complex approach: the C dynamics was studied in different forest ecosystem components (e.g. trees, undergrowth, soil etc.), which allowed to compile C budgets for silver birch stands of different ages. Complete estimation of different C fluxes and storages in a chronosequence of silver birch stands with the aim to compile carbon budget has not been dealt with earlier. The presented results are appropriate for developing local C accumulation models of silver birch stands

Biomass production and nitrogen balance of naturally afforested silver birch (Betula pendula Roth.) stand in Estonia

Silver birch ( Roth.) is one of the main pioneer tree species occupying large areas of abandoned agricultural lands under natural succession in Estonia. We estimated aboveground biomass (AGB) dynamics during 17 growing seasons, and analysed soil nitrogen (N) and carbon (C) dynamics for 10 year period in a silver birch stand growing on former arable land. Main N fluxes were estimated and nitrogen budget for 10-year-old stand was compiled. The leafless AGB and stem mass of the stand at the age of 17-years were 94 and 76 Mg ha respectively. The current annual increment (CAI) of stemwood fluctuated, peaking at 10 Mg ha yr at the age of 15 years; the mean annual increment (MAI) fluctuated at around 4â5 Mg ha. The annual leaf mass of the stand stabilised at around 3 Mg ha yr. The stand density decreased from 11600 to 2700 trees ha in the 8- and 17-year-old stand, respectively. The largest fluxes in N budget were net nitrogen mineralization and gaseous N-N emission. The estimated fluxes of NO and N were 0.12 and 83 kg ha yr, respectively; N leaching was negligible. Nitrogen retranslocation from senescing leaves was approximately 45 kg ha, N was mainly retranslocated into stembark. The N content in the upper 0â10 cm soil layer increased significantly (145 kg ha) from 2004 to 2014; soil C content remained stable. Both the woody biomass dynamics and the N cycling of the stand witness the potential for bioenergetics of such ecosystems.Betula pendulaâ1â1â1â1â1â1â1222â1â1â1â

The effect of stump harvesting on tree growth and the infection of root rot in young Norway spruce stands in hemiboreal Estonia

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