Abiootiliste ja biootiliste tegurite väikeseskaalalise varieerumise mõju metsa alustaimestiku struktuurile ja koosseisule

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Taimed „tajuvad“ neid vahetult ümbritsevat keskkonda ja suudavad oma kasvu vastavalt sellele kohandada. Näiteks on teada, et taimed suudavad suunata oma juuri toitaineterikkasse laiku. Samuti sõltub taime kasv sümbiontsetest arbuskulaar- mükoriissetest (AM) seentest, mis aitavad neil mullast toitaineid omastada. Metsa alustaimestikus kasvavad taimed on oluliselt mõjutatud ka puittaimede poolt, mille varis ümbritsevat keskkonda suuresti kujundab. Hoolimata senisest teadmisest ei ole siiani selge, kuivõrd olulised on eelpool toodud faktorid alustaimestiku produktiivsuse, paljunemisedukuse ja liigilise koosseisu mõjutamisel. Nimetatud lünkade täitmiseks meie teadmistes valisin mudelsüsteemiks vana salukuusiku, mille põõsarindes domineerib harilik sarapuu ja alustaimestik on väga liigirikas. Tulemused näitasid, et väikesel skaalal mõjutab toitainetesisaldus ja AM seente ohtrus mullas rohttaimede maapealset biomassi. Leitud muster viitab sellele, et paranenud ressursside kättesaadavuse kasutavad taimed ära valguskonkurentsis edukamad olemiseks. Samas ei mõjutanud mulla toitainetesisaldus ega AM seente ohtrus taimede maa-alust biomassi. Suure toitainetesisalduse juures suudavad taimed neid edukalt mullast omastada ning toitainete madala kättesaadavuse korral suudavad nad „veenda“ AM seeni oma juuri asustama ning tõhusamalt toitaineid trantsportima. Sellise mehhanismi olemasolu näitas kaudselt ka salukuusikule iseloomuliku taimeliigi idandite parem kasv koos AM seentega olukorras, kus toitaineid mullas nappis. Laia ökoloogilise amplituudiga taimeliigi idandite kasv aga ei sõltunud oluliselt AM seente ohtrusest ei toitainetevaesel ega rikkal mullal. Lisaks näitasid tulemused, et metsa alustaimestiku taimeliikide idanemine ja idandite kasv sõltub oluliselt varisekihi paksusest ja tüübist— kuuse varis pärssis neid arenguetappe, samas kui sarapuu varis mõjus pigem soodustavalt. Varise mõju oli ilmne ka looduses — sarapuu all, kus oli kolm korda õhem varisekiht, leidus alustaimestikus poole rohkem liike kui kuuse all. Selle doktoritöö tulemused aitavad meil paremini mõista metsa alustaimestiku dünaaamikat. Suurenenud teadmiste hulka aitab säilitada metsadele iseloomulikku taimede liigirikkust kuna suure enamiku metsas kasvavatest taimeliikidest leiab alustaimestikust.Plants can perceive their close surrounding and adapt to those conditions. For example, it is known that plants can locate their roots into nutrient rich areas; and increase growth in the presence of symbiotic micro-organisms like arbuscular mycorrhizal (AM) fungi that help plants to acquire nutrients from soil. In addition, plants in forest understorey are highly influenced by overstorey and this can occur through the effects of tree and shrub litter. Despite this knowledge, we have still little information about the relative importance of abiotic and biotic factors (e.g. the ones listed above) in determining understorey productivity, regeneration success and species richness in natural ecosystem. Boreonemoral spruce forest with hazel sub-canopy and species-rich understorey was selected as a model system to fill abovementioned gaps in our knowledge. I found that high availability of soil nutrients and abundance of AM fungi enhances plant aboveground biomass, which implies to the importance of light competition among understorey plants. At the same time, soil nutrient content and the abundance of AM fungi did not influence plant belowground biomass. Plants seem to be able to acquire more nutrients directly from the soil when nutrient level is high or alternatively via symbiotic relationship with AM fungi when nutrient content is low. This mechanism seems to operate also at regeneration phase as I found that seedling growth of a characteristic forest plant species benefited from the presence of AM fungi when soil nutrient content was low. At the same time, seedling growth of a plant species occurring in a wide range of habitats was not influenced by AM fungi despite of soil nutrient content. In addition, the regeneration of the plant species in the understorey was highly influenced by presence and type of overstorey litter as I found that hazel litter is more beneficial to seedling growth and emergence than spruce litter. The effect of different factors, especially the effect of litter, leads to spatial differentiation in species composition in the forest understorey as I recorded twice as high herbaceous species richness under hazel compared to spruce. Results of this thesis lead to better understanding of forest understorey dynamics. Improved knowledge enables to preserve the species richness characteristic to forests as most of the of plant species growing in forests can be found in the understorey

Species-Specific Effects of Woody Litter on Seedling Emergence and Growth of Herbaceous Plants

The effect of litter on seedling establishment can influence species richness in plant communities. The effect of litter depends on amount, and also on litter type, but relatively little is known about the species-specific effects of litter. We conducted a factorial greenhouse experiment to examine the effect of litter type, using two woody species that commonly co-occur in boreonemoral forest—evergreen spruce (Picea abies), deciduous hazel (Corylus avellana), and a mixture of the two species—and litter amount—shallow (4 mm), deep (12 mm) and leachate—on seedling emergence and biomass of three understorey species. The effect of litter amount on seedling emergence was highly dependent on litter type; while spruce needle litter had a significant negative effect that increased with depth, seedling emergence in the presence of hazel broadleaf litter did not differ from control pots containing no litter. Mixed litter of both species also had a negative effect on seedling emergence that was intermediate compared to the single-species treatments. Spruce litter had a marginally positive (shallow) or neutral effect (deep) on seedling biomass, while hazel and mixed litter treatments had significant positive effects on biomass that increased with depth. We found non-additive effects of litter mixtures on seedling biomass indicating that high quality hazel litter can reduce the negative effects of spruce. Hazel litter does not inhibit seedling emergence; it increases seedling growth, and creates better conditions for seedling growth in mixtures by reducing the suppressive effect of spruce litter, having a positive effect on understorey species richness

Hedgerows increase the diversity and modify the composition of arbuscular mycorrhizal fungi in Mediterranean agricultural landscapes

Sustainable agriculture is essential to address global challenges such as climate change and biodiversity loss. Hedgerows enhance aboveground biodiversity and provide ecosystem services, but little is known about their impact on soil biota. Arbuscular mycorrhizal (AM) fungi are one of the key components of belowground biodiversity. We compared the diversity and composition of AM fungal communities at four farmland sites located in Central Spain, where 132 soil samples in total were collected to assess soil physical and chemical properties and the AM fungal communities. We compared the richness (number of AM fungal taxa), taxonomic, functional, and phylogenetic diversity, and structure of the AM fungal communities across three farmland habitat types, namely hedgerows, woody crops (olive groves and vineyard), and herbaceous crops (barley, sunfower, and wheat). Our results showed positive efects of hedgerows on most diversity metrics. Almost 60% of the AM fungal taxa were shared among the three farmland habitat types. Hedgerows increased AM fungal taxonomic richness (31%) and alpha diversity (25%), and especially so compared to herbaceous crops (45% and 28%, respectively). Hedgerows harbored elevated proportions of AM fungi with non-ruderal life-history strategies. AM fungal communities were more similar between hedgerows and woody crops than between hedgerows and adjacent herbaceous crops, possibly because of diferences in tillage and fertilization. Unexpectedly, hedgerows reduced phylogenetic diversity, which might be related to more selective associations of AM fungi with woody plants than with herbaceous crops. Overall, the results suggest that planting hedgerows contributes to maintain belowground diversity. Thus, European farmers should plant more hedgerows to attain the goals of the EU Biodiversity Strategy for 2030.Ministerio de Educación y Formación ProfesionalComunidad de Madrid, REMEDINALUniversidad de AlcaláFondo Europeo de Desarrollo Regional-FEDEREstonian Research Counci

Metabarcoding of soil environmental DNA to estimate plant diversity globally

IntroductionTraditional approaches to collecting large-scale biodiversity data pose huge logistical and technical challenges. We aimed to assess how a comparatively simple method based on sequencing environmental DNA (eDNA) characterises global variation in plant diversity and community composition compared with data derived from traditional plant inventory methods. MethodsWe sequenced a short fragment (P6 loop) of the chloroplast trnL intron from from 325 globally distributed soil samples and compared estimates of diversity and composition with those derived from traditional sources based on empirical (GBIF) or extrapolated plant distribution and diversity data. ResultsLarge-scale plant diversity and community composition patterns revealed by sequencing eDNA were broadly in accordance with those derived from traditional sources. The success of the eDNA taxonomy assignment, and the overlap of taxon lists between eDNA and GBIF, was greatest at moderate to high latitudes of the northern hemisphere. On average, around half (mean: 51.5% SD 17.6) of local GBIF records were represented in eDNA databases at the species level, depending on the geographic region. DiscussioneDNA trnL gene sequencing data accurately represent global patterns in plant diversity and composition and thus can provide a basis for large-scale vegetation studies. Important experimental considerations for plant eDNA studies include using a sampling volume and design to maximise the number of taxa detected and optimising the sequencing depth. However, increasing the coverage of reference sequence databases would yield the most significant improvements in the accuracy of taxonomic assignments made using the P6 loop of the trnL region

Global diversity and distribution of nitrogen-fixing bacteria in the soil

Our knowledge of microbial biogeography has advanced in recent years, yet we lack knowledge of the global diversity of some important functional groups. Here, we used environmental DNA from 327 globally collected soil samples to investigate the biodiversity patterns of nitrogen-fixing bacteria by focusing on the nifH gene but also amplifying the general prokaryotic 16S SSU region. Globally, N-fixing prokaryotic communities are driven mainly by climatic conditions, with most groups being positively correlated with stable hot or seasonally humid climates. Among soil parameters, pH, but also soil N content were most often shown to correlate with the diversity of N-fixer groups. However, specific groups of N-fixing prokaryotes show contrasting responses to the same variables, notably in Cyanobacteria that were negatively correlated with stable hot climates, and showed a U-shaped correlation with soil pH, contrary to other N-fixers. Also, the non-N-fixing prokaryotic community composition was differentially correlated with the diversity and abundance of N-fixer groups, showing the often-neglected impact of biotic interactions among bacteria

Data from: Nematode community responses to range-expanding and native plant communities in original and new range soils

Many plant species expand their range to higher latitudes in response to climate change. However, it is poorly understood how biotic interactions in the new range differ from interactions in the original range. Here, in a mesocosm experiment, we analyze nematode community responses in original and new range soils to plant communities with either 1) species native in both the original and new range, 2) range-expanding species related to these natives (related range-expanders), or 3) range-expanders without native congeneric species in the new range (unrelated range-expanders). We hypothesized that nematode community shifts between ranges are strongest for unrelated range-expanders and minimal for plant species that are native in both ranges. As a part of these community shifts, we hypothesized that range-expanders, but not natives, would accumulate fewer root-feeding nematodes in their new range compared to their original range. Analyses of responses of nematodes from both original and new ranges and comparison between range-expanders with and without close relatives have not been made before. Our study reveals that none of the plant communities experienced evident nematode community shifts between the original and new range. However, in soils from the new range, root-feeding nematode communities of natives and related range-expanders were more similar than in soils from the original range, whereas the nematode community of unrelated range-expanders was distinct from the communities of natives and related range-expanders in soils from both ranges. The abundances of root-feeding nematodes were comparable between the original and new range for all plant communities. Unexpectedly, unrelated range-expanders overall accumulated most root-feeding nematodes, whereas related range-expanders accumulated fewest. We conclude that nematode communities associated to native and range-expanding plant species differ between the original and the new range, but that range-expanding plant species do not accumulate fewer root-feeding nematodes in their new than in their original range

Nematode_data_wilschutetal

File contains nematode counts (per 100 g dry weight soil) of the major nematode feeding types and several root-feeding nematode families and genera, and relative counts of root-feeding nematode groups (per gram of root)

Nematode community responses to range-expanding and native plant communities in original and new range soils

Many plant species expand their range to higher latitudes in response to climate change. However, it is poorly understood how biotic interactions in the new range differ from interactions in the original range. Here, in a mesocosm experiment, we analyze nematode community responses in original and new range soils to plant communities with either (a) species native in both the original and new range, (b) range-expanding species related to these natives (related range expanders), or (c) range expanders without native congeneric species in the new range (unrelated range expanders). We hypothesized that nematode community shifts between ranges are strongest for unrelated range expanders and minimal for plant species that are native in both ranges. As a part of these community shifts, we hypothesized that range expanders, but not natives, would accumulate fewer root-feeding nematodes in their new range compared to their original range. Analyses of responses of nematodes from both original and new ranges and comparison between range expanders with and without close relatives have not been made before. Our study reveals that none of the plant communities experienced evident nematode community shifts between the original and new range. However, in soils from the new range, root-feeding nematode communities of natives and related range expanders were more similar than in soils from the original range, whereas the nematode community of unrelated range expanders was distinct from the communities of natives and related range expanders in soils from both ranges. The abundances of root-feeding nematodes were comparable between the original and new range for all plant communities. Unexpectedly, unrelated range expanders overall accumulated most root-feeding nematodes, whereas related range expanders accumulated fewest. We conclude that nematode communities associated with native and range-expanding plant species differ between the original and the new range, but that range-expanding plant species do not accumulate fewer root-feeding nematodes in their new than in their original range.</p