Tree roots in a changing world

Globally, forests cover 4 billion hectares or 30% of the Earth's land surface, and 20%-40% of the forest biomass is made up of roots. Roots play a key role for trees: they take up water and nutrients from the soil, store carbon (C) compounds, and provide physical stabilization. Estimations from temperate forests of Central Europe reveal that C storage in trees accounts for about 110 t C ha−1, of which 26 t C ha−1 is in coarse roots and 1.2 t C ha−1 is in fine roots. Compared with soil C, which is about 65 t C ha−1 (without roots), the contribution of the root C to the total belowground C pool is about 42%. Flux of C into soils by plant litter (stemwood excluded) compared with the total soil C pool, however, is relatively small (4.4 t C ha−1 year−1) with the coarse and fine roots each contributing about 20%. Elevated CO2 concentrations and N depositions lead to increased plant biomass, including that of roots. Recent analysis in experiments with elevated CO2 concentrations have shown increases of the forest net primary productivity by about 23%, and, in the case of poplars, an increase of the standing root biomass by about 62%. The turnover of fine roots is also positively influenced by elevated CO2 concentrations and can be increased in poplars by 25%-45%. A recently established international platform for scientists working on woody root processes, COST action E38, allows the exchange of information, ideas, and personnel, and it has the aim to identify knowledge gaps and initiate future collaborations and research activitie

Plant and Soil / Mycorrhizas and soil ecosystem function of co-existing woody vegetation islands at the alpine tree line

Zusammenfassung in deutscher Sprache nicht verf\ufcgbarBackground and aims Picea abies, Pinus mugo and Rhododendron ferrugineum co-exist at the alpine tree line, and can have different mycorrhizal communities. The activity and diversity of mycorrhizal fungi are considered to be important factors in regulation of soil function. Methods At a tree line site and a lower elevation site in the Austrian Alps, the community structure of ectomycorrhiza on Picea abies and Pinus mugo was determined. The activity of surface enzymes was determined on ectomycorrhizal and ericoid mycorrhizal roots. In soils, the activity of a range of enzymes, nitrogen (N) mineralization and biomass decomposition were determined. Results The community structure of the ectomycorrhizal community of Picea abies and Pinus mugo differed strongly, but the average activity of surface enzymes of the ectomycorrhizal communities was similar. A lower root surface enzyme activity was determined on Rhododendron ferrugineum. Soil N-mineralization under Rhododendron ferrugineum was significantly lower than under Picea abies and Pinus mugo. In soil, the activity of a range of enzymes did not differ at the tree line but differed between the tree line and the lower elevation sites. Conclusion The different ectomycorrhizal communities on Picea abies and Pinus mugo and ericoid mycorrhizas on Rhododendron ferrugineum support similar ecosystem functions in soil

Plant and Soil / Overyielding of temperate deciduous tree mixtures is maintained under throughfall reduction

Abstract in deutscher Sprache nicht verf\ufcgbarBackground and aims A changing climate in the future with more severe drought events will affect the conditions for forest growth and vitality. Most knowledge on tree species response to drought is based on monocultures, even though many of the forests in the world consist of mixed stands. We aimed to investigate how trees respond to summer drought when grown in a three species mixture. Methods For two subsequent summers canopy throughfall, and subsequently soil water potential, was reduced using sub-canopy roofs in monocultures and mixtures of Betula pendula, Alnus glutinosa and Fagus sylvatica. Results The overyielding of the mixed stand was not affected by the drought using either above or below ground production, standing fine root biomass or soil respiration as parameters. However, Alnus glutinosa was the most negatively affected when growing in monoculture, whereas this species was less affected when growing in mixture. In contrast, Betula pendula was most negatively affected when growing in mixture. Fagus sylvatica was least affected by the drought and maintained growth over the two years. Conclusions A water demanding species as Alnus glutinosa can perform well in a mixture during drought and not be outcompeted. This is opposite to what is assumed in most models of forest responses to climate change

Potential of Phytoremediation to clean up uranium-contaminated soil with Acacia species

Pollution by depleted uranium (DU) is considered one of the major problems faced by many countries, where this by-product is considered as a major  source of radiotoxic and chemotoxic heavy metal soil pollution. An experiment was designed for uranium uptake from sandy soil treated with different concentration of uranium  by using two species of Acacia  (Acacia albida and A. nelotica ). Results showed there is a difference in the ability of the Acacia seedlings tested to absorb different concentrations of uranium through their roots. Acacia nilotica registered the highest levels of absorption and accumulation of uranium in dry weight of roots in different concentrations (202, 339, 1175, and 1477 µg.g-1 ) respectively of  the concentrations (50, 100, 200, and 500 mgkg-1). Compared to the root of Acacia albida, the absorption of uranium was (60, 54, 133, and 526 µg.g-1) in the concentrations of the same samples. The ability of A. nilotica is better than that of A. albida to uptake uranium from the soil, where 80-90% of the uranium is absorbed by the seedlings, compared to 44-85% in  A. albida. In the case of low concentrations  of uranium (50 and 100 mgkg-1)  A. nilotica seedlings absorbed  about 80-90%  of the original concentration, whereast A. albida absorbed only 44-70% of the same treatment.  In high concentrations (500mgkg-1), we found  that the A. nilotica uptake of 90% of uranium was higher compared to that of  A. albida whose average uptake was about  77%. Also, we found a difference between species and treatment in the remainder of the uranium in the soil. The uranium remaining in the soil at the end of the period of uranium application showed a difference between species and treatments. The uptake of uranium by A. albida was 14-41% while in A. nilotica it it was 58-67%, based upon the concentration in soil solution. In low concentrations (100mg.kg-1) A. albida absorbed only 16%, while A. nilotica absorbed about 67% from the uranium in soil solution. In high concentrations (2000mg.kg-1) of uranium, 23%  was found in A. albida and 66% in A. nilotica. This shows that A. nilotica can uptake uranium from soil solution three times more than A. albida. The  biomass results, the shoot height of  A.nilotica plants decreased with the progression of time during the treatment with high concentrations of uranium, but in low and moderate concentrations (50,100, and 200mg.kg-1) it was less affected than high concentrations (500mg.kg-1). A. albida height was reduced  when treated with (200mg.kg-1)   in all the growth periods, whereas the growth of seedlings gave values less than when treated with the height concentration of uranium (500mg.kg-1) for the two species. Keywords: Phytoremediation,  Depleted Uranium, Acacia albida,  A. Nilotica

Detection of Uranium Contamination in Acacia Cell Sap by Capillary Zone Electrophoresis (CZE) Technique

The  study was carried out to detect uranium level in the cell sap of acacia plant cells, for this purpose callus cultures of Acacia albida was used as well as plants. Cell saps from both callus and plant leaf were taken using Micro capillary syringe and detected using Capillary zone electrophoresis technique. It was shown that using citrate buffer of 3.0pH help in detecting uranium accumulated in the cells. Prospective calculation for the level of uranium uptake showed that 1.64mM is the level of uranium in the leaf cells that had been grown on soil with addition of 500 mg.kg-1 uranyl nitrate for 3 months, while for callus which grown on MS medium with addition of 500 mg/l uranyl nitrate for the same time (3 months), uptake of uranium reached 0.8 mM. The comparison between TXRF analysis of uranium accumulated in plant tissues and CZE efficiency in detecting uranium level in cell sap of both leaves and callus cells, it was shown that both techniques prove that A.albida plants can accumulate uranium with a level double as that taken by callus cells. Keywords : Capillary Zone Electrophoresis, Acacia albida, Uraniu

Elevated CO2 and Tree Species Affect Microbial Activity and Associated Aggregate Stability in Soil Amended with Litter

(1) Elevated atmospheric CO2 (eCO2) may affect organic inputs to woodland soils with potential consequences for C dynamics and associated aggregation; (2) The Bangor Free Air Concentration Enrichment experiment compared ambient (330 ppmv) and elevated (550 ppmv) CO2 regimes over four growing seasons (2005–2008) under Alnus glutinosa, Betula pendula and Fagus sylvatica. Litter from the experiment (autumn 2008) and Lumbricus terrestris were added to mesocosm soils. Microbial properties and aggregate stability were investigated in soil and earthworm casts. Soils taken from the field experiment in spring 2009 were also investigated; (3) eCO2 litter had lower N and higher C:N ratios. F. sylvatica and B. pendula litter had lower N and P than A. glutinosa; F. sylvatica had higher cellulose. In mesocosms, eCO2 litter decreased respiration, mineralization constant (respired C:total organic C) and soluble carbon in soil but not earthworm casts; microbial‐C and fungal hyphal length differed by species (A. glutinosa = B. pendula > F. sylvatica) not CO2 regime. eCO2 increased respiration in field aggregates but increased stability only under F. sylvatica; (4) Lower litter quality under eCO2 may restrict its initial decomposition, affecting C stabilization in aggregates. Later resistant materials may support microbial activity and increase aggregate stability. In woodland, C and soil aggregation dynamics may alter under eCO2, but outcomes may be influenced by tree species and earthworm activity

Lobes on Alnus glutinosa nodules contain a single major ribotype of Frankia

This work investigated the microbial content of nodules from alders to determine how many ribotypes of Frankia were present and which, if any, other bacteria existed within nodes from the nodules. The bacterial content of alder nodules was investigated by 454 sequencing of 16S rDNA genes. Over half of the sequences were from a single ribotype of Frankia, with nearly all other sequences coming from the chloroplast of the host plant, and other sequences (including other ribotypes of Frankia) being at < 1%. It is concluded that a single ribotype of Frankia is the major, although not unique, bacterium present in an individual lobe from an alder nodule

Elevated Atmospheric CO2 Affects Ectomycorrhizal Species Abundance and Increases Sporocarp Production under Field Conditions

Anthropogenic activities during the last century have increased levels of atmospheric CO2. Forest net primary productivity increases in response to elevated CO2, altering the quantity and quality of carbon supplied to the rhizosphere. Ectomycorrhizal fungi form obligate symbiotic associations with the fine roots of trees that mediate improved scavenging for nutrients in exchange for a carbohydrate supply. Understanding how the community structure of ectomycorrhizal fungi is altered by climate change is important to further our understanding of ecosystem function. Betula pendula and Fagus sylvatica were grown in an elevated CO2 atmosphere delivered using free air carbon dioxide enrichment (FACE) under field conditions in the U.K., and Picea abies was grown under elevated CO2 in glass domes in the Czech Republic. We used morphotyping and sequencing of the internal transcribed spacer region of the fungal ribosomal operon to study ectomycorrhizal community structure. Under FACE, un-colonised roots tips increased in abundance for Fagus sylvatica, and during 2006, sporocarp biomass of Peziza badia significantly increased. In domes, ectomycorrhizal community composition shifted from short-distance and smooth medium-distance to contact exploration types. Supply and competition for carbon belowground can influence ectomycorrhizal community structure with the potential to alter ecosystem function