Specific root length (SRL, m g71 ) is probably the most frequently measured morphological parameter of fine roots. It is believed to characterize economic aspects of the root system and to be indicative of environmental changes. The main objectives of this paper were to review and summarize the published SRL data for different tree species throughout Europe and to assess SRL under varying environmental conditions. Meta-analysis was used to summarize the response of SRL to the following manipulated environmental conditions: fertilization, irrigation, elevated temperature, elevated CO 2 , Al-stress, reduced light, heavy metal stress and physical disturbance of soil. SRL was found to be strongly dependent on the fine root classes, i.e. on the ectomycorrhizal short roots (ECM), and on the roots 50.5 mm, 51 mm, 52 mm and 1 -2 mm in diameter SRL was largest for ECM and decreased with increasing diameter. Changes in soil factors influenced most strongly the SRL of ECM and roots 50.5 mm. The variation in the SRL components, root diameter and root tissue density, and their impact on the SRL value were computed. Meta-analyses showed that SRL decreased significantly under fertilization and Al-stress; it responded negatively to reduced light, elevated temperature and CO 2. We suggest that SRL can be used successfully as an indicator of nutrient availability to trees in experimental conditions.

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Summary• The aim here was to separately assess mycorrhizal fungal and plant responses under elevated atmospheric CO 2 , and to test a mycocentric model that assumes that increased carbon availability to the fungus will not automatically feed back to enhanced plant growth performance.• Meta-analyses were applied across independent studies. Responses were compared in ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi, and ECM and AM plants.• Responses of both mycorrhizal fungi and mycorrhizal plants to elevated CO 2 were significantly positive. The response ratio for ECM fungi was 1.34 (an increase of 34%) and for AM fungi 1.21 (21%), indicating a significantly different response. The response ratio for ECM plants was 1.26, similar to that of AM plants (1.25). Fractional colonization proved to be an unsuitable fungal parameter. Evidence was found for the mycocentric view in ECM, but not in AM systems.• Fungal identity and plant identity were important parameters that affected response ratios. The need for better descriptors of fungal and plant responses is emphasized.

Although increasing concentrations of atmospheric CO 2 are predicted to have substantial impacts on plant growth and functioning of ecosystems, there is insufficient understanding of the responses of belowground processes to such increases. We investigated the effects of different dark septate root endophytic (DSE) fungi on growth and nutrient acquisition by Pinus Under elevated CO 2 , the biomass of seedlings inoculated with DSE fungi was on average 17% higher than in control seedlings. Simultaneously, below-ground respiration doubled or trebled, and as a consequence carbon use efficiency by the DSE fungi significantly decreased. Shoot N concentration decreased on average by 57% under elevated CO 2 and was lowest in seedlings inoculated with S. vaccinii. Carbon gain by the seedlings despite reduced shoot N concentration indicates that DSE fungi increase plant nutrient use efficiency and are therefore more beneficial to the plant under elevated CO 2 .