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We used a nonintrusive field experiment carried out at six sites -Wales (UK), Denmark (DK), the Netherlands (NL), Hungary (HU), Sardinia (Italy -IT), and Catalonia (Spain -SP) -along a climatic and latitudinal gradient to examine the response of plant species richness and primary productivity to warming and drought in shrubland ecosystems. The warming treatment raised the plot daily temperature by ca. 1 1C, while the drought treatment led to a reduction in soil moisture at the peak of the growing season that ranged from 26% at the SP site to 82% in the NL site. During the 7 years the experiment lasted (1999)(2000)(2001)(2002)(2003)(2004)(2005), we used the pin-point method to measure the species composition of plant communities and plant biomass, litterfall, and shoot growth of the dominant plant species at each site. A significantly lower increase in the number of species pin-pointed per transect was found in the drought plots at the SP site, where the plant community was still in a process of recovering from a forest fire in 1994. No changes in species richness were found at the other sites, which were at a more mature and stable state of succession and, thus less liable to recruitment of new species. The relationship between annual biomass accumulation and temperature of the growing season was positive at the coldest site and negative at the warmest site. The warming treatment tended to increase the aboveground net primary productivity (ANPP) at the northern sites. The relationship between annual biomass accumulation and soil moisture during the growing season was not significant at the wettest sites, but was positive at the driest sites. The drought treatment tended to reduce the ANPP in the NL, HU, IT, and SP sites. The responses to warming were very strongly related to the Gaussen aridity index (stronger responses the lower the aridity), whereas the responses to drought were not. Changes in the annual 2563 aboveground biomass accumulation, litterfall, and, thus, the ANPP, mirrored the interannual variation in climate conditions: the most outstanding change was a decrease in biomass accumulation and an increase in litterfall at most sites during the abnormally hot year of 2003. Species richness also tended to decrease in 2003 at all sites except the cold and wet UK site. Species-specific responses to warming were found in shoot growth: at the SP site, Globularia alypum was not affected, while the other dominant species, Erica multiflora, grew 30% more; at the UK site, Calluna vulgaris tended to grow more in the warming plots, while Empetrum nigrum tended to grow less. Drought treatment decreased plant growth in several studied species, although there were some species such as Pinus halepensis at the SP site or C. vulgaris at the UK site that were not affected. The magnitude of responses to warming and drought thus depended greatly on the differences between sites, years, and species and these multiple plant responses may be expected to have consequences at ecosystem and community level. Decreases in biodiver...

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Summary The results of a single publication stating that terrestrial plants emit methane has sparked a discussion in several scientific journals, but an independent test has not yet been performed. Here it is shown, with the use of the stable isotope 13C and a laser‐based measuring technique, that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% (0.4 ng g−1 h−1) of the previously published values. Data presented here indicate that the contribution of terrestrial plants to global methane emission is very small at best. Therefore, a revision of carbon sequestration accounting practices based on the earlier reported contribution of methane from terrestrial vegetation is redundant.

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.

summary Three perennial grass species, Lolium perenne L., Agrottis capillaris L. and Festuca uvina L., were homogeneously labelled in phytotrons with 14CO2 at two CO2 concentrations (350 and 700μl l−1). Plants were grown under two nitrogen regimes: one with a minor addition of 8 kg N ha−1, the other with an addition of 278 kg N ha−1. Carbon allocation over the different compartments of the plant/soil systems was measured: shoots, roots, rhizosphere soil (soil solution, microbial biomass and soil residue), and bulk soil. Elevated CO., increased total net 14C recovery in all species by 14%, and significantly enhanced the below‐ground 14C allocation by 26%, this enhancement was 24%, 39% and 21 % for root, rhizosphere soil and bulk soil, respectively. Within the rhizosphere soil, the 14C amounts in the soil solution (+ 69%) and soil residue (+ 49%,) increased significantly. Total microbial biomass‐C in the rhizosphere soil was also increased (15 %) by the elevated CO2 treatment, but only in proportion to the increased root mass. No interactions were observed between the elevated CO2, and N treatments. The N treatment increased total net 14C recovery by more than 300% and 14C was preferentially allocated to the shoots, leading to a significant increase in shoot‐to‐root ratio. However, N fertilization also increased (+111%) the absolute amount of 14C in soil. The three species behaved differently, but no interactions were observed between CO2 treatment and plant species. These results show that elevated CO2 induces an increased C input into soil for all three grass species at both N levels. However, the highest absolute amounts were found in the soils of the fastest growing species and at the highest N level.

We investigated fungal species-specific responses of ectomycorrhizal (ECM) Scots pine (Pinus sylvestris) seedlings on growth and nutrient acquisition together with mycelial development under ambient and elevated CO 2 . Each seedling was associated with one of the following ECM species: Hebeloma cylindrosporum, Laccaria bicolor, Suillus bovinus, S. luteus, Piloderma croceum, Paxillus involutus, Boletus badius, or non-mycorrhizal, under ambient, and elevated CO 2 (350 or 700 ml l À1 CO 2 ); each treatment contained six replicates. The trial lasted 156 days. During the final 28 days, the seedlings were labeled with 14 CO 2 . We measured hyphal length, plant biomass, 14 C allocation, and plant nitrogen and phosphorus concentration. Almost all parameters were significantly affected by fungal species and/or CO 2 . There were very few significant interactions. Elevated CO 2 decreased shoot-to-root ratio, most strongly so in species with the largest extraradical mycelium. Under elevated CO 2 , ECM root growth increased significantly more than hyphal growth. Extraradical hyphal length was significantly negatively correlated with shoot biomass, shoot N content, and total plant N uptake. Root dry weight was significantly negatively correlated with root N and P concentration. Fungal sink strength for N strongly affected plant growth through N immobilization. Mycorrhizal fungal-induced progressive nitrogen limitation (PNL) has the potential to generate negative feedback with plant growth under elevated CO 2 .

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