Ericoid mycorrhizal fungi are common root associates of a Mediterranean ectomycorrhizal plant (Quercus ilex)

Mycorrhiza samples of neighbouring Quercus ilex and Erica arborea plants collected in a postcutting habitat were processed to see whether plants differing in mycorrhizal status harbour the same root endophytes. Three experiments were performed in parallel: (i) isolation, identification and molecular characterization of fungi from surface-sterilized roots of both plant species; (ii) re-inoculation of fungal isolates on axenic E. arborea and Q. ilex seedlings; (iii) direct inoculation of field-collected Q. ilex ectomycorrhizas onto E. arborea seedlings. About 70 and 150 fungal isolates were obtained from roots of Q. ilex and E. arborea, respectively. Among them, Oidiodendron species and five cultural morphotypes of sterile isolates formed typical ericoid mycorrhizas on E. arborea in vitro. Fungi with such mycorrhizal ability were derived from both host plants. Isolates belonging to one of these morphotypes (sd9) also exhibited an unusual pattern of colonization, with an additional extracellular hyphal net. Ericoid mycorrhizas were also readily obtained by direct inoculation of E. arborea seedlings with Q. ilex ectomycorrhizal tips. Polymerase chain-restriction fragment length polymorphism and random amplified polymorphic DNA analyses of the shared sterile morphotypes demonstrate, in the case of sd9, the occurrence of the same genet on the two host plants. These results indicate that ericoid mycorrhizal fungi associate with ectomycorrhizal roots, and the ecological significance of this finding is discussed.     

Diversity of saproxylic basidiomycetes in Quercus ilex woodlands of central and insular Greece

The sclerophyllous forests of Quercus ilex (holm oak) possess a unique position in earth’s biosphere, existing only in countries of the Mediterranean basin. However, very little information exists about mushrooms associated with holm oak in east Mediterranean, including Greece, where Q. ilex appears mostly in relict forests and fragmented stands. A pertinent long-term investigation was undertaken in selected Q. ilex dominated habitats of Crete, Andros, Naxos and Ikaria islands (Aegean Archipelago) as well as in mountains of Attica. Specimens of xylotrophic basidiomycetes were collected and identified. As a result, 74 species were recorded; among them Hemimycena cephalotricha, Hyphoderma cremeoalbum, Hyphodontia radula, Irpex litschaueri, Mycena algeriensis, Phanerochaete martelliana, Phloeomana alba and Phlebia unica constitute new records for the Greek mycobiota, while 68 species are reported for the first time on Q. ilex in Greece. Moreover, the presence of Fomitiporia mediterranea on this host was evidenced through ITS sequencing, and comments are made about its relationship to F. punctata and F. pseudopunctata. The importance of findings is discussed in conjunction with their environmental value; five species could be assigned in the “Species of Special Interest” categories, and other five polypores are proposed as suitable indicators for Q. ilex habitat assessment and conservation.     

秦岭辛家山林区锐齿栎外生菌根真菌多样性

以秦岭辛家山林区锐齿栎为研究对象,通过野外调查结合形态学和分子生物学方法,观察和鉴定与其共生的外生菌根真菌。结果确定了3种子囊菌和48种担子菌,分属于10科14属,其中毛革菌属Tomentella是优势类群,丝伞盖属1 Inocybe 1、Russula persicina、毛革菌属1 Tomentella 1、毛革菌属2 Tomentella 2、块菌属Tuber、绒盖牛肝菌属Xerocomus是常见种,其余都为稀有种。两样地锐齿栎外生菌根真菌除丰富度指数外,Simpson指数、Shannon指数以及Pielou均匀度指数差异不显著;Jaccard相似性指数和Sorenson相似性指数分别为0.1154和0.2069。     

Transpiration and stomatal behaviour of Quercus ilex plants during the summer in a Mediterranean carbon dioxide spring

Variations in the water relations and stomatal response of Quercus ilex were analysed under field conditions by comparing trees at two locations in a Mediterranean environment during two consecutive summers (1993 and 1994). We used the heat-pulse velocity technique to estimate transpirational water use of trees during a 5 month period from June to November 1994. At the end of sap flow measurements, the trees were harvested, and the foliage and sapwood area measured. A distinct environmental gradient exists between the two sites with higher atmospheric CO₂ concentrations in the proximity of a natural CO₂ spring. Trees at the spring site have been growing for generations in elevated atmospheric CO₂ concentrations. At both sites, maximum leaf conductance was related to predawn shoot water potential. The effects of water deficits on water relations and whole-plant transpiration during the summer drought were severe. Leaf conductance and water potential recovered after major rainfall in September to predrought values. Sap flow, leaf conductance and predawn water potential decreased in parallel with increases in hydraulic resistance, reaching a minimum in mid-summer. These relationships are in agreement with the hypothesis of the stomatal control of transpiration to prevent desiccation damage but also to avoid ‘runaway embolism’. Trees at the CO₂ spring underwent less reduction in hydraulic resistance for a given value of predawn water potential. The decrease in leaf conductance caused by elevated CO₂ was limited and tended to be less at high than at low atmospheric vapour pressure deficit. Mean (and diurnal) sap flux were consistently higher in the control site trees than in the CO₂ spring trees. The degree of reduction in water use between the two sites varied among the summer periods. The control site trees had consistently higher sap flow at corresponding values of either sapwood cross-sectional area or foliage area. Larger trees displayed smaller differences than smaller trees, between the control and the CO₂ spring trees. A strong association between foliage area and sapwood cross-sectional area was found in both the control and the CO₂ spring trees, the latter supporting a smaller foliage area at the corresponding sapwood stem cross-sectional area. The specific leaf area (SLA) of the foliage was not influenced by site. The results are discussed in terms of the effects of elevated CO₂ on plant water use at the organ and whole-tree scale.     

Seasonal and annual variation of carbon exchange in an evergreen Mediterranean forest in southern France

We present 9 years of eddy covariance measurements made over an evergreen Mediterranean forest in southern France. The goal of this study was to quantify the different components of the carbon (C) cycle, gross primary production (GPP) and ecosystem respiration (R_eco), and to assess the effects of climatic variables on these fluxes and on the net ecosystem exchange of carbon dioxide. The Puéchabon forest acted as a net C sink of ?254 g C m^?2 yr^?1, with a GPP of 1275 g C m^?2 yr^?1 and a R_eco of 1021 g C m^?2 yr^?1. On average, 83% of the net annual C sink occurred between March and June. The effects of exceptional events such the insect‐induced partial canopy defoliation that occurred in spring 2005, and the spring droughts of 2005 and 2006 are discussed. A high interannual variability of ecosystem C fluxes during summer and autumn was observed but the resulting effect on the annual net C budget was moderate. Increased severity and/or duration of summer drought under climate change do not appear to have the potential to negatively impact the average C budget of this ecosystem. On the contrary, factors affecting ecosystem functioning (drought and/or defoliation) during March–June period may reduce dramatically the annual C balance of evergreen Mediterranean forests.     

Estimation of Mediterranean forest transpiration and photosynthesis through the use of an ecosystem simulation model driven by remotely sensed data

Aim This paper investigates the use of an ecosystem simulation model, FOREST‐BGC, to estimate the main ecophysiological processes (transpiration and photosynthesis) of Mediterranean coastal forest areas using remotely sensed data. Location Model testing was carried out at two protected forest sites in central Italy, one of which was covered by Turkey oak (Circeo National Park) and the other by holm‐oak (Castelporziano Estate). Methods At both sites, transpiration and photosynthesis measurements were collected in the field during the growing seasons over a four‐year period (1999 and 2001 for the Turkey oak; 1997, 1999 and 2000 for the holm‐oak). Calibration of the model was obtained through combining information derived from ground measurements and remotely sensed data. In particular, remote sensing estimates of the Leaf Area Index derived from 1 × 1‐km NOAA AVHRR Normalized Difference Vegetation Index data were used to improve the adaptation of the model to local forest conditions. Results The results indicated different strategies regarding water use efficiency, ‘water spending’ for Turkey oak and ‘water saving’ for holm‐oak. The water use efficiency for the holm‐oak was consistently higher than that for the Turkey oak and the relationship between VPD and WUE for the holm‐oak showed a higher coefficient of determination (R² = 0.9238). Comparisons made between the field measurements of transpiration and photosynthesis and the model estimates showed that the integration procedure used for the deciduous oak forest was effective, but that there is a need for further studies regarding the sclerophyllous evergreen forest. In particular, for Turkey oak the simulations of transpiration yielded very good results, with errors lower than 0.3 mm H₂O/day, while the simulation accuracy for photosynthesis was lower. In the case of holm‐oak, transpiration was markedly overestimated for all days considered, while the simulations of photosynthesis were very accurate. Main conclusions Overall, the approach offers interesting operational possibilities for the monitoring of Mediterranean forest ecosystems, particularly in view of the availability of new satellite sensors with a higher spatial and temporal resolution, which have been launched in recent years.     

Altitudinal differences in UV absorbance,UV reflectance and related morphological traits of Quercus ilex and Rhododendron ferrugineum in the Mediterranean region

We studied the variations in different physiological parameters associated with UV-B radiation defense: UV-B radiation absorbance, UV-visible spectral reflectance, carotenoids concentration, leaf thickness, SLW (specific leaf weigth) and trichome density in Quercus ilex growing at 200 and 1200 m and Rhododendron ferrugineum growing at 2200 m. We examined the role of these parameters as protection mechanisms in an altitudinal gradient of increasing UV radiation in northern Catalonia and in sun and shade leaves. The concentration of UV-B radiation absorbing pigments was 15% higher in sun leaves of Q. ilex at 1200 m than in those from 200 m altitude. Sun leaves of R. ferrugineum presented concentrations three times higher than those of Q. ilex. Reflectance ranged between 5% (in the region 300–400 nm) and 12% (in the region 280–300 nm). The variation of reflectance with altitude followed an inverse trend respect to absorbance in the 280–300 nm region, with higher values the lower the altitude, but in the 300–400 nm region, reflectance of the lower site was the lowest. In both species and altitudes sun leaves presented higher concentrations of UV-B radiation absorbing pigments and UV reflectance than shade leaves. Quercus ilex trees of the higher location presented higher NDPI (Normalized Difference Pigment Reflectance Index) values, indicating higher carotenoids/chlorophyll a ratio. Actual measurements of carotenoid/chlorophyll a ratio confirmed this pattern. The photochemical reflectance index (PRI) presented higher values the higher the location indicating lower photosynthetic radiation-use efficiency. Specific leaf weight (SLW) and leaf thickness were larger in Q. ilex trees of higher location than in those of lower location. In both sites, sun leaves also presented larger SLW values than shade leaves. Adaxial leaf hair density in sun leaves was significantlly higher in the lower location. UV absorption and linked morphological traits (SLW, leaf thickness measured in Q. ilex) presented the larger differences among studied plants at different altitudes and seem to be the dominant UV protecting mechanisms.     

The combined effects of a long‐term experimental drought and an extreme drought on the use of plant‐water sources in a Mediterranean forest

Vegetation in water‐limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species‐specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long‐term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long‐term experimental drought shifted water uptake toward deeper (10–35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought‐affected plants. This study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions.