Miguel Ángel Casermeiro

Influence of scrubs on runoff and sediment loss in soils of Mediterranean climate

Abstract Scrubland communities are the most common plant communities in eroded areas with Mediterranean climate. These protect the soil in different ways including the interception of raindrops (which lowers their erosive capacity) and the provision of organic carbon (necessary for the formation of organomineral aggregates). Vegetation were analysed and rainfall simulations performed in 29 natural plots in areas of significant erosion in the Madrid (Spain) region. The results show that plant cover is the main factor reducing surface runoff and the movement of sediments. Vegetation structure is also important, with pluri-stratified communities offering more protection against water erosion than mono-stratified communities. The plant growth forms were also found to be influential. Nanophanerophytes as Rosmarinus officinalis were the most efficient of those studied. Biodiversity did not seem to be important in soil protection in the studied area.

Soil factors that influence the fruiting of Tuber melanosporum (black truffle)

Although soil is one of the factors in the biology of Tuber melanosporum (black truffle of Perigord), which has been the subject of much study, there are few quantitative analyses relating to its effects on carpophore production. The aim of this work is to establish the statistical relationship between T. melanosporum productivity in 20 soil surface horizons and their conventional soil properties (granulometric texture, pH, calcareous fractions, organic carbon, total nitrogen, exchangeable cations). The study area is situated in the centre of the Iberian Peninsula under a Mediterranean climate. Statistical analysis shows that the collective influence of these conventional soil features is low, as principal component analysis explains only 27% of the variance in T. melanosporum production. However, a high percentage of active limestone (calcium carbonate extractable with ammonium oxalate) accounts for 40% of the variance in T. melanosporum production. Active limestone is very important to T. melanosporum because it regulates soil pH and exchangeable Ca2+ availability and participates in the organisation and maintenance of the soil structure; it also plays a role in the truffle’s nutrition. These results obtained for active limestone may be of use in truffle cultivation.

Bryophyte-Cyanobacteria Associations during Primary Succession in Recently Deglaciated Areas of Tierra del Fuego (Chile)

Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g−1 bryo. d−1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g−1 bryo. d−1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition.

Effect of active carbonate, exchangeable calcium, and stoniness of soil on Tuber melanosporum carpophore production

Abstract In the present study, the active carbonate soil concentration explained 43% of the variance in Tuber melanosporum production. This carbonate is also associated with other soil variables, such as pH, exchangeable Ca2+ content, and stoniness abundance, all of which affect the successful productivity of T. melanosporum carpophores. Moreover, active carbonate and exchangeable Ca2+ participate in the maintenance of the soils structure and in fungus nutrition. Statistical analysis shows that active carbonate accounted for 42% of the variance in exchangeable Ca2+ concentration, and the exchangeable Ca2+ abundance explained 20% of the variance in carpophore production. In addition, a significant correlation was found between carbonate concentration and surface stoniness. Finally, abundance of surface stoniness explained 24% of the variance in T. melanosporum carpophore production. We suggest that studies should be conducted on the effects of amendments in truffle culture.

Climate factors mediate soil respiration dynamics in Mediterranean agricultural environments: an empirical approach

Soil CO2 emissions, the result of soil respiration processes, may be essential in climate change modelling. The complex phenomenon of soil respiration is regulated by a range of mainly climate-related environmental factors. We tested the latest published empirical models in a field experiment in an agricultural soil under Mediterranean conditions. Soil respiration was monitored biweekly with a portable infrared gas analyser, and climate features were monitored for 1 year (2010–11). An additional rewetting assay (watering the soil) was done at the end of the experiment in summer when the soil water content was dry. We tested different approaches to represent the simple effect of climate factors on soil respiration and found Gaussian models to be the best. We also tested the most recent models designed to represent the synergic effects of climate factors, and our modification of the Martin and Bolstad model showed the best coefficient of determination. The results suggest that linear approaches and the use of a fixed Q10 value should be revised to represent climate and soil respiration relations, especially in high-variability environments where soil respiration variability is controlled by soil temperature and moisture interactions, while precipitation pulses induce CO2 emission peaks. Finally, our results showed that the influence of soil temperature and moisture on soil respiration is lower under Mediterranean conditions than in temperate climate types.

Sodium chloride accumulation in glycophyte plants with cyanobacterial symbionts.

We have found a novel group of plants that appear to obligately accumulate salt (sodium chloride) although the level in their environment is low. The group is taxonomically diverse including angiosperms (Gunnera spp.), gymnosperms (Cycas) and a fern (Azolla species) but all of them form a symbiosis with a cyanobacterium (blue-green alga) that carries out nitrogen fixation, a rare occurrence in plants. The functional basis for the high salt contents is not clear and, despite the high internal salt levels, the plants are unable to grow in high salt environments.