Inmaculada Valverde-Asenjo

Calcareous amendments to soils to eradicate Tuber brumale from T. melanosporum cultivations: a multivariate statistical approach

Calcareous amendments are being used in Tuber melanosporum truffle plantations in attempts to eradicate Tuber brumale. However, there are no studies available which provide soil analysis and statistical data on this topic. We studied 77 soil samples to compare the values for carbonates, pH and total organic carbon in T. brumale truffières with the values for T. melanosporum truffières on contaminated farms and in natural areas. Statistical analyses indicate that the concentrations of active carbonate and total carbonate in the soil are significantly higher in T. brumale truffières than in T. melanosporum truffières, but that there are no significant differences in pH and total organic carbon. We conclude that liming would not suppress T. brumale ectomycorrhizas in contaminated T. melanosporum farms, and calcareous amendments do not therefore seem be a means of eradicating T. brumale in these farms.

Influence of Edaphic Factors on Edible Ectomycorrhizal Mushrooms: New Hypotheses on Soil Nutrition and C Sinks Associated to Ectomycorrhizae and Soil Fauna Using the Tuber Brûlé Model

Fungi can strongly acidify their immediate soil environment and can cause a change in the equilibrium of soil carbonates. The Tuber melanosporum brule is an interesting biological model for studying soil reaction (pH) and decarbonation–recarbonation soil processes associated with ectomycorrhizal plants and soil fauna communities. Over the past 10 years ,we have observed that (1) a high concentration of active carbonate and exchangeable Ca2+ in the soil favors T. melanosporum fruiting body production and larger brules, (2) the amount of active carbonate is significantly higher and the total carbonate is significantly lower inside the T. melanosporum brule than outside the brule, (3) T. melanosporum ectomycorrhizae impact biodiversity and soil quality, and (4) the calciferous glands of Lumbricidae have an impact on soil reaction and carbonate availability in the brules. Here we propose new hypotheses on ectomycorrhizal fungal ecology, soil biology, and inorganic C soil sinks, suggesting that (1) the model that best explains the cause and effect of all brule observations is a feedback process; (2) this model assumes that T. melanosporum’s ability to modify soil properties has a direct impact on plant nutrition and degree of plant mycorrhization, and this hypothesis could have a considerable impact from the evolutionary standpoint of ectomycorrhizal fungi; and (3) the integrated action of T. melanosporum and/or other ectomycorrhizal fungal populations, and earthworms, could be of major importance in the cycling and sequestration of inorganic C in the soil.

Statistical patterns of carbonates and total organic carbon on soils of Tuber rufum and T. melanosporum (black truffle) brûlés

The ascocarps of several truffle species, such as Tuber rufum, are harvested in T. melanosporum brules; these species reduce T. melanosporum production. Some authors argue that this competition might be due to the evolution of organic matter in the soil. However, soil conditions in brules have yet to be clarified, and most studies on T. melanosporum fail to supply statistical data. We propose a study of 40 soils to compare the values for total organic carbon (TOC), pH, and carbonates inside the brules with the values for the outer edges of the same brules, where T. rufum ascocarps are collected. A principal component analysis relates the soils from the inner brules with high active carbonate content and soils outside the brules with high TOC and total carbonate content. ANOVA analyses indicate that the mean concentration of active carbonate, total CO32–, and % active/total carbonate differ significantly depending on soil location, but there are no significant differences for pH and TOC. These results lead us to propose a new hypothesis: T. melanosporum mycelia may solubilise active carbonate ( 50 μm) inside the brules; however the environmental conditions of the brules could favour a secondary carbonate precipitation with a net increase in active carbonate. This increase would counterbalance carbonate losses from leaching, which would in turn favour T. melanosporum mycelia, suggesting a feedback process.

Impact of vineyard abandonment and natural recolonization on metal content and availability in Mediterranean soils

Abandonment of vineyards after uprooting has dramatically increased in last decades in Mediterranean countries, often followed by vegetation expansion processes. Inadequate management strategies can have negative consequences on soil quality. We studied how the age and type of vegetation cover and several environmental characteristics (lithology, soil properties, vineyard slope and so on) after vineyard uprooting and abandonment contribute to the variation patterns in total, HAc (acetic acid-method, HAc) and EDTA-extractable (ethylenediaminetetraacetic acid-method) concentrations of Cd, Cu, Pb and Zn in soils. We sampled 141 points from vineyards and abandoned vineyard Mediterranean soils recolonized by natural vegetation in recent decades. The contribution of several environmental variables (e.g. age and type of vegetation cover, lithology, soil properties and vineyard slope) to the total and extractable concentrations of metals was evaluated by canonical ordination based on redundancy analysis, considering the interaction between both environmental and response variables. The ranges of total metal contents were: 0.01-0.15 (Cd), 2.6-34 (Cu), 6.6-30 (Pb), and 29-92mgkg(-1) (Zn). Cadmium (11-100%) had the highest relative extractability with both extractants, and Zn and Pb the lowest. The total and EDTA-extractable of Cd, Pb and Zn were positively related to the age of abandonment, to the presence of Agrostis castellana and Retama sphaerocarpa, and to the contents of Fe-oxides, clay and organic matter (OM). A different pattern was noted for Cu, positively related to vineyard soils. Soil properties successfully explained HAc-extractable Cd, Cu, Pb and Zn but the age and type of vegetation cover lost significance. Clay content was negatively related to HAc-extractable Cu and Pb; and OM was positively related to HAc-Cd and Zn. In conclusion, the time elapsed after vineyard uprooting, and subsequent land abandonment, affects the soil content and availability of metals, and this impact depended on the colonizing plant species and soil properties.

Enzyme activity indicates soil functionality affectation with low levels of trace elements

The use of the soil can alter its functionality and influence the (bio)availability of any contaminants present. Our study considers two types of agricultural soils, rainfed and olive soils, managed according to conventional practices that apply contaminants directly to the soil (fertilizers, pesticides, fungicides, etc.) and receive contaminants from the atmosphere (traffic, industry, etc.); and a forest soil that is not subject to these agricultural practices. In this scenario, we consider a mixture of 16 trace elements (As, Ba, Be, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Se, Sb, Sn, V and Zn), since their interactions with the soil can produce synergistic and/or antagonistic effects that are not considered in most studies. We studied whether the content and (bio)availability of low concentrations of a mixture of trace elements affect the soil functionality in terms of the activity of some key enzymes We analysed the total, potentially and immediately available fractions, the soil parameters and soil enzyme activity. The results show that the functionality of the soils studied was affected despite the low concentrations of trace elements. The highest concentrations of total trace elements and available fractions were found in forest soils compared to the other two uses. Soil enzyme activity is best explained by the potentially available fraction of a mixture of trace elements and physico-chemical soil variables. In our study, pH, total nitrogen, organic carbon and fine mineral particles (silt and clay) had an influence on soil enzyme activity and the (bio)available fractions of trace elements.

Towards Integrated Understanding of the Rhizosphere Phenomenon as Ecological Driver: Can Rhizoculture Improve Agricultural and Forestry Systems?

Agriculture and forestry traditionally focus on improving plant growth traits based on an anthropocentric point of view. This paradigm has led to global problems associated to soil overexploitation such as soil losses, reductions of the C stock in soils, and the generalized use of fertilizers, which particularly increases the costs of production and pollution treatment. This view may also have limited our understanding of mutualistic symbioses of plants and microorganisms assuming that the main role of non-photosynthetic symbionts is to mobilize the nutrients that are necessary for plant growth and development, and being plants the dominant agents of the symbiotic relationship. In response to these issues, this chapter offers an alternative approach taking advantage of the “rhizo-centric” point of view, where non-photosynthetic partners are the main protagonists in play; and secondly, it builds a multidisciplinary body of knowledge that could be called “rhizoculture”, which includes techniques focussing on the intensification of the development and activity of roots, mycorrhizae, and other symbiotic and free living rhizosphere organisms. In short, rhizoculture may lead to decrease plant production dependence on fertilization and provides other benefits to agriculture, forestry, and the environment. Within this conceptual framework, the first objective of this book chapter is to explore whether there is a “paradox of calcium salts” (i.e., Ca2+ and its salts are simultaneously nutrients, promoters, and stressors for the host plants) that would explain a dominance of mycorrhizal fungi over plants based on inducing a Ca(pH)–mediated chlorosis to the host plants. If this paradigm shifting hypothesis were finally fully verified, it would provide conceptual bases to reconsider our current technologies in agriculture and forestry by introducing the “rhizocultural” approach, based on the management of roots (introducing alternative cultural practices), Ca2+ salts (using liming and other techniques), rock-eating mycorrhizae, organic matter, and the soil microbiome (increasing the presence of symbiotic microorganisms against saprophytes), N and P contents (by aquaculture and smart recycling of organic waste), and the physical properties of the soil (by the activity of soil symbiotic microorganisms and soil fauna, such as ants, termites and earthworms). The development of such new technological approaches in rhizoculture would significantly decrease the high cost and associated pollution of the application of fertilizers and phytochemicals; as well as it would increase soil C stocks, improve the resilience of agricultural and forest systems to environmental disturbances, such as climate change, and enhance food production and security.