Rhizoculture model to mitigate environmental impacts of greenhouse gases (ghg) and diffuse contaminationfocus on carbon, phosphorus and nitrogen in soils of forests and agroecosystems

Resumen

Agriculture and forestry traditionally focus on improving plant growth traits based on a plant-centric 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 (increasing production costs and diffuse contamination). This view may also have limited our understanding of mutualistic symbioses of plants assuming that the main role of nonphotosynthetic symbionts is to mobilize the nutrients, and being plants the dominant agents of the symbiotic relationship. In response to these issues, this thesis 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 ecological intensification of the roots and rhizosphere in agro-ecosystems and forests. After review the evolutionary and ecological dynamics of ectomycorrhizas and lichens, this rhizo-centric approach can be illustrated using the lichenic model, because some authors proposes that the lichenic fungi rather 'farm' the photobionts under 'controlled parasitism'. In a similar way, this thesis proposes to explore a ground-breaking hypothesis suggesting that some ectomycorrhizal fungi, such as truffles, could modify the soil environment to 'farm their host plants' under a controlled parasitic relationship. After monitored truffle cultures and their natural habitats, this thesis confirms that the truffle brûlés -productive spots of Tuber melanosporum and T. aestivum- show an ecological intensification of the rhizosphere of the host plants. This ecological engineering process would be related with (i) the “paradox of calcium” (i.e., Ca2+ and its salts are simultaneously nutrients and stressors for the plants) that would explain a dominance of mycorrhizal fungi over plants based on inducing a Ca[pH]-mediated chlorosis to the host plants; and (ii) decreased soil contents of the total carbonate (through ECM fungal rock-eating activity) and total organic carbon (presumably aimed to modify the ratios of symbiotic/saprophytic soil communities). Soil fauna, such as earthworms and microarthropods, also participate in the ecological engineering processes inside the brûlé. Comparable patterns could be performed by other ectomycorrhizal fungi, such as Tuber brumale, T. oregonense, T. pseudoexcavatum, T. indicum and mat-fungi species of Piloderma, Hysterangium and Ramaria. The brûlé model would provide the conceptual bases to introducing the rhizoculture approach, aimed to the ecological intensification of roots and rhizosphere in agriculture and forestry, that would allow to manage N-P-C-water loops in the soil, through: the handling of Ca2+ salts (by liming), mycorrhizal rock-eating activity, soil organic matter (to increase the ratio symbiotic/saprophytes microorganisms through livestock and biomass control), N-P-water availability and recycling (by smart use of aquaculture and organic waste), C sequestration and soil physical properties (through liming, and soil microorganisms and fauna). The rhizoculture could significantly decrease the high cost and associated diffuse pollution of the application of fertilizers; as well as it could 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. The results of this thesis have been published or disemminated through 17 contributions: 8 articles (2007-2014) in journals indexed in the JCR list (3 in Q1, 3 in Q2, 1 in Q3 and 1 in Q4, quartiles); 3 chapters of international books (2012; 2014; 2017); 3 communications in international congresses (2010; 2015a; 2015b); 1 seminars cycle (2012-2015) presented in OSU and 2 institutions in Oregon, University of Parma, University of Montpellier SupAgro, and University TUBerlin; and 2 proposals for research H2020 projects (2017; 2018) have been led by the UPM, which have been presented in separate European calls for Horizon 2020.