Biocrusts control the nitrogen dynamics and microbial functional diversity of semi-arid soils in response to nutrient additions

Plant and Soil (Impact Factor: 2.95). 05/2013; DOI: 10.1007/s11104-013-1779-9


Aims Human activities are causing imbalances in the nutrient cycles in natural ecosystems. However, we have limited knowledge of how these changes will affect the soil microbial functional diversity and the nitrogen (N) cycle in drylands, the biggest biome on Earth. Communities dominated by lichens, mosses and cyanobacteria (biocrusts) influence multiple processes from the N cycle such as N fixation and mineralization rates. We evaluated how biocrusts modulate the effects of different N, carbon (C) and phosphorus (P) additions on theN availability, the dominance of different available N forms and the microbial functional diversity in dryland soils.
Methods Soil samples from bare ground (BG) and biocrust-dominated areas were gathered from the center of Spain and incubated during seven or 21 days under different combinations of N, C and P additions (N, C, P, N + C, N + P, P + C, and C + N + P).
Results The relative dominance of dissolved organic N (DON) and the microbial functional diversity were higher in biocrust than in BG microsites when C or P were added. Changes in the C to N ratio, more than N availability, seem to modulate N transformation processes in the soils studied. In general, biocrusts increased the resilience to N impacts (N, C+N, N+P, C+N+P) of the total available N, ammonium, nitrate and DON when C was present.
Conclusions Our results suggest that biocrusts may buffer the effects of changes in nutrient ratios on microbial functional diversity and DON dominance in dryland soils. Thus, these organisms may have an important role in increasing the resilience of the N cycle to imbalances in C, N and P derived from human activities.

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Available from: Manuel Delgado-Baquerizo
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    • "soil respiration) that only provide an overall estimation of soil activity (Miralles et al., 2012a,b). The evaluation of carbon-substrates utilization by community-level physiological profiles (CLPPs) revealed also that biocrusts have a higher level of functional biodiversity than bare soils and that biocrusts may provide soils with a higher capacity to recover from harmful processes by increasing the heterotrophic microbial diversity (Delgado-Baquerizo et al., 2013). Information about the phylogenetic and functional roles of BSCs and their relationship with the associated soil microbial community is still rather limited. "
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    ABSTRACT: In arid and semiarid areas of the planet, biological soil crusts (BSCs) participate in functions critical to the ecosystem sustainability and are usually located in inter-vegetation spaces. These crusts are structurally and in terms of biomass dominated by mosses and lichens. Associated with them, a great variety of fungi, bacteria, and cyanobacteria have been found. Despite their ecological importance, major details of the functionalities of the microbial communities inhabiting BSCs and the underlying soil are still missing. Here, we explore the biomass, functionality, and protein-based phylogeny of the microbial communities associated with lichen-dominated BSCs under a semiarid climate. Two lichen-dominated BSCs (Fulgensia desertorum -dominated BSC, F-BSC; and Squamarina cartilaginea -dominated BSC, S-BSC) were sampled in a semiarid soil located in South-East Spain. Samples of the BSCs and the underlying soils were collected. The biomass and activity of the microbial community in both BSCs was higher than in the soil underlying them, as estimated by their PLFA content, basal respiration, and enzyme activities. The factor analysis of PLFAs and the putative phylogenetic analysis of the identified proteins indicated scarce differences in the composition of the microbial communities of the two biocrusts at the phylum level. In contrast, community-level physiological profiles (CLPPs) revealed that the microbial communities inhabiting BSCs metabolized substrates differently. The identification of ribulose-1,5 biphosphate carboxylase oxygenase (RuBisCO) peptides points to a specialization in carbon fixation which is carried out by some cyanobacterial species in F-BSC, such as Prochlorothrix hollandica and Microcoleus vaginatus, but not in S-BSC. The structure of the microbial community in the soil underlying each BSC was different, as estimated by factor analysis of PLFAs, but such differences did not correspond to changes in the functional structure, as indicated by the CLPPs. The multidisciplinary approach used in this study revealed remarkable differences between the microbial communities inhabiting F. desertorum and S. cartilaginea -dominated biological crusts, whereas the microbial communities in the soils underlying the two crusts behaved similarly.
    Full-text · Article · Sep 2014 · Soil Biology and Biochemistry
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    • "They are often called ecosystem engineers because they are a key factor of many matter fluxes in their particular ecosystems. They influence the C and N cycles through N-fixation, photosynthetic activity and dust capture (Belnap 2002; Delgado-Baquerizo et al. 2013; Drahorad et al. 2013; Verrecchia et al. 1995), affect the emergence and vitality of both annual and perennial plants (Berkeley et al. 2005; Hernandez and Sandquist 2011; Prasse and Bornkamm 2000; Su et al. 2009) and create favorable habitats for soil fauna (Darby et al. 2010; Liu et al. 2011). Especially in arid and semiarid ecosystems, where water is scarce and usually restricted to a given season, the most important effect on the ecosystem might be the modification of hydrological processes by changing infiltration properties and thereby generating runoff, which ultimately determines many of the aforementioned functions (Chamizo et al. 2012; Kidron et al. 2012; Yair et al. 2011). "
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    ABSTRACT: Biological soil crusts (BSCs) can play an important role in hydrological cycles, especially in dryland ecosystems where the availability of water is limited. Many factors influence the hydrological behavior of BSCs, one of which is the microstructure. In order to describe the influence of the soil microstructure of BSCs on water redistribution, we investigated the change of the pore system of three different successional stages of BSCs, as well as their respective subcrusts in the NW Negev desert, Israel, using 2-dimensional thin sections, as well as non-invasive X-ray 3D computed microtomography (XCMT) and mercury intrusion porosimetry. Our results show that the pore system undergoes significant changes during crust succession. Both the total porosity, as well as the pore sizes significantly increased from cyano- to lichen- to mosscrust and the pore geometry changed from tortuous to straight pore shapes. We introduce two new mechanisms that contribute to the hydrological properties of the BSCs in the NW Negev that impede infiltration: (i) vesicular pores and (ii) a discontinuous pore system with capillary barrier effects, caused by a rapid change of grain sizes due to sand burial. Since both of these mechanisms are present mostly in early stage cyanobacterial crusts and their abundance decreases strongly with succession, it is very likely that they influence BSC hydrology to different extents in the various crust types and that they are partly responsible for differences in runoff in the NW Negev.
    Full-text · Article · Apr 2014 · Biodiversity and Conservation
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    ABSTRACT: 1. Climate change will raise temperatures and modify precipitation patterns in drylands worldwide, affecting their structure and functioning. Despite the recognized importance of soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) as a driver of nutrient cycling in drylands, little is known on how biocrusts will modulate the resistance (i.e., the amount of change caused by a disturbance) of the N cycle in response to climate change.2. Here, we evaluate how warming (ambient vs. ~2.5ºC increase), rainfall exclusion (ambient vs. ~30% reduction of total annual rainfall) and biocrust cover (incipient vs. well-developed biocrusts) affect multiple variables linked to soil N availability (inorganic and organic N and potential net N mineralization rate) and its resistance to climate change during four years in a field experiment. We also evaluate how climate change-induced modifications in biocrust and microbial communities indirectly affect such resistance.3. Biocrusts promoted the resistance of soil N availability regardless of the climatic conditions considered. However, the dynamics of N availability diverged progressively from their original conditions with warming and/or rainfall exclusion, as both treatments enhanced N availability and promoted the dominance of inorganic over organic N. In addition, the increase of fungal: bacterial ratio and the decrease of biocrust cover observed under warming had a negative indirect effect on the resistance of N cycle variables.4. Synthesis. Our results indicate that climate change will have negative direct and indirect (i.e. through changes in biocrust and microbial communities) impacts on the resistance of the N cycle in dryland soils. While biocrusts can play an important role slowing down the impacts of climate change on the N cycle due to their positive and continued effects on the resistance of multiple variables from the N cycle, such change will progressively alter N cycling in biocrust-dominated ecosystems, enhancing both N availability and inorganic N dominance.This article is protected by copyright. All rights reserved.
    Full-text · Article · Jul 2014 · Journal of Ecology
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