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

Plant and Soil (Impact Factor: 3.24). 05/2013; DOI: 10.1007/s11104-013-1779-9

ABSTRACT 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.


Available from: Manuel Delgado-Baquerizo, May 29, 2015
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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.
    Journal of Ecology 07/2014; 102(6). DOI:10.1111/1365-2745.12303 · 5.69 Impact Factor
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    ABSTRACT: It is well-known that vascular plants have species-specific effects on soil properties. However, little is known on how individual species forming biocrusts, communities dominated by lichens, mosses and cyanobacteria that are prevalent in many ecosystems worldwide, affect microbial communities and soil variables related to nutrient cycling.We evaluated the relationship of six biocrust-forming lichens (Buellia epipolia, Diploschistes diacapsis, Fulgensia subbracteata, Psora decipiens, Squamarina cartilaginea and Squamarina lentigera) with microbial abundance and multiple variables associated to soil nitrogen (N), carbon (C) and phosphorus (P) cycling and storage. We also evaluated whether the composition of lichen tissues (contents in C, N, P and polyphenols) is related to the C, N, P availability and microbial abundance in soils. Finally, we assessed what lichen species positively and negatively relate to soil fertility compared to bare ground areas without biocrusts.We found contrasted C, N and P availability, and soil microbial abundance under the different biocrusts-forming lichens. Interestingly, inorganic P and amino acids were the most important factors differentiating lichen microsites. These differences in nutrient availability seem to be related to the C, N and P composition of the lichen tissues. For example, soils under D. diacapsis and P. decipiens, which had the lowest and highest C, N and P contents in their tissues, respectively, had the lowest and highest nutrient availability, respectively. We also found contrasted soil microbes abundance under the different soil lichens. For instance, F. subbracteata and D. diacapsis were negatively related to the abundance of bacteria compared to bare ground areas.Our results support the idea that, as found with vascular plants, biocrust-forming lichens have species-specific effects on soil microbial communities and C, N and P cycling. Thus, continuing considering biocrusts as a unique entity will only add confusion to our knowledge of how they control nutrient availability and microbial abundance in the ecosystems where this key community is prevalent.This article is protected by copyright. All rights reserved.
    Functional Ecology 12/2014; DOI:10.1111/1365-2435.12403 · 4.86 Impact Factor
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    ABSTRACT: Aims Freeze–thaw fluctuation is a natural phenomenon, which is frequently encountered by biological soil crusts (BSCs) in late autumn and early spring in cold deserts. The objective of our study was to investigate the effects of freeze–thaw cycles (FTCs) on the soil nutrient balances, infiltration, and stability of cyanobacterial soil crusts (CSCs) in the temperate desert region. Methods A controlled incubation experiment was carried out to study the effects of diurnal freeze–thaw cycles (FTCs) on total soil carbon (TC), total soil nitrogen (TN), soil TC/TN, hydraulic conductivity, and strength of light and dark cyanobacterial crusts, respectively. Six successive diurnal FTCs were applied as three temperature regimes (i.e., six successive mild FTCs (mild), six successive severe FTCs (severe), three successive mild FTCs followed by three successive severe FTCs (medium)). The experiment intended to simulate natural temperature changes in one of the temperate regions of northern China. Results Compared with dark CSCs cores, light CSCs cores lost a greater proportion of nitrogen. For both crust cores, severe FTCs decreased TC and TN more than mild FTCs. However, TC and TN remained relative constant when CSCs cores were treated with severe FTCs after experiencing mild FTCs. TC and TN of both CSCs cores decreased in the earlier FTCs and then remained stable in the later FTCs. TC/TN increased significantly for light CSCs, but only changed slightly for dark CSCs after successive FTCs. The effects of FTCs on the hydraulic conductivity and strength of CSCs were not consistent with our expectations that FTCs would increase hydrological conductivity and decrease strength. These effects depended on crust type, FTC number, and freeze/thaw intensity. Increase in hydraulic conductivity and decrease in strength only occurred in severe treatment in the dark CSCs during the later FTCs. Conclusions Light CSCs are more sensitive to FTCs than dark CSCs. Mild FTCs decrease less TC and TN than severe FTCs and mostly increase the stability of the CSCs. However, severe FTCs may decrease TC and TN drastically, thereby, degrading the BSCs.
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