Dataset Information

Soil microbial responses to nitrogen addition in arid ecosystems.

ABSTRACT: The N cycle of arid ecosystems is influenced by low soil organic matter, high soil pH, and extremes in water potential and temperature that lead to open canopies and development of biological soil crusts (biocrusts). We investigated the effects of N amendment on soil microbial dynamics in a Larrea tridentata-Ambrosia dumosa shrubland site in southern Nevada USA. Sites were fertilized with a NO3-NH4 mix at 0, 7, and 15 kg N ha(-1) y(-1) from March 2012 to March 2013. In March 2013, biocrust (0-0.5 cm) and bulk soils (0-10 cm) were collected beneath Ambrosia canopies and in the interspaces between plants. Biomass responses were assessed as bacterial and fungal SSU rRNA gene copy number and chlorophyll a concentration. Metabolic responses were measured by five ecoenzyme activities and rates of N transformation. By most measures, nutrient availability, microbial biomass, and process rates were greater in soils beneath the shrub canopy compared to the interspace between plants, and greater in the surface biocrust horizon compared to the deeper 10 cm soil profile. Most measures responded positively to experimental N addition. Effect sizes were generally greater for bulk soil than biocrust. Results were incorporated into a meta-analysis of arid ecosystem responses to N amendment that included data from 14 other studies. Effect sizes were calculated for biomass and metabolic responses. Regressions of effect sizes, calculated for biomass, and metabolic responses, showed similar trends in relation to N application rate and N load (rate × duration). The critical points separating positive from negative treatment effects were 88 kg ha(-1) y(-1) and 159 kg ha(-1), respectively, for biomass, and 70 kg ha(-1) y(-1) and 114 kg ha(-1), respectively, for metabolism. These critical values are comparable to those for microbial biomass, decomposition rates and respiration reported in broader meta-analyses of N amendment effects in mesic ecosystems. However, large effect sizes at low N addition rates indicate that arid ecosystems are sensitive to modest increments in anthropogenic N deposition.

SUBMITTER: Sinsabaugh RL

PROVIDER: S-EPMC4536368 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Soil microbial responses to nitrogen addition in arid ecosystems.

Sinsabaugh Robert L RL Belnap Jayne J Rudgers Jennifer J Kuske Cheryl R CR Martinez Noelle N Sandquist Darren D

Frontiers in microbiology 20150814

The N cycle of arid ecosystems is influenced by low soil organic matter, high soil pH, and extremes in water potential and temperature that lead to open canopies and development of biological soil crusts (biocrusts). We investigated the effects of N amendment on soil microbial dynamics in a Larrea tridentata-Ambrosia dumosa shrubland site in southern Nevada USA. Sites were fertilized with a NO3-NH4 mix at 0, 7, and 15 kg N ha(-1) y(-1) from March 2012 to March 2013. In March 2013, biocrust (0-0. ...[more]

PMID: 26322030

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Project description:This research investigates the impact of long-term nitrogen (N) addition on fluvo-aquic and black soils in north China, with a focus on soil microbial communities and enzyme activities. In each site, there were three N fertilization treatments, i.e., control, moderate-N, and high-N. Phospholipid Fatty Acid Analysis was employed to analyze the microbial community composition, and enzyme activities related to N, carbon (C), and phosphorus (P) cycling were assessed. The results showed that increasing N fertilization levels led to higher soil organic carbon (SOC) and total N (TN) concentrations, indicating enhanced nutrient availability. N fertilization reduced soil pH across both soils, with a more pronounced acidification effect observed in the black soil. Across both soils, N addition increased maize yield, but the higher crop yield was attained in moderate-N rate compared with high-N rate. Microbial community composition analysis revealed that N fertilization induced shifts in the relative abundances of specific microbial groups. The black soil exhibited pronounced shifts in the microbial groups compared to the fluvo-aquic soil, i.e., decreased fungal abundance and fungi: bacteria ratio in response to N input. In addition, the application of N fertilizer led to an elevated ratio of gram-positive to gram-negative (GP:GN) bacteria, but this effect was observed only in black soil. N fertilization had an impact on the enzyme activities related to C, N, and P cycling in both soil types, but black soil showed more pronounced changes in enzyme activities. Permutational multivariate analysis of variance indicated that soil types rather than N fertilization mediated the response of the soil microbial community and enzyme activities. Partial least square path modeling demonstrated that soil pH was the only key driver impacting soil microbial groups and enzyme activities in both soils. In conclusion, our findings highlighted that N fertilization exerted more pronounced impacts on soil biochemical properties, microbial community composition, and enzyme activities in black soil furthermore, moderate N rate resulted in higher crop productivity over high N rate.

Project description:Tremendous amounts of nitrogen (N) fertilizer have been added to arable lands, often resulting in substantial effects on terrestrial ecosystems, including soil acidification, altered enzyme activities and changes in microbial community composition. Soil microbes are the major drivers of soil carbon (C) and N cycling; therefore, understanding the response of microbial communities to elevated N inputs is of significant importance. This study was carried out to investigate the influences of different N fertilization rates (0, 182, and 225 kg ha-1 representing control, low, and high N supply for each crop season for summer maize and winter wheat) on soil biochemical attributes, extracellular enzyme activities, and the microbial community composition in a winter wheat-summer maize rotation cropping system in north-central China. The results showed that N addition significantly decreased the soil pH in both the wheat and maize seasons. Microbial biomass N (MBN) decreased following N fertilization in the wheat season, while the opposite trend in MBN was observed in the maize season. Response ratio analysis showed that the activities of enzymes involved in C, N, and phosphorus cycling were significantly enhanced under N enrichment in both the wheat and maize seasons, and higher enzyme activities were noted in the high N addition treatment than in the low N addition treatment. A linear increase in fungal abundance with the N addition gradient was observed in the wheat season, whereas the fungal abundance increased and then decreased in the maize season. The bacterial abundance showed an increased and then decreased trend in response to the N addition gradient in both the wheat and maize crop seasons. Moreover, the partial least squares path model (PLS-PM) analysis showed that soil pH and soil organic carbon (SOC) were the most important soil variables, causing shifts in the soil bacteria. Furthermore, compared with the N-cycling enzymes, the C-cycling enzymes were significantly affected by the soil pH and SOC. Taken together, these results suggest that the effect of N addition on enzyme activities was consistent in both crop seasons, while the effects on MBN and microbial community composition to N addition were highly variable in the two crop seasons. Moreover, N fertilization-induced changes in the soil chemical properties such as soil acidity and SOC played a substantial role in shaping the microbial community.

Project description:Background:Soil microbial communities and their associated enzyme activities play key roles in carbon cycling in terrestrial ecosystems. Soil microbial communities are sensitive to resource availability, but the mechanisms of microbial regulation have not been thoroughly investigated. Here, we tested the mechanistic relationships between microbial responses and multiple interacting resources. Methods:We examined soil carbon properties, soil microbial community structure and carbon-related functions under nitrogen addition and plant inputs removal (litter removal (NL), root trench and litter removal (NRL)) in a pure Larix principis-rupprechtii plantation in northern China. Results:We found that nitrogen addition affected the soil microbial community structure, and that microbial biomass increased significantly once 100 kg ha-1 a-1 of nitrogen was added. The interactions between nitrogen addition and plant inputs removal significantly affected soil bacteria and their enzymatic activities (oxidases). The NL treatment enhanced soil microbial biomass under nitrogen addition. We also found that the biomass of gram-negative bacteria and saprotrophic fungi directly affected the soil microbial functions related to carbon turnover. The biomass of gram-negative bacteria and peroxidase activity were key factors controlling soil carbon dynamics. The interactions between nitrogen addition and plant inputs removal strengthened the correlation between the hydrolases and soil carbon. Conclusions:This study showed that nitrogen addition and plant inputs removal could alter soil enzyme activities and further affect soil carbon turnover via microbial regulation. The increase in soil microbial biomass and the microbial regulation of soil carbon both need to be considered when developing effective sustainable forest management practices for northern China. Moreover, further studies are also needed to exactly understand how the complex interaction between the plant and below-ground processes affects the soil microbial community structure.

Dataset Information

Soil microbial responses to nitrogen addition in arid ecosystems.

Publications

Soil microbial responses to nitrogen addition in arid ecosystems.

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