Dataset Information

Grass and forbs respond differently to nitrogen addition: a meta-analysis of global grassland ecosystems.

ABSTRACT: Nitrogen (N) deposition has increased globally and has profoundly influenced the structure and function of grasslands. Previous studies have discussed how N addition affects aboveground biomass (AGB), but the effects of N addition on the AGB of different functional groups in grasslands remain unclear. We conducted a meta-analysis to identify the responses of AGB and the AGB of grasses (AGB_grass) and forbs (AGB_forb) to N addition across global grasslands. Our results showed that N addition significantly increased AGB and AGB_grass by 31 and 79%, respectively, but had no significant effect on AGB_forb. The effects of N addition on AGB and AGB_grass increased with increasing N addition rates, but which on AGB_forb decreased. Although study durations did not regulate the response ratio of N addition for AGB, which for AGB_grass increased and for AGB_forb decreased with increasing study durations. Furthermore, the N addition response ratios for AGB and AGB_grass increased more strongly when the mean annual precipitation (MAP) was 300-600?mm but decreased with an increase in the mean annual temperature (MAT). AGB_forb was only slightly affected by MAP and MAT. Our findings suggest that an acceleration of N deposition will increase grassland AGB by altering species composition.

SUBMITTER: You C

PROVIDER: S-EPMC5431500 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Grass and forbs respond differently to nitrogen addition: a meta-analysis of global grassland ecosystems.

You Chengming C Wu Fuzhong F Gan Youmin Y Yang Wanqin W Hu Zhongmin Z Xu Zhenfeng Z Tan Bo B Liu Lin L Ni Xiangyin X

Scientific reports 20170508 1

Nitrogen (N) deposition has increased globally and has profoundly influenced the structure and function of grasslands. Previous studies have discussed how N addition affects aboveground biomass (AGB), but the effects of N addition on the AGB of different functional groups in grasslands remain unclear. We conducted a meta-analysis to identify the responses of AGB and the AGB of grasses (AGB<sub>grass</sub>) and forbs (AGB<sub>forb</sub>) to N addition across global grasslands. Our results showed ...[more]

PMID: 28484219

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Project description:Background and Aims:Atmospheric nitrogen deposition and natural fire regime suppression are key drivers of vegetation change in urbanizing grasslands. Some species thrive under these conditions, while others face local extinction. In the natural grasslands that surround Melbourne, Australia, biotic homogenization has occurred with intensifying urbanization. Some native species have become rarer (decreaser species) across the landscape, while others have become more widespread (increaser species). This study experimentally examined the response of increaser and decreaser plant species to nitrogen addition/depletion, and examined the presence/absence of annual disturbance to the vegetation. Methods:Decreaser and increaser species were planted into 60 field plots established in an urban Melbourne grassland and examined over 2 years. Annual removal of above-ground biomass occurred in half the plots to simulate biomass removal via fire, with the remaining plots undisturbed. Soil nitrogen was depleted in one-third of plots, one-third received no nitrogen treatment and one-third were fertilized with nitrogen. Increaser plant species were predicted to persist in the absence of disturbance, and thrive when fertilized. In contrast, high mortality was predicted for decreaser species in the absence of disturbance, with fertilization providing no advantage. Key Results:Seedling mortality for increaser and decreaser species was unrelated to the treatments. The mortality of decreaser species was high (69 %), and the mortality of increaser species low (20 %). However, seedling growth was related to the treatments. The total biomass of decreaser species was highest in annually disturbed plots, with growth suppressed in undisturbed plots. In contrast, the total biomass of increaser species was unrelated to the disturbance regime, but responded positively to nitrogen enrichment. Conclusions:The results provide evidence that by affecting plant growth, declines in biomass removal and atmospheric nitrogen deposition could be key drivers of biotic homogenization in urban grasslands.

Project description: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.

Dataset Information

Grass and forbs respond differently to nitrogen addition: a meta-analysis of global grassland ecosystems.

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Grass and forbs respond differently to nitrogen addition: a meta-analysis of global grassland ecosystems.

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