Disruption of metal ion homeostasis in soils is associated with nitrogen deposition-induced species loss in an Inner Mongolia steppe

Abstract

Abstract. Enhanced deposition of atmospheric nitrogen (N) resulting from anthropogenic activities has negative impacts on plant diversity in ecosystems. Several mechanisms have been proposed to explain the species loss. Ion toxicity due to N deposition-induced soil acidification has been suggested to be responsible for species loss in acidic grasslands, while few studies have evaluated the role of soil-mediated homeostasis of ions in species loss under elevated N deposition in grasslands with neutral or alkaline soils. To determine whether soil-mediated processes are involved in changes in biodiversity induced by N deposition, the effects of 9-year N addition on soil properties, aboveground biomass (AGB) and species richness were investigated in an Inner Mongolia steppe. Low to moderate N addition rate (2, 4, 8 g N m −2 yr −1 ) significantly enhanced AGB of graminoids, while high N addition rate (≥ 16 g N m −2 yr −1 ) reduced AGB of forbs, leading to an overall increase in AGB of the community under low to moderate N addition rates. Forb richness was significantly reduced by N addition at rates greater than 8 g N m −2 yr −1 , while no effect of N addition on graminoid richness was observed, resulting in decline in total species richness. N addition reduced soil pH, depleted base cations (Ca 2+ , Mg 2+ and K + ) and mobilized Mn 2+ , Fe 3+ , Cu 2+ and Al 3+ ions in soils. Soil inorganic-N concentration was negatively correlated with forb richness and biomass, explaining 23.59 % variation of forb biomass. The concentrations of base cations (Ca 2+ and Mg 2+ ) and metal ions (Mn 2+ , Cu 2+ and, Fe 3+ ) showed positively and negatively linear correlation with forb richness, respectively. Changes in the metal ion concentrations accounted for 42.77 % variation of forb richness, while reduction of base cations was not associated with the reduction in forb richness. These results reveal that patterns of plant biodiversity in the temperate steppe of Inner Mongolia are primarily driven by increases in metal ion availability, particularly enhanced release of soil Mn 2+ .

Nitrogen addition alters elemental stoichiometry within soil aggregates in a temperate steppe

“…5d, e, f) suggested accumulation of available Fe relative to Mn under soil acidification as affected by enhanced N inputs. Consistent with our findings, Tian et al (2015Tian et al ( , 2016 found soil acidification enhanced Mn uptake and reduced Fe absorption by forbs which result in lower photosynthetic rates and growth and loss of forb species. Plant Fe deficiency was reported to induce chlorosis and decrease photosynthesis in calcareous grassland (Rogovska et al, 2007).…”

Contrasting pH buffering patterns in neutral-alkaline soils along a 3600 km transect in northern China

“…High atmospheric sulfur deposition (dry and wet) is also predicted to continue in the short term in these regions, despite stricter regulation of sulfur dioxide emissions being implemented in recent years (Pan et al, 2013;Zhang et al, 2012;Zhao, 2009;Hijmans et al, 2005). Hence, soil acidification may continue for a long time in northern China (Guo et al, 2010;Lieb et al, 2011), posing a severe ecological threat to these ecosystems (Chen et al, 2013;Tian et al, 2015). For instance, soil acidification changed the belowground communities and soil properties, decreased the plant diversity and productivity, and reduced the community stability (Chen et al, 2013).…”

“…For instance, soil acidification changed the belowground communities and soil properties, decreased the plant diversity and productivity, and reduced the community stability (Chen et al, 2013). The soil acidification induced by N addition resulted in the disruption of metal ion homeostasis in soils and hence species loss (Tian et al, 2015). Nonetheless, there has been no comprehensive assessment of the extent, trends and mechanisms of soil pH decline in response to acid deposition across these ecosystems.…”

“…Stepwise regression of the relationships between soil pHBC and other variables identified carbonate and CEC (both positive influence) as the most significant explanatory variables for pHBC, in the carbonate-and non-carbonate-containing soils, respectively (Table 2). These results may be attributed to the differences in their acid buffering systems (Bowman et al, 2008;Van Breemen, 1983). In the carbonatecontaining soils, the primary buffering process is acid neutralization, i.e., CO (Van Breemen, 1983).…”

“…These results may be attributed to the differences in their acid buffering systems (Bowman et al, 2008;Van Breemen, 1983). In the carbonatecontaining soils, the primary buffering process is acid neutralization, i.e., CO (Van Breemen, 1983). In contrast, cation exchange reactions were the primary buffering process in non-carbonate-containing soils.…”