The potential bias of nitrogen deposition effects on primary productivity and biodiversity

Tao

et al. 2023

Global Change Biology

Soil acidification induced by reactive nitrogen (N) inputs can alter the structure and function of terrestrial ecosystems. Because different N-transformation processes contribute to the production and consumption of H + , the magnitude of acidification likely depends on the relative amounts of organic N (ON) and inorganic N (IN) inputs.However, few studies have explicitly measured the effects of N composition on soil acidification. In this study, we first conducted a meta-analysis to test the effects of ON or IN inputs on soil acidification across 53 studies in grasslands. We then compared soil acidification across five different ON:IN ratios and two input rates based on long-term field N addition experiments. The meta-analysis showed that ON had weaker effects on soil acidification than IN when the N addition rate was above 20 g N m −2 year −1 . The field experiment confirmed the findings from meta-analysis: N addition with proportions of ON ≥ 20% caused less soil acidification, especially at a high input rate (30 g N m −2 year −1 ). Structural equation model analysis showed that this result was largely due to a relatively low rate of H + production from ON as NH 3 volatilization and uptake of ON and NH 4 + by the dominant grass species Leymus chinensis (which are both lower net contributors to H + production) result in less NH 4 + available for nitrification (which is a higher net contributor to H + production). These results indicate that the evaluation of soil acidification induced by N inputs should consider N | 4045 WANG et al.

Section: Discussionsupporting

confidence: 87%

Forms of nitrogen inputs regulate the intensity of soil acidification

Tao

et al. 2023

Global Change Biology

“…biodiversity, community stability, nitrogen, phosphorus, seedling dynamics, subtropical forest activities and functions (Li et al, 2014), seedling growth (Lim et al, 2022) and species richness (Ke et al, 2023). In a temperate grassland with a long-term N addition experiment (Ke et al, 2023), N addition with different inorganic and organic N ratios had differential impacts on the diversity and net primary productivity of the plant community.…”

Section: Introductionmentioning

confidence: 99%

Long‐term stability of sapling dynamics is regulated by soil phosphorus availability in subtropical forest

Liang,

Zheng,

Johnson

et al. 2024

Journal of Ecology

The abiotic and biotic factors that regulate stability in species‐rich forests are poorly resolved, and this limits the ability to predict how climate change and other perturbations impact forest dynamics. Phosphorus limitation and nitrogen deposition are important factors affecting the dynamics and functioning of tropical and subtropical forests, but how long‐term temporal stability of tree communities is affected by availability and heterogeneity of soil phosphorus and nitrogen remains unclear. We collected annual dynamic data of 20,768 regenerating saplings, which were censused from 2008 to 2019 in a subtropical forest, to investigate how soil nutrients affect the temporal stability of productivity at both population and community levels. We found that concentrations of soil inorganic phosphorus were significantly and positively correlated with sapling richness and phylogenetic diversity, leading to significantly higher species asynchrony and community temporal stability. By contrast, higher concentrations of organic phosphorus weakened community stability via a negative effect on species richness. Structural equation models provide further strong evidence that increasing concentrations of soil inorganic phosphorus strongly promoted community temporal stability via increased species diversity, species asynchrony and population stability, while organic phosphorus displayed opposite effects. Meanwhile, soil concentrations of available and unavailable forms of nitrogen showed much weaker and negative associations with community stability. Synthesis. Using a 12‐year data set of sapling demography from a subtropical forest of south China, our study demonstrates that soil phosphorus is an important determinant of the long‐term stability of sapling dynamics and consequently the whole‐community structure, and the composition of soil phosphorus pools predicts the temporal stability and diversity of tree communities in phosphorus‐limited forests.

“…Human‐induced environmental change can alter these community assembly factors, which could impact colonisation and extirpation in communities world‐wide. For example, human activities directly and indirectly: elevate rates of novel disturbances, which can change abiotic conditions, increase resource availability and alter community diversity and composition (Moles et al, 2012); increase the dispersal and introduction of some types of species, and decrease the dispersal of others (Runghen et al, 2021; Tucker et al, 2021); and alter the composition of vegetation communities through land use change like agriculture (Dawson et al, 2017) and nitrogen deposition (Borer & Stevens, 2022; Ke et al, 2023). Unless their effects are disentangled, it is hard to identify which factors are driving increased colonisation, and whether colonisation and resident species loss are both simply outcomes of broader environmental change, or whether colonisation is a driver of resident species loss itself (Catford et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Higher plant colonisation and lower resident diversity in grasslands more recently abandoned from agriculture

Catford,

Shepherd,

Tennant

et al. 2023

Journal of Ecology

Rates of species colonisation and extirpation are increasing in plant communities world‐wide. Colonisation could potentially help compensate for, or compound, resident diversity loss that results from global environmental change. We use a multifactorial seed addition grassland experiment to examine relationships between plant colonisation, resident species diversity and key community assembly factors over 3 years. By manipulating colonist seed rate, imposing disturbance and examining abundance and diversity impacts of 14 formerly absent sown colonists in communities that varied in successional stage and time since agricultural abandonment, we were able to disentangle effects of global change factors (species introduction, novel disturbance and land use change) that are usually confounded. Evidence suggested that cover abundance of sown colonists was most strongly influenced by successional stage of recipient communities, though number of growing seasons was also important for the group of seven colonists with resource conservative ‘slow’ life history traits. Colonist type, seed rate and disturbance had weaker relationships with colonist cover. Factors affecting sown colonist cover were highly conditional. A negative relationship between plot‐level disturbance and colonist cover in early successional communities meant that, despite a positive relationship in late succession, colonisation was negatively related to disturbance overall, defying theoretical expectations. Non‐sown resident diversity was negatively related to colonist cover and positively related to successional stage. Resource acquisitive colonists with ‘fast’ life history traits appeared to limit cover of ‘slow colonists’ when the two groups were sown together, likely reflecting niche pre‐emption. Communities at earlier stages of succession had lower resident diversity and experienced higher levels of colonisation than communities at later stages of succession. Elevated colonisation and lower resident diversity both appeared to be symptoms of human‐induced land use change. However, results suggested that resource competition from plant colonists may also limit resident diversity in grasslands abandoned from agriculture more recently. Synthesis. Our findings point to the importance of resource availability and competition on plant colonisation and colonist impacts on residents. Although colonisation is potentially a source of biodiversity in the short term, our results suggest that plant colonists that reach high abundance may be a further threat to resident plant diversity in secondary grasslands recovering from a recent history of agriculture.