Abstract
Nitrogen enrichment is pervasive in forest ecosystems, but its influence on understory plant communities and their stoichiometric characteristics is poorly understood. We hypothesize that when forest is enriched with nitrogen (N), the stoichiometric characteristics of plant species explain changes in understory plant diversity. A 13‐year field experiment was conducted to explore the effects of N addition on foliar carbon (C): N: phosphorus (P) stoichiometry, understory plant species richness, and intrinsic water use efficiency (iWUE) in a subtropical Chinese fir forest. Four levels of N addition were applied: 0, 6, 12, and 24 g m−2 year−1. Individual plant species were categorized into resistant plants, intermediate resistant plants, and sensitive plants based on their response to nitrogen addition. Results showed that N addition significantly decreased the number of species, genera, and families of herbaceous plants. Foliar N:P ratios were greater in sensitive plants than resistant or intermediate resistant plants, while iWUE showed an opposite trend. However, no relationship was detected between soil available N and foliar N, and soil N:P and foliar N:P ratios. Our results indicated that long‐term N addition decreased the diversity of understory plants in a subtropical forest. Through regulating water use efficiency with N addition, sensitive plants change their N:P stoichiometry and have a higher risk of mortality, while resistant plants maintain a stable N:P stoichiometry, which contributes to their survival. These findings suggest that plant N:P stoichiometry plays an important role in understory plant performance in response to environmental change of N.
Highlights
Over the past century, fossil-fuel burning and artificial fertilizer application have substantially increased the global nitrogen (N) deposition (Decina et al 2020; Galloway et al, 2008; IPCC, 2014)
We confirm that long-term N deposition can decrease plant diversity in subtropical plantation forests
Understory plants are important components of forest ecosystems and the consequence of losing plant diversity needs to be considered under global change phenomenon
Summary
Fossil-fuel burning and artificial fertilizer application have substantially increased the global nitrogen (N) deposition (Decina et al 2020; Galloway et al, 2008; IPCC, 2014). Much research has focused on understanding how ecosystem processes and plant diversity respond to increasing N deposition (Valliere et al 2020; Yang et al 2020; Zak et al 2019), and many studies show that N deposition poses a significant threat to plant diversity and causes substantial changes in the plant community composition in terrestrial ecosystems (de Vries & Bobbink, 2017; Zhang et al 2019) Major drivers of such effects of N on plant communities are soil acidification (Lu et al 2014) and altered plant-plant interactions (Gilliam et al, 2016; Liu et al 2017). The relationships between the stoichiometric N:P ratios and plant species richness under long-term anthropogenic N deposition are poorly understood
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