Addition of nitrogen to canopy versus understorey has different effects on leaf traits of understorey plants in a subtropical evergreen broad‐leaved forest

Abstract

Atmospheric nitrogen (N) deposition has substantial effects on forest ecosystems. The effects of N deposition on understorey plants have been simulated by spraying N on the forest floor. Such understorey addition of N (UAN) might simulate atmospheric N deposition in a biased manner, because it bypasses the canopy. We compared the effects of UAN and canopy addition of N (CAN) at 0, 25 and 50 kg N ha−1 year–1 on SLA, leaf construction costs (CC), concentrations of leaf carbon ([C]), nitrogen ([N]), phosphorus ([P]), minerals ([Mineral]), nitrate ([NO3‐]), lignin ([Lignin]), lipids ([Lipid]), organic acids ([OA]), soluble phenolics ([SP]), total non‐structural carbohydrates ([TNC]) and total structural carbohydrates ([TSC]) in six dominant understorey species in a subtropical evergreen forest after 5 years of N treatments. We found that leaf CC, [C], [Lignin], [OA], [TNC] and [TSC] were significantly affected by N addition approach and rate, but leaf [P] and [Lipid] were affected by N addition approach and N addition rate respectively; leaf CC, [C], [P], [OA] and [TNC] were significantly lower under UAN than under CAN, but leaf [TSC] and [Lignin] were significantly higher and lower, respectively, under UAN than under CAN at 50 kg N ha−1 year–1; the decline of leaf [C] and [Lignin] contributed to the significantly lower leaf CC under UAN than under CAN. Synthesis. We show that canopy and understorey N addition exerted significantly different effects on leaf traits of understorey plants. The results indicate that understorey plants in subtropical forest respond differently to UAN from those to atmospheric deposition of N. Further studies are warranted to evaluate the unbiased ecological processes and functions of forest ecosystem responding to atmospheric N deposition via both CAN and UAN experiments over a longer term.

Long-term water use efficiency and non-structural carbohydrates of dominant tree species in response to nitrogen and water additions in a warm temperate forest

“…In this study, leaf NSCs, starch, and total soluble sugar concentrations showed less variation with treatments ( Figure 2 ), which was consistent with the findings of other studies ( Li et al., 2018 ; Mo et al., 2020 ; Tang et al., 2020 ). Previous studies have implied that the N and P levels in leaves can influence the production of NSCs ( Xie et al., 2018 ).…”

“…The traditional method is mainly to add N directly to the understory, but this ignores the N interception effect of the forest canopy ( Tian et al., 2019 ; Tang et al., 2020 ). In this experiment, we selected two dominant tree species in a temperate forest to conduct multi-year canopy N addition and precipitation enhancement, and we determined the effect of N and water addition on NSCs and leaf long-term WUE in the dominant tree species in the growing season.…”

Nitrogen addition stimulates soil aggregation and enhances carbon storage in terrestrial ecosystems of China: A meta‐analysis

“…Understory N-addition experiment overlooks the absorption, retention, and transformation of N by forest canopy and thus may overestimate the effect of atmospheric N addition on forest soils (Lu et al, 2021). Recent canopy N-addition studies suggest that canopy N addition and understory N addition have different effects on tree growth (Tang et al, 2020), soil microbial properties (Liu et al, 2020), and soil C dynamics (Lu et al, 2021). These findings have implications for future research to examine the potential effects of forest canopies in simulated N deposition experiments.…”

Effects of Simulated Nitrogen Deposition and Micro-Environment on the Functional Traits of Two Rare and Endangered Fern Species in a Subtropical Forest

“…Plants may also delay their reproductive phenology to adapt to environmental changes such as a decreasing nutrient supply [ 15 , 16 ]. However, studies to date have concentrated mainly on the responses of dominant species, with research gaps on the impact of the N deposition on the functional traits of REFs [ 3 , 5 , 17 , 18 ].…”

“…Furthermore, among growth, defense, and reproductive traits, previous studies including simulated N deposition have mainly focused on growth response (rather than defense or reproduction) in forest ecosystems [ 17 , 19 , 20 ], with inconsistent conclusions. For example, N addition directly enhanced leaf N and P concentrations, but declines or non-significant changes in leaf N and P concentrations were also found [ 21 , 22 , 23 ].…”