Effects of long-term nitrogen addition on understory plant functional traits in a boreal forest

doi:10.17521/cjpe.2025.0079

Abstract

Abstract:

Aims Plant functional traits reflect the trade-off mechanism for resource acquisition, and plants can be classified as resource-acquisitive and resource-conservative based on their trait combinations. Nitrogen (N) is essential for plant growth, and increased N deposition can affect plant traits and resource acquisition strategies by altering the ecosystem N cycle. However, most studies on the effects of N deposition on plant traits and strategies have focused on the tree layer, with relatively little research on understory plant communities, especially in boreal forests.

Methods This study relied on a thirteen-year of N addition experiments in Larix gmelinii forests to explore the effects of N addition on understory plant traits at the species and community levels, and to analyse changes in plant resource use strategies.

Important findings The results showed that N addition promoted plant height, specific leaf area and relative cover of acquisitive species (e.g. Betula fruticosa and Deyeuxia angustifolia), while it suppressed the plant height, relative cover and photosynthetic rate of conservative plants (e.g. Vaccinium vitis-idaea), suggesting that N addition favoured the growth of plants with acquisitive strategies. At the community level, N addition significantly promoted leaf N content, specific leaf area, and plant height; and significantly reduced leaf phosphorus content in community-weighted mean traits, and these changes were mainly caused by intraspecific variation. In contrast, N addition did not significantly change the functional dispersion of most traits, and these changes were mainly related to interspecific variation. More importantly, the changes in community traits reflect that N addition has shifted in the resource use strategy of boreal forest understory plant communities from conservative to acquisitive. In summary, this study reveals how long-term N addition changes resource use strategies of boreal forest understory plant communities and their relationship with plant community composition and growth response.

Key words: boreal forest, nitrogen deposition, plant trait, resource use strategy, intraspecific variation, interspecific variation

WANG Zi-Xuan, XING Ai-Jun, CHEN Zi-Xin, SHEN Hai-Hua, FANG Jing-Yun. Effects of long-term nitrogen addition on understory plant functional traits in a boreal forest[J]. Chin J Plant Ecol, 2026, 50(2): 244-255.

Add to citation manager EndNote|Ris|BibTeX

URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2025.0079

https://www.plant-ecology.com/EN/Y2026/V50/I2/244

Figures/Tables 10

Fig. 1 Comparison of plant functional traits and leaf photosynthetic parameters among different understory species under different nitrogen addition levels (mean ± SE). Different lowercase letters indicate significant differences among different nitrogen addition levels under the same species (p < 0.05). Bf, Betula fruticosa; Da, Deyeuxia angustifolia; Lp, Ledum palustre; Rl, Rhododendron lapponicum; Vu, Vaccinium uliginosum; Vv, Vaccinium vitis-idaea. CK, no nitrogen addition; N20, nitrogen addition 20 kg N·hm-2·a-1; N50, nitrogen addition 50 kg N·hm-2·a-1; N100, nitrogen addition 100 kg N·hm-2·a-1. Ci, intercellular CO2 concentration; C:N, leaf carbon to nitrogen ratio; C:P, leaf carbon to phosphorus ratio; Gs, stomatal conductance; LCC, leaf carbon content; LNC, leaf nitrogen content; LPC, leaf phosphorus content; N:P, leaf nitrogen to phosphorus ratio; Pn, net photosynthetic rate; SLA, specific leaf area; Tr, transpiration rate.

Table 1 Comparison of relative cover (%) of different understory species under different nitrogen addition levels (mean ± SE)

物种 Species	对照 CK	N20	N50	N100
Bf	30.32 ± 14.47^a	49.07 ± 9.85^a	56.28 ± 8.57^a	52.78 ± 8.84^a
Da	1.12 ± 0.40^b	6.91 ± 2.12^b	20.37 ± 5.09^a	39.52 ± 11.09^a
Lp	23.44 ± 13.46^a	18.39 ± 4.78^a	17.33 ± 2.77^a	3.64 ± 0.02^a
Rl	16.27 ± 10.35^a	7.34 ± 3.79^a	3.85 ± 2.24^a	6.07 ± 4.30^a
Vu	3.22 ± 2.20^a	4.92 ± 4.02^a	0.60 ± 0.00^a	0.97 ± 0.25^a
Vv	25.62 ± 1.00^a	13.38 ± 3.12^b	3.25 ± 1.15^c	0.85 ± 0.24^c

Fig. 2 Principal component analysis (PCA) of plant functional traits among different understory species under different nitrogen addition levels (A) and the linear relationship between species principal component 1 (PC1) scores and net photosynthetic rates (Pn) (B). FPC1 and FPC2 represent the F-values obtained from ANOVA testing the differences of scores across different species on PC1 and PC2, respectively. ***, p < 0.001; ns, p > 0.05. C:N, leaf carbon to nitrogen ratio; C:P, leaf carbon to phosphorus ratio; Height, plant height; LCC, leaf carbon content; LNC, leaf nitrogen content; LPC, leaf phosphorus content; N:P, leaf nitrogen to phosphorus ratio; SLA, specific leaf area. Bf, Betula fruticosa; Da, Deyeuxia angustifolia; Lp, Ledum palustre; Rl, Rhododendron lapponicum; Vu, Vaccinium uliginosum; Vv, Vaccinium vitis-idaea.

Fig. 3 Comparison of understory plant community-weighted trait means (CWM) (A-H) and functional dispersion index (FDis) (I-P) under different nitrogen addition levels (mean ± SE). Different lowercase letters indicate significant differences among nitrogen addition levels within the same species (p < 0.05). CK, no nitrogen addition; N20, nitrogen addition 20 kg N·hm-2·a-1; N50, nitrogen addition 50 kg N·hm-2·a-1; N100, nitrogen addition 100 kg N·hm-2·a-1. C:N, leaf carbon to nitrogen ratio; C:P, leaf carbon to phosphorus ratio; LCC, leaf carbon content; LNC, leaf nitrogen content; LPC, leaf phosphorus content; N:P, leaf nitrogen to phosphorus ratio; SLA, specific leaf area.

Table 2 ANOVA results of understory net primary productivity (NPP) under different nitrogen addition levels (mean ± SE)

处理 Treatment	NPP (kg·m^-2·a^-1)
CK	0.013 ± 0.004^a
N20	0.024 ± 0.004^a
N50	0.026 ± 0.003^a
N100	0.031 ± 0.009^a

Fig. 4 Contribution of intraspecific trait variation (ITV) and species turnover (ST) to changes in community-weighted trait mean (CWM, A) and functional dispersion index (FDis, B) in response to nitrogen addition. The vertical bars represent total variation. The −/−/− symbols represent statistical significance of the ITV/ST/Total variation, respectively: ns, p > 0.05; *, p < 0.05; **, p < 0.01; ***, p < 0.001. C:N, leaf carbon to nitrogen ratio; C:P, leaf carbon to phosphorus ratio; Height, plant height; LCC, leaf carbon content; LNC, leaf nitrogen content; LPC, leaf phosphorus content; N:P, leaf nitrogen to phosphorus ratio; SLA, specific leaf area.

Fig. 5 Principal component analysis (PCA) of community-weighted trait mean (CWM) under different nitrogen addition levels (A) and the linear relationship between CWM principal component 1 (PC1) scores and understory community net primary productivity (NPP) (B). FPC1 and FPC2 represent the F-values obtained from ANOVA testing for differences in scores across nitrogen addition levels on PC1 and PC2, respectively. ns, p > 0.05; ***, p < 0.001. CK, no nitrogen addition; N20, nitrogen addition 20 kg N·hm-2·a-1; N50, nitrogen addition 50 kg N·hm-2·a-1; N100, nitrogen addition 100 kg N·hm-2·a-1. C:N, leaf carbon to nitrogen ratio; C:P, leaf carbon to phosphorus ratio; Height, plant height; LCC, leaf carbon content; LNC, leaf nitrogen content; LPC, leaf phosphorus content; N:P, leaf nitrogen to phosphorus ratio; SLA, specific leaf area.

Supplement I Relationship between cover and biomass of Vaccinium vitis-idaea in 2023 CK, no nitrogen addition; N20, nitrogen addition 20 kg N·hm-2·a-1; N50, nitrogen addition 50 kg N·hm-2·a-1; N100, nitrogen addition 100 kg N·hm-2·a-1.

Supplement II ANOVA results of species principal component 1 (PC1) scores of different species

物种 Species	PC1
Bf	-1.97 ± 0.15^e
Da	-1.23 ± 0.36^d
Lp	1.07 ± 0.21^b
Rl	-0.45 ± 0.16^c
Vu	-0.84 ± 0.18^cd
Vv	3.22 ± 0.20^a

Supplement III ANOVA results of community-weighted trait mean (CWM) principal component 1 (PC1) scores in different nitrogen addition levels

处理 Treatment	CWM PC1
CK	3.36 ± 0.30^a
N20	0.37 ± 0.72^b
N50	-1.37 ± 0.32^c
N100	-2.36 ± 0.23^c

References 45

[1]	Cleveland CC, Townsend AR, Taylor P, Alvarez-Clare S, Bustamante MMC, Chuyong G, Dobrowski SZ, Grierson P, Harms KE, Houlton BZ, Marklein A, Parton W, Porder S, Reed SC, Sierra CA, et al. (2011). Relationships among net primary productivity, nutrients and climate in tropical rain forest: a pan-tropical analysis. Ecology Letters, 14, 939-947. DOI PMID
[2]	Du EZ, Zhou Z, Li P, Hu XY, Ma YC, Wang W, Zheng CY, Zhu JX, He JS, Fang JY (2013). NEECF: a project of nutrient enrichment experiments in China’s forests. Journal of Plant Ecology, 6, 428-435. DOI URL
[3]	Dyola N, Liang E, Peñuelas J, Camarero JJ, Sigdel SR, Aryal S, Lin W, Liu X, Liu Y, Xu X, Rossi S (2024). Linking leaf elemental traits to biomass across forest biomes in the Himalayas. Science China Earth Sciences, 67, 1518-1528. DOI
[4]	Eskelinen A, Harrison SP (2015). Resource colimitation governs plant community responses to altered precipitation. Proceedings of the National Academy of Sciences of the United States of America, 112, 13009-13014. DOI PMID
[5]	Gao WQ, Lei XD, Gao DL, Li YT (2021). Mass-ratio and complementarity effects simultaneously drive aboveground biomass in temperate Quercus forests through stand structure. Ecology and Evolution, 11, 16806-16816. DOI URL
[6]	Getman-Pickering ZL, Campbell A, Aflitto N, Grele A, Davis JK, Ugine TA (2020). LeafByte: a mobile application that measures leaf area and herbivory quickly and accurately. Methods in Ecology and Evolution, 11, 215-221. DOI
[7]	Gilliam FS, Hockenberry AW, Adams MB (2006). Effects of atmospheric nitrogen deposition on the herbaceous layer of a central Appalachian hardwood forest. The Journal of the Torrey Botanical Society, 133, 240-254. DOI URL
[8]	Gilliam FS, Welch NT, Phillips AH, Billmyer JH, Peterjohn WT, Fowler ZK, Walter CA, Burnham MB, May JD, Adams MB (2016). Twenty-five-year response of the herbaceous layer of a temperate hardwood forest to elevated nitrogen deposition. Ecosphere, 7, e01250. DOI: 10.1002/ecs2.1250.
[9]	Gundale MJ (2022). The impact of anthropogenic nitrogen deposition on global forests: negative impacts far exceed the carbon benefits. Global Change Biology, 28, 690-692. DOI URL
[10]	Hagh-Doust N, Mikryukov V, Anslan S, Bahram M, Puusepp R, Dulya O, Tedersoo L (2023). Effects of nitrogen deposition on carbon and nutrient cycling along a natural soil acidity gradient as revealed by metagenomics. New Phytologist, 238, 2607-2620. DOI URL
[11]	Hofmeister J, Hošek J, Modrý M, Roleček J (2009). The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia. Plant Ecology, 205, 57-75. DOI URL
[12]	Hu MJ, Wan SQ (2019). Effects of fire and nitrogen addition on photosynthesis and growth of three dominant understory plant species in a temperate forest. Journal of Plant Ecology, 12, 759-768. DOI
[13]	Jin YQ, Liu CG, Qian SS, Luo YQ, Zhou RW, Tang JW, Bao WK (2022). Large-scale patterns of understory biomass and its allocation across China’s forests. Science of the Total Environment, 804, 150169. DOI: 10.1016/j.scitotenv.2021.150169.
[14]	Kichenin E, Wardle DA, Peltzer DA, Morse CW, Freschet GT (2013). Contrasting effects of plant inter- and intraspecific variation on community-level trait measures along an environmental gradient. Functional Ecology, 27, 1254-1261. DOI URL
[15]	Kimball S, Funk JL, Spasojevic MJ, Suding KN, Parker S, Goulden ML (2016). Can functional traits predict plant community response to global change. Ecosphere, 7, e01602. DOI: 10.1002/ecs2.1602.
[16]	La Pierre KJ, Smith MD (2015). Functional trait expression of grassland species shift with short- and long-term nutrient additions. Plant Ecology, 216, 307-318. DOI URL
[17]	Laliberté E, Legendre P (2010). A distance-based framework for measuring functional diversity from multiple traits. Ecology, 91, 299-305. PMID
[18]	Lavorel S, Grigulis K, McIntyre S, Williams NSG, Garden D, Dorrough J, Berman S, Quétier F, Thébault A, Bonis A (2008). Assessing functional diversity in the field-methodology matters! Functional Ecology, 22, 134-147. DOI URL
[19]	Lepš J, de Bello F, Šmilauer P, Doležal J (2011). Community trait response to environment: disentangling species turnover vs intraspecific trait variability effects. Ecography, 34, 856-863. DOI URL
[20]	Lin GG, Zeng DH, Mao R (2020). Traits and their plasticity determine responses of plant performance and community functional property to nitrogen enrichment in a boreal peatland. Plant and Soil, 449, 151-167. DOI
[21]	Liu H, Yin DY, He PC, Cadotte MW, Ye Q (2024a). Linking plant functional traits to biodiversity under environmental change. Biological Diversity, 1, 22-28. DOI URL
[22]	Liu JS, Li XF, Ma QH, Zhang X, Chen Y, Isbell F, Wang DL (2019). Nitrogen addition reduced ecosystem stability regardless of its impacts on plant diversity. Journal of Ecology, 107, 2427-2435. DOI URL
[23]	Liu L, Wen Z, Liu S, Zhang XY, Liu XJ (2024b). Decline in atmospheric nitrogen deposition in China between 2010 and 2020. Nature Geoscience, 17, 733-736. DOI
[24]	Luo YK (2017). Functional Traits of Shrub Species in Eastern China. PhD dissertation, University of Chinese Academy of Sciences, Beijing. 85-87.
	[罗永开 (2017). 中国东部地区灌木相关生长及功能性状的研究. 博士学位论文, 中国科学院大学, 北京. 85-87.]
[25]	Mao QG, Lu XK, Wang C, Zhou KJ, Mo JM (2017). Responses of understory plant physiological traits to a decade of nitrogen addition in a tropical reforested ecosystem. Forest Ecology and Management, 401, 65-74. DOI URL
[26]	Palmroth S, Holm Bach L, Nordin A, Palmqvist K (2014). Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs. Oecologia, 175, 457-470. DOI PMID
[27]	Pan S, Wang Y, Qiu YP, Chen DM, Zhang L, Ye CL, Guo H, Zhu WX, Chen AQ, Xu GH, Zhang Y, Bai YF, Hu SJ (2020). Nitrogen-induced acidification, not N-nutrient, dominates suppressive N effects on arbuscular mycorrhizal fungi. Global Change Biology, 26, 6568-6580. DOI URL
[28]	Peng JL, Ma FF, Tian DS, Quan Q, Chen C, Liao JQ, Zhou QP, Niu SL (2023). Plant C:N ratio predicts community composition changes under N addition in an alpine meadow. Journal of Ecology, 111, 589-600. DOI URL
[29]	Read QD, Moorhead LC, Swenson NG, Bailey JK, Sanders NJ (2014). Convergent effects of elevation on functional leaf traits within and among species. Functional Ecology, 28, 37-45. DOI URL
[30]	Reich PB (2014). The world-wide “fast-slow” plant economics spectrum: a traits manifesto. Journal of Ecology, 102, 275-301. DOI URL
[31]	Siefert A, Violle C, Chalmandrier L, Albert CH, Taudiere A, Fajardo A, Aarssen LW, Baraloto C, Carlucci MB, Cianciaruso MV, de L Dantas V, de Bello F, Duarte LDS, Fonseca CR, Freschet GT, et al. (2015). A global meta-analysis of the relative extent of intraspecific trait variation in plant communities. Ecology Letters, 18, 1406-1419. DOI PMID
[32]	Tian D, Du EZ, Jiang L, Ma SH, Zeng WJ, Zou AL, Feng CY, Xu LC, Xing AJ, Wang W, Zheng CY, Ji CJ, Shen HH, Fang JY (2018). Responses of forest ecosystems to increasing N deposition in China: a critical review. Environmental Pollution, 243, 75-86. DOI PMID
[33]	Tian DS, Niu SL (2015). A global analysis of soil acidification caused by nitrogen addition. Environmental Research Letters, 10, 024019. DOI: 10.1088/1748-9326/10/2/024019.
[34]	Walter CA, Raiff DT, Burnham MB, Gilliam FS, Adams MB, Peterjohn WT (2016). Nitrogen fertilization interacts with light to increase Rubus spp. cover in a temperate forest. Plant Ecology, 217, 421-430. DOI URL
[35]	Wang XY, Yan XB, Huang KL, Luo X, Zhang YY, Zhou LY, Yang F, Xu XH, Zhou XH, Niu KC, Guo H (2022). Nitrogen enrichment and warming shift community functional composition via distinct mechanisms: the role of intraspecific trait variability and species turnover. Functional Ecology, 36, 1230-1242. DOI URL
[36]	Wei B, Zhang DY, Wang GQ, Liu Y, Li QL, Zheng ZH, Yang GB, Peng YF, Niu KC, Yang YH (2023). Experimental warming altered plant functional traits and their coordination in a permafrost ecosystem. New Phytologist, 240, 1802-1816.
[37]	Wright IJ, Reich PB, Westoby M, Ackerly DD, Baruch Z, Bongers F, Cavender-Bares J, Chapin T, Cornelissen JHC, Diemer M, Flexas J, Garnier E, Groom PK, Gulias J, Hikosaka K, et al. (2004). The worldwide leaf economics spectrum. Nature, 428, 821-827. DOI
[38]	Xing AJ, Du EZ, Shen HH, Xu LC, de Vries W, Zhao MY, Liu XY, Fang JY (2022). Nonlinear responses of ecosystem carbon fluxes to nitrogen deposition in an old-growth boreal forest. Ecology Letters, 25, 77-88. DOI URL
[39]	Xing AJ, Xu LC, Shen HH, Du EZ, Liu XY, Fang JY (2019). Long term effect of nitrogen addition on understory community in a Chinese boreal forest. Science of the Total Environment, 646, 989-995. DOI URL
[40]	Xu LC, Xing AJ, Du EZ, Shen HH, Yan ZB, Jiang L, Tian D, Hu HF, Fang JY (2021). Effects of nitrogen addition on leaf nutrient stoichiometry in an old-growth boreal forest. Ecosphere, 12, e03335. DOI: 10.1002/ecs2.3335.
[41]	Yang YT, Chen ZF, Xu BC, Ghanizadeh H, Li W, Ding CQ, Zhou RL, Wen ZM (2023). Contrasting patterns of community-weighted mean traits and functional diversity in driving grassland productivity changes under N and P addition. Frontiers in Plant Science, 14, 1145709. DOI: 10.3389/fpls.2023.1145709.
[42]	Yang YT, Chen ZF, Xu BC, Wei JQ, Zhu XX, Yao HB, Wen ZM (2022). Using trait-based methods to study the response of grassland to fertilization in the grassland in semiarid areas in the Loess Plateau of China. Plants, 11, 2045. DOI: 10.3390/plants11152045.
[43]	Ye XM, Bu WS, Hu XF, Liu B, Liang K, Chen FS (2023). Species divergence in seedling leaf traits and tree growth response to nitrogen and phosphorus additions in an evergreen broadleaved forest of subtropical China. Journal of Forestry Research, 34, 137-150. DOI
[44]	Zhao CT, Lin QH, Tian D, Ji CJ, Shen HH, Fan DY, Wang XP, Fang JY (2023). Nitrogen addition promotes conservative resource-use strategies via aggravating phosphorus limitation of evergreen trees in subtropical forest. Science of the Total Environment, 889, 164047. DOI: 10.1016/j.scitotenv.2023.164047.
[45]	Zhou SX, Huang CD, Han BH, Xiao,YX, Tang JD, Xiang YB, Luo C (2017). Simulated nitrogen deposition significantly suppresses the decomposition of forest litter in a natural evergreen broad-leaved forest in the Rainy Area of Western China. Plant and Soil, 420, 135-145. DOI