Effects of nitrogen and phosphorus additions on leaf herbivory damage and its underlying mechanisms in saplings in an evergreen broad-leaved forest

doi:10.17521/cjpe.2025.0248

Abstract

Abstract:

Aims Insect herbivory leads to leaf damage in subtropical forests, but it remains unclear whether nitrogen (N) and phosphorus (P) additions alter the insect resistance of saplings. This study focused on the saplings of six dominant tree species in the evergreen broad-leaved forest of Jiulian Mountain, Jiangxi Province. An eight-year N and P addition experiment was conducted to examine the effects of these nutrients on insect resistance. We measured leaf herbivory damage rate, stoichiometric ratios, mechanical resistance, and chemical resistance under different treatments.

Methods In this study, we conducted an eight-year N and P addition experiment in an evergreen broad-leaved forest in Jiulianshan, Jiangxi Province to determine effects of N and P on the saplings of six dominant tree species leaf herbivory damage, leaf stoichiometry, mechanical resistance, and chemical resistance of saplings.

Important findings Saplings exhibited strong resistance to herbivory, with an average leaf damage rate of 5.4%, which was neither affected by N addition, nor by P addition nor by both. However, significant interspecific differences were found, with light-demanding species showing significantly higher damage rates than shade-tolerant species. N addition and combined N and P addition significantly increased leaf nitrogen concentration per unit mass but did not significantly alter leaf stoichiometric ratios. P addition significantly increased leaf phosphorus concentration and decreased the carbon-to-phosphorus ratio. Both N addition and P addition showed no significant changes in leaf mechanical resistance such as force to tear and force to punch. In contrast, N addition significantly increased amino acid content, and P addition elevated total phenolics content, while tannin levels remained stable. Notably, light-demanding species exhibited higher damage due to higher leaf N concentration, whereas shade-tolerant species exhibited lower damage due to stronger mechanical resistance and chemical defense. These findings suggest that saplings in subtropical forests maintain high resistance to background insect herbivory pressure through stable physical defenses and flexible chemical defenses, potentially enhancing the ecological stability of natural regeneration within the context of global change.

Key words: long-term nutrient additions, in-situ experiment, leaf chewing, secondary metabolites

YE Xue-Min, GAO Wei, TANG Xing-Lin, CHEN Fu-Sheng, SUN Rong-Xi, LUO Kun-Shui. Effects of nitrogen and phosphorus additions on leaf herbivory damage and its underlying mechanisms in saplings in an evergreen broad-leaved forest[J]. Chin J Plant Ecol, 2026, 50(2): 256-267.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2025.0248

https://www.plant-ecology.com/EN/Y2026/V50/I2/256

Figures/Tables 9

Table 1 Number of individuals of different species measured by leaf herbivorous damage rate

物种 Species	合计 Total	取样个体数量 Number of sampled individuals
物种 Species	合计 Total	对照 Control	氮添加 Nitrogen (N) addition	磷添加 Phosphorus (P) addition	氮磷共同添加 Combined N + P
木荷 Schima superba	115	30	29	29	27
短序润楠 Machilus breviflora	81	19	24	21	17
绒毛润楠 M. velutina	85	22	24	23	16
丝栗栲 Castanopsis fargesii	83	23	21	16	23
米槠 C. carlesii	76	19	16	26	15
甜槠 C. eyrei	68	20	15	18	15
幼树 Saplings	508	133	129	133	113

Fig. 1 Responses of leaf herbivorous damage rate of saplings to nitrogen and phosphorus addition (A), interspecific differences (B) in an evergreen broad-leaved forest. Different lowercase letters indicate differences among different treatments or species (p < 0.05), *** indicate differences between light-demaning species and shade-tolerant species (p < 0.001). +N, nitrogen addition; +P, phosphorus addition; N+P, nitrogen and phosphorus combined addition.

Table 2 Linear mixed model (LMM) analysis for leaf herbivorous damage rate (LHDR) of six dominant tree species in an evergreen broad-leaved forest treated with nitrogen and phosphorus addition

LMM	LHDR	p	LMM	LHDR	p	LMM	LHDR	p
固定效应 Fixed effect	物种 Species	<0.001	固定效应 Fixed effect	叶片大小 Leaf size	0.002	固定效应 Fixed effect	株高 Height	0.004
	氮添加 N	0.289		氮添加 N	0.123		氮添加 N	0.265
	磷添加 P	0.217		磷添加 P	0.209		磷添加 P	0.209
	N × P	0.998		N × P	0.717		N × P	0.635
	N × species	0.052		N × leaf size	0.003		N × height	0.018
	P × species	0.724		P × leaf size	0.836		P × height	0.544
	N × P × species	0.756		N × P × leaf size	0.089		N × P × height	0.758
模型解释度 Model statistics	R²_m	0.141	模型解释度 Model statistics	R²_m	0.048	模型解释度 Model statistics	R²_m	0.034
模型解释度 Model statistics	R²_c	0.141	模型解释度 Model statistics	R²_c	0.048	模型解释度 Model statistics	R²_c	0.034

Fig. 2 Responses of leaf stoichiometry of saplings to nitrogen and phosphorus addition in an evergreen broad-leaved forest. Different lowercase letters indicate differences among different treatments (p < 0.05). CK, control; +N, nitrogen addition; +P, phosphorus addition; N+P, nitrogen and phosphorus combined addition. Cmass, carbon content per unit mass; Nmass, nitrogen content per unit mass; Pmass, phosphorus content per unit mass.

Fig. 3 Responses of leaf mass per area (LMA) and leaf mechanical resistance of saplings to nitrogen and phosphorus addition in an evergreen broad-leaved forest. Different lowercase letters indicate differences among different treatments (p < 0.05). CK, control; +N, nitrogen addition; +P, phosphorus addition; N+P, nitrogen and phosphorus combined addition. Fp, leaf force to punch; Ft, leaf force to tear.

Fig. 4 Responses of leaf chemical resistance of saplings to nitrogen and phosphorus addition in an evergreen broad-leaved forest. Different lowercase letters indicate differences among different treatments (p < 0.05). CK, control; +N, nitrogen addition; +P, phosphorus addition; N+P, nitrogen and phosphorus combined addition. AA, amino acid content; TA, tannin content; TPh, total phenolic content.

Table 3 Comparison of leaf traits between light-demanding and shade-tolerant species in an evergreen broad-leaved forest

叶片性状 Leaf trait	喜光树种 Light-demanding species	耐阴树种 Shadow-tolerant species	p
叶片植食损伤率 LHDR (%)	7.13 ± 0.51	3.38 ± 0.28	^***
单位质量碳含量 C_mass (mg·g^-1)	478.19 ± 2.47	480.20 ± 3.04	0.22
单位质量氮含量 N_mass (mg·g^-1)	15.71 ± 0.32	13.79 ± 0.27	^***
单位质量磷含量 P_mass (mg·g^-1)	0.864 ± 0.026	0.824 ± 0.022	0.18
C:N	31.20 ± 0.67	35.79 ± 0.83	^***
C:P	622.2 ± 24.0	637.1 ± 20.7	0.54
N:P	19.70 ± 0.78	17.78 ± 0.57	0.13
比叶质量 LMA (g·m^-2)	89.44 ± 3.17	96.31 ± 3.36	0.06
叶片撕裂力 F_t (KN·m^-1)	0.299 ± 0.007	0.402 ± 0.009	^***
叶片穿透力 F_p (KN·m^-1)	0.198 ± 0.004	0.281 ± 0.007	^***
氨基酸含量 AA (μg·g^-1)	84.13 ± 3.66	90.83 ± 2.83	^*
总酚含量 TPh (mg·g^-1)	11.18 ± 0.79	14.68 ± 1.08	^**
单宁含量 TA (mg·g^-1)	33.21 ± 2.26	30.79 ± 1.62	0.21

Fig. 5 Principal component (PC) analysis on the leaf herbivory damage and leaf traits. The first two principal components and scores are represented along the axes for light-demanding (gray circle) and shade-tolerant (green circle) species. Abbreviations of leaf traits are provided in Table 3.

Supplement Contribution of leaf herbivory damage and leaf traits to the first two principal components AA, amino acid content; Cmass, carbon content per unit mass; Fp, leaf force to punch; Ft, leaf force to tear; LHDR, leaf herbivorous damage rate; LMA, leaf mass per area; Nmass, nitrogen content per unit mass; Pmass, phosphorus content per unit mass; PC1, the first principal component; PC2, the second principal component; TA, tannin content; TPh, total phenolic content.

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