Effects of the level and regime of nitrogen addition on seedling growth of four major tree species in subtropical China

doi:10.17521/cjpe.2015.0092

Abstract

Abstract: Aims

Numerous studies have been carried out concerning the effects of atmospheric nitrogen (N) deposition on forest ecosystems. However, most of previous experiments were conducted by adding N fertilizer to the surface soil directly. Realistically simulated canopy N deposition and comparison of the effects of soil N addition and canopy N addition on ecosystems were rare. Our purpose is to better understand the effects of two N addition regimes at different N addition levels on seeding growth in major tree species of subtropical China.

Methods

A 2-year pot experiment was conducted, with seedlings of four species (Ormosia pinnata, Acacia mangium, Schima superba, Pinus massoniana) grown in pots subjected to treatments of three levels (ambient, medium, and high) and two regimes (in soil vs. on canopy) of N addition, specifically including S-CK (ambient N addition in soil), S-MN (medium N addition in soil), S-HN (high N addition in soil), C-CK (ambient N addition on canopy), C-MN (medium N addition on canopy), and C-HN (high N addition on canopy). The total amounts of added N in the three N levels were 5.6, 15.6 and 20.6 g·m^-2·a^-1, respectively. Tree basal diameter and tree height were measured in June and December 2012, and November 2013. All trees were harvested in November 2013, and then the biomass was calculated according to the dry-mass of roots, shoots and leaves; the root-shoot ratios were calculated.

Important findings

N treatments affected seeding growth, along with significant interactive effects among N addition level, N addition regime and species. Compared to CK, S-MN stimulated the biomass in seedlings of A. mangium and S. superba, but decreased the tree height and biomass in seedlings of P. massoniana; C-MN increased the biomass in seedlings of A. mangium; S-HN promoted the biomass in seedlings of A. mangium, but significantly decreased the biomass, basal diameter and tree height in seedlings of P. massoniana (p < 0.01); C-HN led to the greater growth in seedlings of A. mangium, S. superba and P. massoniana (p < 0.01). N addition responses were dependent upon plant species: while seedlings in O. pinnata and A. mangium grew faster than S. superba and P. massoniana under all N treatments, the differences in the growth of S. superba and P. massoniana seedlings between the two N addition regimes were more pronounced than in O. pinnata and A. mangium seedlings. We concluded that legumes (O. pinnata and A. mangium) grew faster than non-legumes (S. superba). And growth stimulation in broadleaved trees (O. pinnata, A. mangium, and S. superba) by N addition was significantly greater than in coniferous trees (P. massoniana). Our findings suggest that the relatively high and chronic atmospheric N deposition in subtropical forest ecosystems may lead to changes in species composition.

Key words: biomass, high N addition levels, legumes, N addition on the canopy

LIU Shuang-E,LI Yi-Yong,FANG Xiong,HUANG Wen-Juan,LONG Feng-Ling,LIU Ju-Xiu. Effects of the level and regime of nitrogen addition on seedling growth of four major tree species in subtropical China[J]. Chin J Plan Ecolo, 2015, 39(10): 950-961.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2015.0092

https://www.plant-ecology.com/EN/Y2015/V39/I10/950

Figures/Tables 10

Table 1 Background values of soil physicochemical properties at beginning of the experiment (mean ± SD, n = 12)

土壤深度 Soil depth (cm)	pH值 pH value	有效磷 Available phosphorus (mg·kg^-1)	硝态氮 Nitrate nitrogen (mg·kg^-1)	铵态氮 Ammonium nitrogen (mg·kg^-1)	有机质 Organic matter (g·kg^-1)
0-20	3.99 ± 0.096	0.84 ± 0.072	17.39 ± 1.34	6.01 ± 0.69	22.72 ± 1.20

Supplement I Soil water content (%) under two N addition regimes (mean ± SD)

物种 Species	对照 Ambient N addition		中氮 Medium N addition		高氮 High N addition
物种 Species	土壤施氮 SN	冠层施氮 CN	土壤施氮 SN	冠层施氮 CN	土壤施氮 SN	冠层施氮 CN
海南红豆 Ormosia pinnata	17.11 ± 1.68	14.07 ± 1.40	18.28 ± 1.08	15.74 ± 1.99	17.06 ± 1.25	16.67 ± 1.01
马占相思 Acacia mangium	17.63 ± 2.17	13.87 ± 2.48	19.69 ± 0.39^a	13.83 ± 2.74^b	16.65 ± 1.12	14.33 ± 3.51
木荷 Schima superba	18.14 ± 1.13	16.73 ± 1.61	19.18 ± 0.80^a	16.03 ± 1.68^b	17.22 ± 0.81	15.70 ± 0.60
马尾松 Pinus massoniana	17.39 ± 2.49	15.52 ± 1.72	18.03 ± 1.18	17.28 ± 0.33	17.60 ± 0.74	15.85 ± 0.93

Table 2 Effects of N addition level and regime on seedling growth in four major tree species (three-way ANOVA)

主要因素及相互作用 Main factors and interactions	基径 Basal diameter		株高 Tree height		生物量 Biomass		土壤pH Soil pH
主要因素及相互作用 Main factors and interactions	F and p values	d.f.	F and p values	d.f.	F and p values	d.f.	F and p values	d.f.
处理水平 Level	6.721 0.002	2	4.013 0.021	2	3.608 0.039	2	70.555 <0.001	2
施氮方式 Regime	0.906 0.344	1	0.544 0.463	1	6.421 0.017	2	107.545 <0.001	1
物种 Species	48.661 <0.001	3	386.887 <0.001	3	122.901 <0.001	3	31.299 <0.001	3
水平×施氮方式 Level × regime	19.591 <0.001	2	1.799 0.171	2	12.949 <0.001	2	7.314 0.002	3
水平×物种 Level × species	5.293 <0.001	6	2.088 0.062	6	12.266 <0.001	6	1.681 0.146	6
施氮方式×物种 Regime × species	7.207 <0.001	3	8.017 <0.001	3	11.592 <0.001	3	3.458 0.023	3
水平×施氮方式×物种 Level × regime × species	9.227 <0.001	6	1.673 0.136	6	10.981 <0.001	6	5.313 <0.001	6
误差 Error		95		95		103		48

Fig. 1 Effects of N addition level and regime on tree basal diameter in four tree species (mean ± SD). Different lowercase letters (a, b) and capital letters (A, B) above the error bars indicate significant differences among N addition levels in soil and on canopy, respectively, in each species (p < 0.05); * above the error bars indicate significant difference between two N addition regimes (Duncan multiple range test; * p < 0.05, ** p < 0.01). CK, ambient N addition; HN, high N addition; MN, medium N addition. CN, N addition on canopy; SN, N addition in soil. AM, Acacia mangium; OP, Ormosia pinnata; PM, Pinus massoniana; SS, Schima superba.

Fig. 2 Effects of N addition level and regime on tree height in four tree species (mean ± SD). Different lowercase letters (a, b) and capital letters (A, B) above the error bars indicate significant differences among N addition levels in soil and on canopy, respectively, in each species (p < 0.05); * above the error bars indicate significant differences between two N addition regimes (Duncan multiple range test; * p < 0.05, ** p < 0.01). CK, ambient N addition; HN, high N addition; MN, medium N addition. CN, N addition on canopy; SN, N addition in soil. AM, Acacia mangium; OP, Ormosia pinnata; PM, Pinus massoniana; SS, Schima superba.

Fig. 3 Effects of N addition level and regime on biomass in four tree species (mean ± SD). Different lowercase letters (a, b) and capital letters (A, B) above the error bars indicate significant differences among N addition levels in soil and on canopy, respectively, in each species (p < 0.05); * above the error bars indicate significant differences between two N addition regimes (Duncan multiple range test; * p < 0.05, ** p < 0.01). CK, ambient N addition; HN, high N addition; MN, medium N addition. CN, N addition on canopy; SN, N addition in soil. AM, Acacia mangium; OP, Ormosia pinnata; PM, Pinus massoniana; SS, Schima superba.

Fig. 4 Effects of N addition level and regime on biomass accumulation in leaves, stem and coarse-roots and fine-roots (mean ± SD). Different lowercase letters (a, b) and capital letters (A, B) above the error bars indicate significant differences among N addition levels in soil and on canopy, respectively, in each species (p < 0.05); * above the error bars indicate significant differences between two N addition regimes (Duncan multiple range test; * p < 0.05, ** p < 0.01). CK, ambient N addition; HN, high N addition; MN, medium N addition. CN, N addition on canopy; SN, N addition in soil. AM, Acacia mangium; OP, Ormosia pinnata; PM, Pinus massoniana; SS, Schima superba.

Table 3 Root-shoot ratios under different nitrogen (N) treatments (mean ± SD)

物种 Species	冠层施N N addition on canopy			土壤施N N addition in soil
物种 Species	CK	MN	HN	CK	MN	HN
海南红豆 Ormosia pinnata	0.275 ± 0.029	0.307 ± 0.003	0.315 ± 0.067	0.453 ± 0.103^a	0.332 ± 0.018^ab	0.253 ± 0.009^b
马占相思 Acacia mangium	0.251 ± 0.071	0.222 ± 0.039	0.317 ± 0.059	0.262 ± 0.059	0.235 ± 0.005	0.391 ± 0.175
木荷 Schima superba	0.514 ± 0.128	0.489 ± 0.021	0.754 ± 0.241	0.575 ± 0.055	0.544 ± 0.124	0.608 ± 0.008
马尾松 Pinus massoniana	0.336 ± 0.119	0.277 ± 0.021	0.223 ± 0.070	0.170 ± 0.035^b	0.299 ± 0.075^ab	0.343 ± 0.003^a

Table 4 Differential responses of seedling growth to N addition regime and level among different tree seedlings (Duncan multiple range test)

		土壤施N N addition in soil			冠层施N N addition on canopy
		CK	MN	HN	CK	MN	HN
豆科与非豆科相比 Legumes versus non-legumes	基径 Base diameter	18.450 0.001	36.161 <0.001	5.461 0.038	5.747 0.03	15.424 0.002	3.38 0.087
	株高 Tree height	46.039 <0.001	32.859 <0.001	8.979 0.011	16.937 0.001	9.629 0.008	9.111 0.009
	生物量 Biomass	9.126 0.029	21.174 0.006	30.829 0.002	0.932 0.379	11.908 0.026	6.263 0.046
阔叶与针叶相比 Broadleaf versus conifers	基径 Basal diameter	0.679 0.338	1.262 0.276	24.355 <0.001	23.799 <0.001	32.911 <0.001	1.297 0.269
	株高 Tree height	2.516 0.129	6.264 0.022	7.065 0.018	11.620 0.003	17.643 <0.001	10.767 0.004
	生物量 Biomass	0.110 0.750	10.299 0.013	8.170 0.017	16.323 0.004	33.324 0.001	1.11 0.323

Fig. 5 Effects of N addition level and regime on soil pH value (mean ± SD). Different lowercase letters (a, b) and capital letters (A, B) above the error bars indicate significant differences among N addition levels in soil and on canopy, respectively, in each species (p < 0.05); * above the error bars indicate significant differences between two N addition regimes (Duncan multiple range test; * p < 0.05, ** p < 0.01). CK, ambient N addition; HN, high N addition; MN, medium N addition. CN, N addition on canopy; SN, N addition in soil. AM, Acacia mangium; OP, Ormosia pinnata; PM, Pinus massoniana; SS, Schima superba.

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