Difference of microbial nutrient limiting characteristics in rhizosphere and bulk soil of coniferous forests under nitrogen deposition in southwest mountain, China

doi:10.17521/cjpe.2021.0346

Abstract

Abstract:

Aims Long-term nitrogen (N) deposition induces soil nutrient imbalance and profoundly affects nutrient cycling processes, ecological functions and the sustainable development of forest ecosystems. Although previous studies have found that N deposition increased phosphorus (P) limitation of forest trees in southwest mountainous areas, China, whether soil microorganisms showed synergistic response with plants remains unclear.

Methods In this study, we measured soil available nutrients, soil microbial biomass carbon (C), N, P and extracellular enzyme activities in a typical subalpine coniferous plantation (Pinus armandii) with chronic N addition treatments in southwest China. Furthermore, three models of ecoenzymatic stoichiometry, i.e., enzymatic ratio model, vector analysis model and threshold element ratio model were used to evaluate changes of microbial nutrient limitation under N addition.

Important findings The results showed that: 1) N addition significantly increased the P-acquiring enzyme activities by 52.5% and 53.2% in rhizosphere soil and bulk soil respectively, leading to a decrease of enzymatic N:P ratio by 7.8% and 4.8% compared to the control in rhizosphere soil and bulk soil respectively. 2) Vector model analysis found that vector angles of two soil compartments under N addition exceeded 45°, and the vector angles of rhizosphere soil and bulk soil were 52.2° and 49.0°, respectively. 3) The C:P threshold ratios (TER_C:P) of microbes in two soil compartments were significantly reduced by N addition. Consequently, the ratio of TER_C:P to available C:P (Av_C:P) was much less than 1, and the response of rhizosphere microbes was more significant. Collectively, all three models of ecoenzymatic stoichiometry indicated that N deposition aggravated P-limitation of microbial metabolism, and the extent of P limitation was more intense in the rhizosphere soil, which was closely related to nutrient contents and stoichiometric ratios of soil and microbes. The findings of this study provide an important scientific basis for adaptive management of forest ecosystems under global climate change.

Key words: microbial nutrient limitation, soil enzyme stoichiometry, nitrogen deposition, rhizosphere/bulk soil, coniferous forest

ZHANG Ying, ZHANG Chang-Hong, WANG Qi-Tong, ZHU Xiao-Min, YIN Hua-Jun. Difference of microbial nutrient limiting characteristics in rhizosphere and bulk soil of coniferous forests under nitrogen deposition in southwest mountain, China[J]. Chin J Plant Ecol, 2022, 46(4): 473-483.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2021.0346

https://www.plant-ecology.com/EN/Y2022/V46/I4/473

Figures/Tables 6

Table 1 Soil physicochemical properties of rhizosphere and bulk soil in Pinus armandii forest in southwest mountain, China (mean ± SE)

土壤位置 Soil position	处理 Treatment	DOC (mmol·kg^-1)	DIN (mmol·kg^-1)	Available P (mmol·kg^-1)	有效C:N Available C:N	有效C:P Available C:P	有效N:P Available N:P	pH	EEA_C (μmol·h^-1·g^-1 DOC)	EEA_N (μmol·h^-1·g^-1 DOC)	EEA_P (μmol·h^-1·g^-1 DOC)	MBC (mmol·kg^-1)	MBN (mmol·kg^-1)	MBP (mmol·kg^-1)
RS	对照 CK	21.71 ± 0.57^a	3.41 ± 0.06^a	0.31 ± 0.03	6.36 ± 0.17^a	70.16 ± 1.83^a	11.03 ± 0.21^a	5.79 ± 0.08^a	100.01 ± 2.19^A	185.11 ± 9.89^a	490.02 ± 9.19^A	47.31 ± 3.54^Aa	7.60 ± 0.67^a	0.55 ± 0.03^A
	施氮 N	21.69 ± 1.91	3.54 ± 0.18	0.33 ± 0.05	6.13 ± 0.54	66.03 ± 5.80	10.77 ± 0.55	5.67 ± 0.01	56.51 ± 11.18^B	199.43 ± 23.25	747.26 ± 113.88^B	55.54 ± 2.07^B	7.45 ± 0.59	0.70 ± 0.08^B
BS	对照 CK	17.18 ± 0.13^Ab	1.82 ± 0.14^Ab	0.37 ± 0.03^A	9.44 ± 0.07^b	46.62 ± 0.38^Ab	4.94 ± 0.38^b	6.03 ± 0.03^b	85.41 ± 5.88	249.10 ± 6.28^b	422.74 ± 5.85^A	25.48 ± 1.20^b	3.14 ± 0.50^Ab	0.57 ± 0.08
	施氮 N	13.87 ± 0.75^B	1.28 ± 0.02^B	0.22 ± 0.04^B	10.82 ± 0.59	64.10 ± 3.48^B	5.93 ± 0.08	5.84 ± 0.08	73.33 ± 15.86	277.46 ± 14.63	647.81 ± 32.33^B	26.49 ± 1.16	7.67 ± 0.26^B	0.49 ± 0.04
S		***	***	ns	***	ns	**	*	ns	**	ns	***	**	ns
N		ns	ns	ns	ns	ns	ns	*	*	ns	**	ns	**	ns
S × N		ns	*	*	ns	ns	ns	ns	ns	ns	ns	ns	**	*

Fig. 1 Effect of nitrogen addition on soil extracellular enzyme stoichiometry in rhizosphere and bulk soil in Pinus armandii forest in southwest mountain, China (mean ± SE). CK, control treatment; N, nitrogen addition treatment; S, soil position; S × N, interaction effect between soil position and nitrogen addition treatment. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ns, p > 0.05; n = 3.

Fig. 2 Effect of nitrogen addition on vector angle in rhizosphere and bulk soil in Pinus armandii forest in southwest mountain, China (mean ± SE). CK, control treatment; N, nitrogen addition treatment; S, soil position; S × N, interaction effect between soil position and nitrogen addition treatment. *, p < 0.05; **, p < 0.01; ns, p > 0.05; n = 3.

Fig. 3 Relationships between element ratio threshold of microbial community and soil available nutrient ratio in rhizosphere and bulk soil under nitrogen addition in Pinus armandii forest in southwest mountain, China (mean ± SE). CK, control treatment; N, nitrogen addition treatment; S, soil position; S × N, interaction effect between soil position and nitrogen addition treatment. CKB, control in bulk soil; CKR, control in rhizosphere soil; NB, nitrogen addition in bulk soil; NR, nitrogen addition in rhizosphere soil. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ns, p > 0.05; n = 3.

Table 2 Controlling factors of soil phosphorus (P) limitation in rhizosphere and bulk soil in Pinus armandii forest in southwest mountain, China

磷限制相关因子 Relevant factors of P limitation	土壤位置 Soil position	土壤因素 Soil factor	微生物因素 Microbial factor
矢量角度 Vector angle	根际土壤 Rhizosphere soil	0.304	0.532^*
	非根际土壤 Bulk soil	0.704^*	0.629
碳磷阈值比/土壤养分比 TER_C:P/Av_C:P	根际土壤 Rhizosphere soil	-0.232	0.889^**
	非根际土壤 Bulk soil	0.557^*	0.811^**

Fig. 4 Pearson correlation coefficient matrix between stoichiometry characteristics of available nutrients, microbial biomass and enzyme in rhizosphere soil (A) and bulk soil (B) and microbial phosphorus (P) limiting related indicators in Pinus armandii forest in southwest mountain, China. AvC:N, available C:N ratio; AvC:P, available C:P ratio; AvN:P, available N:P ratio; EEAC:N, Enzyme C:N ratio; EEAC:P, Enzyme C:P ratio; EEAN:P, Enzyme N:P ratio; MBC:MBN, microbial biomass C:N ratio; MBC:MBP, microbial biomass C:P ratio; MBN:MBP, microbial biomass N:P ratio; TERC:P, C:P threshold ratio; TERC:P/AvC:P, C:P threshold ratio/available C:P ratio; VA, vector angle. *, p < 0.05; **, p < 0.01; ***, p < 0.001; n = 3.

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