Effects of N and P additions on net nitrogen mineralization in temperate typical grasslands in Nei Mongol, China

doi:10.17521/cjpe.2015.0374

Abstract

Abstract: <i>Aims</i>

Nitrogen (N) mineralization is an important ecological process which determines soil N supplying ability, and it is a key research domain of soil N cycling worldwide at present. Nutrient addition can play a key role in regulating soil N transformations. The objective of the study was to evaluate the effects of different levels of N and P additions on in situ N mineralization during growing seasons in the temperate grasslands.

<i>Methods</i>

We conducted an field N and P fertilization addition experiment in the temperate grassland in Nei Mongol in June 2014. Five levels of N (0-25 g N·m^?2·a^?1), five levels of P (0-12.5 g P₂O₅·m^-2·a^-1) addition treatments, and a control were set up. We measured the in situ net mineralization rate, ammonification rate, and nitrification rate using the resin core incubation technique once a month from July to October 2014. Aboveground biomass and some selected soil chemical and microbial properties were also measured in the study.

Important findings

High nitrogen addition did significantly affect the contents of inorganic N. High N addition levels (25 g N·m^?2·a^?1+ 1 g P₂O₅·m^-2·a^-1 and 10 g N·m^?2·a^?1+ 1 g P₂O₅·m^-2·a^-1) significantly increased soil inorganic N content, and the 25 g N·m^?2·a^?1+ 1 g P₂O₅·m^-2·a^-1 treatment markedly increased soil nitrate- (NO₃^--N) and ammonium-N (NH₄⁺-N). Compared to N addition, P addition had limited effects on soil inorganic N, NO₃^--N and NH₄⁺-N. Only the 12.5 g P₂O₅·m^-2·a^-1 + 2 g N·m^?2·a^?1treatment significantly increased soil ammonium-N and inorganic N. N addition did significantly affect microbial N transformation rates. The 25 g N·m^?2·a^?1+ 1 g P₂O₅·m^-2·a^-1 treatment significantly stimulated soil net N nitrification rate, mineralization rate and ammonification rate, suggesting that high N addition can effectively improve soil available N supply. N was a limiting factor to soil organic N mineralization in the study area. P addition had negligible effects on soil net N mineralization and nitrification rates, and only the 12.5 g P₂O₅·m^-2·a^-1+ 2 g N·m^?2·a^?1treatment significantly enhanced ammonification rate in the middle of growing season. The results also indicated that impacts of P addition on soil N mineralization were weaker than impacts of N. Moreover, N and P addition significantly increased aboveground biomass. Under the N and P addition, soil moisture was significantly correlated with net mineralization and nitrification rate, which suggested that it was one of the dominant factors affecting N. Net N mineralization and nitrification rate under N fertilization was significantly correlated with environmental factors (soil organic C, soil C/N and soil total N). Soil N mineralization was not positively correlated with the soil microbial biomass N or C.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201605006

Key words: temperate grassland, N and P additions, nitrogen mineralization, soil inorganic N, affecting factor

Qin-Pu LUO, Ji-Rui GONG, Sha XU, Taogetao BAOYIN, Yi-Hui WANG, Zhan-Wei ZHAI, Yan PAN, Min LIU, Li-Li YANG. Effects of N and P additions on net nitrogen mineralization in temperate typical grasslands in Nei Mongol, China[J]. Chin J Plant Ecol, 2016, 40(5): 480-492.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2015.0374

https://www.plant-ecology.com/EN/Y2016/V40/I5/480

Figures/Tables 7

Fig. 1 Temporal variations of soil NO3--N (A), NH4+-N (B) and soil inorganic N concentration (C) under different N treatments (mean ± SD, n = 3). The vertical line denotes the least significant difference among different N treatments (p < 0.05). CK, control, without nitrogen and phosphorus. N1, N2, N3, N4, N5 add nitrogen 0, 2, 5, 10, 25 g N·m?2·a?1, respectively. Other than in the control, 1 g P2O5·m?2·a?1 is added to each treatment.

Fig. 2 Temporal variations of soil NO3--N (A), NH4+-N (B) and soil inorganic N concentration (C) under different P treatments (mean ± SD, n = 3). The vertical line denotes the least significant difference among different P treatments (p < 0.05). CK, control, without nitrogen and phosphorus. P1, P2, P3, P4, P5 add phosphorus 0, 1, 2.5, 5, 12.5 g P2O5·m?2·a?1, respectively. Other than in the control, 2 g N·m?2·a?1 is added to each treatment.

Fig. 3 Soil net N nitrification (A), ammonification rates (B) and mineralization rates (C) in different periods under different N treatments (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. Non-significant differences are indicated by n.s. Treatment see Fig. 1.

Fig. 4 Soil net N nitrification (A), ammonification rates (B) and mineralization rates (C) in different periods under different P treatments (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. Non-significant differences are indicated by n.s. Treatment see Fig. 2.

Fig. 5 The aboveground biomass under different N (A) and P addition treatments (B) in August of 2014 (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. CK, control, without nitrogen and phosphorus. N1, N2, N3, N4, N5 add nitrogen 0, 2, 5, 10, 25 g N·m?2·a?1, respectively. P1, P2, P3, P4, P5 add phosphorus 0, 1, 2.5, 5, 12.5 g P2O5·m?2·a?1, respectively. Other than in the control, 1 g P2O5·m?2·a?1 is added to each treatment in the N addition experiment, and 2 g N·m?2·a?1 is added to each treatment in the P addition experiment.

Table 1 Correlation between environmental/biological factors and net N mineralization, nitrification, and ammonification rates under different N addition treatments

环境及生物因子 Environment/biological factor	净矿化速率 Mineralization (mg·kg^-1·d^-1)	净硝化速率 Nitrification (mg·kg^-1·d^-1)	净氨化速率 Ammonification (mg·kg^-1·d^-1)
土壤湿度 Soil moisture (V/V)	0.825^***	0.813^***	0.323
土壤温度 Soil temperature (℃)	0.142	0.114	0.245^*
土壤有机碳 Soil organic C (g·kg^-1)	0.887^*	0.879^*	0.418
土壤全氮 Soil total N (%)	0.848^*	0.830^*	0.612
土壤碳氮比 Soil C:N ratio	0.849^*	0.858^*	0.014
微生物碳 Microbial biomass C (mg·kg^-1)	0.422	0.410	0.396
微生物氮 Microbial biomass N (mg·kg^-1)	0.298	0.266	0.791

Table 2 Correlation between environmental/biological factors and net N mineralization, nitrification, and ammonification rates under various P addition treatments

环境及生物因子 Environment/biological factor	矿化速率 Mineralization (mg·kg^-1·d^-1)	硝化速率 Nitrification (mg·kg^-1·d^-1)	氨化速率 Ammonification (mg·kg^-1·d^-1)
土壤湿度 Soil moisture (V/V)	0.730^***	0.673^**	0.10
土壤温度 Soil temperature (℃)	0.246	0.326	0.725^**
土壤有机碳 Soil organic C (g·kg^-1)	0.527	0.626	0.601
土壤全氮 Soil total N (%)	0.372	0.544	0.662
土壤碳氮比 Soil C:N ratio	0.573	0.292	0.251
微生物碳 Microbial biomass C (mg·kg^-1)	0.269	0.308	0.280
微生物氮 Microbial biomass N (mg·kg^-1)	0.391	0.511	0.556

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