Soil enzyme activities and their influencing factors in a desert steppe of northwestern China under changing precipitation regimes and nitrogen addition

doi:10.17521/cjpe.2020.0264

Abstract

Abstract:

Aims Soil enzymes, which are mainly produced by plant roots and soil microbes, involve in the organic matter degradation and element cycling and other key processes in plant-soil systems. Study on the relationships between soil enzyme activity and plant community composition and microbial activity under changing precipitation pattern and increasing nitrogen (N) deposition can provide a new insight for evaluating the influencing mechanism of global change on the biogeochemical cycling in plant-soil systems.
Methods Based on a field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural precipitation, 30% increase, and 50% increase) and two N addition treatments (0 and 5 g·m^-2·a^-1) conducted in a desert steppe of Ningxia since 2017, the changes of soil enzyme activities (sucrase, urease, and phosphatase) were studied and their relationships with plant community composition and microbial ecological stoichiometry were analyzed in 2018 and 2019.
Important findings Compared with decreasing precipitation, increasing precipitation had greater impacts on the three enzyme activities, but its effects were interacted with N addition and sampling year. Increasing precipitation had no significant impacts on the three enzyme activities in 2018, but enhanced them in 2019. By contrast, N addition had less influences on the three enzyme activities, especially in 2019. The biomass of Astragalus melilotoides was negatively correlated with urease and phosphatase activities, while the biomass of Cleistogenes squarrosa had positive correlation with the three enzyme activities. Except the Patrick richness index, plant community diversity indices were generally negatively correlated with the three enzyme activities. Soil enzyme activities were more greatly affected by soil pH, soil total phosphorus (P), and microbial biomass carbon (C):N:P. Therefore, short-term precipitation change and N addition have little effects on the soil enzymes in the studied desert steppe (especially under reducing precipitation); increasing precipitation and N addition could pose direct influences on soil enzyme activities by increasing plant biomass, changing plant diversity, regulating microbial biomass ecological stoichiometry, and enhancing soil P availability. Given the diversity and functional complexity of soil enzymes, it is necessary to deeply analyze the influencing mechanism of global change on enzyme activities by measuring the long-term responses of various enzyme activities.

Key words: arid and semi-arid region, changing precipitation regimes, increasing atmospheric nitrogen deposition, microbial ecological stoichiometry, plant community diversity

ZHU Wan-Wan, WANG Pan, XU Yi-Xin, LI Chun-Huan, YU Hai-Long, HUANG Ju-Ying. Soil enzyme activities and their influencing factors in a desert steppe of northwestern China under changing precipitation regimes and nitrogen addition[J]. Chin J Plant Ecol, 2021, 45(3): 309-320.

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https://www.plant-ecology.com/EN/Y2021/V45/I3/309

Figures/Tables 8

Table 1 Soil physical and chemical properties in 0-20 cm layer of experimental field before precipitation and nitrogen (N) addition treatments (mean ± SE)

pH	有机碳含量 Organic carbon content (g·kg^-1)	全氮含量 Total nitrogen (N) content (g·kg^-1)	全磷含量 Total phosphorus (P) content (g·kg^-1)	NH₄⁺-N含量 Ammonium N content (mg·kg^-1)	NO₃^--N含量 Nitrate N content (mg·kg^-1)	速效磷含量 Available P content (mg·kg^-1)
8.85 ± 0.01	3.70 ± 0.11	0.48 ± 0.00	0.34 ± 0.01	1.83 ± 0.07	9.96 ± 0.59	2.55 ± 0.29

Table 2 Experimental treatments and their abbreviations

试验处理 Experimental treatment	降水量减少50% 50% reduction in precipitation	降水量减少30% 30% reduction in precipitation	自然降水量 Natural precipitation	降水量增加30% 30% increase in precipitation	降水量增加50% 50% increase in precipitation
0 g N·m^-2·a^-1	W1N0	W2N0	W3N0	W4N0	W5N0
5 g N·m^-2·a^-1	W1N5	W2N5	W3N5	W4N5	W5N5

Table 3 Effects of sampling year (α), precipitation (β), nitrogen addition (γ), and their interactions on soil enzyme activities

差异来源 Difference source	α	β	γ	α × β	α × γ	β × γ	α × β × γ
SA	25.571^**	4.421^**	24.767^**	5.802^**	0.179	0.433	0.472
UA	385.536^**	5.662^**	8.980^**	4.755^**	0.563	3.530^*	2.959^*
PA	186.338^**	7.070^**	3.716	16.133	1.207	1.143	3.945^**

Fig. 1 Effects of precipitation and nitrogen addition on soil enzyme activities in 2018 and 2019 (mean ± SE). W1, W2, W3, W4, and W5 represent 50% reduction in precipitation, 30% reduction in precipitation, natural precipitation (control), 30% increase in precipitation, 50% increase in precipitation, respectively. N0 and N5 represent 0 and 5 g·m -2·a-1 of nitrogen addition level, respectively. Different lowercase letters indicate significant difference (p < 0.05) of indices among precipitation treatments under the same nitrogen addition level. * indicates significant difference (p < 0.05) of indices among nitrogen addition treatments under the same precipitation.

Fig. 2 Relationships between soil enzyme activities and plant biomass. A, B, C, D and E represent the population biomass of Lespedeza potaninii, Astragalus melilotoides, Pennisetum centrasiaticum, Stipa capillata, Cleistogenes squarrosa, respectively. F represents the community biomass. SA, UA, and PA represent sucrase, urease, and phosphatase activities, respectively. *, ** and *** indicate p < 0.05, p < 0.01 and p < 0.001, respectively.

Fig. 3 Relationships between soil enzyme activities and plant community diversity in desert steppe. SA, UA, and PA represent sucrase, urease, and phosphatase activities, respectively. *, ** and *** indicate p < 0.05, p < 0.01 and p < 0.001, respectively.

Table 4 Conditional effects of environmental factors in redundancy analysis

指标 Index	pH	TP	C:P_m	C:N_m	N:P_s	MBC	MBP	C:P_s	NH₄⁺-N	MBN	NO₃^--N	N:P_m	SWC	SOC	TN	EC	AP	C:N_s
F	53.7	37.3	28.4	28.0	27.2	22.4	20.1	18.4	17.9	16.4	5.9	2.5	1.1	1.0	0.9	0.4	0.3	0.2
p	0.002	0.002	0.002	0.002	0.002	0.002	0.002	0.002	0.002	0.002	0.016	0.110	0.266	0.318	0.356	0.638	0.676	0.776

Fig. 4 Redundancy analysis (RDA) of soil enzyme activities and microbial ecological stoichiometry and other environmental factors. SA, UA, and PA represent sucrase, urease, and phosphatase activities, respectively. TP, C:Ps and N:Psrepresent soil total phosphorus content, C:P and N:P, respectively. MBC, MBN, MBP, C:Nm and C:Pm represent microbial biomass carbon, nitrogen, phosphorus content, C:N and C:P, respectively. NH4+-N, NO3--N represent soil ammonium nitrogen, nitrate nitrogen content, respectively.

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