Response of soil enzyme stoichiometry to grazing and identification of soil limiting nutrients in typical steppe of Nei Mongol, China

doi:10.17521/cjpe.2024.0113

Abstract

Abstract:

Aims Soil extracellular enzymes are crucial for soil organic matter decomposition and nutrient cycling. Soil enzyme activity and stoichiometry can provide insights into microbial resource limitations and soil nutrient availability. This study investigated the effects of grazing, particularly overgrazing that often leads to grassland degradation, on soil enzyme activity and stoichiometry, and identifies nutrient limitations in temperate grasslands.

Methods We conducted grazing experiments with varying stock rates in a typical steppe of Nei Mongol, and investigated the changes in the activities and stoichiometric ratios of soil extracellular enzymes. Enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) cycling were analyzed, and a vector model was applied to determine soil nutrient limitations under different grazing intensities.

Important findings 1) Soil hydrolase activities in the studied grassland ranged from 0 to 300 nmol·g^-1·h^-1, which is relatively low compared with the global averages. Grazing intensity significantly impacted the activities of soil enzymes, including α-glucosidase, cellulose hydrolysis, xylosidase, β-d-cellubiosidase, β-1,4-N-acetylamino-glucosidase, glycosaminidase, leucine aminopeptidase, and acid phosphatase. The enzyme activities peaked under moderate grazing and recommended grazing. 2) The Standardized Major Axis (SMA) regression analysis revealed strong linear relationships between the enzyme activities associated with C, N, and P cycling. The soil enzyme C:N:P stoichiometric ratio was 1:2.3:1.3, deviating from the global average 1:1:1. 3) The vector model based on soil enzyme stoichiometry indicated that the grasslands were co-limited by N and P, with P limitation becoming more pronounced as grazing intensity increased in Nei Mongol.

Key words: grassland degradation, grazing, soil enzyme activity, nutrient limitation

LI Tian-Qi, CAO Ji-Rong, LIU Xiao-Ni, TIAN Si-Hui, LAN Bo-Lan, QIU Ying, XUE Jian-Guo, ZHANG Qian, CHU Jian-Min, ZHANG Shu-Min, HUANG Jian-Hui, LI Ling-Hao, WANG Qi-Bing. Response of soil enzyme stoichiometry to grazing and identification of soil limiting nutrients in typical steppe of Nei Mongol, China[J]. Chin J Plant Ecol, 2025, 49(1): 19-29.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0113

https://www.plant-ecology.com/EN/Y2025/V49/I1/19

Figures/Tables 5

Table 1 Effect of grazing intensity on soil extracellular enzyme activities (mean ± SE, nmol·g-1·h-1, n = 20)

土壤酶 Soil enzyme	放牧强度 Grazing intensity
土壤酶 Soil enzyme	CK	RG	LG	MG	HG
AG	8.73 ± 0.61^a	8.13 ± 0.40^ab	7.43 ± 0.41^ab	7.75 ± 0.62^ab	6.78 ± 0.43^b
BG	11.03 ± 0.89^a	11.58 ± 1.06^a	9.47 ± 0.42^a	8.98 ± 1.00^a	9.05 ± 0.61^a
CBH	1.70 ± 0.25^b	0.79 ± 0.36^c	1.87 ± 0.33^ab	2.01 ± 0.23^ab	2.67 ± 0.23^a
XS	8.33 ± 0.73^ab	8.82 ± 0.47^a	6.70 ± 0.64^bc	7.55 ± 0.85^ab	4.91 ± 0.58^c
CB	5.47 ± 0.46^a	5.40 ± 0.29^a	4.60 ± 0.42^ab	5.00 ± 0.52^a	3.48 ± 0.30^b
NAG	12.40 ± 0.65^ab	14.52 ± 2.53^a	11.21 ± 0.39^ab	10.76 ± 0.69^ab	9.40 ± 0.51^b
LAP	257.56 ± 14.78^a	254.98 ± 14.28^a	217.66 ± 13.10^ab	229.61 ± 17.56^ab	198.45 ± 7.94^b
AP	26.36 ± 3.29^ab	28.56 ± 2.80^a	17.93 ± 3.10^b	22.21 ± 3.47^ab	8.84 ± 1.37^c

Fig. 1 Soil extracellular enzyme activities associated with carbon (C), nitrogen (N) and phosphorus (P) acquisition under different grazing intensities (mean ± SE, n = 20). Significant differences among grazing intensities are indicated by different lowercase letters (p < 0.05). AP, acid phosphatase; BG, β-1,4-glucosidase; LAP, leucine aminopeptidase; NAG, β-N-acetyl glucosaminidas. CK, control; HG, heavy grazing; LG, light grazing; MG, moderate grazing; RG, recommended grazing.

Fig. 2 Soil extracellular enzyme stoichiometric ratios under different grazing intensities (mean ± SE, n = 20). Significant differences among grazing intensities are denoted by different lowercase letters (p < 0.05). C, carbon; N, nitrogen; P, phosphorus. CK, control; HG, heavy grazing; LG, light grazing; MG, moderate grazing; RG, recommended grazing.

Fig. 3 Standard Major Axis (SMA) regression analyses illustrating the relationships between the activities of acid phosphatase (AP), β-1,4-glucosidase (BG), leucine aminopeptidase (LAP) and β-N-acetyl glucosaminidase (NAG) (n = 100). CK, control; HG, heavy grazing; LG, light grazing; MG, moderate grazing; RG, recommended grazing.

Fig. 4 Vector model analysis based on soil extracellular enzyme stoichiometric ratios under different grazing intensities. A, Variation of vector length with grazing intensity (mean ± SE). B, Variation of vector angle with grazing intensity, the dotted 45° threshold line distinguishes nitrogen (N) and phosphorus (P) limitation (mean ± SE). C, Relationship between soil enzyme carbon (C):N and C:P stoichiometric ratios, with the dashed line indicating the 1:1 threshold. D, Linear regression analysis of vector length and angle, highlighting patterns of nutrient limitation. Different lowercase letters denote significant differences among grazing intensities (p < 0.05). CK, control; HG, heavy grazing; LG, light grazing; MG, moderate grazing; RG, recommended grazing.

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