Characteristics of soil organic carbon and total nitrogen storages for different land-use types in Central Yunnan Plateau

, , , , , ,

(School of Ecology and Environmental Science, Southwest Forestry University, Kunming,Yunnan 650224, China)

Abstract: Two-factor analysis of variance and redundancy analysis were used to analyze the characte-ristics of soil organic carbon total nitrogen storage in garden land, forestland, grassland, farmland, and bare land in the Dachunhe watershed of Jinning District, Kunming City, Yunnan Province, China. The effects of the soil organic carbon,total nitrogen stratification ratio, soil physical and chemical factors on the storage characteristics of organic carbon and total nitrogen of different land-use types were analyzed. The results show that the rates of carbon and nitrogen stratification in soil from 0-20 cm and 40-60 cm of the same land-use types differed are statistically significant (P<0.05). The organic carbon and total nitrogen stratification ratio SR1 of garden land soil are 38.5% and 25.3%, respectively, which are higher than SR2. The soil organic carbon and total nitrogen stratification ratio SR2 of different land-use types are greater than SR1. There are statistically significant differences in the SR2 soil organic carbon and total nitrogen stratification ratios (P<0.05). Soil organic carbon and total nitrogen storage of diffe-rent land-use types gradually decrease with increasing soil depth, with the maximum soil organic carbon and total nitrogen storage in the 0-20 cm soil layer. Soil organic carbon and total nitrogen sto-rage at the same soil depth are significantly different (P<0.05). Soil organic carbon and total nitrogen storage in the garden land are greater than those in the other land-use types. Soil organic carbon and total nitrogen storage in 0-20 cm garden land are 4.96 and 3.19 times than those in bare land, respectively; soil organic carbon and total nitrogen storage are explained by 93.66% and 1.53% in redundancy analysis RDA1 and RDA2, respectively. All physicochemical factors except Available Phosphorus and pH are statistically significance with carbon and nitrogen storage (P<0.05). Soil cationic exchange capacity, Available Phosphorus, C/N ratio, and Moisture Content are positively correlated with organic carbon and total nitrogen storage. In contrast, soil Bulk Density is negatively correlated with organic carbon storage and total nitrogen storage. Available Phosphorus, C/N ratio, and Moisture Content are the main factors promoting soil organic carbon and total nitrogen accumulation.

Key words: soil organic carbon storage;soil total nitrogen storage;stratification ratio;land-use types;Central Yunnan Plateau

Soil organic carbon and total nitrogen are significant plant nutrients and important components of soil carbon and nitrogen pools[1-2]. Soil organic carbon and total nitrogen are important substances that affect soil fertility and crop yield[3-4]. land-use types affect soil carbon and nitrogen storage and ecosystem carbon and nitrogen cycles[5]; they also affect soil carbon and nitrogen sources and mineralization rates, which result in differences in soil carbon and nitrogen storage[6]. CASTRO, et al[7]and KARA, et al[8]found that different land-use types affect the quantity and quality of litter, soil microbial community structure, and enzyme activities. ZHU, et al[9]studied soil organic carbon and total nitrogen storage in fallow grassland, shrubland, woodland, and agricultural land on the Loess Plateau and found that total nitrogen storage in fallow grassland, shrubland, and woodland, compared to agricultural land, was 32%, 90%, and 55% higher, and organic carbon storage, 41%, 119%, and 60% higher, respectively. YAO, et al[10]studied soil organic carbon and nitrogen dynamics in different land-use types in the central and western regions of Cote d′Ivoire and found that soil organic carbon and nitrogen were higher in plantation forests of different tree species than in teak and cocoa forests. In contrast, natural forests had lower organic carbon contents than arbor and food crops, with statistically significant variability in soil organic carbon and nitrogen across land-use types. Soil nutrient content shows stratification with soil depth. Moreover, the soil nutrient element stratification ratio is widely used in soil carbon and nitrogen dynamic quality eva-luations, conservation tillage, and fallow restora-tion[11-12]. FRANZLUEBBERS[13]used a stratification ratio to study the soil organic matter stratification status and found that the level of the soil carbon and nitrogen storage stratification ratio is an indicator of dynamic soil quality. If the stratification ratio is greater than 2, the soil will not degrade.

At present, many domestic and international studies on soil organic carbon and total nitrogen storage in different land-use types have focused on the effects of different spatial and temporal distributions, vegeta-tion responses, irrigation and fertilization methods on soil organic carbon and totalnitrogen storage[14-15]. Moreover, there are fewer studies on the effects of soil physical and chemical factors on carbon and nitrogen storage in different land-use types. However, these factors are significantly correlated with carbon and nitrogen storage[16]. The characteristics of changes in organic carbon and total nitrogen storage of different land-use types, the stratification ratio of soil nutrient elements, and the influence of soil physicochemical factors on carbon and nitrogen storage were studied. It helps to clarify the dynamic change process of the soil carbon and nitrogen cycle in different land-use types and the interrelationship with other nutrients. In this paper, five land types, forestland, garden land, grassland, farmland, and bare land, were used for research in the Dachunhe subbasin of Jinning District, Kunming City, Yunnan Province. The effects of soil organic carbon and total nitrogen stratification ratios and soil physicochemical factors (pH, cation exchange, total phosphorus, available phosphorus, moisture content, and bulk density) on organic carbon and total nitrogen storage in different land-use types were studied. The purpose of studying different land-use types in the Central Yunnan Plateau was to understand the characteris-tics of soil organic carbon and total nitrogen storage changes; to provide a reference for the study of soil carbon and nitrogen fixation capacity; and to provide a theoretical basis for the management of soil carbon and nitrogen pools.

1 Materials and methods

1.1 Field description and experimental design

The experiment was conducted from April to December 2018 in a small watershed of Dachunhe in Jinning District, Kunming City, Yunnan Province. The subbasin of Dachunhe is in Baofeng Town, southwest of Jinning District, with geographic coordinates of 102°33′—102°38′E, 24°33′—24°37′N. It is a low-latitude subtropical plateau climate zone, with an ave-rage annual temperature of 14.9 ℃, average annual precipitation of 950 mm, a clear boundary between dry and wet seasons, a rainy season from June to October, average annual runoff depth of 30 mm, and an average annual evaporation of 900 mm. Soil types are mainly red soil, purple soil, alluvial soil, rocky soil, and rice soil. The Dachunhe subbasin represents typical soil erosion in the red soil area of the central Yunnan Pla-teau, and Yunnan Province has classified it as a critical demonstration area for soil erosion control[17].

1.2 Soil sampling and analysis of soil properties

In the Dachunhe subbasin, five different land-use types were selected: garden land, forestland, grassland, farmland, and bare land. Representative standard sample plots (20 m×20 m) were selected for each land-use type, and bare land was used as the control; there were three replicates of each standard sample plot. Fifteen standard sample plots of different land-use types were in the natural environment, and their primary conditions were investigated, as shown in Tab. 1, the physical quantities in the table are slopec, vegetation coversa, average tree heighth, average diameter at breast heightd, and average deadfall thicknessb. Three sampling points were set up in the upper, middle, and lower parts of each standard sample land. Soil samples were collected from 0-20 cm, 20-40 cm, and 40-60 cm soil depths. Soil samples were removed from the gravel and roots and other debris then were sealed, stored, and brought back to the laboratory in two parts: one part was fresh soil to determine the moisture content; the other was naturally dried and finely ground through 1.00 mm and 0.25 mm sieves to determine soil pH, organic carbon, total nitrogen, total phosphorus, available phosphorus, cation exchange capacity, and other indicators. The sampling dates were April 16, May 14, June 13, July 15, August 16, September 15, October 13, November 15, and December 13, 2018. Soil bulk weight was determined by the ring knife method, soil moisture content was determined by the drying method, pH was determined by the pH acidity meter, organic carbon was determined by the potassium dichromate external heating method, perchloric acid sulfate digestion was determi-ned by the total nitrogen - Kjeldahl method, cation exchange was determined by the ammonium acetate exchange - Kjeldahl distillation method, total phosphorus was determined by the sulfuric acid-perchloric acid method and available phosphorus was determined by UV-visible spectrophotometry. Three replicates of each soil sample were measured in different parts of the standard sample site and at different soil depths, and the average values were obtained.

Tab.1 Basic characteristics of different land-use types

1.3 Calculation of soil organic carbon and total nitrogen storage

Soil organic carbon and total nitrogen storage were calculated using the equivalent soil mass(ESM) met-hod[18], which corrects soil weight inconsistencies due to differences in soil bulk weight in different treatment soil layers.

1) The FD method is based on the fixed depth method of calculating carbon and nitrogen storage as follows:

SOCFD=0.1SOCiBDiDi,

(1)

TNFD=0.1TNiBDiDi,

(2)

whereSOCFDandTNFDare soil organic carbon storage and total nitrogen storage at a fixed depth, mg/hm2, respectively;SOCiandTNiare soil organic carbon and soil total nitrogen content in layeri, g/kg, respectively;BDiis soil bulk density in layeri, g/cm3;Diis the thickness of soil layeri, cm; and 0.1 is the unit conversion factor.

2) The ESM method calculates carbon and nitrogen storage by first calculating the soil mass at a fixed depth with the formula:

(3)

whereMsoilis the soil mass at a fixed depth, mg/hm2; and 100 is the conversion factor.

The lightest soil mass from each land-use type at different soil depths was selected as the reference mass to calculate the excess soil mass:

Mex=Msoil-Mref，

(4)

whereMexis the excess soil mass, mg/hm2;Mrefis the reference soil mass, mg/hm2.

The equation for calculating carbon and nitrogen storage based on the equivalent mass method is as follows:

SOCESM=SOCFD-0.001MexCONsn,

(5)

TNESM=TNFD-0.001MexCONsn,

(6)

whereSOCESMandTNESMare the equivalent weight of soil organic carbon or total nitrogen storage, mg/hm2;CONsnis the deepest soil organic carbon or total nitrogen content, g/kg; and 0.001 is the conversion factor.

3)The calculation of organic carbon and total nitrogen stratification ratios. This paper used the stratification ratio calculation method of Franzluebbers to calculate the stratification ratio of organic carbon and total nitrogen in different land types. Soil organic carbon and total nitrogen storage and their evolution patterns were reasonably evaluated.

SR1 is the stratification ratio of the 0-20 cm soil layer to the 20-40 cm soil layer, andSR2 is the stratification ratio of the 0-20 cm soil layer to the 40-60 cm soil layer.

1.4 Data analysis and processing

SPSS 26.0 was applied for statistical analysis of the data. Moreover, one-way ANOVA was used to test the differences between different land-use types of physical and chemical indicators (α=0.05). Multifac-tor ANOVA was used to analyze the effects of soil depth and its interaction on soil organic carbon and total nitrogen storage in different land-use types. Canoco 5.0 software was used for redundancy analysis, and Origin 2020b software was used for mapping.

2 Results and analysis

2.1 Characteristics of changes in soil physical and chemical properties

The physicochemical quantities in Tab.2 are Soil depthH, Bulk densityBD, Moisture contentMC, Total nitrogenTN, Soil organic carbonSOC, Cation exchange capacityCEC, Total phosphorusTP, Available phosphorusAP, Carbon to Nitrogen ratioC/N, and pH.

Tab.2 Changes in soil physical and chemical factors in different land-use types

As can be seen from the table that the soil Bulk density of the bare land increased by 4.8% and 2.1% in the 40-60 cm and 20-40 cm soil layers, respectively, compared to the 0-20 cm soil layer. The highest soil cation exchange in the garden land, the soil cation exchange increased by 10.1% and 5.1% in the 0-20 cm soil layer and 20-40 cm soil layer, respectively, compared with the 40-60 cm soil layer. The soilC/Ndecreased with increasing soil depth in forestland, garden land, and bare land, increased with increasing soil depth in grassland, increased, then decreased, and then increased again with increasing soil depth in farmland. The carbon and nitrogen ratios of the five land-use types were in the range of 9.77-26.55. The diffe-rence in soilC/Nbetween 0-20 cm and 40-60 cm of the same land use type were statistically significant (P<0.05). The soilC/Nincreased by 38.5% and 25.3% in garden land and bare land 0-20 cm compared to 40-60 cm, respectively. The grassland and farmland 40-60 cm and 0-20 cm soil carbon to nitrogen ratios increased by 36.7% and 26.1%, respectively.

Soil moisture content, bulk density, total phosphorus, organic carbon, available phosphorus, total nitrogen, and pH showed different trends at the same soil depth, the differences were statistically significant (P<0.05). The soil cation exchange, total nitrogen, organic carbon, and moisture contents were higher in garden land and forestland, and the soil moisture content in garden land was the largest and 1.66 times higher than that in bare land. The available phosphorus of garden soil was 51.7%, 62.3%, 75.0%, and 89.3% higher than that of bare land, grassland, forestland, and farmland, respectively. Of all land-use types, garden land and bare land at 0-20 cm and 20-40 cm had the two highest levels of soil available phosphorus content; 40-60 cm soil available phosphorus in garden land had a maximum of 7.45 mg/kg, 15 times more than that of farmland. Soil pH varied most significantly at the same soil depth and was 1.24 times greater in bare land than in farmland in the 0-20 cm and 40-60 cm soil layers. The pH was greatest in the 20-40 cm soil layer of garden land, where it was 1.17 times greater than that of grassland. Soil pH and soil bulk density were positively correlated with soil depth, the difference was statistically significant (P<0.05). Soil cation exchange, total phosphorus, total nitrogen, organic carbon, available phosphorus, and moisture content were negatively correlated with soil depth, the differences were statistically significant (P<0.05). The total phosphorus content of the soil is ranked by land type from large to small farmland, garden land, bare land, forestland, and bare land, and their mean values of soil total phosphorus were 0.96, 0.69, 0.58, 0.52, and 0.49 g/kg, respectively. Soil total nitrogen content in 0-20 cm and 20-40 cm soil depth in descending by land type order was garden land, forestland, grass-land, farmland, and bare land.

2.2 Characteristics of changes in organic carbon and total nitrogen stratification ratios in soil

Fig.1 shows the stratification ratioSRof organic carbon and total nitrogen in different land-use types. The stratification ratio was used to determine the soil quality. A stratification ratio of less than 2 indicates that the soil was degraded. In contrast, a stratification ratio of greater than or equal to 2 indicates that the soil was relatively good. The figure shows the stratification ratios of soil organic carbon and total nitrogenSR2 are greater than those ofSR1 in different land-use types. There was a statistically significant difference between theSR2 stratification ratios of different land-use types (P<0.05).

The soil organic carbon in garden land stratification ratio was 1.9 times higher than that of grassland, and there were statistically significant diffe-rences between garden land and grassland. TheSR2 of soil organic carbon garden land and bare land were 2.32 and 2.11, respectively; both were greater than 2, which indicated that the fertility quality of soil organic carbon in garden land and bare land was good. The minimum organic carbon stratification ratio of grassland was 1.22, indicating that the quality of organic carbon fertility of grassland soil was poor and may be subject to degradation. The soil total nitrogen in grassland and farmlandSR2 were 1.93 and 1.87, respectively. Both were less than 2, indicating that grassland and farmland had a better quality of total nitrogen fertility than other land-use types. Moreover, the total nitrogen stratification ratio of forestland soil was the smallest, indicating that the total nitrogen fertility quality of fo-restland soil was poor.

Fig.1 Soil stratification ratio of organic carbon and total nitrogen

2.3 Characteristics of changes in soil organic carbon and total nitrogen storage in different land-use types

Fig.2 shows the characteristics of the variation of mean soil organic carbon and total nitrogen storagesWwith the depth of soil layer from April to December for different land-use types. The maximum soil organic carbon storage is from 0-20 cm, followed by 20-40 cm, the minimum soil organic carbon storage is from 40-60 cm. The soil organic carbon storage in garden land was 116.16, 80.21, and 50.03 mg/hm2at 0-20 cm, 20-40 cm, and 40-60 cm, respectively. The soil organic carbon storage in garden land increased by 56.9% and 37.6% at 0-20 cm and 20-40 cm, respectively, compared with 40-60 cm. The soil organic carbon storage in descending order of land types was garden land, fo-restland, farmland, grassland, and bare land. Moreo-ver, garden land had 32.9%, 72.1%, 69.5%, and 78.9% greater soil organic carbon storage than forestland, farmland, grassland, and bare land, respectively.

Soil organic carbon storage at different soil depths was statistically significant (P<0.05), and soil organic carbon storage gradually decreased with increasing soil depth. The largest difference between soil organic carbon storage occurred between the depths of 0-20 cm and 40-60 cm. Garden land 0-20 cm soil organic carbon storage was 2.32 times that of 40-60 cm. The difference in soil organic carbon storage in the same soil depth of different land-use types was statistically significant (P<0.05), the soil organic carbon storage in garden land was greater than in other land-use types, and the soil organic carbon storage is 0-20 cm garden land was 4.96 times that of bare land.

Fig.2 Variation of soil organic carbon and total nitrogen storage with soil depth

From the Fig.2, the largest total nitrogen storage was found in 0-20 cm soil, followed by 20-40 cm soil, and the smallest total nitrogen storage was found in 40-60 cm soil. The garden land soil total nitrogen storage at 0-20 cm, 20-40 cm, and 40-60 cm was 4.38, 3.77, and 3.06 mg/hm2, respectively. Garden land soil total nitrogen storage of 0-20 cm and 20-40 cm were 52.1% and 45.1% greater than 40-60 cm, respectively. The soil′s total nitrogen storage is sorted by land type from largest to smallest: garden land, forestland, sloping farmland, barren grassland, and bare land. Garden land had 24.2%, 47.3%, 31.4%, and 67.9% greater soil total nitrogen storage than forestland, farmland, grassland, and bare land, respectively, were statistically significant differences (P<0.05) in soil total nitrogen storage were observed at different soil depths for the same land-use type. Moreover, there was significant variation in soil total nitrogen storage based on soil depth characteristics, as the soil total nitrogen storage gradually decreased with increasing soil depth. The difference between soil total nitrogen storage of 40-60 cm and 0-20 cm was the largest in garden land of 0-20 cm, where soil total nitrogen storage was 1.43 times that of 40-60 cm. The difference in total nitrogen storage in different land-use types at the same soil depth was statistically significant (P<0.05), and the total nitrogen storage in garden land soil was greater than that in other land-use types. The 0-20 cm garden land soil total nitrogen storage was 3.19 times greater than that in bare land.

2.4 Effects of different land-use types and soil depths on organic carbon and total nitrogen storage

Tab. 3 shows the ANOVAs of different land-use types, soil depths, and their interactions on soil organic carbon and total nitrogen storage. At the significance level of 0.05, the effects of land-use type, soil depth, and interaction on soil organic carbon and total nitrogen storage were statistically significant (P<0.01). This shows that there is 95% certainty that land-use types, soil depth, and their interactions had a statistically significant effect on soil organic carbon and total nitrogen storage.

Tab.3 Variance analysis of effects of land-use types, soil depths, and their interaction on organic carbon and total nitrogen storage

2.5 Redundancy analysis of soil physicochemical factors and soil carbon and nitrogen storage in different land-use types

Fig.3 shows the redundancy analysis (RDA) analysis of soil physicochemical factors and carbon and nitrogen storage for different land-use types. There were different degrees of positive and negative correlations between each physicochemical factor and carbon and nitrogen storage. The explanation rates of carbon and nitrogen storage inRDA1 andRDA2 were 93.66% and 1.53%, respectively, indicating that the two axes together explained 95.19% of the variation in carbon and nitrogen storage, thereby reflecting the relationship between physicochemical factors and carbon and nitrogen storage as being mainly determined byRDA1. In the first and second quadrants, soil cation exchange, avai-lable phosphorus, carbon to nitrogen ratio, and moisture content arrows are in the same direction as organic carbon and total nitrogen storage (P<0.05). Moreover, the angle between the arrows is the smallest (<45°), indicating that soil cation exchange, available phosphorus, carbon to nitrogen ratio, and moisture content were the main factors promoting the accumulation of soil organic carbon and total nitrogen. Soil total phosphorus and total nitrogen storage arrows are in the same direction. The angle is (45°, 90°); the positive effect on total nitrogen storage was slightly less than that of soil cation exchange, available phosphorus, and moisture content.

In the third quadrant, the soil bulk density arrow is the farthest from the origin, opposite of the direction of the carbon and nitrogen storage arrow, and at the largest angle (>90°), indicating that soil bulk density has the greatest inhibitory effect on soil carbon and nitrogen storage. The directions of the pH and carbon and nitrogen storage arrows are opposite, and the angle is larger (>90°). The arrow′s distance from the origin is shorter than the soil bulk density. The inhibitory effect on soil carbon and nitrogen storage is second to the bulk density. A Monte Carlo test of physicochemical factors revealed that all physicochemical factors, except Available phosphorus and pH, were signifi-cantly correlated (P<0.05) with carbon and nitrogen storage. The explained values are sorted by the factor from largest to smallest as soil bulk density, carbon to nitrogen ratio, total phosphorus, available phosphorus, pH, moisture content, and soil cation exchange. The correlation between soil bulk density, moisture content, carbon to nitrogen ratio, cation exchange, and soil carbon and nitrogen storage was statistically significant (P<0.01), indicating that soil bulk density, moisture content, carbon to nitrogen ratio, and cation exchange were significantly correlated with soil carbon and nitrogen storage and were the main factors affecting the change in soil carbon and nitrogen storage.

Fig.3 Effects of soil physical and chemical factors on soil organic carbon and total nitrogen storage

3 Discussion

This paper calculated soil organic carbon and total nitrogen storage from April to December by the equivalent soil mass(ESM) method for different land-use types. The study found statistically significant (P<0.05) differences in soil organic carbon and total nitrogen storage between land-use types, which were related to the vegetation cover of different land-use types. The vegetation cover of garden land and forestland was 87% and 81%, respectively. The average litter thicknesses were 3.61 cm and 2.82 cm, respectively. The soil organic carbon and total nitrogen storage of garden land and forestland were significantly higher than those of the other land-use types. Furthermore, this result is similar to ZHU, et al[9]whose study found that soil organic carbon and total nitrogen storage in forestland were greater than those in other types of land, such as agricultural land. The variation in soil carbon and nitrogen storage in bare land in this study area is inconsistent with DONG, et al[19]who found that organic carbon and total nitrogen contents in wasteland were higher than those in farmland. The reason for this inconsistency is that this study area was located in the acidic red loam soil area of the central Yunnan Plateau, which belongs to a subtropical plateau monsoon climate, has high rainfall in the rainy season, and receives much torrential rain. Moreover, a long rainy season combined with a slope of approximately 20 degrees, bare land vegetation coverage of only 9%, average litter thickness of 0.37 cm, and a strong leaching effect lead to serious loss of soil nutrients. Therefore, bare land has the smallest organic carbon and total nitrogen storage among all land-use types. Different land-use types alter the soil microecological environment, leading to changes in soil physicoche-mical properties[20]. This study showed that soil organic carbon and total nitrogen storage were negatively correlated with soil bulk density, soilC/Nwas closely related toSOCandN, andC/Nwas an indicator of soil fertility[21]. SoilC/Ndecreases with increasing soil depth in forestland, garden land, and bare land, indicating that the degree ofSOCdecomposition decreases with increasing soil depth, consistent with LOU, et al′s results[22]. TheC/Nof grassland soil increased with soil depth. TheC/Nof farmland soil showed a trend of increasing, then decreasing, and then increa-sing with soil depth. This is similar to the trend of soilC/Nchanges in alpine grassland ecosystems on the Tibetan Plateau by WANG, et al[23]. Different land-use types have different degrees of positive and negative correlations between soil physicochemical factors and carbon and nitrogen storage[24]. This study found significant correlations (P<0.05) between soil physicochemical factors and carbon and nitrogen storage; available phosphorus and pH, soil cation exchange, available phosphorus, carbon to nitrogen ratio, and moisture content were positively correlated with organic carbon and total nitrogen storage, which are the main factors promoting soil organic carbon and total nitrogen accumulation. In this paper, we only studied the effects of soil physicochemical factors on soil organic carbon and total nitrogen storage, and the effects of different combinations of water and heat and other environmental factors on organic carbon and total nitrogen storage need to be further investigated.

4 Conclusions

Through the study of organic carbon and total nitrogen stratification ratios of the soil of different land-use types and the characteristics of their soil physicochemical factors on the changes of organic carbon and total nitrogen storage, the main conclusions are as follows:

1) The carbon and nitrogen ratios of soil from 0-20 cm and 40-60 cm differed statistically significantly (P<0.05) for the same land-use type. The soil organic carbon and total nitrogen stratification ratios ofSR2 were greater than those ofSR1 in the different land-use types. There were statistically significant differences in soil organic carbon and total nitrogen stratification ratios inSR2 (P<0.05).

2) The soil organic carbon and total nitrogen reserves of different land-use types gradually decrease with increasing soil depth. The organic carbon and total nitrogen reserves of the 0-20 cm soil layer were the largest, showing obvious surface enrichment. The differences in soil organic carbon and total nitrogen storage at the same soil depth were statistically significant (P<0.05), and garden land soil organic carbon and total nitrogen storage were greater than those of the other land-use types. Soil organic carbon and total nitrogen storage in 0-20 cm garden land were 4.96 and 3.19 times higher than those in bare land, indicating that garden land has stronger soil carbon and nitrogen sequestration.

3) Soil organic carbon and total nitrogen storage were explained by 93.66% and 1.53% in redundancyRDA1 andRDA2, respectively. All physicochemical factors except Available phosphorus and pH were statistically significant with carbon and nitrogen storage (P<0.01). Soil cation exchange, available phospho-rus, carbon to nitrogen ratio, and moisture content were positively correlated with organic carbon and total nitrogen storage. They were the main factors promoting the accumulation of soil organic carbon and total nitrogen. Soil bulk density was negatively correlated with organic carbon and total nitrogen storage and had an inhibitory effect on soil carbon and nitrogen storage.

4) This study to provide references for the soil carbon and nitrogen fixation capacity of different land-use types in the Central Yunnan Plateau and provides a theoretical basis for managing soil carbon and nitrogen pools in different land-use types.