Storage and controlling factors of soil organic carbon in alpine wetlands and meadow across the Tibetan Plateau

Alpine wetlands and meadows across the Three Rivers Source Region (TRSR) store high soil organic carbon (SOC). However, information on factors affecting SOC storage is scanty. Herein, we investigated SOC storage and explored factors affecting SOC storage, including climate, soil properties and above- and belowground biomass, using 50 soil profiles across the TRSR on the Tibetan Plateau. The SOC storage was 491.9 ± 158.5 Tg C and 545.2 ± 160.8 Tg C in the TRSR alpine wetlands and meadow, respectively. The SOC stock was positively correlated with the mean annual precipitation. However, no significant correlation between SOC stock and mean annual temperature was observed, as opposed to the global trend. In addition, SOC stock was positively correlated with both the aboveground biomass (AGB) and belowground biomass (BGB). Soil pH indirectly affected SOC stock, while SOC stock positively correlated with Al and Fe oxyhydroxides. Compared with vegetation biomass and climatic factors, soil properties, including soil pH and Al and Fe oxyhydroxides (Al_o and Fe_o), affected not only SOC stock variation but also affected the impact of vegetation and climatic factors on SOC stock. Climate factors, AGB, BGB, soil pH, Al_o and Fe_o jointly accounted for 59% of SOC stock variation in alpine wetlands and 64% of SOC stock variation in alpine meadow. This study suggests that soil properties are the dominant factors affecting SOC variation in alpine wetlands and meadow on the Tibetan Plateau.     

藏东南色季拉山西坡不同植被土壤有机碳垂直分布特征及其影响因素

  【目的】  藏东南地区高山生态系统有巨大的土壤碳汇潜力，研究其不同生态系统下土壤有机碳 (SOC) 储存的变化特征及其影响因子，有助于深入了解青藏高原土壤碳循环及区域碳源汇平衡。  【方法】  本研究在西藏色季拉山西坡海拔3000～4600 m开展密集土壤采样，研究不同海拔高度下不同植被类型SOC的储存特征，并分析其关键影响因子。  【结果】  表层0—5 cm的SOC含量随海拔升高而增加，4个植被带SOC含量平均值表现为高寒草甸 (8.31% ± 0.77%) > 暗针叶林 (7.20% ± 0.90%) > 高寒灌丛草甸 (6.74% ± 0.80%) > 针阔混交林 (3.88% ± 0.46%)。在剖面5—10、10—15、15—20、20—30、30—40、40—60 cm各层SOC含量随海拔升高呈先增加后降低趋势，SOC含量在4种植被带的平均值表现为暗针叶林 > 高寒灌丛草甸 > 高寒草甸 > 针阔混交林。SOC含量随剖面深度增加而显著下降，高寒草甸和高寒灌丛草甸SOC垂直分布特征为表层聚集型，而针阔混交林和暗针叶林SOC垂直分布特征为普通递减型。剖面0—20、20—40、40—60 cm的SOC储量随海拔升高呈先增加后降低的特征。在表层0—20 cm高寒草甸SOC储量最高 (C 95.66 ± 4.81 t/hm2)；在剖面20—40和40—60 cm暗针叶林SOC储量最高，且其在整个0—60 cm剖面的SOC总储量在所有植被类型中最高 (C 199.14 ± 11.10 t/hm2)；针阔混交林SOC储量在剖面各层均为最低，且其在整个剖面的SOC总储量 (C 111.45 ± 10.30 t/hm2) 显著低于其他植被类型。剖面各层SOC储量与年平均温度、凋落物碳氮比呈显著负相关，而与海拔高度、年平均降水量和土壤含水量呈显著正相关。逐步回归显示土壤含水量是影响剖面各层以及整个剖面SOC储存的关键因子。随机森林模型对SOC储存的解释度为50.32%～65.82%，土壤含水量对表层土体SOC预测的相对贡献最高，年平均温度、年平均降水量和凋落物质量对各层SOC预测均有显著贡献，而植被类型对SOC预测的相对贡献随剖面加深而逐步增加。  【结论】  色季拉山西坡不同海拔高度下SOC的储存特征随不同植被类型和剖面深度而发生显著变化，环境因子(如土壤水分) 对表层土体SOC储存有关键影响，植被类型对深层土体SOC储量变化的预测有重要贡献。     

Soil organic carbon in semiarid alpine regions: the spatial distribution,stock estimation,and environmental controls

Purpose

Soil organic carbon (SOC) in alpine regions is characterized by a strong local heterogeneity, which may contribute to relatively large uncertainties in regional SOC stock estimation. However, the patterns, stock, and environmental controls of SOC in semiarid alpine regions are still less understood. Therefore, the purpose of this study is to comprehensively quantify the stock and controls of SOC in semiarid alpine regions.

Materials and methods

Soils from 138 study sites across a typical semiarid alpine basin (1755–5051 m, ~1?×?10⁴ km²) are sampled at 0–10, 10–20, 20–40, and 40–60 cm. SOC content, bulk density, soil texture, and soil pH are determined. Both a classical statistical model (i.e., a multiple linear regression, MLR) and a machine learning technique (i.e., a random forest, RF) are applied to estimate the SOC stock at a basin scale. The study further quantifies the environmental controls of SOC based on a general linear model (GLM) coupled with the structural equation modeling (SEM).

Results and discussion

SOC density varies significantly with topographic factors, with the highest values occurring at an elevation zone of ~3400 m. The results show that the SOC is more accurately estimated by the RF compared to the MLR model, with a total stock of 219.33 Tg C and an average density of 21.25 kg C m^?2 at 0–60 cm across the study basin. The GLM approach reveals that the topography is seen to explain about 58.11% of the total variation in SOC density at 0–10 cm, of which the largest two proportions are attributable to the elevation (44.32%) and the aspect factor (11.25%). The SEM approach further indicates that, of the climatic, vegetative, and edaphic factors examined, the mean annual temperature, which is mainly shaped by topography, exerts the most significant control on SOC, mainly through its direct effect, and also, through indirect effect as delivered by vegetation type.

Conclusions

The results of this study highlight the presence of high stocks of organic carbon in soils of semiarid alpine regions, indicating a fundamental role played by topography in affecting the overall SOC, which is mainly attained through its effects on the mean annual temperature.

     

Grassland conversion along a climate gradient in northwest China: Implications for soil carbon and nutrients

Soil organic carbon (SOC) stocks and nutrient availability are key indicators of soil quality, and both can be influenced by land-use change. However, it is still unclear whether the impact of land-use change on SOC and nutrient stocks differs between ecoregions. Grasslands near the northeast border of the Qinghai-Tibetan Plateau (QTP) occur across several ecoregions that have recently been subjected to substantial land-use change. Based on long-term land-use history, we conducted a field investigation comparing soil C and nutrient stocks between natural grassland (NGL) and three types of converted grassland (agricultural grassland, AGL; farmland, FL; and abandoned farmland, AFL) in three ecoregions along a climate gradient: alpine meadow, temperate steppe and temperate desert. Compared with NGL, soil C stocks in converted grasslands were 22%–30% lower in the alpine meadow, but 60–82% higher in the temperate steppe and 6%–76% higher in the temperate desert. Converted grasslands also contained higher stocks of available nitrogen and phosphorus than NGL in the temperate steppe and desert. Soils (0–40 cm) in NGL contained 14.8 ± 0.1 kg C m⁻² in alpine meadow, 6.7 ± 0.6 kg C m⁻² in temperate steppe and 1.7 ± 0.3 kg C m⁻² in temperate desert. Together, our results indicate that the responses of soil C and nutrients to grassland conversion differed between ecoregions. Thus, to optimize soil C sequestration rates and overall soil quality, we suggest that land-use policies in this area should take into account local environmental conditions.     

Effects of topography on soil organic carbon stocks in grasslands of a semiarid alpine region,northwestern China

Purpose

Soil organic carbon (SOC) in mountainous regions is characterized by strong topography-induced heterogeneity, which may contribute to large uncertainties in regional SOC stock estimation. However, the quantitative effects of topography on SOC stocks in semiarid alpine grasslands are currently not well understood. Therefore, the purpose of this research study is to determine the role of topography in shaping the spatial patterns of SOC stocks.

Materials and methods

Soils from the summit, shoulder, backslope, footslope, and toeslope positions along nine toposequences within three elevation-dependent grassland types (i.e., montane desert steppe at ~?2450 m, montane steppe at ~?2900 m, and subalpine meadow at ~?3350 m) are sampled at four depths (0–10, 10–20, 20–40, and 40–60 cm). SOC content, bulk density, soil texture, soil water content, and grassland biomass are determined. The general linear model (GLM) is employed to quantify the effects of topography on the SOC stocks. Ordinary least squares regressions are performed to explore the underlying relationships between SOC stocks and the other edaphic factors.

Results and discussion

In accordance with the present results, the SOC stocks at 0–60 cm show an increasing trend in respect to the elevation zone, with the highest stock being approximately 37.70 g m^?2 in the subalpine meadow, about 2.07 and 3.41 times larger than that in the montane steppe and montane desert steppe, respectively. Along the toposequences, it is revealed the SOC stocks are maximal at toeslope, reaching to 14.98, 31.76, and 49.52 kg m^?2, which are also significantly larger than those at the shoulder by a factor of 1.38, 2.31, and 1.44, in montane desert steppe, montane steppe, and subalpine meadow, respectively. Topography totally is seen to explain about 84% of the overall variation in SOC stocks, of which 70.61 and 9.74% are attributed to elevation zone and slope position, while the slope aspect and slope gradient are seen to plausibly explain only about 1.84 and 0.01%, respectively.

Conclusions

The elevation zone and the slope position are seen to markedly shape the spatial patterns of the SOC stocks, and thus, they may be considered as key indicating factors in constructing the optimal SOC estimation model in such semiarid alpine grasslands.

     

Response of soil C:N:P stoichiometry,organic carbon stock,and release to wetland grasslandification in Mu Us Desert

Purpose

Wetlands in Mu Us Desert have severely been threatened by grasslandification over the past decades. Therefore, we studied the impacts of grasslandification on soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry, soil organic carbon (SOC) stock, and release in wetland-grassland transitional zone in Mu Us Desert.

Materials and methods

From wetland to grassland, the transition zone was divided into five different successional stages according to plant communities and soil water conditions. At every stage, soil physical and chemical properties were determined and C:N:P ratios were calculated. SOC stock and soil respirations were also determined to assess soil carbon storage and release.

Results and discussion

After grasslandification, SOC contents of top soils (0–10 cm) decreased from 100.2 to 31.79 g kg^?1 in June and from 103.7 to 32.5 g kg^?1 in October; total nitrogen (TN) contents of top soils (0–10 cm) decreased from 3.65 to 1.85 g kg^?1 in June and from 6.43 to 3.36 g kg^?1 in October; and total phosphorus (TP) contents of top soils (0–10 cm) decreased from 179.4 to 117.4 mg kg^?1 in June and from 368.6 to 227.8 mg kg^?1 in October. From stages Typha angustifolia wetland (TAW) to Phalaris arundinacea L. (PAL), in the top soil (0–10 cm), C:N ratios decreased from 32.2 to 16.9 in June and from 19.0 to 11.8 in October; C:P ratios decreased from 1519.2 to 580.5 in June and from 19.0 to 11.8 in October; and N:P ratios decreased from 46.9 to 34.8 in June and changed from 34.9 to 34.0 in October. SOC stock decreased and soil respiration increased with grasslandification. The decrease of SOC, TN, and TP contents was attributed to the reduction of aboveground biomass and mineralization of SOM, and the decrease of soil C:N, C:P, and N:P ratios was mainly attributed to the faster decreasing speeds of SOC than TN and TP. The reduction of aboveground biomass and increased SOC release led by enhanced soil respiration were the main reasons of SOC stock decrease.

Conclusions

Grasslandification led to lowers levels of SOC, TN, TP, and soil C:N, C:P, and N:P ratios. Grasslandification also led to higher SOC loss, and increased soil respiration was the main reason. Since it is difficult to restore grassland to original wetland, efficient practices should be conducted to reduce water drainage from wetland to prevent grasslandification.

     

Variation of soil organic carbon,nitrogen, and phosphorus stoichiometry and biogeographic factors across the desert ecosystem of Hexi Corridor,northwestern China

Purpose

The purposes of present study were to display the vertical distribution of soil organic carbon (SOC), nitrogen (N), and phosphorus (P) stoichiometry; identify the biogeographic characteristics of SOC, N, and P stoichiometry along an aridity gradient across the desert ecosystem of Hexi Corridor; and determine how biogeographic distribution patterns of SOC, N, and P stoichiometry are related to vegetation, soil texture, geography, and climate.

Materials and methods

We investigated the distribution and characteristics of SOC, N, and P stoichiometry based on samples collected from Hexi Corridor during 2011–2012 with total 400 plots of 80 sites. This region presents a precipitation gradient from about 250 mm in the east to less than 50 mm in the west. The measured variables included belowground and aboveground biomass, pH, bulk density, sand, clay, silt, SOC, N, and P contents. ANOVA analysis, reduced major axis, redundancy analysis, Person’s correlation, and regression analysis were used to analysis the variation of SOC, N, and P stoichiometry and related biogeographic factors.

Results and discussion

In present study, SOC, N, and P contents decreased significantly with increasing soil depth. C/N did not change significantly, while C/P and N/P decreased significantly. SOC and N, SOC and P, and N and P were well constrained within 0–100 cm. SOC, N, and P contents in 0–20 cm were higher than them in other studies. Vegetation, soil texture, climate, and geography could explain 91.6% of the total variance of soil stoichiometry. The impact of latitude and longitude on SOC, N, and P stoichiometry was mainly caused by the redistribution of precipitation, while the impact of altitude mainly resulted from the variation of temperature. With increasing aridity, SOC, N, and P contents and C/N/P ratios reduced consistently with inconsistent decrease rates.

Conclusions

Our results suggested that the interaction of vegetation structure, soil condition, and shortage of precipitation should be the main driver for the lower contents and much shallower distributions of SOC, N, and P of Hexi Corridor. The increasing aridity should be the critical factor that is responsible for the decrease of SOC, N, and P contents and C/N/P ratios. This study contributes to the understanding of soil stoichiometry in the desert ecosystem.

     

Five-year warming does not change soil organic carbon stock but alters its chemical composition in an alpine peatland

Climate warming may promote soil organic carbon(SOC) decomposition and alter SOC stocks in terrestrial ecosystems, which would in turn affect climate warming. We manipulated a warming experiment using open-top chambers to investigate the effect of warming on SOC stock and chemical composition in an alpine peatland in Zoigê on the eastern Tibetan Plateau, China. Results showed that 5 years of warming soil temperatures enhanced ecosystem respiration during the growing season, promoted above-and be...     

Decreased glomalin-related soil protein with nitrogen deposition in a 3-year-old Cunninghamia lanceolata plantation

Purpose

Glomalin-related soil protein (GRSP) is an essential component of soil organic C for maintaining soil quality and structure and plays a critical role in soil carbon (C) sequestration. However, how GRSP changes under nitrogen (N) deposition remains poorly understood.

Materials and methods

We assessed total GRSP (T-GRSP) and easily extractable GRSP (EE-GRSP) under a control (no N input), low N addition (LN, 40 kg N ha^?1 year^?1), and high N addition (HN, 80 kg N ha^?1 year^?1) treatments in 2015 and 2016 in a Chinese fir (Cunninghamia lanceolata) plantation in the subtropical China. We also analyzed soil properties contents and explored the stoichiometric ratios of soil organic C (SOC), total N (TN), and total phosphorus (TP) with GRSPs.

Results

Compared to the control, both T-GRSP and EE-GRSP were significantly reduced under the HN treatment, but had no significant difference under the LN treatment. The ratio of T-GRSP and EE-GRSP was reduced by the N addition. Soil organic C (SOC) and dissolved organic C (DOC) were significantly affected by N addition treatments. The ratios of GRSP-C to SOC and of EEGRSP-C to SOC ranged from 6.29 to 16.07% and 1.34 to 3.52%, respectively. T-GRSP and EE-GRSP were positively correlated with SOC/TN ratio, but negatively correlated with soil TN/TP and SOC/TP ratios.

Conclusion

Our results indicated that the GRSP reductions under N deposition in soil are mediated by soil C, N, and P stoichiometry, and particularly, the reduction of EE-GRSP by DOC. This study improved our mechanistic understanding of dynamics of GRSPs under increasing N enrichment in subtropical plantation ecosystems.

     

Soil organic carbon stock and fractional distribution across central-south China

The stock and stability of soil organic carbon (SOC) are critical to soil functions and global carbon cycle, but little quantitative information is available on the precise location and chemical components of SOC for soils across a wide range of climatic gradients. Here, a broad range of zonal soils were collected in forest land at topsoil (0–15 cm) and subsoil (15–30 cm) from temperate to tropical climatic gradient in central to south China. The stock and stability of SOC were determined in terms of aggregate and humic fractionation. SOC in bulk soils with a less significant geographic variation was comparably higher at Haplic Luvisoils in temperate regions (3637.61 g m⁻²) and Rhodi-Humic Ferrosols in tropical regions (3446.12 g m⁻²) than in the other experimental soils, but a consistent decreasing trend was observed along the soil profiles with the SOC stock was 1.11–1.97 times higher in the topsoil than in the subsoils. In addition, insoluble humin residue (HMr) as the dominant components of SOC ranged from 643.95 to 2696.90 g m⁻² and decreased from temperate to tropical regions, which was consistent with the zonal variation of humic acids (HAs), but contrary to the zonal variation of fulvic acids (FAs) that fluctuated in a range of 39.67–389.55 g m⁻² across the experimental sites. According to the results of partial correlation analysis, the variation of FAs stock was significantly attributed to soil pH, bulk density, iron and aluminum oxides, clay, and clay mineral content (|r|>0.61, p < 0.05), while these soil physical properties showed a contradictory effects on HAs, iron-linked humin (HMi), clay-combined humin (HMc), and HMr. Moreover, the aggregate-associated carbon stock was mainly stored in macroaggregates (36.34–76.09%) for both SOC and its chemical components, especially in topsoils, and its zonal variation was associated with that of bulk soils. In general, the redundancy analysis (RDA) revealed that mean annual precipitation (MAP) accounted for 81.8% and 13.8% of the variance in SOC chemical and physical fractionation, respectively, while the corresponding contribution of mean annual temperature (MAT) was 1.5% and 34.7%. With the increase of MAT and MAP, the chemical stability of SOC decreased in the molecular structure, and the physical protection of SOC by aggregate exhibited a unimodal trend. The obtained results would facilitate the development of regional soil carbon prediction and land management against global warming.     

Change in soil microbial biomass and regulating factors in an alpine meadow site on the Qinghai-Tibetan Plateau

ABSTRACT

The change in soil microbial biomass (SMB) content and its direct links to soil organic matter (SOM) and environmental factors are not well understood for high-elevation regions. Therefore, this research investigated the temporal variation of SMB and its relationship with SOM and environmental factors in an alpine meadow site on the Qinghai-Tibetan Plateau. The soil organic carbon (SOC) and total nitrogen (TN) contents in alpine meadows showed monthly and seasonal variations and were higher in colder months, and the soil C/N ratio was higher in winter and in autumn than it was in the other seasons (P < 0.05). In addition, the changes in the SMB C and SMB N contents were notable at monthly and seasonal scales, whereas the SMB C and SMB N contents were higher in the winter and spring than they were in the other seasons (P < 0.05); the ratio of SMB C/SOC was higher in spring than it was in the other seasons; the ratio of the SMB N/TN content was higher in cold or cool months than it was in the other months; and the ratio of the SMB C/SMB N was highest in August (P < 0.05). Moreover, the SMB C and SMB N contents were significantly positively correlated to the SOC and TN contents (P < 0.01), and the SMB content was also significantly positively correlated to soil water content and air temperature (P < 0.05), or to soil bulk density and soil pH (P < 0.05). The results suggested that the change in the SMB in the alpine meadows was highly regulated by the SOC and TN and by monthly and seasonal changes in the soil bulk density, the soil pH, soil moisture, and air temperatures.     

Nitrogen deposition impacts on the amount and stability of soil organic matter in an alpine meadow ecosystem depend on the form and rate of applied nitrogen

The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon (SOC) in terrestrial ecosystems. In this study, a multi‐form, small‐input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH₄Cl, (NH₄)₂SO₄ and KNO₃, were applied at four rates: 0, 10, 20 and 40 kg N ha^?1 year^?1. One hundred and eight soil samples were collected at 10‐cm intervals to a depth of 30 cm in 2011. Contents and δ¹³C values of bulk SOC were measured, as well as three particle‐size fractions: macroparticulate organic C (MacroPOC, > 250 µm), microparticulate organic C (MicroPOC, 53–250 µm) and mineral‐associated organic C (MAOC, < 53 µm). The results show that 5 years of N addition changed SOC contents, δ¹³C values of the bulk soils and various particle‐size fractions in the surface 10‐cm layer, and that they were dependent on the amounts and forms of N application. Ammonium‐N addition had more significant effects on SOC content than nitrate‐N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m^?2), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m^?2) and 8.8% (0.85 kg C m^?2), respectively. The critical load of N deposition appears to be about 20 kg N ha^?1 year^?1. The newly formed C in the small‐input N treatment remained mostly in the > 250 µm soil MacroPOC, and the C lost in the medium or large N treatments was from the > 53 µm POC fraction. Five years of ammonium‐N addition increased significantly the surface soil POC:MAOC ratio and increased the instability of soil organic matter (SOM). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term.     

Long-term fertilization effects on carbon pools and carbon management index of loamy soil under grass–forage legumes mixture in semi-arid environment

ABSTRACT

Soil organic carbon (SOC) is a key component for sustaining crop production. A field experiment was conducted during 2004–2018 to assess the changes in soil carbon fractions under different fertilization practices in grass-legumes mixture. The result indicates that application of farmyard manure (FYM) at 80 Mg ha^–1 has increased SOC concentration leading to carbon sequestration rate of 4.2 Mg ha^–1 year^–1. Further, it has increased the proportion of labile carbon in the total SOC and have accumulated 126, 60, 83 and 95% higher very labile, labile, less labile and non-labile C stock than that of control plot, respectively, in top 30 cm soil layer. Inorganic fertilization and FYM 20 Mg ha^–1 influenced SOC concentration, SOC stock and C sequestration rate similarly. The highest carbon management index (264) was found in the treatment receiving FYM 80 Mg ha^–1 and it was positively correlated with SOC (r = 0.84**). The sensitivity index of the SOC varied from 26 to 152% and the differences were greatest in FYM treatments. The result indicates that grass-legumes mixture build-up the SOC in long term and the addition of FYM further increases it.     

Impact of grassland contract policy on soil organic carbon losses from alpine grassland on the Qinghai–Tibetan Plateau

Carbon storage in the soils on the Qinghai–Tibetan Plateau plays a very important role in the global carbon budget. In the 1990s, a policy of contracting collective grasslands to smaller units was implemented, resulting in a change from the traditional collective grassland management to two new management patterns: a multi‐household management pattern (MMP: grassland shared by several households without enclosures) and a single‐household management pattern (SMP: grassland enclosed and used by only one household). In 2016, 50 MMP and 54 SMP winter pastures on the Qinghai–Tibetan Plateau were sampled to assess the differences in soil organic carbon (SOC) between the two management patterns. Results showed that average SOC was significantly greater under MMP than under SMP, with an estimated 0.41 Mg C/ha/yr lost due to SMP following the new grassland contract. Based on the government's grassland policy, four grassland utilization scenarios were developed for both summer and winter pastures. We found that if the grassland were managed under SMP, likely C losses ranged between 0.31 × 10⁷ and 6.15 × 10⁷ Mg C/yr across the Qinghai–Tibetan Plateau relative to MMP, which more closely resembles pre‐1990s grassland management. Previous estimates of C losses have only considered land use change (with cover change) and ignored the impacts driven by land management pattern changes (without cover change). The new data suggest that C losses from the Qinghai–Tibetan Plateau are greater than previously estimated, and therefore that the grassland contract policy should be reviewed and SMP households should be encouraged to reunite into the MMP. These findings have potential implications for land management strategies not only on the Qinghai–Tibetan Plateau but also other grazing regions globally where such practices may exist.     

基于137Cs的青藏高原高寒草甸土壤侵蚀及碳流失估算

[目的] 定量分析青藏高原高寒草甸土壤侵蚀状况及其伴随的碳流失,为全面评估土壤侵蚀影响,实施有效水土保持措施提供参考。[方法] 结合¹³⁷Cs示踪技术与前人研究,对青藏高原高寒草甸土壤的整体侵蚀水平及其土壤有机碳流失进行了估算。[结果] 未受人为扰动的高寒草甸土壤自上而下表现出3个层次(A,B和C层)的理化性质特征,其¹³⁷Cs分布遵循显著指数递减模式。目前,高原草甸土壤年均侵蚀模数约为77~230 t/km²,推测其每年直接导致的土壤有机碳损失量平均不低于4.86 t/km²。[结论] 青藏高原高寒草甸土壤侵蚀水平整体较弱,但因土壤侵蚀流失的有机碳不容忽视。在未来气候变化背景下,升温导致的土壤湿度下降对植被生长的限制,以及人类活动的影响,较大可能成为诱使青藏高原草甸土壤退化和有机碳流失的潜在因素。     

Soil organic carbon depletion in global Mollisols regions and restoration by management practices: a review

Purpose

Mollisols are the most fertile, high-yielding soils in the world. During the past several decades, Mollisols have lost about 50% of their antecedent organic carbon (C) pool due to soil erosion, degradation, and other unsuitable human activities. Therefore, restoring soil organic C (SOC) to Mollisols via reasonable management is crucial to sustainable development and is important for environmental stability. However, the existing literature on SOC and soil quality has focused on one soil type or on a given region where Mollisols occur, and the degree of SOC depletion and stabilization in Mollisols have not been comprehensively evaluated. Overall, we propose to develop an optimum scheme for managing Mollisols, and we outline specific issues concerning SOC restoration and prevention of SOC depletion.

Materials and methods

In this review, we identify the uncertainties involved in analyses of SOC in Mollisols as related to management practices. According to the existing literature on SOC in Mollisols at the global scale, we analyzed the results of SOC depletion research to assess management practices and to estimate the C amount stabilized in Mollisols.

Results and discussion

The review shows that the SOC stocks in Mollisols in North America under cropped systems had 51?±?4 (equiv. mass) Mg ha^?1 in the top 30 cm soil layer. The SOC contents in Northeast China decreased from 52 to 24 g kg^?1 (46%) after 150 years of cultivation management. All of the Mollisols regions in the world are facing the challenge of SOC loss, and this trend could have a negative influence on global climate change. Hence, it is very important to take proper measures to maintain and enhance organic C contents in Mollisols.

Conclusions

We concluded that reasonable management practices, including no-tillage, manure and compost fertilization, crop straw returning, and mulching cultivation, are the recommended technologies. The C restoration in Mollisols is a truly win-win strategy for ensuring the security of food and soil resources while effectively mitigating global climate change. Thus, more attention should be given to protective management and land use for its impacts on SOC dynamics and soil properties in Mollisols regions.

     

Assessment of frozen ground organic carbon pool on the Qinghai-Tibet Plateau

Purpose

Under rapid climate change, soil organic carbon (SOC) dynamic in frozen ground may significantly influence terrestrial carbon cycles. The aim of this study was to investigate the storage, spatial patterns, and influencing factors of SOC in frozen ground on the Qinghai-Tibet Plateau, which known as the earth’s Third Pole.

Materials and methods

Using the observed edaphic data from China’s Second National Soil Survey, we estimated the SOC storage (SOCS) of frozen ground (including permafrost, seasonally, and short time frozen ground) on the plateau with a depth of 0–3 m. Furthermore, the effect of vegetation and climate factors on spatial variance of SOC density (SOCD) was analyzed.

Results and discussion

The SOCD decreased from the southeastern to the northwestern part of the plateau, and increased with shorten of freezing duration. SOCS of permafrost, seasonally, and short time frozen ground were calculated as 40.9 (34.2–47.6), 26.7 (24.1–29.4), and 6 (5.6–6.4) Pg, making a total of 73.6 (63.9–83.3) Pg in 0–3 m depth on the plateau. Normalized difference vegetation index and mean annual precipitation could significantly affect the spatial distribution of SOC in permafrost and seasonally frozen ground.

Conclusions

The soil in plateau frozen ground contained substantial organic carbon, which could be affected by plant and climate variables. However, the heterogeneous landform may make the fate of carbon more complicated in the future.

     

A State‐Space Analysis of Soil Organic Carbon in China's Loess Plateau

An accurate estimation of soil organic carbon (SOC) is important for the evaluation and management of carbon (C) flux in terrestrial ecosystems. However, there is little work on the spatial variability of SOC in deep soils and its driving factors. Thus, the objective of the study was to derive the primary factors dominating the spatial distribution of SOC in different soil layers with the use of the autoregressive state‐space approach. The concentration of SOC was measured to the depth of 500 cm (n  = 86) along a south–north transect of China's Loess Plateau. The mean SOC of the 500‐cm soil profile generally decreased from south to north following the decreasing rainfall gradient. Based on the investigated factors, the state‐space model was able to capture 90.3–99.9% of the spatial variability of SOC in the various soil layers. According to the coefficients in the optimal state‐space model for each soil layer, climatic factors such as precipitation and temperature had a dominant control over the spatial distribution of SOC at shallow depths. However, both climatic and edaphic (e.g. soil texture) factors, and to a small extent land use, influenced the spatial behavior of SOC at the 40–200 cm soil depth. For soil layers below 200 cm, the importance of land use was revealed, and the spatial characteristics of SOC were together driven by land use, climatic and edaphic factors. This is critical for the management of soil C flux in deep soils and the C stock and cycle in terrestrial ecosystems. Table SI. Basic properties of soils and climate and elevation under three land uses along the south–north transect on the Loess Plateau (mean ± standard deviation). Note that SWC is gravimetric soil water content. Copyright © 2016 John Wiley & Sons, Ltd.     

Variations of Soil Organic Carbon Following Land Use Change on Deep‐Loess Hillsopes in China

Land use change is a key factor driving changes in soil organic carbon (SOC) around the world. However, the changes in SOC following land use changes have not been fully elucidated, especially for deep soils (>100 cm). Thus, we investigated the variations of SOC under different land uses (cropland, jujube orchard, 7‐year‐old grassland and 30‐year‐old grassland) on hillslopes in the Yuanzegou watershed of the Loess Plateau in China based on soil datasets related to soils within the 0–100 cm. Furthermore, we quantified the contribution of deep‐layer SOC (200–1,800 cm) to that of whole soil profiles based on soil datasets within the 0–1,800 cm. The results showed that in shallow profiles (0–100 cm), land uses significantly (p  < 0·05) influenced the distribution of SOC contents and stocks in surface layer (0–20 cm) but not subsurface layers (20–100 cm). Pearson correlation analysis indicated that soil texture fractions and total N were significantly (p  < 0·05 or 0·01) correlated with SOC content, which may have masked effects of land use change on SOC. In deep profiles (0–1,800 cm), SOC stock generally decreased with soil depth. But deep soils showed high SOC sequestration capacity. The SOC accumulated in the 100–1,800 m equalled 90·6%, 91·6%, 87·5% and 88·6% of amounts in the top 100 cm under cropland, 7‐year‐old grassland, 30‐year‐old grassland and jujube orchard, respectively. The results provide insights into SOC dynamics following land use changes and stressed the importance of deep‐layer SOC in estimating SOC inventory in deep loess soils. Copyright © 2017 John Wiley & Sons, Ltd.     

Soil organic carbon distribution in relation to land use and its storage in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0-10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0-60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0-60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0-60 cm).