Straw mulching increased soil organic carbon content and stability by stimulating mineral protection in a Moso bamboo plantation

Land-use change significantly affects the soil organic C (SOC) dynamics and microbial activities. However, the roles of chemical composition of SOC and enzyme activity in the change in the SOC mineralization rate caused by land-use change are poorly understood. This study aimed to investigate the impact of land-use conversion from natural evergreen broadleaf forests to intensively managed moso bamboo (Phyllostachys edulis) plantations on the pool size and mineralization rate of SOC, as well as the activities of C-cycling enzymes (invertase, β-glucosidase, and cellobiohydrolase) and dehydrogenase. Four paired soil samples in two layers (0–20 and 20–40 cm) were taken from adjacent evergreen broadleaf forest-moso bamboo plantation sites in Lin’an County, Zhejiang Province, China. Soil water-soluble organic C (WSOC), hot-water-soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), the activities of C-cycling enzymes and dehydrogenase, and mineralization rates of SOC were measured. The chemical composition of SOC was also determined with 13C-nuclear magnetic resonance spectroscopy. The conversion of broadleaf forests to bamboo plantations reduced SOC stock as well as WSOC, HWOC, MBC, and ROC concentrations (P < 0.05), decreased O-alkyl, aromatic, and carbonyl C contents, but increased alkyl C content and the alkyl C to O-alkyl (A/O-A) ratio, suggesting that the land-use conversion significantly altered the chemical structure of SOC. Further, such land-use change lowered (P < 0.05) the SOC mineralization rate and activities of the four enzymes in the 0–20-cm soil. The decreased SOC mineralization rate associated with the land-use conversion was closely linked to the decreased labile organic C concentration and soil enzyme activities. The results demonstrate that converting broadleaf forests to moso bamboo plantations markedly decreased the total and labile SOC stocks and reveal that this conversion decreased the mineralization rate of SOC via changing the chemical composition of SOC and decreasing activities of C-cycling enzymes. Management practices that enhance C input into the soil are recommended to mitigate the depletion of SOC associated with land-use conversion to moso bamboo plantations.

Partial substitution of chemical fertilizer with organic amendments affects soil organic carbon composition and stability in a greenhouse vegetable production system

Effects of agricultural abandonment on soil aggregation, soil organic carbon storage and stabilization: Results from observation in a small karst catchment, Southwest China

The composition of soil organic carbon and its stability mechanism are the key to understanding the terrestrial carbon sink capacity. The stability of soil organic carbon in a karst ecosystem greatly affects the soil carbon fixation capacity. In order to understand the impact of human activities on the stability of soil organic carbon in karst areas, the karst valley area of Zhongliang Mountain in Chongqing was selected as an example, and soil samples of four typical land use modes (mixed forest, bamboo forest, grassland, and cultivated land) were collected in layers to analyze the total organic carbon (TOC) and heavy fraction organic carbon (HFOC). The distribution characteristics of light fraction organic carbon (LFOC), labile organic carbon (LOC), and recalcitrant organic carbon (ROC) were analyzed quantitatively by using a structural equation model to provide basic data for soil carbon sink assessment and soil quality protection in karst areas. The results showed that the organic carbon components under different land use patterns in karst areas had obvious surface accumulation, and the content of organic carbon components in the surface layer was 1.2 times that in the bottom layer. Except for LFOC, the content of other organic carbon components was the highest in the mixed forest, followed by that in the bamboo forest and wasteland, with the lowest in cultivated land. Mixed forest ω(TOC) content was the highest, 42.5 g·kg-1, followed by that of bamboo forest (36.6 g·kg-1) and grassland (18.7 g·kg-1), and cultivated land content was the lowest, 13.4 g·kg-1. The soil organic carbon content of cultivated land was 68.5%, 63.5%, and 28.3% lower than that of mixed forest, bamboo forest, and grassland, respectively. Mixed forest had the highest content of ω(HFOC), 21 g·kg-1, followed by those of bamboo forest (20.9 g·kg-1), grassland (18.2 g·kg-1), and cultivated land (13.5 g·kg-1). The mixed forest ω(LOC) content was the highest, 16.3 g·kg-1, followed by those of bamboo forest (14.9 g·kg-1), grassland (11.5 g·kg-1), and cultivated land (5.3 g·kg-1). Mixed forest ω (ROC) content was the highest, 25.7 g·kg-1, followed by those of bamboo forest (21.6 g·kg-1), grassland (15.9 g·kg-1), and cultivated land (10.3 g·kg-1). The bamboo forest land ω(LFOC) content was 15.9 g·kg-1, followed by those of mixed forest (13.9 g·kg-1), grassland (7.3 g·kg-1), and cultivated land (4.9 g·kg-1). The recalcitrant organic carbon index (ROCI) was used to indicate the stability of soil organic carbon. The variation range of ROCI was 33.9%-64.5%, of which the highest was mixed forest (64.5%-66.3%), and the lowest was cultivated land (33.8%-39.6%). The ROCI of mixed forest, bamboo forest, and grassland were 1.8 times, 1.6 times, and 1.4 times that of cultivated land, respectively. Karst area ω (inert organic carbon) content and ROCI showed that human agricultural activities caused the reduction in soil organic carbon content and the destruction of soil physical structure, resulting in the accelerated decomposition and turnover rate of soil organic matter. The most important factor affecting soil stability in karst areas was soil pH. Tillage activities caused soil pH to rise, reduced soil microbial activity, and were not conducive to the accumulation of the inert organic carbon and soil organic carbon pool in the soil.

ABSTRACTIn desert ecosystems, afforestation with xerophytic shrubs has the potential to significantly increase soil nutrient levels by mitigating wind and soil erosion. Nevertheless, further investigation is required to elucidate the changes in soil organic carbon (SOC) fractions and stability on different soil depths with afforestation years. We collected soil samples from the 0–20, 20–60, and 60–100 cm depths of three xerophytic shrublands ages (3, 7, and 10 years), with a natural desert as the control, in a hyper‐arid desert region. We investigated the variations of SOC fractions (stable and active C) and stability (stability index and MAOC:POC ratios) after afforestation. The results showed that the rate of increase in SOC fractions and stability did not follow a linear trajectory with afforestation years. Instead, they accelerated around 7 years but then decreased after 10 years. The increase in SOC stability was primarily attributed to the greater increase in stable C within the total SOC pool. Afforestation increased the concentration of ROC from 0.26 to 0.89 g kg−1 and MAOC from 0.11 to 0.78 g kg−1. Afforestation increased SOC stability by 74.36%–231% compared to the CK in the 0–100 cm. SOC stability in the 60–100 cm was higher than that in the 0–20 cm layer, while SOC stability varied insignificantly across soil layers. The strongest direct positive impact on SOC stability was attributed to changes in soil physicochemical properties rather than soil microbial biomass or aggregate stability. These findings contribute to our understanding of the importance of afforestation in increasing SOC stability in desert ecosystems.

To examine the effects of management measures on carbon and nitrogen contents, as well as their distribution and structural characteristics of different soil fractions in Moso bamboo plantations, we compared three types of the bamboo forests (undisturbed, extensively managed, and intensively managed) and the control secondary broadleaved evergreen forest using the methods of physical fractionation, chemical and biological analysis and Fourier-transform infrared spectroscopy (FTIR). The results showed that soil total organic carbon (TOC) and total nitrogen (TN) content, as well as free particulate organic carbon and nitrogen, soluble organic carbon and nitrogen (DOC, DON), and mineral-associated organic carbon and nitrogen in the undisturbed and extensively managed Moso bamboo plantations were significantly increased compared with that in the control. The distribution ratio of free particulate organic carbon and nitrogen in the undisturbed Moso bamboo plantation significantly increased, with mineral-associated organic carbon being the largest reservoir of soil organic carbon (67.6%). Intensive management resulted in the decrease of soil organic carbon, total nitrogen storage, and the contents of each component, but significantly increased DOC/TOC, the ratio of microbial biomass nitrogen to TN as well as the ratio of microbial biomass carbon to TOC (microbial quotient). Management measures significantly affected the chemical structure of SOC. Compared with the control, the relative intensities of phenolic and alcoholic-OH, aliphatic methyl and methylene, aromatic C=C, and carbonyl C=O absorption were higher in the SOC of undisturbed and extensively managed Moso bamboo plantations, and soil hydrophobicity was significantly increased. Results from correlation analysis showed that soil hydrophobicity and the content of aliphatic and aromatic groups were negatively correlated with microbial quotient and positively correlated with TOC and TN content. In conclusion, the increased inputs of organic matter residues (such as litter and roots) could contribute to the relative accumulation of chemical resistance compounds with reduced human disturbance, which significantly enhanced chemical stability of soil organic carbon. Soil clay minerals played a key role in protecting soil organic carbon through the formation of mineral-organic compounds, which facilitate the stability of soil carbon storage and the long-term preservation of soil carbon.

&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Effects of the construction of the lower Yarlung Tsangpo River tunnel project on the stability of organic carbon in forest soils&amp;lt;/strong&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Abstract:&amp;lt;/strong&amp;gt; Tunnels are widely used in road construction in areas such as the highlands and mountains, however, their effect on soil organic carbon stability has been less studied. Soil organic carbon stability is a sensitive index to evaluate the response of soil ecosystem to environmental changes. In order to detect the soil organic carbon (SOC) the anti-interference ability of the engineering construction of the tunnel, the stability of soil organic carbon was analyzed by using labile soil organic carbon&amp;amp;#65288;LOC&amp;amp;#65289;, soil aggregates and enzyme activities. Based on the construction of the lower Yarlung Tsangpo River tunnel, fixed monitoring plots were set up in the Engineering disturbance areas (ED) and undisturbed areas (CK) as a control to investigate the influence of tunnel construction on SOC stability . Results showed that the SOC and LOC in the ED were 291.40 mg/kg and 110.28 mg/kg, respectively, which were slightly higher than those in the CK area 255.31 mg/kg and 91.19 mg/kg, but the difference was not significant (&amp;lt;em&amp;gt;p=0.6&amp;lt;/em&amp;gt;). The proportion of &amp;gt;0.25 mm aggregates in all soil fractions was more than 80%. With the decrease of aggregate size, the content of organic carbon in aggregate showed a decreasing trend, but there was no significant difference between ED and CK areas. This study showed that tunnel construction has no significant effect on soil organic carbon stability, which may be associated to the abundant precipitation in the study area. Because vegetation mainly absorbed soil water in top layer and the input and output of soil organic matter were not affected. The results of the study provide a reference basis for the evaluation of the impact of tunnel construction on the environment and for the management of the forest ecosystem in the lower Yarlung Tsangpo River.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Keywords:&amp;lt;/strong&amp;gt; Tunneling; Forest soils; Organic carbon stability; labile organic carbon; Soil enzyme; soil aggregates&amp;lt;/p&amp;gt;

Mechanisms of carbon sequestration and stabilization by restoration of arable soils after abandonment: A chronosequence study on Phaeozems and Chernozems

In order to elucidate the effects of intensive management on soil carbon pool, nitrogen pool, enzyme activities in Moso bamboo (Phyllostachys pubescens) plantations, we collected soil samples from the soil surface (0-20 cm) and subsurface (20-40 cm) layers in the adjacent Moso bamboo plantations with extensive and intensive managements in Sankou Township, Lin'an City, Zhejiang Province. We determined different forms of C, N and soil invertase, urease, catalase and acid phosphatase activities. The results showed that long-term intensive management of Moso bamboo plantations significantly decreased the content and storage of soil organic carbon (SOC), with the SOC storage in the soil surface and subsurface layers decreased by 13.2% and 18.0%, respectively. After 15 years' intensive management of Masoo bamboo plantations, the contents of soil water soluble carbon (WSOC), hot water soluble carbon (HWSOC), microbial carbon (MBC) and readily oxidizable carbon (ROC) were significantly decreased in the soil surface and subsurface layers. The soil N storage in the soil surface and subsurface layers in intensively managed Moso bamboo plantations increased by 50.8% and 36.6%, respectively. Intensive management significantly increased the contents of nitrate-N (NO3--N) and ammonium-N (NH4+-N), but decreased the contents of water-soluble nitrogen (WSON) and microbial biomass nitrogen (MBN). After 15 years' intensive management of Masoo bamboo plantations, the soil invertase, urease, catalase and acid phosphatase activities in the soil surface layer were significantly decreased, the soil acid phosphatase activity in the soil subsurface layer were significantly decreased, and other enzyme activities in the soil subsurface layer did not change. In conclusion, long-term intensive management led to a significant decline of soil organic carbon storage, soil labile carbon and microbial activity in Moso bamboo plantations. Therefore, we should consider the use of organic fertilizer in the intensive mana-gement process for the sustainable management of Moso bamboo plantations in the future.

Fine-root distribution, production, decomposition, and effect on soil organic carbon of three revegetation shrub species in northwest China

Disturbance alters soil organic carbon content and stability in Carex tussock wetland, Northeast China

Grassland degradation usually results in significant shifts in vegetation species composition and plant biomass, thus altering the soil organic carbon (SOC) content and stability. Dynamics of labile carbon fractions after grassland degradation were well addressed; however, the changes in stable carbon fractions were poorly quantified. Soil samples at 0–10 cm and 10–20 cm depth were collected from a native grassland (NA), a lightly degraded grassland (LD), a moderately degraded grassland (MD), and a severely degraded grassland (SD) in northwest China to assess the influence of grassland degradation on the total SOC content, four SOC fractions (very labile carbon, CF1; labile carbon, CF2; less labile carbon, CF3; non-labile carbon, CF4), and SOC stability. Compared with the NA, the contents under LD, MD, and SD at 0–20 cm depth reduced by 20.58%, 29.22%, and 64.58% for total SOC, 21.38%, 23.00%, and 63.66% for CF1, 13.81%, 20.58%, and 62.26% for CF2, 24.30%, 35.05%, and 68.63% for CF3, and 22.17%, 38.80%, and 63.82% for CF4, respectively. The linear relationships between the total SOC and the four fractions of CF1, CF2, CF3, and CF4 were significant in this study. The lability index of SOC under the NA, LD, MD, and SD was 1.57, 1.59, 1.67, and 1.57, respectively, and no significant difference was found among the four grasslands. To conclude, grassland degradation changes the contents of total SOC and its labile and stable fractions but did not change the SOC stability in northwest China.

The influence of tree species on soil organic carbon stability under three temperate forests in the Baihua Mountain Reserve, China

The turnover and stabilization of soil organic carbon are tightly associated with the properties of litter input. Due to the complexity of litter decomposition and the high heterogeneity of forest soils, there are considerable uncertainties about how soil minerals, microorganisms, and environmental factors jointly regulate the transformation and stability of litter-derived soil organic carbon. Here, we present an overview of the "microbial efficiency-matrix stabilization" framework centered on microbial metabolism and organic carbon transformation, as well as the new "microbial carbon pump" and "mineral carbon pump" theories in forest soil organic carbon transformation and stabilization. We specifically highlighted a differential mechanism of "organo-organic interfaces" from the "organo-mineral interfaces" in the effects on soil organic carbon accumulation. We further expounded the transformation processes and stability of soil organic carbon based on the "carbon material cycling" and "energy fluxes", aiming to provide theoretical support for the research on carbon sequestration in forest soils.

Monoculture and improper management may reduce soil fertility and deteriorate soil structure in Black soils (Mollisols) of Northeast China. The experiment was carried out from 2015 to 2016 in Black Soils comprising five cropping systems: continuous corn (CC), soybean-corn rotation (SC), corn-soybean rotation (CS), fallow-corn (FC), and fallow-soybean (FS). Our results showed that CS and FS treatments significantly increased mean weight diameter (MWD) and fractal dimension (D) in mechanical stability aggregates (MSAs), and increased MWD and geometric mean diameter (GMD) in water-stable aggregates (WSAs) compared with CC treatment. These two treatments were also significantly increased water-stable aggregates stability rate (WSAR), but decreased percentage of aggregates destruction (PAD) than CC treatment. Meanwhile, CS and FS treatments exhibited a higher carbon accumulation than CC treatment in bulk soils. Soil organic carbon (SOC) concentration in WSA0.106-0.25,WSA2-5 mm and WSA0.5-1 mm had a dominant effect on aggregate stability. Simutaneously, SOC in WSA>5 mm affected SOC concentration in bulk soils. As a whole, the CS and FS treatments can increase the percentage of macro-aggregates, enhance aggregate stability, as well as increase SOC concentration in bulk soils and all soil aggregate sizes.