Long-term Natural Vegetation Restoration Research Articles

Soil carbon and nitrogen accumulation during long-term natural vegetation restoration following agricultural abandonment in Qingling Mountains

Agricultural land abandonment has been proposed as a strategy for reducing greenhouse gas emissions, increasing soil carbon (C) sequestration, and enhancing soil nitrogen (N) levels in degraded ecosystems. However, the dynamic patterns of soil C and N pools and fractions following long-term agricultural abandonment are not well understood. In this study, we investigated the dynamics of soil organic C (SOC), recalcitrant organic C (RC), total N (TN), and recalcitrant organic N (RN) in 0–40 cm soils along a natural vegetation restoration gradient (i.e., croplands→grasslands→shrublands→forests) following agricultural abandonment in China's Qinling Mountains. Our results showed that the concentrations of SOC, RC, TN, and RN increased significantly along with vegetation restoration, but the SOC and TN stocks only increased in the 0–10 and 0–20 cm layers, respectively. The highest growth rates of new SOC (28.96 g m−2 yr−1) and new RC (9.87 g m−2 yr−1) were observed in shrublands, followed by the grasslands (new SOC, 14.80 g m−2 yr−1; new RC, 5.02 g m−2 yr−1) and forests (new SOC, 9.06 g m−2 yr−1; new RC, 3.74 g m−2 yr−1). The δ15N values of litter, fine root, and soil decreased significantly with stand age, indicating that the N cycling in abandoned ecosystems gradually became less open than that of croplands during vegetation restoration processes. The ratios of RN/TN decreased significantly with stand age across all soil layers, while the ratios of RC/SOC at 0–40 cm soils did not change with stand age and the differences among croplands, grasslands, shrublands, and forests were not significant. Our study reveals that soil C and N stocks only accumulate in topsoils during ∼110 years of natural vegetation restoration and the recalcitrancy indices of soil C and N displayed different dynamic patterns, and also indicates that agricultural abandonment is an effective approach to increasing soil C and N stocks and mitigating the negative effects of agriculture on soil C and N pools.

Plant diversity drives soil carbon sequestration: evidence from 150 years of vegetation restoration in the temperate zone.

Large-scale afforestation is considered a natural way to address climate challenges (e.g., the greenhouse effect). However, there is a paucity of evidence linking plant diversity to soil carbon sequestration pathways during long-term natural restoration of temperate vegetation. In particular, the carbon sequestration mechanisms and functions of woody plants require further study. Therefore, we conducted a comparative study of plant diversity and soil carbon sequestration characteristics during 150 years of natural vegetation restoration in the temperate zone to provide a comprehensive assessment of the effects of long-term natural vegetation restoration processes on soil organic carbon stocks. The results suggested positive effects of woody plant diversity on carbon sequestration. In addition, fine root biomass and deadfall accumulation were significantly positively correlated with soil organic carbon stocks, and carbon was stored in large grain size aggregates (1-5 mm). Meanwhile, the diversity of Fabaceae and Rosaceae was observed to be important for soil organic carbon accumulation, and the carbon sequestration function of shrubs should not be neglected during vegetation restoration. Finally, we identified three plants that showed high potential for carbon sequestration: Lespedeza bicolor, Sophora davidii, and Cotoneaster multiflorus, which should be considered for inclusion in the construction of local artificial vegetation. Among them, L. bicolor is probably the best choice.

Variations of soil organic carbon fractions in response to conservative vegetation successions on the Loess Plateau of China

Land use changes profoundly affect the equilibrium of soil organic carbon (SOC) sequestration and greenhouse gas emissions. With the current global climatic changes, it is vital to understand the influence of ecological restoration and conservation management on the dynamics of SOC under different land uses, especially in erosion-endangered Loess soils. Therefore, we investigated changes in SOC through a suit of labile fractions, namely: light fraction organic C (LFOC), heavy fraction organic C (HFOC), coarse particulate organic C (CPOC), fine particulate organic C (FPOC), and dissolved organic C (DOC), from two forests i.e., Robinia pseudoacacia (RP) and Platycladus orientalis (PO), with different ages, in comparison with farmland (FL). The SOC and STN contents significantly increased over 42 years in the RP forest where the contents of CPOC and FPOC were significantly higher than in the FL. Moreover, total SOC and its labile fractions, in the studied land use types, significantly correlated with soil CaCO3, pH, and STN contents, indicating their key roles in SOC sequestration. The results reported here from different vegetation with different ages provide a better understanding of SOC and STN alterations at different stages of vegetation restoration. Our findings suggest that long-term natural vegetation restoration could be an effective approach for SOC sequestration and soil conservation on the Loess soil.

Changes in soil organic carbon and nitrogen pool sizes, dynamics, and biochemical stability during ∼160 years natural vegetation restoration on the Loess Plateau, China

Natural vegetation restoration has been reported as an effective strategy for the enhancement of soil organic carbon (SOC) and nitrogen (SON) sequestration in degraded ecosystems. However, changes in SOC and SON pool sizes, dynamics, and biochemical stability to natural vegetation restoration remain inadequately addressed. For this study, we investigated carbon (C) and nitrogen (N) contents and δ13C and δ15N values of SOC and SON pools, their labile C and N (LSOC and LSON, respectively), and recalcitrant C and N (RSOC and RSON, respectively) along 0–60 cm soil depths spanning ∼160 years of natural vegetation restoration on the Loess Plateau, China. Our results revealed that natural vegetation restoration greatly enhanced SOC, SON, LSOC, LSON, RSOC, total N, water-soluble organic C, and mineralizable organic C in the topsoil (0–20 cm), while it had little influence on the deeper soil layers (20–60 cm). The concentrations and stocks of SOC and SON in the topsoil increased significantly during the later restoration stages. The recalcitrant index for C at the 0–40 cm soil depths was highest in climax Quercus liaotungensis forest, while the recalcitrant index for N was unchanged at 0–20 and 40–60 cm soil depths between vegetation restoration stages. The δ13C values of SOC, LSOC, and RSOC, and δ15N values of SON and LSON were more enriched in the deeper soil layers relative to the topsoil, for the majority of restoration stages. The δ15N values of SON, LSON, and RSON in the topsoil were more enriched during the early restoration stages compared to the later restoration stages. Our results suggested that long-term natural vegetation restoration enhanced SOC and SON sequestration, increased biochemical stability of SOC, altered the dynamics of SOC and SON in the topsoil of degraded ecosystems through the increased inputs of plant residuals, and reduced the decomposition soil organic matter.

Changes in soil carbon fractions and enzyme activities under different vegetation types of the northern Loess Plateau.

Knowledge of the soil organic carbon components and enzyme activities during long‐term natural vegetation restoration is essential for managing the restoration of vegetation. In this study, the variations of soil organic carbon components (i.e., soil organic carbon (SOC), microbial biomass carbon (MBC), easily oxidized carbon (EOC), particulate organic carbon (POC)) and enzyme activities (i.e., amylase, catalase, urease, and sucrase) were measured in four vegetation types: control (grasslands, GL), forest (Xanthoceras sorbifolia, XS), and shrublands (Hippophae rhamnoides, HR; Caragana korshinskii, CK). We found that vegetation types significantly affect soil organic carbon components and enzyme activities. The SOC content of the XS plot is higher than HR, CK, and GL by 88.43%, 117.09%, and 37.53% at the 0–20 cm layer; the soil SOC content of the XS plot is higher than HR and CK by 27.04% and 26.87%, and lower than GL 12.90% at the 20–40 cm layer. The highest POC and urease were observed in the XS plot at a depth of 0–20 cm, that is, 1.32 g/kg and 98.51 mg/kg, respectively. The highest EOC, amylase, and sucrase were observed in GL at a depth of 0–20 cm, that is, 5.44 g/kg, 39.23, and 607.62 mg/g. On the vertical section of the soil, the SOC fractions and the enzyme activities were greater in the upper layer than in the lower layer for each vegetation type except for MBC and catalase activity. Correlation analysis demonstrated that the SOC and POC content significantly influenced urease and sucrase activities and that MBC significantly influenced catalase activity. These results provide important information about SOC fractions and enzyme activities resulting from vegetation types in the Loess Plateau and also supplement our understanding of soil C sequestration in vegetation restoration.

Shifts in soil nutrient concentrations and C:N:P stoichiometry during long-term natural vegetation restoration.

BackgroundEcological stoichiometry (C:N:P ratios) in soil is an important indicator of the elemental balance in ecological interactions and processes. Long-term natural vegetation plays an important role in the accumulation and distribution of soil stoichiometry. However, information about the effects of long-term secondary forest succession on soil stoichiometry along a deep soil profile is still limited.MethodsWe selected Ziwuling secondary succession forest developed from farmland as the study area, investigated the concentrations and stoichiometry of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) at a depth of 0–100 cm along a 90-year succession chronosequence, including farmland (control), grassland, shrub, early forest, and climax forest.ResultsSOC and TN concentrations significantly increased with increasing restoration age, whereas soil P concentration remained relatively stable across various successional stages. SOC and TN concentrations decreased with an increase in soil depth, exhibiting distinct soil nutrient “surface-aggregation” (high nutrients concentration in the top soil layer). The soil C:P and N:P ratios increased with an increase in restoration age, whereas the variation of the C:N ratio was small and relatively stable across vegetation succession. The nutrient limitation changed along with vegetation succession, transitioning from limited N in the earlier successional stages to limited P in the later successional stages.ConclusionOur results suggest that more nitrogen input should be applied to earlier succession stages, and more phosphorus input should be utilized in later succession stages in order to address limited availability of these elements. In general, natural vegetation restoration was an ecologically beneficial practice for the recovery of degraded soils in this area. The findings of this study strengthen our understanding of the changes of soil nutrient concentration and nutrient limitation after vegetation restoration, and provide a simple guideline for future vegetation restoration and reconstruction efforts on the Loess Plateau.

Long-term forest succession improves plant diversity and soil quality but not significantly increase soil microbial diversity: Evidence from the Loess Plateau

Many studies have focused on the processes of vegetation succession, however, the dynamics of soil microbes and the synergy between vegetation and soil are still poorly understood following vegetation succession. This study focused on a forest succession sequence including farmland, grassland, shrubland (i.e., Hippophae rhamnoides), pioneer forest (i.e., Populus davidiana), and climax forest (i.e., Quercus liaotungensis) on the Loess Plateau of China, to explore plant and soil changes, as well as soil microbial community dynamics. The results showed that litter biomass, soil organic carbon (SOC), total nitrogen (TN) and the ratio of SOC to TN exhibited an increasing trend in the whole process of the forest succession, and NH4+, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and the ratio of dissolved organic carbon (DOC) to dissolved organic nitrogen (DON) had significantly increased before the shrubland stage, and then they were going to be stable. During the forest succession, the main bacterial phyla present were Proteobacteria, Actinobacteria, and Acidobacteria, and the predominant fungal phyla were Ascomycota and Basidiomycota. The soil microbial community composition was stable and did not change significantly, but the bacteria and fungal communities were associated with specific plant or soil properties. It was proved that the change of soil microbial community was closely related to vegetation and soil community changes. The results suggested that long-term forest succession not only improves plant diversity, but also improves soil biology and quality, even though it does not significantly increase soil microbial diversity. The findings enhance the understanding of the impact of soil microbial ecological characteristics and provide an important guidance for the sustainable management of forest ecosystems following long-term natural vegetation restoration.

Species diversity of Arabis alpina L. communities in two Pb/Zn mining areas with different smelting history in Yunnan Province, China

In order to explore the species compositions and species diversity (Dominance (Do), Shannon-Wiener index (H′), Simpson diversity index (Dsi), Species richness (DMG), Pielou evenness index (Epi) and Frequency (Fr)) of twenty Arabis alpina L. var. parviflora Franch communities, field investigation was conducted in Huize county, Yunnan province, China. Some 20 A. alpina communities were distributed in two traditional smelting tailing piles of Minbingyingjiying (TST) and Shangduoduo village (SDD) with different Pb smelting history. The morphological characteristics (plant height, branch number, basal leaf length, basal leaf width and root morphology) of A. alpina, contents and accumulation characteristics of eight potentially toxic metals (As, Cd, Cr, Cu, Pb, Zn, Al, Fe) in soil and plants were analyzed. The results showed that the morphological characteristics of A. alpina were mean plant height 12.25 cm, the basal leaf length 17.69 cm, leaf width 5.40 cm, the total root length 117.86 cm plant−1, the root diameter 0.90 mm. The leaves of A. alpina in SDD were longer and narrower with higher plant height compared with in TST. The main companion plants of A. alpina were Sporobolus fertilis (Steud.) W. D. Clayt, Arenaria orbiculata Royle ex Edgew. et Hook. F. and Eulalia speciosa. (Debeaux). The H′ and Dsi were 0.56–2.04 and 0.44–0.95, respectively. The plant species numbers, H’, Dsi and Epi of A. alpina communities in TST were higher than those in SDD. Pb contents in shoot of two A. alpina samples were more than 1000 mg kg−1, Cd content in shoot of one A. alpina sample >100 mg kg−1 and Zn contents in shoot of seven A. alpina samples >10,000 mg kg−1 with the enrichment factors and transport coefficients greater than 1. The results indicate that A. alpina as a Zn, Pb and Cd hyperaccumulator, could be used for long-term phytoremediation of soils contaminated by Cd, Pb and Zn. Species diversity of A. alpina community during long-term natural vegetation restoration was high in the middle succession with single-peak model, and A. alpina would be dominant in the succession climax stage in potentially toxic metal contamination areas.

Changes of soil carbon in five land use stages following 10 years of vegetation succession on the Loess Plateau, China

Changes in land use caused by natural vegetation succession can enhance the soil organic carbon (SOC) and carbon (C) stock of terrestrial ecosystems, as reported in many studies throughout the world. However, the dynamics of SOC and soil C stocks and their changes in each succession stage are not clearly following restoration age. Additionally, whether litter and fine roots have positive effects on SOC and soil C sequestration is unclear. We simultaneously studied litter and fine root production and SOC and C stocks along a natural vegetation succession – abandoned farmland, grassland, shrubland, pioneer woodland to natural climax forest – in 2005 and 2015 on the Loess Plateau of China. This allowed a better understanding of the variations of SOC and soil C stock in different land use stages in relation to soil layers and effects of litter and fine roots following vegetation restoration. The land use stages and soil layers significantly affected the rates of SOC and soil C sequestration change. The SOC and soil C stocks in the 0–60 cm soil profile rapidly increased over the course of the long-term natural vegetation succession. During 2005 to 2015, the topsoils (0–20 and 20–40 cm) had higher rates of SOC change (from 0.06 to 0.55 and from 0.23 to 0.51 g kg−1 yr−1, respectively) and soil C sequestration rates (from 0.37 to 1.09 and from 0.40 to 1.16 Mg ha−1 yr−1, respectively) than subsoils (40–60 cm, from 0.04 to 0.36 and from 0.05 to 1.16 Mg ha−1 yr−1). The litter and fine root production increased with age of the natural vegetation succession, and had significant positive effects on changes in SOC and soil C sequestration. Therefore, long-term natural vegetation restoration improved the SOC accumulation, and increased litter and fine root inputs were probably the main factors contributing to soil C sequestration.

Interaction of soil water storage and stoichiometrical characteristics in the long-term natural vegetation restoration on the Loess Plateau

Knowledge of the soil water and stoichiometrical characteristics (SC) during long-term natural vegetation restoration is essential for managing the restoration of vegetation. To evaluate the response of soil water storage (SWS), soil organic carbon (SOC), total nitrogen content (TN) and total phosphorous content (TP) to long-term natural vegetation restoration (∼160 a), we examined the soil moisture and SC in areas with different restoration ages located in the central part of the Loess Plateau, China. Our results showed that the SWS decreased significantly with vegetation restoration and that the C:P ratio, N:P ratio, TN and TP increased significantly. The SWS increased gradually, whereas the SOC, C:P ratio, N:P ratio, TN and TP in each restoration stage decreased significantly with increasing soil depth in the 0–60 cm soil layer. These parameters tended to be stable in the soil layer below 60 cm. Vegetation acts as a link between SWS and soil SC, and they interact with each other indirectly. SWS and SWC showed an significant positive relationship (P < 0.01), whereas SWS and SOC, TN, TP, C:P ratio, and N:P ratio showed significant negative relationships (P < 0.01), thus, SOC, TN and TP are the key chemical factors affecting SWS.. These results could help estimating the productivity and sustainability of semiarid ecosystems and improve future eco-environmental reconstructions.

The coupling interaction of soil water and organic carbon storage in the long vegetation restoration on the Loess Plateau

Secondary succession can recover the properties of degraded soil. The moisture stored in different soil layers is recognized as an important driver of the productivity and sustainability of semi-arid terrestrial ecosystems, and land-use change has a significant effect on the global carbon (C) cycle through changing soil C accumulation rates. To evaluate the response of soil water storage (SWS) and soil organic carbon storage (SOCS) to long-term natural vegetation succession (∼150a) and the coupling interaction between them, we examined the soil moisture and soil organic carbon content in the land for different restoration ages in the Ziwuling Forest region located in the central part of the Loess Plateau, China. Our results showed that the SWS decreased and the SOCS increased with long-term natural vegetation restoration. The SOCS decreased along with the increase in the soil depth, and it was highest in the topsoil (0–20cm). In addition, the soil depth at which the SWS intensely varied and at which the SOCS tended to be stable moved downward and upward, respectively, with the vegetation succession. Furthermore, the correlation between SWS and SOCS was significant (P<0.05) in the long-term restoration and gradually weakened with the increase in the soil depth and the vegetation restoration stages. Clay, silt, sand, total porosity (TP), inactive porosity (IP), aeration porosity (AP) and capillary porosity (CP) were important factors that influenced the coupling interaction of SWS and SOCS at the grass restoration stages (<50a), and BD influenced this interaction in the shrub and early forest restoration stages (<130a). The effect of soil physical factors on the interaction of SWS and SOCS gradually weakened during the vegetation restoration succession. These results are expected to help improve the understanding of the response of deep soil water and soil organic carbon to long-term natural vegetation restoration and to provide insights into the coupling interaction between soil water and soil organic carbon influenced by vegetation.

Interaction of soil water storage dynamics and long-term natural vegetation succession on the Loess Plateau, China

Soil water is a key terrestrial water resource, particularly in arid and semi-arid regions of the world such as the Loess Plateau of China. Information on the dynamics of soil moisture following vegetation restoration is essential for managing water resources and can be helpful for adjusting relevant government policies. To evaluate the response of soil water storage (SWS) to long-term natural vegetation succession (~160a), we examined the soil moisture for different restoration ages in the Ziwuling forest region, which is located in the central part of the Loess Plateau. Our results showed that the SWS decreased with long-term natural vegetation restoration. The bulk density (BD), soil water content (SWC), and clay and silt content presented similar trends to those of the SWS throughout the entire vegetation succession. The SWS was significantly and positively correlated with the SWC and aeration porosity (P<0.05). The SWC was lower in the upper soils (0–50cm) than in the deeper soils (>50cm) at every restoration stage, as was the SWS; however, the SWS in the 200–300cm soil layer was the highest (164.61–212.80mm) compared to other layers in all restoration stages. These results are expected to help improve the understanding of the response of deep soil water to long-term natural vegetation restoration and to provide insights into the dynamics of deep soil water influenced by vegetation.

Variation of soil infiltrability across a 79-year chronosequence of naturally restored grassland on the Loess Plateau, China

Soil infiltrability plays a critical role in controlling soil erosion and enhancing water storage in arid and semi-arid areas. Presently, knowledge is lacking regarding the dynamic mechanism and characteristics of soil infiltration during long-term natural vegetation restoration. This study evaluated how soil infiltrability changes along a 79-year chronosequence of natural restoration from cropland to permanently restored grassland. A slope cropland (control) and five grasslands of successive age-classes (6-, 16-, 36-, 56-, and 79-year natural restoration treatments) were selected to establish a chronosequence on China’s Loess Plateau. Soil infiltrability was measured under simulated rainfall conditions at three intensities (20, 40, and 60 mm/h) using a run off–on–out method. The steady-state infiltration rate (SIR) of the control treatment decreased with increasing intensity of rainfall while those of the natural restoration treatments showed a contrary tendency. With the extension of restoration period, the SIR was gradually increased while the runoff was decreased and the time-to-runoff and time-to-SIR were prolonged. The SIR had a significant negative exponential relationship with the restoration period under different rainfall conditions (P < 0.01). Soil infiltrability showed rapid increases within 16 year of natural restoration and slight changes thereafter. Soil parameters including SIR and the contents of macroaggregates (>0.25 mm) and organic matter were significantly correlated with each other (P < 0.01). Long-term natural restoration of grassland, especially for 16-year, significantly enhanced soil infiltrability and reduced soil erosion through organic matter accumulation and the resulting improvement of structural properties. This study provides reference data for describing hydrological parameters on the Loess Plateau.

Change of soil physical properties under long-term natural vegetation restoration in the Loess Plateau of China

A 150-year chronological study of semi-arid abandoned farmland in the central Loess Plateau of China indicated that soil physical properties were closely related to the date of being abandoned and the vegetation recovery stages. Bulk density of the surface layer (0–20 cm) significantly reduced with time while soil porosity, water-holding capacity, aggregate stability, and saturated hydraulic conductivity significantly increased. In the early period of abandonment, up to 14 years, these changes were relatively fast due to a significant increase of soil organic matter content. However, amelioration of soil physical properties of subsurface layers (20–40 cm) was relatively slow. Decline of soil bulk density of surface layers could be used as an indicator of soil structure amelioration since it was related to most other properties. Changes of soil textural properties and specific surface area were not significant, which suggested that these properties were mainly inherited from parent materials and difficult to change. Emergence of dominant woody plants during the natural vegetation recovery process could be a useful and reliable indicator of obvious improvement in soil physical properties.