Revegetation Chronosequence Research Articles

Phosphorus desorption regulates phosphorus fraction dynamics in soil aggregates of revegetated ecosystems

To elucidate the mechanisms and effects of phosphorus (P) desorption on P fractions in soil aggregates of revegetated ecosystems is fundamental for regulating the P supply and biogeochemical cycle. We selected four aggregate sizes (1–5, 0.5–1, 0.25–0.5, and <0.25 mm) from a desert revegetation chronosequence (11, 31, 40, 57, and 65 years) as our study targets and used the Freundlich model to reveal the dynamics of P desorption and changes in P fractions. The results showed that the calibrated model Q=A−KFdtnd for different size aggregates in seven deserts (two natural and five revegetated) described the P desorption characteristics well. In soil aggregates of revegetated deserts, smaller aggregates with higher specific surface area did not desorb more P, nor did older aggregates after revegetation. The natural P desorption process in aggregates resulted in significant changes in Ca2–P, Ca8–P, Al–P and Fe–P fractions (p < 0.05), and revegetation years also affected P fraction dynamics significantly (p < 0.05). This study highlights that the calibrated kinetic model in the revegetated soil aggregates elucidated the P desorption characteristics, and that the P desorption process drove P fraction changes.

Phosphorus sorption–desorption changes phosphorus fraction dynamic in a desert revegetation chronosequence

AbstractUnderstanding the characteristics of soil phosphorus (P) sorption and desorption is essential for comprehending P biogeochemical cycling and effectively managing ecosystems in a desert revegetation chronosequence. The present study utilized the Freundlich model and enzymatic activity to characterize the features of P sorption–desorption, and microbial activity, which aims to elucidate the effect of P kinetics and microbial activity on P fractions in the soils of a desert revegetation chronosequence, consisting of 11, 31, 40, 57, and 65 years old revegetated deserts. The findings revealed that the 31 years old soil showed the highest alkaline phosphomonoesterase and phosphodiesterase activities, and the 40 years old displayed the highest inorganic pyrophosphatase activity. In revegetated desert soils, microbial activity changed P sorption–desorption kinetics by decreased or increased the parameters including sorption/desorption energy site, P sorption/desorption ability, and the maximum buffering capacity of P sorption/desorption. And in microbial activity soils of 31–40 years old, P desorption significantly decreased T‐P and A‐P concentrations (p &lt; 0.05). P sorption process and enzyme activity explained 35.10% and 22.20% of P fraction variation, respectively; and P desorption process and enzyme activity explained 48.3% and 22.3% of P fraction variation, respectively. These findings provide valuable insights into the contribution of P kinetics coupled with microbial activity in desert ecosystems, aiding in the effective management of these fragile ecosystems.

Differences in the soil and hydrology responses of two revegetation chronosequences in the Loess Plateau, China

Vegetation restoration has been widely implemented to restore degraded land. However, vegetation expansion may result in the overconsumption of soil moisture and soil desiccation, which in turn exacerbates land degradation. To ensure the sustainability of ecological restoration, it is necessary to optimise restoration patterns. Two restoration patterns (afforestation with Robinia pseudoacacia L. (RP) and abandoned farmland (AL)) along a revegetation chronosequence (0, 9, 17, 27, and 42 years) were selected to analyse variations in soil and hydrological characteristics on the Loess Plateau, China. The results showed that for the two revegetation types, the soil quality index (SQI) increased markedly (p < 0.05) and the soil loss (SL) and surface runoff (R) decreased significantly (p < 0.05) over time, indicating that vegetation restoration improves soil quality and prevents soil and water erosion. The annual increments of soil moisture storage (Ws) within a 200 cm depth notably decreased during the late restoration stage (>27 years) for the artificial forest. Moreover, forest also showed increasing actual evapotranspiration (ET) trends and decreasing Ws trends. These results suggest that afforestation might lead to overconsumption of water and soil water depletion during the late restoration stage. Although RP sites had higher SQI (22.2–36.7 %) values and lower SL (47.0–81.4 %) and R (86.5–196.8 %) values when compared with AL sites, the change rates of the SQI, R, and SL at RP sites were stable or decreased over a period of restoration, while these rates showed increasing tendencies under AL sites. These suggests that natural grasslands may be more beneficial than artificial forests during the late restoration stage. Therefore, naturally restored grasslands are highly recommended for sustainable ecological restoration in the semiarid and arid areas of the Loess Plateau or in similar areas elsewhere.

Comparison of water use efficiency of sand-binding species along revegetation chronosequence in an alpine desert

Afforestation is an effective measure for ecological restoration in the desert ecosystem. The long-term water use efficiency (WUE) of leaves is an important indicator for evaluating the water adaptation strategy of sand-fixing species. However, the WUE of typical sand-fixing plants in the alpine desert and its responses to local climatic, micro-geomorphology, environmental conditions and nutrient limitations are still unclear. In this study, sand-fixing vegetation community along a revegetation chronosequence (Hippophae rhammoides planted on dunes in 1987, 2008, and 2015, respectively. H. rhammoides with the longest recovery period were defined as mature plantations, and the shortest recovery period were defined as juveniles.) at the alpine desert at the eastern shore of the Qinghai Lake were used as the research plots. Stable carbon isotope was used to evaluate species WUE. The results showed that: (1) the δ13C values of H. rhammoides showed a decreasing trend as plants grew. The seasonal δ13C variation was mainly affected by average relative humidity (MRH). (2) The δ13C in the dunes revegetated in 2008 and 2015 were significantly higher than that in 1987 at the windward slope (P < 0.05). The values of δ13C had various responses to the available soil water under the influence of topography, and soil water content was the key factor for the WUE of individuals in communities. There was a significant negative correlation between the ratio of carbon and nitrogen content in H. rhammoides leaves and WUE. The research indicated that mature plantations had adopted a more stable water use pattern than the juveniles, which provide an effective insight for ecological restoration in fragile ecological regions.

Soil dissolved carbon and nitrogen dynamics along a revegetation chronosequence of Caragana korshinskii plantations in the Loess hilly region of China

Widespread vegetation restoration is an effective measure used to control soil erosion and improve soil organic carbon (SOC) and total nitrogen (TN) storage; however, knowledge of soil dissolved carbon and nitrogen has not been well characterized. Caragana korshinskii plantations are valued for their critical role in soil and water conservation in the Loess Hilly Region. This study aimed to estimate the levels of soil carbon and nitrogen and their dissolved fractions in one farmland (Zea mays L.) and three C. korshinskii plantations at 15, 30 and 40 years; additionally, the distribution of soil carbon and nitrogen stocks among various soil depths were estimated. The results showed that afforestation with C. korshinskii resulted in a significant increase in the contents and stocks of SOC and TN and their dissolved fractions. At a depth of 0–10 cm, the 30-year-old C. korshinskii had the highest stocks of SOC and TN, but at depths of 40–100 and 100–200 cm, the highest SOC and TN stocks were found in the soil of 15-year-old C. korshinskii. The 15-year-old C. korshinskii had the highest stocks of SOC and TN at depths of 0–200 cm and the highest stocks of dissolved nitrogen across almost all soil layers. The soil at 100–200 cm contained 34%–54% of the total percentages of the cumulative stocks of SOC and TN and their fractions. The SOC stock was the most important factor affecting the variation in soil nitrogen fractions and contributed to more than 80% of the total variation; additionally, the nitrate (NO3-N) content and stock were the most important factors affecting the soil carbon fractions, contributing to 78% of the total variation. This study demonstrates that revegetation age and soil depth play important roles in determining carbon and nitrogen levels. The results also suggest that C. korshinskii plantations should be harvested and revegetated during the rapid growth period (∼15 years) during which they show the largest accumulations of soil carbon and nitrogen.

Revegetation of a degraded karst ecosystem triggers shifts in diazotroph communities (composition, diversity, function and assembly processes)

Ecological restoration is an important intervention strategy to halt biodiversity loss and land degradation. Under natural conditions, diazotrophs regulate terrestrial productivity by alleviating nitrogen limitation. However, little is known on the effects of revegetation on diazotroph community (composition, diversity and functioning). Here, by using nifH gene amplicon sequencing, community assembly models, and 15N2-labeling technique, we investigated the dynamics of soil diazotroph communities along a revegetation chronosequence of 0 (cropland), 5, 10, 20 and 30 years of Chinese prickly ash (CP) in a karst area of Southwest China. Diazotroph diversity decreased and its composition was significantly changed after revegetation. Soil pH was the edaphic factor which correlated the most with diazotroph community composition and diversity. The most abundant diazotrophs belonged to the Proteobacteria phylum and changed along revegetation chronosequence: the genus Azohydromonas dominated at early stages (5-y CP), while at later stages (20-y CP) the genera Azospirillum and Bradyrhizobium became more abundant. The N-fixation rates were highest in the 5-y CP plantation, and relatively lower N-fixation rates were observed in the cropland and 10-y CP plantation. The Sloan neutral and null models showed: i) a phylogenetic turnover in the diazotrophic taxa assembly, which was largely deterministic at 5- and 10-y, and stochastic at 20- and 30-y; and ii) a bacterial community which was assembled largely by stochastic processes along the revegetation chronosequence. Taken together, our results highlight that knowledge on dynamics of diazotroph community (composition, diversity and functioning) is important to understand ecological mechanisms regulating belowground community along revegetation process.

Does revegetation cause soil microbiota recovery? Evidence from revisiting a revegetation chronosequence 6 years after initial sampling

The global biodiversity and land degradation crises have brought about an urgent need and great demand for restoration actions. However, restoration outcomes are often less than ideal, indicating a need for improved restoration practices. Soil microbiota are extremely diverse and functionally important and should be further considered in restoration. However, despite their importance, there remains a gap in understanding of how soil microbiota respond following native plant revegetation. Several studies have used cross‐sectional study designs of restoration chronosequences to infer that revegetation causes the recovery of soil microbiota, but it is near‐impossible to determine cause and effect relationships with cross‐sectional study designs. Here we used high‐throughput amplicon sequencing of the bacterial 16s rRNA gene from soil samples collected at two timepoints, 6 years apart, at a revegetation chronosequence in South Australia. Our results show some indications of recovery but not the additional recovery in bacterial community composition toward the reference sites as expected after this 6‐year period—a result that appears at odds to the expected patterns of revegetation causing recovery of soil microbiota. Spatially dependent factors (e.g. soil chemistry), biotic and abiotic barriers, seasonal differences in sampling, and variability among the ecological reference sites could each help explain this apparent lack of additional microbial recovery. More detailed longitudinal and/or experimental manipulation work is required to further examine the cause‐effect relationships. Our study contributes important new information and highlights knowledge gaps in how soil microbiota respond to revegetation, and we urge caution when attempting to infer causation from cross‐sectional chronosequence studies.

Bacteria and fungi differentially contribute to carbon and nitrogen cycles during biological soil crust succession in arid ecosystems

Biological soil crusts (BSCs) are widely considered critical for soil fertility in arid ecosystems. However, how microbial communities regulate the C and N cycles during BSC succession is not well understood. We utilized GeoChip 5.0 to analyze the functional potential of bacteria and fungi involved in the C and N cycles of BSCs along a 61-year revegetation chronosequence. The normalized average signal intensities of different functional genes involved in C and N metabolism in 61-year-old BSCs were significantly different from those in younger BSCs and most functional gene subcategories and the corresponding dominant functional populations were derived from bacterial rather than fungal communities. Most C degradation genes (dominated by the starch-degrading gene amyA) were derived from Actinobacteria (mainly Streptomyces) in bacteria, but Ascomycota (mainly Aspergillus) was the key population for lignin degradation (dominated by the phenol oxidase gene) during BSC succession. N cycle genes involved in denitrification (such as narG, nirK/S, and nosZ) and N fixation (nifH) were mainly derived from Unclassified Bacteria, whereas genes involved in ammonification (ureC) were mainly derived from Streptomyces. Moreover, redundancy analysis showed that soil biogeochemical properties were closely related to bacterial and fungal functional gene structures during BSC succession. These findings indicate that bacteria play a crucial role in the regulation of C and N cycles during BSC succession in arid ecosystems, while fungi perform supplementary degradation of lignin, and these communities can successfully stimulate an increase in C and N metabolism in soil during the later successional stages of BSCs.

Development of archaeal communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, north central China

Archaea are major contributors to biogeochemical cycles and energy metabolism among soil microorganisms under extremely acidic and high-temperature conditions, however, the biodiversity and ecological function of archaea in biological soil crusts (BSCs) of desert ecosystems are not fully understood. Here, we used Illumina MiSeq sequencing and microbial functional gene array (GeoChip 5.0) to test the following hypotheses: (1) the composition and function related to biogeochemical cycles of the archaeal community would change significantly in the development process of BSCs; and (2) the key factors driving these changes may be soil biogeochemical properties. The results showed that the diversity, abundance, and functional potential of the archaeal community showed their highest levels in 5-year-old BSCs. The dominant phyla were Thaumarchaeota, Euryarchaeota, and an unclassified phylum in the archaeal community during BSC succession. The functional genes of the archaeal community were mainly involved in carbon (C) and nitrogen (N) cycles, and the functions of the three dominant phyla were complementary in these cycles. Moreover, redundancy analysis showed that soil biogeochemical properties were negatively related to the composition and function of the archaeal community during BSC succession, and the soil C:N ratio might be the major limiting factor. These results provided evidences for our hypotheses and revealed that the archaeal community played an important ecological role in the early development stage of BSCs, and might be pioneer species of soil microbial communities during BSC succession.

Biological soil crusts enhance the recovery of nutrient levels of surface dune soil in arid desert regions

Abstract Revegetation, an effective method for restoring desertified lands, helps enhance the colonization and development of biological soil crusts (BSCs) and improves the nutrient conditions of desert soils. This study aims to shed light on the changes of elemental concentrations and their enrichment in fixed surface soil of sand dunes over a 50-year revegetation chronosequence linked to BSCs of different successional stages in the Tengger desert of China. We investigated the elemental levels of K, Na, Ca, Mg, Mn, Zn, Cu, and Fe in surface soil covered by cyanobacteria-lichen crusts, moss crusts and subsoil. Nutrient enrichment of BSCs and soils were analyzed to reflect the nutrient changes in the revegetated desert ecosystem. Concentrations of K, Na, Ca, Mn, Zn, and Cu in cyanobacteria-lichen crusts were significantly higher than in mobile sand dunes. Nutrient enrichment rate (except for Na) exhibited unimodal patterns, and year 31 was a key turning point after which the rate switched from increasing to decreasing over time. Our long-term study indicated that both cyanobacteria-lichen crusts and moss crusts can effectively improve nutrient accumulation and promote edaphic conditions, which is beneficial to the development and nutrient cycling of desert ecosystems.

Shifts in community structure and function of ammonia-oxidizing archaea in biological soil crusts along a revegetation chronosequence in the Tengger Desert

Shifts in community structure and function of ammonia-oxidizing archaea in biological soil crusts along a revegetation chronosequence in the Tengger Desert

Shifts in soil microbial community functional gene structure across a 61-year desert revegetation chronosequence

Vegetation and soil properties are crucial in shaping soil microbial communities. However, little is known about temporal changes in the functional structure of soil microbial communities to managed revegetation in desert ecosystems. Here, we adopted GeoChip 5.0-180 K, a functional gene array, to investigate the succession of soil microbial functional genes structure and potential across a 61-year revegetation chronosequence in the Tengger Desert, China. The abundance of bacterial, fungal and archaeal genes generally increased during succession. However, variation in α-diversity of microbial functional genes and signal intensity of most C-, N- and P-cycling related genes showed hump-shaped patterns along the successional gradient. Although microbial functional structure changed during succession, these revegetation sites shared a high percentage of functional genes and nestedness-resultant component dominantly determined β-diversity. Furthermore, microbial functional structure significantly correlated with crustal and shrub coverage, thickness and mass of crusts, soil fine particles, total C, total P and the ratios of C to N and C to P. The canonical correspondence analysis (CCA) and CCA-based variation partitioning analysis showed that environmental variables explained 56.6% and 85.3% of the variance in overall microbial functional genes, respectively. These results indicate that vegetation development, especially the colonization and development of soil crusts together with changes in soil abiotic properties, play key roles in driving the functional shifts in soil microbial community structure after desert revegetation.

Ecoenzymatic stoichiometry and nutrient dynamics along a revegetation chronosequence in the soils of abandoned land and Robinia pseudoacacia plantation on the Loess Plateau, China

The effects of vegetation restoration on plant characteristics and soil physicochemical properties have been widely documented; however, knowledge of the variation in soil ecoenzymatic activity and stoichiometry remains limited, particularly with respect to their relationship with plant and soil variables in restored ecosystems. Here, the vegetation and soil from one farmland and two restored land-use types (Robinia pseudoacacia plantations: RP and abandoned lands: AL) of four age classes (10, 18, 28, and 43-years) were investigated and sampled on the Loess Plateau, China. The activity of C, N, and P-acquiring enzymes (β-1,4-glucosidase, BG; β-1,4-N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP; and alkaline phosphatase, AP) and other major influencing factors (soil physical properties, soil nutrient contents, and microbial biomass) were determined. It was found that both restoration time and vegetation types significantly affect plant characteristics, soil physical properties, soil nutrient content, and microbial biomass. Soil BG, NAG + LAP, and AP enzyme activities were higher in RP and AL than in farmland, and increased with restoration time in AL. For RP, the activity of these enzymes increased from year 10 to year 28, then decreased from year 28 to year 43. Soil ecoenzymatic C:P and N:P activity ratios were ordered: farmland > AL > RP, and decreased with restoration time in AL and RP; thus, P limitation was stronger in RP than in AL and increased with restoration time in both AL and RP. Soil ecoenzymatic C:N:P acquisition ratios of farmland, AL, and RP deviated from the 1:1:1 ratio and depended on the availability of environmental nutrients and demand for microbial nutrients. The vegetation characteristics and soil physical properties were closely related to the nutrient acquisitions of microbes and, ultimately, contributed towards shaping soil ecoenzymatic activity and stoichiometry (particularly vegetation coverage, belowground biomass, soil water content, soil bulk density, and pH). Furthermore, variation in soil ecoenzymatic activity and stoichiometry was better accounted by dissolved nutrients in the soil (particularly C and N) and microbial biomass (particularly N and P) than by plant characteristics and soil properties. Overall, this study demonstrates that the C:N:P stoichiometry of soil microbes and ecoenzymatic activity is nutrient dependent, rather homeostatic, with the potential to influence nutrient cycling on the Loess Plateau.

Changes in Soil Organic Carbon and Total Nitrogen at a Small Watershed Scale as the Result of Land Use Conversion on the Loess Plateau

Soil organic carbon (SOC) and total nitrogen (total N) are important soil components for agricultural production. Soil quality is related to the total amount of SOC and total N sequestered in the soil. Land use plays a major role in the distribution and amount of SOC and total N. This study analyses the amount of SOC and total N under various land cover types in 1987, 2005 and 2010, and evaluated their storage in land use conversions in a comprehensively managed watershed on the Loess Plateau, China. Results show that concentrations of SOC and total N in shrub land and natural grassland areas were significantly higher than for other land uses (farmland, orchard, abandoned farmland, manmade grassland) while cropland had the lowest concentration. Storage of SOC and total N increased along the revegetation chronosequence. As the storage of SOC in 2005 and 2010, they were 3461.86 × 108 and 4504.04 × 108 g respectively. Soil organic carbon storage were enhanced one third just during 5 years. The effects of land use on SOC and total N were the most significant in the upper soil layers. The correlation between SOC, total N, and the C/N ratio indicated that the best combination of land uses were natural grassland and shrub land. They efficiently influenced the distribution and storage of SOC and total N, and benefited vegetation restoration.

Dynamics of storage and relative availability of soil inorganic nitrogen along revegetation chronosequence in the loess hilly region of China

In the Loess Hilly Region of China, the widespread conversion of farmland to forestland and grassland has resulted in great changes in soil carbon (C) and nitrogen (N) storage in the shallow soil layers. However, knowledge regarding changes in the status and relative availability of inorganic nitrogen (IN) is still limited. To determine the responses of soil IN storage and its relative availability to revegetation patterns and chronosequence, a 0–200 cm soil profile was collected from two typical vegetation restoration patterns in the heartland of the region, artificial forestland (Robinia pseudoacacia) and natural grassland, with a stand age sequences of 15, 20, 25, 30 and 40 years. The farmland near the sites was selected as a control. As a whole, the NH4-N, NO3-N and total inorganic nitrogen (TIN) concentrations and stocks in the forestlands were significantly higher than those in the grasslands, especially in the topsoil (0–10 cm). With increasing revegetation chronosequence, afforestation improved soil NH4–N, NO3–N and TIN concentrations and stocks until Robinia pseudoacacia reached maturity at an age of 25–30, but abandoned on former farmland had minor effects on soil IN. After revegetation, soil NH4–N was higher than NO3–N, and the NH4–N/NO3–N ratio (ANR) was greater than 1 and increased with soil depth. The soil at 40–200 cm accounted for 60–90% of the total IN stock of the 0–200 cm soil profile, and the soil at 100–200 cm accounted for more than 35% of the total levels. Moreover, soil physicochemical properties were significantly correlated with soil IN variables, and ANR had a greater correlation coefficient with soil physicochemical properties than the other IN variables. It was concluded that afforestation was a better choice for soil IN restoration of degraded land, and subdeep and deep soil provided an extremely important resource for evaluating soil IN pools and their relative availability. Furthermore, soil IN dynamics, particularly ANR, could be regarded as indicators for assessing the dynamics of soil fertility.

Changes in functional gene structure and metabolic potential of the microbial community in biological soil crusts along a revegetation chronosequence in the Tengger Desert

Biological soil crusts (BSCs), the pioneers of restoration of degraded vegetation, act as an organizing principle in drylands largely through metabolic activities of microbial communities. However, little is known about the microbial functional potential involved in biogeochemical processes during BSC succession in desert ecosystems. Here, we utilized a functional gene array (GeoChip 5.0) in conjunction with determinants of microbial community compositions of BSCs along a revegetation chronosequence in the Tengger Desert, to address the following: (a) how the functional structure of the microbial community changes with BSC age in different soils and (b) how genes involved in carbon (C)- and nitrogen (N)-cycling change and whether they promoted an increased microbial metabolic potential during BSC succession in desert revegetation. The results showed that the relative abundance of functional genes was determined by the microbial community compositions in the BSC development process, and the significant differences in microbial functional genes were detected in 61-year-old BSCs from other aged BSCs. Redundancy analysis indicated that the abundance of fungi and moss and soil physicochemical properties were the important factors determining differences in microbial functional structures. Functional genes associated with C degradation and N denitrification were the major components involved in C and N cycles, which were closely related to the increased fungal abundance during succession. The increased gene abundance of 61-year-old BSCs in both C and N cycles promoted microbial metabolic potential. These results indicated that fungi might be the key microbial mediators in C and N cycling in the later development of BSCs, and microbial functional structure could be a potential indicator of revegetation sustainability in desert ecosystems.

Soil carbon storage along a 46-year revegetation chronosequence in a desert area of northern China

Soil contains the majority of terrestrial carbon; however, most studies only focus on soil organic carbon (SOC) in the first meter or even shallower layers, and soil inorganic carbon (SIC) and root-derived carbon (RDC) are often overlooked. Here, we investigated the distribution of soil carbon at a depth of 0–3.0 m over a 46-year revegetation chronosequence on moving sand dunes and evaluated the potential influence of soil water content on soil carbon. The SOC density increased significantly along the 0–3.0 m profile, and showed a faster increasing rate in shallow layer (0–0.4 m) than that of the deep layers below 0.4 m. Although the SIC density did not increase significantly, it accounted for >65% of the total soil carbon in shallow layer and at least 82% in deep layer. The live and dead RDC increased significantly over the chronosequence in both shallow and deep layers. The RDC accounted for a small amount of the total soil carbon at an average of 3.19%. The SOC was closely linked with live RDC in both the shallow and deep layers. The soil water content was only positively correlated with the SOC in the shallow layer. The SOC storage in the shallow layer required 57.4 years to reach the level at the natural vegetation site, whereas the storage in the deep layers required >100 years. Our results indicated that soil carbon accumulation is a slow process in both shallow and deep layers after revegetation, and the most notable increase in soil carbon was accounted by SOC. We suggest that SOC, SIC and RDC should be considered when assessing the effects of revegetation on soil carbon in water-limited ecosystems.

Development of bacterial communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, northwest China

Abstract. Knowledge of structure and function of microbial communities in different successional stages of biological soil crusts (BSCs) is still scarce for desert areas. In this study, Illumina MiSeq sequencing was used to assess the compositional changes of bacterial communities in different ages of BSCs in the revegetation of Shapotou in the Tengger Desert. The most dominant phyla of bacterial communities shifted with the changed types of BSCs in the successional stages, from Firmicutes in mobile sand and physical crusts to Actinobacteria and Proteobacteria in BSCs, and the most dominant genera shifted from Bacillus, Enterococcus and Lactococcus to RB41_norank and JG34-KF-361_norank. Alpha diversity and quantitative real-time polymerase chain reaction (PCR) analysis indicated that bacterial richness and abundance reached their highest levels after 15 years of BSC development. Redundancy analysis showed that silt + clay content and total K were the prime determinants of the bacterial communities of BSCs. The results suggested that bacterial communities of BSCs recovered quickly with the improved soil physicochemical properties in the early stages of BSC succession. Changes in the bacterial community structure may be an important indicator in the biogeochemical cycling and nutrient storage in early successional stages of BSCs in desert ecosystems.

Co-variation of fine-root distribution with vegetation and soil properties along a revegetation chronosequence in a desert area in northwestern China

This study investigated the changes in the distributions of fine roots and explored their responses to changes in vegetation and soil properties along a 46-year revegetation chronosequence in a desert area in northwestern China. Fine roots and soil samples at depths of 0–3.0m soil profile were obtained from revegetated sand-binding areas and compared with those from moving sand dunes, natural undisturbed vegetated dunes, and a desert steppe. The soil physicochemical properties in the top 0.8m layer were analyzed, and the soil water contents at depths of 0–3.0m soil profile were measured. Redundancy and regression analyses were conducted to explore the relationships between fine roots, vegetation and soil properties. Both the cumulative fine-root length and mass in the 0–0.4m layer and throughout the 0–3.0m profile increased along the revegetation chronosequence, and those of the 1.0–3.0m layer increased up to 29years and then decreased. Additionally, the proportion of fine roots in the 0–0.4m layer increased and the proportion of fine roots from 1.0–3.0m decreased along the revegetation chronosequence. The fine-root length in 0–0.4m layer was mainly influenced by herbaceous cover, while the fine-root mass at depth of 0–3.0m was affected by shrub cover and biomass. The amounts of fine soil particles, soil organic carbon, and total nitrogen were the main edaphic factors that influenced the distribution of fine roots. The fine-root length and mass in the 0–0.4m layer were weakly and positively correlated with soil water contents, while those in the 1.0–3.0m layer had strong negative relations with the soil water contents in corresponding layers. Our results demonstrated that the fine-root distribution in revegetated sand dunes was regulated by the succession of the vegetation-soil system after revegetation.

Changes in soil organic carbon and nitrogen capacities of &amp;lt;i&amp;gt;Salix cheilophila&amp;lt;/i&amp;gt; Schneid along a revegetation chronosequence in semi-arid degraded sandy land of the Gonghe Basin, Tibet Plateau

Abstract. The Gonghe Basin is a sandified and desertified region of China, but the distribution of soil organic carbon (SOC) and total nitrogen (TN) along the cultivation chronosequence across this ecologically fragile region is not well understood. This study was carried out to understand the effects of restoration with Salix cheilophila for different periods of time (6, 11, 16, 21 years) to test whether it enhanced C and N storage. Soil samples, in four replications from seven depth increments (0–10, 10–20, 20–30, 30–50, 50–100, 100–150 and 150–200 cm), were collected in each stand. Soil bulk density, SOC, TN, aboveground biomass and root biomass were measured. Results indicated that changes occurred in both the upper and deeper soil layers with an increase in revegetation time. The 0–200 cm soil showed that the 6-year stand gained 3.89 Mg C ha−1 and 1.00 Mg N ha−1, which accounted for 40.82% of the original SOC and 11.06% of the TN of the 0-year stand. The 11-year stand gained 7.82 Mg C ha−1 and 1.98 Mg N ha−1 in the 0–200 cm soil layers, accounting for 58.06% of the SOC and 19.80% of the TN of the 0-year stand. The 16-year stand gained 11.32 Mg C ha−1 and 3.30 Mg N ha−1 in the 0–200 cm soil layers, accounting for 66.71% of the SOC and 21.98% of the TN of the 0-year stand. The 21-year stand gained 13.05 Mg C ha−1 and 5.45 Mg N ha−1 from the same soil depth, accounting for 69.79% of the SOC and 40.47% of the TN compared with the 0-year stand. The extent of these changes depended on soil depth and plantation age. The results demonstrated that, as stand age increased, the storage of SOC and TN increased. These results further indicated that restoration with S. cheilophila has positive impacts on the Gonghe Basin and has increased the capacity of SOC sequestration and N storage. The shrub's role as carbon sink is compatible with system management and persistence. The findings are significant for assessing C and N sequestration accurately in semi-arid degraded high, cold sandy regions in the future.