Revegetation Time Research Articles

Revegetation of mined areas influences the physiological profile of bacterial communities and improves the biochemical functions of soil

Mining activities have expanded worldwide to meet industrial demands and technological development. However, these activities have a negative impact on the environment that must be addressed. Thus, this study aimed to monitor the effects of the revegetation process on microbial proxies in an iron mine-degraded landscape using the biomass, activity, and metabolic capacity of the soil microbial community. We analysed an area that was recently mined and nonrevegetated (NR), areas that were mined and were under active revegetation (for 2 yrs and 3 yrs) and an unmined area covered with native vegetation (RA) in the mining province of Corumbá, Brazil. The results showed that there was an average gain of 44.6% and 48.15% in microbial biomass carbon in the 2 yr and 3 yr revegetated areas, respectively, compared to the NR area. We observed that after 3 yrs of revegetation, microbial biomass nitrogen increased by 86% compared to that in the nonrevegetated area. The enzymatic activity of phosphatase, fluorescence diacetate hydrolysis (FDA), and urease also increased as a function of revegetation time compared to the NR area. Phosphatase increased by 90% in the 3 yr revegetated area, FDA increased by 53% in the 2 yr revegetated area and 68% in the 3 yr revegetated area, and urease increased by 52% and 66% in the 2 yr and 3 yr revegetated areas, respectively, when compared to the NR area. The metabolic capacity of microorganism communities to degrade carbon sources returned rapidly, indicating an improvement in soil functioning in short time periods. Soil microbial proxies showed a high sensitivity to soil alterations in response to revegetation activities, highlighting their role as potential indicators in the rehabilitation process of mining-degraded landscapes.

Root cellulose drives soil fulvic acid carbon sequestration in the grassland restoration process

Revegetation is an effective means to increase the soil organic carbon (SOC) stock and reverse SOC loss worldwide. Restoration through grasslands has great potential primarily due to the contribution of the root system. However, the impacts of grassland restoration remain uncertain, as current understandings of the direction and magnitude of changes in different SOC fractions and the influence of root properties on SOC are still unclear. To address this problem, we conducted a field study to investigate variations in SOC fractions and root properties under different grassland restoration times (1, 5, 10, 15, 25 and 30 years following restoration) in the Loess Plateau, China. Specifically, we measured fractions of soil labile organic carbon including microbial biomass carbon (MBC) and dissolved organic carbon (DOC) and fractions of soil stable organic C including humus carbon (HS), fulvic acid carbon (FA) and humic acid carbon (HA) in the 1 m soil profile. Furthermore, we evaluated root biomass, root C, root lignin and cellulose as potential drivers of SOC patterns. We found that SOC, soil labile organic C and soil stable organic C fractions generally increased with the revegetation time, except for brief decreases at the 5- and 15-year marks. Across the entire period (year 1 to 30), the proportions of HS and FA to SOC increased by 10.64% and 14.72% at 30 years, respectively, while the ratios of MBC and DOC to SOC were relatively stable. The average SOC accumulation rate was 0.72 Mg ha−1 yr−1 in the 1 m soil profile over the 30-year grassland revegetation period. The average rate of change of FA (0.67 Mg ha−1 yr−1) was higher than that of the HA, HS and soil labile organic C fractions, which indicated that SOC stability increased and SOC accumulation was mainly derived from the enhancement of FA. Decreases in root biomass and cellulose storage drove reductions in SOC fraction stores with soil depth. The root cellulose exerted significant influences on the SOC and SOC fractions, especially on FA (R2 = 0.82, p < 0.01). These findings show that grassland restoration plays an important role in improving and increasing SOC; in particular, the increase of FA results from the augmentations of root cellulose.

Effects of grassland degradation and re-vegetation on carbon and nitrogen storage in the soils of the Headwater Area Nature Reserve on the Qinghai-Tibetan Plateau, China

Both overgrazing and climate change contribute to grassland degradation in the alpine regions of China and negatively affect soil carbon and nitrogen pools. We quantified changes in soil organic carbon (SOC) and total nitrogen (TN) in black soil beach (BSB). We measured SOC and TN in severely degraded and non-degraded grasslands to calculate differences in carbon and nitrogen storage, and field survey results were extrapolated to the entire headwaters area of the Qinghai-Tibetan Plateau (36.3×105 km2) to determine SOC and TN losses from these grasslands. We also evaluated changes in SOC and TN in severely degraded grasslands that were artificially re-vegetated five, seven and nine years ago. Totally 92.43 Tg C and 7.08 Tg N were lost from the BSB in the headwater area, which was approximately 50% of the original C and N soil pools. Re-vegetation of the degraded grasslands in the headwater area would result in a gain of 32.71 Tg C in the soil after five years, a loss of 5.52 Tg C after seven years and an increase of 44.15 Tg C after nine years. The TN increased by 53.09% and 59.98% after five and nine years, respectively, while it decreased by 4.92% after seven years of re-vegetation. The results indicate that C and N stocks followed a “V” shaped pattern with re-vegetation time. Understanding plant-soil interactions during succession of artificially planting grassland ecosystems is essential for developing scientifically sound management strategies for the effectively re-vegetated BSB.

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.

English

Arbuscular mycorrhizal fungi (AMF) are obligatory biotrophs that have a symbiotic evolutionary relationship with about 80% of all terrestrial plant species. The fungus mainly supplies water and nutrients to the plant and receives photoassimilates. The AMF diversity affects both the competition among species and floristic composition of an area. Fluctuations in the population of this group of microorganisms can cause fluctuations in plant populations above ground. In this work, the AMF community profile in areas with different ages of revegetation was evaluated by morphological identification of spores and denaturing gradient gel electrophoresis (DGGE) techniques. We found 12 AMF species and dominance of the species Glomus macrocarpum determined by spore density. Since the richness level observed in each plot was low and there was predominance of one species of AMF, it can be concluded that these areas still present a high degree of disturbance. It was possible to detect complex band profiles by DGGE analyses for the two plant species studied, Visnia latifolia and Cecropia hololeuca. No relationship between AMF diversity and revegetation time was observed in these areas. Key words: Denaturing gradient gel electrophoresis (DGGE), symbiosis, succession, survey.

Evaluation of Soil Chemical Properties and Actinomycete Community Structure following a Temporal Sequence of Revegetation through Paulownia Fortunei in the Heavy Metal–Contaminated Soil

The present work tested effects of a revegetation pattern conducted using Paulownia fortunei (Seem.) Hemsl. (Scrophulariaceae) on soil chemical properties and actinomycete community structure identified by terminal restriction fragment length polymorphism (T-RFLP) technology of 16S rDNA. The results indicated that P. fortunei planting with time effectively improved organic carbon and total nitrogen contents, as well as pH in heavy metal-contaminated soils and, at the same time, enhanced the retention of heavy metals such as Pb, Zn, Cu and Cd in soils. T-RFLP profiles of soil actinomycete communities digested from two restriction enzymes (HhaI and RsaI) showed different specific TRF patterns across four sites with different revegetation time. Nonetheless, number and diversity of terminal restriction fragments for soil actinomycete community increased gradually with P. fortunei planting time and followed consistent patterns with soil organic carbon, total nitrogen, pH and heavy metal contents. Our results revealed a great potential of P. fortunei to remediate heavy metal-contaminated soils.

Hydrological responses and soil erosion potential of abandoned cropland in the Loess Plateau, China

Recent changes in hydrological processes and soil erosion in the Loess Plateau, China, are immediate responses to cropland abandonment for revegetation, which lead to a long-term decrease in runoff generation and soil erosion. However, detailed hydrological responses and soil erosion changes have not been clearly evaluated. In this study, two issues were focused on the plot scale. The first issue relates to changes in vegetation cover and soil properties during the early stages of revegetation. Given the occurrence of soil compaction, it was hypothesized that runoff increased during this period and the soil erosion did not significantly decline, even though vegetation increased. The second issue is the effect of scale on runoff and soil erosion. Three plot groups of three vegetation types and two restoration stages were established for comparative experiments. The results from these experiments confirmed that the soil compaction occurred during revegetation in this region. Greater runoff was produced in plot group that experienced both a longer restoration time and with higher vegetation cover (such as Groups 2 and 3 in this study) than that with a shorter restoration time and lower vegetation cover (Group 1). In addition, the total soil loss rates of all plot groups were rather low and did not significantly differ from each other. This indicates that a reduction in runoff generation and soil erosion, as a result of revegetation, was limited in the early stages of restoration following the cropland abandonment. With increasing plot area, the runoff coefficient decreased for the plot group with a longer revegetation time (Groups 2 and 3), but gently increased for the one with a shorter restoration time (Group 1). In Groups 2 and 3, soil loss rate decreased when plot area enlarged. In Group 1, it decreased before a plot area threshold of 18 m 2 was exceeded. However, the increase occurred when plot area crossed the threshold value. In conclusion, the high vegetation cover alone did not lead to reduction in the runoff coefficient during the early stages of revegetation. When evaluating hydrological and soil erosion responses to revegetation, the soil compaction processes should be considered. Additionally, the effect of scale on runoff and soil erosion was found to be dependent on restoration extent, and thus on restoration time.

Changes in microbial‐community structure with depth and time in a chronosequence of restored grassland soils on the Loess Plateau in northwest China

AbstractMicrobial‐community structure is closely associated with plant‐community composition. The objective of this study was to evaluate the effects of depth and revegetation time on the microbial‐community structure of restored grassland soils of the Loess Plateau of China. Microbial‐community structure at 0–10 cm (depth 1) and 10–20 cm (depth 2) of eight sites of a grassland chronosequence with revegetation time ranging from 1 to 78 y was determined using phospholipid fatty acid (PLFA) analysis. Except for the youngest site microbial‐community structure at the two depths varied distinctly with actinomycetes and vesicular arbuscular mycorrhiza as the most important discriminators. Total PLFA content decreased with depth and increased with revegetation time. Protozoa were the only functional group whose proportion did not change with depth. Their relative abundance tended to decrease with increasing revegetation time. The microbial community at all sites was bacteria‐dominated with Gram‐negative bacteria representing the largest proportion. Principal‐component and cluster analysis revealed that microbial‐community structure in the surface soil (depth 1) of the older sites (23–78 y of revegetation) was rather similar which may be due to only small effects of the plant species present on the soil environment. Differences in microbial‐community composition at 0–20 cm depth of the eight sites were partly related to variations in the physico‐chemical characteristics. Relations to organic C, alkali‐extractable N, pH, and available P were found. Revegetation of former agricultural sites on the Loess Plateau improves the soil status and leads to shifts in microbial‐community structure more pronounced with depth than time.

The distribution and phytoavailability of heavy metal fractions in rhizosphere soils of Paulowniu fortunei (seem) Hems near a Pb/Zn smelter in Guangdong, PR China

In order to understand the change of soil environment induced by re-vegetation, the physico-chemical properties, heavy metal (Cu, Pb, Cd and Zn) distribution and bioavailability was investigated in four different sites with different re-vegetation time. Results showed that soil physico-chemical properties and total content of heavy metals consistently increased with the re-vegetation time. The proportions of carbonate, Fe–Mn oxide and organically bound fractions in the rhizosphere soils were higher than those in the bulk soils. However, the proportions of exchangeable and residual fractions were less. The pH, electrical conductivity (EC) and organic matter (OM) were the most important factors affecting the distribution of heavy metal fraction. The exchangeable and organically bound fractions were easily available for Paulownia fortunei, but carbonate, Fe–Mn oxide and residual fractions were not. The correlation analysis indicated that the heavy metal contents in roots were generally and significantly correlated with total metal contents and metal contents bound to different fractions, thus might be better indicators of heavy metals bioavailability in soil than those in aboveground tissues.

Landslide Erosion Rate in the Eastern Cordillera of Northern Bolivia

AbstractThe northeastern edge of the Bolivian Eastern Cordillera is an example of a tectonically active plateau margin where orographically enhanced precipitation facilitates very high rates of erosion. The topography of the steepest part of the margin exhibits the classic signature of high erosion rates consisting of high-relief V-shaped valleys where landsliding is the dominant process of hillslope erosion and bedrock rivers are incising into the landscape. The authors mapped landslide scars on multitemporal aerial photographs to estimate hillslope erosion rates. Field surveys of landslide scars are used to calibrate a landslide volume versus area relationship. The mapped area of landsliding, in combination with an estimate of the time for landslide scars to revegetate, leads to an erosion rate estimate. The estimated revegetation time, 10–35 yr, is based on analysis of multitemporal aerial photographs and tree rings. About 4%–6% of two watersheds in the region considered were affected by landslides over the last 10–35 yr. This result implies an erosion rate of 9 ± 5 mm yr−1 assuming that 90% of a single landslide reaches the river on average. Classified Landsat Thematic Mapper images show that landslides are occurring at approximately the same rate all across an approximately 40-km-wide swath within the high-relief zones of the cordillera.

Characterization of Soil Physico-Chemical and Microbial Parameters after Revegetation Near Shaoguan Pb/Zn Smelter, Guangdong, P.R. China

The criterion for judging the successful revegetation largely focuses on the aboveground indicators, whereas the information for soil ecosystem during the revegetation is often ignored. To better understand the effects of the revegetation on the development of the soil ecosystem near Shaoguan Pb/Zn Smelter, Guangdong Province of Southern China, we compared the difference of the microbial and physico-chemical parameters between the four revegetated sites and two control sites (bare ground and native forest area). The soil organic C, total N, total P, NH4-N, NO3-N, available P, WHC and porosity significantly increased and bulk density decreased in the four revegetated sites compared with those in bare ground, indicating the processive effects of the revegetation on the reestablishment of the soil nutrient pools. The heavy metal contents were higher in the four revegetated sites than in the bare ground, thus the revegetation resulted in the accumulation of heavy metals released from smelter in surface soil. The soil microbial composition and activities, except that the oligotrophic bacterial number decreased over revegetation time, significantly increased in the revegetated sites compared with those in the bare ground, and predominantly correlated with soil organic C, total N, NH4-N, NO3-N and WHC. The soil oligotrophic bacteria was negatively related to all individual heavy metal contents, thus was the most sensitive indicator in reflecting heavy metal stress, while other microbial parameters, despite not showing negative relationships to the individual heavy metal contents, were sensitive to the potential availability of Pb and Cu (ratio of available to total heavy metal contents), but less sensitive to those of Zn and Cd. Both the principal component analysis (PCA) and the discriminant analysis (DA) resulted from microbial and physico-chemical datasets not only revealed the shifts of the soil physico-chemical and microbial patterns from the unrevegetated to non-polluted conditions, but also implied the possible loss of effects of revegetation on soil remediation in the sites revegetated for four (RIV) and five (RV) years, respectively.

The resilience of calcareous and mesotrophic grasslands following disturbance

Summary Understanding habitat disturbance and recovery is vital for successful conservation management and restoration, particularly of subseral communities with high nature conservation interest and sites subject to unavoidable disturbance pressures, such as that arising from access and recreational activities. Grassland resilience was investigated on the Salisbury Plain Training Area (SPTA) in southern England, the largest of the UK military training areas. SPTA contains the greatest expanse of unimproved chalk grassland in north‐west Europe, a habitat of particular nature conservation interest. Historical aerial photographs were used to identify 82 calcareous and mesotrophic grassland sites disturbed over a 50‐year time period. Vegetation, soils and seed bank data were collected from each old disturbance site. Revegetation time periods following disturbance were compared, and habitat resilience following disturbance investigated using the succession of surface vegetation along the chronosequence, the combined changes of vegetation and soil chemistry, and finally vegetation and seed bank composition. The sampled calcareous grasslands were less resilient following disturbance than the mesotrophic grasslands, with slower colonization of bare ground and target species re‐assembly. The mesotrophic grasslands typically took between 30 and 40 years to re‐establish following disturbance, whereas calcareous grasslands took at least 50 years. Even after such long time periods, there remained subtle but significant differences between the vegetation composition of the disturbed and undisturbed swards. Perennial forb species, particularly hemicryptophytes, persisted at higher frequencies in swards disturbed 50 years ago than in undisturbed swards. Synthesis and applications. Prediction of habitat resilience following disturbance is dependent on which components of the system are investigated. However, data such as that presented here can help land managers understand how palimpsests of current habitat characteristics may have evolved, and how disturbance regimes may be managed in the future. It is likely that the resilience of grasslands such as those on SPTA may have been overestimated, and perceptions of habitat carrying capacity for disturbance events may require re‐evaluation.