Soil PhytOC Research Articles

Soil PhytOC accumulation of Masson pine forests in Southwest China

Soil PhytOC accumulation of Masson pine forests in Southwest China

The phytolith carbon sequestration in terrestrial ecosystems: the underestimated potential of bamboo forest

BackgroundTerrestrial ecosystems contain significant carbon storage, vital to the global carbon cycle and climate change. Alterations in human production activities and environmental factors affect the stability of carbon storage in soil. Carbon sequestration in plant phytoliths offers a sustainable method for long-term carbon stabilization. Carbon occluded in phytoliths (PhytOC) is a kind of carbon that can be stable and not decomposed for a long time, so it is crucial to conduct more in-depth research on it.ResultsWe undertook a meta-analysis on PhytOC across global terrestrial ecosystems, analyzing 60 articles, encapsulating 534 observations. We observed notable differences in phytolith and PhytOC contents across various ecosystems. Bamboo forest ecosystems exhibited the highest vegetation phytolith and PhytOC content, while soil phytolith content was most prominent in bamboo forests and PhytOC content in croplands. Human activities, such as grassland grazing, had a lesser impact on soil PhytOC transport than actions like cutting and tillage in croplands and forests. Our study separated bamboo ecosystems, analyzing their PhytOC content and revealing an underestimation of their carbon sink capacity.ConclusionsNotwithstanding our findings, phytoliths’ intricate environmental interactions warrant further exploration, crucial for refining ecosystem management and accurately estimating PhytOC stocks. This deepened understanding lays the foundation for studying phytoliths and the carbon sink dynamics.

The Influence of Exogenous Nitrogen Input on the Characteristics of Phytolith-Occluded Carbon in the Kandelia obovata Soil System

Phytolith-occluded Ccarbon (PhytOC) is an important carbon sink in wetland ecosystems and a mechanism for long-term carbon sequestration. In recent years, nitrogen pollution has become increasingly severe and poses a threat to the healthy development of coastal ecological environments and socio-economic development; therefore, studying the impact of nitrogen deposition on the sequestration potential of PhytOC in the soil of coastal wetlands is highly significant. In the present study, two indoor tidal simulation experiments were set up with and without the planting of vegetation. The sequestration capacity and factors that influence soil PhytOC in the Kandelia obovata soil system were compared and analyzed under five nitrogen concentrations. The analysis shows that with the introduction of Kandelia obovata, the occluded carbon content of the soil phytoliths was significantly increased by 31.45% compared with the non-plant group, and the PhytOC content of the soil increased by 7.94%. The exogenous nitrogen input reduced the PhytOC content of the soil, with a rate of decline exceeding 26%. The PhytOC of the soil phytoliths and the PhytOC content of the soil in the planting group increased with increasing nitrogen concentration, while that of the non-plant group decreased as the concentration of nitrogen increased. The non-plant group was more affected by the exogenous nitrogen concentration than the planting group, and the soil microbial biomass carbon and microbial biomass nitrogen were the main factors that influenced changes in the PhytOC. In conclusion, nitrogen input has a significant inhibitory effect on soil PhytOC sequestration potential in coastal wetlands. Planting Kandelia obovata helps to improve the stability of carbon in wetland soil.

Changes in land use are associated with the accumulation of soil phytolith-occluded organic carbon

Organic carbon occluded in phytoliths is extremely stable and plays important roles in long-term preservation of soil and stable carbon sequestration in terrestrial ecosystems. To clarify the effects of land-use changes on the accumulation of soil phytolith-occluded organic carbon (PhytOC), the typical six land-use types of forest, open forest, shrub, grassland, corn field and abandoned farmland in Southwest China were used to study the associations of soil PhytOC accumulation with land-use change. The present results showed that land-use changes significantly affected soil PhytOC accumulation and its proportion to TSOC (total soil organic carbon). Compared to vegetation coverage, vegetation productivity increased soil PhytOC accumulation more effectively. The content and reserves of soil PhytOC in the open forest all ranked highest among the six land uses studied. Forest thinning not only substantially increased soil stable organic carbon sequestration but also obviously increased the TSOC pool. When land use changed from forest to grassland, there were obvious releases or run off of soil organic carbon, but the stability of the soil organic C pool improved obviously. After the corn field was abandoned, the PhytOC pool did not vary obviously. Soil pH was the important factor influencing the soil PhytOC pool, and acidic soils were made against PhytOC accumulation in soils. Soil PhytOC accumulation was significantly affected by soil C, N and P nutrition contents and stoichiometric ratios. Significant negative effects of bulk density on PhytOC accumulation in soils were observed. The present results are of great significance in land use regulation for increasing the soil carbon sink of terrestrial ecosystems.

Response of soil phytolith occluded organic carbon accumulation to long‐term vegetation restoration in Southwest China karst

AbstractAboveground vegetation can significantly affect soil PhytOC (phytolith occluded organic carbon) accumulation. To clarify the response of soil PhytOC accumulation to long‐term vegetation restoration in Southwest China karst, the four typical vegetation restoration engineering types of tree, shrub, vine forest, and grassland construction including seven species planting measures carried out 28–31 years ago were selected as study objects. And studies on their effects on soil PhytOC content and storage were conducted. Results showed that long‐term vegetation restorations obviously increased soil PhytOC accumulation and changed the proportion of soil PhytOC to total soil organic carbon. Among the different engineering types or species planting measures of vegetation restoration, there were significant or extremely significant differences in effects on soil PhytOC accumulation. Among the four types of restoration engineering, the tree forest construction had the best increase effect on soil PhytOC accumulation. And among the seven kinds of planting measures, the increased effect on soil PhytOC accumulation of Tectona grandis ('teak' an angiosperm tree species) planting was the highest. Vegetation biomass and litters were the key influencing factors on soil PhytOC accumulation. Soil C:P and N:P had significant effects on soil PhytOC accumulation by changing aboveground vegetation biomass and litters. Human activities could significantly change soil PhytOC content and storage, and reducing human activities of tilling and harvesting would be beneficial to soil PhytOC accumulation. The present results not only provided scientific bases for the vegetation rehabilitation of increasing soil PhytOC accumulation in outhwest China karst but also were great of significance in promoting stable soil C sequestration of the global terrestrial ecosystems.

High potential of stable carbon sequestration in phytoliths of China's grasslands.

Phytolith carbon (C) sequestration plays a key role in mitigating global climate change at a centennial to millennial time scale. However, previous estimates of phytolith-occluded carbon (PhytOC) storage and potential in China's grasslands have large uncertainties mainly due to multiple data sources. This contributes to the uncertainty in predicting long-term C sequestration in terrestrial ecosystems using Earth System Models. In this study, we carried out an intensive field investigation (79sites, 237soil profiles [0-100cm], and 61 vegetation assessments) to quantify PhytOC storage in China's grasslands and to better explore the biogeographical patterns and influencing factors. Generally, PhytOC production flux and soil PhytOC density in both the Tibetan Plateau and the Inner Mongolian Plateau had a decreasing trend from the Northeast to the Southwest. The aboveground PhytOC production rate in China's grassland was 0.48×106 t CO2 a-1 , and the soil PhytOC storage was 383×106 t CO2 . About 45% of soil PhytOC was stored in the deep soil layers (50-100cm), highlighting the importance of deep soil layers for C stock assessments. Importantly, the Tibetan Plateau had the greatest contribution (more than 70%) to the PhytOC storage in China's grasslands. The results of multiple regression analysis indicated that altitude and soil texture significantly influenced the spatial distribution of soil PhytOC, explaining 78.1% of the total variation. Soil phytolith turnover time in China's grasslands was mainly controlled by climatic conditions, with the turnover time on the Tibetan Plateau being significantly longer than that on the Inner Mongolian Plateau. Our results offer more accurate estimates of the potential for phytolith C sequestration from ecological restoration projects in degraded grassland ecosystems. These estimates are essential to parameterizing and validating global C models.

Effect of land cover change on total SOC and soil PhytOC accumulation in the karst subtropical forest ecosystem, SW China

Soil organic carbon (SOC), especially the stable SOC, have the important ecological function in the carbon cycle. As a typical stable SOC, soil phytolith-occluded organic carbon (PhytOC) is one of the important mechanisms of long-term soil carbon sink in terrestrial ecosystems. However, the distribution characteristics, accumulation law, and cycle process of soil PhytOC in fragile karst ecosystems are still not cognized. The purpose of the present study is to obtain the distribution pattern and change law of total SOC and soil PhytOC in different land cover types and to clarify the influencing factors and driving mechanism of land cover change on total SOC and soil PhytOC content and storage in the karst ecosystem. In the typical karst area of Southwest China, five representative land cover types, including bamboo forest (BF), coniferous and broad-leaved mixed forest (CBF), shrub (SH), grassland (GL), and agricultural abandoned land (AAL), were selected as the research objects. The total SOC contents, soil PhytOC contents, and soil physical and chemical properties were determined in the lab. Soil PhytOC and total SOC storage were calculated by the formulas. Data were analyzed statistically by linear regression, Pearson correlation analysis, LSD multiple comparison, and principal component analysis. Land cover change can affect obviously total SOC and soil PhytOC content and storage in the karst subtropical forest. Among the five land cover types, soil phytolith content, soil PhytOC content and storage, and total SOC storage of each soil profile in the BF were all significantly higher than those of the other four land covers. Among the three different soil profiles of 0~10, 10~20, and 20~30 cm, total SOC and soil PhytOC contents of the surface soil layer in the five land cover types were all the most, and the content decreased obviously with the increase of soil depth. There were significant positive correlation between the contents of soil available silicon, phytolith, and PhytOC. Soil available silicon content, soil phytolith content, and soil C/N were significantly positive related with the accumulation of total SOC and soil PhytOC. Soil PhytOC content or storage was significant or extremely significant related with total SOC content or storage. The results of the present study provided scientific bases for further evaluating the carbon sink capacity of soil PhytOC in the karst ecosystem, in SW China, and have important values in the reduction of carbon emission and increase of carbon sink to combat the global warming. In addition, the results of the present study also can provide theoretical references for the vegetation restoration of karst rocky desertification in Southwest China.

Effects of alpine marsh degradation on soil phytoliths and phytolith-occluded carbon on the Zoige Plateau, China

Phytoliths are microscopic particles of amorphous silica produced by plants that have vital importance for environmental change and carbon sequestration. This study investigated phytoliths and their morphotype assemblages, and phytolith-occluded carbon (PhytOC) along a marsh degradation gradient to clarify the significance of phytoliths for evaluating carbon sequestration dynamics during marsh degradation on the Zoige Plateau, China. Soil samples from non-degraded marsh (NDM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and seriously degraded marsh (SDM) were collected. Soil phytolith shape and PhytOC were determined using heavy liquid suspension, microscope observations, and alkali-solution spectrophotometry. The dominant phytolith morphotypes among the 15 identified in the soils from the differently degraded marshes were lanceolate, rectangular, and elongate, which originated from Poaceae and Cyperaceae. Soil phytolith morphotype assemblages show potential for studying past vegetation and climatic succession in alpine wetlands. The soil phytolith and PhytOC content exhibited no significant differences between the NDM and LDM samples. Compared with the NDM soil, phytolith content was significantly lower in the MDM (33.8–58.8%) and SDM (52.7–65.4%) soils, respectively, and PhytOC content was also significantly lower (by 31.0–57.1% and 47.5–74.4%, respectively). The soil phytolith and PhytOC content decreased significantly with soil depth, especially once the marsh has become moderately degraded. Alpine marsh degradation reduced the accumulation of soil PhytOC by decreasing the PhytOC input flux, thereby altering the long-term carbon sequestration mechanism of phytoliths in this alpine-marsh wetland ecosystem.

Effects of long-term planting on PhytOC storage and its distribution in soil physical fractions in Moso bamboo forests in subtropical China

Phytoliths are siliceous substances that are abundant within intercellular spaces and inside cells of numerous types of plants. During the formation of phytoliths, between 0.2 and 5.8% of organic carbon (C) can be occluded within the phytoliths. Phytolith-occluded C (PhytOC) in terrestrial ecosystems is a stable C sink and can be distributed in organic matter that is not strongly associated with soil minerals (LFOM) or that is strongly associated with mineral particles (forming organo-mineral complexes) (HFOM). We (1) investigated the impact of plantation age and soil depth on the size of the PhytOC pool and its distribution in soil physical fractions in Moso bamboo (Phyllostachys pubescens) forests; and (2) explore the relationship among phytoliths and PhytOC (and their fractions) concentrations and the soil properties. We used a chronosequence approach by sampling 5-, 10-, 20-, 50-, and 100-year-old Moso bamboo stands to examine the effect of plantation age on PhytOC storage and its distribution between the LFOM and HFOM pools. Our results showed that PhytOC concentration and the concentration of PhytOC in LFOM and HFOM increased with increasing stand age in the topsoil (0–30 cm) but not in the subsoil (30–100 cm). Long-term planting of Moso bamboo forests increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions. The LFOM- and HFOM-PhytOC concentrations were positively correlated with soil organic C concentrations. The HFOM-PhytOC concentration was positively correlated with that of water-soluble silicon. We conclude that the increasing bamboo plantation age will promote PhytOC storage in the bulk soil and physical fractions in subtropical China. Management practices that increase PhytOC input and decrease PhytOC output should be developed in the future to increase PhytOC storage in bamboo plantations.

Storage of soil phytoliths and phytolith-occluded carbon along a precipitation gradient in grasslands of northern China

Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle in terrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestration mechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatial variability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluating the impact of global climate change on terrestrial ecosystem functions. However, little is known about the responses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24 natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 in northern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths and PhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to 88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage were significantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage in bulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variables accounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in the Inner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primary productivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect that ecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOC storage. These findings have important implications for understanding the dynamics of soil phytoliths, and predicting the impacts of global climate change on ecosystem functions and management practices in the East Asian steppe ecosystems.

Silicon fertilizer and biochar effects on plant and soil PhytOC concentration and soil PhytOC stability and fractionation in subtropical bamboo plantations.

The use of exogenous silicon (Si) amendments, such as Si fertilizers and biochar, can effectively increase crop Si uptake and the formation of phytoliths, which are siliceous substances that are abundant in numerous plant species. Phytolith-occluded carbon (C) (PhytOC) accumulation in soil plays an important role in long-term soil organic C (SOC) storage. Nevertheless, the effects of both Si fertilizer and biochar application on PhytOC sequestration in forest plant-soil systems have not been studied. We investigated the impact of Si fertilizer and biochar applications on 1) the PhytOC pool size, the solubility of plant and soil phytoliths, and soil PhytOC in soil physical fractions (light (LFOM) and heavy fractions of organic matter (HFOM)) in Moso bamboo (Phyllostachys pubescens) forests; and 2) the relationships among plant and soil PhytOC concentrations and soil properties. We used a factorial design with three Si fertilizer application rates: 0 (S0), 225 (S1) and 450 (S2) kg Si ha-1, and two biochar application rates: 0 (B0) and 10 (B1) t ha-1. The concentrations of PhytOC in the bamboo plants and topsoil (0-10cm) increased with increasing Si fertilizer addition, regardless of biochar application. Biochar addition increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions, regardless of Si fertilizer application. The Si fertilizer application increased or had no effect on soil phytolith solubility with or without biochar application, respectively. Soil PhytOC was correlated with the concentration of soil organic nitrogen (R2=0.32), SOC (R2=0.51), pH (R2=0.28), and available Si (R2=0.23). Furthermore, Si fertilizer application increased plant and soil PhytOC by increasing soil available Si. Moreover, biochar application increased soil PhytOC concentration in LFOM-PhytOC and the unstable fraction of PhytOC. We conclude that Si fertilizer and biochar application promoted PhytOC sequestration in the plant-soil system and changed its distribution in physical fractions in the Moso bamboo plantation in subtropical China.

Intensive Management Increases Phytolith-Occluded Carbon Sequestration in Moso Bamboo Plantations in Subtropical China

Plantation management practices could markedly change the sequestration of phytolith-occluded carbon (PhytOC) in plants and soils. However, for Moso bamboo (Phyllostachys pubescens) plantations, the effect of intensive plantation management (including fertilization, tillage, and removal of understory vegetation) on the accretion rate of PhytOC in the soil-plant system is much less understood than extensive management (without fertilization, tillage, and removal of understory vegetation). The objectives of this study were to investigate the effect of intensive and extensive management practices on the production, accumulation, and runoff of PhytOC and their distribution in physical fractions in Moso bamboo plantations. Our results showed that intensive management (1) increased PhytOC production mainly due to increased forest productivity; (2) increased PhytOC storage in the heavy fraction but decreased its storage in the light fraction of organic matter, resulting in the lack of effect on soil PhytOC storage; (3) increased the rate of dissolution of phytolith and the loss of PhytOC in runoff; and (4) promoted PhytOC sequestration in the soil-plant system, mostly in the plants, due to the greater rate of PhytOC production than the rate of loss. We conclude that intensive bamboo plantation management practices are beneficial to increasing long-term PhytOC sequestration in the soil-plant system.

Content of Soil Phytolith-Occluded Organic Carbon in Different Land Use Patterns at Jinyun Mountain

Phytolith-occluded organic carbon (PhytOC) is a form of long-term storage of soil organic carbon, which is of great significance for soil carbon sequestration. Taking six land use patterns in southwest China as the research object, including coniferous and broad-leaved mixed forest, bamboo forest, orchard, dry land, paddy field, and grassland, we compare the distribution of the PhytOC content under the different land use patterns in different depth sections of 0-20, 20-40, 40-60, and 60-100 cm. In addition, we estimate the storage of phytOC and analyze the carbon sequestration characteristics of the terrestrial ecosystems. According to the results, the soil organic carbon and phytolith mean content in the bamboo forest were the highest in the soil profile, at 16.75 g·kg-1 and 59.66 g·kg-1, respectively. In all soil layers, the phytolith content of the bamboo forest soil was significantly higher than that in other land use patterns (P<0.05). The average content of soil phytOC in the six land use patterns ranged from 0.55 to 1.96 g·kg-1, and the phytOC content of each layer of bamboo forest was higher than that in other land uses. The total carbon storage of phytOC in the bamboo forest soil, at 23.45 t·hm-2, was significantly higher than that of other soil use methods (P<0.05). Statistical analysis showed that soil silicon had a significant positive correlation with the soil phytolith and the soil phytOC (P<0.01). The soil phytolith and phytolith carbon content in different land use patterns generally showed a decrease with an increase in soil depth, and a certain surface enrichment phenomenon was noted.

Conversion from tussock grassland to pine forest: effect on soil phytoliths and phytolith-occluded carbon (PhytOC)

Photolith morphotypes differ between plant species which can be utilized to reconstruct past vegetation. More recently, the role of phytoliths in soil carbon (C) storage and soil C and silicon (Si) cycling has received increasing attention. The aim of this study was to investigate the impact of recent land cover change on soil phytolith assemblage, soil phytolith concentration, and phytolith-occluded carbon (PhytOC) storage. Mineral soil samples (0–10 cm) were collected from a tussock grassland (n = 18) and an adjacent 32-year-old pine forest (n = 21) in Otago, New Zealand. The pine forest was established on tussock grassland. Microwave digestion was followed by sedimentation and flotation procedures to obtain a purified phytolith extract to identify soil phytolith morphotypes by microscopy and to quantify PhytOC concentrations using an elemental analyzer. Soil phytolith assemblage was similar under tussock grassland and pine forest. Bulliform and short cells which were derived from grass species accounted for more than 80% of the phytoliths. Woody plant-derived phytoliths found under tussock grassland (1) may originate from shrubs which are encroaching into the tussock grassland and/or (2) are a legacy of the past woody-dominated vegetation. Soil phytolith concentration ranged between 1 and 3%. Soil PhytOC storage was 0.15 kg C/m2 and 0.14 kg C/m2 under tussock grassland and pine forest, respectively, and accounted for around 3% of total soil carbon storage. Soil phytolith assemblage, soil phytolith concentration, and soil PhytOC storage did not differ significantly between the tussock grassland and the pine forest that was converted from tussock grassland recently. The dominance of grass-derived phytoliths under the pine forest may reflect the legacy of the tussock vegetation which dominated the study site before the afforestation with pine in 1992. This study also revealed that the intrinsic feature of tussock grass species and the accumulation of phytoliths over centuries is likely the cause for the high soil phytolith and PhytOC concentrations.

Advance of research on modern soil phytolith

Phytolith study is a new branch of micropaleontology with an increasingly important role in geology, archaeology, and plant taxonomy. Phytoliths have several advantages considering their characteristics of small particle size, high production, wide distribution, anti-decomposition, in situ deposition, distinctive morphologies, and element sequestrating capacity. Phytolith assemblages in modern soil have been found to be closely related to modern vegetation types and climate conditions, which forms the basis for the quantitative study of paleoecology, paleoclimate, and bio-geochemical cycles. At present, phytolith studies generally focus on the following four aspects: (1) Morphology: about 260 unduplicated types of phytoliths have been identified in modern soil, of which 110 types are from grasses, 50 types from ferns, woody plants and other angiosperms, whereas the origin plants of the remaining 100 types are still under investigation. (2) Soil phytolith assemblages and vegetation: phytolith assemblages from the topsoil have been used to distinguish surface vegetation types including different forests and grasslands over a typical region. This model has been applied to restore past vegetation conditions and monitor the dynamic evolution of specific vegetation types at different temporal and spatial scales. (3) Soil phytolith assemblages and climate: quantitative and semi-quantitative relationships between phytolith assemblages and a series of climate parameters, such as annual mean temperature, annual mean precipitation and altitude, have been established through mathematical analysis. In this manner, quantitative reconstruction of paleoclimatic parameters has been achieved through the phytolith-climate transfer function model. (4) Soil phytolith and its sequestered elements: in this topic, the content of soil PhytOC (Phytolith-occluded Organic Carbon) and the importance of PhytOC in the bio-geochemical cycle have been the focus. The study of modern soil phytoliths has provided new approaches and many successful cases for solving specific problems in various fields, such as Earth science and archaeology. This study analyzed existing issues in addition to the abovementioned significant progresses, and provides directions for future research on modern soil phytoliths.

Phytolith accumulation in broadleaf and conifer forests of northern China: Implications for phytolith carbon sequestration

Carbon (C) occlusion within phytoliths (PhytOC) has a significant potential for long-term C sequestration in forest ecosystems. To unravel the role of forest composition on phytolith production, soil phytolith distribution, and phytolith C sequestration in soils, we investigated community composition and examined phytoliths and PhytOC of mature leaves or needles of dominant trees and understory herbs, as well as soil profiles (50cm depth) within Quercus, Betula, Larix and Pinus forest ecosystems of northern China. Results showed that herb layers contributed 72%, 52%, 40%, and 5% to the flux of phytolith production within Betula forest (18.0±1.26kgha−1yr−1), Quercus forest (28.5±0.77kgha−1yr−1), Larix forest (37.7±1.80kgha−1yr−1) and Pinus forest (16.9±0.30kgha−1yr−1), respectively. The distribution pattern of soil phytoliths from topsoil to subsoil could be classified into three types: significantly decreasing pattern (Betula forest and Quercus forest), non-significantly decreasing pattern (Larix forest), and initially increasing and then decreasing pattern (Pinus forest). Within 0–50cm soil depth, the PhytOC storage of Betula forest, Quercus forest, Larix forest and Pinus forest were 0.29±0.02tha−1, 0.67±0.03tha−1, 0.46±0.03tha−1 and 0.37±0.02tha−1, respectively. Moreover, the soil PhytOC turnover times of these four forest types were estimated to be 537,503,363 and 560year, respectively, which were at least 8–20 times slower than soil organic carbon contributing to climate change mitigation. Overall, our findings indicate that composition of the forest community controls the production flux of phytoliths and the distribution of soil phytoliths, and influences the biogenic silica and its coupled carbon cycles.

Impact of grassland degradation on soil phytolith carbon sequestration in Inner Mongolian steppe of China

Grasslands play an important role in the terrestrial biogeochemical carbon (C) cycle and partly mitigate climate change through C occlusion within phytoliths. Grassland degradation has a significant influence on the coupled biogeochemical cycles of C and silicon in the Inner Mongolian steppe of China, but there are few reports about the impact of grassland degradation on phytolith C sequestration in the steppe, the main grassland in northern China. Twelve sampling sites were chosen in the Xilingol League. Soil samples (0–50cm) were collected from grasslands of four different degradation degrees to investigate the impact of grassland degradation on the soil phytolith and phytolith-occluded C (PhytOC) accumulation using a mass-balance approach. Soil phytolith storages were 12.97±2.15, 15.90±0.65, 14.35±0.79 and 13.22±1.07tha−1 in non-degraded, lightly degraded, moderately degraded and seriously degraded grasslands, respectively. The corresponding storages of soil PhytOC were 0.11±0.02, 0.16±0.02, 0.12±0.01 and 0.07±0.01tha−1, respectively. The observed significant differences in soil phytoliths and PhytOC among grasslands of different degradation degrees indicate that grassland degradation influenced the phytolith and PhytOC accumulation in grassland soils. Grazing and harvesting are likely the major factors affecting soil phytolith and PhytOC storages through reducing the litterfall returning fluxes. Our preliminary findings imply that grassland restoration could be a promising way to increase long-term phytolith C sequestration through maximizing plant PhytOC production fluxes and soil PhytOC accumulation in degraded grasslands.

The accumulation of phytolith-occluded carbon in soils of different grasslands

A better understanding of the role of grassland systems in producing and storing phytolith-occluded carbon (PhytOC) will provide crucial information in addressing global climate change caused by a rapid increase in the atmospheric CO2 concentration. Soil samples of typical steppe, meadow steppe, and meadow in Inner Mongolia, China, were taken at 0–10-, 10–20-, 20–40-, and 40–60-cm depths in July and August of 2015. The soil phytoliths were isolated by heavy liquid (ZnBr2), and the soil PhytOC was determined by the traditional potassium dichromate method. The results of our study showed that the storage of soil phytoliths was significantly higher in the meadow (33.44 ± 0.91 t ha−1) cf. meadow steppe (26.8 ± 0.98 t ha−1) and typical steppe (21.19 ± 4.91 t ha−1), which were not different. The soil PhytOC storage was significantly different among grassland types, being: meadow (0.39 ± 0.01 t ha−1) > meadow steppe (0.29 ± 0.02 t ha−1) > typical steppe (0.23 ± 0.02 t ha−1). PhytOC storage in typical steppe soil within the 0–60-cm soil layer is the lowest and that in meadow soils is the highest. The grassland type and the soil condition play significant roles in accumulation of phytoliths and PhytOC in different grassland soils. We suggest that the aboveground net primary productivity (ANPP) is important in soil phytolith accumulation and PhytOC content. Phytolith and PhytOC storages in grassland soil are influenced by factors such as grass type, local climate and soil conditions, and management practices. Management practices to increase grass biomass production can significantly enhance phytolith C sequestration.

Phytolith-occluded organic carbon in intensively managed Lei bamboo (Phyllostachys praecox) stands and implications for carbon sequestration

Phytolith-occluded organic carbon (PhytOC) is an important long-term (up to several thousand years) terrestrial carbon (C) fraction in forest ecosystems. The objectives of this study were to (i) investigate the spatial distribution of PhytOC in Lei bamboo (Phyllostachys praecox C.D. Chu &amp; C.S. Chao.) forests under intensive management (mulching and fertilization) and (ii) assess the role of PhytOC in C sequestration in a Lei bamboo stand and across subtropical China. Phytolith concentrations in Lei bamboo plant components were (P &lt; 0.05) in the following order: rhizome ≈ stump &gt; leaf ≈ branch &gt; culm. The distribution of PhytOC in bamboo leaves, branches, culms, rhizomes, and stumps was 22.2%, 12.1%, 16.1%, 15.9%, and 33.7%, respectively. The PhytOC stock was in the following order (P &lt; 0.05): soil (9361 kg C·ha−1) &gt; mulching materials (197.5 kg C·ha−1) &gt; belowground plant parts (13.0 kg C·ha−1) ≈ aboveground plant parts (12.8 kg C·ha−1) ≈ litterfall (11.3 kg C·ha−1). The PhytOC accretion rate in the vegetation in the Lei bamboo stand was 19.4 kg C·ha−1·year−1, equivalent to 71 kg CO2-eq·ha−1·year−1. The soil PhytOC stock decreased markedly with depth and had an accretion rate of 325 kg C·ha−1·year−1 for the 0–60 cm soil layer. Based on a PhytOC accretion rate of 0.795 Mg CO2-eq·ha−1·year−1, PhytOC accretion rate in the 2.62 × 106 ha of Lei bamboo stands in southern China is estimated to be 2.08 × 106 Mg CO2-eq·year−1. In conclusion, intensively managed Lei bamboo stands have a large potential in long-term C sequestration in the form of PhytOC, and the PhytOC stock belowground should not be ignored due to its contribution to the ecosystem level PhytOC stock.

Long-term intensive management increased carbon occluded in phytolith (PhytOC) in bamboo forest soils

Carbon (C) occluded in phytolith (PhytOC) is highly stable at millennium scale and its accumulation in soils can help increase long-term C sequestration. Here, we report that soil PhytOC storage significantly increased with increasing duration under intensive management (mulching and fertilization) in Lei bamboo (Phyllostachys praecox) plantations. The PhytOC storage in 0–40 cm soil layer in bamboo plantations increased by 217 Mg C ha−1, 20 years after being converted from paddy fields. The PhytOC accumulated at 79 kg C ha−1 yr−1, a rate far exceeding the global mean long-term soil C accumulation rate of 24 kg C ha−1 yr−1 reported in the literature. Approximately 86% of the increased PhytOC came from the large amount of mulch applied. Our data clearly demonstrate the decadal scale management effect on PhytOC accumulation, suggesting that heavy mulching is a potential method for increasing long-term organic C storage in soils for mitigating global climate change.