Phytolith carbon sequestration in global terrestrial biomes

PhytOC sequestration characteristics and phytolith carbon sink capacity of the karst grasslands in southwest China

Grassland is an important component of terrestrial ecosystems and plays a crucial role in the global carbon cycle. PhytOC (phytolith-occluded organic carbon) is an extremely important long-term and stable carbon pool in terrestrial ecosystems. Southwest China karst soil exhibits obvious characteristics of alkalinity, high silicon content, and rich calcium, which can significantly influence the characteristics and mechanisms of PhytOC sequestration in vegetation. To elucidate the sequestration characteristics and mechanisms of PhytOC in the karst grasslands, three typical karst grasslands of tropical shrub tussock (TST), warm-temperate shrub tussock (WST), and mountain meadow (MM) from Guizhou province of southwest China were studied. The following results and conclusions were obtained that: 1) the range of PhytOC content of aboveground plant parts, underground roots, and soil in the karst grasslands was 4.03-16.54 g·kg-1, 10.67-33.92 g·kg-1, and 0.63-1.89 g·kg-1, respectively. The underground roots are an important site for phytolith carbon sequestration in grassland ecosystems, and the PhytOC content of underground roots may be higher than that of the aboveground parts. 2) The PhytOC sequestration rate of vegetation was 7.34-15.93 kg·ha-1·yr-1, and the annual sequestration amount of PhytOC of the whole grasslands in southwest China could reach 0.48 × 103-1.48 × 103 t CO2. Compared to grasslands in non-karst regions of China, karst grasslands in southwest China have a higher sequestration rate of PhytOC in vegetation and a greater capacity for phytolith carbon sequestration. 3) Soil available silicon, pH, and stoichiometric characteristics of C, N and P nutrients significantly affected the phytolith carbon sequestration of vegetation and the soil accumulation of PhytOC in the karst grasslands. The research results are of great significance for estimating the phytolith carbon sequestration capacity of grassland ecosystems and for grassland construction and management based on enhancing carbon sequestration.

Silicon in paddy fields: Benefits for rice production and the potential of rice phytoliths for biogeochemical carbon sequestration

Silicon (Si) biogeochemical cycling is beneficial for crop productivity and carbon (C) sequestration in agricultural ecosystem, thus offering a nonnegligible role in alleviating global warming and food crisis. Compared with other crops, rice plants have a greater quantity of phytolith production, because they are able to take up a lot of Si. However, it remains unclear on Si supply capacity of paddy soils across the world, general rice yield-increasing effect after Si fertilizer addition, and factors affecting phytolith production and potential of phytolith C sequestration in paddy fields. This study used a meta-analysis of >3500 data from 87 studies to investigate Si supply capacity of global paddy soils and elaborate the benefits of Si regarding rice productivity and phytolith C sequestration in paddy fields. Analytical results showed that the Si supply capacity of paddy soils was insufficient in the major rice producing countries/regions. Dealing with this predicament, Si fertilization was an effective strategy to supply plant-available Si to improve rice productivity. Our meta-analysis results further revealed that Si fertilization led to the average increasing rate of 36 % and 39 % in rice yield and biomass, which could reach up to 52 % and 46 % with the increasing doses of Si fertilizer, respectively. Especially, this strategy also improved the potential of phytolith C sequestration through the increased phytolith content and rice biomass, despite that this potential might have a decline in old paddy soils (≥ 7000 year) compared to in young paddy soils (≤ 1000 year) due to the slow migration and dissolution of phytoliths at millennial scale. Our findings thus indicate that a deep investigation on the benefits of Si in agroecosystem will further improve our understanding on regulating crop production and the potential of biogeochemical C sequestration within phytoliths in global cropland.

Deciphering the regulatory role of PheSnRK genes in Moso bamboo: insights into hormonal, energy, and stress responses

The SnRK (sucrose non-fermentation-related protein kinase) plays an important role in regulating various signals in plants. However, as an important bamboo shoot and wood species, the response mechanism of PheSnRK in Phyllostachys edulis to hormones, low energy and stress remains unclear. In this paper, we focused on the structure, expression, and response of SnRK to hormones and sugars. In this study, we identified 75 PheSnRK genes from the Moso bamboo genome, which can be divided into three groups according to the evolutionary relationship. Cis-element analysis has shown that the PheSnRK gene can respond to various hormones, light, and stress. The PheSnRK2.9 proteins were localized in the nucleus and cytoplasm. Transgenic experiments showed that overexpression of PheSnRK2.9 inhibited root development, the plants were salt-tolerant and exhibited slowed starch consumption in Arabidopsis in the dark. The results of yeast one-hybrid and dual luciferase assay showed that PheIAAs and PheNACs can regulate PheSnRK2.9 gene expression by binding to the promoter of PheSnRK2.9. This study provided a comprehensive understanding of PheSnRK genes of Moso bamboo, which provides valuable information for further research on energy regulation mechanism and stress response during the growth and development of Moso bamboo.

Production of phytolith and PhytOC and distribution of extractable Si Pools in aerobic rice as influenced by different Si sources

Phytoliths are composed of 66 to 91% SiO2 and 1 to 6% organic carbon (C) known as phytolith occluded carbon (PhytOC). PhytOC is critical for long-term C storage in the agroecosystem. A field experiment was carried out to investigate the effect of three different sources of exogenous Si, i.e., diatomaceous earth (DE), silicic acid (SA) and rice husk biochar (RHB) on 1) plant phytolith, C content in phytolith and PhytOC content in different rice organs; 2) relationship between plant phytolith, C content in phytolith, PhytOC content, and soil properties (soil physicochemical properties and readily soluble silicon pools). Different Si sources produced significantly higher phytolith, PhytOC content, and readily soluble Si pools (CCSi, AASi, and ASi) than the control (RDF), with treatment receiving 4 t RHB ha-1 outperforming the other treatments. Phytolith and PhytOC production were found to be significantly correlated to soil organic carbon (OC), available nitrogen (N) and potassium (K), 0.01 M CaCl2 extractable Si (CCSi) and amorphous Si (ASi) content in the soil. Redundancy analysis showed that treatments receiving 4 t RHB ha-1 have a stronger relationship with the CCSi and ASi which majorly contributed to the higher phytolith and PhytOC production. Thus, practices such as Si fertilizers and RHB application have a high potential for phytolith production and PhytOC sequestration, a critical mechanism of the global biogeochemical C sink.

Amorphous silica dissolution kinetics in freshwater environments: Effects of Fe2+ and other solution compositional controls

The availability of dissolved silicon (DSi) exerts an important control on phytoplankton communities in freshwater environments: DSi limitation can shift species dominance to non-siliceous algae and increase the likelihood of harmful algal blooms. The availability of DSi in the water column in turn depends on the dissolution kinetics of amorphous silica (ASi), including diatoms frustules and phytoliths. Here, batch dissolution experiments conducted with diatom frustules from three diatom species and synthetic Aerosil OX 50 confirmed the previously reported non-linear dependence of ASi dissolution rate on the degree of undersaturation of the aqueous solution. At least two first-order dissolution rate constants are therefore required to describe the dissolution kinetics at high (typically, ≥0.55) and low (typically, <0.55) degrees of undersaturation. Our results further showed aqueous ferrous ion (Fe²⁺), which is ubiquitous in anoxic waters, strongly inhibited ASi dissolution. The inhibition is attributed to the preferential binding of Fe²⁺ to Q₂ groups (i.e., surface silicate groups bonded to the silica lattice via two bridging oxygen) which stabilizes the silica surface. However, further increasing the aqueous Fe²⁺ concentration likely catalyzes the detachment of Q₃ groups (i.e., silicate groups bonded to the silica lattice via three bridging oxygen) from the surface. Overall, our study illustrates the manyfold effects the aqueous solution composition, notably the inhibition effect of Fe²⁺ under anoxic conditions, has on ASi dissolution. The results help to explain the controversial redox dependence of DSi internal loading from sediments, which is vital to quantitatively understanding silicon (Si) cycling in freshwater systems.

The spatial distribution of phytoliths and phytolith-occluded carbon in wheat (Triticum aestivum L.) ecosystem in China

Phytolith is a form of SiO₂ in plants. Carbon can be sequestrated as phytolith-occluded carbon (PhytOC) during the formation of phytoliths. PhytOC is characterized by its high resistance to temperature, oxidation and decomposition under protection of phytoliths and can be stored in the soil for thousands of years. Soil also is a huge PhytOC sink; however, most studies focus on PhytOC storage in straw and other residues. Wheat is a major staple food crop accumulating high content of Si and distributed widely, while its potential for PhytOC is not clear. At present, PhytOC storage only considers on the average value, but not on the relationship between ecological factors and the spatial distribution of PhytOC sequestration. Climatic factors and soil physiochemical properties together affect the formation process and stability of phytoliths. In our study, we collected wheat straw and soil samples from 95 sites among five provinces to extract phytolith and PhytOC. We constructed XGBoost model to predict the spatial distribution of phytolith and PhytOC across the country using the national soil testing and formula fertilization nutrient dataset and climate data. As a result, soil physiochemical factors such as available silicon (Si_avail), total carbon (C_tot) and total nitrogen (N_tot) and climate factors related to temperature and precipitation have a great positive impact on the production of phytoliths and PhytOC. Meanwhile, PhytOC storage in wheat ecosystems was estimated to be 7.59 × 10⁶ t, which is equivalent to 27.83 Tg of CO₂. In China, the distribution characteristics of phytoliths and PhytOC in wheat straw and soil display a trend of decrease from south to north. He'nan Province is the largest wheat production area, producing approximately 1.59 × 10⁶ t PhytOC per year. Therefore, PhytOC is a stable CO₂ sink pathway in the agricultural ecosystems, which is of great importance for mitigating climate warming.

Phytolith-occluded carbon in leaves of Dendrocalamus Ronganensis influenced by drought during growing season

Being an important carbon (C) sink, phytolith-occluded carbon (PhytOC) has been investigated in various soil-plant systems. However, the effects of environmental factors (i.e., drought) on phytoliths, including altered deposition in plant tissues, morphological variation, and amounts of carbon occluded within phytoliths, are less studied. In this study, we analyzed the monthly variations of phytolith production and PhytOC in the leaves of Dendrocalamus ronganensis grown on a karst mountain in southwestern China during a drought year. This study thus sought to understand the effects of drought on phytolith formation, morphological variations and carbon sequestration within phytoliths in plants. Our results showed that the phytolith assemblages and PhytOC between new and old leaves differed significantly and varied with plant growth stages. The average PhytOC values of old leaves and tip leaves were 3.2% and 2.2%, respectively. In particular, both PhytOC and proportions of ELONGATE, BULLIFORM FLABELLATE, and STOMA phytoliths in tip leaves significantly decreased from September to January the following year because of drought effects. This study suggests that PhytOC in plants varies between phytolith morphotypes and is significantly affected by plant growth stage and hydrologic conditions. This indicates that we can improve the efficiency of phytolith carbon sequestration in plants by improving the soil water conditions required for plant growth.

Phytolith-occluded carbon in residues and economic benefits under rice/single-season Zizania latifolia rotation

Zizania latifolia is a wild rice that contains phytoliths (Phyt) that have considerable potential for carbon sequestration. We hypothesized that the capacity of phytolith-occluded carbon (PhytOC) sequestration in residues might increase by 20%, and economic profit would be twice as high under a rice/single-season Z. latifolia rotation as under rice monoculture. To test this hypothesis, we collected rice and Z. latifolia plants and their corresponding soil samples from Zhejiang Province to determine the ability of both crops to fix carbon in the phytoliths. We showed that the soil concentrations of available Si, total carbon (Ctot) and total nitrogen (N_tot) were highly positively correlated with the concentrations of phytoliths and phytolith-occluded carbon in the residues of both crops. The cold waterlogged paddy fields in China have low productivity but their environmental conditions are suitable for planting Z. latifolia. Our model scenario, built on secondary data, demonstrated that, on a national basis, if the cold waterlogged paddy fields (occupying approximately 15% of the total paddy fields) were under rice/single-season Z. latifolia rotation, the contents of phytoliths and PhytOC in rice and Z. latifolia residues would be up to 19.46 × 10⁶ t yr^-1 and 8.82 × 10⁴ t yr^-1 (0.32 Tg CO₂ yr^-1), respectively. As a result, the economic benefit would be increased by 1.12 × 10¹¹ USD per year compared to rice monoculture. Therefore, adopting rotational cropping of rice with single-season Z. latifolia will not only increase the content of PhytOC sequestration in residues and improve cold waterlogged paddy fields but also bring economic benefits to farmers.

Phytolith-Occluded Carbon Sequestration Potential of Oil Palm Plantation in Tamil Nadu

Oil palm (Elaeis guineensis) has proven to be a phytolith-occluded carbon (PhytOC)-rich species that plays a vital role in acting as a carbon sink for reducing atmospheric carbon dioxide (CO₂) concentration. The present research estimated the silicon, phytolith, and PhytOC contents in four (OP4), eight (OP8), and fifteen (OP15)-year-old oil palm plantations. Qualitative analysis using a scanning electron microscope (SEM) revealed the presence of abundant globular echinate phytoliths with varied diameter (8.484-10.18 μm) in fronds, empty fruit bunches, and roots. Furthermore, a wide band (400-490 cm^-1) underlined a higher relative abundance of Si-OH groups in empty fruit bunches, fronds, and roots, which emphasized the amorphous nature of silica. Quantitative analysis revealed that the phytolith (phytolith/dry biomass), PhytOC (PhytOC/phytolith), and PhytOC (PhytOC/dry biomass) contents in all oil palms differed significantly (p < 0.05) and increased with age. The PhytOC stock showed significant variation, with the trend of OP15 > OP8 > OP4. The belowground biomass of OP4 (16.43 g kg^-1) and OP8 (17.13 g kg^-1) had a maximum PhytOC concentration compared to the aboveground biomass, and the belowground proportion varied from 20.62 to 20.65%. The study demonstrated a positive correlation between the phytolith and PhytOC contents of oil palm; thereby, oil palm should be cultivated for enhanced long-term sequestration as a phytolith accumulator.

Silicon in the Soil-Plant Continuum: Intricate Feedback Mechanisms within Ecosystems

Plants' ability to take up silicon from the soil, accumulate it within their tissues and then reincorporate it into the soil through litter creates an intricate network of feedback mechanisms in ecosystems. Here, we provide a concise review of silicon's roles in soil chemistry and physics and in plant physiology and ecology, focusing on the processes that form these feedback mechanisms. Through this review and analysis, we demonstrate how this feedback network drives ecosystem processes and affects ecosystem functioning. Consequently, we show that Si uptake and accumulation by plants is involved in several ecosystem services like soil appropriation, biomass supply, and carbon sequestration. Considering the demand for food of an increasing global population and the challenges of climate change, a detailed understanding of the underlying processes of these ecosystem services is of prime importance. Silicon and its role in ecosystem functioning and services thus should be the main focus of future research.

Silicon Cycling in Soils Revisited

Silicon (Si) speciation and availability in soils is highly important for ecosystem functioning, because Si is a beneficial element for plant growth. Si chemistry is highly complex compared to other elements in soils, because Si reaction rates are relatively slow and dependent on Si species. Consequently, we review the occurrence of different Si species in soil solution and their changes by polymerization, depolymerization, and condensation in relation to important soil processes. We show that an argumentation based on thermodynamic endmembers of Si dependent processes, as currently done, is often difficult, because some reactions such as mineral crystallization require months to years (sometimes even centuries or millennia). Furthermore, we give an overview of Si reactions in soil solution and the predominance of certain solid compounds, which is a neglected but important parameter controlling the availability, reactivity, and function of Si in soils. We further discuss the drivers of soil Si cycling and how humans interfere with these processes. The soil Si cycle is of major importance for ecosystem functioning; therefore, a deeper understanding of drivers of Si cycling (e.g., predominant speciation), human disturbances and the implication for important soil properties (water storage, nutrient availability, and micro aggregate stability) is of fundamental relevance.

Phytolith-occluded carbon sequestration potential in three major steppe types along a precipitation gradient in Northern China

Phytolith-occluded carbon (PhytOC) is an important long-term stable carbon fraction in grassland ecosystems and plays a promising role in global carbon sequestration. Determination of the PhytOC traits of different plants in major grassland types is crucial for precisely assessing their phytolith carbon sequestration potential. Precipitation is the predominant factor in controlling net primary productivity (NPP) and species composition of the semiarid steppe grasslands. We selected three representative steppe communities of the desert steppe, the dry typical steppe, and the wet typical steppe in Northern Grasslands of China along a precipitation gradient, to investigate their species composition, biomass production, and PhytOC content for quantifying its long-term carbon sequestration potential. Our results showed that (a) the phytolith and PhytOC contents in plants differed significantly among species, with dominant grass and sedge species having relatively high contents, and the contents are significantly higher in the below- than the aboveground parts. (b) The phytolith contents of plant communities were 16.68, 17.94, and 15.85 g/kg in the above- and 86.44, 58.73, and 76.94 g/kg in the belowground biomass of the desert steppe, the dry typical steppe, and the wet typical steppe, respectively; and the PhytOC contents were 0.68, 0.48, and 0.59 g/kg in the above- and 1.11, 0.72, and 1.02 g/kg in the belowground biomass of the three steppe types. (c) Climatic factors affected phytolith and PhytOC production fluxes of steppe communities mainly through altering plant production, whereas their effects on phytolith and PhytOC contents were relatively small. Our study provides more evidence on the importance of incorporating belowground PhytOC production for estimating phytolith carbon sequestration potential and suggests it crucial to quantify belowground PhytOC production taking into account of plant perenniality and PhytOC deposition over multiple years.

High silicon concentrations in grasses are linked to environmental conditions and not associated with C4 photosynthesis

The uptake and deposition of silicon (Si) as silica phytoliths is common among land plants and is associated with a variety of functions. Among these, herbivore defense has received significant attention, particularly with regard to grasses and grasslands. Grasses are well known for their high silica content, a trait which has important implications ranging from defense to global Si cycling. Here, we test the classic hypothesis that C₄ grasses evolved stronger mechanical defenses than C₃ grasses through increased phytolith deposition, in response to extensive ungulate herbivory ("C₄ -grazer hypothesis"). Despite mixed support, this hypothesis has received broad attention, even outside the realm of plant biology. Because C₃ and C₄ grasses typically dominate in different climates, with the latter more abundant in hot, dry regions, we also investigated the effects of water availability and temperature on Si deposition. We compiled a large dataset of grasses grown under controlled environmental conditions. Using phylogenetically informed generalized linear mixed models and character evolution models, we evaluated whether photosynthetic pathway or growth condition influenced Si concentration. We found that C₄ grasses did not show consistently elevated Si concentrations compared with C₃ grasses. High temperature treatments were associated with increased concentration, especially in taxa adapted to warm regions. Although the effect was less pronounced, reduced water treatment also promoted silica deposition, with slightly stronger response in dry habitat species. The evidence presented here rejects the "C₄ -grazer hypothesis." Instead, we propose that the tendency for C₄ grasses to outcompete C₃ species under hot, dry conditions explains previous observations supporting this hypothesis. These findings also suggest a mechanism via which anthropogenic climate change may influence silica deposition in grasses and, by extension, alter the important ecological and geochemical processes it affects.

Variation of biogeochemical cycle of riverine dissolved inorganic carbon and silicon with the cascade damming

To investigate the variation of the biogeochemical cycle of riverine dissolved inorganic carbon (DIC) and silicon (DSi) with the cascade damming, the bicarbonate ([Formula: see text]), dissolved silicon (DSi), and other environmental factors within the cascade reservoirs of the lower reaches of Yalongjiang River, passing through the southeastern Qinghai-Tibet Plateau, were systematically analyzed by collecting water samples during the wet season and dry season from 2018 to 2019, respectively. The results showed that the lower ratio of DSi to[Formula: see text] (0.044 ± 0.001) was mainly controlled by the domination of carbonate mineral in the sedimentary rock of the Yalongjiang River drainage basin. The DSi:[Formula: see text] ratio was positively correlated with discharge (P < 0.05), and negatively correlated with the water retention time (P < 0.01) and chlorophyll a, implying that the variations of DSi:[Formula: see text] ratio were mainly determined by the rock chemical weathering processes and the hydrologic process outside the reservoirs and the biological processes within the cascade reservoirs. The phytoplankton photosynthetic process stoichiometrically assimilated DSi and [Formula: see text], resulted in 3.46 × 10⁴ t·Si a^-1 and 1.89 × 10⁴ t·C a^-1 sequestering in the cascade reservoirs, respectively. Compared with the situation of dam-free in the lower reaches of Yalongjiang River, the export flux of [Formula: see text] and DSi at the mouth of Yalongjiang River was reduced by 11.87% and 62.50%, respectively; the ratio of DSi:[Formula: see text] decreased by 36.01% for only building the Ertan dam and 53.15% for the cascade damming, respectively. The water renewal time prolonged from 45 to 126.6 days due to the regulation of the cascade reservoirs in the mainstream. Ultimately, a conceptual model on migration-transformation of DIC and DSi within the cascade reservoirs in the lower reaches of Yalongjiang River was established. These findings demonstrated that riverine cascade damming could extend the biogeochemical coupling cycle of DIC and DSi within the inland aquatic ecosystems and ensure the ecological environment security in the hot-dry valley.

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 (0-10 cm) 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.

Silicon and Plant-Animal Interactions: Towards an Evolutionary Framework

Herbivory is fundamental in ecology, being a major driver of ecosystem structure and functioning. Plant Si and phytoliths play a significant antiherbivory role, the understanding of which and of its evolutionary context will increase our understanding of this phenomenon, its origins, and its significance for past, extant, and future ecosystems. To achieve this goal, we need a superdisciplinary evolutionary framework connecting the role of Si in plant–herbivore interactions, in global processes, and in plant and herbivore evolution. To do this properly, we should acknowledge and incorporate into our work some basic facts that are too often overlooked. First, there is great taxonomic variance both in plant Si contents, forms, and roles, but also in herbivore responses, dietary preferences, and in fossil evidence. Second, species and their traits, as well as whole ecosystems, should be seen in the context of their entire evolutionary history and may therefore reflect not only adaptations to extant selective factors but also anachronistic traits. Third, evolutionary history and evolutionary transitions are complex, resulting in true and apparent asynchronisms. Fourth, evolution and ecology are multiscalar, in which various phenomena and processes act at various scales. Taking these issues into consideration will improve our ability to develop this needed theoretical framework and will bring us closer to gaining a more complete understanding of one of the most exciting and elusive phenomena in plant biology and ecology.

Analyzing the effects of various forest management strategies and carbon prices on carbon dynamics in western Turkey

Determining appropriate management strategies to reduce greenhouse gas emissions using optimization techniques to understand how forest management activities affect the carbon dynamics is critical in implementing effective carbon management policies. This paper quantitatively analyzes the long-term effects of different management policies and silvicultural interventions using linear programming. In the analyses, afforestation targets for bare forest lands, tree species, carbon prices, planning approaches and sets of various targets and constraints on carbon dynamics were evaluated. The results were based on twenty-five forest management scenarios formulated for the Korucu Forest Planning Unit of Turkey. The results showed that, compared to timber-based planning strategies (TM), ecosystem-based planning approach (EM) contributes to a significant reduction in carbon sequestration in many cases. When different afforestation targets were incorporated into forest management strategies, cumulative carbon sequestration increased constantly compared to baseline scenario without any afforestation areas. In addition, the highest total carbon sequestration was observed when black pine (P. nigra) was used in afforestation activities rather than oak species (Quercus sp.) and other available tree species. While total timber production and timber net present value (NPV) decreased, carbon sequestration increased significantly with increasing carbon price. As a result of increasing carbon price from $20/ton to $100/ton, joint NPV increased by about five times. The results highlighted the importance of forest ecosystem and developing and implementing climate adaption measures into forest management activities in tackling climate change phenomenon.

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.

Phytolith-Occluded Carbon Storages in Forest Litter Layers in Southern China: Implications for Evaluation of Long-Term Forest Carbon Budget

Phytolith-occluded carbon (PhytOC) can be preserved in soils or sediments for thousands of years and might be a promising potential mechanism for long-term terrestrial carbon (C) sequestration. As the principal pathway for the return of organic matters to soils, the forest litter layers make a considerable contribution to terrestrial C sequestration. Although previous studies have estimated the phytolith production fluxes in the above-ground vegetations of various terrestrial ecosystems, the storages of phytoliths and PhytOC in litter layers have not been thoroughly investigated, especially in forest ecosystems. Using analytical data of silica, phytoliths, return fluxes and storages of forest litter, this study estimated the phytolith and PhytOC storages in litter layers in different forest types in southern China. The results indicated that the total phytolith storage in forest litter layers in southern China was 24.34 ± 8.72 Tg. Among the different forest types, the phytolith storage in bamboo forest litter layers (15.40 ± 3.40 Tg) was much higher than that in other forests. At the same time, the total PhytOC storage reached up to 2.68 ± 0.96 Tg CO2 in forest litter layers in southern China, of which approximately 60% was contributed by bamboo forest litter layers. Based on the current litter turnover time of different forest types in southern China, a total of 1.01 ± 0.32 Tg of PhytOC per year would be released into soil profiles as a stable C pool during litter decomposition, which would make an important contribution to the global terrestrial long-term biogeochemical C sink. Therefore, the important role of PhytOC storage in forest litter layers should be taken into account in evaluating long-term forest C budgets.

Silicon Fertilizer Application Promotes Phytolith Accumulation in Rice Plants

In this study, a pot experiment was designed to elucidate the effect of varying dosages of silicon (Si) fertilizer application in Si-deficient and enriched paddy soils on rice phytolith and carbon (C) bio-sequestration within phytoliths (PhytOC). The maximum Si fertilizer dosage treatment (XG3) in the Si-deficit paddy soil resulted in an increase in the rice phytolith content by 100.77% in the stem, 29.46% in the sheath and 36.84% in the leaf compared to treatment without Si fertilizer treatment (CK). However, the maximum Si fertilizer dosage treatment (WG3) in the Si -enriched soil increased the rice phytolith content by only 32.83% in the stem, 27.01% in the sheath and 32.06% in the leaf. Overall, Si fertilizer application significantly (p < 0.05) increased the content of the rice phytoliths in the stem, leaf and sheath in both the Si-deficient and enriched paddy soils, and the statistical results showed a positive correlation between the amount of Si fertilizer applied and the rice phytolith content, with correlation coefficients of 0.998 (p < 0.01) in the Si-deficient soil and 0.952 (p < 0.05) in the Si-enriched soil. In addition, the existence of phytoliths in the stem, leaf, and sheath of rice and its content in the Si-enriched soil were markedly higher than that in the Si-deficient soil. Therefore, Si fertilizer application helped to improve the phytolith content of the rice plant.

Phytolith Radiocarbon Dating: A Review of Previous Studies in China and the Current State of the Debate

Phytolith radiocarbon dating can be traced back to the 1960s. However, its reliability has recently been called into question. Piperno summarized recent dating evidence, but most phytolith dating results from China were not included in the review because they are written in Chinese. Herein, we summarize and evaluate previous phytolith dating results from China. We also review recent debates on the nature and origin of phytolith-occluded carbon (abbreviated as PhytOC), as well as the older age of phytoliths retrieved from modern plants. We conclude that although PhytOC includes a small amount of old carbon absorbed from the soil, this carbon fraction has not always biased phytolith ages, indicating that in certain situations, phytoliths can be tried as an alternative dating tool in archaeological and paleoecological research when other datable materials are not available.

Belowground Phytolith-Occluded Carbon of Monopodial Bamboo in China: An Overlooked Carbon Stock

Phytolith-occluded carbon (PhytOC), a highly stable carbon (C) fraction resistant to decomposition, plays an important role in long-term global C sequestration. Previous studies have demonstrated that bamboo plants contribute greatly to PhytOC sink in forests based on their aboveground biomass. However, little is known about the contribution of belowground parts of bamboo to the PhytOC stock. Here, we reported the phytolith and PhytOC accumulation in belowground trunk and rhizome of eight monopodial bamboo species that widely distributed across China. The results showed that the belowground parts made up an average of 39.41% of the total plant biomass of the eight bamboo species. There were significant (p < 0.05) variations in the phytolith and PhytOC concentrations in the belowground trunk and rhizome between the bamboo species. The mean concentrations of PhytOC in dry biomass ranged from 0.34 to 0.83 g kg-1 in the belowground rhizome and from 0.10 to 0.94 g kg-1 in the belowground trunk across the eight bamboo species, respectively. The mean PhytOC stocks in belowground biomass ranged from 2.57 to 23.71 kg ha-1, occupying an average of 23.36% of the total plant PhytOC stocks. This implies that 1.01 × 105 t PhytOC was overlooked based on the distribution of monopodial bamboos across China. Therefore, our results suggest that the belowground biomass of bamboo represents an important PhytOC stock, and should be taken into account in future studies in order to better quantifying PhytOC sequestration capacity.

Comparison of phytolith-occluded carbon in 51 main cultivated rice (Oryzasativa) cultivars of China

In this study, the carbon (i.e., C) bio-sequestration within phytoliths (PhytOC) in 51 rice cultivars was evaluated to breed cultivars with a high efficiency of carbon sequestration in phytoliths and high productivity.