N-fixing tree species promote the chemical stability of soil organic carbon in subtropical plantations through increasing the relative contribution of plant-derived lipids

Biodiversity experiments have shown that soil organic carbon(SOC)is not only a function of plant diversity,but is also closely related to the nitrogen(N)-fixing plants.However,the effect of N-fixing trees on SOC chemical stability is still little known,especially with the compounding effects of tree species diversity.An experimental field manipulation was established in subtropical plantations of southern China to explore the impacts of tree species richness(i.e.,one,two,four and six tree species)and with/without N-fixing trees on SOC chemical stability,as indicated by the ratio of easily oxidized organic carbon to SOC(EOC/SOC).Plant-derived C components in terms of hydrolysable plant lipids and lignin phenols were isolated from soils for evaluating their relative contributions to SOC chemical stability.The results showed that N-fixing tree species rather than tree species richness had a significant effect on EOC/SOC.Hydrolysable plant lipids and lignin phenols were negatively correlated with EOC/SOC,while hydrolysable plant lipids contributed more to EOC/SOC than lignin phenols,especially in the occurrence of N-fixing trees.The presence of N-fixing tree species led to an increase in soil N availability and a decrease in fungal abundance,promoting the selective retention of certain key components of hydrolysable plant lipids,thus enhancing SOC chemical stability.These findings underpin the crucial role of N-fixing trees in shaping SOC chemical stability,and therefore,preferential selection of N-fixing tree species in mixed plantations is an appropriate silvicultural strategy to improve SOC chemical stability in subtropical plantations.

Source and composition of sedimentary organic matter in the head of Three Gorges Reservoir: a multiproxy approach using δ^(13)C,lignin phenols, and lipid biomarker analyses

A multiproxy approach including bulk organic carbon, δ^(13) C, lignin phenols, and lipid biomarker analyses were applied to characterize the source and composition of sedimentary organic matter in the head part of Three Gorges Reservoir. OM consisted of both natural(autochthonous and allochthonous) and anthropogenic inputs.The natural OM included input from vascular plants,especially non-woody angiosperms. The allochthonous input included plankton and microbial production, likely due to localized eutrophication. Anthropogenic inputs likely derived from petroleum input and/or urban activities.Other anthropogenic inputs were untreated sewage waste.These influences were concluded to be regionally specific point sources of pollution based on relative distributions and on the fact that molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.

Interception, degradation and contributions of terrestrial organic carbon obtained from lignin analysis in Wujiang River, southwest China

Understanding the fate of terrestrial organic carbon(OC)in a cascade impoundment system is critical for recognizing the role of carbon sink for reservoirs.Surface sediments collected from eight cascade reservoirs across the Wujiang River,southwestern China,were analyzed for elemental and stable carbon isotopic(δ^13C)composition,and lignin phenols(∑8 andΛ8)to investigate the spatial distribution,contribution,origin and degradation of sedimentary terrestrial OC.The values of total organic carbon(TOC)and∑8 exhibited a remarkable reduction along the upstream-downstream transect suggesting the trapping effect of cascade-damming.A relatively broad range ofδ^13C(-26.61 to-25.54%,95%CI)and C/N(6.80-18.20)indicated mixed allochthonous/autochthonous OC sources in surface sediments.The quantitative simulation indicates that the OC of the sediments mainly was derived from terrestrial organic matter.Soilderived OC rather than C_(3)vascular plant-derived OC makes a major contribution to sedimentary terrestrial OC in reservoirs on karst terrain.As evidenced by lignin compositions andδ^13C,the predominant vascular plant origins of terrestrial OC along the Wujiang River are non-woody angiosperm C_(3)plants.The aged reservoirs showed a trend of increasing contribution of autochthonous OC,which potentially weaken the role of carbon sink for reservoirs.The relationship between runoff inputs,watershed area/water surface area ratios,and water residence time and Λ8 were explored,indicating the natural and anthropogenic influences on terrestrial OC remains very complex in a cascade-damming river.

Carbon isotopes and lignin phenols for tracing the floods during the past 70 years in the middle reach of the Changjiang River

The Lake Tian E Zhou(TEZ,an oxbow lake)was formed during the rerouting of the Changjiang River in 1972,with strong influences from the main river channel and flood events.Herein,a sediment core was collected from the Lake TEZ for the measurements of carbon isotopes and biomarkers,including stable carbon isotopes(δ13C),radiocarbon composition(?14C),and lignin phenols,as well as lead-210 to reconstruct recent heavy flood events over the past 70 years.At the 24–26 cm interval,the sediment contained the highest OC%,TN%,and lignin phenols content,as well as significantly depleted 13C but enriched 14C,corresponding to the extreme flood event in 1998.In addition,statistics from t-test showed that lignin phenols normalized to OC(Λ8),the concentration of 3,5-dihydroxy benzoic acid(3,5-BD),and the ratio of p-hydroxy benzophenone to total hydroxyl phenols(PHB/HP)were all significantly different between the layers containing flood deposits and the layers deposited under normal non-flood conditions(p<0.05).These results indicate that the later three parameters are highly related to flood events and can be used as compelling proxies,along with sediment chronology,for hydrological changes and storm/flood events in the river basin and coastal marine environments.

Molecularly engineered lignin to polyphenol via organocatalysis as an active sunscreen ingredient

Phenolation is one of the effective strategies to synthesize lignin-based polyphenols,improve lignin’s properties,and extend its value-added applications in biological,medicinal and cosmetic fields.Herein,by taking the structural feature advantage of lignin,an effective and green strategy was developed to molecularly engineer lignin into a robust lignin-3-(2-hydroxyphenyl)propionate ester(LPPE)derivative via a transesterification reaction between 3,4-dihydrocoumarin(DHC)and the aliphatic hydroxyls in lignin under organocatalysis.The strategy is optimized and the novel derivative was systematically characterized by ^(1)H,^(13)C and ^(31)P nuclear magnetic resonance(NMR)and Fourier transform infrared(FT-IR)spectroscopy.The findings indicated that the successful introduction of 3-(2-hydroxyphenyl)propionate groups using a OH groups/DHC/organic base mo-lar ratio of 1꞉1꞉0.3 at 120℃ for 6 h increased the content of phenolic hydroxyl groups from 1.7931 to 3.0179 mmol/g,and the LPPE exhibited excellent ultraviolet-absorbing and antioxidant per-formance with up to 90%free radical scavenging activity within 20 min using 5 mg/mL of LPPE.In addition,good biocompatibility and a high Sun protection factor(SPF)value of 40.9 were achieved at 5%(w)dosage of LPPE in the cream,indicating its significant application potential in sunscreen.

Sources and distributions of terrigenous organic matter in a mangrove fringed small tropical estuary in South China

The sources and distributions ofterrigenous organic matter （OM） were investigated in a small tropical estu- ary in the Hainan Island, South China. Plants, suspended particulate matter （SPM）, and surface sediments samples in the estuary and coast were collected. Bulk properties [organic carbon （OC%）, total nitrogen （TN%）, stable carbon isotope （613C） and grain size] and lignin phenol concentrations were measured. OC% of mangrove plants was （43.44-2.1） %, which is similar to the values reported for mangrove plants in other re- gions. OC% of sediment samples ranged from 0.07% to 1.42%, and theywere related to the sediment texture. Lignin phenols in the sediment ranged from 5.16 rag/100 mg OC in the uppermost station to 0.51 mg/100 mg OC in the coast. The molar ratio of organic carbon to total nitrogen （C/N） （~7） and 613C （^-31.1 ~ 10-a） of riverine SPM revealed that the major OM sources of riverine SPM were aquatic OM （phytoplankton and/or bacteria）. Moreover, the lower lignin concentration （AS） and higher （Ad/A1）v of lignin phenols suggest that terrestrial OM in riverine SPM were mainly from soil. Furthermore, C/N ratio, 6 ~a C and lignin phenols reveal that mangrove plants were the predominant OM sources of mangrove surface sediment. Based on the 61aC and lignin phenols, it can be concluded that the major OM sources in estuarine and coastal surface sedi- ments were marine phytoplankton, riverine SPM and mangrove surface sediment. In addition, the higher （Ad/A1）v of lignin phenols in those coastal sediments indicate that seagrass might be a potential OM source in coastal sediments, however, the lower （Ad/A1）v in the estuarine sediments in turn suggests that seagrass could not be transported to the mangrove fringed region. A three-end-member model which is based on lignin concentrations and 6 I3C was applied to evaluate the contribution of mangroves to the organic matter preserved in the surface sediments. Around the mangrove fringed region, mangrove could contribute more than 50% to the sedimentary OM, and this value is much higher than riverine OM. Nevertheless, mangrove OM could not be efficiently transported to the coastal region. Our study suggests that mangrove forest is an important OM source in this small estuary.

Radical synthesis of tetrameric lignin model compound

The lack of suitable lignin model compound limits the understanding of the characteristics of lignin, and hence hinders the efficient utilization of this kind of bioresource. A tetramer phenolic lignin model compound composed of 5-5, α-O-4 and β-5 linkages was prepared by a two-step of free radical reaction with hydrogen peroxide/horseradish peroxidase and S2O8^2- /Fe^2＋ as the initiator. Compared with enzymatic process, this synthetic process gives a higher yield of 33.8% within a shorter time. HRMS and ^13C NMR spectroscopy show that synthesized model compound contains phenylpropane structure linked by 5-5, α-O-4 and β-5 bonds, which can mimic some chemical characteristics of lignin.

Sources and dynamics of sedimentary organic matter in Sundarban mangrove estuary from Indo-Gangetic delta

Introduction:Mangrove forests are highly productive ecosystems distributed along the tropical coast line.Nutrient biogeochemistry of mangroves are primarly driven by both allochthonous and autochthonous sources.Characterization of organic matter in coastal ecosystems enables to understand the biogeochemical transformation of organic matter and its influence on ecosystem productivity in response to various changing environmental conditions.Therefore,the elemental and stable carbon and nitrogen levels were employed to understand the organic matter(OM)dynamics in the Sundarban mangrove ecosystem(India-Bangladesh).Results:Differences in stable isotope values indicate that variable sources influence the OM dynamics in Sundarban sediments.The progressive enrichment inδ13C levels along the land-coastal continuum indicates that the terrestrial and marine inputs are dominant at the landward and seaward ends,respectively.The CuO oxidationderived lignin phenol monomers describe significant levels of total lignin are preserved in Sundarban mangrove sediments during diagenesis.The phenol monomer ratios are lower than the plant litter explaining that aromatic ring cleavage is the dominant mechanism for the lignin degradation.Furthermore,the Ad/Al ratios were higher than the plant litter explaining the oxidation of propyl side chain of vascular OM influencing the carbon cycling in Sundarban sediments.Largely,the Ad/Al ratios describe the vascular OM degradation is through the oxidation of propyl side chain.Conclusions:The regional variability in land-use regulates the spatial variability in C,N,OC/TN ratio,δ13C andδ15N between the Indian and the Bangladesh Sundarban mangroves and indicates that in the upstream terrestrial organic matter and/or mangrove plant litter contribute significant amount of organic matter,whereas the marine POC influences the organic matter dynamics in downstream.The three end-member mixing model applying terrestrial plant litter,seston,and marine POC as end-members explains the relative contribution of OM from various sources,and marine inputs were dominant in Sundarban sediments.