Physiology of medicinal and aromatic plants under drought stress

Drought poses a significant challenge,restricting the productivity of medicinal and aromatic plants.The strain induced by drought can impede vital processes like respiration and photosynthesis,affecting various aspects of plants’growth and metabolism.In response to this adversity,medicinal plants employ mechanisms such as morphological and structural adjustments,modulation of drought-resistant genes,and augmented synthesis of secondary metabolites and osmotic regulatory substances to alleviate the stress.Extreme water scarcity can lead to leaf wilting and may ultimately result in plant death.The cultivation and management of medicinal plants under stress conditions often differ from those of other crops.This is because the main goal with medicinal plants is not only to increase the yield of the above-ground parts but also to enhance the production of active ingredients such as essential oils.To elucidate these mechanisms of drought resistance in medicinal and aromatic plants,the current review provides a summary of recent literature encompassing studies on the morphology,physiology,and biochemistry of medicinal and aromatic plants under drought conditions.

Interactive effects of drought stress and chitosan application on physiological characteristics and essential oil yield of Thymus daenensis Celak

Thymus daenensis, a perennial herb, is often grown in areas that experience drought conditions during its growing period. Application of chitosan may compensate for the negative impact of drought stress on the yield of oil and secondary metabolites in Thymus.The interactive effects of foliar application of chitosan and drought stress on dry matter,essential oil yield, and selected physiological characteristics including photosynthetic pigments, osmotic adjustment, and lipid peroxidation of Thymus were investigated in a two-year study from 2014 to 2015. Treatments consisted of 0, 200, and 400(iL L'1 chitosan applied to plants grown under field capacity, mild drought stress(50% field capacity), and severe drought stress(25% field capacity). Dry matter yield decreased substantially as drought stress intensified. However, essential oil content increased under stress conditions,with the highest essential oil yield obtained from plants under mild drought stress. Foliar application of chitosan compensated to some extent for dry matter and oil yield reduction of plants grown under drought stress. The highest essential oil yield(1.52 g plant-1) was obtained by application of 400 \iL L_1 chitosan under the mild stress condition in 2015 when plants were mature. The compensatory effect of chitosan in reducing the negative impact of stress conditions on dry matter and oil yield was due mainly to stimulation of osmotic adjustment through proline accumulation and reduction of lipid peroxidase level, which increased the integrity of cell membranes of thyme leaves.

Biofumigation: An alternative strategy for the control of plant parasitic nematodes

Plant-parasitic nematodes wreak havoc on the yield and quality of crops worldwide.Damage from these pests is estimated to exceed US$100 bllion annually but is likely higher due to misdiagnosis.Nematode damage may be catastrophic,but historically the solution has been damaging as well.Use of the synthetic nematicide methyl bromide(MBr)poses risks to the environment and to human health.Biofumigation,the use of plant material and naturally produced compounds to control pests,is an increasingly feasible method of pest management.The process acts through the growth or incorporation of plant material into the soil,that,over the course of its degradation,releases glucosinolates that break down into nematotoxic isothiocyanates.These secondary plant metabolites exist naturally in commonly grown plants,most of which belong to the Brassicaceae family.Research endeavors have increasingly explored the potential of biofumigation.The reaction of target pests,the selection of biofumigant,and ideal environments for efficacy continue to be evaluated.This review seeks to provide a cost and benefit assessment of the status of biofumigation for the control of plant-parasitic nematodes as an alternative to conventional methyl bromide usage.

Accumulation of L-DOPA in various organs of faba bean and influence of drought, nitrogen stress, and processing methods on L-DOPA yield

Faba bean(Vicia faba L.)has been identified as a rich source of L-DOPA,which is used in treating Parkinson's disease.Biosynthesis and accumulation of active substances such as L-DOPA in plant tissues may interact with growing conditions and processing methods.Accumulation trends of L-DOPA in various faba bean organs and the effect of drought stress and N fertilization on L-DOPA content were studied in a field and two greenhouse experiments.The influence of various processing methods on L-DOPA content of faba bean tissues was evaluated.The highest L-DOPA content was detected in fresh leaves(22.4 mg g^(-1))followed by flowers,young pods,mature seeds,and roots.Regardless of processing method,L-DOPA concentration in faba bean tissues was significantly reduced when tissues were boiled or dried.Among various methods of processing,freezing had the lowest detrimental effect,reducing L-DOPA concentrations by 24.1%and 21.1%in leaves and seeds,respectively.Drought stress elevated L-DOPA concentration,and maximum L-DOPA(23.3 mg g^(-1)of biomass)was extracted from plants grown under severe drought stress.However,L-DOPA yield(L-DOPA concentration×biomass)was compromised,owing to the adverse influence of drought stress on dry matter production.No significant difference in L-DOPA concentration was detected among various N application rates.

Phytochemical composition of the essential oil of different populations of Stachys lavandulifolia Vahl

Objective:To examine the chemical variability in inflorescences of wild populations of Stachys lavandulifolia Vahl(S.lavandulifolia)collected throughout two provinces(lsfahan and Chaharmahal va Bakhtiary),Southwest Iran.Methods:The essential oils of S.lavandulifolia Vahl from seven locations were obtained by hydro-distillation and analysed by gas chromatography and gas chromatography-mass spectrometry.Results:The results revealed that distinct differences in the content of compounds depending on region of sample collection.The main constituents of the essential oils wereα-thujone(0.3%-32.3%),α-pinene(trace to 37.3%),myrcene(0.5%-15.9%),β-phellandrene(1.1%-37.9%),germacrene D(0.4%-11.3%),△-cadinene(trace to 11.6%)and 1,4-methano-1 H-indene(trace to 10.1%).Conclusions:The results of the present study indicated that essential oil components of S.lavandulifolia Vahl can be varied with genetic(ecotype),environmental conditions and geographic origin,In general,the essential oils of various populations of S.lavandulifolia Vahl were rich in monoterpenoids and sesquiterpenoids.

Diversity in chemical compositions of essential oil of myrtle leaves from various natural habitats in south and southwest Iran

Myrtle, Myrtus communis L. （Myrtaceae）, an evergreen shrub also known as wild myrtle, has a history of use as a culinary and medicinal plant. To determine the diversity within the species, plant leaves of myrtle were collected in 12 natural habitats in Iran for investigation of chemical constituents in the essential oil. Extraction of the essential oils produced yields ranging from 0.7 to 1.5 mL per 100 g dry tissue. An analysis of the oils by GC and GC/MS revealed 40 compounds, constituting 90.1-99.9 % of the essential oils. Chemical constituents varied with the site of sample origin, although the principal essential oil compo- nents from all populations, were pinene （17.5-37.1%）, 1,8-cineole （9.9-29.8 %）, linalool （7.0-23.1%）, and a-ter- pineol （5.3-8.3 %）. Limonene （tr, 22.7 %） was a major constituent in three populations. Characterized chemotypes included Chemotype pinene/1,8-cineole/linalool, Chemotype II： a-pinene/linalool, Chemotype III： a-pinene/1,8- cineole, and Chemotype IV： pinene/1,8-cineole/limonene.The main source of variabifity in chemical composition and oil yield appeared to be differences in environmental conditions and chemotypes as plant populations collected from close geographical areas could be classified in a cluster.

Comparison of sucrose intake and production of elimination spots among adult Musca domestica, Musca autumnalis, Phormia regina and Protophormia terraenovae

Objective: To compare the differences in intake and excretion between Musca domestica and other three species from families Muscidae and Calliphoridae which may help explaining the significance of house fly in the transmission of pathogens.Methods: The four adult species were supplied with two concentrations of sucrose via modified capillary feeder assay system. The two sucrose concentrations were applied to one adult male/each experiment and the elimination spots were counted. Using 0.25 mol/L sucrose + 0.25% bromophenol blue, one active non-starved male/cup was observed carefully for 1 h to record its behavior. As a growing medium used in bacterial transmission experiments, undiluted trypticase soy broth was used to feed 3-day-old females and males of Musca domestica following two different diets upon emergence and the frequency of elimination spots was estimated.Results: The two Musca species have half the weight of the two Phormia species.Comparing the volume of intake per hour, house fly took as much as the other species, all of which were larger. House fly produced twice, or more, the number of elimination spots/h than the other three species. Feeding the flies a sugar liquid diet resulted in producing more fecal spots than regurgitation spots. The male house flies produced less elimination spots/h when fed with trypticase soy broth than with the two sucrose solutions.Conclusions: House flies eliminated more than the other examined fly species and most of these elimination events were defecation which implicates the fecal route for pathogen transmission by this important vector.

Steam disinfection enhances bioaccessibility of metallic nanoparticles in nano-enabled silicone-rubber baby bottle teats,pacifiers,and teethers

Nano-enabled silicone-rubber articles for feeding or chewing could be a source of metallic nanoparticles(NPs)directly exposed to infants and young children.However,the impact of steam disinfection on release of NPs and the related potential risks to children's health are unknown.Here,we investigated contents and form of Ag and Zn in 57 nano-enabled silicone-rubber baby bottle teats,pacifiers,and teethers of seven countries and examined the impacts of steam disinfection on in vitro bioaccessibility(IVBA)of Ag and Zn in the articles.Nearly 89%articles had a mixture of Ag-and Zn-containing NPs and the teethers had relatively high Ag and Zn contents(up to 501 and 254μg/g,respectively).Steam disinfection caused rubber decomposition into micro(nano)plastics(0.54-15.7μm)and NP release from the interior of bulk rubber and micro-sized plastics,thus enhancing the IVBA of Ag and Zn by up to 5.5 times.The findings provide insights into mechanisms for NP release by steam disinfection.Though oral exposure risk assessment suggested low health concerns on individual metal release,our study points out the need to assess the potential health risks of child co-exposure to metallic NPs and micro(nano)plastics.

Accelerated aging: The hidden harm of microplastic exposure

The widespread contamination of plastic materials has become a significant ecological concern, hindering progress toward sustainable development [1,2]. Plastic waste is widespread across various natural habitats, including terrestrial and marine ecosystems[3,4]. Microplastics (MPs) primarily originate from the fragmentation of larger plastic pieces. Due to their small size, MPs are easily ingested by organisms and subsequently transferred through food webs, posing risks to human health [5,6].

作物-土壤氮循环对大气CO_(2)浓度和温度升高响应的研究进展

在地球化学元素循环中,氮素是最重要、最活跃的营养元素之一。农田生态系统中的氮素很大程度上决定农作物的产量和品质。然而,在全球气候变化背景下,随着大气CO_(2)浓度和温度升高,作物-土壤氮循环的变化可能显著影响农田生态系统中的作物生产。因此,研究作物-土壤氮循环对大气CO_(2)浓度和温度升高的响应,能够为科学合理地预测未来气候条件下,农田生态系统中作物的氮素需求,以及保障农作物产量的稳定供应提供理论依据,对于全面认识全球气候变化背景下的农田生态系统氮素循环过程及土壤可持续利用具有重要意义。本文综述了大气CO_(2)和温度升高对作物氮素吸收和分配,以及与氮有效性密切相关的土壤氮转化的影响,并系统总结了二者对作物-土壤氮循环过程产生的交互作用。总结以往研究发现,在大气CO_(2)浓度升高条件下,作物的蒸腾作用减弱,但光合作用增强,生物量加大,根系分支和根表面积增加,豆科作物的根瘤固氮能力提高,因此整体上促进作物对氮的吸收,并且增加作物向籽粒中分配氮的比例,但作物的平均氮浓度降低。此外,高CO_(2)浓度提高了土壤酶活性,增强了土壤有机氮矿化作用、硝化及反硝化作用,加速了土壤氮转化。升温和CO_(2)浓度升高对作物-土壤氮循环产生正向或负向的交互作用,主要表现在:高温和高CO_(2)浓度对作物的生物量、光合作用、地下部氮分配、根系分支以及根表面积具有协同促进作用,升高温度减轻了高CO_(2)浓度对作物蒸腾作用和作物氮浓度的抑制作用。然而,升温抑制了高CO_(2)浓度对作物向籽粒中氮分配、氮吸收以及产量的促进作用;升温虽然能进一步增强高CO_(2)浓度对土壤酶活性和有机氮矿化的促进作用,但是对于土壤硝化和反硝化作用,二者的交互作用以及相关的分子机制尚不明确。大气CO_(2)升高和温度升高对土壤微生物,以及微生物与作物之间的耦合关系的研究比较薄弱,特别是由微生物主导的氮循环过程及其对全球气候变化的反馈机制是未来研究的重点。本文提出利用16S rRNA、DGGE、T-RFLP、qPCR、RT-PCR技术、蛋白组学以及稳定性同位素探针原位研究技术,可以将复杂环境中微生物物种组成及其生理功能进行耦合分析,揭示大气CO_(2)浓度与温度对作物-土壤氮循环过程的交互作用机理,增强对气候变化下农田生态系统氮素循环响应的预测能力,为农田生态系统有效地适应气候变化提供科学的理论依据。

大气CO_(2)浓度和温度升高对农田土壤碳库及微生物群落结构的影响

大气CO_(2)浓度和温度升高会通过影响作物的光合作用,从而影响光合碳向土壤中的输送。输入到土壤中光合碳含量的变化势必会对土壤外源碳的主要分解者--微生物的群落结构产生影响。土壤微生物在土壤有机质的转化过程中发挥着重要的作用,是土壤碳循环的主要驱动者,其群落结构和功能的改变会影响土壤有机质的动态变化,而这些变化会进一步增加或者降低大气中的CO_(2)浓度,从而对气候变化产生反馈作用。未来土壤的碳平衡取决于大气CO_(2)浓度和全球变暖对土壤中碳的输入、输出以及碳在土壤中的驻留时间。因此,只有全面了解大气CO_(2)浓度和温度升高将对土壤碳库及土壤微生物群落结构产生何种影响,才能明确地揭示陆地生态系统对气候变化的反馈机制,对未来农田土壤有机碳库的管理和生产力的维持有重要意义。文章综述了大气CO_(2)浓度和温度升高及其交互作用对土壤碳库和土壤微生物群落结构的影响。主要结论为:(1)大气CO_(2)浓度和温度升高对土壤碳库的影响可以相互抵消,但是土壤碳库是否成为碳“源”与温度升高的幅度密切相关;(2)大气CO_(2)浓度升高增加了光合碳在玉米、小麦等植株各部分的分配,温度升高同样对光合碳的分配规律产生影响,但对不同部位的影响不一致,多呈降低或无显著影响;(3)大气CO_(2)浓度和温度升高可能对土壤微生物活性及其群落结构产生交互影响,且对不同微生物(细菌、真菌和古菌)群落的影响程度不同,进一步对土壤有机碳的转化产生影响。最后提出未来的研究方向:(1)从气候变化影响植物-土壤互作角度解析根系分泌物的转化过程及其对微生物的影响;(2)通过DNA-SIP进一步研究大气CO_(2)浓度和温度升高条件下土壤微生物对不同植物来源碳的选择性利用与碳循环的关系,从而阐明气候变化条件下微生物底物利用策略以及微生物群落结构的变化。

植物-土壤-微生物间碳流对大气CO_2浓度升高的响应

大气二氧化碳(CO_2)浓度升高促进很多植物的光合同化能力,同时增加光合同化碳向土壤中的释放,即增加根系脱落物。在根际范围内,根系脱落物为土壤微生物提供养分和能量来源,根沉积物量和质的改变必然影响到土壤微生物的活性以及群落结构和功能。由于土壤微生物在影响土壤碳循环方面的关键作用,大气CO_2浓度升高条件下根际微生物如何参与植物光合碳转化将很大程度上决定未来气候变化条件下土壤碳库的稳定性。本文综述了植物光合碳同化、土壤碳循环以及土壤微生物活性与群落结构对大气CO_2浓度升高的响应,从植物-土壤-微生物系统中碳流角度分析高CO_2浓度对土壤碳转化的影响机制,并对未来的研究方向进行了展望,提出高CO_2浓度条件下同位素标记结合宏基因组技术解析根际碳转化机制将成为农田生态系统领域的研究热点。

有机质官能团及微孔特性对疏水性有机污染物吸附的影响机制

作为重要的地质吸附剂,土壤/沉积物中的有机质是环境中疏水性有机污染物主要的汇.由于有机质的结构异质性,疏水性有机污染物一旦进入其中,会被吸附在不同的位点上,反应活性和生态风险进而会发生变化.对疏水性有机污染物在有机质上的吸附进行研究有助于了解其在环境中的分布,传输及生物有效性.本文就疏水性有机污染物在土壤/沉积物中的有机质上吸附的国内外研究进展进行了综述,讨论了重要有机质组分(腐殖质和碳黑)的结构和吸附作用差异性,重点分析了有机质的微孔特性和官能团对吸附的影响机制.

单宁酸和没食子酸对纳米碳管悬浮的影响

以单宁酸(TA)和没食子酸(GA)为模型悬浮剂,探讨悬浮剂分子大小、空间结构及憎水性等对CNTs悬浮的影响.结果表明,在低吸附量下,TA具有较强的悬浮CNTs的能力,而高吸附量下,GA悬浮CNTs能力更强.含氧量高的CNTs表现出更好的悬浮性能.尽管悬浮剂的吸附量影响了CNTs的悬浮,但悬浮剂的分子结构、空间构象及化学性质等可能才是控制CNTs的悬浮的主要因素,同时,CNTs本身的化学性质也对悬浮起着重要作用.

Long-term agricultural activity affects anthropogenic soil on the Chinese Loess Plateau

Anthropogenic activities largely influence the soil quality of agricultural fields and the composition of soil. Samples of typical anthropogenic Loutu soil in the Guanzhong area of the Loess Plateau, Shaanxi Province, China were collected and measured for soil compaction, bulk density, total organic carbon（TOC）, active organic carbon（AOC）, and soil enzyme activities to investigate spatial variations in soil quality. The results indicate that soil compaction and bulk density increased with increasing distance from the farm village, whereas soil TOC, AOC, and soil enzyme activities firstly increased and subsequently decreased with increasing distance from the farm village. All of the tested parameters presented clear concentric distribution. Vertically, soil compaction and bulk density in the topsoil were lower than those in the subsoil, but all other tested parameters in the topsoil were significantly higher than those in the subsoil. In addition, there was a significant positive correlation between organic carbon content and enzyme activities, confirming that the spatial distribution of Loutu soil characteristics has been affected by long-term anthropogenic activities to some extent. The results of this study imply that the use of farmyard manure and appropriate deep plowing are important and effective ways to maintain and improve soil quality.

Co-exposure of sulfur nanoparticles and Cu alleviate Cu stress and toxicity to oilseed rape Brassica napus L.

Experimentswere performed to explore the impact of sulfur nanoparticles(SNPs)on growth,Cu accumulation,and physiological and biochemical responses of oilseed rape(Brassica napus L.)inoculated with 5 mg/L Cu-amended MS medium supplemented with or without 300 mg/L SNPs exposure.Cu exerted severe phytotoxicity and inhibited plant growth.SNPs application enhanced the shoot height,root length,and dry weight of shoot and root by 34.6%,282%,41.7%and 37.1%,respectively,over Cu treatment alone,while the shoot and root Cu contents and Cu-induced lipid perodixation as the malondialdehyde(MDA)levels in shoots and roots were decreased by 37.6%,35%,28.4%and 26.8%.Further,the increases in superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX),glutathione reductase(GR)and glutathione S-transferase(GST)enzyme activities caused by Cu stress were mitigated in shoots(10.9%–37.1%)and roots(14.6%–35.3%)with SNPs addition.SNPs also positively counteracted the negative effects on shoot K,Ca,P,Mg,Mn,Zn and Fe contents and root K,Ca,Mg and Mn contents from Cu exposure alone,and significantly promoted the nutrients accumulation in plant.Additionally,in comparison with common bulk sulfur particles(BSPs)and sulfate,SNPs showed more positive effects on promoting growth in shoots(6.7%and 19.5%)and roots(10.9%and 15.1%),as well as lowering the shoot Cu content(40.1%and 43.3%)under Cu stress.Thus,SNPs application has potential to be a green and sustainable technology for increasing plant productivity and reducing accumulation of toxic metals in heavy metal polluted soils.

Mutual influence of copper and paraquat on their adsorption in soil

Paraquat and copper (Cu) are commonly used and detected in soil.Therefore,it is important to understand their mobility in the environment.In this study,the competitive effects of paraquat and Cu on their adsorption in five representative Chinese soils were investigated using batch adsorption equilibrium experiments and spectroscopic analysis.The results showed that the adsorption of paraquat in soil varied with soil type and was positively correlated with both soil cation exchange capacity and organic matter content.Paraquat exerted a more remarkable suppression effect on the adsorption of Cu than Cu on the adsorption of paraquat.In the presence of 0.12 and 0.19 mmol L-1paraquat,Cu adsorption decreased by 16%and 22%in Heilongjiang soil and by 24%and37%in Jiangxi soil,respectively.In the presence of 0.1 and 0.2 mmol L-1Cu,paraquat adsorption decreased by 4%and 8%in Heilongjiang soil and by15%and 19%in Jiangxi soil,respectively.Exchange selectivity involving symmetric cation (paraquat2+and Cu2+) exchange is the probable basis for the suppression effect.The ultraviolet-visible absorption experiments suggested that the formation of Cu-paraquat complexes was unlikely to happen in a solution or at the soil surface.Copper K-edge X-ray absorption spectroscopy indicated that Cu in soil may have some water as hydration layers as the nearest neighbors,and each Cu atom was coordinated with five oxygen atoms.These findings greatly improve our knowledge of the molecular-scale adsorption mechanisms of paraquat and Cu in soil and can be used to predict the behavior,transport,and fate of paraquat and Cu in agricultural soils.

The frontier of microplastics and nanoplastics: Soil health and carbon neutrality

Microplastics and nanoplastics(MNPs)in soil have drawn increasing concerns about their potential threats to soil ecosystems due to their ubiquitous occurrence and persistence.The interactions of MNPs with soil components,microbial community,plants,and fauna determine their impacts on soil biogeochemical processes and food security.However,they are not largely explored.Further research is also needed to develop reliable and standardized techniques and methods to characterize the relevant MNPs interacting with different types of soil ecosystems and to deeply examine their impacts on soil health,food security,and climate changes.In addition,mitigation protocols and regulation guidelines need to be developed.New findings will provide scientific and technological support for the understanding and management of soil health and carbon neutrality as influenced by MNPs.

Insights into the enzymatic degradation of DNA expedited by typical perfluoroalkyl acids

Perfluoroalkyl acids(PFAAs)are considered forever chemicals,gaining increasing attention for their hazardous impacts.However,the ecological effects of PFAAs remain unclear.Environmental DNA(eDNA),as the environmental gene pool,is often collected for evaluating the ecotoxicological effects of pollutants.In this study,we found that all PFAAs investigated,including perfluorohexanoic acid,perfluorooctanoic acid,perfluorononanoic acid,and perfluorooctane sulfonate,even at low concentrations(0.02 and 0.05 mg/L),expedited the enzymatic degradation of DNA in a nonlinear dose–effect relationship,with DNA degradation fragment sizes being lower than 1,000 bp and 200 bp after 15 and 30 min of degradation,respectively.This phenomenon was attributed to the binding interaction between PFAAs and AT bases in DNA via groove binding.van der Waals force(especially dispersion force)and hydrogen bonding are the main binding forces.DNA binding with PFAAs led to decreased base stacking and right-handed helicity,resulting in loose DNA structure exposing more digestion sites for degrading enzymes,and accelerating the enzymatic degradation of DNA.The global ecological risk evaluation results indicated that PFAA contamination could cause medium and high molecular ecological risk in 497 samples from 11 contamination-hot countries(such as the USA,Canada,and China).The findings of this study show new insights into the influence of PFAAs on the environmental fates of biomacromolecules and reveal the hidden molecular ecological effects of PFAAs in the environment.

Fluorescence regional integration and differential fluorescence spectroscopy for analysis of structural characteristics and proton binding properties of fulvic acid sub-fractions

Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.