Organic Materials Could Improve the Phytoremediation Efficiency of Soil Potentially Hazardous Metal by Sedum alfredii Hance

Soil potentially hazardous metal(PHM)is continually attracting public attention worldwide,due to its highly toxic properties and potentially huge damage to human being through food chain.Phytoremediation is an effective and eco-friendly way in remediation technology.A pot experiment was carried out to investigate the effect of different organic materials(biogas residue(BR),mushroom residue(MR),and bamboo-shoot shell(BS))application on phytoremediation of two PHM-contaminated soils(Fuyang soil as‘heavily-polluted soil’and Wenzhou soil as‘moderately-polluted soil’,respectively)by Sedum alfrecdii Hance.The results indicated:1)for moderately-polluted soil,the 5%BR treatment had the strongest activation to Cu and Zn,for heavily-polluted soil,1%BS treatment had the highest activation effect for Cu,Zn,Pb and Cd.2)the above-ground biomass of Sedum alfredii Hance increased with the addition rate of organic materials.3)for Cd uptake of Sedum alfredii Hance in moderately-polluted soil,only 1%BS treatment had a better accumulation effect,compared to the control,for Zn element,MR treatments were weaker than the control,while other treatments were better than the control,of which 5%BR,1%BS and 5%BS accumulated more Zn element by 39.6%,32.6%and 23.8%,respectively;in heavily-polluted soil,the treatments of 5%BS,1%BR and 5%BR accumulated more Cd than the control by 12.9%,12.8%and 6.2%,respectively,the treatments with organic materials addition promoted Zn accumulation in shoots of Sedum alfredii Hance,and the best treatment was 5%BS.Therefore,an appropriate application rate of BS and BR could improve the remediation efficiency for Zn/Cd contaminated soils by Sedum alfredii Hance.

A study of the soil water potential threshold values to trigger irrigation of ‘Shimizu Hakuto’ peach at pivotal fruit developmental stages

Water management is an important practice that affects fruit size and quality.Effective implementation of irrigation scheduling requires knowledge of the appropriate indicators and thresholds,which are established manly based on the effects of water deficits on final fruit quality.Few studies have focused on the real-time effects of water status on fruit and shoot growth.To establish soil water potential (ψ_(soil)) thresholds to trigger irrigation of peach at pivotal fruit developmental stages,photogrammetry,^(13)C labelling,and other techniques were used in this study to investigate real-time changes in stem diameter,fruit projected area,net leaf photosynthetic rate (P_(n)),and allocation of photoassimilates to fruit under soil water potential conditions ranging from saturation to stress in 6-year-old Shimizu hakuto’peach.Stem growth,fruit growth,and P_n exhibited gradually decreasing sensitivity to water deficits during fruit developmental stages I,II,and III.Stem diameter growth was significantly inhibited whenψ_(soil)dropped to-8.5,-7.6,and-5.4 k Pa,respectively.Fruit growth rate was low,reaching zero when theψ_(soil)was-9.0 to-23.1,-14.9 to-21.4,and-16.5 to-23.3 k Pa,respectively,and P_ndecreased significantly when theψ_(soil)reached-24.2,-22.7,and-20.4 kPa,respectively.In addition,more photoassimilates were allocated to fruit under moderateψ_(soil)conditions (-10.1 to-17.0 k Pa) than under otherψ_(soil)values.Our results revealed threeψ_(soil)thresholds,-10.0,-15.0,and-15.0 kPa,suitable for triggering irrigation during stages I,II,and III,respectively.These thresholds can be helpful for controlling excessive tree vigor,maintaining rapid fruit growth and leaf photosynthesis,and promoting the allocation of more photoassimilates to fruit.

Elevated CO_(2) increases soil redox potential by promoting root radial oxygen loss in paddy field

Soil redox potential(Eh)plays an important role in the biogeochemical cycling of soil nutrients.Whereas its effect soil process and nutrients'availability under elevated atmospheric CO_(2) concentration and warming has seldom been investigated.Thus,in this study,a field experiment was used to elucidate the effect of elevated CO_(2) concentration and warming on soil Eh,redox-sensitive elements and root radial oxygen loss(ROL).We hypothesized elevated CO_(2) and warming could alter soil Eh by promoting or inhibiting ROL.We found that soil Eh in the rhizosphere was significantly higher than that of non-rhizosphere.Elevated CO_(2) enhanced soil Eh by 11.5%,which corresponded to a significant decrease in soil Fe^(2+)and Mn^(2+)concentration.Under elevated CO_(2),the concentration of Fe^(2+)and Mn^(2+)decreased by 14.7%and 13.7%,respectively.We also found that elevated CO_(2) altered rice root aerenchyma structure and promoted rice root ROL.Under elevated CO_(2),rice root ROL increased by 79.5%and 112.2%for Yangdao 6 and Changyou 5,respectively.Warming had no effect on soil Eh and rice root ROL.While warming increased the concentration of Mn^(2+)and SO_(4)^(2-)by 4.9%and 19.3%,respectively.There was a significant interaction between elevated CO_(2) and warming on Fe^(2+)and Mn^(2+).Under elevated CO_(2),warming had no effect on the concentration of Fe^(2+)but decreased Mn^(2+)concentration significantly.Our study demonstrated that elevated atmospheric CO_(2) in the future could increase soil Eh by promoting rice root ROL,which will alter some soil nutrients'availability,such as Fe^(2+)and Mn^(2+).

Analysis of soil moisture variation by forest cover structure in lower western Himalayas, India

Soil moisture affects various hydrological processes, including evapotranspiration, infiltration, and runoff. Forested areas in the lower western Himalaya in India constitute the headwater catchments for many hill streams and have experienced degradation in forest cover due to grazing, deforestation and other human activities. This change in forest cover is likely to alter the soil moisture regime and, consequently, flow regimes in streams. The effect of change in forest cover on soil moisture regimes of this dry region has not been studied through long term field observations. We monitored soil matric potentials in two small watersheds in the lower western Himalaya of India. The watersheds consisted of homogeneous land covers of moderately dense oak forest and moderately degraded mixed oak forest. Observations were recorded at three sites at three depths in each watershed at fortnightly intervals for a period of three years. The soil moisture contents derived from soil potential measurements were analyzed to understand the spatial, temporal and profile variations under the two structures of forest cover. The analysis revealed large variations in soil moisture storage at different sites and depths and also during different seasons in each watershed. Mean soil moisture storage during monsoon, winter and summer seasons was higher under dense forest than under degraded forest. Highest soil moisture content occurred at shallow soil profiles, decreasing with depth in both watersheds. A high positive correlation was found between tree density and soil moisture content. Mean soil moisture content over the entire study period was higher under dense forest than under degraded forest. This indicated a potential for soil water storage under well managed oak forest. Because soil water storage is vital for sustenance of low flows, attention is needed on the management of oak forests in the Himalayan region.

COMPARATIVE STUDY ON DROUGHT RESISTANCE OF LARIX OLGENSIS HENRY AND PINUS SYLVESTRIS VAR.MONGOLICA(Ⅰ)──THE INFLUENCE OF SOIL WATER CONTENT ON SEEDLINGS PLANTING IN FLOWERPOT

Water potential (φ w .) and net photosynthetic rate (Pn) of Larix olgensis and Pinns.sylvestris var. mongolica deercased with the deerease of soil water content φw and Pn of L.olgensis changed hardly during the first 9 davs after stopping watering, then deereased sharply at the 10th dav Pn of P sylvestris var mongolica deereased slightly during the lirst 8 days, then deereased sharply at the 9th day Their respiration rate, chlorophyll content and their a/b ratio changed hardly. The tollowing 3 conclusions were obtained and discussed exhaustively . (Ⅰ) φ w can be used to direct watering as a sensitive index of judging whether L. olgensis and P.sylvestris var. mongolica lacking water (2 )The deereasc of Pn of L. olgensis and P. sylvestris var. mongolica when drought had nothing to do with chlorophyll. (3) P. sylvestris var. mongolica had morphological drought resistance . while L,olgensis had physiological drought resistance, and their drought resistance was discnssed comparatively first time.

SOC storage and potential of grasslands from 2000 to 2012 in central and eastern Inner Mongolia, China

Grassland ecosystem is an important component of the terrestrial carbon cycle system. Clear comprehension of soil organic carbon（SOC） storage and potential of grasslands is very important for the effective management of grassland ecosystems. Grasslands in Inner Mongolia have undergone evident impacts from human activities and natural factors in recent decades. To explore the changes of carbon sequestration capacity of grasslands from 2000 to 2012, we carried out studies on the estimation of SOC storage and potential of grasslands in central and eastern Inner Mongolia, China based on field investigations and MODIS image data. First, we calculated vegetation cover using the dimidiate pixel model based on MODIS-EVI images. Following field investigations of aboveground biomass and plant height, we used a grassland quality evaluation model to get the grassland evaluation index, which is typically used to represent grassland quality. Second, a correlation regression model was established between grassland evaluation index and SOC density. Finally, by this regression model, we calculated the SOC storage and potential of the studied grasslands. Results indicated that SOC storage increased with fluctuations in the study area, and the annual changes varied among different sub-regions. The SOC storage of grasslands in 2012 increased by 0.51×1012 kg C compared to that in 2000. The average carbon sequestration rate was 0.04×1012 kg C/a. The slope of the values of SOC storage showed that SOC storage exhibited an overall increase since 2000, particularly for the grasslands of Hulun Buir city and Xilin Gol League, where the typical grassland type was mainly distributed. Taking the SOC storage under the best grassland quality between 2000 and 2012 as a reference, this study predicted that the SOC potential of grasslands in central and eastern Inner Mongolia in 2012 is 1.38×1012 kg C. This study will contribute to researches on related methods and fundamental database, as well as provide a reference for the protection of grassland ecosystems and the formulation of local policies on sustainable grassland development.

Assessment of pollution of potentially harmful elements in soils surrounding a municipal solid waste incinerator, China

We assessed the contamination levels of Mn, Zn, Cr, Cu, Ni, Pb, As and Hg and the risks posed by these potentially harmful elements in top-soils around a municipal solid waste incinerator （MSWI）. We collected 20 soil samples, with an average pH of 8.1, and another fly ash sample emitted from the MSWI to investigate the concentrations of these elements in soils. We determined the concentrations of these elements by inductively coupled plasma-optical emission spectrometer （ICP-OES）, except for Hg, which we measured by AF-610B atomic fluorescence spectrometer （AFS）. We assessed the risks of these elements through the use of geoaccumulation index （/geo）, potential ecological risk index （R/）, hazard quotient （HQi） and cancer risk （Riski）. The results showed that concentrations of potentially harmful elements in soil were influenced by the wind direction, and the concentrations of most elements were higher in the area northwest of the MSWI, compared with the area southeast of the incinerator, with the exception of As; these results were in accordance with those results acquired from our contour maps. According to the I^o values, some soil samples were clearly polluted by Hg emissions. However, the health risk assessment indicated that the concentrations of Hg and other elements in soil did not pose non-carcinogenic risks to the local populations. This was also the case for the carcinogenic risks posed by As Cr and Ni. The carcinogenic risk posed by As was higher in the range 6.49 × 10 -9.58 × 10 -6, but this was still considered to be an acceptable level of risk.

Water-Saving and High-Yielding Irrigation for Lowland Rice by Controlling Limiting Values of Soil Water Potential

The present study investigated whether an irrigation system could be established to save water and increase grain yield to enhance water productivity by proper water management at the field level in irrigated lowland rice （Oryza sativa L.）. Using two field-grown rice cultivars, two irrigation systems; conventional irrigation and water-saving irrigation, were conducted. In the water-saving irrigation system, limiting values of soil water potential related to specific growth stages were proposed as irrigation indices. Compared with conventional irrigation where drainage was in mid-season and flooded at other times, the water-saving irrigation increased grain yield by 7.4% to 11.3%, reduced irrigation water by 24.5% to 29.2%, and increased water productivity （grain yield per cubic meter of irrigation water） by 43.1% to 50.3%. The water-saving irrigation significantly increased harvest index, improved milling and appearance qualities, elevated zeatin-I-zeaUn riboside concentrations in root bleedings and enhanced activities of sucrose synthase, adenosine diphosphate glucose pyrophosphorylase, starch synthase and starch branching enzyme in grains. Our results indicate that water-saving irrigation by controlling limiting values of soil water potential related to specific growth stages can enhance physiological activities of roots and grains, reduce water input, and increase grain yield.

Variations among rice cultivars on root oxidation and Cd uptake

In order to understand the mechanisms on the variation between rice cultivars in Cd uptake and accumulation, two pot soil experiments were conducted with typical rice cultivars that varied greatly in soil Cd uptake. The experiments with six rice cultivars showed that the root oxidation abilities of rice differed with rice cultivars and also with types of the cultivars, the cultivars with indica consanguinity were significantly higher than the cultivars with japonica consanguinity. Root oxidation abilities of the rice cultivars correlated positively and significantly （P〈0.01） with their Cd concentrations and Cd quantity accumulations in rice plants. The experiments with two rice cultivars showed that significant differences also existed between the two cultivars in pot soil redox potentials, which of Shan you 63 （higher soil Cd accumulator） were significantly higher than that of Wu yun jing 7 （lower soil Cd accumulator） under different soil Cd levels, but the degrees of the differences varied with soil Cd levels. The differences were larger under soil Cd treatments than the control. The results indicate that root oxidation ability, especially in Cd contaminated soil, is one of the main mechanisms which dominate Cd uptake and accumulation by rice plant.

Soil microbial attributes along a chronosequence of Scots pine(Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.

Nature of redox concentrations in a sequence of agriculturally developed acid sulfate soils in Thailand

Potential acid sulfate soils(PASS) are drained for agriculture, resulting in the formation of active acid sulfate soils(AASS), which gradually evolve into post-active acid sulfate soils(PAASS). Various redox concentrations(precipitates, costings, and mottles) occur in these soils as a result of pedogenic processes including biological activity and effects of land management. Although several studies have determined the mineralogy and geochemistry of ASS,the mineralogy and geochemistry of redox concentrations occurring in a sequence of ASS through PASS to PAASS have not been investigated. This study examined the mineralogy and geochemistry of redox concentrations and matrices within 5 PASS, 8 AASS, and 5 PAASS in Thailand. The labile minerals were predominantly controlled by oxidation status and management inputs. The unoxidized layers of PASS, AASS, and PAASS contained pyrite and mackinawite.The oxidation of Fe sulfides caused acidification and accumulation of yellow redox concentrations of jarosite and Fe(hydr)oxides at shallow depths. As the soils became well developed, they were recognized as PAASS, and the jarosite and goethite transformed to hematite. As ASS were drained, Co, Mn, Ni, and Zn moved downward and were associated with Fe sulfides and Mn oxides in the unoxided layer. Concentrations of As, Cu, Cr, Fe, and V did not change with depth because these elements became associated with jarosite and Fe(hydr)oxides in yellow and red redox concentrations, as well as the root zone, in the partly oxidized layer of AASS and PAASS. Arsenic was associated with pyrite under reducing conditions.

Methane emissions from rice fields under continuous straw return in the middle-lower reaches of the Yangtze River

A three-year experiment was conducted in the middle-lower reaches of the Yangtze River in China to study the influence of continuous wheat straw return during the rice season and continuous rice straw return in wheat on methane （CH 4 ） emissions from rice fields in which, the rice-wheat rotation system is the most dominant planting pattern. The field experiment was initiated in October 2009 and has continued since the wheat-growing season of that year. The analyses for the present study were conducted in the second （2011） and third （2012） rice growing seasons. Four treatments, namely, the continuous return of wheat straw and rice straw in every season （WR）, of rice straw but no wheat straw return （R）, of wheat straw but no rice straw return （W） and a control with no straw return （CK）, were laid out in a randomized split-plot design. The total seasonal CH 4 emissions ranged from 107.4 to 491.7 kg/ha （2011） and 160.3 to 909.6 kg/ha （2012）. The increase in CH 4 emissions for treatments WR and W were 289% and 230% in the second year and 185% and 225% in the third year, respectively, in relation to CK. We observed less methane emissions in the treatment R than in CK by 14%-43%, but not statistically significant. Treatment R could increase rice productivity while no more CH 4 emission occurs. The difference in the total CH 4 emissions mainly related to a difference in the methane flux rate during the first 30-35 days after transplant in the rice growing season, which was caused by the amount of dissolved oxygen in paddy water and the amount of reducible soil materials.

Elevated atmospheric CO_(2) reduces CH_(4)and N_(2)O emissions under two contrasting rice cultivars from a subtropical paddy field in China

Elevated CO_(2)(eCO_(2))and rice cultivars can strongly alter CH_(4)and N_(2)O emissions from paddy fields.However,detailed information on how their interaction affects greenhouse gas fluxes in the field is still lacking.In this study,we investigated CH_(4)and N_(2)O emissions and rice growth under two contrasting rice cultivars(the strongly and weakly responsive cultivars)in response to eCO_(2),200μmol mol^(-1)higher than the ambient CO_(2)(aCO_(2)),in Chinese subtropical rice systems relying on a multi-year in-situ free-air CO_(2)enrichment platform from 2016 to 2018.The results showed that compared to aCO_(2),eCO_(2)increased rice yield by 7%-31%,while it decreased seasonal cumulative CH_(4)and N_(2)O emissions by 10%-59%and 33%-70%,respectively,regardless of rice cultivar.The decrease in CH_(4) emissions under eCO_(2)was possibly ascribed to the lower CH_(4)production potential(MPP)and the higher CH_(4)oxidation potential(MOP)correlated with the higher soil redox potential(Eh)and O_(2)concentration([O_(2)])in the surface soil.The mitigating effect of eCO_(2)on N_(2)O emissions was likely associated with the reduction of soil soluble N content.The strongly responsive cultivars had lower CH_(4)and N_(2)O emissions than the weakly re sponsive cultivars,and the main reason might be that the former induced higher soil Eh and[O_(2)]in the surface soil and had larger plant biomass and greater N uptake.The findings indicated that breeding strongly responsive cultivars with the potential for greater rice production and lower greenhouse gas emissions is an effective agricultural practice to ensure food security and environmental sustainability under future climate change scenarios.

中国旱作区土壤有机碳密度三维模拟与固碳潜力估算

Soil organic carbon density(SOCD)and soil organic carbon sequestration potential(SOCP)play an important role in carbon cycle and mitigation of greenhouse gas emissions.However,the majority of studies focused on a two-dimensional scale,especially lacking of field measured data.We employed the interpolation method with gradient plane nodal function(GPNF)and Shepard(SPD)across a range of parameters to simulate SOCD with a 40 cm soil layer depth in a dryland farming region(DFR)of China.The SOCP was estimated using a carbon saturation model.Results demonstrated the GPNF method was proved to be more effective in simulating the spatial distribution of SOCD at the vertical magnification multiple and search point values of 3.0×106 and 25,respectively.The soil organic carbon storage(SOCS)of 40 cm and 20 cm soil layers were estimated as 22.28×10^(11)kg and 13.12×10^(11)kg simulated by GPNF method in DFR.The SOCP was estimated as 0.95×10^(11)kg considered as a carbon sink at the 20–40 cm soil layer.Furthermore,the SOCP was estimated as–2.49×10^(11)kg considered as a carbon source at the 0–20 cm soil layer.This research has important values for the scientific use of soil resources and the mitigation of greenhouse gas emissions.

EVALUATING QUINOA LODGING RISK AND YIELD UNDER DIFFERENT IRRIGATION THRESHOLDS, NITROGEN RATES AND PLANTING DENSITIES IN NORTH-WESTERN CHINA

Lodging is a major yield-limiting factor of quinoa production.In 2018 and 2019,the orthogonal field experiments were conducted to investigate the responses of quinoa lodging risk and yield to irrigation threshold(soil matric potential of−15,−25 and−55 kPa),nitrogen rate(80,160 and 240 kg·ha^(−1))and planting density(20,30 and 40 plants m^(−2)).Results showed that high irrigation thresholds and nitrogen rates significantly(P<0.05)increased plant height and fresh weight per plant,and high planting densities reduced stem diameter and strength,all of those led to significantly(P<0.05)high lodging risks.The−15 and−55 kPa treatments gave the lowest actual yield(P<0.05)in 2018 and 2019,respectively.Higher lodging rate with a nitrogen rate of 240 kg·ha^(−1) resulted in a lower actual yield than 80 and 160 kg·ha^(−1) in both years.Planting density of 30 plants m^(−2) gave a significantly(P<0.05)greater estimated yield than 20 plants m^(−2) and had a lower lodging rate than 40 plants m^(−2),resulting in the maximum actual yield among planting densities.In conclusion,a moderate irrigation threshold of−25 kPa,a nitrogen rate of 80−160 kg·ha^(−1) and an intermediate planting density of 30 plants m−2 were determined to be best for quinoa cultivation in North-western China.In addition,the lower-stem lodging index(quarter plant height)could evaluate lodging risk more accurately than middle-stem(half plant height)or upper-stem(three quarters plant height)lodging indexes.