Fine mapping and causal gene identification of a novel QTL for early flowering by QTL-seq, Target-seq and RNA-seq in spring oilseed rape.

KEY MESSAGE: A novel quantitative trait locus for early flowering in spring oilseed rape, BnaC08cqDTF, was mapped to an 86-kb region on chromosome C08, and its causal gene, CRY2, was uncovered. Days to flowering is a very important agronomic and adaptive trait of Brassica napus oilseed rape (AACC, 2n = 38). We previously identified BnaC08cqDTF as a novel candidate quantitative trait locus (QTL) for early flowering in spring oilseed rape. Here, we present fine mapping of the locus and a study of its causal gene. Initial mapping was performed by QTL sequencing of DNA pools of BC3F2 plants with extreme flowering times derived from crosses between the spring-type cv. No. 4512 (early flowering) and cv. No. 5246 (late flowering), along with fine mapping by target sequencing of the BC3F2 and BC4F2 populations. Fine mapping narrowed down BnaC08cqDTF to an 86-kb region on chromosome C08. The region harbored fifteen genes. After comparative analyses of the DNA sequences for mutation between A and C syntenic regions and detected by RNA-seq and qRT-PCR between the two parents, we found that BnaC08G0010400ZS harbors an A/G nonsynonymous mutation in exon 3. This single nucleotide polymorphism (SNP) haplotype was also correlated with early flowering in a 256 accession panel. BnaC08G0010400ZS is a homolog of the AT1G04400 gene (CRY2) in Arabidopsis. The analyses of transgenic Arabidopsis verified that BnaC08G0010400ZS is responsible for early flowering. Our results contribute to a better understanding of the genetic control mechanism of early flowering in spring Brassica napus and will promote the breeding for early mature varieties.

Fine root production, mortality, and turnover in response to simulated nitrogen deposition in the subtropical Abies georgei (Orr) forest.

Increased nitrogen deposition has important effects on below-ground ecological processes. Fine roots are the most active part of the root system in terms of physiological activity and the main organs for nutrient and water uptake by plants. However, there is still a limited understanding of how nitrogen deposition affects the fine root dynamics in subtropical Abies georgei (Orr) forests. Consequently, a three-year field experiment was conducted to quantify the effects of three forms of nitrogen sources ((NH4)2SO4, NaNO3, and NH4NO3) at four levels (0, 5, 15, and 30 kg N·ha-1·yr-1) on the fine root dynamics in Abies georgei forests using a randomized block-group experimental design and minirhizotron technique. The first year of nitrogen addition did not affect the first-class fine roots (FR1, 0 < diameter < 0.5 mm) and second-class fine roots (FR2, 0.5 < diameter < 1.0 mm). The next two years of nitrogen addition significantly increased the production, mortality, and turnover of FR1 and FR2; the three year of nitrogen addition did not affect the dynamics of the third- class fine roots (FR3, 1.0 < diameter < 1.5 mm) and fourth- class fine roots (FR4,1.5 < diameter < 2.0 mm). Nitrogen addition positively affected the dynamics of FR1, FR2, FR3 and FR4 by positively affecting the carbon, nitrogen, and phosphorus contents of fine roots and indirectly affecting the soil pH. Increased carbon allocation to FR1 and FR2 may represent a phosphorus acquisition strategy when nitrogen is not the limiting factor. The nitrogen addition forms and levels affected the fine root dynamics in the following orde: NH4NO3 > (NH4)2SO4 > NaNO3 and high nitrogen > medium nitrogen > low nitrogen. The results suggest that the different-diameter fine root dynamics respond differently to different nitrogen addition forms and levels, and linking the different-diameter fine roots to nitrogen deposition is crucial.

Heavy metal(loid)s in agriculture soils, rice, and wheat across China: Status assessment and spatiotemporal analysis.

Heavy metal(loid)s (HMs) accumulation in agricultural soils, rice, and wheat is of particular concern in China, while the status and spatio-temporal distribution of HMs in the soil-crops system have been rarely reported at the national scale. This study aimed to summarize the overall pollution status, spatiotemporal patterns, and drivers of HMs in agricultural soil, rice, and wheat nationwide. The metal-polluted data from 1030 agricultural soils, rice, and wheat in China were collected from the literature published from 2000 to 2022. The results showed that Cd was the most prevailing contaminant in soils based on its spatiotemporal distribution and accumulation. The pollution cases and severe pollution percentage of Cd (103 %) and Hg (128 %) show an increasing trend pattern. Mining activities are the main anthropogenic sources of agricultural soil HMs in China. Cd and Pb had the highest exceedance rate in rice (33.5 and 32.2 %) and wheat (25.8 and 30.3 %). The rice from Hunan, Fujian, and Guangxi showed the highest average concentration of Cd and Pb, respectively, while wheat samples from Hubei had the greatest exceedance rate of Pb. Besides, HMs in crops was not usually corresponding to soil HMs but increased gradually from north to south areas. Several mitigation strategies and accurate health risk assessments model of HMs based on bioavailability were also proposed and recommended. Collectively, this review provides valuable information to improve the management of farmland nationwide, optimize the accurate risk assessment, and reduce HMs pollution.

Genetic characterization and fine mapping of a yellow-seeded gene in Dahuang (a Brassica rapa landrace).

The development of yellow-seeded cultivars in Brassica rapa (B. rapa) would improve the quality and quantity of available oil. The identification and mapping of the seed coat color gene may aid in the development of yellow-seeded cultivars and facilitate introgression of the yellow-seeded gene into desirable Brassica napus (B. napus) lines through marker-assisted selection. In the current study, we investigated the inheritance of a yellow-seeded landrace in B. rapa, "Dahuang", originating from the Qinghai-Tibetan plateau. Genetic analysis revealed that the phenotype of the yellow-seeded trait in Dahuang is controlled by one recessive gene, termed Brsc1. Mapping of the Brsc1 gene was subsequently conducted in a BC(1) population comprised 456 individuals, derived from (Dahuang × 09A-126) × Dahuang. From a survey of 256 amplified fragment length polymorphism (AFLP) primer combinations, 10 tightly linked AFLP markers were obtained. The closest AFLP markers flanking Brsc1, Y10 and Y06, were 0.2 and 0.4 cM away, respectively. Subsequently, using simple sequence repeat (SSR) markers in the reference map, the Brsc1 gene was mapped on A09 in B. rapa. Blast analysis revealed that seven AFLP markers showed sequence homology to A09 of B. rapa, wherein six AFLP markers in our map were in the same order as those in A09 of B. rapa. The two closest markers, Y10 and Y06, delimited the Brsc1 gene within a 2.8 Mb interval. Furthermore, Y05 and Y06, the two closest AFLP markers on one side linked to Brsc1, were located in scaffold000059 on A09 of B. rapa, whereas the closet AFLP marker on the opposite side of Brsc1, Y10, was located in scaffold000081 on A09 of B. rapa. Molecular markers developed from these studies may facilitate marker-assisted selection (MAS) of yellow-seeded lines in B. rapa and B. napus and expedite the process of map-based cloning of Brsc1.

Plant interactions control the carbon distribution of Dodonaea viscosa in karst regions.

Biomass and carbon (C) distribution are suggested as strategies of plant responses to resource stress. Understanding the distribution patterns of biomass and C is the key to vegetation restoration in fragile ecosystems, however, there is limited understanding of the intraspecific biomass and C distributions of shrubs resulting from plant interactions in karst areas. In this study, three vegetation restoration types, a Dodonaea viscosa monoculture (DM), a Eucalyptus maideni and D. viscosa mixed-species plantation (EDP) and a Pinus massoniana and D. viscosa mixed-species plantation (PDP), were selected to determine the effects of plant interactions on the variations in the C distributions of D. viscosa among the three vegetation restoration types following 7 years of restoration. The results showed that: (1) plant interactions decreased the leaf biomass fraction. The interaction of P. massoniana and D. viscosa decreased the branch biomass fraction and increased the stem and root biomass fraction, but not the interaction of E. maideni and D. viscosa. Plant interactions changed the C concentrations of stems and roots rather than those of leaves and branches. (2) Plant interactions affected the soil nutrients and forest characteristics significantly. Meanwhile, the biomass distribution was affected by soil total nitrogen, clumping index and gap fraction; the C concentrations were influenced by the leaf area index and soil total phosphorus. (3) The C storage proportions of all the components correlated significantly with the proportion of biomass. Our results suggested that both the biomass distribution and C concentration of D. viscosa were affected by plant interactions, however, the biomass fraction not the C concentration determines the C storage fraction characteristics for D. viscosa.

The impacts of flowering phenology on the reproductive success of the narrow endemic Nouelia insignis Franch. (Asteraceae).

Nouelia insignis Franch. (Asteraceae) is a short, narrow endemic and endangered tree, growing with a natural population in the dry and hot valley of the Jinsha River in the southwest area of China. In this work, flowering phenology (time and duration), floral biology, visit frequency and behavior of pollinators, and pollination characteristics were studied based on investigation in the field and analysis in the laboratory with the help of a stereomicroscope, and the relationship between seed setting rate and reproductive traits, as well as the relationship between flowering time and rainfall before flowering, was tested using the method of general linear regression model. The results showed that natural population of N. insignis exhibited high flowering synchrony with relatively stable flowering duration, and the flowering time fluctuated greatly depending on the rainfall 5 months before flowering. The pollination of N. insignis required pollinators, and insect activities played a very important role in the pollination process. However, lack of the pollinators was not a limitation for reproductive fitness in N. insignis, although the number of pollinators was small and the frequency of visits was low. In addition, no pollen limitation was found during pollination. The average seed setting rate of N. insignis in the natural condition was only 1.52%-3.73%, and it was generally affected by changes in flowering phenology between years and had a higher seed set in early flowering year. The annual variation of seed set might be related to the annual variations of stamen and pistil functions, such as changes of pollen viability and stigma receptivity, which were closely related to flowering time. The results of this study are of value for further conservation actions on natural population of this threatened endemic plant.

[Short-term Mechanism of Warming-induced Stability for Organic Carbon in the Karst Plateau Soil].

Elucidating the mechanisms of warming-induced stability for soil organic C is one of the keys for evaluating the tendency of soil C sources/sinks in projected global warming models. Organic C densities in soil, and soil physical and biochemical fractions, under different warming scenarios in the Karst Plateau were investigated following a 4-yr continuous warming using infrared radiators, via density fractionation and acid hydrolysis. Six treatments were arranged: no warming (ambient temp, CK); symmetric warming (ambient+2.0℃ full year); and lowly, moderately, highly, and extremely asymmetric warming (ambient+2.5℃/1.5℃, 3.0℃/1.0℃, 3.5℃/0.5℃, and 4.0℃/0℃ in winter-spring/summer-autumn seasons, respectively; LAW, MAW, HAW, and EAW). The moderately asymmetric warming was highly similar to a multi-year warming scenario in the study region. The results showed there were no significant differences in soil organic C densities in the surface layer (0-15 cm) among the warming treatments, with a range of 1.95 kg·m-2 to 2.02 kg·m-2, which is insignificantly different to the CK (1.94 kg·m-2). There were no significant differences in the C density of light and heavy fractions, and the recalcitrant heavy-fraction among the warming treatments, and between the warming and no warming treatments. The average recalcitrant C density of the light fraction in the warming treatments was 1.18 times higher than the CK, with a significantly higher recalcitrant C density of the light fraction in the symmetric warming, and lowly and moderately asymmetric warming treatments, compared to that of the CK. The recalcitrant C density and recalcitrant C index of the light fraction showed a tendency to decrease as the asymmetry of warming increased under the five warming scenarios. Warming had negligible effects on the organic C density in soil, and soil physical and biochemical fractions in the subsurface layer (15-30 cm). The results revealed that in the short-term, warming may increase the recalcitrance of non-protected C in the Karst Plateau soil. This is not necessarily an over- or underestimation of the effects of global warming on soil organic C density and the capacity of soil to protect C when subjected to symmetric warming, but may potentially overestimate the recalcitrance of organic C in the non-protected fraction of the surface layer (0-15 cm).

[Effects of Seasonal Asymmetric Warming on Soil CO2 Release in Karst Region].

Seasonal asymmetric warming is one of the distinguishing features of global warming. However, if this feature is not considered in studying the effects of global changes on terrestrial ecosystems, it might probably cause misunderstanding of these studies. The releasing features of soil CO2 in Karst regions under various warming scenarios were simulated following a four-year continuous warming period using infrared radiators. A total of six treatments was arranged:no warming (ambient temp, CK); symmetric warming (ambient plus 2.0℃ full year, SW); and, lowly, moderately, highly, and extremely asymmetric warming (ambient plus 2.5℃/1.5℃, 3.0℃/1.0℃, 3.5℃/0.5℃, and 4.0℃/0℃ in the winter-spring/summer-autumn seasons, respectively, LAW, MAW, HAW, and EAW). The results showed that compared to CK, soil CO2 efflux in all the warming plots significantly increased by 0.26 µmol·(m2·s)-1, or 17.41%. In the winter-spring seasons, soil CO2 efflux in the warming treatments increased by 0.23 µmol·(m2·s)-1. The Q10 values ranged from 1.53 to 3.24 with an average of 2.23 under the scenario of warming up by 2.0℃. The warming-induced contribution of CO2 efflux in the summer-autumn seasons (80%) was obviously higher than that in the winter-spring seasons (20%) in the SW treatment, whereas the mean contribution in the summer-autumn seasons (46%) was closer to that in the winter-spring seasons (54%) in the asymmetric warming treatments. Both soil CO2 efflux and Q10 showed a tendency towards decrease with the increase in the asymmetry of warming under the five warming scenarios. The soil CO2 efflux in the SW treatment was significantly (P<0.05) higher than those in the MAW, HAW, and EAW treatments. The Q10 values in the summer-autumn seasons was larger than those in the winter-spring seasons under each warming treatment or across all warming treatments, which was probably related to soil water content, soil microbe, dissolved inorganic carbon, and vegetation growth. The results revealed that it may potentially overestimate the effects of global warming on soil CO2 releasing subject to symmetric warming.

[Nutrient accumulation and cycling in pure and mixed plantations of Azadirachta indica and Acacia auriculiformis in a dry-hot valley, Yunnan Province, southwest China].

To ease the implementation of effective nutrient management for plantations with different vegetation restoration patterns and to assist in the selection of appropriate species and forestation patterns, nutrient (N, P, K, Ca and Mg) accumulation and cycling were investigated and compared in three plantations (10-year-old Azadirachta indica, Acacia auriculiformis and mixed A. indica--A. auriculiformis plantations) in Yuanmou Valley, a dry-hot valley of Yunnan Province, Southwestern China. The result showed that total nutrient accumulations were 333.05, 725.61 and 533.85 kg x hm(-2) in pure plantations of A. indica and A. auriculiformis, and in A. indica--A. auriculiformis mixed plantation, respectively. The nutrient accumulation of various organs was ranked as branches > stems > roots > leaves > bark in the A. indica plantation and branches > stems > leaves > roots > bark both in the A. auriculiformis plantation and in the mixed plantation. Changes in accumulation of various nutrients in the mixed plantation were similar to that in the A. auriculiformis plantation (Ca > N > K > Mg > P), which were different from the A. indica plantation (Ca > K > N > Mg > P). Annual net nutrient accumulation, return and absorption in these plantations ranged from 62.72 to 162.19 kg x hm(-2) x a(-1), 48.82 to 88.86 kg x hm-2 a-1 and 111.54 to 251.05 kg x hm(-2) x a(-1), respectively, which were all the highest in the A. auriculiformis planta- tion, followed by the mixed plantation, and were the lowest in the A. indica plantation. The nutrient utilization coefficient, the cycling coefficient and the recycling period were estimated to be from 0.34 to 0.39, 0.35 to 0.44, and 6.54 to 8.17 a, respectively. The lower nutrient return and circulation rate of N or P in the A. indica plantation showed that this plantation had a poor ability to maintain soil fertility, while the highest nutrient circulation rate of N or P was observed in the A. auriculiformis plantation that displayed the advantage in maintaining soil nutrients and stand productivity. The nutrient return and nutrient absorption in the mixed plantation were 167.2% and 186.2%, of those in the A. indica plantation, and the circulation rate of N, P and K were higher than those in the A. indica plantation, while the recycling period of Ca in mixed plantation was 50% shorter than that in A. auriculiformis plantation. Soil fertility and nutrient supply were improved in the A. indica and A. auriculiformis mixed plantation.

[Relationship between changes of herbaceous plants and Oncomelania hupensis snail distribution under walnut forest of inhibition of snails in mountainous regions of Yunnan Province].

OBJECTIVE: To explore the relationship between the changes of herbaceous plants and Oncomelania hupensis snail distribution under the walnut forest of inhibition of snails in mountainous regions of Yunnan Province. METHODS: The experimental field was established at Sanying Village of Eryuan County, Yunnan Province, where the "Flourishing Forest and Controlling Snails Project" was implemented. The different stand ages (2, 4, 6, 8, 10 years)of walnut forest in experimental groups were selected based on the method of space replacing time, and the non-stocked land was served as a control group. The growth of forest, change of snails, number, biomass, overcast, height of the herbaceous plant and the soil moisture were investigated. RESULTS: The crown closure of 6-year-old walnut forest of inhibition of snails was 0.65. There were 11 species of herbaceous plant belonging to 11 genera, 6 families in 10-year-old forest and its crown closure was 0.77. Compared with the control group, the numbers of families, genera, and species of the 10-year-old forest were decreased by 64.71%, 69.44%, and 77.08%, and the biomass, overcast, and height of it decreased by 12.63%, 19%, and 22.18%, respectively. The soil moisture content (0-20 cm) monthly changes were increased obviously with the increase of stand age. There were no snails besides the control group and 2-year-old walnut forest. Compare with the control group, the occurrence rate of frames with living snails in the 2-year-old walnut forest was decreased by 50%, which was 1.25%. The density of living snails was decreased by 60.16%. CONCLUSIONS: The construction of walnut forest of inhibition of snails in mountainous regions of Yunnan Province are suitable for controlling the growth of herbaceous plants and altering the environment of snails. If the coalescence intercropped with crops is carried out, it is not only beneficial to the construction of good ecological environment, but also improves the utilization efficiencies of land, light, and thermal resource, and the income of peasants.

[Vegetation biomass allocation and its spatial distribution after 20 years ecological restoration in a dry-hot valley in Yuanmou, Yunnan Province of Southwest China].

By using layering harvest method, a comparative study was conducted on the biomass allocation and its spatial distribution of 20-year-old Eucalyptus camaldulensis plantation, Leucaena leucocephala plantation, and E. camaldulensis-L. leucocephala plantation in Yuanmou dry-hot valley of Yunnan Province, Southwest China. The stand biomass in the mixed E. camaldulensis-L. leucocephala plantation (82.99 t x hm(-2)) was between that of monoculture E. camaldulensis plantation (60.64 t x hm(-2)) and L. leucocephala plantation (127.79 t x hm(-2)). The individual tree biomass of E. camaldulensis in the mixed plantation (44.32 kg) was 49.8% higher than that in monoculture plantation (29.58 kg). The branch and leaf biomass of L. leucocephala (25.4%) in monoculture plantation was larger than that of E. camaldulensis (8.9%) in monoculture plantation, and the aboveground biomass distribution ratio (78.0%) of L. leucocephala (25.4%) was also higher than that of E. camaldulensis (73.4%). The roots of L. leucocephala in both monoculture and mixed plantations were mainly distributed in 0-40 cm soil layer, while those of E. camaldulensis in monoculture and mixed plantations were mainly found in 0-80 cm and 0-60 cm, respectively. The proportion of biomass allocated to roots including medium roots, small roots, and fine roots of L. leucocephala in mixed plantation was higher than that in monoculture plantation, but it was contrary for E. camaldulensis. It was suggested that introducing L. leucocephala in E. camaldulensis plantation promoted the growth of E. camaldulensis, especially for its aboveground biomass, and increased the amount of lateral roots in 0-20 cm soil layer, which had significance in soil and water conservation in the study area.

[Effect of agroforestry model on inhibition of Oncomelania snails in plateau mountainous area of Yunnan Province].

OBJECTIVE: To evaluate the effect of agroforestry models on the inhibition of Oncomelania snails in the plateau mountainous area of Yunnan Province. METHODS: The experimental field was established at Sanying Village of Eryuan County, Yunnan Province, where the "Flourishing Forest and Controlling Snails Project" was implemented. Different drought crops (alfalfa, vegetables, broad bean, garlic, lettuce, celery, green onions, and wheat) were intercropped under walnut forest in experimental groups, and the crops were not intercropped under walnut forest in a control group. The growth of forest, the change of snails and short-term income of residents were investigated. RESULTS: Agroforestry models promoted the forestry growth and effectively inhibited the growth of snails. There was a little snail in one of the experimental group that forest was intercropped with alfalfa (the occurrence rate of frames with living snails was 3.33%, the average density of living snails was 0.004/0.1 m2, and the declining rates were both 50.00%). The snails were not found in other intercropped models. The income of residents in the experimental groups increased (900-6 800 Yuan per year) compared with that in the control group. CONCLUSION: The model of walnut forest intercropped with crops not only has the obvious effect on inhibition of snails, but also has good economic and ecological benefits in the plateau mountainous area of Yunnan Province.

[Characteristics of carbon sequestration and apparent stability of new sequestered carbon in forested torrid red soil at dry-hot valley].

Great concerns about potential for carbon (C) sequestration in forested soil and the stability of the sequestered C have been exerted under the background of global climate change. Organic C density in soil and in soil physical and biochemical fractions at various stages (1991, 1997, 2003 and 2010) in Acacia auriculiformis stand afforested in 1991 were investigated at Dry-Hot Valley via density fractionation and acid hydrolysis. The results showed that organic C density at surface (0-15 cm) and subsurface (15-30 cm) soil layers was 1.40 kg x m(-2) and 0.99 kg x m(-2) after 19 years of afforestation, respectively. The annual C sequestration rates of surface and subsurface soil layers were 37.89 g x (m2 x a)(-1) and 16.84 g x (m2 x a)(-1) during 1991-2010, respectively, and the sequestration was accelerating. The ratio of organic C in heavy fraction to in surface soil was 71.44% in 2003, which was significantly higher than that in 2010 (67.99%). The recalcitrant carbon index (I(RC)) in light fraction was significantly higher than that in heavy fraction at surface or subsurface layers in 2003, but both decreased with aging of plantation, especially I(RC) in light fraction. Approximately 57% - 70% of new sequestered C was protected by physical mechanism and 33-49 percent was biochemical recalcitrant C during the stage from 12 to 19 years after afforestation. The results reveal that forested torrid red soil at Dry-Hot Valley may have a considerable capability of C sequestration. The biochemical stability of physically protected C is lower than the unprotected. Both the stability, however, decreases with the plantation age.

[Distribution of oncomelania hupensis snails and effect of plantations on snail control under different land uses at a gentle hilly region].

OBJECTIVE: To provide better afforestation/forestation patterns for snail (Oncomelania hupensis) control in gentle hilly region in China. METHODS: The snails were investigated and the effects of afforestation on snail community were analyzed at the plots with or without snail-controlling forest. RESULTS: The community of snails exhibited a middling variation at the area without snail-controlling forest (control area), where the living snail frame occurrence (LSFO) and mean snail density (MSD) were 26.81% and 0.940 snails per 0.1 m2, respectively. There were significant differences in LSFO (F = 11.29, P < 0.01) or MSD (F = 12.71, P < 0.01) among the eight land use types at control area. Higher snail numbers occurred in lowland, paddy field and paddy-upland rotation land, whereas the lower were in dry-farming land and plantation. After 5 years of plantation, LSFO and MSD reduced by 62.70%-89.98% and 74.03%-94.00% under 5 land use types, respectively. LSFO and MSD reduced by 52.04%-87.36% and 52.20%-95.45%, respectively at the demonstration area compared with those at control area. CONCLUSION: Afforestation/forestation would effectively reduce snail community irrespectively of land uses at gentle hilly region in plateau.

[Soil labile organic carbon contents and their allocation characteristics under different land uses at dry-hot valley].

Soil organic carbon (SOC), readily oxidation organic carbon (ROC), microbial biomass carbon (MBC)and dissolved organic carbon (DOC) contents and their allocation ratios were comparatively investigated under Leucaena leucocephala woodland, Acacia auriculiformis woodland, dry cropland and wasteland in dry-hot valley. Results showed that SOC contents were not significant differences among the four land uses with the range of 4.22-5.19 g x kg(-1). ROC contents under L. leucocephala (2.14 g x kg(-1)) and A. auriculiformis woodland (2.03 g x kg(-1)) were both significantly higher than those under dry cropland (1.38 g x kg(-1)) and wasteland (1.34 g x kg(-1)). The highest MBC and DOC contents both presented under dry cropland among the four land uses, whereas the lowest occurred under wasteland. ROC allocation ratios under woodlands were 1.3 to 1.6 times to those under dry cropland and wasteland. MBC and DOC allocation ratios under cropland were higher than those under other three land uses, and the ratios were closely among woodlands and wasteland. Plant residue amounts and management were primarily determined ROC contents, and soil water content and plant residue quantity were mainly affected the variation of MBC and DOC contents under the four land uses. The change of ROC contents could sensitively indicate SOC dynamics in dry-hot valley, but the change of MBC or DOC could not.

TG-FTIR study on co-pyrolysis of municipal solid waste with biomass.

Co-pyrolysis of cotton stalk, a representative agricultural biomass in China, mixed with municipal solid waste (MSW) with high ash content and low calorific value was carried out using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer in Ar atmosphere. Pyrolysis characteristic and pollutant emission performance from MSW and stalk blends at different mass proportions were studied. The results show that as the mass proportion of stalk added increases, the total weight loss of the blend during pyrolysis increases. The addition of stalk has substantial effects on the N-selectivity to HCN, NH(3) and HNCO. In the presence of stalk, lower concentrations of HCl are detected.

[Effects of soil texture and water content on the mineralization of soil organic carbon in paddy soils].

To understand how soil texture and water content affect the mineralization of organic C in paddy soil, 3 selected soils (sandy loam, clay loam, and silty clay) were incubated (25 degrees C) with 14 C-labelled rice straw (1.0 g x kg(-1)) at water content varied from 45% to 105% of water holding capacity (WHC). Data indicated that, in the sandy loam and clay loam, the mineralization rate of 14 C-labelled rice straw reached the maximum at 75% WHC, as 53% and 58% of the straw C mineralized in the incubation period of 160 d, whereas in the silty clay, it increased gradually (from 41.8% to 49.0%) as water content increased up to 105% WHC. For all of the three soils, the mineralization rate of soil native organic C reached the maximum at 75% WHC, with 5.8% of the organic C mineralized in the same period for the sandy loam, and 8.0% and 4.8% for the clay loam and silty clay, respectively. As water content increased further, the mineralization rate of native organic C in the three soils significantly declined. The mineralization rate of added rice straw and native organic C in all the three soils, was well fitted with a conic curve. These results suggest that water-logging can decrease the mineralization of organic C in paddy soils.

[Content and density characteristics of soil organic carbon in typical landscapes of subtropical region].

The contrasts of the content and density characteristics of surface soil organic carbon among four typical landscapes of subtropical region in China were investigated. The results show that the area-weighted mean content of SOC varies widely with landscapes and the highest mean content is present in the lacustrine plain landscape (25.10 g x kg(-1)), followed by the karst landscape (20.84 g x kg(-1)) and mountainous landscape (17.75 g x kg(-1)), whereas the lowest occurs in the hilly red soil landscape (12.07 g x kg(-1)). The coefficient of variation of SOC content ranges from 24.06% to 43.76%, being moderate variation. The main distribution ranges of SOC content are higher than 20 g x kg(-1) in the lacustrine plain landscape and lower than 20 g x kg(-1) in the other three landscapes. The sequence of SOC density in the four landscapes is highly consistent with the sequence of SOC content, and the sequence is as follows: lacustrine plain landscape (6.12 kg x m(-2) > karst landscape (4.30 kg x m(-2)) > mountainous landscape (4.25 kg x m(-2)) > hilly red soil landscape (3.04 kg x m(-2)). The results reveal that the difference of soil parent material, cultivation strength, topography and proportion of land use may be the main reasons caused the variation of SOC content among the four landscapes. Surface soils in typical landscapes of subtropical region are important carbon pool in China.

[Evolvement characteristics and coupling relationship of soil organic carbon and total nitrogen in subtropical paddy field ecosystem under different fertilization practices].

Soil samples were collected from long-term monitoring plots of paddy field ecosystem in Hunan Province to study the evolvement characteristics and coupling relationship of soil organic carbon and total nitrogen under different fertilization practices. The results showed that in 1986-2003, the contents of soil organic carbon and total nitrogen had a slight decrease under no fertilization (CK), basically remained stable under chemical fertilization (NPK), and increased under the combined application of organic manure and chemical fertilizers. Compared with those in CK, the contents of soil organic carbon and total nitrogen in treatments NPK, low application rate organic manure, and high application rate organic manure were increased by 13% and 18%, 54% and 45%, and 89% and 67% respectively. There was a significant positive correlation (P < 0.01) between soil organic carbon and total nitrogen. The soil C/N was around 10, with the majority ranged from 8.5 to 12.9. It was suggested that a combined application of organic manure and chemical fertilizers on paddy field could increase the sequestration and accumulation of soil carbon and nitrogen to a certain extent, and there existed a better coupling relationship between soil organic carbon and total nitrogen in paddy field ecosystem.

[Effects of temperature on organic carbon mineralization in paddy soils with different clay content].

An incubation test with three kinds of paddy soil (sandy loam, clay loam, and silty clay soils) in subtropical region was conducted at 10, 15, 20, 25 and 30 degrees C to examine the response of the mineralization of soil organic carbon (SOC) to temperature change. The results showed that during the period of 160 d incubation, the accumulative mineralized amount of SOC in sandy loam, clay loam, and silty clay soils at 30 degrees C was 3.5, 5.2 and 4.7 times as much as that at 10 degrees C, respectively. The mineralization rate was lower and relatively stable at lower temperatures (< or = 20 C), but was higher at the beginning of incubation and decreased and became stable as the time prolonged at higher temperatures (> or = 25 degrees C). During incubation, the temperature coefficient (Q10) of SOC mineralization in test soils fluctuated, with an average Q10 in sandy loam, clay loam, and silty clay soils being 1.92, 2.37 and 2.32, respectively. There was a positive exponential correlation between SOC mineralization constant k and temperature (P < 0.01), and the response of SOC mineralization to temperature change was in the order of clay loam soil > silty clay soil > sandy loam soil.