Search

Hazel (Corylus avellana) is easily attacked by Curculio nucum L. To better understand the physiological mechanisms underlying the different resistance of cultivars to C. nucum, we determined the insect-resistant compounds, plant hormones contents, and enzyme activities in the nutshells of three hazel cultivars (DW, B21, and MZ) before (preexisting defense) and after (induced defense) C. nucum chewing. The findings demonstrated that the resistance of three hazel cultivars to C. nucum differed significantly (p < 0.05): the damage rate of MZ with 17.57% was highest, followed by DW (11.23%), and then B21 (7.15%). The contents of insect-resistant compounds (total terpenoid, tannin, total phenol, flavonoids, cellulose, and lignin) varied with hazel cultivars, both before and after C. nucum chewing, except for cellulose and lignin before induction. The level of plant hormones and defense enzyme activities of hazelnut enhanced due to C. nucum induction. Pearson correlation results revealed that the hazelnut damage rate was significantly negatively correlated with jasmonic acid (JA) (R2 = 0.812), SOD (R2 = 0.671), salicylic acid (SA) (R2 = 0.878), and terpenoids (R2 = 0.774), and significantly positively correlated with flavonoids (R2 = 0.696), celluloses (R2 = 0.501), POD (R2 = 0.758), and abscisic acid (ABA) (R2 = 0.978). The hazelnut defense to C. nucum was negatively related to cellulose contents, and not to lignin contents, but was significantly positively related to the ratio of cellulose-to-lignin (R2 = 0.703). Our results suggested that the hazel against C. nucum attack responded by improving plant hormones contents and enzyme activities in the nutshells. A particular cellulose-to-lignin ratio provides the most effective physical structural defense properties in the nutshells.

Conservation tillage has become the core technology to conquer the degradation of black soil, the ‘giant panda in arable land’. Since soil is a home to a variety of organisms, it is very important to regard soil as a living system to evaluate the impact of conservation tillage on the health of black soil. Therefore, based on the long-term conservation tillage trial established by the Key Laboratory of Mollisols Agroecology of the Chinese Academy of Sciences, the responses of soil biodiversity and its function to conservation tillage were comprehensively elucidated in this study. Compared with conventional tillage, conservation tillage strongly improved the species richness (1-8%), density (25-57%), and biomass (30-50%) of the entire soil assemblages, including microorganisms, nematodes, collembolans, mites and earthworms, as well as the connectance of soil food web (14-32%). Furthermore, conservation tillage promotes the performance of soil biotic function in soil structure formation, soil carbon sequestration and nitrogen efficient utilization and crop yield stability. These results suggest that conservation tillage can effectively utilize the functional potential of soil organisms, which is of great significance to supporting the healthy and sustainable development of agriculture in the black soil region of northeast China.

The incorporation of earthworms and straw into cropland soil can greatly affect soil structure and soil organic C (SOC) dynamics. However, information regarding how earthworms affect both carbon (C) in its transition from residue into soil and SOC turnover under conventional tillage (CT) and conservation tillage is limited, and some results are even contradictory. Moreover, most of studies were conducted out based on sieved soil samples. In this study, intact soil samples were used to analyze the effects of earthworms (Eisenia foetida) and both of earthworms and straw addition on SOC fractions and soil CO2 emission in a 30-day incubation experiment with CT and no tillage (NT) treatments. The results showed that CT accelerated the straw decomposition and increased the content of soil active C. In contrast, NT resulted in slower decomposition of the original straw and reduction of the total amount of SOC and soil active C. The earthworms could inhibit the straw from decomposing in CT and stimulate the decomposition of straw in NT. Whatever in NT or CT, earthworms did not affect soil CO2 emission, but straw addition significantly increased soil CO2 emission. The results of this study provide the selection of the appropriate tillage practice as well as the amount of returned straw to fertilize the soil.

Earthworm casts have been recognized as contributing to long-term carbon protection, but few studies have focused on the mechanism by which this is achieved. Most of the literature documenting earthworm casts revolves around the difference between the earthworm cast and natural soil, whereas little attention has been given to deciphering the effects of different tillage systems on earthworm casts. Further, whether or not an earthworm cast, like soil, affects its own organic carbon content through physical structure stability is still somewhat vague, and very little is known. The objective for this study was to determine the effect of tillage on organic carbon and physical structure stability parameters in earthworm casts. Undisturbed soil columns were collected from a 17-year tillage experiment including no tillage (NT), ridge tillage (RT) and mouldboard ploughing (MP) in Northeast China. Each column was seeded with ten earthworms (Eisenia foetida), incubated at 18 °C for 120 days and casts were collected and analysed. Both NT and RT led to significantly greater organic carbon (20.5% and 14.4%), total pore volume (54.6% and 75.6%), total pore area (45.4% and 60.4%), permeability (21.8% and 66.4%), fluid conductivity (26.2% and 31.1%), tensile strength (34.1% and 51.2%) and water resistance index (16.7% and 22.3%) in the casts compared to MP (P

Adaptation of fine root plasticity to soil nutrients heterogeneity in natural forest ecosystems has not been well explored. The study aimed to determine seasonal variations of fine root traits in Pinus koraiensis natural forests and explore the relationship between fine root traits and soil properties. Root and soil samples were collected from the coniferous broad-leaved mixed forest (BP), monospecific P. koraiensis forest (MP), and coniferous mixed forest (CP). Soil available phosphorus (P) content for MP was 31.7% and 39.8% lower than for BP and CP. Soil cation exchange capacity (CEC) for MP was lower by 23.5% and 27.2% than for BP and CP, respectively. In July, specific root lengths and root surface areas for BP and CP (mixed forests) were significantly higher than for MP (monospecific forest). A structural equation model showed that CEC had a significant effect on fine root traits. Root diameter, root volume density, and root surface area density were negatively correlated with CEC. Fine root traits plasticity of P. koraiensis are closely related to soil available nutrient contents, CEC, and species composition at the ecosystem level.

Fertilization influences the soil microbiome. However, little is known about the effects of long-term fertilization on soil microbial metabolic pathways. In this study, we investigated the soil microbiome composition and function and microbial participation in the N cycle according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO) functional annotation of different genes in a metagenomic analysis after long-term fertilization. Fertilizer application significantly changed the soil C/N ratio. Chemical fertilizer (NPK) treatment decreased soil pH, and chemical fertilizer combined with straw (NPK+S0.5) treatment increased ammonium nitrogen (NH4+-N) but decreased nitrate nitrogen (NO3&minus, N). NPK, NPK+S0.5 and S0.5 applications did not change the soil microbiome composition or dominant phylum but changed the relative abundances of microbiome components. Moreover, fertilizer significantly influenced metabolic processes, cellular processes and single-organism processes. Compared with a no-fertilizer treatment (CK), the NPK treatment resulted in more differentially expressed gene (DEG) pathways than the NPK+S0.5 and S0.5 treatments, and these pathways significantly correlated with soil nitrate nitrogen (NO3&minus, N), available phosphorus (AP) and the moisture content of soil (MC). KEGG analysis found that fertilizer application mainly affected the ribosome, photosynthesis and oxidative phosphorylation pathways. S0.5 and NPK+S0.5 increased microbial nitrogen fixation, and NPK and NPK+S0.5 decreased amoA and amoB and accelerated denitrification. Thus, organic fertilizer increased N fixation and nitrification, and inorganic N fertilizer accelerated denitrification. We found that the function of the soil microbiome under different fertilizer applications could be important for the rational application of fertilizer and for environmental and sustainable development.

Limitations of traditional measurement methods have impeded progress in understanding the role of soil aggregation in protecting soil organic carbon (SOC) from decomposition by soil microbes living in pore spaces. In this paper, we used the Scanning Electronic Microscope (SEM) and X-ray micro Computed Tomography (micro-CT) to study the relationships of the aggregate pore structure and microbial distribution in the interior and exterior of soil aggregates, and thereby gained an insight into protection of carbon within macroaggregates of an undisturbed Mollisol in northeastern China. There were close relationships between soil pore structure and distribution of soil microbes and soil organic carbon (SOC), but they were different on the exterior and interior of soil aggregate. On the exterior of macroaggregates, there were negative relationships between soil porosities, the number of pores and SOC, especially for soil pores in the 10–30 μm and 30–100 μm classes, indicating these two pore sizes are unlikely to help sequester C. In contrast, there was a positive correlation between soil pores > 100 μm and SOC. Furthermore, soil pore structure had no impact on soil microbial biomass and density or on SOC contents in the interior of soil aggregates. This study provides a new method by combining SEM with micro-CT technology for linking soil structure and soil microbial properties with C sequestration and SOC changes.

Soil erosion is a complex process which causes loss of soil mineral material together with soil organic carbon (SOC). Little is known about the impact of soil water erosion on catchment exports of soil aggregates and associated SOC, especially at a small agricultural catchment. SOC delivered from a small catchment located in Northeast China was assessed for three erosive rainfall events in 2011. The quantity and size of the exported soil aggregates and their concentration of SOC were assessed along with runoff rate, sediment loss and rainfall characteristics to further the understanding of SOC erosion and its potential fate. Aggregate size distribution in sediments was different from that in source soil and was significantly correlated to sediment concentration in runoff. Fine size aggregate fractions in the sediments were the most abundant. The SOC was enriched in the sediments and indicated a high selectivity of the erosion processes. The SOC concentration differed among different sizes of aggregate fractions with coarse size aggregate fractions generally having the largest concentration. We concluded that the soil water erosion processes impact the aggregate size distribution and SOC enrichment in the delivered sediment, which subsequently influence the catchment exports of SOC. Additional measurements over several rainy seasons are required to further quantify the impact of soil water erosion on catchment exports of soil aggregates and associated SOC.

Previous research has shown the varied effect of earthworms on soil carbon dynamics. We carried out a 180-day incubation experiment with earthworms and maize residue additions under conventional tillage (CT) and no tillage (NT) system conditions to quantify the earthworm effect in the black soil of northeastern China. Earthworms did not affect soil CO2 emissions, while residue addition significantly increased such emissions. The effects of earthworms on dissolved organic carbon (DOC) and microbial biomass carbon (MBC) gradually weakened with time in CT with and without residue addition, but gradually increased with time in NT with residue addition. In the CT system, earthworms accelerated the soil organic carbon (SOC) mineralization, and the newly added residue decomposed into SOC. In the NT system, earthworms accelerated the decomposition of native residues increasing the SOC content, this increase in decomposition rates by earthworms was greater than the inhibitory effect imposed by the addition of the new residue. Earthworms and residues combine to play a single role in CT and NT. This result will help in the understanding of the role of earthworms and residue in SOC dynamics, and in the development of management strategies to improve SOC.

Selecting appropriate soil management practices (e.g. tillage treatments) provides an opportunity to sequester soil carbon (C), improve soil health, and achieve ample food production in an agricultural system. The responses of soil CO2 emission, soil microbial community, and crop yield to precipitation are crucial for assessing sustainability of conservation tillage. Soil CO2 flux, soil microbial phospholipid fatty acid (PLFA) contents and crop yield were measured in a long-term (15 years) tillage study in the Northeast of China under a normal year in 2013 and natural drought year in 2015. The results showed in a normal year with precipitation similar to the 30-year mean, soil temperatures at 5, 10 and 20 cm in June under mouldboard plough (MP) were higher by 0.9, 1.0 and 1.1 °C, respectively, than under no-tillage (NT); soil water content in the top 22 cm under MP was significantly lower than that under NT in 04 June and 31 July; and MP significantly increased maize (Zea mays L.) yield and C emission efficiency (the ratio of yield to annual soil CO2 emission) by 22% and 25%, respectively. In a dry year (2015), soil temperatures at 5, 10, and 20 cm in June and July under MP were higher by 2.0, 1.8 and 1.7 °C than under NT, respectively; soil water content in the top 22 cm under MP was significantly lower than under NT by 28% in July; moreover, MP significantly decreased maize yield and C emission efficiency by 47% and 63%, respectively. However, there were no significant differences in annual soil CO2 emission between NT and MP in the normal and dry years. Compared with MP, NT significantly increased soil microbial PLFA contents in pre-planting (April) and late segments of the growing season (August-September) of a normal year, but significantly increased soil microbial PLFAs content in pre-planting and all of early, mid and late segments of the growing season in a dry year. Structural equation modelling (SEM) revealed that soil water content, temperature, bacteria and fungi directly contributed to C emission efficiency. Tillage was indirectly associated with C emission efficiency through soil water content, temperature, soil fungi and bacteria. These results suggested that the higher maize yield and C emission efficiency under NT compared to CT were related to improved soil water content and soil microbial PLFA contents and the lower soil temperature in a dry year. Our results suggested that NT (a subset of conservation tillage) might be a positive adaptation strategy to cope with drought under monoculture maize in northeast China.

Gamma irradiation is becoming a promising technique in soil ecological studies because it has a particular advantage in selectively eliminating the target organism. But this selective sterilization technique is still in its initial exploratory stage and the subsequent impacts on soil carbon (C) and nitrogen (N) pools are relatively unknown for the majority of soils. Therefore, the responses of soil respiration, soil collembola, nematodes and microbial communities, and soil C and N pools (extracted with KCl, K 2 SO 4 and H 2 SO 4 ) to a range of gamma irradiation doses (0, 5, 10, 20 and 40 kGy) were determined under a clay loam soil in a 4-week incubation study. A flush of CO 2 was observed at the beginning of the incubation period (1–2 days) post-irradiation, and then strongly decreased relative to the unirradiated soils. At the middle of incubation period (11–14 days), there was a recovery of CO 2 efflux in the 5 kGy treatment. The effects of radiation on biological communities were dependent on taxa groups. The majority of collembola (>80%) and nematodes (>90%) were killed immediately in the higher doses (>5 kGy), but at lower doses of 5 kGy they were killed within 2 weeks after irradiation. The relative abundance of saprophytic fungi and protozoa decreased with increasing irradiation dose throughout the incubation period, while an opposite trend was found for some special bacterial taxa (19:1ω8c and i17:1ω9c). The resistance threshold of the entire microbial community to gamma irradiation was 10 kGy. The C and N contents in the KCl/K 2 SO 4 -extracted pools (except the dissolved organic C), in the H 2 SO 4 -extracted labile pool II (LP II) and in the recalcitrant pool (RP) decreased with increasing irradiation dose across the incubation period. The decreases in LP II and RP were accompanied by the increase in labile pool I. The variation in the level of all soil C and N pools was significantly affected by the radiation doses higher than 5 kGy. Our results indicate that the gamma dose between 5 and 10 kGy is sufficient to eliminate soil fauna without significant effect on microbial community compared to the unirradiated treatments. Moreover, a radiation dose of 5 kGy for selective defaunation has minor impacts on soil C and N pools of a clay loam soil. Our results also suggest that dose optimization is necessary due to high variability associated with irradiation levels effect on biological taxa in different soils.

Soil erosion is a serious problem around the world, in addition to soil loss, erosion is also considered to have a significant impact on SOC dynamics and CO2 release to the atmosphere. There is disagreement on the overall effect of soil erosion on CO2 emission at the landscape level. We measured the proportion of various aggregate size fractions at different slope positions which were affected by erosion. The cumulative CO2 emitted from bulk soil samples and different aggregate sizes fractions from five slope positions in a landscape was examined in a 128-d incubation study to estimate how the breakdown and dispersion of soil aggregates by erosion affect C loss to the atmosphere via CO2 emission. The proportion of coarse size aggregate fractions (> 0.25 mm) at eroded slope positions was greater than that at depositional positions. Bulk soil samples at the summit emitted the greatest cumulative CO2-C (0.49 ± 0.04 g C kg− 1 soil) among all the slope positions. During the initial 22 days of incubation, the CO2 emission rate from coarse size aggregate fractions (0.024 ± 0.009 g C kg− 1 soil d− 1) was six times higher than that from small size aggregate fractions (0.0038 ± 0.0011 g C kg− 1 soil d− 1) at the depositional toe-slope position. The CO2 emission rate from coarse size aggregate fractions at depositional slope positions (toe-slope and foot-slope) was significantly greater than that at eroded slope positions (summit, shoulder-slope and back-slope). We concluded that the breakdown and dispersion of aggregates by erosion impacts both aggregate size distribution and CO2 emission from the aggregates at different slope positions, thus, affects the C loss to the atmosphere.

Our understanding of seasonal dynamics of fungal communities under different agricultural management practices remains limited. In this study, phospholipid fatty acid (PLFA) analysis and Illumina MiSeq high-throughput sequencing targeting fungal ITS1 region were combined to assess the responses of soil fungal communities to different tillage practices and cropping systems during the crop growing season. Bulk soils were collected from two long-term tillage practices (conventional tillage, CT and no-tillage, NT) under two cropping systems (maize (Zea mays L.)-soybean (Glycine max Merr.) rotation and continuous maize) in April, June and August of 2015 at 0–5 cm and 5–15 cm depths. Our results clearly highlighted the importance of cropping system and tillage for soil fungi; seasonal effect, by contrast, was weaker. The fungal PLFA content, used as an indicator of fungal biomass, appeared higher under continuous maize system than maize-soybean rotation system at depths of 0–5 cm and 5–15 cm, and higher in NT than CT at 0–5 cm depth, irrespective of sampling time. DNA-based sequencing results showed that soil fungal diversity (i.e. Shannon) and evenness (i.e. Pielou) indices were higher under rotation cropping system than continuous maize system at both soil depths. Soil fungal richness (i.e. Chao1) index was higher in NT than in CT at 0–5 cm depth. None of these three α diversity indices were significantly affected by sampling time. Cropping system and tillage played the most important roles in shaping soil fungal community at both soil depths. At 0–5 cm depth, there was an obvious consistent trend of enrichment from Ascomycota in maize-soybean rotation system to Basidiomycota in continuous maize system over the growing season. At 5–15 cm depth, there was an obvious consistent trend of enrichment from Tausonia and Chaetomidium in CT to Leptodontidium, Ceratobasidium in NT over the crop growing season. Notably NT favored symbiotrophs throughout the growing season, irrespective of cropping system and soil depth.

Soil structure plays a key role in soil organic carbon (SOC) dynamics. To determine how soil structure and aggregate affects SOC, we collected undisturbed soil cores of 0-5 cm layer (Typic Hapludoll) at an experimental site in Northeast China. The site had been under continuous tillage treatments of conventional tillage (CT) and no tillage (NT) for 17 years. We measured SOC by elemental analysis, aggregate size distribution by wet sieving, and soil pore parameters of pore size distribution, pore average diameter, pore numbers, pore connectivity, pore anisotropy, and pore fractal dimension by X-ray computer tomography. SOC content was significantly correlated with aggregate-associated SOC and soil water-stable aggregate content. CT with residue removal and annual plowing and cultivation increased53 μm and 53-250 μm aggregates. CT decreased total SOC of 0-5 cm soil layer but increased aggregate-associated SOC of53 μm. NT with greater residue input increased total SOC of 0-5 cm soil layer by 26.0% and aggregate mean weight diameter by 111.8% and increased aggregates of 250-1000 μm and1000 μm. Soil under NT had a greater total number of micropores and greater connectivity whereas CT had a greater total number of macropores, average macropore diameter, anisotropy, and fractal dimension. Structural equation modeling showed that CT can decrease SOC of 0-5 cm soil layer by different paths, including increased anisotropy and macropore porosity, and NT can increase SOC of 0-5 cm soil layer by different paths, including increased mean weight diameter and connectivity. These results enhance our understanding of the relationship between soil structure and SOC, and could guide tillage management decisions to increase SOC.

Tillage practice can alter the content and distribution of soil organic matter by burying crop residue and soil disturbance, which would impact soil microbial properties. The objective of the present study was to evaluate the effects of tillage practices (no tillage, NT; ridge tillage, RT; mouldboard plow, MP) and sampling date (April, June, September) on soil microbial properties at different soil depths. Soil core samples were taken at 0–5, 5–10 and 10–20 cm depths from a long-term tillage experiment site (initiated in 2001) in black soils in northeast China. Microbial biomass and extractable organic C were determined using by chloroform-fumigation-extraction method. Microbial abundance and community structure were determined using the phospholipid fatty acid (PLFA) method. Principal response curve (PRC) analysis revealed the magnitude of the effect of sampling date on the PLFA relative abundance decreased with depth within the tilled layer, whereas increased with depth for tillage practice. Microbial biomass carbon, abundance and the F/B ratio varied with the variation in available substrates at the 0–5 cm depths. NT and RT improved microbial abundance (total, fungal and bacterial abundance) in the 0–5 cm depth soil, but they did not contribute to a higher F/B ratio in the 0–5 cm depth soil, and had a lower F/B ratio than MP in the deeper soils below 5 cm depth. These results demonstrated that long-term conservation tillage practice has potential for improving microbial properties in surface soil, but may not cause a shift of microbial community structure in Northeast China.

Soil microbial community can vary with different agricultural managements, which in turn can affect soil quality. The objective of this work was to evaluate the effects of long-term tillage practice (no tillage (NT) and conventional tillage (CT)) and crop rotation (maize-soybean (MS) rotation and monoculture maize (MM)) on soil microbial community composition and metabolic capacity in different soil layers. Long-term NT increased the soil organic carbon (SOC) and total nitrogen (TN) mainly at the 0-5 cm depth which was accompanied with a greater microbial abundance. The greater fungi-to-bacteria (F/B) ratio was found in NTMS at the 0-5 cm depth. Both tillage and crop rotation had a significant effect on the metabolic activity, with the greatest average well color development (AWCD) value in NTMS soil at all three soil depths. Redundancy analysis (RDA) showed that the shift in microbial community composition was accompanied with the changes in capacity of utilizing different carbon substrates. Therefore, no tillage combined with crop rotation could improve soil biological quality and make agricultural systems more sustainable.

The severe soil deterioration and the accompanying decline in maize yield are the main factors jeopardizing the sustainability of agricultural production in the black soil region of Northeast China. Conservation tillage practices have been proposed as new practices to enhance soil fertility and to produce food from a dwindling land resource in this region, but wide adoption of these practices can occur only when the practices demonstrate a steady increase in agricultural production. To compare the effects of tillage on corn yield, the structural equation modeling (SEM) was used in analyzing the relationships between maize growth/yield and soil properties (physical and chemical characteristics) based on a long-term (12 years) tillage study that included no tillage (NT), ridge tillage (RT) and conventional tillage (CT) practices. Compared with CT, NT and RT had higher maize grain yield, soil carbon/nitrogen ratio and soil moisture, and lower soil temperature and seedling emergence rate. The advantages of NT and RT in maize yield were primarily ascribed to the favorable soil nutrients and soil water content, which could increase plant size at the later growing season and ultimately yield more maize grain. The lower soil temperature and subsequently lower emergence rates in NT and RT at early stages (sowing to emergence) of maize growth did not exert negative effects on maize yield. These adverse effects of low soil temperature and low emergence rates could be offset by postponing sowing date without compromising the maize yield. Our study indicated that both NT and RT practices could offer a potentially significant improvement over the current conventional tillage practice in the black soil region of Northeast China.

Conservation tillage can significantly affect the biological, chemical, and physical properties of soil. This study aimed to determine the effect of conservation tillage on the soil microbial community and respiration and on soil CO2 emissions. In this study, the effects of 10 years of conservation tillage (no-till: NT and ridge tillage: RT) on soil CO2 fluxes and soil microbial communities were assessed in a black soil in Northeast China. The annual soil CO2 emissions were higher under moldboard plow (MP) than under NT by 7.8 % (P

Soil food webs are important in maintaining agricultural productivity and ecosystem health. However, our understanding is still limited with respect to the influences of tillage transitions on soil food webs. The present study aimed to quantify the response of microflora and microfauna, and their linkage to different tillage treatments: no tillage (NT), ridge tillage (RT) and conventional tillage (CT). Soil samples were collected from 0 to 20 cm depth in April of 2011 after 10 years of conservation tillage. The abundance and richness of bacteria and arbuscular mycorrhizal fungi were greater in NT and RT than in CT. In case of microfauna also, similar patterns were observed with greater protozoa, bacterivores and omnivores–carnivores in NT and RT compared to CT. The connectance of the bacterial and predator–prey pathways was greater in NT and RT than in CT and that of fungal pathway was greatest in RT. The trophic relationship of the bacterial and predator–prey pathways was strengthened due to the higher water content of soil and the lower NO 3 – -N after the conversion of CT to NT and RT. Our study suggested that 10 years of conservation tillage can effectively enhance the structure and function of soil food webs through bottom–up effects in the black soil region of Northeast China.

The CO 2 flux from soils is an important part of the global carbon (C) cycle, whose dependence on erosion is as yet largely unknown. We hypothesized that erosion affects CO 2 flux from the soil surface because of its effects on soil temperature and soil moisture. The CO 2 flux, soil temperature, and soil moisture were monitored on summit, shoulder-slope, back-slope, and toe-slope on a sloping corn field in the black soil zone in northeast China once a day for 47 days between August 3 and September 18. The average CO 2 flux varied significantly with slope positions ranging from 2.5 ± 0.29 (mean ± standard deviation) μmol m −2 s −1 at summit to 1.5 ± 0.32 μmol m −2 s −1 at toe-slope in the initial 27 days, but no significant difference among slope positions was observed in the last 20 days. Soil moisture contributed largely to CO 2 flux in the initial 27 days, and soil temperature became the most important factor affecting CO 2 flux in the last 20 days. In our study, second-order and first order regressions were fit the best models to predict CO 2 flux at various slope positions based, respectively, on soil moisture content and soil temperature, with respective R 2 ranging from 0.532 to 0.661 and 0.234 to 0.448.

Soil management is aimed at the maintenance of optimal soil physical quality for crop production. In order to explore the effects of tillage practices on soil physical properties, a study was conducted to compare the effects of no tillage (NT), moldboard plow (MP) and ridge tillage (RT) on soil bulk density (BD), soil penetration resistance (SPR), soil water content (SWC), soil macroporosity (MAC) and soil air-filled porosity (AFP) in Northeast China. Results showed that both NT and RT led to significant BD increment than MP at 0–20 cm ( P < 0.05). Compared with MP, NT and RT increased SPR at the depths of 2.5–17.5 cm (P < 0.05). SWC of 0–10 cm layer was significantly higher in NT and RT than MP soils (P < 0.05). NT showed a significantly lower MAC than MP and RT at 0–20 cm soil depths (P < 0.05). All AFP values were above the limit of 0.10 cm 3 /cm 3 under all tillage treatments. RT improved the soil physical quality as evidenced by decreased BD and SPR, and increased SWC, MAC and AFP relative to NT.

SUMMARYThe present work built on a previous study of tillage trials, which found the effectiveness of least limiting water range (LLWR) as an indicator of soil organic carbon (SOC) mineralization under different tillage practices in a black soil of Northeast China in 2009. To improve the understanding of soil structure controls over SOC dynamics, a study was conducted to explore the relationship between LLWR, which was calculated based on soil bulk density and soil pore-size distribution, and the effects of LLWR, which was calculated based on soil bulk density and soil pore-size distribution on SOC mineralization following no tillage (NT) and mouldboard ploughing (MP). In contrast to MP, NT had a significantly greater volume of large macropores (>100 μm) at depths of 0–0·05 and 0·2–0·3 m, but a significantly lower volume of small macropores (30–100 μm) at depths of 0–0·05, 0·05–0·1, 0·1–0·2 and 0·2–0·3 m. The volume of meso- (0·2–30 μm) and micro-pores (μm) at different depths under the two tillage practices were similar. Tillage-induced changes in soil bulk density and pore-size volumes affected the ability of soil to fulfil essential soil functions in relation to organic matter turnover. Soil pore-size distribution, especially small macropores greatly affected LLWR and there was a significant correlation between LLWR, which was calculated based on soil bulk density, and the proportion of small macropores. The proportion of small macropores were used to calculate LLWR instead of soil bulk density and the values for NT and MP soils ranged from 0·073 to 0·148 m3water/m3soil. Using the proportion of small macropores rather than bulk density in the calculation of LLWR resulted in more sensitive indications of SOC mineralization. Variation in the proportion of small macropores can help characterize the impacts of tillage practices on dynamics of LLWR and SOC sequestration.

Limited information is available for understanding the spatial variation of soil penetration resistance (SPR) and water content induced by different tillage methods and crop rotations in a black soil of Northeast China. A 11-year tillage experiment in Dehui County, Jilin Province, Northeast China was conducted to evaluate the effects of tillage treatments [no tillage (NT), moldboard plow (MP), and ridge tillage (RT)] and crop rotations (corn-soybean rotation and continuous corn) on SPR and water content in relation to horizontal and vertical variations. Effect of NT, MP, and RT differed on the spatial distributions of SPR and water content among the rows, shoulders, and inter-rows. Compared with MP, NT, and RT treatments increased SPR in row and inter-row positions at the depth of 2.5–17.5 and 2.5–15 cm, respectively (p < 0.05). NT and RT led to significant decrement of soil water content than MP treatment in the rows and inter-rows of 0–15 cm layer (p < 0.05). Greater variability of SPR and water content...

Tree roots are highly heterogeneous in form and function. Previous studies revealed that fine root respiration was related to root morphology, tissue nitrogen (N) concentration and temperature, and varied with both soil depth and season. The underlying mechanisms governing the relationship between root respiration and root morphology, chemistry and anatomy along the root branch order have not been addressed. Here, we examined these relationships of the first- to fifth-order roots for near surface roots (0-10 cm) of 22-year-old larch (Larix gmelinii L.) and ash (Fraxinus mandshurica L.) plantations. Root respiration rate at 18 °C was measured by gas phase O2 electrodes across the first five branching order roots (the distal roots numbered as first order) at three times of the year. Root parameters of root diameter, specific root length (SRL), tissue N concentration, total non-structural carbohydrates (starch and soluble sugar) concentration (TNC), cortical thickness and stele diameter were also measured concurrently. With increasing root order, root diameter, TNC and the ratio of root TNC to tissue N concentration increased, while the SRL, tissue N concentration and cortical proportion decreased. Root respiration rate also monotonically decreased with increasing root order in both species. Cortical tissue (including exodermis, cortical parenchyma and endodermis) was present in the first three order roots, and cross sections of the cortex for the first-order root accounted for 68% (larch) and 86% (ash) of the total cross section of the root. Root respiration was closely related to root traits such as diameter, SRL, tissue N concentration, root TNC : tissue N ratio and stele-to-root diameter proportion among the first five orders, which explained up to 81-94% of variation in the rate of root respiration for larch and up to 83-93% for ash. These results suggest that the systematic variations of root respiration rate within tree fine root system are possibly due to the changes of tissue N concentration and anatomical structure along root branch orders in both tree species, which provide deeper understanding in the mechanism of how root traits affect root respiration in woody plants.

Root respiration is closely related to root morphology, yet it is unclear precisely how to distinguish respiration-related root physiological functions within the branching fine root system. Root respiration and tissue N concentration were examined for different N fertilization treatments, sampling dates, branch orders and temperatures of larch (Larix gmelinii L.) and ash (Fraxinus mandshurica L.) using the excised roots method. The results showed that N fertilization enhanced both root respiration and tissue N concentration for all five branch orders. The greatest increases in average root respiration for N fertilization treatment were 13.30% in larch and 18.25% in ash at 6°C. However, N fertilization did not change the seasonal dynamics of root respiration. Both root respiration and root tissue N concentration decreased with increase in root branch order. First-order (finest) roots exhibited the highest respiration rates and tissue N concentrations out of the five root branch orders examined. There was a highly significant linear relationship between fine root N concentration and root respiration rate. Root N concentration explained >60% of the variation in respiration rate at any given combination of root order and temperature. Root respiration showed a classical exponential relationship with temperature, with the Q(10) for root respiration in roots of different branching orders ranging from 1.62 to 2.20. The variation in root respiration by order illustrates that first-order roots are more metabolically active, suggesting that roots at different branch order positions have different physiological functions. The highly significant relationship between root respiration at different branch orders and root tissue N concentration suggests that root tissue N concentration may be used as a surrogate for root respiration, simplifying future research into the C dynamics of rooting systems.

The response of belowground biological processes to soil N availability in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations was studied. Soil and root respiration were measured with Li-Cor 6400 and gas-phase O2 electrodes, respectively. Compared with the control, N fertilization induced the decreases of fine root biomass by 52% and 25%, and soil respiration by 30% and 24% in larch and ash plantations, respectively. The average soil microbial biomass C and N were decreased by 29% and 42% under larch stand and 39% and 47% under ash stand, respectively. While the fine root tissue N concentration under fertilized plots was higher 26% and 12% than that under control plots, respectively, the average fine root respiration rates were increased by 10% and 13% in larch and ash stands under fertilized plot, respectively. Soil respiration rates showed significantly positive exponential relationships with soil temperature, and a seasonal dynamic. These findings suggest that N fertilization can suppress fine root biomass at five branch orders (

Fine root turnover is a major pathway for carbon and nutrient cycling in forest ecosystems. However, to estimate fine root turnover, it is important to first understand the fine root dynamic processes associated with soil resource availability and climate factors. The objectives of this study were: (1) to examine patterns of fine root production and mortality in different seasons and soil depths in the Larix gmelinii and Fraxinus mandshurica plantations, (2) to analyze the correlation of fine root production and mortality with environmental factors such as air temperature, precipitation, soil temperature and available nitrogen, and (3) to estimate fine root turnover. We installed 36 Minirhizotron tubes in six mono-specific plots of each species in September 2003 in the Mao’ershan Experimental Forest Station. Minirhizotron sampling was conducted every two weeks from April 2004 to April 2005. We calculated the average fine root length, annual fine root length production and mortality using image data of Minirhizotrons, and estimated fine root turnover using three approaches. Results show that the average growth rate and mortality rate in L. melinii were markedly smaller than in F. mandshurica, and were highest in the surface soil and lowest at the bottom among all the four soil layers. The annual fine root production and mortality in F. mandshurica were significantly higher than in L. gmelinii. The fine root production in spring and summer accounted for 41.7% and 39.7% of the total annual production in F. mandshurica and 24.0% and 51.2% in L. gmelinii. The majority of fine root mortality occurred in spring and summer for F. mandshurica and in summer and autumn for L. gmelinii. The turnover rate was 3.1 a−1 for L. gmelinii and 2.7 a−1 for F. mandshurica. Multiple regression analysis indicates that climate and soil resource factors together could explain 80% of the variations of the fine root seasonal growth and 95% of the seasonal mortality. In conclusion, fine root production and mortality in L. gmelinii and F. mandshurica have different patterns in different seasons and at different soil depths. Air temperature, precipitation, soil temperature and soil available nitrogen integratively control the dynamics of fine root production, mortality and turnover in both species.

[1] Winter soil CO2 emission is a very important component of the annual carbon budgets, however, almost no information on winter CO2 emission is available from the cropland soil in northeast China. In this study, soil CO2flux was measured for a 2-year period from an ongoing tillage trial on Black soil in northeast China to quantify seasonal patterns in soil CO2 flux rate and wintertime contribution to annual soil respiration. Average soil CO2 flux rates in the winter (November to March) were between 0.64 to 1.22 g CO2 m−2 d−1, in the non-growing season (October and April) were 2.09–3.56 g CO2 m−2 d−1, whereas in the growing season (May to September) they were between 10.9 to 12.7 g CO2 m−2 d−1, with no significant differences among tillage treatments. Total winter, non-growing and growing season soil CO2 emissions were 0.28–0.45 Mg C ha−1, 0.36–0.53 Mg C ha−1, and 4.52–5.55 Mg C ha−1, respectively, among tillage treatments. The contributions of winter soil respiration to annual soil CO2emission ranged from 5.1 to 7.1%, and the non-growing season emission ranged from 11.4 to 15.2% among tillage treatments. Our results indicate that in northeast China, cropland Black soil continuously emits CO2throughout the non-growing season, and the wintertime soil respiration plays a significant role in annual soil carbon budgets. Hence winter soil CO2 emission must be taken into consideration when the role of the soil ecosystem is assessed as either a sink or source of CO2 to the atmosphere.