Effects of growing roots of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) on rhizosphere soil solution chemistry

The chemical conditions of the rhizosphere can be very different from that of bulk soil. Up to now, little attention has been given to the problem of spatial heterogeneity and temporal dynamics of rhizosphere soil solution and little is known about the influence of different tree species on rhizosphere chemistry. In the present study, we used micro suction cups to collect soil solution from the rhizosphere of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) seedlings in high spatial resolution and capillary electrophoresis for the determination of major cations and anions. The results indicate, that in a soil with a base saturation of about 20—25% and a pH of 6.5, growing roots of beech and spruce lower the concentrations of nutrient cations and nitrate in the rhizosphere soil solution and decrease significantly the pH. The H⁺ release leads to an enhanced mineral weathering as indicated by an increase of CEC and base saturation and to a mobilization of soluble Al, however, on a very low concentration level. In our experiment rhizosphere effects of spruce have been more pronounced than those of beech, indicating, that with respect to below ground activity young spruce trees have a better competitive power than beech.     

Microbial biomass phosphorus in soils of beech (Fagus sylvatica L.) forests

Thirty-eight soils from forest sites in central Germany dominated by beech trees (Fagus sylvatica L.) were sampled to a depth of about 10 cm after careful removal of the overlying organic layers. Microbial biomass P was estimated by the fumigation — extraction method, measuring the increase in NaHCO₃-extractable phosphate. The size of the microbial P pool varied between 17.7 and 174.3 g P g^-1 soil and was on average more than seven times larger than NaHCO₃-extractable phosphate. Microbial P was positively correlated with soil organic C and total P, reflecting the importance of soil organic matter as a P source. The mean microbial P concentration was 13.1% of total P, varying in most soils between 6 and 18. Microbial P and microbial C were significantly correlated with each other and had a mean ratio of 14.3. A wide (5.1–26.3) microbial C: P ratio indicates that there is no simple relatinship between these two parameters. The microbial C: P ratio showed strong and positive correlations with soil pH and cation exchange capacity.     

Nutritional composition of hazelnut (Corylus avellana L.) as influenced by basic fertilization

Nitrogen (N), phosphorus (P), and potassium (K) deficiencies are a widespread phenomenon throughout the world, and are one of the most common nutritional disorders in Turkish hazelnut (Corylus avellana L.) cultivation. In this research, the effects of macronutrient fertilizers on mineral contents and some biochemical contents of ‘Tombul’ hazelnut (Corylus avellana L.) variety cultivated in the Black Sea Region of Turkey were investigated, and the contribution of these nuts to human nutrition was determined. The trials were carried out at ‘Tombul’ hazelnut orchards, and the hazelnuts were fertilized with five different doses of nitrogen, phosphorus, and potassium in each year for three consecutive years. The basic fertilizers (N, P₂O₅, and K₂O) significantly affected some biochemical contents and mineral compositions of the hazelnuts. In order to improve the biochemical and mineral compositions of hazelnut, 200 kg ha^?1 and 400 kg ha^?1 N fertilizations, 120 kg ha^?1 and 160 kg ha^?1 P₂O₅ fertilizations, and 400 kg ha^?1 and 600 kg ha^?1 K₂O fertilizations could be recommended for practice. According to the daily mineral element requirements, 100 g of hazelnuts provided about 43.5% P, 13.2% K, 19.4% Ca, 37.0% Mg, 0.2% Na, 53.8% Fe, 24.5% Zn, 14.5% B, and 66.7% Mo of the recommended dietary allowances. Cu and Mn contents of 100 g hazelnut were higher than the respective daily requirements. These results indicated that the mineral composition of hazelnut depended not only on the variety but also on the cultivation techniques such as soil condition and especially basic fertilization practices.     

Corn (Zea mays L.) Grain and Stover Yield as Affected by Soil Residual Mineral Nitrogen

Evaluation of nitrogen (N) dynamic in soil using regression equations is important for proper determination of N fertilization. A 3-year field experiment was conducted to (1) develop the best-fitted regression model relating corn grain and stover yield to soil residual ammonium (NH₄)-N and nitrate (NO₃)-N for corn yield prediction and (2) evaluate how such a model can be beneficial to the health of ecosystem by predicting the appropriate rates of N fertilization for corn production. Soil NH₄-N and NO₃-N were determined at corn harvest at the depths of 0–30 and 30–60 cm. Nitrogen fertilizer rates and soil mineral N accounted for a maximum of 93% variation in corn grain yield. Soil mineral N enhanced corn yield more than N fertilizer. Totals of 63.1 and 14.1 kg/ha of soil residual NO₃-N and NH₄-N were found in the 0- to 60-cm depth, indicating the importance of performing soil N tests.     

Change of Zinc Forms in Rhizosphere and Nonrhizosphere Soils of Maize (Zea mays L.) Plants as Influenced by Soil Drought Condition

A rhizobox experiment was conducted to study the changes of various zinc (Zn) forms in rhizosphere and nonrhizosphere soils of maize (Zea mays L.) plants grown under well-watered and drought conditions. The tested soil was earth-cumulic orthic anthrosol sampled from the Shaanxi Province of China. The experiment was set at two levels of Zn, 0 and 5.0 mg Zn kg^?1 soil, and at two treatments of soil water content, 45%–50% (drought) and 70%–75% (well watered) of soil water-holding capacity. A completely randomized factorial design (2 Zn treatments × 2 water levels × 3 replicates) was set up. Adequate soil water supply enhanced growth and Zn accumulation of maize plants. Applying Zn increased plant biomass and Zn content more notably under well-watered conditions rather than drought conditions. Soil Zn was defined as water-soluble plus exchangeable (WSEXC) Zn, carbonate-bound Zn (CA), iron–manganese oxide–bound Zn (FeMnOX), organic matter–bound Zn (OM), and residual Zn (RES) forms using the sequential extraction procedure. Most of Zn was predominantly in the RES fraction. Zinc application increased the contents of WSEXC Zn, CA Zn, and FeMnOX Zn in soil. When Zn was added to the soil, the concentrations of CA Zn within 0–2 mm and 0–4 mm apart from the central root compartment (CC) were greater than other zones under the conditions of adequate and limited soil water supplies, respectively. Zinc application also resulted in an accumulation of FeMnOX fractions at a distance of 2 mm from CC. The FeMnOX Zn content in this compartment increased with soil drought. Under well-watered conditions, dry-matter weight and Zn concentration of shoots presented better correlations with CA Zn and FeMnOX Zn fractions in and near the rhizosphere as compared with drought conditions. It is suggested that in an earth-cumulic orthic anthrosol, soil moisture conditions affect the transformation of the added Zn into the CA and FeMnOX fractions near the rhizosphere and their bioavailability to maize plants.     

Efficiency of foliar selenium application on oilseed rape (Brassica napus L.) as influenced by rainfall and soil characteristics

The Czech Republic is characterized by a low Se soil content, resulting in Se deficiency in crops, humans, and animals. This study investigated the response of oilseed rape to foliar application of selenate solution in a microscale field experiment conducted at two locations differing in soil and climatic conditions but with comparable total Se contents. Sodium selenate (Na₂SeO₄) was applied at two rates (25 and 50 g Se ha^?1). The potential effect of Se application on the uptake of essential elements was also evaluated. The foliar Se application resulted in an effective stepwise increase in the Se contents of all the plant components studied (leaves > stems > roots > siliques ~ seeds), as expected. No significant influence of Se fortification on the other investigated macro- and microelements was observed. However, the soil and climatic conditions influenced the Se uptake, such that a higher Se content was observed in plants grown in the most acidic location (Cambisol soil) that had a higher oxidizable carbon content and higher average annual rainfall compared to the less acidic location (Luvisol soil). These observations indicated the necessity to optimize the Se application for the particular soil and climatic conditions to achieve a maximum biofortification effect.     

Selenium Speciation and Distribution Characteristics in the Rhizosphere Soil of Rice (Oryza sativa L.) Seedlings

A five-step sequential extraction procedure was used for the fractionation of selenium (Se) in rhizosphere and nonrhizosphere soils with rice (Oryza sativa L.) seedlings. Results showed that in rhizosphere soils without the addition of Se, the soluble Se (Sol-Se), exchangeable Se and Se bound to carbonates (Exc-Se), Se bound to organic-sulfide matter and elemental Se (OM-Se), and total Se contents were significantly greater than those in nonrhizosphere soils, whereas the residual Se (Res-Se) was less than that in the nonrhizosphere soils. After the addition of Se, the Sol-Se and OM-Se contents in the rhizosphere soils were still evidently greater than those in nonrhizosphere soils, but the Exc-Se was significantly less in rhizosphere soils than in nonrhizosphere soils. Our overall results suggest that the Se bioavailability in rice rhizosphere soils is greater than that in nonrhizosphere soils. Selenium bioavailability in the rhizosphere soil is not correlated with Se accumulation in rice seedlings.     

Growth and Phosphorus Uptake of Oat (Arena nuda L.) as Affected by Mineral Nitrogen Forms Supplied in Hydroponics and Soil Culture

Plants show different growth responses to N sources supplied with either NH4+ or NO3-.The uptake of different N sources also affects the rhizosphere pH and therefore the bioavailability of soil phosphorus,particularly in alkaline soils.The plant growth,P uptake,and P availability in the rhizosphere of oat (Arena nuda L.) grown in hydroponics and in soil culture were investigated under supply with sole NH4+-N,sole NO3--N,or a combination.Sole NO3-fed oat plants accumulated more biomass than sole NH4+-fed ones.The highest biomass accumulation was observed when N was supplied with both NH4+-N and NO3--N.Growth of the plant root increased with the proportion of NO3-in the cultural medium.Better root growth and higher root/shoot ratio were consistently observed in NO3--fed plants.However,root vigor was the highest when N was supplied with NO3-+NH4+.NH4+ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source.No P deficiency was observed,and plant P concentrations were generally above 2 g kg-1.P uptake was increased when N was supplied partly or solely as NO3--N,similarly as biomass accumulation.The results suggested that oat was an NO3-prcferring plant,and NO3--N was essential for plant growth and the maintenance of root absorption capacity.N supply with NH4+-N did not improve P nutrition,which was most likely due to the absence of P deficiency.     

Spatial variability of soil solution chemistry under Hinoki cypress (Chamaecyparis obtusa) in Tama Hills

A monitoring study on precipitation and soil solution was conducted to analyze soil acidification processes at the Rolling Land Laboratory (RLL), Hachioji, Tokyo based on the spatial variability of the soil solution chemistry around the Hinoki cypress (Chamaecyparis obtusa) trunk. Soil solution samples were taken at various distances from the tree trunks and at various depths. Soil solution pH at the depth of 10 cm decreased to 4.1–4.2 on the downslope side of large tree trunks, presumably due to the heterogeneity of throughfall input and extensive infiltration of acidic stemflow. Ammonium ions brought by throughfall and stemflow were nitrified and provided large amounts of H⁺. Protons were replaced with exchangeable cations. When base cations were depleted, aluminum ion became the dominant cation species. On the average, Ca²⁺ concentration in the soil solutions at the depth of 10 cm decreased from 0.28 mmol_c L^-1 at the reference site to 0.18 mmol_c L^-1 on the downslope side and Mg²⁺ concentration decreased from 0.30 mmol_c L^-1 to 0.15 mmol_c L^-1. Arithmetic mean aluminum concentration at the depth of 10 cm on the downslope side was 0.35 mmol_c L^-1. Here aluminum dissolution was the main acid sink. Based on the spatial variability of the soil solution chemistry, soil solution acidification processes were divided into four stages.     

Heavy Metal Accumulation in Soil Amended with Roadside Pond Sediment and Uptake by Rice (Oryza sativa L.)

The effect of addition of roadside pond sediments on heavy metal contents of flooded rice paddies was studied to investigate the yield of rice and uptake of heavy metal by rice straw and grain. Sequential extraction of heavy metals on sediments shows that the percentage contribution of metals in the labile fraction follows the order lead (Pb, 48%) > copper (Cu, 42%) > zinc (Zn, 31%) > cadmium (Cd, 16%) > chromium (Cr, 9%) > nickel (Ni, 6%). The risk assessment code (RAC) for pond sediment revealed that Cr and Ni were found in the low-risk zone, Zn and Cd in the medium-risk zone, and Cu and Pb in the high-risk zone. However, though the heavy metal concentration in rice grain does not exceed the range acceptable for human consumption, it still represents a significant additional source of heavy metals in the diet. The addition of pond sediment significantly increased the rice yield over control. Therefore, pond sediment would be a valuable resource for agriculture if it is properly used.     

Carbon and nitrogen relationships in the microbial biomass of soils in beech (Fagus sylvatica L.) forests

Soils from 38 German forest sites, dominated by beech trees (Fagus sylvatica L.) were sampled to a depth of about 10 cm after careful removal of overlying organic layers. Microbial biomass N and C were measured by fumigation-extraction. The pH of the soils varied between 3.5 and 8.3, covering a wide range of cation exchange capacity, organic C, total N, and soil C:N values. Maximum biomass C and biomass N contents were 2116 g C m^-2 and 347 g N m^-2, while minimum contents were 317 and 30 g m^-2, respectively. Microbial biomass N and C were closely correlated. Large variations in microbial biomass C:N ratios were observed (between 5.4 and 17.3, mean 7.7), indicating that no simple relationship exists between these two parameters. The frequency distribution of the parameters for C and N availability to the microflora divided the soils into two subgroups (with the exception of one soil): (1) microbial: organic C>12 mg g^-1, microbial:total N>28 mg g^-1 (n=23), a group with high C and N availability, and (2) microbial:organic C12 mg g^-1, microbial:total N28 mg g^-1 (n=14), a group with low C and N availability. With the exception of a periodically waterlogged soil, the pH of all soils belonging to subgroup 2 was below 5.0 and the soil C:N ratios were comparatively high. Within these two subgroups no significant correlation between the microbial C:N ratio and soil pH or any other parameter measured was found. The data suggest that above a certain threshold (pH 5.0) microbial C:N values vary within a very small range over a wide range of pH values. Below this threshold, in contrast, the range of microbial C:N values becomes very large.     

崇明西红花根际土壤和球茎微生物多样性分析

为研究崇明西红花栽培地根际土壤和球茎中微生物多样性,采用Illumina MiSeq高通量测序技术对其微生物群落组成进行了比对分析。结果表明,西红花根际土壤和球茎中细菌和真菌在门类水平上菌群类别差异不显著,但在丰富度和多样性方面根际土壤明显高于球茎;在属和种水平上差异显著;在种水平上,根际土壤或球茎均有各自特有的细菌或真菌,且具有较高的相对丰度。西红花致病真菌瓶霉(Phialophora)和背芽突霉(Cadophora)在崇明西红花球茎大量存在。因此,推测西红花病害发生,除与土壤菌群相关外,与其内生细菌和真菌也紧密相关。本研究结果初步分析了崇明栽培地西红花根际土壤和球茎中微生物多样性及群落结构组成,为进一步筛选合适的崇明西红花栽培地土壤和种球杀菌剂提供了理论依据。     

Oligotrophic pseudomonads in the rhizosphere: Suppressiveness to Pythium damping-off of cucumber seedlings (Cucumis sativus L.)

Summary Pseudomonads recovered from the cucumber rhizosphere were evaluated for their ability to suppress Pythium ultimum damping-off. Full-strength and 250-fold diluted selective media formulations with King's B medium (KB and KB/250, respectively) as the basal medium were used as the recovery media. Eight per cent of the isolates recovered (11/138) could induce suppression to Pythium damping-off and 45% of these biocontrol agents produced fluorescent pigments. No differences in the ability to induce suppression among the isolates recovered on full-strength and diluted media were detected. The growth rates of the selected isolates indicated that growth in KB broth was faster or equal to that in KB/10. Therefore, no obligate oligotrophs were recovered. Additionally, growth was observed in 15 000-fold diluted KB for 10 of 11 test isolates, which indicated that these isolates were facultative oligotrophs. In general, the faster growing isolates were more likely to induce suppression when used as seed treatments. Finally, the in vitro antifungal properties of test isolates against P. ultimum indicated that 4 of the 11 isolates inhibited P. ultimum.     

Changes in bacterial populations along roots of wheat (Triticum aestivum L.) seedlings

Summary In this study the bacterial populations on root tips (1–2 days old) of wheat (Triticum aestivum L.) were compared with the populations on root segments about 1 week older (root base). The isolates were characterized with a set of physiological tests and the test results were used to group the bacteria by means of cluster analysis. Some clusters contained bacteria that occurred mainly on the root tips and were characterized by the ability to produce acid from different sugars and by the presence of the enzymes nitrate reductase, lipase, and oxidase; they were sensitive to high salt concentrations in the media. Another cluster included significantly more isolates from the root-base segments; these bacteria were characterized by a negative reaction to most of the physiological tests; the colonies formed by these bacteria had yellow pigmentation. Possiblemechanisms for the changes in the bacterial populations are discussed.     

Acidity,nutrient stocks,and organic‐matter content in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.)

The production and composition of leaf litter, soil acidity, exchangeable nutrients, and the amount and distribution of soil organic matter were analyzed in a broad‐leaved mixed forest on loess over limestone in Central Germany. The study aimed at determining the current variability of surface‐soil acidification and nutrient status, and at identifying and evaluating the main factors that contributed to the variability of these soil properties along a gradient of decreasing predominance of European beech (Fagus sylvatica L.) and increasing tree‐species diversity. Analyses were carried out in (1) mature monospecific stands with a predominance of beech (DL 1), (2) mature stands dominated by three deciduous‐tree species (DL 2: beech, ash [Fraxinus excelsior L.], lime [Tilia cordata Mill. and/or T. platyphyllos Scop.]), and (3) mature stands dominated by five deciduous‐tree species (DL 3: beech, ash, lime, hornbeam [Carpinus betulus L.], maple [Acer pseudoplatanus L. and/or A. platanoides L.]). The production of leaf litter was similar in all stands (3.2 to 3.9 Mg dry matter ha^–1 y^–1) but the total quantity of Ca and Mg deposited on the soil surface by leaf litter increased with increasing tree‐species diversity and decreasing abundance of beech (47 to 88 kg Ca ha^–1 y^–1; 3.8 to 7.9 kg Mg ha^–1 y^–1). The soil pH_(H2O) and base saturation (BS) measured at three soil depths down to 30 cm (0–10 cm, 10–20 cm, 20–30 cm) were lower in stands dominated by beech (pH = 4.2 to 4.4, BS = 15% to 20%) than in mixed stands (pH = 5.1 to 6.5, BS = 80% to 100%). The quantities of exchangeable Al and Mn increased with decreasing pH and were highest beneath beech. Total stocks of exchangeable Ca (0–30 cm) were 12 to 15 times larger in mixed stands (6660 to 9650 kg ha^–1) than in beech stands (620 kg ha^–1). Similar results were found for stocks of exchangeable Mg that were 4 to 13 times larger in mixed stands (270 to 864 kg ha^–1) than in beech stands (66 kg ha^–1). Subsoil clay content and differences in litter composition were identified as important factors that contributed to the observed variability of soil acidification and stocks of exchangeable Ca and Mg. Organic‐C accumulation in the humus layer was highest in beech stands (0.81 kg m^–2) and lowest in stands with the highest level of tree‐species diversity and the lowest abundance of beech (0.27 kg m^–2). The results suggest that redistribution of nutrients via leaf litter has a high potential to increase BS in these loess‐derived surface soils that are underlain by limestone. Species‐related differences of the intensity of soil–tree cation cycling can thus influence the rate of soil acidification and the stocks and distribution of nutrients.     

Responses to Low P-Supply in Breeding Lines of White Clover (Trifolium Repens L.) Reveals Two Tiers of Responses

Four breeding lines (BLs) of white clover, which range in terms of their disposition to increase biomass in response to low or high phosphate (P) levels in soil, were evaluated further when grown hydroponically. BL 45 increased both fresh and dry weight in response to P-deprivation, while BL 49 displayed the same significant stimulation in response to sufficient P. However, when compared these lines did not accumulate any significantly higher levels of P, and all four lines showed the same changes to root:shoot ratio in response to P-deprivation, as well as the induction of both soluble and cell-wall-associated acid phosphatase activity. These results confirm that there is no direct relationship between growth (as an increase in biomass) and acid phosphatase activity and further some responses to P-deprivation may be common to all genetic backgrounds suggesting that they are not part of the intricate mechanisms governing these responses.     

缓释硼肥种肥用量对红壤油菜生长发育和产量的影响

为明确种肥同播条件下红壤耕地的适宜硼肥用量,在红壤旱地和水田通过开展种肥同播不同硼肥用量试验,本研究设置施硼肥量为0(T1,对照)、4.5(T2)、9.0(T3)、13.5 kg·hm^-2(T4)4个处理,研究其对油菜出苗、生长发育、硼肥吸收利用效果、籽粒产量、品质等的影响。结果表明,红壤耕地增施硼肥,油菜花期可缩短9~20 d,全生育期缩短2~11 d。红壤中有效硼含量严重缺乏,增施硼肥可显著提高油菜生物量和菜籽产量。适宜的硼肥用量可通过增加成株率、单株角果数和每角粒数提高产量。施硼量为9.0 kg·hm^-2时,菜籽产量达最佳水平,为2 131.6 kg·hm^-2,较对照增产336.1%。收获期硼吸收量和各器官中硼含量随施硼量增加而增加,施硼量为13.5 kg·hm^-2时硼吸收量和各器官中硼含量均达到最大值。硼肥利用率随施硼量增加呈降低趋势,土壤基础有效硼含量越低,硼肥贡献率越大,施硼增产效果越好。施硼量为9.0 kg·hm^-2时,菜籽含油量和产油量达最佳水平,与对照相比含油量增加6.7个百分点,产油量达996.4 kg·hm^-2,较对照增加401.5%。综合菜籽产量、含油量、硼肥利用率和产油量等因素,推荐红壤旱地硼肥施用量为9.0 kg·hm^-2,水田可适当增加施用量,但不宜超过13.5 kg·hm^-2。本研究为我省红壤耕地油菜生产硼肥施用和油菜全程机械化生产提供了技术参考和理论依据。