Effects of early mycorrhization and colonized root length on low‐soil‐phosphorus resistance of West African pearl millet

Phosphorus (P) deficiency at early seedling stages is a critical determinant for survival and final yield of pearl millet in multi‐stress Sahelian environments. Longer roots and colonization with arbuscular mycorrhizal fungi (AMF) enhance P uptake and crop performance of millet. Assessing the genotypic variation of early mycorrhization and its effect on plant growth is necessary to better understand mechanisms of resistance to low soil P and to use them in breeding strategies for low P. Therefore, in this study, eight pearl millet varieties contrasting in low‐P resistance were grown in pots under low P (no additional P supply) and high P (+ 0.4 g P pot^?1) conditions, and harvested 2, 4, 6, and 8 weeks after sowing (WAS). Root length was calculated 2 WAS by scanning of dissected roots and evaluation with WinRhizo software. AM infection (%) and P uptake (shoot P concentration multiplied per shoot dry matter) were measured at each harvest. Across harvests under low P (3.3 mg Bray P kg^?1), resistant genotypes had greater total root length infected with AMF (837 m), higher percentage of AMF colonization (11.6%), and increased P uptake (69.4 mg P plant^?1) than sensitive genotypes (177 m, 7.1% colonization and 46.4 mg P plant^?1, respectively). Two WAS, resistant genotypes were infected almost twice as much as sensitive ones (4.1% and 2.1%) and the individual resistant genotypes differed in the percentage of AMF infection. AMF colonization was positively related to final dry matter production in pots, which corresponded to field performance. Early mycorrhization enhanced P uptake in pearl millet grown under P‐deficient conditions, with the genotypic variation for this parameter allowing selection for better performance under field conditions.     

Soil base saturation affects root growth of European beech seedlings§

To assess the potential effects of Al toxicity on the roots of young European beech (Fagus sylvatica L.), seeds were sown in soil monoliths taken from the Ah and B horizons of forest soils with very low base saturation (BS) and placed in the greenhouse. The Ah horizons offered a larger supply of exchangeable cation nutrients than the B horizons. After 8 weeks of growth under optimal moisture conditions, the seedlings were further grown for 14 d under drought conditions. Root‐growth dynamics were observed in rhizoboxes containing soils from the Ah and B horizons. The concentrations of Al³⁺, base cations, and nitrate in the soil solution and element concentrations in the root tissue were compared with above‐ and belowground growth parameters and root physiological parameters. There was no strong evidence that seedling roots suffered from high soil‐solution Al³⁺ concentrations. Within the tested range of BS (1.2%–6.5%) our results indicated that root physiological parameters such as O₂ consumption decreased and callose concentration increased in soils with a BS < 3%. In contrast to the B horizons, seedlings in the Ah horizons had higher relative shoot‐growth rates, specific root lengths, and lengths and branching increments, but a lower root‐to‐shoot ratio and root‐branching frequency. In conclusion, these differences in growth patterns were most likely due to differences in nutrient availability and to the drought application and not attributable to differences in Al³⁺ concentrations in the soil solution.     

Biogeochemical processes and arsenic enrichment around rice roots in paddy soil: results from micro‐focused X‐ray spectroscopy

The spatial distribution and speciation of iron (Fe), manganese (Mn) and arsenic (As) around rice roots grown in an As‐affected paddy field in Bangladesh were investigated on soil sampled after rice harvest. Synchrotron micro‐X‐ray fluorescence spectrometry on soil thin sections revealed that roots influence soil Fe, Mn and As distribution up to 1 mm away from the root–soil interface. Around thick roots (diameter around 500 µm), Mn was concentrated in discrete enrichments close to the root surface without associated As, whereas concentric Fe accumulations formed farther away and were closely correlated with As accumulations. Near thin roots (diameter < 100 µm), in contrast, a pronounced enrichment of Fe and As next to the root surface and a lack of Mn enrichments was observed. X‐ray absorption fine structure spectroscopy suggested that (i) accumulated Fe was mainly contained in a two‐line ferrihydrite‐like phase, (ii) associated As was mostly As(V) and (iii) Mn enrichments consisted of Mn(III/IV) oxyhydroxides. The distinct enrichment patterns can be related to the extent of O₂ release from primary and lateral rice roots and the thermodynamics and kinetics of Fe, Mn and As redox transformations. Our results suggest that in addition to Fe(III) plaque at the root surface, element accumulation and speciation in the surrounding rhizosphere soil must be taken into account when addressing the transfer of nutrients or contaminants into rice roots.     

Einfluß des Bodengefüges auf Wurzelwachstum und Phosphataufnahme von Sommerweizen

Influence of Soil Structure on Root Growth and P Uptake of Spring Wheat The effect of soil structure (fine aggregat, coarse aggregate and compacted structure) on root growth, root morphology, and P availability of spring wheat (Triticum aestivum L.) was studied in pot and split root experiments using three soils (2 × Alfisol-Udalf, Alluvium). CAL-soluble P was 63–90 mg P · kg^?1 soil, indicating a sufficient P supply. Root length, root surface, root fresh weight, shoot weight, and seed yield were decreased due to coarse aggregate and compacted structure. Roots were significantly thickened and roots hairs were longer in the fine aggregate structure than in the compacted and coarse aggregate structures. P concentration in the shoot and P uptake of spring wheat growing in the coarse aggregate and compacted structure were lower because root growth was decreased. In the split root experiment, in contrast to pot experiment, P uptake was lower in the compacted than in the fine aggregate treatment. The results demonstrate that P availability was influenced by soil structure via the influence on root growth and thus access of roots to P.     

Automated analysis of fine‐root dynamics using a series of digital images

Information related to the growth of fine roots is important for understanding C allocation in trees and the mechanisms of C cycling in ecosystems. Observations using a camera or scanner embedded in the soil enabled us to obtain continuous images of fine‐root‐growth dynamics. However, these methods are still labor‐intensive because the image analysis has to be conducted manually. We developed an automated method for tracking movement or elongation of fine roots using a sequence of scanner images. We also show how data obtained with these methods can be used for calculating fine‐root behavior. Two A4‐size scanners were buried in a mixed forest in Japan and images were taken continuously from within the soil. We preprocessed these images by extracting the fine‐root area from the images and developed an automated calculation plug‐in we named A‐root for tracking growth movement of the tips of fine roots. A‐root and manual‐tracking results were compared using the same images. The results show the A‐root and manual‐tracking methods yielded similar levels of accuracy. The average growth rate of 17 fine roots tracked using the program was 0.16 mm h^–1. The observation of the direction of growth in fine roots showed the direction may be influenced by the original root's growth where the fine roots branched, distribution of soil particles, other roots, and the force of gravity. The A‐root analysis also suggested there may be an interaction between speed of growth and changes in direction of growing fine roots.     

Vertical root distribution in single‐crop and intercropping agricultural systems in Central Kenya

Intercropping is an important and widespread land‐management system in the tropics. At two agricultural sites in Central Kenya differing in elevation and soil type Haplic Nitisols (eutric) and Vitric Gleysols (eutric, epiclayic, endoclayic), we investigated the vertical root distributions using the trench wall profile method in single‐crop systems of maize (Zea mays L.) and in intercropping systems of maize and legumes (common bean, Phaseolus vulgaris L.; pigeon pea, Cajanus cajan [L.] Millsp.) to test for possible differences in the use of water and nutrient resources. The physico‐chemical soil properties of the sites were similar and imposed no restrictions to the vertical growth of the roots into soil depths of 1.4 m. The vertical distributions of the fine roots (?? 0.5–2 mm) and very fine roots (?? < 0.5 mm) were quantified by calculating the parameter β which was computed from the cumulative fraction (Y) of the root densities along the depth (d) of the soil profiles (Y = 1 – β^d). We found no consistent differences between the single‐crop and the intercropping systems in the rooting depth down to 1.4 m. However, higher β values for fine roots of the intercropping systems were indicative of a more homogeneous vertical root distribution than in the single‐crop fields. In the intercropping fields, 50% of the total number of fine roots were distributed over the uppermost 36 cm of the soil, whereas in the single‐crop fields, 50% of the fine roots were concentrated in the uppermost 15–21 cm. Medium‐sized roots (?? > 2–5 mm) were detected in the intercropping fields only. The more homogeneous root distribution in the intercropping fields likely indicates a more efficient use of the limited resources nutrients and water.     

Root‐growth characteristics contributing to genotypic variation in nitrogen efficiency of oilseed rape

A 3‐year field experiment was carried out to determine the significance of root‐growth characteristics contributing to N‐uptake efficiency of two oilseed rape (Brassica napus L.) cultivars differing in N efficiency. Two N treatments were applied, and the core and minirhizotron techniques were used to study root‐length density and number of living roots, respectively. Fertilizer‐N supply increased shoot dry matter, grain yield, total N uptake, and total soil N_min contents particularly in the top soil. Although significant differences occurred in all parameters between years, the interactions between years and cultivars were mostly not significant. Compared to cv. Capitol, the N‐efficient cv. Apex was characterized by a higher grain yield at N0 and a higher N uptake during reproductive growth. This genotype also had a higher root‐length density and more living fine roots particularly in the topsoil layer. Root growth of this genotype was especially high from beginning of shooting to beginning of flowering, while shoot growth and N uptake during vegetative growth were comparatively low. Our results suggest that N‐efficient cultivars can be characterized by a high investment in root growth during the vegetative stage with a comparatively slow shoot growth and N‐uptake rate until beginning of flowering, which, however, continues during reproductive growth. High root production only during reproductive growth seems to be less effective to achieve high N efficiency, because this may lead to a shortage of assimilates for seed filling. High root‐length density at vegetative stages may thus be advantageous for N uptake and reproductive growth and could be a useful morphological character for the selection and breeding of N‐efficient cultivars.     

Root growth and nutrient element status of creeping bentgrass cultivars differing in heat tolerance as influenced by supraoptimal shoot and root temperatures

This study was designed to determine and compare root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to differential, supraoptimal, shoot and root temperatures. Shoots and roots of ‘Penncross’ (heat sensitive) and ‘L‐93’ (heat tolerant) were exposed to four air/soil temperature regimes (20/20°C‐control, 20/35°C, 35/20°C, and 35/35°C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35°C) while maintaining shoots at normal temperature (20°C) or particularly at 35°C reduced root fresh weight, root number, and contents of nitrogen (N), phosphorus (P), and potassium (K) in shoots and roots and accelerated root death for both cultivars. High root temperature had greater detrimental effects on root growth and nutrient element accumulation than high shoot temperature for both cultivars. A low root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality; and increased N, P, and K contents in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L‐93 generally maintained higher fresh weight and number of roots and higher N, P, and K contents in shoots and roots, particularly K in roots, under high root (20/35°C) or shoot/root (35/35°C) temperatures. The results indicated that root growth and nutrient element accumulation, particularly of K, played an important role in creeping bentgrass tolerance to heat stress imposed on shoots by high air temperature or to roots by high soil temperatures. The enhanced root growth and nutrient element relations with a low root temperature at supraoptimal ambient temperatures could lead to the improved shoot growth in cool‐season grasses observed under these conditions.     

Elemental toxicity effects on germination and growth of pearl millet seedlings 1

Variability in millet stands in West Africa is clearly visible as early as three weeks after planting. The objectives of this study were to determine the influence of pH and chemical toxicities on millet germination and seedling growth and to compare varietal tolerance of toxic conditions. A nutrient solution study was carried out with a series of Hoagland‐based nutrient solutions. Germination percentage was calculated, and root and shoot lengths were measured for one week. Critical values were determined for toxic elements. The only treatment which reduced germination percentage significantly was copper (Cu) concentrations >0.05M. Solution pH values between 5 and 7 resulted in the best root growth, though shoot growth was unaffected by pH. The roots were more sensitive than the shoots to several [aluminum (Al), boron (B), zinc (Zn)] of the elemental toxicities studied. Soil Al and manganese (Mn) levels may be high enough to have toxic effects on millet roots. However, natural soil iron (Fe), Cu, and Zn levels were much lower than the critical levels determined in the nutrient solution study. The improved varieties were more tolerant of Fe and Zn toxicity than the LOCAL variety, but the LOCAL variety was more tolerant of high B concentrations.     

A sensitivity analysis for assessing the relevance of fine‐root turnover for P and K uptake

Plant fine roots are subject to continual turnover, i.e., old roots die during the plant life cycle and are quickly replaced by new roots. New roots grow partly into undepleted soil areas and can take up nutrients at a higher rate than old roots. This is one possible advantage of root turnover. It has been shown that root turnover of several plant species increases when P and/or K supply is limited, indicating an efficiency mechanism. The objective of this study was to assess the maximum benefit for nutrient uptake by root turnover and to determine which soil or plant properties influence this process. Based on a data set of field‐grown faba beans, a sensitivity analysis with a transport and uptake model was performed, i.e., several input parameters were systematically varied to assess their importance for nutrient uptake of a root system with and without fine‐root turnover. The calculations were based on the assumptions that all new roots grow into undepleted soil areas and that no inter‐root competition occurs. Model calculations indicated that a root system with a high but realistic turnover rate can take up twice the amount of P or K compared to a stable root system without any turnover. This benefit on uptake is higher at low concentrations of these nutrients in soil solution, low soil water content, or high maximum inflow. However, measured uptake under poor conditions of nutrient supply is often higher than calculated uptake, even when root turnover is taken into account. This indicates that root turnover might be an efficiency mechanism, but not the only one.     

低肥力土壤施用氮磷钾肥影响柏木家系根系发育和养分吸收对钙肥的响应

  【目的】  探讨柏木(Cupressus funebris Endl)家系在不同养分条件下根系发育和营养吸收对钙添加的响应,为提高柏木苗木质量和林木生产力及造林地选择提供理论依据。  【方法】  以柏木5个家系的1年生幼苗为材料,分别在施3 g/kg NPK肥和未施NPK肥两小区内,设置施CaSO₄ 0、3和6 g/kg (依次记为Ca₀、Ca₃和Ca₆) 3 个水平,分析柏木家系生长与根系形态及氮磷钙吸收量对钙肥添加的响应。  【结果】  在施 3 g/kg NPK肥的小区中,添加钙对柏木的苗高、干物质量积累和氮磷吸收量影响不显著,抑制了D2和D3径级根系的发育;柏木钙吸收量在Ca₆处理下最高,比Ca₀处理提高73.86%;柏木苗高、干物质量及氮磷钙素的吸收量在家系间差异显著,T2家系表现最好。在未施NPK肥的小区中,Ca₃处理明显提高了柏木的苗高、根干物质量和茎干物质量,增加了磷和钙的吸收量,分别比Ca₀处理高出9.15%、19.85%、16.67%、27.46%和44.02%;Ca₆处理提高了钙吸收量,比Ca₀处理高出39.95%,但抑制柏木幼苗苗高和D1~D4径级根系的发育。不论施NPK肥与否,家系与钙处理对柏木的株高和根干物质量存在着显著的互作效应。  【结论】  在低肥力土壤上,施用氮磷钾肥会降低钙肥对柏木苗生长和养分吸收的影响,应选择优良家系进行育苗造林,不需要增加钙肥;在不施用氮磷钾肥时,应添加少量钙肥(CaSO₄ 3 g/kg),以促进苗木对钙和磷的吸收。     

Effect of fly ash extract on growth and development of corn and soybean seedlings

Different concentrations of aqueous extract of fly ash were prepared by soaking air dried fly ash and mixing thoroughly with an electric blender. Extracts were then applied to the seeds of corn (Zea mays L.) and soybean (Glycine max L.) after being filtered through a Whatman No. 42 filter paper. Fly ash extract in the lower concentration range of 0.5 to 1.0% (W/V) had no significant effect on germination and seedling growth of each of the two crops. Higher concentrations of fly ash extracts, however, had deleterious effects on the percentage of germination, viability, number of roots, shoot and root length, fresh weight and dry weight of seedlings of both the crops. The elemental concentrations in shoot and root systems of control seedlings of corn and soybean were found to be the same, whereas in the extract treated corn and soybean seedlings, a relatively high elemental concentration was found in roots as compared to shoots.     

Effects of drought stress on photosynthesis,rhizosphere respiration,and fine‐root characteristics of beech saplings: A rhizotron field study

Soil drought influences the C turnover as well as the fine‐root system of tree saplings. Particularly during the period of establishment, the susceptibility to drought stress of saplings is increased because of incompletely developed root systems and reduced access to soil water. Here, we subjected beech saplings (Fagus sylvatica L.) to different levels of drought stress. Beech saplings were planted in rhizotrons, which were installed in the soil of a Norway spruce forest before bud burst. Soil moisture was manipulated in the following year during May to September. We measured photosynthetic net CO₂ uptake, volume production of fine roots, and rhizosphere respiration during the growing season. Biometric parameters of the fine‐root system, biomass, and nonstructural carbohydrates were analyzed upon harvest in October. Photosynthesis and rhizosphere respiration decreased with increasing drought‐stress dose (cumulated soil water potential), and cumulative rhizosphere respiration was significantly negatively correlated with drought‐stress dose. Fine‐root length and volume production were highest at moderate soil drought, but decreased at severe soil drought. The proportion of fine‐roots diameter < 0.2 mm and the root‐to‐shoot ratio increased whereas the live‐to‐dead ratio of fine roots decreased with increasing drought‐stress dose. We conclude that the belowground C allocation as well as the relative water‐uptake efficiency of beech saplings is increased under drought.     

Image analysis for non‐destructive and non‐invasive quantification of root growth and soil water content in rhizotrons

Studies aiming at quantification of roots growing in soil are often constrained by the lack of suitable methods for continuous, non‐destructive measurements. A system is presented in which maize (Zea mays L.) seedlings were grown in acrylic containers — rhizotrons — in a soil layer 6‐mm thick. These thin‐layer soil rhizotrons facilitate homogeneous soil preparation and non‐destructive observation of root growth. Rhizotrons with plants were placed in a growth chamber on a rack slanted to a 45° angle to promote growth of roots along the transparent acrylic sheet. At 2‐ to 3‐day intervals, rhizotrons were placed on a flatbed scanner to collect digital images from which root length and root diameters were measured using RMS software. Images taken during the course of the experiment were also analyzed with QUACOS software that measures average pixel color values. Color readings obtained were converted to soil water content using images of reference soils of known soil water contents. To verify that roots observed at the surface of the rhizotrons were representative of the total root system in the rhizotrons, they were compared with destructive samples of roots that were carefully washed from soil and analyzed for total root length and root diameter. A significant positive relation was found between visible and washed out roots. However, the influence of soil water content and soil bulk density was reflected on seminal roots rather than first order laterals that are responsible for more than 80 % of the total root length. Changes in soil water content during plant growth could be quantitifed in the range of 0.04 to 0.26 cm³ cm^—3 if image areas of 500 x 500 pixel were analyzed and averaged. With spatial resolution of 12 x 12 pixel, however, soil water contents could only be discriminated below 0.09 cm³ cm^—3 due to the spatial variation of color readings. Results show that this thin‐layer soil rhizotron system allows researchers to observe and quantify simultaneously the time courses of seedling root development and soil water content without disturbance to the soil or roots.     

Fertilizer location modifies root zone salinity,root morphology,and water‐stress resistance of tree seedlings according to the watering regime in a dryland reforestation

There is a direct relationship between soil nutrient concentration in localized zones and root proliferation and elongation under well‐watered conditions. However, in field studies under semiarid conditions this relationship can change due to higher salt accumulation and soil dryness that affect root growth, water stress resistance, and seedling survival. We assessed the effect of different locations of fertilizer placement in the soil profile and water availability on root zone salinity, root development and ecophysiological responses of Quillaja saponaria Mol. after outplanting. A single dose (6 g L^?1) of controlled‐release nitrogen fertilizer (CRF_N) was placed at 0 cm (top layer), 15 cm (middle layer), or 30 cm (bottom layer) depth in the containers in a greenhouse, in addition to an unfertilized treatment (control). After 6 months, seedlings were transplanted to the field and subjected to weekly watering regimes (2 L plant^?1 and unwatered). Morphological and ecophysiological parameters were periodically measured on seedlings, as well as soil electrical conductivity (EC). After 1 year, the shoot : root ratio of unwatered seedlings decreased as a function of CRF_N placement depth, which was attributed to lower shoot growth and not to greater root growth. The root morphology of the bottom layer treatment was negatively affected by high EC in unwatered seedlings. Greater total root length and root volume of the middle layer treatment was found only when well‐watered; however, this did not contribute to improve physiological responses against water stress. The lowest EC and the highest photochemical efficiency, net photosynthesis, and stomatal conductance were shown by unfertilized seedlings, independent of water availability. Our findings suggest that varying depth of CRF_N placement does not contribute significantly to improve root growth under water restriction. Water supplements, independently of the CRF_N location in the substrate, contribute to decrease root zone salinity, and consequently, improve root volume growth.     

在富营养土壤斑块中根增值对玉米养分吸收和生长的贡献

Root proliferation can be stimulated in a heterogeneous nutrient patch; however, the functions of the root proliferation in the nutrient-rich soil patches are not fully understood. In the present study, a two-year field experiment was conducted to examine the comparative effects of localized application of ammonium and phosphorus (P) at early or late stages on root growth, nutrient uptake, and biomass of maize (Zea mays L.) on a calcareous soil in an intensive farming system. Localized supply of ammonium and P had a more evident effect on shoot and root growth, and especially stimulated fine root development at the early seedling stage, with most of the maize roots being allocated to the nutrient-rich patch in the topsoil. Although localized ammonium and P supply at the late stage also enhanced the fine root growth, the plant roots in the patch accounted for a low proportion of the whole maize roots in the topsoil at the flowering stage. Compared with the early stage, fine root length in the short-lived nutrient patch decreased by 44%-62% and the shoot dry weight was not different between heterogeneous and homogeneous nutrient supply at the late growth stage. Localized supply of ammonium and P significantly increased N and P accumulation by maize at 35 and 47 days after sowing (DAS); however, no significant difference was found among the treatments at 82 DAS and the later growth stages. The increased nutrient uptake and plant growth was related to the higher proportion of root length in the localized nutrient-enriched patch. The results indicated that root proliferation in nutrient patches contributed more to maize growth and nutrient uptake at the early than late stages.     

Zinc‐biofortified seeds improved seedling growth under zinc deficiency and drought stress in durum wheat

High zinc (Zn) concentration of seeds has beneficial effects both on seed vigor and human nutrition. This study investigated the effect of Zn biofortification on growth of young durum wheat (Triticum durum cv. Yelken) seedlings under varied Zn and water supply. The seeds differing in Zn concentrations were obtained by spraying ZnSO₄ to durum wheat plants at different rates under field conditions. Three groups of seeds were obtained with the following Zn concentrations: 9, 20, and 50 mg Zn kg^?1. The seeds differing in Zn were tested for germination rate, seedling height, shoot dry matter production, and shoot Zn concentration under limited and well irrigated conditions in a Zn‐deficient soil with and without Zn application. In an additional experiment carried out in solution culture, root and shoot growth and superoxide dismutase activity (SOD) of seedlings were studied under low and adequate Zn supply. Low seed Zn concentration resulted in significant decreases in seedling height both in Zn‐deficient and sufficient soil, but more clearly under water‐limited soil condition. Decrease in seed germination due to low seed Zn was also more evident under limited water supply. Increasing seed Zn concentration significantly restored impairments in seedling development. Drought‐induced decrease in seedling growth at a given seed Zn concentration was much higher when soil was Zn‐deficient. Increasing seed Zn concentration also significantly improved SOD activity in seedlings grown under low Zn supply, but not under adequate Zn supply. The results suggest that using Zn‐biofortified seeds assures better seed vigor and seedling growth, particularly when Zn and water are limited in the growth medium. The role of a higher antioxidative potential (i.e., higher SOD activity) is discussed as a possible major factor in better germination and development of seedlings resulting from Zn‐biofortified seeds.     

Effects of crop‐straw biochar on crop growth and soil fertility over a wheat‐millet rotation in soils of China

We conducted a pot experiment using a wheat‐millet rotation to examine the effects of two successive rice‐straw biochar applications on crop growth and soil properties in acidic oxisols and alkaline cambosols from China. Biochar was incorporated into soil at rates of 0, 2.25 or 22.5 Mg/ha at the beginning of each crop season with identical applications of NPK fertilizer. In the oxisols, the largest biochar treatment enhanced soil pH and cation exchange capacity, decreased soil bulk density, improved soil P, K, Ca and Mg availability and enhanced their uptake, and increased wheat and millet yields by 157 and 150% for wheat grain and straw, respectively, and 72.6% for millet straw. In the cambosols, biochar treatment decreased soil bulk density, improved P and K availability, increased N, P and K uptake by crops and increased wheat and millet straw yields by 19.6 and 60.6%, respectively. Total soil organic carbon increased in response to successive biochar applications over the rotation. No difference in water‐soluble organic carbon was recorded between biochar‐treated and control soils. Converting straw to biochar and treating soils with successive applications may be a viable option for improving soil quality, sequestering carbon and utilizing straw resources in China.     

Partitioning CO2 Respiration among Soil,Rhizosphere Microorganisms,and Roots of Wheat under Greenhouse Conditions

Abstract

The measurement of soil, root, and rhizomicrobial respiration has become very important in evaluating the role of soil on atmospheric carbon dioxide (CO₂) concentration. The objective of this study was to partition root, rhizosphere, and nonrhizosphere soil respiration during wheat growth. A secondary objective was to compare three techniques for measuring root respiration: without removing shoot of wheat, shading shoot of wheat, and removing shoot of wheat. Soil, root, and rhizomicrobial respiration were determined during wheat growth under greenhouse conditions in a Carwile loam soil (fine, mixed, superactive, thermic Typic Argiaquolls). Total below ground respiration from planted pots increased after planting through early boot stage and then decreased through physiological maturity. Root‐rhizomicrobial respiration was determined by taking the difference in CO₂ flux between planted and unplanted pots. Also, root and rhizomicrobial respirations were directly measured from roots by placing them inside a Mason jar. It was determined that root‐rhizomicrobial respiration accounted for 60% of total CO₂ flux, whereas 40% was from heterotrophic respiration in unplanted pots. Rhizomicrobial respiration accounted for 18 to 25% of total CO₂ flux. Shade and no‐shoot had similar effects on root respiration. The three techniques were not significantly different (p>0.05).     

Root morphology of Thlaspi goesingense Hálácsy grown on a serpentine soil

The contribution of root morphology to enhanced uptake of heavy metals by hyperaccumulating plants is not well understood. The objective of this study was to describe root‐morphological characteristics of the natural nickel (Ni) hyperaccumulator Thlaspi goesingense Hálácsy. Plant samples were collected from a serpentine site near Redlschlag (East Austria), characterized by large soil Ni concentrations. Roots were evaluated for mass, length, surface area, diameter, and related ratios using an image‐analysis approach. Results showed that on the indigenous site, T. goesingense Hálácsy developed a fine‐branched root system, confined within a shallow soil depth. Coarse roots (>1 mm) accounted for about 60% of the total root mass (fresh and dry), while their contribution to the surface area and especially to the length of the system was small. Conversely, fine roots (<1 mm) represented 99% of the total root length and 88% of the surface area. The largest proportion of root length and area was found in the smallest diameter class of 0.0 to 0.5 mm. Shoot‐biomass production per unit root was high, in spite of the adverse soil conditions. Roots accounted for 8% of the total plant mass and about 4% of the total Ni accumulation. We conclude that the root system of natively grown T. goesingense Hálácsy exhibits a potential for enhanced Ni extraction from soil, since it mainly consists of very fine roots with extended absorptive area.