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1.
《Communications in Soil Science and Plant Analysis》2012,43(5-6):411-419
Abstract Earlier research has shown that in a phosphorus (P) placement experiment the amount of increase in root proliferation in the fertilized volume, F, depended on the ratio of the available soil P levels in F and the unfertilized volume, U. The objective of this research was to determine the effect of the level of nitrogen (N) in F, and U on root proliferation in F. The research was conducted using the same procedures as were used for P. Corn (Zea mays L.) was grown in pots of soil where 20% of the soil was fertilized with N at 10 rates and three replications using ammonium sulfate [(NH4)2SO4]. All the soil was treated with nitrification inhibitor to reduce nitrification of ammonium (NH4 +) since nitrate (NO3‐) would diffuse to the unfertilized volume much more rapidly than NH4. The fertilized volume was separated with plastic screen and the root growth in this volume was compared with root growth in a comparable volume of unfertilized soil that was also separated with plastic screen. After 10 days of growth in the pots, the plants were harvested and the root length in F and U of each pot measured. As rate of N in F increased, root length in F increased and in U decreased. This differs from the results with P where root length in U did not vary with rate of P used in F. Root weight in both F and U decreased as N in F increased. An increase in root length and root surface area in F was due to the increase in fine root production as N in F increased. A relation was obtained between the ratio of soil N in F and U, CsiF/CsiU and the ratio of root length in F and U, RLF/RLU. It was similar to what occurred in a study with P. Hence, knowledge of the effect of adding N to a specific soil volume will affect root proliferation in relation to the ratio of soil N level in F and U. This information can be used for predicting N uptake as related to N placement. 相似文献
2.
Information is needed about root growth and N uptake of crops under different soil conditions to increase nitrogen use efficiency in horticultural production. The purpose of this study was to investigate if differences in vertical distribution of soil nitrogen (Ninorg) affected root growth and N uptake of a variety of horticultural crops. Two field experiments were performed each over 2 years with shallow or deep placement of soil Ninorg obtained by management of cover crops. Vegetable crops of leek, potato, Chinese cabbage, beetroot, summer squash and white cabbage reached root depths of 0.5, 0.7, 1.3, 1.9, 1.9 and more than 2.4 m, respectively, at harvest, and showed rates of root depth penetration from 0.2 to 1.5 mm day?1 °C?1. Shallow placement of soil Ninorg resulted in greater N uptake in the shallow‐rooted leek and potato. Deep placement of soil Ninorg resulted in greater rates of root depth penetration in the deep‐rooted Chinese cabbage, summer squash and white cabbage, which increased their depth by 0.2–0.4 m. The root frequency was decreased in shallow soil layers (white cabbage) and increased in deep soil layers (Chinese cabbage, summer squash and white cabbage). The influence of vertical distribution of soil Ninorg on root distribution and capacity for depletion of soil Ninorg was much less than the effect of inherent differences between species. Thus, knowledge about differences in root growth between species should be used when designing crop rotations with high N use efficiency. 相似文献
3.
Mycorrhiza-released glomalin-related soil protein (GRSP) influences rhizosphere properties, but it is not clear whether exogenous GRSP enhances drought tolerance of plants. In this work, easily extracted GRSP (EE-GRSP) was isolated from Satsuma mandarin soil, and half-strength EE-GRSP (0.007 mg protein mL?1) was weekly applied into rhizosphere of potted trifoliate orange (Poncirus trifoliata) exposed to well watered (WW) and drought stress (DS). After four months, EE-GRSP-treated seedlings exhibited significantly higher plant growth (plant height, leaf number and fresh weight) and root growth-related parameters (lateral root numbers and root morphology) than non-EE-GRSP-treated seedlings under both WW and DS conditions. Exogenous EE-GRSP generally significantly increased leaf water potential, net photosynthesis rate, transpiration rate, stomatal conductance and intercellular CO2 concentration, while dramatically decreased leaf temperature, regardless of soil water status. The seedlings treated with exogenous EE-GRSP observed significantly higher activities of leaf Fe-SOD and root Mn-SOD, Cu/Zn-SOD, and Fe-SOD than untreated control under DS. Leaf abscisic acid, indole-acetic acid and methyl jasmonate concentrations were significantly higher in EE-GRSP-treated seedlings than untreated control under DS. This work firstly reported that exogenous application of EE-GRSP improved drought tolerance of trifoliate orange, thereby, offering a strong possibility in favour of EE-GRSP to be used as a plant growth regulator. 相似文献
4.
Root response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP140, SC599, TAM428, SC283, and SC574) were grown in white quartz flintshot sand and watered with 0.01M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 and Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, or 140.0 mgl‐1 as HnCl2). At the acid soil tolerance impact response phase (< 10 days old), Ca++ did not influence initial root growth. Increased H+ concentration inhibited juvenile root growth equivalently in all six cultivars. This inhibition was reversed by exogenous GA3 in Funks G522DR but not in SC283 or SC574. Excess Mn++ (140 mgl‐1) further decreased root growth. Induction of an auxinase inhibitor by GA3 would support a hypothesis of H+ concentration influence on IAA transport and/or availability. Root growth matched IAA water partitioning and exogenous IAA (10‐10 and 10‐9 M) reversed the H+ concentration influence on root growth of SC283. We suggest that low pH (<4.8) soil influence on root growth is explicable as an influence on IAA synthesis and/or transport and that excess Mn++, which is known to induce IAA oxidation, further exacerbates the deleterious growing conditions. 相似文献
5.
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. 相似文献
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7.
Response of cotton root growth and yield to root restriction under various water and nitrogen regimes 总被引:2,自引:0,他引:2
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Water and nitrogen (N) are two major factors limiting cotton growth and yield. The ability of plants to absorb water and nutrients is closely related to the size of the root system and the rooting space. Better understanding of the physiological mechanisms by which cotton (Gossypium hirsutum L.) adapts to water and N supply when rooting volume is restricted would be useful for improving cotton yield. In this study, cotton was grown in soil columns to control rooting depth to either 60 cm (root‐restriction treatment) or 120 cm (no‐root‐restriction treatment). Four water–N combinations were applied to the plants: (1) deficit irrigation and no N fertilizer (W0N0), (2) deficit irrigation and moderate N fertilizer rate (W0N1), (3) moderate irrigation and no N fertilizer (W1N0), and (4) moderate irrigation and moderate N fertilizer rate (W1N1). Results revealed that root restriction reduced root length density (RLD), root volume density (RVD), root mass density (RMD), superoxide dismutase (SOD) activity, nitrate reductase (NR) activity, total plant biomass, and root : shoot ratio. In contrast, root restriction increased aboveground biomass and yield. The RLD, RVD, RMD, and root : shoot ratio decreased in the order W0N0 > W1N0 > W0N1 > W1N1 in both the root‐restriction and no‐root‐restriction treatments. However, the opposite order (i.e., W1N1 > W0N1 > W1N0 > W0N0) was observed for SOD activity, NR activity, aboveground biomass, and seed yield. Our results suggest that, when N and water supplies are adequate, root restriction increases both root activity and the availability of photosynthates to aboveground plant parts. This increases shoot growth, the shoot : root ratio, and yield. 相似文献
8.
The paper summarizes the results of a series of experiments on enumeration of N2-fixing bacteria (diazotrophs) and hormonal effects of Azospirillum on root development. Numbers of N2-fixing and N-heterotrophic bacteria were determined on the root (rhizoplane plus “inner” root surface) and in the rhizosphere soil (0–3 mm from the root surface) of Arrhenatherum elatius, other forage grasses and some herbaceous plant species. Pot experiments involved freshly collected soil from an unfertilized grassland area containing its natural population of N2-fixing bacteria. The MPN (most probable number) of diazotrophs in relation to the MPN of the total bacterial population was always lower on the root than in the rhizosphere soil, suggesting that diazotrophs were not selectively advantaged at the root surface. Supply of mineral nitrogen (NH4NO3) decreased the proportion of N2-fixing bacteria at the rhizoplane as well as in the rhizosphere soil. Similar results were obtained when N was supplied via the leaves. The data suggest that N2-fixing bacteria in the rhizosphere are poor competitors once they loose their competitive advantage of binding dinitrogen. Correspondingly, the increase in the MPN of the diazotrophs found during plant development was interpreted as a result of decreased available combined N in the rhizosphere. The proportion of N2-fixing bacteria relative to the total number of bacteria was generally below 1%. Considering the potential amount of substrate released from the roots and the substrate requirement of the bacterial population, N2-fixation was considered insignificant for plant growth under the given conditions. For the investigations on possible beneficial effects on plant development by bacterial hormones, Azospirillum brasilense was chosen because evidence suggests that amongst the soil bacteria releasing hormones, especially IAA, certain strains of this species are more important than other bacteria. Application of A. brasilense Cd (ATCC 29710) onto the roots of young wheat plants grown in soil increased the number of lateral roots, the total root length and the number of root hairs. Similar results were obtained after application of IAA. This suggests that IAA is an important factor responsible for the effects observed after inoculation with A. brasilense. The increase in root surface may improve acquisition of nutrients and enhance growth of plants. Another hormonal effect of A. brasilense was an increase in nodulation of Medicago sativa grown on agar. Again pure IAA resulted in a similar increase in nodule number. Increases in nodule number were only in part associated with a change in root morphology. Therefore an effect of IAA on the plant immanent regulation system for nodulation is likely. 相似文献
9.
Anika K. Richter Yasuhiro Hirano Jörg Luster Emmanuel Frossard Ivano Brunner 《植物养料与土壤学杂志》2011,174(3):408-419
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. 相似文献
10.
《Communications in Soil Science and Plant Analysis》2012,43(19-20):3089-3101
Abstract Crops can be effectively grown on hardpan soils and water effectively used from deep in the profile if hard layers in soils can be penetrated or if they are broken up by tillage. Addition of gypsum to the soil or exploitation of genetic differences in root penetrability may help improve root penetration through hard layers with less need to depend on the energy requirements of deep tillage. To test this theory, a single‐grained Ap horizon of Norfolk loamy sand soil was compacted into soil columns to compare root penetrability of soybean [Glycine max (L.) Merr.] genotypes Essex and PI 416937 in the presence and absence of gypsum and at two soil compaction levels (columns with uniform compaction at 1.4 g cm‐1 and columns with increasing compaction with depth from 1.4 to 1.75 g cm‐1). Compaction treatments were imposed by constructing soil columns composed of 2.5‐cm‐deep, 7.5‐cm‐diameter cylindrical cores compacted to predetermined bulk densities (1.40,1.55,1.65,and 1.75 g cm.3). Soil penetration resistances were measured on duplicate cores using a 3‐mm‐diameter cone‐tipped penetrometer. Columns were not watered during the study; soybean genotypes were grown in the columns until they died. Both genotypes lived one day longer in columns with lower bulk density and penetration resistance. Although root growth was more abundant for Essex than for PI 416937, root growth of PI 416937 was not decreased by compaction as much as it was for Essex. These results suggest that PI 416937 may possess the genetic capability to produce more root growth in soils with high penetration resistance. This study suggests that genetic improvement for root growth in soils with hard or acidic layers may potentially reduce our dependence on tillage. Gypsum did not affect root growth in this study. 相似文献
11.
pH changes in the rhizosphere of peanut and maize roots pH changes in soil near growing peanuts and maize seedlings were measured using antimony microelectrodes. The roots of each plant actively altered pH, both at the root tip and root hair zone (maize) and immediately behind the root elongation zone (peanut). Along the root elongation zone and at distances greater than 10-15 cm from the root tip, pH moved towards the value in the soil outside of the rhizosphere. Peanut seedlings grown in unfertilized and NO3-fertilized soil (initial pH 5.5) lowered soil pH by 1.5 and by 0.7 units, respectively; whereas maize seedlings caused pH increases of 1.0 and 1.5 units, respectively. In NH4-fertilized soil, both seedlings caused soil pH to fall by 2-3 units. In an acid soil, pH changes occurred at distances of up to approximately 2.5 mm from root surfaces. 相似文献
12.
Effect of nitrogen fertilization, cropping and irrigation on soil air composition and nitrous oxide emission in a loamy clay 总被引:4,自引:0,他引:4
Most of the nitrous oxide (N2O) in the atmosphere, thought to be involved in global warming, is emitted from soil. Although the main factors controlling the production of N2O in soil are well known, we need more quantitative data on the interactions of soil and the environment in the soil that affect the emission. We therefore studied the effects of irrigation, cropping (fallow, barley with grass undersown) and N fertilization (unfertilized, 103 kg N ha?1) on the composition of soil air and direct N2O emission from soil (using the closed chamber method) in a factorial field experiment on a well‐structured loamy clay soil during 1 June?22 October 1993. The measurements were made weekly during the growing season and three times after harvesting. The composition of the soil air did not indicate severe anoxia in any treatment or combination of treatments, but the accumulation of N2O in the soil air indicated that hypoxia was common. At the start of the irrigation the emissions were small, even though there was much ammonium and nitrate in the soil and therefore a potential for emission of N2O produced by both nitrification and denitrification. Larger emissions occurred later. The largest emissions were found when 60–90% of the soil pore space was filled with water. Irrigation and fertilization with N both roughly doubled the cumulative N2O emission. Growing a crop decreased it by a factor of 3–7. Most N2O was lost from the irrigated fertilized soil under fallow (3.5 kg N ha?1), and least from the unirrigated unfertilized soil under barley (0.1 kg N ha?1). 相似文献
13.
Eduardo Martínez Juan-Pablo Fuentes Paola Silva Susana Valle Edmundo Acevedo 《Soil & Tillage Research》2008,99(2):232-244
No-tillage systems affect soil properties depending on the soil, climate, and the time since its implementation. In heavy no-tilled soils a surface compacted layer is commonly found. Such layer can affect root growth and soil water infiltration. In several cases, surface organic carbon can buffer these problems. The aim of this study was to evaluate the effect of 4- and 7-year-old conventional (CT) and no-tillage (NT) treatments on soil physical properties, root growth, and wheat (Triticum turgidum L. var. durum) yield in an Entic Haploxeroll of Central Chile. In both tillage treatments we study soil water retention, bulk density (ρb), soil particle density (ρs), soil water infiltration, mean-weight diameter of soil aggregates (MWD), penetration resistance, grain yield, and root length density (Lv) up to a depth of 15 cm. The MWD and the penetration resistance were higher under NT as compared to CT. For the top 5 cm of soil, Lv was greater under NT as compared to CT. Differences of Lv between NT and CT were 2.09, 7.60, and 4.31 cm root cm−3 soil during the two leaves, flowering and grain filling phenological stages, respectively. Generally, the effect of NT on these properties was more evident near the soil surface. In contrast, fast drainage macropores, ρs, and soil water infiltration rates were higher under CT than under NT. Tillage treatments did not significantly affect ρb and yield. A longer time under no-tillage enhanced aggregate stability, however, other soil physical properties were negatively affected. 相似文献
14.
局部根系盐胁迫对冬小麦生长和光合特征的影响 总被引:3,自引:1,他引:2
通过分根装置设置无盐胁迫(0|0)、局部根系150 mmol-L-1NaCl胁迫(0|150)、全部根系75 mmol-L-1NaCl胁迫(75|75)、全部根系150 mmol-L-1NaCl胁迫(150|150)4种处理,研究根系局部盐胁迫对冬小麦生长及光合特征的影响。结果表明:盐胁迫显著抑制了小麦幼苗的生长,并且随着盐胁迫浓度的增加,小麦受抑制程度加重;根系盐胁迫方式对小麦幼苗生长影响显著,局部根系胁迫处理(0|150)小麦幼苗地上部干重比等浓度150 mmol-L-1NaCl全部盐胁迫处理(150|150)增加23.5%,比等浓度75 mmol-L-1NaCl全部盐胁迫处理(75|75)增加17.2%。在局部根系盐胁迫下,非盐胁迫一侧根系(0|150-0)补偿生长,其根长、侧根数、侧根长比盐胁迫一侧根系(0|150-150)分别增加195.2%、206.2%和237.8%,盐胁迫一侧根系吸收的Na+部分向非盐胁迫一侧根系运输,盐胁迫一侧根系(0|150-150)的Na+含量比全部胁迫处理(150|150)减少12.1%。与全部根系盐胁迫相比,局部根系盐胁迫减少了Na+在叶片中的积累,降低了钠/钾值。局部根系盐胁迫叶片净光合速率、气孔导度、胞间CO2浓度和叶绿素荧光参数(Fv/Fm)均高于同浓度完全盐胁迫处理的小麦幼苗,进而增加地上部和根系的生物量。因此,局部根系胁迫显著缓解了全部盐胁迫对小麦地上部和根系生长的抑制作用。 相似文献
15.
Piyawan Phuphong Ismail Cakmak Atilla Yazici Benjavan Rerkasem 《Journal of plant nutrition》2020,43(9):1259-1267
AbstractThe present study investigated how foliar zinc (Zn) application affects seedling growth and Zn concentration of rice grown in a Zn-deficient calcareous soil with different soil Zn treatments. Seeds were sown in soil with five rates of Zn (0, 0.02, 0.1, 0.5 and 5.0?mg kg?1 soil) with and without foliar application of 0.5% ZnSO4. Seedlings were harvested at 35?days and separated into (i) the youngest leaves, (ii) the remaining shoot parts and (iii) roots. In soil with no Zn supply, shoot and root dry weight of the rice seedlings were significantly increased by foliar and soil Zn treatments. Plant growth was not clearly increased in low soil Zn treatments, while at each soil Zn treatment, foliar Zn application promoted growth of plants. Plants with adequate Zn supply had the highest Zn concentrations in the youngest leaf. Foliar Zn spray improved Zn concentration of the new growth formed after foliar spraying which shows that Zn is phloem mobile and moved from treated leaves into youngest new leaves. The results indicate clearly in rice seedlings that shoot growth shows more responsive to low Zn than the root growth. The results obtained in the present study are of great interest for proper rice growth in Zn-deficient calcareous soils but needs to be confirmed in other rice genotypes. 相似文献
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17.
Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm3 cm–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm3 cm–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm3 cm–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions. 相似文献
18.
《Soil Science and Plant Nutrition》2012,58(5):479-489
ABSTRACTThe specific mechanism by which nitrogen application affects nodulation and nitrogen fixation in legume crops remains uncertain. To further study the effects of nitrogen application on soybean nodulation and nitrogen accumulation, three consecutive tests were performed during the VC-V4, V4-R1 (10 days), and R1-R2 (10 days) growth periods of soybean. In a dual-root soybean system, seedlings on one side were watered with a nutrient solution containing NH4+ or NO3? as the N source (N+ side), and those on the other side were watered with a nitrogen-free nutrient solution (N- side). During the VC-R2 period, on the N+ side, high nitrogen treatment inhibited nodule growth and nitrogenase activity (EC 1.18.6.1), and the inhibition was significantly increased with increasing high nitrogen supply time (10 days, 20 days). When the high nitrogen treatment time reached 20 days, the specific nitrogenase activity (C2H4 μmol?1 g?1 nodule dry mass h?1) was similar to that in the low nitrogen treatment, indicating that the nitrogen fixation capacity per gram of dry mass nodules was almost the same. Therefore, it is assumed that long-term high nitrogen treatment mainly reduces nitrogen fixation by reducing the nodule number. The effect of nitrogen concentration on the roots on the N+ side was greater than that on the N- side. Taken together, these results indicate that nitrogen application affects a contact-dependent local inhibition of root nodule growth, nitrogenase activity, and nitrogen accumulation. The whole plant systematically regulates specific nitrogenase activity, and high nitrogen inhibition is recoverable. 相似文献
19.
Yo Toma Fumiaki Takakai Untung Darung Kanta Kuramochi Suwido H. Limin Salampak Dohong 《Soil Science and Plant Nutrition》2013,59(3):436-451
Our previous research showed large amounts of nitrous oxide (N2O) emission (>200?kg?N?ha?1?year?1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N2O fluxes and the source of nitrogen (N) substrate for N2O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N2O and carbon dioxide (CO2) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N2O emission from two treatments, contribution of the N source for N2O was calculated. Nitrous oxide concentrations at five depths (5–80?cm) were also measured for calculating net N2O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607?kg?N?ha?1?year?1. There were no significant differences in between N2O fluxes in the two treatments at each site. Annual N2O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858?kg?N?ha?1?year?1, respectively. However, there was also no significant difference between annual N2O emissions in the two treatments at each site. This suggests most of the emitted N2O was derived from the decomposition of peat. There were significant positive correlations between N2O and CO2 fluxes in bare treatment in two croplands where N2O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N2O was mainly produced in the surface soil down to 15?cm in the soil. The logarithmic value of the ratio of N2O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N2O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N2O was mainly produced by denitrification at high range of WFPS in surface soil. 相似文献
20.
The ability of plants to extract water from soil is controlled by the water‐potential gradient between root and soil, by the hydraulic conductivity of roots, and, as the soil dries, by that of the soil near the roots (rhizosphere). Recent experiments showed that the rhizosphere turned hydrophobic after drying and it remained temporarily dry after rewetting. Our objective was to investigate whether rhizosphere hydrophobicity is associated with a reduction in root water uptake after drying and rewetting. We used neutron radiography to trace the transport of deuterated water (D2O) in the roots of lupines growing in a sandy soil. The plants were grown in aluminum containers (28 × 28 × 1 cm3) filled with a sandy soil. The soil was initially partitioned into different compartments using a 1‐cm layer of coarse sand (three vertical × three horizontal compartments). We grew plants in relatively moist conditions (0.1 < θ < 0.2). Three weeks after planting, we let the upper left compartment of soil to dry for 2–3 d while we irrigated the rest of the soil. Then, we injected D2O in this compartment and in the upper right compartment that was kept wet. We monitored D2O transport in soil and roots with time‐series neutron radiography. From the changes of D2O concentration inside roots, we estimated the root water uptake. We found that root water uptake in the soil region that was let dry and rewetted was 4–8 times smaller than that in the region that was kept moist. The reduced uptake persisted for > 1–0.5 h. We conclude that a reduction in hydraulic conductivity occurred during drying and persisted after rewetting. This reduction in conductivity could have occurred in roots, in the rhizosphere, or more likely in both of them. 相似文献