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1.
Changes in plant antioxidant enzymes (AOEs) in response to cadmium (Cd) pollution are an important mechanism for plant growth and tolerance to Cd-induced stress. The main objective of this greenhouse study was to determine the combined influence of earthworm and arbuscular mycorrhiza (AM) fungal inoculation and their interactions with Cd on AOEs and proline accumulation in leaves of two major crops under Cd stress. Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were exposed to Cd stress (10 and 20 mg kg−1 soil), inoculated with either earthworm (Lumbricus rubellus L.) or AM fungi (Glomus intraradices and Glomus mosseae species) in a pot experiment for three months. Exposure to Cd decreased shoot dry weights, increased shoot Cd and P concentrations, leaf proline accumulation and the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and polyphenol oxidase (PPO) in both mycorrhizal and non-mycorrhizal plants and both in the presence and absence of earthworms. Inoculation of both model plants with earthworms and AM fungi decreased shoot Cd concentrations and the activity of all AOEs, except PPO. Although earthworm activity enhanced the proline content of sunflower in Cd-polluted soils, the proline level of both plants remained unaffected by AM fungi. AM fungi and earthworms may decrease the activity of AOEs through a decline in shoot Cd toxicity and concentration, confirming that plant inoculation with these soil organisms improves maize and sunflower tolerance and protection against Cd toxicity. Generally, the effect of AM fungal inoculation on plant responses to Cd addition was greater than that of earthworm activity. Nonetheless, the interactive effect of AM fungus and earthworm is of minor importance for most of the plant AOEs in Cd-polluted soils.  相似文献   

2.
Water scarcity threatens global food security and agricultural systems are challenged to achieve high yields while optimizing water usage. Water deficit can be accentuated by soil physical degradation, which also triggers water losses through runoff and consequently soil erosion. Although soil health in cropping systems within the Brazilian Cerrado biome have been surveyed throughout the years, information about soil erosion impacts and its mitigation are still not well understood; especially concerning the role of cropping system diversification and its effects on crop yield. Thus, the aim of this study was to assess whether ecological intensification of cropping systems –inclusion of a consorted perennial grass and crop rotation– could promote soil coverage and consequently decrease water erosion and soil, water, and nutrient losses. This work studied the effects of crop rotation and consorted Brachiaria, along with different levels of investment in fertilization on soil physical quality and on soil, water, and nutrient losses, and crop yields. Results proved that soybean monoculture (SS) is a system of low sustainability even under no-till in the Brazilian Cerrado conditions. It exhibited high susceptibility to soil, water, and nutrient losses, causing low crop yields. Our results showed that water losses in SS cropping system were approximately 10% of the total annual rainfall, and total K losses would require an additional 35% of K application. Conversely, ecological intensification of cropping systems resulted in enhanced soil environmental and agronomic functions, increased grain yield, and promoted soil and water conservation: high soil cover rate, and low soil, water and nutrient losses. Ecological intensification proved to be an adequate practice to boost crop resilience to water deficit in the Brazilian Cerrado.  相似文献   

3.
Disturbance and change to C inputs can alter microbial community structure and impact ecosystem function. Particularly in temperate regions, seasonal change also has an effect on microbial communities both directly through climate and indirectly through plant function. The temporal change in microbial communities of an undisturbed pasture, disturbed pasture (similar to a single tillage event) and pasture soil amended with two forms of particulate carbon were monitored over eight consecutive seasons after grass was reestablished. The soil microbial community was assessed by a DNA fingerprinting technique (terminal restriction fragment length polymorphism, TRFLP) of bacterial, fungal and archaeal communities, and also from phospholipid fatty acid (PLFA) analysis. The single disturbance had a significant effect on fungal microbial community structure (by TRFLP) and significantly decreased the fungal:bacterial ratio. Though the change was relatively small, it persisted throughout the sampling period. Nitrate was also higher on the disturbed treatment providing evidence for the theory that changes to fungal:bacterial ratios can alter nutrient cycling and retention. Fungal communities were the most altered by the C amendments, and while bacteria were also affected by the C amendments, seasonal change was a greater cause of variation. Correlation to soil and climatic variables explained more of the total variability for PLFA (78% for all treatments) than bacterial (50%), fungal (35%) and archaeal (14%) restriction fragments. Most climate and soil variables explained significant variation for seasonal patterns in the multivariate community structures but measurements of soil moisture were important for all communities while pH was relatively more important for bacteria, temperature for fungi, and soil C:N ratio for archaea. Autumn was particularly distinct from other seasons for bacteria (less so for the fungal community) and although there was seasonal change in pH suggesting pasture management was a factor, the significant correlation of other soil characteristics suggests that plant physiological changes (most probably root exudates) also played a significant role. The large change in the saprotrophic fungal community due to the particulate C addition but minor seasonal change would tend to suggest that the fungal community may be more responsive to changes in litter inputs rather than root exudates while the reverse is true for bacteria.  相似文献   

4.
Soil aggregate (SA) can be formed and stabilized when soil organic matter (SOM) is decomposed in the soil. However, the relationships between the SA dynamics and SOM with different decomposition rates have not been clarified. Therefore, this study examined the effects of the addition of polysaccharides to soil on SA formation and stability. A Japanese tropical soil was incubated for 99 d at 30 °C in a dark environment following the addition of 0.5% (w/w) starch or cellulose. The decomposition rates of the amendments, and SA formation and stability were evaluated by measuring soil respiration rates, and distribution fractions of soil aggregate sizes and mean weight diameter (MWD) of SA, respectively. The cumulative soil respirations with all treatments rapidly increased until Day 12 of the incubation. The initial slope of the cumulative soil respiration in the soil with starch was significantly higher than that in the soil with cellulose. In either soil with starch or cellulose, the fractions of macro-aggregates (>1000 μm in diameter) significantly increased, respectively, compared with control soil. However, the fractions of meso-aggregates (250–1000 μm) and nano-aggregate (<20 μm) in the soil with starch significantly decreased, while those fractions in the soil with cellulose fluctuated until Day 6. The MWDs reached the maximum on Day 6, indicating the SA formation in the soils with starch or cellulose. The increasing rate of the SA formation in the starch-amended soil was greatly higher than that in the cellulose-amended soil. After Day 6, the MWDs in the soils with either polysaccharide decreased with similar trends with no significant differences between treatments, indicating similar stability of the SA in both treatments. This study showed that the different decomposability of the organic amendments might influence the SA formation differently, but not the SA stability.  相似文献   

5.
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6.
Successful restoration of an ecosystem following disturbance is typically assessed according to similarity between the restored site and a relatively undisturbed reference area. While most comparisons use the average or mean parameter to represent measured properties, other aspects of the distribution, including the variance of the properties may assist in a more robust assessment of site recovery. Our purpose was to compare soil properties in different ages of reclaimed soils with those in reference areas by incorporating the potentially different distributions according to areas. On two sampling dates, in consecutive years, we examined soil properties on a chronosequence of reclaimed natural gas pipelines spanning recovery ages of <1–54 years, obtaining data on soil moisture, organic carbon, nitrogen, electrical conductivity, pH, and microbial abundance. To make the comparisons, we analyzed our data with a Bayesian hierarchical linear mixed model and obtained posterior predictive distributions for the soil properties. This allowed us to probabilistically quantify the extent to which a soil property from a reclaimed treatment was similar to that from an undisturbed reference. We found that the posterior predictive variance of most soil properties was particularly sensitive to disturbance and reclamation, especially, within the first few years of recovery. Response of this variance to disturbance, reclamation, and recovery was not necessarily accompanied by a shift in the posterior predictive mean value of the property. Patterns for all soil properties changed over time, with posterior predictive distributions of soil properties generally becoming more similar to those of the undisturbed reference sites as recovery time increased. We suspect these trends in altered variability coincide with the degree of spatial heterogeneity in soil properties that results following disturbance and reclamation, which is also coupled to patterns of vegetation recovery.  相似文献   

7.
To investigate the climate impacts on the different components of ecosystem respiration, we combined soil efflux data from a tree-girdling experiment with eddy covariance CO2 fluxes in a Mediterranean maritime pine (Pinus pinaster) forest in Central Italy. 73 trees were stem girdled to stop the flux of photosynthates from the canopy to the roots, and weekly soil respiration surveys were carried out for one year. Heterotrophic respiration (RH) was estimated from the soil CO2 flux measured in girdled plots, and rhizosphere respiration (RAb) was calculated as the difference between respiration from controls (RS) and girdled plots (RH).Results show that the RS dynamics were clearly driven by RH (average RH/RS ratio 0.74). RH predictably responded to environmental variables, being predominantly controlled by soil water availability during the hot and dry growing season (May–October) and by soil temperature during the wetter and colder months (November–March). High RS and RH peaks were recorded after rain pulses greater than 10 mm on dry soil, indicating that large soil carbon emissions were driven by the rapid microbial oxidation of labile carbon compounds. We also observed a time-lag of one week between water pulses and RAb peaks, which might be due to the delay in the translocation of recently assimilated photosynthates from the canopy to the root system. At the ecosystem scale, total autotrophic respiration (RAt, i.e. the sum of carbon respired by the rhizosphere and aboveground biomass) amounted to 60% of ecosystem respiration. RAt was predominantly controlled by photosynthesis, and showed high temperature sensitivity (Q10) only during the wet periods. Despite the fact that the study coincided with an anomalous dry year and results might therefore not represent a general pattern, these data highlight the complex climatic control of the respiratory processes responsible for ecosystem CO2 emissions.  相似文献   

8.
通过盆栽试验,研究了在低氮(不施氮)和高氮(施氮0.2 g·kg~(-1))水平下接种不同种类丛枝菌根(AM)真菌[Funneliformis mosseae(BGC-NM03D)、Claroideoglomus etunicatum(BGC-NM01B)和Rhizophagus intraradices(BJ09)]对小麦生长、氮吸收及根内4个硝态氮转运蛋白(NRT)基因、1个辅助蛋白(NAR)基因和2个铵态氮转运蛋白(AMT)基因表达的影响。结果表明,3种AM真菌均能够侵染小麦根系,以R.intraradices菌根的侵染率最高;接种R.intraradices或C.etunicatum能够显著提高小麦的生物量或地上部氮吸收量;无论是高氮还是低氮处理,接种AM真菌后均显著下调了小麦根内NRT、NAR和AMT基因的表达水平,且不同AM真菌调控小麦根内氮转运蛋白基因表达的能力具有明显差异。  相似文献   

9.
接种丛枝菌根真菌(AMF)能显著促进大豆生长和对磷的吸收,但不同磷效率基因型大豆对AMF接种的响应还少有报道。为探究接种AMF对不同磷效率基因型大豆生长和磷转运基因表达的影响,以磷高效大豆BX10和磷低效大豆BD2为试验材料进行盆栽试验,设置接菌和不接菌处理,对大豆干重、菌根侵染性状、氮磷养分含量、根系性状,以及菌根诱导的磷转运基因表达进行了分析。结果表明, AMF接种显著促进了大豆的磷吸收,并且接菌效果存在显著的基因型差异,接种AMF显著增加了BD2的地上部干重、磷含量以及植株总磷吸收量,但只增加了BX10的地上部磷含量和总磷吸收量,对植株地上部干重没有显著影响。无论接种与否,BD2的地上部磷含量均显著高于BX10,表明磷低效的BD2具有较高的植株体内磷转运能力。不接菌条件下,两个大豆基因型根系性状无显著差异;接种AMF后BX10的根系体积和根系平均直径均显著高于BD2。BD2的菌根生长反应(MGR)和菌根磷反应(MPR)均显著高于BX10,对菌根依赖性更高。此外,在接菌处理的BD2根系,代表菌根途径磷吸收的磷转运基因GmPT8、GmPT9和GmPT10表达均显著高于BX10;相应地,BD2的总磷吸收量也显著高于BX10。以上结果表明,接种AMF对促进磷低效大豆BD2生长和磷吸收的作用更大,这可能主要是由于BD2菌根途径的磷吸收量较高,体内磷转运效率较高。以上结果将为研究AMF接种对磷吸收的贡献提供理论依据。  相似文献   

10.
The effectiveness of reforestation programs on degraded soils in the Mediterranean region is frequently limited by a low soil availability and a poor plant uptake and assimilation of nutrients. While organic amendments can improve the nutrient supply, inoculation with mycorrhizal fungi can enhance plant nutrient uptake. A pot experiment was conducted in 2004 to study the influence of inoculation with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola Trappe, Bloss. & Menge, and G. mosseae (Nicol & Gerd.) Gerd. & Trappe) and of an addition of composted sewage sludge or Aspergillus niger–treated dry‐olive‐cake residue on plant growth, nutrient uptake, mycorrhizal colonization, and nitrate reductase (NR) activity in shoot and roots of Juniperus oxycedrus L. Six months after planting, the inoculation of the seedlings with G. intraradices or a mixture of three AM fungi was the most effective treatment for stimulating growth of J. oxycedrus. There were no differences between the two mycorrhizal treatments. All treatments increased plant growth and foliar N and P contents compared to the control plants. Mycorrhizal inoculation and organic amendments, particularly fermented dry olive cake, increased significantly the NR activity in roots.  相似文献   

11.
Most research on the mycorrhizal positive–negative responsiveness continuum (or “mutualism–parasitism continuum”) has focused on individual plant species growing at different levels of P availability. Here, we explore this continuum in an experimental plant community inoculated with three arbuscular mycorrhizal (AM) fungal strains (both single and mixed) growing under four resource availability scenarios. These scenarios are a factorial combination of two levels of water and N availability. Each AM fungal strain had a different origin: an arid ecosystem, a farmland, and a mine. We hypothesized that the response of the plant community to mycorrhizal inoculum would depend on the associated AM fungal strain and would be negatively related with increased nitrogen and water availability. Our results showed that mixed‐strain AM fungal inoculation had more positive effects along a wider range of water and N availability scenarios than single‐strain inoculation. In contrast, mycorrhizal growth response of plants inoculated with a single AM fungal strain shifted from positive to neutral and negative depending on resource availability. Adaptation of each strain to its local conditions might confer different properties to the mycorrhizal symbiosis. Therefore, we conclude that AM fungal origin and environmental limiting resources are crucial factors to predict plant community mycorrhizal growth response in changing ecosystems.  相似文献   

12.
Our objective was to evaluate how increasing levels of N in the medium (0, 4, 8 and 16 mmol N added kg-1 soil) affect the interaction between Sinorhizobium and arbuscular mycorrhiza (AM) fungi in the tripartite symbiosis with Medicago sativa. Growth response, nutrient acquisition, protein content, and nitrate reductase (NR) activity were measured both in plant shoots and roots. Results showed that N levels in soil did not affect mycorrhizal colonization but they strongly influenced nodulation, particularly of mycorrhizal plants. Mycorrhizal colonization was required for a proper nodulation when no N was applied to soil. In contrast, the addition of 4 mmol N kg-1 soil reduced nodulation only in mycorrhizal plants and 8 mmol N added kg-1 soil allowed nodule formation only in non-mycorrhizal plants. Nodulation was totally inhibited in all treatments with the addition of 16 mmol N added kg-1 soil. N addition enhanced NR activity in all the treatments, while AM colonization increased the proportion of NR allocated to roots. This effect was more pronounced under the lowest N levels in the medium. The two AM fungal species showed different distribution pattern of enzymatic activities in plant tissues indicating specific physiological traits. Protein content as well as the relative proportion of protein in roots were greatly increased after mycorrhizal colonization. Glomus intraradices-colonized plants had the highest protein content in shoot and root. Mycorrhizal effects on growth, N acquisition and biochemical variables cannot be interpreted as an indirect P-mediated effect since P content was lower in mycorrhizal plants than in those which were P fertilized. Mycorrhizal colonization increased the N content in plants irrespective of the N level, but the effectiveness of AM fungi on plant N acquisition depended on the AM fungus involved, G. intraradices being the most effective, particularly at the highest N rate. N2 fixation, enhanced by AM colonization, contributed to N acquisition when a moderate N quantity was available in the soil. Nevertheless, under a high N amount the nodulating process and/or fixing capacity by Sinorhizobium was reduced in AM plants. In contrast, the AM fungal mycelium from a particular mycorrhizal fungus may continue to contribute efficiently to the N uptake from the soil even at high N levels. These results demonstrate the particular sensitivity of AM fungal species in terms of their growth and/or function to increasing N amounts in the medium. A selection of AM fungi used to address specific environmental conditions, such as N fertilization regimes comparable to those used in agronomic practices, is required for a better use of N applied to soil.  相似文献   

13.
We compare the effect of arbuscular mycorrhizal (AM) colonization and PO4?3 fertilization on nitrate assimilation, plant growth and proline content in lettuce plants growing under well‐watered (?0.04 MPa) or drought (?0.17 MPa) conditions. We also tested how AM‐colonization and PO4?3 fertilization influenced N uptake (15N) and the percentage of N derived from the fertilizer (% NdfF) by plants under a concentration gradient of N in soil. Growth of mycorrhizal plants was comparable with that of P‐fertilized plants only under well‐watered conditions. Shoot nitrogen content, proline and nitrate reductase activity were greater in AM than in P‐fertilized plants under drought. The addition of 100 μg g?1 P to the soil did not replace the AM effect under drought. Under well‐watered conditions, AM plants showed similar (at 3 mmol N), greater (at 6 mmol N) or lesser (at 9 mmol N) %NdfF than P‐fertilized plants. Comparing a control (without AM inoculation) to AM plants, differences in % NdfF ranged from 138% (3 mmol N) to 22.6% (6 mmol N) whereas no differences were found at 9 mmol N. In comparison with P fertilization, mycorrhizal effects on %NdfF were only evident at the lowest N levels, which indicated a regulatory mechanism for N uptake in AM plants affected by N availability in the soil. At the highest N level, P‐fertilized plants showed the greatest %NdfF. In conclusion, AM symbiosis is important for N acquisition and N fertilizer utilization but this beneficial mycorrhizal effect on N nutrition is reduced under large quantities of N fertilizer.  相似文献   

14.
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15.
The breakdown of organic nitrogen in soil is a potential rate-limiting step in nitrogen cycling. Arbuscular mycorrhizal (AM) fungi are root symbionts that might improve the ability of plants to compete for organic nitrogen products against other decomposer microbes. However, AM uptake of organic nitrogen, especially in natural systems, has traditionally been difficult to test. We developed a novel quantitative nanotechnological technique to determine in situ that organic nitrogen uptake by AM fungi can occur to a greater extent than has previously been assumed. Specifically, we found that AM fungi acquired recalcitrant and labile forms of organic nitrogen. Moreover, N enrichment of soil reduced plot-scale uptake of these compounds. Since most plants host AM fungi, AM use of organic nitrogen could widely influence plant productivity, especially where N availability is relatively low.  相似文献   

16.
The aim of this work was to study the effect of arbuscular mycorrhizal fungus Glomus mosseae on growth and nitrogen (N) metabolism of durum wheat (Tritcum durum) under various P soil contents. The analyses were extended to macro and micronutrient tissue concentrations, nitrate reductase and glutamine synthetase activities, as well as protein, aminoacids, pyridine dinucleotides and adenine nucleotides. Arbuscular mycorrhiza increased wheat growth in soil in which P availability was low and nitrate was the dominant N form. The root colonization occurred at the highest level in plants grown in limiting soil P and was inversely related to soil P content. The micorrhizal wheat plants contained also the highest concentrations of macro (P, K, Ca, N) and micronutrients (Fe, Zn, Mn) as well as free amino acids, protein, NAD, NADP, AMP, ADP, ATP in roots and leaves. In particular, the micronutrient tissue concentrations (Zn, Mn) supported that mycorrhiza actively modulated their uptake limiting interferences and optimizing growth better than the plant roots, like a very efficient “rootstock”. Control plants grown at the highest soil P did not reach the same concentration as the mycorrhizal plants. Nitrate reductase activities in the roots of mycorrhizal plants were higher than in the control ones, while glutamine synthetase activities were highest in the leaves. Protein and amino acids concentrations, as well as AMP, ADP, ATP, NAD(P), and NAD(P)H were also higher than in the control. Among the free amino acids in the roots, the high levels of glutamine, asparagine, arginine, support the view that ammonium was transferred through the arbuscules to the root cells where it was re‐assimilated in the cortical cells, forming high N : C ratio‐amino acids. They were transferred to the leaves where all the other N compounds could be largely synthesized using the carbon skeletons supplied by photosynthesis.  相似文献   

17.
《Journal of plant nutrition》2013,36(6):1089-1101
Abstract

Indian mustard (Brassica juncea L. cv. RH-30) was grown under different types and levels of nitrogen (N) sources, i.e. nitrate, ammonical, and nitrate plus ammonical, at 40, 80, and 120 kg ha? 1 under green house conditions. The plants were salinized with 8 and 12 dSm? 1 at 35 and 55 days after sowing. A progressive inhibition of the activity of enzymes of N metabolism, i.e., nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), was observed with increasing level of salinity. However, the magnitude of such reductions was lowest at the highest level of N (120 kg ha? 1) as compared with the lowest level (40 kg ha? 1) irrespective of N source. The activity of nitrate-assimilating enzymes (NR and NiR) was maximum with nitrate fertilizer, and minimum with the ammonical form. The alleviation of detrimental effects of salinity on NR and NiR was better with the highest level of N (120 kg ha? 1) in nitrate form as compared with the lowest level of N (40 kg ha? 1). In contrast, the maximum activity of ammonium-assimilating enzymes (GS, GOGAT, and GDH) was observed with the highest level of N (120 kg ha? 1) and the minimum with the nitrate form of N under salinity. These results indicate that despite the high salinity, an increase in the concentration and uptake of N stimulates the activities of nitrate-assimilating enzymes (NR and NiR) as well as of the ammonia-assimilating enzymes (GS, GOGAT, and GDH).  相似文献   

18.
Mycorrhizal plants from a variety of ecosystems have the capacity to take up organic forms of nitrogen, yet the fraction of plant nitrogen demand met by organic N (ON) uptake remains unclear. ON uptake by mycorrhizal plants is a biochemical process that involves multiple steps, including breakdown and uptake of soil ON by mycorrhizal fungi, internal transformation of ON, and transfer of N to the host plant. We present hypothetical mechanisms controlling each of these steps and outline predictions for how these mechanisms structure patterns of ON uptake by mycorrhizal plants in ecosystems. Using a synthesis of published data, we found that uptake of amino acids by mycorrhizal fungi is related to the relative abundance, N content, and carbon structure of the amino acid. We hypothesize that the bond strength and structural diversity of soil ON controls the breakdown of polymeric ON by mycorrhizal fungi. In addition, the availability of carbon resources for the mycorrhizal fungus influences the capacity for mycorrhizal fungi to assimilate amino acids and produce extracellular enzymes that catalyze the breakdown of polymeric ON.  相似文献   

19.
In most plant species, nutrient uptake is facilitated upon root association with symbiotic arbuscular mycorrhizal (AM) fungi. The aim of the present experiment was to test how the form in which nitrogen (N) is supplied to the growth medium affects substrate pH, AM development, and contribution of the symbiosis to phosphorus (P) uptake from sparingly available or soluble resources. Cowpea (Vigna unguiculata L. Walp) plants inoculated or noninoculated with AM fungi (Glomus sp.) were grown in pots with a sand substrate supplied with nutrient solution. The nutrient solution was prepared either with a high or a low concentration of soluble P, and NO ‐N : NH ‐N ratios of 9:1 or 5:5. The substrate supplied with low‐P nutrient solution was either or not additionally amended with ground rock phosphate. Despite a high level of root colonization, AM fungi used in the present study did not appear to increase plant availability of rock phosphate. It cannot be excluded that the ability of AM root systems to acquire P from sparingly available resources differs depending on the plant and fungal genotypes or environmental conditions. The absence from the growth substrate of P‐solubilizing microorganisms able to associate with AM mycelia might also have been a reason for this observation in our study. Increased supply of NH relative to NO improved plant P availability from rock phosphate, but also had a negative effect on the extent of AM‐fungal root colonization, irrespective of the plant P‐nutritional status. Whether increasing levels of NH can also negatively affect the functioning of the AM symbiosis in terms of plant element uptake, pathogen protection or soil‐structure stabilization deserves further investigation.  相似文献   

20.
Abstract. We studied the effect of inoculation with three arbuscular-mycorrhizal (AM) fungi ( Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae ([Nicol & Gerd.] Gerd. & Trappe) and the addition of composted sewage sludge on root nitrate reductase (NR, EC 1.6.6.1.) activity, mycorrhizal colonization, plant growth and nutrient uptake in Retama sphaerocarpa L. seedlings afforested in a semiarid, degraded Mediterranean soil under well-watered and non-watered conditions. Six months after planting, the mycorrhizal inoculation and the irrigation of plants had a strong effect on the growth parameters. The effect on plant growth was a negative interaction between plant irrigation and mycorrhizal inoculation and a positive interaction between plant irrigation and composted sewage sludge addition. The latter treatment had a significant, but moderate, effect on the growth but conferred no additional benefit when combined with mycorrhizal inoculation. Mycorrhizal inoculation, composted sewage sludge and irrigation had a significant effect on NR activity in roots and on foliar nutrients. The irrigation significantly increased the positive effect of composted sewage sludge on NR activity and the concentrations of foliar N and K. The effect of mycorrhizal inoculation on NR activity did not depend on the water regime. The effectiveness of mycorrhizal inoculation on the establishment and growth of R. sphaerocarpa seedlings in these Mediterranean conditions was independent of water regime. The addition of composted sewage sludge was only effective when soil water was freely available. The combination of mycorrhizal inoculation and composted sewage sludge addition had no synergistic effect on plant growth.  相似文献   

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