Background and Aims Biochar has been shown to aid soil fertility and crop production in some circumstances. We investigated effects of the addition of Jarrah (Eucalyptus marginata) biochar to a ...coarse textured soil on soil carbon and nitrogen dynamics. Methods Wheat was grown for 10 weeks, in soil treated with biochar (0, 5, or 25 t ha−1) in full factorial combination with nitrogen (N) treatments (organic N, inorganic N, or control). Samples were analysed for plant biomass, soil microbial biomass carbon (MBC) and nitrogen (MBN), N mineralisation, CO2 evolution, community level physiological profiles (CLPP) and ammonia oxidising bacterial community structure. Results MBC significantly decreased with biochar addition while MBN was unaltered. Net N mineralisation was highest in control soil and significantly decreased with increasing addition of biochar. These findings could not be attributed to sorption of inorganic N to biochar. CO2 evolution decreased with 5 t ha−1 biochar but not 25 t ha−1. Biochar addition at 25 t ha−1 changed the CLPP, while the ammonia oxidising bacterial community structure changed only when biochar was added with a N source. Conclusion We conclude that the activity of the microbial community decreased in the presence of biochar, through decreased soil organic matter decomposition and N mineralisation which may have been caused by the decreased MBC.
Drivers of nitrogen (N) mineralization in paddy soils, especially under anaerobic soil conditions, are elusive. The influences of exogenous organic matter (OM) and fertilizer application on the ...activities of five relevant enzymes (β-glucosaminidase, β-glucosidase, l-glutaminase, urease and arylamidase) were measured in two long-term field experiments. Of the two field experiments, the 18-year field experiment was established in a weathered terrace soil with rice-wheat crop rotation at the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) farm with five OM treatments and two levels of mineral N fertilizer. The 30-year experiment was established in a young floodplain soil with rice-rice crop rotation at the Bangladesh Agricultural University (BAU) farm with five mineral fertilizer treatments including one with farm yard manure. At BSMRAU, N fertilizer and OM amendments significantly increased all enzyme activities, suggesting the availability of primarily substrate for microbial activity. Whereas at BAU, non-responsiveness of β-glucosidase activity, suggesting that fertilizer and OM amendments had little effect on overall soil microbial activity. Nevertheless the microbial demand for N, β-glucosaminidase and l-glutaminase activities differed among the treatments (P < 0.05) and showed opposite trends with soil N mineralization. Hence enzymatic pathways to acquire N differed with the treatment at BAU site, indicates differences in soil N quality and bio-availability. l-glutaminase activity was the sole investigated variable that positively correlated to both the aerobic and anaerobic N mineralization rates in both field experiments. Combined with a negative correlation between β-glucosaminidase activity and N mineralization rate, it appears that terminal amino acid NH2 hydrolysis was a rate-limiting step for soil N mineralization at the BAU site. Future investigations with joint quantification of polyphenol accumulation and binding of N alongside an array of extracellular enzymes, including oxidases for phenols and hydrolases for N-compounds, would enable verification of the hypothesized binding and stabilization of N with accumulating polyphenols at BAU site under SOM storing management.
•Whether paddy soil N mineralization is product-demand or substrate-supply driven stays elusive.•In a rice-wheat rotation organic matter application determined hydrolytic enzyme activities.•In a double rice rotation instead fertilizer treatments solely altered dehydrogenase activity.•Over both experiments l-glutaminase activity was the best predictor for N mineralization.•Terminal amino acid cleavage might thus be rate limiting paddy soil anaerobic N mineralization.
• The enzymatic separation of physiologically active intraradical hyphae of arbuscular mycorrhiza (AM) fungi from host tissue is an effective way to analyse the physiological characteristics of ...intraradical hyphae. • Applying this technique, first, both biomass and phosphorus (P) distribution were quantified in the intraradical and extraradical part of Gigaspora margarita colonizing onion. Second, the separated intraradical hyphae were incubated in vitro; efflux of phosphate from the hyphae and the hyphal polyphosphate (poly P) content were determined. • A substantial proportion of P in mycorrhizal roots was fungal P, while the proportion of fungal biomass to root biomass was < 2%. Phosphate efflux and the decrease in poly-P content in the hyphae were both enhanced by the addition of glucose and 2-deoxyglucose, an analogue of glucose. The degrees of enhancement for phosphate efflux and poly-P decrease were comparable, suggesting that P efflux from intraradical hyphae was coupled with poly-P hydrolysis. • Based on these findings, the translocation of P from fungus to host was estimated in relation to the distribution of hyphal P in extraradical and intraradical parts of the AM fungus.
Lotus japonicus has been proposed as a model plant for the molecular genetic study of plant-microbe interaction including Mesorhizobium loti and arbuscular mycorrhizal (AM) fungi. Non-mycorrhizal ...mutants of Lotus japonicus were screened from a collection of 12 mutants showing non-nodulating (Nod−), ineffectively nodulating (Fix−) and hypernodulating (Nod++) phenotypes with monogenic recessive inheritance induced by EMS (ethylmethane sulfonate) mutagenesis. Three mycorrhizal mutant lines showing highly reduced arbuscular mycorrhizal colonization were obtained. All of them were derived from Nod− phenotypes. In Ljsym72, the root colonization by Glomus sp. R-10 is characterized by poor development of the external mycelium, formation of extremely branched appressoria, and the blocking of hyphal penetration at the root epidermis. Neither arbuscules nor vesicles were formed in Ljsym72 roots. Fungal recognition on the root surface was strongly affected by the mutation in the LjSym72 gene. Unique characteristics in mutant lines Ljsym71-1 and Ljsym71-2 were the overproduction of deformed appressoria and arrested hyphal penetration of the exodermis. Small amounts of internal colonization including degenerated arbuscule formation occurred infrequently in these types of mutants. Not only fungal development on the root surface but also that in the root exodermis and cortex was affected by the mutation in LjSym71 gene. These mutants represent a key advance in molecular research on the AM symbiosis.
We investigated the effect of nursery inoculation techniques on mycorrhizal colonization and sporulation, growth responses, and nutrient (N and P) uptake to determine the suitable nursery inoculation ...method of wetland rice (Oryza sativa L.) under high-fertility soil conditions. Seedlings were produced in dry-nursery (DN, watered to 60% of -0.03 MPa) and wet-nursery (WN, 3-5 cm water from the soil surface) conditions with or without arbuscular mycorrihizal fungal (Glomus spp.) inoculation. Soil was gamma-ray sterilized before use in this experiment. Mycorrizal fungal colonization was 56% in DN and 23% in WN plants at 6 weeks of growth. The arbuscular mycorrhizal fungal colonization was significantly higher in plants of DN origin than in WN plants after transplantation to the pots, irrespective of growing stages. Mycorrhizal colonization was significantly decreased to 28% in DN plants and to 25% in WN plants at harvest. The grain yield was significantly influenced by nursery conditions. N and P acqusition of wetland rice plants inoculated with Glomus spp. was significantly greater than that of non- inoculated plants at maturity, especially in those originating from DN conditions. P translocation from shoots to grain was accelerated by mycorrhizas.
We examined the effect of arbuscular mycorrhizal fungi inoculation at the nursery stage on the growth and nutrient acquisition of wetland rice (Oryza sativa L.) under field and pot conditions. ...Seedlings were grown on γ-ray sterilized paddy soil in two types of nurseries, namely dry nursery and wet nursery, with or without arbuscular mycorrhizal fungi (AMF) inoculation which was a mixture of indigenous AMF (Glomus spp.) spores collected from the paddy field. Five-to-six week old seedlings were transplanted to the unsterilized soil under field and pot, respectively. Mycorrhizal seedlings had higher shoot biomass under both nursery conditions 5 weeks after sowing. Mycorrhizal colonization and sporulation were 2 to 3 times higher in the dry nursery than the wet nursery at the transplanting stage. Mycorrhizal colonization of plants inoculated in the nursery remained higher than those not inoculated under both field and pot conditions. Sporulation after transplanting to field conditions was about 10 times higher than in the pot. Inoculated plants produced higher biomass at maturity under field conditions, and the grain yield was 14-21% higher than those not inoculated. Conversely, grain yield and shoot biomass were not significantly influenced by AMF colonization under pot conditions. For plants originating from the dry nursery, N, P, Zn and Cu concentrations of field-grown plants at harvest were significantly increased by preinoculation with AMF over those left uninoculated. We conclude that the AMF inoculation at the nursery stage under both dry and wet conditions increased growth, grain yield and nutrient acquisition of wetland rice under field conditions.
Evolution of 14CO2 from onion roots and the
intraradical hyphae of Gigaspora margarita Becker & Hall was
examined by radiorespirometry after addition of 14C-labelled
glucose or sucrose to mycorrhizal ...or non-mycorrhizal roots. In mycorrhizas,
the respiration rate from glucose was about twice that from sucrose. The
respiration rate from glucose in the mycorrhizas was much higher than that
in the non-mycorrhizal roots, but no
differences between mycorrhizal and non-mycorrhizal roots were found in
the respiration from sucrose.
Intraradical hyphae were isolated from mycorrhizas by enzyme digestion and
homogenization followed by
Percoll® gradient centrifugation. The 14C-labelled glucose,
fructose or sucrose was added to the isolated hyphae
and the subsequent evolution of 14CO2
was measured. The hyphae mainly used glucose as a substrate for
respiration. Although sucrose or fructose was utilized to some degree, the
respiration rate from glucose was much
higher than that from sucrose and fructose. This is the first direct evidence
of use of glucose by the intraradical
hyphae of arbuscular mycorrhizal fungi in the symbiotic state.
Arbuscular mycorrhizal (AM) fungi differ in their response to soil pH. Thus, change in soil pH may influence the relative abundance of mycorrhizal fungi inside roots. Root colonization by two AM ...fungi was studied in relation to addition of lime (CaCO3), quantity of inoculum and inoculum placement. Addition of CaCO3 to an acid soil decreased the colonization of roots by Acaulospora laevis but increased colonization by Glomus invermaium when both fungi were present. In acid soil (pH 4.7), almost all roots were colonized by A. laevis, while G. invermaium was dominant when soil pH was increased to pH 7.3. This occurred regardless of whether the inoculum was banded or mixed throughout the soil. There was no effect of CaCO3 on the relative abundance of fungi inside roots at intermediate rates of CaCO3 application (pH 5.3-6.3) when both fungi were inoculated together. In this experiment, both fungi colonized roots at all levels of CaCO3 when inoculated alone, except for A. laevis at the highest level of CaCO3. We conclude that soil pH affects the competitive ability of these two AM fungi during mycorrhiza formation primarily by affecting hyphae growth in soil and thus the relative abundance of hyphae at the root surface and subsequently inside the root.
To examine the utilization of current common treatments by providers from different specialties and the effect on delaying spinal surgery in patients with disk degenerative disease (DDD) related low ...back pain.
Retrospective observational study using data from the MarketScan Commercial Claims and Encounters database (2005-2013).
Not applicable.
Patients (N=6229) newly diagnosed with DDD-related low back pain who received interventional treatments from only 1 provider specialty and continuously enrolled in the database for 3 years after diagnosis.
Measures of treatment utilization and cost were constructed for patients who received spinal surgery within 3 years after diagnosis. Cox proportional hazards models were used to examine time to surgery among provider specialties and generalized linear models were used to examine cost differences among provider specialties.
Of the 6229 patients, 427 (6.86%) underwent spinal surgery with unadjusted mean interventional treatment costs ranging from $555 to $851. Although the differences in mean costs across provider specialties were large, they were not statistically significant. Cox proportional hazards models showed that there was no significant difference between provider specialties in the time from DDD diagnosis to spinal surgery. However, patients diagnosed with DDD at a younger age and receiving physical therapy had significantly delayed time to surgery (hazard ratio, 0.66; 95% confidence interval CI, 0.54-0.81 and hazard ratio, 0.77; 95% CI, 0.62-0.96, respectively).
Although there were no statistically significant differences among provider specialties for time to surgery and cost, patients receiving physical therapy had significantly delayed time to surgery.
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