Diversity and Functionality of Arbuscular Mycorrhizal Fungi in Three Plant Communities in Semiarid Grasslands National Park, Canada

Septate endophytes proliferating in the roots of grasslands’ plants shed doubts on the importance of arbuscular mycorrhizal (AM) symbioses in dry soils. The functionality and diversity of the AM symbioses formed in four replicates of three adjacent plant communities (agricultural, native, and restored) in Grasslands National Park, Canada were assessed in periods of moisture sufficiency and deficiency typical of early and late summer in the region. The community structure of AM fungi, as determined by polymerase chain reaction-denaturing gradient gel electrophoresis, varied with sampling time and plant community. Soil properties other than soil moisture did not change significantly with sampling time. The DNA sequences dominating AM extraradical networks in dry soil apparently belonged to rare taxa unreported in GenBank. DNA sequences of Glomus viscosum, Glomus mosseae, and Glomus hoi were dominant under conditions of moisture sufficiency. In total, nine different AM fungal sequences were found suggesting a role for the AM symbioses in semiarid areas. Significant positive linear relationships between plant P and N concentrations and active extraradical AM fungal biomass, estimated by the abundance of the phospholipid fatty acid marker 16:1ω5, existed under conditions of moisture sufficiency, but not under dry conditions. Active extraradical AM fungal biomass had significantly positive linear relationship with the abundance of two early season grasses, Agropyron cristatum (L.) Gaertn. and Koeleria gracilis Pers., but no relationship was found under dry conditions. The AM symbioses formed under conditions of moisture sufficiency typical of early summer at this location appear to be important for the nutrition of grassland plant communities, but no evidence of mutualism was found under the dry conditions of late summer.     

Humic acid differentially improves nitrate kinetics under low‐ and high‐affinity systems and alters the expression of plasma membrane H+‐ATPases and nitrate transporters in rice

Humic acids (HAs) have a major effect on nutrient uptake, metabolism, growth and development in plants. Here, we evaluated the effect of HA pretreatment applied with a nutrient solution on the uptake kinetics of nitrate nitrogen (N‐NO₃^?) and the metabolism of nitrogen (N) in rice under conditions of high and low NO₃^? supply. In addition, the kinetic parameters of NO₃^? uptake, N metabolites, and nitrate transporters (NRTs) and the plasma membrane (PM) H⁺‐ATPase gene expression were examined. The plants were grown in a growth chamber with modified Hoagland and Arnon solution until 21 days after germination (DAG), and they were then transferred to a solution without N for 48 h and then to another solution without N and with and without the addition of HAs for another 48 h. After this period of N deprivation, the plants received new nutrient solutions containing 0.2 and 2.0 mM N‐NO₃^?. Treatment of rice plants with HA promoted the induction of the genes OsNRT2.1‐2.2/OsNAR2.1 and some isoforms PM H⁺‐ATPase in roots. The application of HAs differentially modified the parameters of the uptake kinetics of NO₃^? under both concentrations. When grown with 0.2 mM NO₃^?, the plants pretreated with HA had lower K_m and C_min values as well as a higher V_max/K_m ratio. When grown with 2 mM NO₃^?, the plants pretreated with HA had a higher V_max value, a greater root and shoot mass, and a lower root/shoot ratio. The N fractions were also altered by pretreatment with HA, and a greater accumulation of NO₃^? and N‐amino was observed in the roots and shoots, respectively, of plants pretreated with HA. The results suggest that pretreatment with HA modifies root morphology and gene expression of PM H⁺‐ATPases and NO₃^? transporters, resulting in a greater efficiency of NO₃^? acquisition by high‐ and low‐affinity systems.     

<Emphasis Type="Italic">Candida middelhoveniana</Emphasis> sp. nov., a new yeast species found on the rhizoplane of organically cultivated sugarcane

A novel yeast species within the Metschnikowiaceae is described based on a strain from the sugarcane (Saccharum sp.) rhizoplane of an organically managed farm in Rio de Janeiro, Brazil. The D1/D2 domain of the large subunit ribosomal RNA gene sequence analysis showed that the closest related species were Candida tsuchiyae with 86.2% and Candida thailandica with 86.7% of sequence identity. All three are anamorphs in the Clavispora opuntiae clade. The name Candida middelhoveniana sp. nov. is proposed to accommodate this highly divergent organism with the type strain Instituto de Microbiologia, Universidade Federal do Rio de Janeiro (IMUFRJ) 51965^T (=Centraalbureau voor Schimmelcultures (CBS) 12306^T, Universidade Federal de Minas Gerais (UFMG)-70^T, DBVPG 8031^T) and the GenBank/EMBL/DDBJ accession number for the D1/D2 domain LSU rDNA sequence is FN428871. The Mycobank deposit number is MB 519801.     

Shoot δ15N and δ13C values of non-host Brassica rapa change when exposed to ±Glomus etunicatum inoculum and three levels of phosphorus and nitrogen

Glasshouse experiments were conducted to study the response of non-host Brassica rapa and host Sorghum bicolor to inoculation with the arbuscular mycorrhizal fungus (AMF) Glomus etunicatum when given different levels of N (0.9 mmol kg^-1 sand, 2.7 mmol kg^-1 sand, 8.1 mmol kg^-1 sand) and P (3.6 µmol kg^-1 sand, 10.7 µmol kg^-1 sand, 32.0 µmol kg^-1 sand) fertiliser. On both plant species, the presence of G. etunicatum inoculum (+AMF) was associated with significant changes of shoot '¹⁵N values, with +AMF plants having larger average '¹⁵N values than uninoculated plants (-AMF). These values are the largest average differences in shoot '¹⁵N yet recorded for AMF and nutrient effects. B. rapa shoot '¹⁵N average differences ranged from 1.67‰ to 2.70‰, while for S. bicolor they range between 2.07‰ and 4.40‰. For shoot '¹³C only the non-host B. rapa responded to -AMF and added N. Although the harvested dry weight biomass (-35.2% B. rapa; +39.8% S. bicolor) of both plant species responded to AMF inoculation, no direct relationship was observed between isotopic discrimination and growth inhibition for the non-host B. rapa. In this paper we discuss some implications regarding AMF inocula on the basis of our findings and current literature.     

Lunularia cruciata, a potential in vitro host for Glomus proliferum and G. intraradices

A study was conducted to define culture conditions for in vitro growth arbuscular mycorrhizal fungi (AMF) with liverworts as hosts. Lunularia cruciata (L.) Dumortier ex. Lindberg developed in vitro monoxenic mycothalli with both Glomus proliferum Dalpé & Declerck (MUCL 41827) and Glomus intraradices Schenck & Smith (MUCL 43204). AMF inoculated plants were co-cultured in plastic Petri dishes with semi-solidified medium supplemented with sucrose and grown under filtered light. Mycothalli of L. cruciata produced external hyphae and spores in quantities equivalent to those obtained with Ri T-DNA transformed root systems.     

The influence of litter quality on the relationship between vegetation and below-ground compartments: a Procrustean approach

Aims

We used a Procrustean superimposition approach associated with regression analysis to test hypotheses regarding the relationship between plant communities and distinct below-ground compartments—soil chemistry (SC) and soil microbial activity (SMA). Additionally, we evaluated litter chemical quality as an interface between the above and below-ground compartments.

Methods

Plant community, and soil chemical and biochemical data from three post-mining degraded sites under reclamation and from one nearby forest site in the Brazilian Amazon Basin were analyzed.

Results

All studied sites presented distinct plant community, litter quality, SC and SMA. Plant community consistently affected the below-ground variation in both SC and SMA compartments. The influence of litter quality was greater in the plant community versus SMA relationship than in the plant community versus SC. Nevertheless, the SC affected significantly the SMA, but without influence of litter quality.

Conclusions

Differently from previous studies, our findings suggest that plant community and soil chemistry can affect the soil microbial activity independently. Specifically for our study area, these results point to a rupture of the ‘in nested’ structure of the causal relationship between changes in vegetation, changes in the chemical litter quality, changes in the SC and the response of SMA.