Effects of formic acid, formaldehyde and two levels of tannic acid on changes in the distribution of nitrogen (N) and plant enzymatic activity during ensilage of lucerne (Medicago sativa) were studied. Lucerne [300 g dry matter (DM) kg )1 forage] silages were prepared untreated (control) and with formic acid (4 g kg )1 DM), formaldehyde (1 g kg )1 DM) and two levels of tannic acid (20 and 50 g kg )1 DM) as additives. Inhibition of proteolysis by formic acid was more effective than the other additives during the first 7 d of ensiling. Tannic acid was as effective at inhibiting production of nonprotein-N, ammonia-N and free amino acid-N as formic acid and formaldehyde. However, increased concentrations of non-protein-N and free amino acid-N in silage from day 1 to 35 of ensiling were less with the higher level of tannic acid than that in the control and other additive-treated silages. Carboxypeptidase lost its activity slowly with increasing time of ensiling. At day 2, it still had 0AE79 of the original activity in the control silage. After 21 d of ensiling, high levels of carboxypeptidase activity, proportionately 0AE41, 0AE49, 0AE10, 0AE35 and 0AE30 of the original activity, remained in the control silage, and silages made with formic acid, formaldehyde, and low and high levels of tannic acid respectively. There were higher levels of activity of acid proteinase in formic acid-treated silage than in the control silage until day 2 of ensilage indicating that the reduction of proteolysis by formic acid was probably due to acidifying the forage below the pH optima of plant protease. Aminopeptidase activity in all silages declined rapidly after ensiling.

No abstract

Ralstonia solanacearum is a major phytopathogenic bacterium that attacks many crops and other plants around the world. In this study, a novel actinomycete, designated strain NEAU-SSA 1T, which exhibited antibacterial activity against Ralstonia solanacearum, was isolated from soil collected from Mount Song and characterized using a polyphasic approach. Morphological and chemotaxonomic characteristics of the strain coincided with those of the genus Streptomyces. The 16S rRNA gene sequence analysis showed that the isolate was most closely related to Streptomyces aureoverticillatus JCM 4347T (97.9%). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain formed a cluster with Streptomyces vastus JCM4524T (97.4%), S. cinereus DSM43033T (97.2%), S. xiangluensis NEAU-LA29T (97.1%) and S. flaveus JCM3035T (97.1%). The cell wall contained LL-diaminopimelic acid and the whole-cell hydrolysates were ribose, mannose and galactose. The polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), hydroxy-phosphatidylethanolamine (OH-PE), phosphatidylinositol (PI), two phosphatidylinositol mannosides (PIMs) and an unidentified phospholipid (PL). The menaquinones were MK-9(H4), MK-9(H6), and MK-9(H8). The major fatty acids were iso-C17:0, C16:0 and C17:1 ω9c. The DNA G+C content was 69.9 mol %. However, multilocus sequence analysis (MLSA) based on five other house-keeping genes (atpD, gyrB, recA, rpoB, and trpB), DNA–DNA relatedness, and physiological and biochemical data showed that the strain could be distinguished from its closest relatives. Therefore, it is proposed that strain NEAU-SSA 1T should be classified as representatives of a novel species of the genus Streptomyces, for which the name Streptomyces sporangiiformans sp. nov. is proposed. The type strain is NEAU-SSA 1T (=CCTCC AA 2017028T = DSM 105692T).

Accurately quantifying evapotranspiration (ET) is crucial to fully understanding regional water resource management and potential feedbacks to climate change in alpine grasslands. The quantitative relationships between ET and environmental controls were investigated by a continuous eddy covariance dataset from June 2014 to December 2016 over an alpine Kobresia meadow on the northeastern Qinghai‐Tibetan Plateau. The results showed that daily ET averaged 1.7± 1.5 mm/day (Mean ± 1 S.D.), with values of 2.9 ± 1.3, 1.6 ± 1.0, and 0.7± 0.6 mm/day during the growing season, seasonal transition period, and nongrowing season, respectively. Cumulative growing season ET was 63% of annual ET with little annual variability (349.9 ± 12.1 mm). Paired‐samples t‐test analysis indicated that monthly ET was larger than maximum potential ET derived from the FAO‐56 reference crop ET by 17% (p < .001, N = 12) in the growing season, likely because of high aerodynamic conductance, but was less than the minimum equilibrium ET by 19% (p < .001, N = 14) during the nongrowing season owing to limited surface moisture availability from the frozen soil. The structural equation models revealed that daily ET was mostly dominated by net radiation (the standardized coefficient of the total effect was 0.78). Soil surface moisture and leaf area index played secondary roles in daily ET variability during the nongrowing season and growing season, respectively. At an annual scale, the bulk surface conductance (8.25–10.65 mm/s), decoupling coefficient (0.43–0.48, 0.61 in the growing season), and the ratio of ET to equilibrium ET (1.08–1.33) were consistent with the strongly energy‐limited conditions in the alpine meadow. This study indicated that initial vegetation rehabilitation on the severely degraded meadow would be at the risk of rapid water consumption in humid alpine regions.

No abstract

Abstract. In the past two decades, increasing human activity (i.e., overgrazing) in the Tibetan Plateau has strongly influenced plant succession processes, resulting in the degradation of alpine grasslands. Therefore, it is necessary to diagnose the degree of degradation to enable implementation of appropriate management for sustainable exploitation and protection of alpine grasslands. Here, we investigated environmental factors and plant functional group (PFG) quantity factors during the alpine grassland succession processes. Principal component analysis (PCA) was used to identify the parameters indicative of degradation. We divided the entire degradation process into six stages. PFG types shifted from rhizome bunchgrasses to rhizome plexus and denseplexus grasses during the degradation process. Leguminosae and Gramineae plants were replaced by sedges during the advanced stages of degradation. The PFGs were classified into two reaction groups: the grazing-sensitive group, containing Kobresia humilis Mey, and Gramineae and Leguminosae plants, and the grazing-insensitive group, containing Kobresia pygmaea Clarke. The first group was correlated with live root biomass in the surface soil (0-10 cm), whereas the second group was strongly correlated with mattic epipedon thickness and K. pygmaea characteristics. The degree of degradation of alpine meadows may be delineated by development of mattic epipedon and PFG composition. Thus, meadows could be easily graded and their use adjusted based on our scaling system, which would help prevent irreversible degradation of important grasslands. Because relatively few environmental factors are investigated, this approach can save time and labor to formulate a conservation management plan for degraded alpine meadows.

Actinobacteria associated with insects represent one potentially rich source of novel natural products with antifungal activity. Here, we investigated the phylogenetic diversity and community composition of actinobacteria associated with ants using a combination of culture-dependent and-independent methods. Further, we assessed the antagonistic activity against phytopathogenic fungi and identified the secondary metabolites from isolates with bioactivity. A total of 416 actinobacterial isolates were obtained from three ant species (Camponotus japonicus, Lasius fuliginosus, and Lasius flavus) located in five nests. The largest amount of isolates were observed in the head samples. 16S rRNA gene sequencing showed that the isolates were diverse and belonged to ten genera within the phylum Actinobacteria, with Streptomyces and Micromonospora comprising the most abundant genera. High-throughput sequencing analyses revealed that the actinobacterial communities were more diverse and dominated by the families Nocardioidaceae, Nocardiaceae, Dermacoccaceae, Intrasporangiaceae, and Streptomycetaceae. In addition, 52.3% of the representative isolates had inhibitory properties against phytopathogenic fungi. Chemical analysis of one Streptomyces strain led to the discovery of two known compounds and one new compound. These results demonstrated that ant-derived actinobacteria represented an underexplored bioresource library of diverse and novel taxa that may be of potential interest in the discovery of new agroactive compounds.

The present study was conducted to examine the influence of a pathogen Sclerotinia sclerotiorum (Lib.) de Bary on the actinobacterial community associated with the soybean roots. A total of 70 endophytic actinobacteria were isolated from the surface-sterilized roots of either healthy or diseased soybeans, and they were distributed under 14 genera. Some rare genera, including Rhodococcus, Kribbella, Glycomyces, Saccharothrix, Streptosporangium and Cellulosimicrobium, were endemic to the diseased samples, and the actinobacterial community was more diverse in the diseased samples compared with that in the heathy samples. Culture-independent analysis of root-associated actinobacterial community using the high-throughput sequencing approach also showed similar results. Four Streptomyces strains that were significantly abundant in the diseased samples exhibited strong antagonistic activity with the inhibition percentage of 54.1–87.6%. A bioactivity-guided approach was then employed to isolate and determine the chemical identity of antifungal constituents derived from the four strains. One new maremycin analogue, together with eight known compounds, were detected. All compounds showed significantly antifungal activity against S. sclerotiorum with the 50% inhibition (EC50) values of 49.14–0.21 mg/L. The higher actinobacterial diversity and more antifungal strains associated with roots of diseased plants indicate a possible role of the root-associated actinobacteria in natural defense against phytopathogens. Furthermore, these results also suggest that the root of diseased plant may be a potential reservoir of actinobacteria producing new agroactive compounds.