‘Candidatus Liberibacter solanacearum’ detected in Trioza urticae using suction trap-based monitoring of psyllids in Germany

Journal of Plant Diseases and Protection - Psyllids are small, phloem-feeding insects. Several species are vectors of economically important pathogens, such as ‘Candidatus Liberibacter...     

Temporal variability of the Atlantic meridional overturning circulation at 26.5 degrees N

The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5 degrees N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 +/- 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 10(6) cubic meters per second). Interannual changes in the overturning can be monitored with a resolution of 1.5 Sv.     

Identification of transgenes from wood of genetically transformed poplar trees

We have extracted total DNA from different fractions of fresh wood as well as from cold-stored and air-dried wood harvested from transgenic aspen grown in the field. The highest amounts of DNA were obtained from bark/cambium tissue; the DNA quality, however, was poor. Best results in PCR and Southern blot analyses were obtained from DNA extracted from early wood. Using appropriate primer pairs, amplification products were obtained from both the foreign gene (transgene) and aspen genomic sequences. In Southern blot analyses transgene-specific hybridisation signals were obtained. This is the first report on the detection of foreign genes in wood sampled from genetically modified trees.     

Assessing long term effects of compost fertilization on soil fertility and nitrogen mineralization rate

Background

Fertilization with organic waste compost can close the nutrient cycles between urban and rural environments. However, its effect on yield and soil fertility must be investigated.

Aim

This study investigated the long-term effect of compost on soil nutrient and potentially toxic elements (PTEs) concentration, nutrient budgets, and nitrogen (N) mineralization and efficiency.

Methods

After 21 years of annual compost application (100/400 kg N ha^–1 year^–1 [100BC/400BC]) alone and combined with mineral fertilization, soil was analyzed for pH, organic carbon (SOC), nutrient (total N and P, N_min, extractable CAL-P, CAL-K, and Mg), and PTE (Cu, Ni, Zn) concentrations. Yields were recorded and nutrient/PTE budgets and apparent net mineralization (ANM, only 2019) were calculated.

Results

N efficiency was the highest in maize and for mineral fertilization. Compost application led to lower N efficiencies, but increased ANM, SOC, pH, and soil N, and surpluses of N, P, and all PTEs. Higher PTE concentrations were only found in 400BC for Cu. Nutrient budgets correlated with soil nutrient concentration. A surplus of 16.1 kg P ha^–1 year^–1 and 19.5 kg K ha^–1 year^–1 resulted in 1 mg kg^–1 increase in CAL-P and CAL-K over 21 years.

Conclusion

Compost application supplies nutrients to crops with a minor risk of soil-accumulation of PTEs. However, the nutrient stoichiometry provided by compost does not match crop offtakes causing imbalances. Synchronization of compost N mineralization and plant N demand does not match and limits the yield effect. In winter wheat only 65–70% of N mineralization occurred during the growth period.     

Adaptation of Chinese and German maize-based food-feed-energy systems to limited phosphate resources—a new Sino-German international research training group

Phosphate is supplied to agriculture by mining and fertilizer production, followed by different steps of phosphate utilization, including primary production, feed and food consumption, and conversion of biomass, with accumulation in soils, but little recycling and severe environmental losses. Phosphate is a limited essential nutrient, however, with very uneven distribution worldwide. Closing the cycle and reducing primary phosphate consumption are fundamental future challenges. Maize has a relatively high phosphate requirement. China and Germany together cover the whole range of maize production systems. The new Sino-German international research training group “Adaptation of Chinese and German maize-based food-feed-energy systems to limited phosphate resources” (AMAIZE-P) was initiated in 2018 as a joint venture of the China Agricultural University (Beijing, China) and the University of Hohenheim (Stuttgart, Germany). The interdisciplinary and complementary research is driven by the hypothesis that under phosphate limited conditions, high productivity and high phosphate use efficiency can be achieved simultaneously by adapting phosphate cycling and availability (sources) to the multipurpose phosphate demands (sinks) in maize-based food-feed-energy systems. The educational program for doctoral researchers in China and Germany includes joint block seminars, thematic field trips, case studies, methodological courses, doctoral researchers’ conferences, intercultural training sessions and personal training.     

Nitrogen rhizodeposition in agricultural crops: Methods,estimates and future prospects

The objective of the present review was to present the current knowledge on nitrogen (N) rhizodeposition, including techniques for ¹⁵N labelling of agricultural plants, amounts of N rhizodeposition and its fate in soil. Rhizodeposition is the process of release of organic and inorganic compounds from living plant roots. It is often quantified in terms of carbon (C) and less often as N derived from rhizodeposition (NdfR). Rhizodeposition of N can be estimated by labelling plants with ¹⁵N and following its fate in soil. Most methods used for labelling plants with ¹⁵N can only be applied after appearance of the first leaf and only allow pulse or multiple pulse labelling. Only the split-root technique and the application of gaseous ¹⁵N allow continuous labelling. All methods available at present have their flaccidities mostly due to the fact that the application of N is not following its physiological pathway of assimilation or by using artificial conditions. In the studies reviewed, amounts of N rhizodeposits ranged from 4% to 71% of total assimilated plant N. In legumes the median was 16% and in cereals it was 14%. Rhizodeposits were 15–96% of the below-ground plant biomass (BGP). In legumes the median was 73% and in cereal it was 57%. The high variability of these results shows the need for more investigations on N rhizodeposition looking especially on the factors influencing the amounts released in different plant species under field conditions.     

Intraspecific growth variation among rainbow trout and brook trout: impact of initial body weight and feeding level

This study describes growth variation within groups of salmonids and the relation to initial fish weights and feeding levels. PIT-tagged rainbow trout (RT) and brook trout (BT) of start weight 120–170 g were reared in separate tanks for 9 weeks. Both species were fed each day either a high ration close to satiation (H) or half of this ration (L). Four experimental groups (RT-H, RT-L, BT-H, BT-L) were studied with regard to their propensity to increase weight in accord with their initial weight. The slope of the regression line between initial weights (g) and weight increases for individuals in each tank in each period was applied as indicator for this propensity (termed “slope”). All calculated slopes in the experiment were positive which indicates the general ability of weighty fish to gain more weight than smaller individuals. The average slope during all 9 weeks was 2–4 times higher for RT-L (5.91) than for all other groups (RT-H: 1.50, P < 0.01; BT-H: 1.76, P < 0.01 and BT-L: 2.88, P < 0.05), indicating the particular propensity of large RT to gain weight when feed was restricted. Overall, ration level had large impact on slopes (H: 1.63, L: 4.39, P < 0.01), while this was not the case for species (RT: 3.71, BT: 2.32, P > 0.05). The magnitude of slopes decreased over time (weeks 0–3:4.27, weeks 3–6:3.02 and weeks 6–9:1.74, P < 0.05). The observed differences in weight gains between experimental groups were reflected in differences in coefficients of variations (CVs) for body growth. RT had larger body weight (BW) CVs compared to BT (0.257 vs. 0.206, P < 0.01) indicating more uneven feed share among RT than among BT in general. RT-L had significantly higher BW CVs than all other groups (0.300 vs. 0.184–0.229, P < 0.01). The observed differences in weight gains enhance size variations in terms of higher CVs, and this may have implications for feeding tactics in aquaculture where large size variations in groups may be disadvantageous to fish farmers.     

The problem of pretreatment and unintentional variations in the fumigation-extraction method for time-course measurements in the field

A control soil stored at 4°C was analyzed 38 times by fumigation-extraction during a period of 11 months to correct for variations caused by the analytical procedure. The difference in extractable C between fumigated and unfumigated samples oscillated around the average without a positive or negative trend. When data from contemporaneously extracted field samples were corrected with control soil data the variations were lowered. The deviations between corrected and uncorrected biomass C values had maxima of ±12%. Data obtained for seven dates using pre-extraction, wet-sieving, and centrifuging were compared with data obtained by the conventional procedure without any pretreatment. A negative difference from data obtained without pretreatment was found when the soil water content was decreased to 6%. The largest positive difference (+38%) was found in May during the period of highest root growth.     

Lichen diversity in temperate montane forests is influenced by forest structure more than climate

Although the effect of forest management on lichens in temperate forests has been widely examined, little is known about the influence of management-related factors on their biodiversity relative to factors that cannot be altered by management. Here we determined whether forest structure or climate determines lichen diversity in the Bavarian Forest National Park in southeastern Germany, taking spatial variables into account. We investigated 517 single tree stems along 4 transects in 113 pre-stratified plots (8 m in diameter) in this montane forest. We grouped environmental variables into three sets: climate (macroclimate, non-manageable), forest structure (manageable), and space. The explanatory powers of these sets of variables for lichen diversity were compared using variance partitioning for the lichen community, species density, and threatened species density. The relationships of single characteristics of forest structure with lichen species diversity were analyzed using generalized linear models (GLM). Lichen diversity was better explained by stand structures than by climate. Spatial effects influenced the number of species per plot. Among the structural features, the availability of dead wood and sycamore maple as well as forest continuity were most important for the enhancement of lichen diversity. Open canopy structures affected the total diversity positively. Although the availability of large trees was not an influential factor in the GLM at the plot level, high diversity levels were generally associated with large stem diameters at the level of single stems. We provide recommendations for sustainable forest-management practices that aim at specifically enhancing lichen diversity in temperate areas experiencing low levels of air pollution.     

Impact of effective microorganisms and other biofertilizers on soil microbial characteristics,organic‐matter decomposition,and plant growth

Incubation and pot experiments were conducted to investigate the impact of commercially distributed biofertilizers (effective microorganisms [EM], BIOSTIMULATOR, BACTOFIL‐A, and BACTOFIL‐B) on soil microbial‐biomass content and activity, net N mineralization in soil, and growth of Lolium perenne. According to the manufacturers, the products tested are based on microbial inoculants or organic growth stimulants, and are supposed to influence soil microbial properties and improve soil conditions, organic‐matter decomposition, and plant growth. In the incubation experiment (40 d, 20.6°C, 50% maximum water‐holding capacity), EM was repeatedly applied to soil together with different organic amendments (nonamended, chopped straw, and lupine seed meal). Under the experimental conditions of this study, no or only marginal effects of EM on organic C, total N, and mineral N in soil could be observed. In soil treatments without any organic amendment, EM suspension slightly enhanced microbial activity measured as soil CO₂ evolution. In soil with easily degradable plant residues (lupine seed meal), EM suspension had a suppressive effect on microbial biomass. However, comparisons with sterilized EM and molasses as the main additive in EM suspension showed that any effect of EM could be explained as a pure substrate effect without the influence of added living organisms. In the pot experiment with Lolium perenne (air‐conditioned greenhouse cabin, 87 d, 16.8°C, 130 klxh d^–1 light quantity), the products EM, BIOSTIMULATOR, BACTOFIL‐A, and BACTOFIL‐B were tested in soil with growing plants. The products were repeatedly applied for a period of 42 d. Within this study, no effects of the different biofertilizers on mineral N in soil were detectable. There were clear suppressive effects of all tested biofertilizers on microbial‐biomass content and activity. Comparisons with sterilized suspensions showed that the effects were not due to living microorganisms in the suspensions, but could be traced back to substrate‐induced processes.