Seed Mucilage Improves Seedling Emergence of a Sand Desert Shrub

The success of seedling establishment of desert plants is determined by seedling emergence response to an unpredictable precipitation regime. Sand burial is a crucial and frequent environmental stress that impacts seedling establishment on sand dunes. However, little is known about the ecological role of seed mucilage in seedling emergence in arid sandy environments. We hypothesized that seed mucilage enhances seedling emergence in a low precipitation regime and under conditions of sand burial. In a greenhouse experiment, two types of Artemisia sphaerocephala achenes (intact and demucilaged) were exposed to different combinations of burial depth (0, 5, 10, 20, 40 and 60 mm) and irrigation regimes (low, medium and high, which simulated the precipitation amount and frequency in May, June and July in the natural habitat, respectively). Seedling emergence increased with increasing irrigation. It was highest at 5 mm sand burial depth and ceased at burial depths greater than 20 mm in all irrigation regimes. Mucilage significantly enhanced seedling emergence at 0, 5 and 10 mm burial depths in low irrigation, at 0 and 5 mm burial depths in medium irrigation and at 0 and 10 mm burial depths in high irrigation. Seed mucilage also reduced seedling mortality at the shallow sand burial depths. Moreover, mucilage significantly affected seedling emergence time and quiescence and dormancy percentages. Our findings suggest that seed mucilage plays an ecologically important role in successful seedling establishment of A. sphaerocephala by improving seedling emergence and reducing seedling mortality in stressful habitats of the sandy desert environment

Regulation of proteinaceous effector expression in phytopathogenic fungi

Effectors are molecules used by microbial pathogens to facilitate infection via effector-triggered susceptibility or tissue necrosis in their host. Much research has been focussed on the identification and elucidating the function of fungal effectors during plant pathogenesis. By comparison, knowledge of how phytopathogenic fungi regulate the expression of effector genes has been lagging. Several recent studies have illustrated the role of various transcription factors, chromosome-based control, effector epistasis, and mobilisation of endosomes within the fungal hyphae in regulating effector expression and virulence on the host plant. Improved knowledge of effector regulation is likely to assist in improving novel crop protection strategies

Variation in capsidiol sensitivity between Phytophthora infestans and Phytophthora capsici is consistent with their host range.

Plants protect themselves against a variety of invading pathogenic organisms via sophisticated defence mechanisms. These responses include deployment of specialized antimicrobial compounds, such as phytoalexins, that rapidly accumulate at pathogen infection sites. However, the extent to which these compounds contribute to species-level resistance and their spectrum of action remain poorly understood. Capsidiol, a defense related phytoalexin, is produced by several solanaceous plants including pepper and tobacco during microbial attack. Interestingly, capsidiol differentially affects growth and germination of the oomycete pathogens Phytophthora infestans and Phytophthora capsici, although the underlying molecular mechanisms remain unknown. In this study we revisited the differential effect of capsidiol on P. infestans and P. capsici, using highly pure capsidiol preparations obtained from yeast engineered to express the capsidiol biosynthetic pathway. Taking advantage of transgenic Phytophthora strains expressing fluorescent markers, we developed a fluorescence-based method to determine the differential effect of capsidiol on Phytophtora growth. Using these assays, we confirm major differences in capsidiol sensitivity between P. infestans and P. capsici and demonstrate that capsidiol alters the growth behaviour of both Phytophthora species. Finally, we report intraspecific variation within P. infestans isolates towards capsidiol tolerance pointing to an arms race between the plant and the pathogens in deployment of defence related phytoalexins

Een metamodel van PCLake

PCLake is een waterkwaliteitsmodel ontwikkeld door het RIVM. Het model kan onder andere gebruikt worden om het effect van voorgestelde maatregelen op de waterkwaliteit van meren te berekenen. De grote gedetailleerdheid van het model leidt tot relatief lange reken-tijden, wat een bezwaar vormt als het model ingezet wordt in scenariostudies met een groot aantal simulaties. Doel van deze studie is het opstellen van een metamodel PCLake, d.w.z. een model van het model PCLake dat - bij benadering - dezelfde resultaten genereert, maar in een aanzienlijk kortere tijd. De operationele doelstelling van deze studie was om het effect van acht belangrijke omgevingsvariabelen op het chlorofylgehalte van het meer, zoals gesimuleerd door PCLake, te beschrijven met behulp van een metamodel. Deze invoer-variabelen waren de oppervlakte en diepte van het meer, de instroomsnelheid van het water, het fosfaat- en slibgehalte van het instromende water, de verhouding tussen het nitraat- en het fosfaatgehalte van het instromende water, de visserijdruk en de oppervlakte moeras. Voor de metamodellering werden drie verschillende methoden toegepast: (1) regressieboom, (2) radial basis function network en (3) interpolatie. In een vergelijking tussen de drie methoden bleek dat interpolatie de meest nauwkeurige benadering gaf van de door PCLake gesimuleerde waarden. De overeenkomst tussen PCLake en het meest nauwkeurige meta-model, toegepast op een aselecte steekproef van 80000 punten uit de invoerruimte, leverde een R2 van 0.965. De rekentijd van alle metamodellen varieerde van 1 - 2 milliseconden per berekening, tegen 9 seconden voor PCLake. Omdat het metamodel is opgesteld voor een breed bereik van invoervariabelen, houdt dit in dat het gebruikt kan worden in scenariostudies, om in de plaats van PCLake voorspellingen te doen voor de waterkwaliteit in toekomstige situaties. Naast een methode-vergelijking bevat dit rapport ook practische aanwijzingen over de toepassing van de bestudeerde methoden in de vorm van een aantal procedures.PCLake is an integrated model simulating the water quality of lakes, developed at RIVM. Among other things, the model may be used to evaluate the effects of measures that are proposed to enhance the water quality of lakes. The level of detail in PCLake is reflected in relatively long execution times. The objective of this study was to develop a metamodel for PCLake - a model of the model PCLake - that generates approximately the same results in a considerably shorter time. The operational question in this study was to describe the effects of eight environmental and management factors on the chlorophyll content of the lake, as simulated by PCLake, with help of a metamodel. The factors were the depth and area of the lake, the inflow rate of water, the concentrations of phosphorus and inorganic matter in the inflowing water, the ratio between nitrogen and phosphorus concentrations in the inflowing water, the fishing rate, and the area of marsh along the lake. Three metamodelling techniques were applied; (1) regression tree, (2) radial basis function network, and (3) interpolation. Comparison of the techniques showed that interpolation gave the most accurate estimation of output values simulated by PCLake. The correspondence between PCLake and the most accurate metamodel, applied to a random sample of 80,000 points in input space, was characterised by R2 = 0.965. The duration of one calculation by all metamodels ranged from 1 - 2 milliseconds, compared to 9 seconds for PCLake. In combination with the broad ranges of input variables that the metamodel was developed for, this implies that the metamodel may be used to substitute PCLake in scenario studies where predictions for future conditions are made. Apart from a comparison of modelling techniques, the report also contains practical instructions for the application of the techniques that were studied.VROM-DG

Een metamodel van PCLake

PCLake is an integrated model simulating the water quality of lakes, developed at RIVM. Among other things, the model may be used to evaluate the effects of measures that are proposed to enhance the water quality of lakes. The level of detail in PCLake is reflected in relatively long execution times. The objective of this study was to develop a metamodel for PCLake - a model of the model PCLake - that generates approximately the same results in a considerably shorter time. The operational question in this study was to describe the effects of eight environmental and management factors on the chlorophyll content of the lake, as simulated by PCLake, with help of a metamodel. The factors were the depth and area of the lake, the inflow rate of water, the concentrations of phosphorus and inorganic matter in the inflowing water, the ratio between nitrogen and phosphorus concentrations in the inflowing water, the fishing rate, and the area of marsh along the lake. Three metamodelling techniques were applied; (1) regression tree, (2) radial basis function network, and (3) interpolation. Comparison of the techniques showed that interpolation gave the most accurate estimation of output values simulated by PCLake. The correspondence between PCLake and the most accurate metamodel, applied to a random sample of 80,000 points in input space, was characterised by R2 = 0.965. The duration of one calculation by all metamodels ranged from 1 - 2 milliseconds, compared to 9 seconds for PCLake. In combination with the broad ranges of input variables that the metamodel was developed for, this implies that the metamodel may be used to substitute PCLake in scenario studies where predictions for future conditions are made. Apart from a comparison of modelling techniques, the report also contains practical instructions for the application of the techniques that were studied.PCLake is een waterkwaliteitsmodel ontwikkeld door het RIVM. Het model kan onder andere gebruikt worden om het effect van voorgestelde maatregelen op de waterkwaliteit van meren te berekenen. De grote gedetailleerdheid van het model leidt tot relatief lange reken-tijden, wat een bezwaar vormt als het model ingezet wordt in scenariostudies met een groot aantal simulaties. Doel van deze studie is het opstellen van een metamodel PCLake, d.w.z. een model van het model PCLake dat - bij benadering - dezelfde resultaten genereert, maar in een aanzienlijk kortere tijd. De operationele doelstelling van deze studie was om het effect van acht belangrijke omgevingsvariabelen op het chlorofylgehalte van het meer, zoals gesimuleerd door PCLake, te beschrijven met behulp van een metamodel. Deze invoer-variabelen waren de oppervlakte en diepte van het meer, de instroomsnelheid van het water, het fosfaat- en slibgehalte van het instromende water, de verhouding tussen het nitraat- en het fosfaatgehalte van het instromende water, de visserijdruk en de oppervlakte moeras. Voor de metamodellering werden drie verschillende methoden toegepast: (1) regressieboom, (2) radial basis function network en (3) interpolatie. In een vergelijking tussen de drie methoden bleek dat interpolatie de meest nauwkeurige benadering gaf van de door PCLake gesimuleerde waarden. De overeenkomst tussen PCLake en het meest nauwkeurige meta-model, toegepast op een aselecte steekproef van 80000 punten uit de invoerruimte, leverde een R2 van 0.965. De rekentijd van alle metamodellen varieerde van 1 - 2 milliseconden per berekening, tegen 9 seconden voor PCLake. Omdat het metamodel is opgesteld voor een breed bereik van invoervariabelen, houdt dit in dat het gebruikt kan worden in scenariostudies, om in de plaats van PCLake voorspellingen te doen voor de waterkwaliteit in toekomstige situaties. Naast een methode-vergelijking bevat dit rapport ook practische aanwijzingen over de toepassing van de bestudeerde methoden in de vorm van een aantal procedures

Long-term impact of chronosequential land use change on soil carbon stocks on a Swedish farm

Agricultural practices and land use significantly influence soil carbon storage. The processes that are affected by land use and management are generally understood, but uncertainties in projections are high. In this paper, we investigate the long-term effects of chronosequential land use change from grassland to cropland and vice versa on soil carbon stock dynamics in four fields on a Swedish farm. Between 1850 and 1920, three of the fields were converted from grassland into cropland, and one was converted back to grassland in 1971. The fourth (control) field is a grassland that has never been ploughed. In 1937, the four fields were sampled at 111 points in a regular grid (25 or 50 m) and the dried soil samples were stored at our Department. In 1971 and 2002, the original grid points were revisited and re-sampled. Land use changes affected the soil C stock significantly. In 1937, carbon stocks were significantly smaller in the arable fields than in the grassland soil. In the field that was converted from arable back to grassland, soil C increased significantly at an average rate of about 0.4 Mg ha-1 year-1. A soil C balance model (ICBM) driven by standard meteorological data and soil carbon input estimated from yield records described soil carbon dynamics reasonably well, although the range of simulated relative changes in C stocks between 1937 and 2002 in the four fields (from -7.4 to +8.8%) was narrower than those measured (from -19.5 to +16.5%). There are only few long-term studies in Northern Europe available for quantifying the effect of land use change on soil carbon stocks and the results presented here are therefore useful for improving predictions of changes in soil carbon driven by land use change

Elicitin recognition confers enhanced resistance to Phytophthora infestans in potato

Potato late blight, caused by the destructive Irish famine pathogen Phytophthora infestans, is a major threat to global food security1,2. All late blight resistance genes identified to date belong to the coiled-coil, nucleotide-binding, leucine-rich repeat class of intracellular immune receptors3. However, virulent races of the pathogen quickly evolved to evade recognition by these cytoplasmic immune receptors4. Here we demonstrate that the receptor-like protein ELR (elicitin response) from the wild potato Solanum microdontum mediates extracellular recognition of the elicitin domain, a molecular pattern that is conserved in Phytophthora species. ELR associates with the immune co-receptor BAK1/SERK3 and mediates broad-spectrum recognition of elicitin proteins from several Phytophthora species, including four diverse elicitins from P. infestans. Transfer of ELR into cultivated potato resulted in enhanced resistance to P. infestans. Pyramiding cell surface pattern recognition receptors with intracellular immune receptors could maximize the potential of generating a broader and potentially more durable resistance to this devastating plant pathogen