Bleaching of leaf litter accelerates the decomposition of recalcitrant components and mobilization of nitrogen in a subtropical forest

Selective removal of lignin and other recalcitrant compounds, collectively registered as acid-unhyrolyzable residue (AUR), results in bleaching of leaf litter, but the importance of bleaching in decomposition processes on forest soil has not been fully evaluated. The aims of this study were to elucidate the occurrence of bleached area in decomposing leaf litter and to compare chemical composition between bleached and nonbleached portions in a subtropical forest in Japan. Field incubation of leaf litter was performed over an 18-month period with the litterbag method. The decomposition processes during the first 9 month were characterized by the relatively rapid mass loss and increase of bleached area, whereas the mass loss was slowed down and the bleached area decreased thereafter. Mass loss of leaf tissues was faster and AUR content was lower in bleached than in nonbleached portions, indicating the acceleration of mass loss in bleached leaf tissues by the selective decomposition of recalcitrant compounds. The decrease in carbonyl-C in the bleached portions was associated with the increase of extractable nitrogen. The results suggest that the bleaching plays a dominant role in the transformation and turnover of organic compounds and nitrogen in decomposing leaf litter.

New insight into spheroidal iron (oxyhydr)oxide concretion formation models: Diagenetic concretion nucleation associated with neutral fluids from a mafic intrusion

<p>Directly west of the San Rafael Swell on the Colorado Plateau in the western U.S., the Jurassic Entrada Sandstone is intruded by a ~2 km long mafic dike. The dike is Miocene; however, the area is also crosscut by Laramide (~50Ma) clusters of deformation bands that are up 500 m long and up to ~3 m wide. The mafic intrusions infused the area with fluids that bleached the red sandstone directly surrounding the dike. On one side of the dike, the bleached area terminates at an adjacent deformation band set ~475 m south of the dike. Field observations suggest that the dike acted as a baffle preventing fluids from migrating further into the sandstone. Spheroidal calcite and iron (oxyhydr)oxide concretions are present in the bleached host rock, although calcite concretions (1-3 cm diameter) are present throughout the area on both sides of the deformation bands and in both red and white host rock. Iron (oxyhydr)oxide concretions (1-5 cm diameter) are limited to the uppermost bleached section between the dike and the deformation band set. Some iron concretions have solid interiors, and some have well-cemented rinds with interiors depleted of cement. Additionally, some iron concretions are nucleated on individual deformation bands that are ~2 mm wide and iron (oxyhydr)oxide cemented joint faces are also present. Thermochemical modeling shows the infiltrating Miocene fluids were CO<sub>2</sub>-bearing, but near neutral pH. The restricted location of the iron (oxyhydr)oxide concretions and relation to the calcite concretions suggest that stagnation of fluid is needed for spheroidal iron oxyhydroxide concretion formation. Calcite concretion nucleation and growth may be quicker resulting in more widespread occurrences, and/or may have preceded the Miocene fluids that infiltrated the unit. The evidence presented here shows that recently proposed models calling for calcite concretion precursors and acidic fluids for iron (oxyhydr)oxide concretion formation may not be correct.</p>

Do nymphs and adults of three Neotropical zoophytophagous mirids damage leaves and fruits of tomato?

The predators Macrolophus basicornis (Stal), Engytatus varians (Distant) and Campyloneuropsis infumatus (Carvalho) consume large numbers of tomato pests such as Bemisia tabaci (Gennadius) and Tuta absoluta (Meyrick). However, they are zoophytophagous and feed on plant parts as well. We evaluated the type and effect of injury caused by nymphs and adults of these mirids on tomato seedlings and fruit in the absence of prey. For each mirid species, seedlings were exposed to groups of 20 nymphs or adults for 72 h, and fruits were exposed for 48 h to groups of four nymphs or adults. Type and the number of injury on stems, petioles and leaflets of tomato seedlings and fruits were recorded after removal of insects. Nymphs and adults of these mirids caused necrotic rings on the leaflets, but no injury was observed on stem and petioles. The necrotic rings on leaflets consisted of blemishes, characterized by feeding punctures surrounded by a yellowish, bleached area. The number of necrotic rings did not exceed one per individual mirid and seedlings developed normally. Nymphs also caused feeding punctures on tomato fruit, but in even lower numbers than on leaflets. Two weeks after the start of the experiment the tomato fruit still looked fresh and feeding punctures had disappeared. Adults did not cause any injury to tomato fruit. The results indicate that nymphs and adults of these zoophytophagous mirids cause little injury to tomato seedlings and fruit, even when present in high densities and in the absence of prey, making them interesting candidates for biological control.

Bleaching of leaf litter and associated microfungi in subboreal and subalpine forests

Fungal decomposition of lignin leads to the whitening, or bleaching, of leaf litter, especially in temperate and tropical forests, but less is known about such bleaching in forests of cooler regions, such as boreal and subalpine forests. The purposes of the present study were to examine the extent of bleached area on the surface of leaf litter and its variation with environmental conditions in subboreal and subalpine forests in Japan and to examine the microfungi associated with the bleaching of leaf litter by isolating fungi from the bleached portions of the litter. Bleached area accounted for 21.7%–32.7% and 2.0%–10.0% of total leaf area of Quercus crispula and Betula ermanii, respectively, in subboreal forests, and for 6.3% and 18.6% of total leaf area of B. ermanii and Picea jezoensis var. hondoensis, respectively, in a subalpine forest. In subboreal forests, elevation, C/N ratio and pH of the FH layer, and slope aspect were selected as predictor variables for the bleached leaf area. Leaf mass per area and lignin content were consistently lower in the bleached area than in the nonbleached area of the same leaves, indicating that the selective decomposition of acid unhydrolyzable residue (recalcitrant compounds such as lignin, tannins, and cutins) enhanced the mass loss of leaf tissues in the bleached portions. Isolates of a total of 11 fungal species (6 species of Ascomycota and 5 of Basidiomycota) exhibited leaf-litter-bleaching activity under pure culture conditions. Two fungal species (Coccomyces sp. and Mycena sp.) occurred in both subboreal and subalpine forests, which were separated from each other by approximately 1100 km.

Fluorescence recovery after photobleaching in material and life sciences: putting theory into practice

Fluorescence recovery after photobleaching (FRAP) is a versatile tool for determining diffusion and interaction/binding properties in biological and material sciences. An understanding of the mechanisms controlling the diffusion requires a deep understanding of structure–interaction–diffusion relationships. In cell biology, for instance, this applies to the movement of proteins and lipids in the plasma membrane, cytoplasm and nucleus. In industrial applications related to pharmaceutics, foods, textiles, hygiene products and cosmetics, the diffusion of solutes and solvent molecules contributes strongly to the properties and functionality of the final product. All these systems are heterogeneous, and accurate quantification of the mass transport processes at the local level is therefore essential to the understanding of the properties of soft (bio)materials. FRAP is a commonly used fluorescence microscopy-based technique to determine local molecular transport at the micrometer scale. A brief high-intensity laser pulse is locally applied to the sample, causing substantial photobleaching of the fluorescent molecules within the illuminated area. This causes a local concentration gradient of fluorescent molecules, leading to diffusional influx of intact fluorophores from the local surroundings into the bleached area. Quantitative information on the molecular transport can be extracted from the time evolution of the fluorescence recovery in the bleached area using a suitable model. A multitude of FRAP models has been developed over the years, each based on specific assumptions. This makes it challenging for the non-specialist to decide which model is best suited for a particular application. Furthermore, there are many subtleties in performing accurate FRAP experiments. For these reasons, this review aims to provide an extensive tutorial covering the essential theoretical and practical aspects so as to enable accurate quantitative FRAP experiments for molecular transport measurements in soft (bio)materials.

Evaluación de la mezcla de ametrina + clomazone en caña de azúcar.

An experiment was established at Rancho Casablanca, located in the Municipality of Puente Nacional, in the State of Veracruz, Mexico, in order to evaluate the toxicity caused by the mixture of the herbicides ametryn + clomazone to the sugarcane varieties MEX-79-431, MEX- 69-290, MEX-68-P23 and CP-72-2086. Four weed control treatments were evaluated: 1. Ametryn + clomazone (1200 + 800 g/ha), 2. Ametryn + clomazone (1800 + 1200 g/ha), 3. Ametryn + 2,4-D (1225 + 650 g/ha) and 4. Weeded control. Herbicides were applied when sugarcane plants had from two to four leaves. The mixture of ametryn + clomazone caused leaf bleaching in all the sugarcane varieties. The bleached area varied from 36.3 to 47.5% with the highest dose of the mixture, and from 25 to 39.4%, with the lowest dose, and it practically disappeared about 45 days after application. On the other hand, the mixture of ametryn + 2,4-D did not cause any bleaching. Toxicity caused by the mixture of ametryn + clomazone did not affect the number of plant leaves, the number of stalks in 2 linear m, nor the plant height. Stalk yield and sucrose content were not affected either.