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High-resolution data on spatial variations in the productivity of bryophytes and the mass of the organic layer are important components in geochemical models for northern forests. We investigated spatial variations in growth rates of the feather moss Hylocomium splendens and the thickness of the organic layer in relation to environmental factors on a north-facing slope in Interior Alaska. The forest floor on the 600 m × 600 m slope was classified into four types, i.e., Classes I–IV, characterized mainly by the dominance of leaf litter, H. splendens, Pleurozium schreberi, and Sphagnum spp., respectively. Spatial autocorrelation analyses showed clustering patterns for some tree and forest floor variables, which were associated with the distribution of the four classes on the slope. Mean growth (length) rates of H. splendens were high in Class II, while growth rates by weight were high in Class I due to a high weight-to-length ratio of shoots. The thickness of the organic layer in bryophyte patches ranged from 6.0 to 40.7 cm and was also controlled by slope orientation. The presence of large trees, particularly Betula neoalaskana, mediated the relationship between topography and forest floor characteristics.

In undisturbed tropical montane rainforests massive organic layers accommodate the majority of roots and only a small fraction of roots penetrate the mineral soil. We investigated the contribution of vegetation to slope stability in such environments by modifying a standard model for slope stability to include an organic layer with distinct mechanical properties. The importance of individual model parameters was evaluated using detailed measurements of soil and vegetation properties to reproduce the observed depth of 11 shallow landslides in the Andes of southern Ecuador. By distinguishing mineral soil, organic layer and above-ground biomass, it is shown that in this environment vegetation provides a destabilizing effect mainly due to its contribution to the mass of the organic layer (up to 973 t ha− 1 under wet conditions). Sensitivity analysis shows that the destabilizing effect of the mass of soil and vegetation can only be effective on slopes steeper than 37.9°. This situation applies to 36% of the study area. Thus, on the steep slopes of this megadiverse ecosystem, the mass of the growing forest promotes landsliding, which in turn promotes a new cycle of succession. This feedback mechanism is worth consideration in further investigations of the impact of landslides on plant diversity in similar environments.

We have observed optical second harmonic generation (SHG) from a space charge layer (SCL) in a stacked indium tin oxide (ITO)/molybdenum trioxide (MoO_3)/N−N′-diphenyl-N−N′-bis(1-naphthly)-1,1′-biphenyl-4,4′-diamine (α-NPD) system. When the MoO_3 thicknesses were increased, the SHG signals from this system decreased sharply at smaller MoO_3 thicknesses, and were saturated at MoO_3 thicknesses larger than 1 nm. These results prove the vital role of SCL in improvement of drive voltages of organic light-emitting diodes.

Tropical nitrogen (N) deposition is projected to increase substantially within the coming decades. Increases in soil emissions of the climate-relevant trace gases NO and N2O are expected, but few studies address this possibility. We used N addition experiments to achieve N-enriched conditions in contrasting montane and lowland forests and assessed changes in the timing and magnitude of soil N-oxide emissions. We evaluated transitory effects, which occurred immediately after N addition, and long-term effects measured at least 6 weeks after N addition. In the montane forest where stem growth was N limited, the first-time N additions caused rapid increases in soil N-oxide emissions. During the first 2 years of N addition, annual N-oxide emissions were five times (transitory effect) and two times (long-term effect) larger than controls. This contradicts the current assumption that N-limited tropical montane forests will respond to N additions with only small and delayed increases in soil N-oxide emissions. We attribute this fast and large response of soil N-oxide emissions to the presence of an organic layer (a characteristic feature of this forest type) in which nitrification increased substantially following N addition. In the lowland forest where stem growth was neither N nor phosphorus (P) limited, the first-time N additions caused only gradual and minimal increases in soil N-oxide emissions. These first N additions were completed at the beginning of the wet season, and low soil water content may have limited nitrification. In contrast, the 9- and 10-year N-addition plots displayed instantaneous and large soil N-oxide emissions. Annual N-oxide emissions under chronic N addition were seven times (transitory effect) and four times (long-term effect) larger than controls. Seasonal changes in soil water content also caused seasonal changes in soil N-oxide emissions from the 9- and 10-year N-addition plots. This suggests that climate change scenarios, where rainfall quan

The ability of self-assembled monolayers to modify the surface electronic states of metals and semiconductors is of interest for a variety of technological applications. When such changes occur at the nanoscale with precise control, an important contribution to nanotechnologies can be achieved. Here, Kelvin probe force microscopy is employed to accurately characterize the work function changes induced by nanopatterns of mercaptohexadecanoic acid deposited on gold by dip-pen nanolithography. Using this technique in conjunction with other AFM scanning modes reveals that, depending on the lithography conditions, the nanodeposits can assume three different structures: an ordered phase with upright molecules; an ordered phase with horizontal molecules; and finally, a disordered phase with molecules adopting different conformations. Thanks to this controlled tunability of the adsorbate structure, the metal work function is demonstrated to be finely tuned within an interval of 50 meV. © 2009 American Chemical Society.