Seasonal dynamics of wood formation: a comparison between pinning,microcoring and dendrometer measurements

Three different methods were evaluated for analysing wood formation of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) in Finland. During two growing seasons, wood formation dynamics were determined both by wounding the cambium with a needle followed by localisation of the wound-associated tissue modification after the growing season (pinning), and by extracting small increment cores during the growing season (microcoring). Stem radius was additionally monitored with band dendrometers. For Norway spruce, pinning and microcoring yielded similar dates for the onset of wood formation. The timing of wood production during the growing season was also similar for pinning and microcoring. For Scots pine, the onset of wood formation was recorded from microcores almost 2 weeks later than from pinning samples. In Scots pine, microcore measurements also produced somewhat later cessation dates for tracheid formation than the pinning samples. For both tree species, the total number of tracheids formed during the growing season was, however, about the same for pinning and microcoring. Dendrometer results clearly differed from those of pinning and microcoring. In particular, the dendrometers showed an increase of stem radius considerably earlier in spring, when the other methods did not detect wood formation. Thus, pinning and microcoring currently represent the most reliable techniques for detailed monitoring of wood formation.     

Effects of thinning and fertilization on wood properties and economic returns for Norway spruce

The effects of silviculture on wood and tracheid properties, and economic returns of Norway spruce (Picea abies (L.) Karst.) were investigated in two case studies, one comparing different thinning intensity in southeastern Finland and the other considering the effects of optimal nutrient addition in northern Sweden. Models for predicting the wood and tracheid properties of Norway spruce were integrated into a distance-independent process-based growth and yield model. Increasing the thinning intensity resulted in a lower mean wood density, tracheid length, and latewood proportion in harvested wood. Wood density and tracheid length of harvested pulpwood slightly decreased in later thinnings and final cuts. Thinning regimes with high early growing stock and decreasing later growing stock were most profitable. Nutrient addition accelerated volume growth and increased the value growth. The increase in volume growth due to nutrient addition more than offset the economic influence of the loss in wood density and tracheid length.     

Temperature sensitivity of soil organic matter decomposition in southern and northern areas of the boreal forest zone

Much effort has been made to improve understanding of factors controlling the temperature dependence of soil organic matter (SOM) decomposition. The question of how soils formed in different geographical locations and conditions respond to temperature changes is still open. In addition to climate, residence times of soil organic matter are controlled by its decomposability and microbial community. In this work we hypothesized that the decomposition of SOM is adapted to the prevailing SOM quality and climatic conditions. This should result in different temperature vs. decomposition curves for northern and southern soils. We studied short-term temperature dependence of SOM decomposition near the northern and southern borders of the boreal forest zone using a Gaussian model. As carbon mineralization rate is driven by microbial activity, we focused on organic carbon fractions available to microbes and the size, composition and functioning of microbial communities in the soil. Despite differences in microbial community structure and behavior, similar amounts and qualities of the microbially available carbon led to similar temperature dependences of carbon mineralization in the north and south. The overall soil respiration rate level was higher in spruce forest sites than in pine forest sites irrespective of climate conditions. Our results do not mean that there is no risk of carbon losses from northern soils due to warming climate conditions. As temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes might lead to significant carbon losses from the soils.     

Temperature sensitivity of young and old soil carbon – Same soil,slight differences in 13C natural abundance method,inconsistent results

Predictions of future climate change critically depend on the temperature sensitivity of soil organic carbon decomposition. One question of debate is whether temperature sensitivity differs between young or labile and old or more stable carbon pools. We re-analysed soil that has previously led to the conclusion that old soil carbon is more temperature sensitive. The re-analysis gave different results compared to the earlier study, most likely due to small differences in an otherwise very similar experimental approach. This study illustrates how conclusions may depend upon details of the experimental setting.     

Potential of dry fractionation of wheat bran for the development of food ingredients,part II: Electrostatic separation of particles

Wheat bran is a composite material made of several layers, such as pericarp, testa and aleurone. It could be fractionated into purified fractions, which might either be used as food ingredients, or serve as a starting material for extraction of bioactive compounds. The aim of this work was to evaluate the potential of using electrostatic separation as a way to obtain purified fractions from wheat bran. Ultrafine-ground bran obtained either by cryogenic grinding or by grinding at ambient temperature was used as starting material. The ultrafine bran was then charged by tribo-electrification and introduced in a chamber containing two high voltage electrodes, where bran particles were separated depending on their acquired charge, allowing positively and negatively charged fractions to be collected separately. The particle size distribution, microstructure and biochemical composition of the obtained fractions were studied. The charge of the particles was influenced by their biochemical composition: particles rich in highly branched and cross-linked arabinoxylans (pericarp) were separated from particles rich in β-glucan, ferulic acid and para-coumaric acid (aleurone cell walls). The testa and the intracellular compounds from aleurone were not highly charged, neither positively nor negatively. The most positively charged fraction represented 34% of the initial bran, and contained 62% of the ferulic acid present in the initial bran. The yield of the separation process was good (5.4% loss), and could be further increased.     

Detection of nitrogen transfer from N<Subscript>2</Subscript>-fixing shade trees to cacao saplings in <Superscript>15</Superscript>N labelled soil: ecological and experimental considerations

Theobroma cacao seedlings were grown alone (TCA) or associated with saplings of N₂-fixing shade trees Gliricidia sepium and Inga edulis in 200 l of ¹⁵N labelled soil within a physical root barrier for studying direct nitrogen transfer between the trees and cacao. Root:shoot partitioning ratio for sapling total N was lower than biomass root:shoot ratio in all species. Sapling total ¹⁵N was partitioned between root and shoot in about the same ratio as total N in cacao and inga but in gliricidia much higher proportion of ¹⁵N than total N was found in roots. Thus, whole plant harvesting should be used in ¹⁵N studies whenever possible. Average percentage of fixed N out of total tree N was 74 and 81% for inga estimated by a yield-independent and yield-dependent method, respectively, and 85% for gliricidia independently of estimation method. Strong isotopic evidence on direct N transfer from trees to cacao was observed in two cases out of ten with both tree species. Direct N transfer was not correlated with mycorrhizal colonisation of either donor or receiver plant roots. Direct N transfer from inga and gliricidia to cacao is conceivable but its prevalence and the transfer pathway via mycorrhizal connections or via reabsorption of N-rich legume root exudates by cacao require further study. Competition in the restricted soil space may also have limited the apparent transfer in this study because the trees accumulated more soil-derived N than cacao in spite of active N₂ fixation.     

Fine root biomass in relation to site and stand characteristics in Norway spruce and Scots pine stands

Variations in fine root biomass of trees and understory in 16 stands throughout Finland were examined and relationships to site and stand characteristics determined. Norway spruce fine root biomass varied between 184 and 370 g m(-2), and that of Scots pine ranged between 149 and 386 g m(-2). In northern Finland, understory roots and rhizomes (< 2 mm diameter) accounted for up to 50% of the stand total fine root biomass. Therefore, the fine root biomass of trees plus understory was larger in northern Finland in stands of both tree species, resulting in a negative relationship between fine root biomass and the temperature sum and a positive relationship between fine root biomass and the carbon:nitrogen ratio of the soil organic layer. The foliage:fine root ratio varied between 2.1 and 6.4 for Norway spruce and between 0.8 and 2.2 for Scots pine. The ratio decreased for both Norway spruce and Scots pine from south to north, as well as from fertile to more infertile site types. The foliage:fine root ratio of Norway spruce was related to basal area and stem surface area. The strong positive correlations of these three parameters with fine root nitrogen concentration implies that more fine roots are needed to maintain a certain amount of foliage when nutrient availability is low. No significant relationships were found between stand parameters and fine root biomass at the stand level, but the relationships considerably improved when both fine root biomass and stand parameters were calculated for the mean tree in the stand. When the northern and southern sites were analyzed separately, fine root biomass per tree of both species was significantly correlated with basal area and stem surface area per tree. Basal area, stem surface area and stand density can be estimated accurately and easily. Thus, our results may have value in predicting fine root biomass at the tree and stand level in boreal Norway spruce and Scots pine forests.     

Conservation of freshwater macroinvertebrate biodiversity in tropical regions

1. Motivated by recent global initiatives for biodiversity conservation and restoration, this article reviews the gaps in our understanding of, and the challenges facing, freshwater macroinvertebrate biodiversity and conservation in tropical regions.
2. This study revealed a lack of adequate taxonomic, phylogenetic, and ecological information for most macroinvertebrate groups, and consequently there are large‐scale knowledge gaps regarding the response of macroinvertebrate diversity to potential climate change and other human impacts in tropical regions.
3. We propose ideas to reduce the impact of key drivers of declines in macroinvertebrate biodiversity, including habitat degradation and loss, hydrological alteration, overexploitation, invasive species, pollution, and the multiple impacts of climate change.
4. The review also provides recommendations to enhance conservation planning in these systems (as well as providing clear management plans at local, regional, and national levels), integrated catchment management, the formulation of regulatory measures, the understanding of the determinants of macroinvertebrate diversity across multiple scales and taxonomic groups, and the collaboration between researchers and conservation professionals.
5. It is suggested that the integrated use of macroinvertebrate biodiversity information in biomonitoring can improve ecosystem management. This goal can be facilitated in part by conservation psychology, marketing, and the use of the media and the Internet.