The role of natural regeneration in silvicultural systems is attracting increasing interest, but much is unknown about how stand development after clear-cutting affects seedling regeneration. We looked at the impact of tree canopy and ground layer vegetation (i.e., ‘stand type’) as well as soil properties (i.e., ‘soil origin’ or stand from which soil originated) on survival and growth of Pinus sylvestris and Picea abies seedlings at three forest developmental stages, i.e., 4, 16 and 34years after clear-cutting. To do this we transplanted soil cores between stands of different stages to separate the effects of soil properties versus canopy closure on seedling performance. We found that seedling survival of both species was highest when planted in the oldest stands independent of soil origin. P. sylvestris seedling growth responded to stand type but not soil origin, and biomass was highest at the youngest stand likely because of greater light availability. Meanwhile, although P. abies seedling root biomass responded to stand type, this species was mostly responsive to soil origin, with shoot and total biomass being greatest when seedlings were grown in soil originating from the oldest stands. These findings have implications for our understanding of tree regeneration of species that differ in their responsiveness to light and soil characteristics. The results can further inform forest managers about how to optimize survival and growth of seedlings by means of canopy regulation as well as provide information to assist the regeneration and development of multi-storied forest stands.
Intense radiation from the UV to green spectral region is known to permanently change the optical properties of silica fibers. This photosensitivity can be used to induce periodic changes in the refractive index along the fiber length, which results in an intracore Bragg grating. In 1978, Hill et. al. observed this effect in germanium-doped silica fibers using 488-nm and 518-nm light from an intense argon-ion laser beam. The progress on the photosensitivity of Andrew elliptical-core Ge-doped birefringent silica optical fiber due to cw krypton-ion laser light is explained.
The temporal variability of the soil microbial biomass is an important component of its turnover, and thus contributes to patterns of soil nutrient release and mineralization. I selected 58 previously published studies in which temporal data for soil microbial biomass C and N had been presented, and analyzed this data for underlying trends, by calculating coefficients of variation (standard deviation/mean) over time from each study as a measure of temporal variability. Contrary to expectations, there was no difference in temporal variability among forest, grassland and arable ecosystems, or between tilled and non-tilled arable systems, indicating that increasing disturbance levels does not have destabilizing effects on the microbial biomass. Correlation, partial correlation and stepwise multiple regression analyses between the coefficients of variation and selected soil and macroclimatic variables across the studies I considered showed that temporal variability of biomass C was most closely related to soil N content in forests, pH and latitude in arable ecosystems, and pH, latitude and soil C contents in grasslands. Relationships involving soil C, N and pH were negative; those involving latitude were positive. For the entire data set, temporal variability was best predicted by a three-component model incorporating pH, soil C and latitude. The effects of increasing latitude on increasing temporal variability of biomass C is interpreted in terms of higher latitudes having higher interseasonal variations in temperature, causing greater interseasonal flux of the biomass. The apparent effects of pH and soil C in reducing temporal variation indicates that alleviating stress on the microbial community has stabilizing effects. It is shown that those factors which stabilize the microbial biomass reduce its turnover, and this is likely to have important consequences for soil nutrient dynamics and ultimately plant growth and ecosystem productivity.
Fine roots, and their functional traits, influence associated rhizosphere microorganisms via root exudation and root litter quality. However, little information is known about their relationship with rhizosphere microbial taxa and functional guilds. We investigated the relationships of 11 fine root traits of 20 sub-arctic tundra meadow plant species and soil microbial community composition, using phospholipid fatty acids (PLFAs) and high-throughput sequencing. We primarily focused on the root economics spectrum, as it provides a useful framework to examine plant strategies by integrating the co-ordination of belowground root traits along a resource acquisition-conservation trade-off axis. We found that the chemical axis of the fine root economics spectrum was positively related to fungal to bacterial ratios, but negatively to Gram-positive to Gram-negative bacterial ratios. However, this spectrum was unrelated to the relative abundance of functional guilds of soil fungi. Nevertheless, the relative abundance of arbuscular mycorrhizal fungi was positively correlated to root carbon content, but negatively to the numbers of root forks per root length. Our results suggest that the fine root economics spectrum is important for predicting broader groups of soil microorganisms (i.e. fungi and bacteria), while individual root traits may be more important for predicting soil microbial taxa and functional guilds.
Although spatial variability in distributions of soil organisms is generally regarded as random noise, this variability often has a predictable spatial structure. Recent studies have provided evidence that a spatially explicit approach to soil ecology can enable identification of factors that drive the spatial heterogeneity of populations and activities of soil organisms, at scales ranging from millimeters to hundreds of meters. Furthermore, there is increasing evidence that spatial soil ecology can yield new insights with regard to understanding the factors that maintain and regulate soil biodiversity, as well as to how the spatial distributions of soil organisms influence both plant growth and plant community structure.
Several theories predict that increasing stress (e.g. decreasing nutrient availability or decreasing temperature) should result in higher amounts of plant phenolic compounds both at the interspecific and intraspecific levels. Further, several theories predict that plant phenolics are major drivers of plantsoil feedbacks whereby they influence litter decomposition rates and the return of nutrients to plants. We investigated the potential influence of shifts in abiotic factors on litter phenolic properties using an elevational gradient in northern Sweden, for which temperature and soil fertility decline with increasing elevation. The system consists of two vegetation types: heath, (associated with low soil fertility) and meadow (associated with higher fertility), which occur across the entire gradient. We hypothesized that total phenolics, tannins and protein complexation capacity (PCC) of leaf litter would increase with elevation within and among plant species. We further hypothesized that at the whole-plot level (using community-weighted averages), these properties would be higher in heath than meadow, and that phenolic properties for meadow vegetation would show stronger responses to elevation than for heath. We measured phenolic properties in leaf litter for 13 species from both vegetation types across an established elevational gradient (500-1000m) in Swedish subarctic tundra. Contrary to our hypotheses, different species showed highly contrasting responses in their phenolic characteristics to elevation. At the across-species level, total phenolic content in litter decreased with elevation. At the whole-plot level, tannin concentrations were higher for the heath than for the meadow, whereas total phenolics and PCC did not differ. However, consistent with our hypothesis, our results showed that phenolic properties were more responsive to elevation for the meadow compared to the heath, as a consequence of greater species turnover for the meadow. Our results are inconsistent with theories predicting higher plant phenolic concentrations with increasing environmental stress or decreasing nutrient availability. They also provide evidence that across abiotic gradients in the subarctic tundra, there are large shifts in litter phenolic properties (including those that are able to complex protein) and highlight that the direction and strength of such shifts may differ greatly among vegetation types.
Methods for investigating the glucose-sensitive component of the soil microbial biomass were applied to soils held at five separate soil moisture contents (i.e. 15,25, 35,45 or 55%) following incubation for 6 h and 3, 10 or 30 days. The O2 uptake method proposed by Van de Werf and Verstraete (1987a, b) for measuring “active” (glucose-sensitive) microbial biomass predicted that this biomass increased with increased moisture status, except for samples that had been previously incubated for 30 days. However, measurements of the glucose-sensitive microbial biomass using total O2 uptake over 10 h following glucose addition [as proposed by Van de Werf and Vestraete (1987a, b)] appears to be influenced in pan by decomposition of microbial biomass killed by prior incubation at low moisture contents, especially between hours 4 and 10. It is proposed that the total O2 uptake in the first 2–4 h following glucose addition is a superior indicator of the response of the soil microbial biomass to soil moisture. Substrate-induced respiration (SIR) and selective inhibition are also proposed for studying the glucose-responsive component of the soil microbial biomass. Selective inhibition checks microbial protein synthesis of this glucosesensitive component. The inhibition of SIR by either bacterial or fungal selective inhibitors was largely independent of soil moisture content when samples were remoistened simultaneously with sample amendment, but was strongly related with soil moisture when samples were not remoistened. The bacterial-fungal ratios derived from these data were typically unaffected by soil moisture.
Soil moisture, temperature, microbial substrate-induced respiration and basal respiration were monitored in two plots in an agricultural field from April 3
An ongoing study initiated in August 1990 investigated the effects of disturbances (organic mulching, cultivation, herbicides) on the detritus food-web in annual (maize) and perennial (asparagus) cropping systems. In this paper we attempt to simultaneously assess the...
