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Coastal wetlands are ecologically important all over the world, and they are relatively unstable with dramatic changes in aboveground vegetation. However, it is still unclear how the aboveground vegetation changes will influence the functioning of coastal wetland ecosystems, especially the decomposition processes. Here, we carried out a cotton strip experiment to examine the effects of Suaeda salsa community on the soil properties and the associated cellulose decomposition rates in the coastal wetlands of Liao River delta (NE China). Our results showed that S. salsa community significantly affected the contents of soil C, N, P, base cations, organic matter and the soil electrical conductivity (EC), and such effects might vary among different types or densities of aboveground vegetation. The soil cellulose decomposition rate (in terms of cotton strip tensile strength loss, CTSL) was slowed down when aboveground S. salsa communities are experiencing degradation or have been totally replaced by Phragmites australis communities. Moreover, there were positive partial correlations between soil N and CTSL, and between soil EC and CTSL, but a negative partial correlation between soil C and CTSL. Our results emphasized the importance of S. salsa community in determining the soil cellulose decomposition rate in this coastal region. The results suggest that vegetation degradation in coastal wetlands might lead to various changes in soil properties and hence affect other aspects of ecosystem functioning and services, especially nutrient cycling.
Nitrogen is an essential nutrient for plant growth. Although much has been learned about its utilization and distribution within the plant body, little is known about the relationship between nitrogen content and standing biomass at the level of entire forests. Data for nitrogen content (N) and biomass (M) of 10 deciduous species in USA at the individual trees level and 37 species grown in three forest biomes (i.e. tropic, subtropics, and temperate) in China at stands level were gathered to determine the N versus M scaling relationships for different tissue- and organ-types (e.g. bark and leaves). Model Type II regression protocols were used to calculate scaling exponents and allometric constants (i.e. slopes and y-intercepts of log-log bivariate plots, respectively) between N and M to. At the level of individual plants, N scaled nearly isometrically with M for the different tissue- and organ-types (i.e. Nα M 0.97–1.04). At the stand-level, N scaled similarly with respect to leaf, branch, and bark M, despite differences in stand size-frequency distributions and species composition. However, total stand N scaled allometrically with respect to total stem or root M and thus to total stand mass (i.e. N α MT 0.77–0.87). This was attributed to the accumulation of wood (and other ‘necromass’ tissue components that have lower N content than physiologically active tissues) in progressively older (and thus more massive) tree stands. When coupled to the scaling of N with respect to annual plant growth rates, these exponents provide important boundary conditions with which to model forest nutrient cycling.
The study of foliage was carried out in two different forest ecosystems: Vaccinio uliginosi- Betuletum pubescentis and Empetro nigri-Pinetum in the Slovinski National Park in the period of 2002-2005. The largest volume of nitrogen and phosphorus in the litter of coniferous needles was found in early summer at the moment of maximum growth. An average concentration of nitrogen in examined needles was between 1.296% and 1.358% N in Vaccinio uliginosi-Betuletum pubescentis and from 1.010% to 1.118% N in Empetro nigri-Pinetum. The decrease of biogenes concentration in plant tissues was observed in the autumn months as a result of lower demand and recession of biogenes connected with storage of valuable elements in the fatter parts of the trees. In the fall season, a gradual recession of nutrients from the litter of coniferous needles was observed. In Vaccinio uliginosi-Betuletum pubescentis insignificant quantity of nitrogen recesses (average 5.6%) from the new and one year old litter of coniferous needles, including 47.2% N-NH4 and 78.6% N-NO3 and about 21.8% P, including 11.7% P-PO4. In Empetro nigri-Pinetum more intensive recession of biogenes was found from the litter of coniferous needles of common pine than in Vaccinio uliginosi-Betuletum pubescentis. On average 11.5% T-N is translocated, including 41.4% N-NH4 and 23.8% N-NO3 as well as 22.3% P, including 11.8% P-PO4.
Grazing exerts a key role in nutrient cycling in grassland ecosystems, however, little is known about the effe cts of short-term enclosure on methane (CH₄) fluxes in a semi-arid steppe biome like this of Inner Mongolia. CH₄ fluxes were measured in the Leymus chinensis (Trin) Tzvel. grassland using static chamber and gas chromatography (GC). Measurements were carried out twice per month over a growing season in 2004 at the two sites (one fenced since 1999 (UG99) and the other subjected to freely grazing (FG)). All CH₄ fluxes were positive, indicating that this grassland functioned as the active atmospheric CH₄ uptakes. During this period, the UG99 site (57.6 ± 6.7 μg C m⁻² h⁻¹) had significantly higher mean CH₄ uptake in comparison to the FG site (37.0 ± 6.3 μg C m⁻² h⁻¹). A significant liner negative correlations between CH₄ uptake and soil moisture (0–5 cm) at the both sites were found (P <0.05). The results indicated that short-term enclosure was helpful to improve CH₄ uptake in this area.
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