Epiphytic cyanolichens are an important component of epiphytes and play a vital role in environmental monitoring and nutrient cycling in various forest ecosystems. The objectives of this study were to (1) quantify the coverage and frequency of epiphytic cyanolichens across forest types, (2) assess the importance of forest type and tree species on the distribution of cyanolichens, and (3) determine the influence of habitat variables on epiphytic cyanolichens at the scale of a forest landscape as well as within communities.

We investigated the coverage and frequency of four common cyanolichen species: Leioderma sorediatum, Leptogium azureum, Lobaria retigera, and Sticta duplolimbata, on 0-2.0 m trunk in 120 plots of two primary and six secondary forest types in the subtropical Ailao Mountains of Yunnan Province, Southwest China. Thirty trees in each plot and a total of 3600 trees were selected for lichen sampling in the eight forests.

Coverage and frequency of the four epiphytic cyanolichens differed significantly among forest types. While the highest values of S. duplolimbata occurred in the primary dwarf mossy forest, those of other three species occurred in the secondary Ternstroemia gymnanthera and Populus bonatii forests. However, they were relatively rare in the primary Lithocarpus forest. All the target cyanolichen species were found on more than ten host tree species, and showed clear preferences for some tree species such as T. gymnanthera, P. bonatii and Lithocarpus hancei while excluded from other tree species such as Camellia forrestii. The results also highlighted the importance of habitat variables such as stand age, tree diameter, maximum diameter, canopy openness, basal area, host stem density and tree species diversity on the distribution of epiphytic cyanolichens. The correlation coefficients between cyanolichens and habitat variables were generally very small at the forest landscape scale, whereas some of the correlations were strong within forest types. Of the habitat variables, stand age, canopy openness and tree diameter were the major factors determining the distribution of cyanolichens.

As part of fiber structures, the hemicellulose degrades and transforms during foliar litter decomposition along with other components of leaf tissue. Forest gaps and crown canopies may regulate hemicellulose dynamics during foliar litter decomposition by redistributing winter snow cover and altering the temperature, precipitation and solar radiation during the growing season, but little information is available concerning those effects and the consequences. Therefore, our objective was to study the effects of forest gap on hemicellulose dynamics during foliar litter decomposition in an subalpine forest.

A field litterbag experiment was conducted in an subalpine fir (Abies faxoniana) forest in a transitional area located in the upper reaches of the Yangtze River and the eastern Qinghai-Xizang Plateau. Litterbags containing cypress (Sabina saltuaria), red birch (Betula albosinensis), larch (Larix mastersiana), azalea (Rhododendron lapponicum) and fir (Abies faxoniana) were placed on forest floor from the gap center to under the closed canopy. Samples of litterbags were retrieved at the stages of snow formation, snow cover, and snowmelt as well as during the growing season. Hemicellulose contents of the remaining litter were measured.

After one-year decomposition, all five types of foliar litter exhibited a tendency of hemicellulose accumulation. The needle-leaved litter and broad-leaved litter showed greater hemicellulose losses at the snow cover and snowmelt stages, respectively. Greater hemicellulose losses in the gap center and under the canopy were observed at both snow cover and snowmelt stages. In contrast, there was less litter hemicellulose accumulation in the gap center during the growing season. Statistical analysis of the resulting data indicated that both environmental factors and litter quality were significantly correlated with the litter hemicellulose losses. Our results suggested that forest gap enhanced the hemicellulose losses in winter and constrained the hemicellulose accumulation during growing season, implying that the formation of forest gap in subalpine forest promoted hemicellulose degradation during litter decomposition.

Land use change affects ecosystem carbon dynamics by changing the plant community structure and soil micro-environment in grassland ecosystems. The aims of this study were to determine the effects of land use on soil respiration and litter decomposition in the temperate grasslands of Nei Mongol and to identify the effects of litter quantity, quality and decomposition on soil respiration during growing season.

We measured soil respiration during growing season in 2011 and 2012 under three land use types, i.e. grazing, mowing, and grazing exclusion, by using an automatic infrared gas analyzer (LI-8100) that was connected to a multiplexer system (LI-8150). Quadrat surveys and litter bags were utilized to measure litter production and decomposition. Several chemical indicators of litter quality were measured to calculate the litter decay rates. All data were analyzed with ANOVA and Pearson correlation procedures of SPSS.

Soil respiration and litter decomposition differed greatly among the three land-use types. In the drought year, the total soil respiration at the grazing site was 1.5 times greater than at the mowing site and 1.29 times greater than at the grazing-exclusion site. However, in the wet year, the total soil respiration at the mowing site reached 309 g C∙m^-2∙a^-1 and was greater than at both the grazing site and the grazing-exclusion site. Precipitation increased soil respiration and litter decomposition, indicating that soil water availability was a primary constraint on plant growth and ecosystem C processes. Also, the responses of soil respiration and litter composition to rainfall differed among the land-use types. Further analysis showed that the litter C:N decreased and the litter N content and lignin:N increased after 2-years of decomposition. In addition, soil respiration was significantly correlated to litter production (r = 0.78, p < 0.01), decay rates, C:N (r = -0.84, p < 0.01), and lignin:N (r = 0.62, p < 0.05).

Our objective was to explore the effects of different levels of nitrogen (N) fertilization on soil respiration and its temperature sensitivity during growing season in winter wheat (Triticum aestivum) in East China.

Three levels of N fertilization, N1 (15 g·m^-2·a^-1), N2 (30 g·m^-2·a^-1), and N3 (45 g·m^-2·a^-1), and the control group (CK) were set up in winter wheat fields. The LI-8100 Automated Soil CO₂ Flux System was used to measure soil respiration rate during the growing season (December 2013 to May 2014) of winter wheat.

During the growing season of winter wheat, mean soil respiration rates of N1, N2 and N3 treatments were 5.29, 6.17 and 6.75 μmol·m^-2·s^-1, respectively, which were 7.8%, 23.6% and 37.8% greater than that of the CK (4.90 μmol·m^-2·s^-1). Compared to CK, the N1, N2, and N3 treatments increased the aboveground biomass by 39.9%, 104.4%, and 200.2%, respectively, and the increases were significantly correlated with total soil respiration during the growing season. Soil respiration increased exponentially with soil temperature at the depth of 5 cm, which explained 65%-75% of the variation (p < 0.05). The temperature sensitivity of soil respiration (Q₁₀) calculated based an exponential equation was between 2.09 and 2.32. These results suggested that nitrogen fertilization promoted plant growth, significantly increased biomass of winter wheat, and stimulated the soil respiration.

Solidago canadensis is one of the major invasive weeds that impose serious threats to native plants. Seeds possess traits suitable for the long distance dispersal by wind. However, the initialization of wind dispersal and the seed release under the influence of abiotic conditions are poorly understood.

Wind tunnel experiments were designed to study the effects of horizontal and vertical wind with different turbulence intensities and humidities on seed abscission in S. canadensis. Four horizontal wind speeds (4, 6, 8 and 10 m·s^-1), five turbulence intensities (0.14, 0.11, 0.08, 0.07 and 0.02) and two relative humidities were used in the wind tunnel experiments. The proportion of seed releases from the inflorescences was measured and calculated in the laboratory. Both attached and falling seeds were measured to test their difference in morphological traits.

The seed abscission in S. canadensis was a nonrandom process, and was influenced by factors such as wind speed, turbulence, humidity and seed maturity, etc. Under the horizontal airflow condition, the seed release threshold was 5.1 m·s^-1. However, the seed release threshold under vertical airflow condition was markedly smaller. Compared with the laminar flow condition, turbulence greatly increased the seed releasing rate by more than 300% on average. Under the turbulent conditions, the turbulence intensity alone did not significantly influence the proportion of seed release. High humidity decreased the seed releasing rate from the inflorescences. In addition, falling seeds tended to have greater pappus numbers and flat angles comparing to the attached seeds.

Phenology model is considered as the most efficient tool to assess the phonological responses of plants to future climate change. Furthermore, as an important component in dynamic ecological models, the performance of phenology model is of significance for the precision in simulating mass and energy exchanges between land and atmosphere. Combining long time series remote sensing data and climate data to construct regional phenology model may be the only way to solve the problem of deficiency in lacking in-situ observational data on phenology and species-specific phenology models. The objective of this study was to develop a new method of sample selections for constructing phenology in the arid zone of Central Asia where only sparse observational data are available.

Based the phenology data retrieved from 250 m-resolution MODIS images for the period 2000-2010, a new method is developed for constructing the vegetation phenology model in arid zone. A set of rules were built to select the representative pixels of PFTs (plant function types) surrounding the climate station, making sure that the climate of the representative pixels of PFTs could be represented by the observed meteorological data at the station, and then the phenology data on the representative pixels of PFTs were extracted from the MODIS images and the corresponding climatic data were set as the sample for model fitting and assessment. Forty-six representative pixels of PFTs for desert grassland vegetation and broadleaved deciduous forests were selected under the rules. The phenology model parameters were estimated using data from odd-numbered years and the simulation accuracy was assessed with the independent even-year data. Particle swarm optimization algorithm was used to parameterize the pre-selected model. The root-mean-square error and coefficient of determination were used to examine the performance of model with independent data.

The best model for desert steppe vegetation was the modified temperature-precipitation model and the best model for deciduous broadleaved forest was the alternative model. Compared with other documented findings, the new method was proven feasible, and the results also suggested that this new method may improve the spatial match of climatic data and vegetation phenology data, and therefore contribute to improvement of the phenology model accuracy.

The objective of this study was to investigate the tolerance of Polytrichum commune to soil contamination by polychlorinated biphenyls (PCBs), and the underlying eco-physiological mechanisms.

Polytrichum commune was propagated and cultured in PCBs contaminated soil by means of micropropagation under laboratory conditions, and eco-physiological variables relating to tolerance to PCBs (Aroclor 1242 and Aroclor 1254) contamination were studied.

The coverage and density of P. commune were higher than 93% and 50 plants·cm^-2 and there was no significant difference between the PCBs treatments and the control. PCBs (Aroclor 1242 and Aroclor 1254) had no adverse effects on the regeneration of gametophyte fragments. The height and fresh mass of P. commune increased with an increase in the concentration of Aroclor 1242, and decreased with an increase in the concentration of Aroclor1254, but they were higher in the PCBs treatment than in the control, indicating that PCBs stimulated the growth of P. commune. The contents of chlorophyll (Chl) a, Chl b and Chl a + b in P. commune were slight higher in the PCBs treatments than in the control, and the ratio of Chl a/b maintained relatively stable in both the PCBs treatments and the control. The content of malondialdehyde and activity of superoxide dismutase in P. commune were not significantly different between the PCBs treatments and the control, whereas the content of glutathione was significantly higher in the PCBs treatments than in the control, indicating that glutathione played a pivotal role in the course of scavenging reactive oxygen species. The study demonstrated that the growth of P. commune was not adversely impacted by PCBs contaminated soil at given concentrations, reflecting its tolerance to PCBs.