Abstract:Little is known about the role of tree sprouting in the regeneration of karst forest communities. In Shilin Stone Forest Geographical Park, southwestern China, all genets with the largest stem ≥3 cm DBH (diameter at breast height) and/or stumps ≥3 cm BD (basal diameter) were identified and number of sprouts counted in 10 transects (10 m × 100 m) in each of three evergreen broadleaved forest stands representing three regeneration stages (about 10, 20, and 30 years old). Species with >10 genets accounted for 72.4% of the 76 species, and all of them showed evidence of sprouting. One-third to two-thirds of the genets in the three forests were sprouting, with an average of 4.0–5.7 sprouts per sprouting genet. Sprouting capability (sprouting genets/total genets) and intensity (sprouts per sprouting genet) differed significantly among the three forest stages. More than 90% of the damaged genets were sprouting. The number of sprouts in a non-damaged genet was determined by intrinsic sprouting ability, and the number of sprouts in damaged genets was determined by stump size. As the forest developed, percentage of damaged genets increased, the portion of shoots ≥3 cm DBH co-existing in a genet decreased, and the portion of shoots <3 cm DBH sprouted from damaged genet increased. Thus the role of sprouting changed from contributing recruitment in the young stage to persistence in the later stage.

Abstract:Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^-1. Integrated primary production ranged from 189.3 to 976.2 mg m^-2 d^-1 in 2007, and ranged from 652.1 to 6601 mg m^-2 d^-1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.

Abstract:Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO₂ release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370–585 mg kg^-1, total nitrogen was 0.298%–0.468%, and organic matter was 13.5%–17.3%. In Rhododendron community, hydrolizable nitrogen was 445–583 mg kg^-1, total nitrogen was 0.465%–0.696%, and organic matter was 15%–22%. Organic matter within 10 cm depth was 4.07 kg m^-2 in Vaccinium community, and 5.31 kg m^-2 in the other. Temperature-dependent equations indicated that Q₁₀ values in both communities were around 2, with the ranges of 1.81–2.67 in Vaccinium community and 1.67–2.21 in Rhododendron community. The temperature-dependent equation was formed as y = ae^bx, where y is respiration rate (μmol kg^-1 h^-1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52–148 in Vaccinium community and 34–167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg^-1 d^-1) equation was y = 0.021733e^0.084063x for Vaccinium community, and y = 0.023482e^0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57–17.96 g C kg^-1 a^-1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg^-1 a^-1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m^-2, 12 g C m^-2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57–21.15 g C kg^-1 a^-1, with its maximum in May. By the integrated equation, it was 10.35 g C kg^-1a^-1or 537 g C m^-2 a^-1. The yearly respiration was 441–544 g C m^-2 a^-1 in Vaccinium community and 449–486 g C m^-2 a^-1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C)^-1 a^-1 in Vaccinium community and 101 g C (kg C)^-1 a^-1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg^-1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg^-1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m^-2 a^-1, and the biomass growth was 400 g C m^-2 a^-1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m^-2 a^-1 versus the respiration rate of 486.60 g C m^-2 a^-1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m^-2 a^-1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.

Abstract:The Qinling giant panda (Ailuropoda melanoleuca) is an endangered endemic species to China. Despite ongoing efforts to ensure its conservation, concerns about maintaining its populations persist. We used GIS fed with data on land use including road network of 2001, third national giant panda survey, and a digital elevation model (DEM) to assess the impact of road construction on giant panda habitat, and estimate the carrying capacity of the Qinling Mountain area. We assessed habitat suitability with a mechanistic model, and conducted correlation analysis to evaluate relationship between the extent of giant panda habitat and amount of sites occupied by pandas within of 5 km × 5 km grid. We also estimated the carrying capacity of the Qinling Mountainous Area.
Our results revealed a significant correlation (R² = 0.447, P < 0.01) between the number of sites with signs left by giant panda and the extent of habitat within of 5 km 5 km grid. The minimum habitat area that can support one panda was 10 km². Before the road network construction, the area of habitat suitable for the panda amounted about 1561 km² and that of marginally suitable habitat about 1499 km². The corresponding carrying capacity represented about 240 individuals. After the road network construction, the suitable habitat area was reduced by nearly 30% to 1093 km². Marginally suitable habitat and unsuitable habitat have both increased by 17% and 1%, respectively. As a result, the potential population size which the habitat could support was reduced to 217 individuals. The study results also suggested that most impacts on habitat from road construction took place in the high elevation areas above 1500 m. However, regarding the impact on the giant panda habitat, road networks developed much more inside the current nature reserves than outside of them.

Abstract:Biological nitrogen fixation through prokaryotic microbe is an important source of nitrogen been input into many natural ecosystems. In this study the active diazotrophic community was investigated in the three treatments of mowed, grazed and enclosed Leymus chinensis steppes in Hulunbeier grassland of Inner Mongolia by using approaches of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR–DGGE) and sequence analysis. The community structure and diversity of the bacterial groups from the different samples was further analyzed by using different techniques, such as statistical analysis and diversity index evaluation of the band patterns etc. The results showed that grazing activity significantly reduced the number of species and quantities of nitrogen-fixing microorganisms, as well as the nifH gene diversity. However, enclosed plots had the lowest diversity of nifH gene. While the highest one found in mowing plots. A total of 30 sequences representing 25 different sequence types were recovered from the DGGE gels after phylogenetic constructions. The results also revealed that most sequences were coming from Alphaproteobacteria of Proteobacteria, and characterized by sequences of members of Rhodobacter, Bradyrhizobium, Mesorhizobium, Rhodopseudomonas, Xanthomonas, Azospirillum, Gluconacetobacter, Methylobacterium and Methylocystis. Symbiotic nitrogen-fixers existed in grazing, mowing and enclosed plots accounted for 21.4%, 47.3% and 31.3% respectively in their dominant nitrogen-fixing bacteria. The result of principal components analysis showed that the influence of different land use patterns on nitrogen-fixing microbial communities composition can be ordered as grazing plots > enclosed plots > mowing plots. Nitrogen-fixing microbial communities in L. chinensis steppe were significantly (P < 0.05) influenced by the levels of nitrate nitrogen, total phosphorus, available phosphorus contents and pH value when canonical correspondence analysis was employed to identify relationship between nifH gene and soil physicochemical factors under different land use patterns. The result obtained from correlation analysis showed that there was a significant (P < 0.05) negative relationship between the nitrate nitrogen and the total phosphorus content, furthermore, the available phosphorus content was strongly correlated (P < 0.01) with the pH value.

Abstract:Peatlands hold a large portion of the Earth’s terrestrial organic carbon and serve as important pools in the global carbon cycle. Due to their strong feedbacks, peatlands are one of the most important ecosystems with respect to climate warming. This paper reviews the effects of climate warming on peatland ecosystems. Climate warming will shift the point in time when vascular peatland plants flower and reach maximum biomass to an earlier date. Flower production for some plants will increase, but how the phenology of peatland bryophytes will react is still unknown. Climate warming may increase productivity of peatlands, especially ombrotrophic Sphagnum bogs, but in the long run the negative effects from decreased water availability may prevail. Climate warming will change the basic characteristics of peatlands: their wetness and the related cold environment and nutrient shortage. By increased mineralization and nitrogen and phosphorus availability, climate warming will facilitate the growth of vascular plants. This will suppress endangered plant species (which usually grow in low-productive, phosphorus-limited habitats) and lead to a change in vegetation composition and a decrease in peatland biodiversity. Climate warming will change the competitive balance between bryophytes and between Sphagnum and vascular plants. Climate warming in the Late Pleistocene facilitated the initiation of peatland formation, but most current experiments show an obvious tendency for climate warming to drive many peatlands to regressive succession with a shift in dominance from Sphagnum to vascular plants. This change in vegetation will increase the flux of CH₄ and possibly also CO₂. The effect of accelerated peat decay as a result of climate warming will vary between types of peatlands. Since climate warming will generally enhance peat respiration more than net primary production, more and more peatlands will become carbon sources rather than carbon sinks, which will aggravate climate warming by positive feedback. Finally, this paper addresses some problems with current manipulative experimental studies on peatland response to climate warming and makes suggestions for further studies.

Abstract:In order to find out how small scale topographical factors affect growth and physiological characters of Caragana microphylla, which is a widely distributed shrub species and has an important role in restoring degraded grassland in natural ecosystem, a natural population of C. microphylla was chosen in a typical steppe community in June, 2009. The population was 34 km to the southeast of Xilinhot City, China, and a total of 54 shrubs were selected from different slope aspects and positions. We investigated the photosynthetic and morphological characters of these shrubs and analyzed the relationship between plant traits of C. microphylla and soil nitrogen and phosphorus availability. Moreover, the relationship between plant traits of C. microphylla and herbaceous aboveground biomass was studied. (1) The maximum net photosynthetic rate (Pn_max) was significantly lower on shady slopes than that on sunny slopes and higher on upper slopes than that on lower slopes. Stomatal conductance (Gs), net photosynthetic rate/intercellular CO₂ concentration (Pn/Ci) and intercellular CO₂ concentration (Ci) under saturated irradiance showed similar trends with slope aspect and position. Likewise, the maximum photochemical efficiency of PSII (Fv/Fm), PSII potential activity (Fv/Fo) and the first-year shoot morphological characters of C. microphylla were also correlated with slope aspect and position. (2) Soil nitrogen availability showed no significant effect on photosynthetic or morphological traits of C. microphylla, however, there were several significant relationships between soil phosphorus availability and plant traits. Dry weight, shoot length, compound leaf size, and leaflet length of first-year shoots of C. microphylla were significantly negatively correlated with soil C:P ratio. Though not significant, photosynthetic parameters under saturated light and other morphological characters of first-year shoots were negatively correlated with soil C:P ratio, i.e., these traits increased with increasing soil phosphorus availability. These suggested that the difference of soil phosphorus availability played an important role in making C. microphylla having different photosynthetic and morphological characters on different slope aspects and positions. The individuals grown in relatively P-rich site had longer shoots and larger leaves and grew better. Low phosphorus content was thought to limit photosynthetic activity through several different mechanisms, including both stomatal and non-stomatal limitations, the latter being more likely in the present study. (3) Photosynthetic and morphological characters of C. microphylla were all negatively correlated with herbaceous aboveground biomass, though only Pn/Ci and length of first-year shoot were significantly correlated with it. This indicated that the difference in plant community was a factor making C. microphylla have different growth and physiological characters on different aspects and positions of slope. A number of studies showed that grazing of the herbaceous layer promoted the establishment and proliferation of woody species, and then led to grassland deterioration; but in arid and semi-arid ecosystems, some widely distributed shrub species like C. microphylla created resource islands and provide favorable microhabitat for grass species. In the present study, we found negative correlations between traits of C. microphylla and herbaceous aboveground biomass. We suggested that the removal of livestock grazing result in the decrease of the distribution C. microphylla and increase of grass coverage, and lead to the restoration of the typical steppe.

Abstract:In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.

Abstract:Nitrogen accumulation in soil is increasing in Inner Mongolia which is resulted mainly from fertilization accompanied by conversion of large area of grasslands to croplands. Ammonia-oxidation is the key step of nitrification which is driven by ammonia-oxidizing microorganisms, and study on the response of ammonia-oxidizing microorganisms is necessary for understanding the effects of nitrogen fertilization on ecosystem functions. In this study, the abundance and community structure of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) under long-term N addition of different rates (0, 1.75, 5.25, 10.5, 17.5, and 28 g N m^-2 yr^-1) in a typical steppe of the Inner Mongolia Grassland were investigated using quantitative real-time PCR, cloning and sequencing based on amoA gene. In addition, soil potential ammonia oxidation rate was analyzed. Our results demonstrated that, with the increase of nitrogen addition rate, soil pH declined gradually from 6.6 to 4.9, and potential ammonia oxidation rate also declined which was positively correlated with soil pH (P < 0.01), while the copy number of bacterial amoA gene increased and positively (P < 0.01) correlated with ammonia concentration in soil. The archaeal amoA gene copy number did not change a lot with N nitrogen addition rate below 10.5 g N/m², but significantly decreased with addition of 17.5 and 28 g N m^-2 yr^-1. Sequencing of clone libraries of treatments revealed that in the treatment without N addition, AOB was dominated by Cluster 3a1 of Nitrosospira with a proportion of 87%, while in the treatment with N addition of 28 g N m^-2 yr^-1, proportion of Cluster 2 increased significantly to 41%. All archaeal amoA sequences were affiliated with the soil/sediment clade, and no significant variation of community structure was found between the treatments without N addition and with 28 g N m^-2 yr^-1 addition rate. In conclusion, this study demonstrated significant effects of nitrogen addition on potential ammonia oxidation rate and compositions of ammonia-oxidation microorganisms, which may have important implications for evaluating the impacts of N accumulation on ecosystem functioning. Further, the effects of pH and ammonia concentration on the ammonia oxidation rate and compositions of ammonia-oxidation microorganisms were discussed.