-->Special Column：Tropical and Subtropical Forest Ecology

Effects of habitat heterogeneity on community functional diversity of Dinghu Mountain evergreen broad-leaved forest

2016/3/9 12:25:26

Species co-existence mechanisms have long been one of the core topics in community ecology. To explore the changes in community functional diversity of Dinghushan evergreen broad-leaf forest under the heterogeneous habitats and to find out the main driving factors of the functional diversity varations, based on the second community survey data of the 20 hm² forest dynamics plot in Dinghushan National Nature Reserve, 27 subplots(20 m×20 m)were selected according to the changes of relative elevation and topograph. These 27 subplots can stand for the heterogeneous habitats in Dinghushan evergreen broad-leaved forest. Leaf functional traits of all the trees with DBH(diameter at breast height)≥1 cm in the 27 subplots were measured to calculate the functional diversity(functional dispersion and community weighted mean are caculated as the functional diversity in this paper)during the summer of 2013. The measured traits included morphological traits(specific leaf area, leaf dry matter content, leaf area and leaf lenth to leaf width ratio)and stoichiometric traits(leaf carbon, nitrogen, phosphorus content). Combining with the topographic and soil information, we analysed the main environmental factors that influence the variation of functional diversity. To elucidate the relative importance of environmental filtering and competitive interactions for species co-existence of Dinghushan evergreen broad-leaved forest, we inferred the shifts in functional diversity patterns across environmental gradients. The results indicated that functional divergence and community-weighted mean were in close relation with environmental factors, especially elevation, convexity and soil fertility. In the optimal environmental conditions(high relative elevation, high convexity and higher soil nutrient content), plants adopt the similar(functional divergence decreased)adaptive strategy of efficient conservation of nutrient(low SLA, high LDMC), which suggested that environmental filtering played a stronger role; while in the adverse environmental conditions(low relative elevation, low convexity and lower soil nutrient content), the traits were various(functional divergence increased)and use fast growing strategy(high SLA, low LDMC), since competitive interactions might play a key role. The functional divergence of leaf area and leaf nitrogen contents increased in better environmental conditions(high relative elevation, high convexity and higher soil nutrient content), and these two traits(leaf area and leaf nitrogen content)were opposite to the others(specfic leaf area, leaf dry matter content, leaf length to leaf width ratio, leaf carbon and phosphorus content). These results indicated that different niche axes(environments)had different importances in the changes in functional traits dispersion, and illustrated that we could use plants diverse strategies to adapt to heterogeneous environments in local scale.

Species composition and diversity of myxomycetes in Dinghu Mountain Nature Reserve

2016/3/9 12:25:26

In an effort to investigate the species composition and diversity of myxomycetes in different habitats of Dinghu Mountain Nature Reserve in Guangdong Province, six sample plots were selected along an elevation gradient. Barks and ground substances were collected from the sample plots and then incubated via moist chamber culture in laboratory. The species were identified and then counted the number of its occurrence. Major diversity indexes were compared to investigate species composition and diversity. Forty-nine species of myxomycetes were classified as 18 genera of 8 families belonging to 6 orders. Among them, Physarales was abundant, including 17 species, followed by 15 species of Trichiales, 11 species of Stemonitales, 4 species of Liceales, 1 speices of Ceratiomyxales and 1 species of Echinosteliales. The species Arcyria cinerea and Diderma effusum were dominant with relative abundances of 27.03% and 21.14%, respectively. With increasing of elevation, species diversity of myxomycetes decreased. The elevation of 300 m was characterized by the lowest Shannon-Wiener diversity index(1.66±0.12), but with the highest dominant concentration index(0.25±0.05). With the increasing of the high difference of each two sites, the common species number and similarity index decreased. Thirty-three species of myxomycetes, classified as 13 genera of 7 families in 6 orders, were recorded in wet season, and forty species of myxomycetes, classified as 17 genera of 6 orders in 8 families, were recorded in dry season. Twenty-two species were the common species between two seasons, and the similarity index was 60.27%. The species diversity index were significantly higher in dry season than in wet season. The species diversity of myxomycetes were significantly higher in ground substances than in bark substances. This study indicated that myxomycetes preferred ground substances to barks substances.

Effects of simulated acid rain on soil respiration in a monsoon evergreen broad-leaved forest at Dinghushan Nature Reserve

2016/3/9 12:25:26

Determining the effects of elevated acid rain on forest soil respiration can provide useful information for understanding of the process of carbon cycle of forest ecosystem and its response to global change. Therefore, a simulated acid rain(SAR)experiment was conducted in a monsoon evergreen broad-leaved forest at the Dinghushan Nature Reserve. SAR treatments included CK(the local lake water, pH4.5), T1(pH4.0), T2(pH3.5), T3(pH3.0)with three replicates. SAR experiments were initiated in June 2009 and were sprayed twice a month during the study period. Responses of soil respiration to SAR were studied from April 2010 to March 2012 with a LI-8100 soil CO₂ efflux system. The results showed that mean annual soil respiration rates for the CK, T1, T2, and T3 treatments were(3.07±0.08),(3.06±0.17),(2.78±0.29),(2.56±0.08)μmol·m^-2·s^-1, respectively, and the T3 treatment was significant lower than the CK and T1 treatments(P<0.05), indicating that soil respiration was depressed under SAR. These negative effects were evident in the warm-wet seasons(P<0.05), but not in the cool-dry ones. In addition, by analyzing the annual soil respiration of each year, we found that these negative effects had been strengthened over time with significant difference among treatments occurred only in the second year. The depression of soil respiration may be related to the reduction of heterotrophic respiration and CO₂ production from litter caused by soil acidification under SAR, as we found that soil pH value and soil microbial biomass carbon and nitrogen significantly decreased after exposure to SAR for two years; and litter decomposition rate was also depressed during the study period. Coincide with the situation of soil respiration, the negative effects SAR on these index had been strengthened over time with significant differences among treatments mostly occurring in the later stage of the study period. Furthermore, we found the effects of SAR on the temperature response of soil respiration, with a decline in Q₁₀ during the study period, suggesting that SAR would decrease the temperature sensitivity of soil respiration. According to the results of this study, soil carbon in forests of subtropical China would accumulate as the reduction of soil respiration under the continued acid rain in the future.

Spatial distribution and habitat-association of snags in the tropical karst seasonal rainforest of Southwest Guangxi, China

2016/3/9 12:25:26

Snag is an important component of forest ecosystems, and studying the spatial distribution of snags abundance and its impacting factors will provide insights of the mechanism of tree death and the succession of community. The objective of this study was to understand how snags would vary with environmental factors, and to infer the underlying mechanisms. Our study was based on data from a 15 hm² study plot investigation in tropical karst seasonal rain forest, Southwest Guangxi, China. The snags with DBH(diameter at breast height)larger than 1 cm were classified. And the spatial distribution of snags abundance and its impact factors like spatial and topographic variables were analyzed using point pattern analysis with K2(r)-index and habitat associations analysis with Torus-translation tests. Snags were mostly randomly distributed in the plot, but aggregated at local scales of 0-5 m for small group. Snags and the small group were significantly positively with ACH(altitude above channel)and abundance, but negatively the mean DBH and maximum DBH of each 20 m×20 m quadrat. The large group was only significantly negatively with convexity, while the middle group was no significant correlation with any environmental factors. Density of snags had no habitat association with three habitat types, but the density of larger groups was different significantly associated with three habitat types. The spatial patterns of snags of karst tropical seasonal rainforest had spatio-temporal discrepancy. Snags were randomly distributed in the mass. The spatial patterns of snags might be formed by density dependence at local scales, but habitat filter and intrinsic aging at larger scales.

Diversity of epiphytic orchids in fragmental limestone forests in Xishuangbanna, China

2016/3/9 12:25:26

There are abundant orchid species in tropical limestone forests in Xishuangbanna. Many are fragmented due to recent large-scale cultivation of rubber trees in the area. The aim of this study is to explore the diversity of epiphytic orchids in fragmented limestone forest and the effects of habitat fragmentation. We established 29 of plots 15 m² in 4 tropical limestone forests,and recorded a total of 1 528 individuals of epiphytic orchids belonging to 76 species and 34 genera using Canonical Correspondence Analysis with species richness and abundance, and with aspect, slope, elevation, topography, canopy density and forest types as environmental factors. We found that the distribution of epiphytic orchids in limestone forests was affected by altitude and forest type significantly. Species richness of epiphytic orchids in higher elevations, Qingyan Village and Baca Village, was higher than Greenstone rain forests and Mannalan in low elevations. Habitat fragmentation had no effect on the diversity and abundance of epiphytic orchids in tropical limestone rain forests which might be fragmented on a short temporal scale. Regarding our findings, protecting harsh limestone forest habitats is highly important for the protection of orchid diversity.

Different sizes of particulate matters deposited on leaf of typical subtropical evergreen species

LIN Xin-Tao，YE Nuo-Nan，WANG Bin，CHEN Jian*，YOU Shi-Xue，ZHANG Xin-Li — 2016/3/9 12:25:26

Both inhalable particulate matter (PM10) and fine particulate matter (PM2.5) are the primary pollutants in most of the cities in China，which are known for the harmness to human health. Urban plants could be used as biological filters，playing an important role in reducing the concentrations of particulate matters in the air as result of adsorbing and arresting particulate matters on their foliage. Three typical types of subtropical evergreen plants (Cyclobalanopsis glauca，Ilex chinensis and Loropetalum chinense var. rubrum)，always used as urban greening species，were selected to study their capacities in capturing particulate matter. The rinse and weight method were used to characterize PM in different particle size fractions (8-100，2.5-8，0.45-2.5 μm). The results showed that the particulate matters on leaves ranged from 30.4 μg·cm-2 to 63.7 μg·cm-2，while the particles deposited by the whole tree ranged from 1.36 g to 9.36 g. Loropetalum chinense var. rubrum was the most efficient species in capturing particulate matters (63.7±12.0 μg·cm-2) for its rough surfaces and large quantity of hairs on the foliage. All the tested species have the strongest (40.9%-57.5%) and the weakest (15.6%-20.6%) dust-capturing capability for the large size fraction (8-100 μm) and the fine size fraction (0.45-2.5 μm) respectively. As for the total amount of surface particulate matters accumulated by the whole tree，Cyclobalanopsis glauca is the most efficient species (9.36 g per tree) for its spacial characteristics. All the results showed that urban plants played important roles in mitigating urban airborn particulate matters.

Distribution patterns and carbon and nitrogen contents of Castanopsis platyacantha fine roots, the constructive species of evergreen broad-leaved secondary forest in Wawushan Mountain of Sichuan Province

PENG Yong, CHEN Guan-Tao, LIANG Zheng, LI Shun, PENG Tian-Chi, TU Li-Hua — 2016/3/9 12:25:26

The Wawushan Mountain National Forest Park in Sichuan Province, where there is relatively intact Castanopsis platyacantha-Schima sinensis formations, is a typical representative of the mid-subtropical moist evergreen broad-leaved forest in West China. Using the soil core method, this study investigated the fine root distribution and characteristics of carbon and nitrogen of sample C. platyacantha which is the main constructive species in this formation. The results were as follows: (1) The total fine root biomass of C. platyacantha was 173.62 g•m−2 and the total biomass of live fine roots was 135.29 g•m−2. (2) The fine root biomass, root length density, root surface area and specific root length decreased with the increase of soil depth, and their proportions in 0－30 cm layers were 67.23%, 69.53%, 69.48% and 57.20%, respectively; root length density, root surface area and specific root length decreased significantly with increasing root diameter, and 58.84%, 52.59% and 51.36% of them were in the roots that diameter was less than 1 mm, respectively. (3) Root extinction coefficient in biomass, length and surface area of C. platyacantha fine root increased with the rise of the root diameter. (4) In the first soil layer, the roots C content increased significantly with the rising root diameter, but there was no significant difference in other soil layers; the C content of the roots whose diameter was less than 2 mm in the first soil layer was significantly lower than other soil layers, while the differences of roots C content of greater than 2 mm among soil layers was insignificant. (5) The roots N content decreased with the increase of soil depth and root diameter, while the C/N ratio value was opposite. These results reflected the vertical distribution of the secondary forest underground fine root system and nutrient characteristics, which would provided some basic data for revealing the subsurface ecological processes and the effects of environmental change on ecological processes in the underground in the ecosystem.

Niche of dominant species populations in an evergreen broad-leaved forest in Baishanzu

2016/3/9 12:25:26

Dominant plant populations have great ability to adapt to the environment and use resources, and they play a decisive role in the community structure and function. What's more, the species niche characteristic reflects the utilization of environmental resources from a perspective. In order to explore the relationship, position and function of each dominant species population in an evergreen broad-leaved forest of Baishanzu, nine subplots of 20 m×20 m regularly from the 5 hm²(250 m×200 m)plot which established in 2003 were selected, where all trees with DBH≥1 cm were tagged, measured, and identified to species. The niche breadths, niche similarities and niche overlaps of 13 species(importance value larger than 1%)were analyzed quantitatively based on the data collected in 2013. The results demonstrated that the niche breadths of Cyclobalanopsis multinervis, Rhododendron latoucheae and Eurya rubiginosa var. attenuate were relatively larger, with Hurlbert niche breadth values(Ba)being 0.878, 0.825, 0.806, respectively, while the niche breadths of Cleyera pachyphylla, Fagus lucida and Sycopsis sinensis were relatively smaller, with Ba values being 0.341, 0.320, 0.272, respectively. The species niche breadth was not related to its importance value, but was significantly positively correlated with the evenness of importance values across different plots. The niche similarity between Cyclobalanopsis multinervis and Camellia cuspidate was the largest, being 0.832, while that between Ilex editicostata and Sycopsis sinensis was the smallest, being 0.248. Despite of small niche breadths, in addition, the niche similarity between Cleyera pachyphylla and Fagus lucida was high(0.758)due to their similar habitat requirements. Low niche similarities were found in two pair of species in the same genus: between Cleyera multinervis and C. stewardiana, and between Ilex formosana and I. editicostata. Species with wide niche breadth often had high degrees of niche overlap with other species, and large niche similarity was often associated with high degrees of niche overlap. Low degrees of niche overlap were found between Cleyera multinervis and C. stewardiana, and between Ilex formosana and I. editicostata. In a word, low degrees of niche overlap found in this study suggested weak interspecies competition among dominant species and therefore a potentially stable plant community in this forest. This paper revealed the niche characteristics of dominant species populations and structural stability of the community, and it would provide theoretical basis for the research of biodiversity conservation, succession, population evolution. And it also could provide reference for the nature reserve management institution to adjust and improve conservation measures.

Ecological and biological characteristics and cutting propagation techniques of Tetrastigma obtectum

2016/3/9 12:25:26

Tetrastigma obtectum is an evergreen or half evergreen vine species of Vitaceae family with great potentials to be used for landscape greening. Leaf morphology in T. obtectum was comparatively studied using epidermal maceration and paraffin methods. The result indicated that T. obtectum had large average leaf area(23.1 cm²)and small leaf mass per area(4.4 mg·cm^-2). The blade thickness of it was about 195.5 μm, with underdeveloped palisade tissue. Large gaps between the cells of both palisade tissue and spongy tissue were good for T. obtectum to decrease the light transmission loss and improve the utilization of luminous energy, showing the suitability of shade and humid environment. With the aid of LI-6400 portable photosynthesis system and PAM-2100 portable chlorophyll fluorometer, the study on photosynthetic physiology was made. The maximal photochemical efficiency of PSII(0.818)was high, which was helpful for light-harvesting. At the same time, the high non-photochemical quenching could be favorable to dissipate excess light energy, which protected the photosynthetic tissue, and mitigated the effect of environment on photosynthesis. Its diurnal net photosynthetic rate in leaves showed a single peaked curve without midday depression. The peak value of net photosynthetic rate was 3.691 μmol·m^-2·s^-1 occurring at about 14:00, and changes were close to the variations of photosynthetic active radiation, air temperature, stomatal conductance, transpiration rate, but opposite to internal CO₂ concentration. With the increase of net photosynthetic rate, CO₂ consumption increased significantly leading to the decrease of internal CO₂ concentration. Meanwhile, the daily average value of instantaneous water use efficiency was 3.056 μmol·mmol^-1, fully embodied the strong utilization ability in water and weak light, and could keep high stomata aperture as well as high photosynthetic capacity. This showed that T. obtectum prefered to grow under shady and humid condition and had some tolerance to drought, without cold resistance. It was suitable to be planted in south China as urban climbing greenery plants. In addition, the 1-2 a hardwood cuttings and new born twigs of T. obtectum were used to do rooting experiments, treated with a series of IBA solution, which showed that the cutting age and IBA solution affected rooting rate obviously with rooting rate from 65% to 100%. Rooting rates of 1-2 a hardwood cuttings treated with 300 mg·L^-1 and 500 mg·L^-1 IBA were distinctively higher than the new born twigs at the same concentration. The highest rooting rate of 1-2 a hardwood cuttings reached 95% under treatment of 300 mg·L^-1 IBA, while the new born twigs without treatment by IBA was the best combination with 100% rooting rate. In a word, T. obtectum grew quickly with high rooting rate under cutting propagation, and this technique could speed the fine variety breeding of T. obtectum as well as the improvement of seedling quality. The results are very useful for cultivation, exploitation and utilization of T. obtectum in urban vertical green landscape.

Seasonal dynamics of soil enzymes and microbial activities in a typical secondary broad-leaved forest at Shiwan Mountain, South China

2016/3/9 12:25:27

Soil enzyme and microbial activities regulate organic matter decomposition and nutrient release, which in turn control nutrient status of forest soils. We conducted field survey and complimentary laboratory analysis of soils of a secondary broad-leaved forest in Shiwan Mountain, Guangxi, China, in 2012. We quantified soil urease, sucrose, acid phosphatase and catalase activities and assessed bacterial, actinomycetes and fungal community in 0-10, 10-20 and 20-30 cm soil layers. We also determined moisture contents of these soils. Soil enzyme activities of catalase, urease, sucrase and acid phosphatase were significantly higher(P<0.05)in 0-10 cm soil than those in 10-20 cm and 20-30 cm soils. We found two peaks of catalase activities, in spring and in autumn at all three depths. In contrast, urease and sucrase activities showed one peak in summer at all depths. Activities of acid phosphatase followed a decreasing trend from autumn to winter: autumn>summer>spring>winter. Bacteria, actinomycetes and fungi decreased significantly(P<0.05)with increasing soil depth and their activities decreased from summer to winter as follows summer>autumn>spring>winter. Seasonal changes in rainfall and soil moisture were attributable to the changes in soil enzyme and microbial activities in this forest.