Karst region of Southwest China is ecologically very fragile. It has been suffering from severe rock-desertification and its vegetation has been damaging heavily. The restoration or reconstruction of the vegetation is extremely difficult. In recent years, a lot of pure and application-oriented basic researches have been performed in order to scientifically and technologically support the management of the rock-desertification. In this paper, we summarize habitat characteristics of the karst region and review the progress in ecological researches on plant adaptation, plant population, plant community and ecosystem in the region. In addition, as for current situation in management of the rock-desertification, we propose, particularly from angle of plant ecology, expectations for further researches in the region.

Aims The trait-based community ecology approach has recently attracted considerable interest from plant ecologists. Our objective is to explore variations and correlations of plant functional traits at the species and community levels along a successional gradient in Karst area of central Guizhou Province in order to improve our understanding about community succession from the perspective of functional ecology.
Methods We investigated species composition of 26 plots in three successional stages (bush, deciduous broad-leaved forests, deciduous-evergreen forests) in Karst area of Puding, central Guizhou Province and quantified three functional traits (leaf area, specific leaf area and maximum height) of 82 woody species in these plots. We calculated the species abundance-weighted mean community trait values and used trait-gradient analysis (TGA) to analyze species functional trait variation along the successional gradient and within communities.
Important findings We found an increasing trend in mean community leaf area and maximum height and decreasing mean community specific leaf area along the successional gradient. For mean plot trait values, there were strong positive correlations between leaf area and maximum height, and significant negative correlations between specific leaf area and both maximum height and leaf area. Species β trait values of the three traits were strongly correlated with each other, but there was no significant correlation for α trait values. Results indicate that the adaptive strategies of dominant species transformed from fast growth to high resource-use efficiency along succession and that co-occurring species in the same community employ different trait assemblies.

Aims Information on the species composition and community structure of vegetation at different successional stages is useful for understanding successional mechanisms and for selecting species for vegetation recovery. Our objective is to describe the dynamics of species composition and community structure during vegetation succession in a karst area of China.
Methods We collected plant community data from 33 plots in different successional stages at an ecological research station in Puding, Guizhou and statistically analyzed the data.
Important findings We recorded 365 plant species belonging to 218 genera and 89 families. Included were 31 species of ferns belonging to 23 genera and 14 families and 334 species of seed plants belonging to 195 genera and 75 families. No gymnosperm species was recorded. The dominant families included Rosaceae, Compositae, Poaceae, Liliaceae, Caprifoliaceae, Labiatae, Cyperaceae, Lauraceae, Vitaceae and Polypodiaceae. We found five successional stages (fern caused by fire disturbance, thin shrub-grassland, shrub, forest-shrub transition and forest communities). During the successional process, species richness increased and community structure tended to become more complex. The shrub and forest-shrub transition communities were not stratified, but the forest community was. From shrub to forest, the proportion of individuals with small diameters gradually decreased. The total, tree and liana density of woody plant taller than 1.3 m first increased and then decreased. Shrub density gradually decreased. Methods of vegetation restoration in karst areas are included.

Aims Litter is a key in nutrient cycling and energy flow of forest ecosystems. Our objective was to study the functions of karst forest litter by analyzing litter dynamics.
Methods Litter samples were collected monthly from karst primary forest, secondary forest and shrubland in our Maolan karst study area from October 2006 to December 2008. We divided the samples into leaves, branches, flowers and fruit, and others and weighed each after drying to constant weight at 80 °C.
Important findings The annual mean litter productions of primary forest, secondary forest and shrubland in the Maolan karst study area were 4.503, 3.505 and 2.912 t·hm^-2, respectively. The proportions of leaves, branches, flowers and fruits, and others for karst primary forest were 64.72%, 14.60%, 12.33% and 8.35%, respectively, while for karst secondary forest were 74.28%, 7.43%, 10.88% and 7.41%, respectively, and for karst shrubland were 75.94%, 8.56%, 12.93% and 2.57%, respectively. Therefore, leaves dominated litter. The monthly litterfall production dynamics for each community exhibited a bimodel distribution, with peaks early in the growing season and at dormancy.

Aims Woody plants in karst regions often grow on the continuous rock outcrops. However, the source of water for these plants is unclear. This study aimed at investigating the seasonal variation of water sources for plants growing on continuous limestone outcrops in southwestern China.
Methods Stable isotope techniques were used to access plant water uptake patterns for five different species in both wet and dry seasons. Then the IsoSource model was used to determine the probable contribution of each potential water source to total plant water uptake.
Important findings In the wet season, an average of >80% of water for four of the five species came from rainwater received in the previous 15 days and stored in fissures in shallow layers. Water accessed by the other species came mostly from recent rainwater; however, the species simultaneously absorbed water from fissures in deep layers that had been recharged from previous precipitation. In the dry season, all five species utilized both recent and previous rainwater, and the two tree species and one large evergreen shrub species used more previous rainwater (>50%).

Aims Studies of spatial variability of soil nutrients are valuable not only to the understanding of formation, structure, and function of soils, but also for understanding soil-plant associations and mechanisms of plant species coexistence. However, little is known about the spatial heterogeneity of soil nutrients in karst forest. Our objectives were to 1) characterize the spatial heterogeneity of soil nutrients in a karst forest, 2) examine correlations between spatial distribution of soil nutrients and local topographic variables and 3) assess the influence of soil nutrients on spatial distributions of tree species.
Methods A 100 m × 100 m forest plot was established on a hillside in a karst area in Maolan National Nature Reserve, Guizhou Province, Southwest China. All woody species with a diameter at breast height ≥1 cm were identified and surveyed. Surface soil samples (0-10 cm) were collected from a grid of 10 m × 10 m for the analysis of soil nutrients. The spatial variability of soil nutrients and its impact on distributions of tree species were analyzed by using geo-statistic methods (semivariogram and Kriging interpolation) and ordination (canonical correspondence analysis, CCA).
Important findings The coefficient of variation for soil nutrients ranges from 10% to 80%, and can be considered relatively moderate. Total phosphorus (TP), total potassium (TK), total magnesium (TMg) and pH show strong spatial autocorrelation, while organic matter (OM), total calcium (TCa), available phosphorus (AP) and available potassium (AK) show moderate spatial autocorrelation. The variation range of soil TCa is the smallest (56.2 m) and those of OM, TP and AK are larger. Spatial distribution of TP, TK, TCa, TMg, AP and pH decreases with increasing elevation and decreasing cover of bare rock, while OM increases with increasing elevation, which indicated that the spatial distributions and variability of soil nutrients were mainly affected by topographic factors and habitat characteristics (especially elevation, slope, slope aspect, slope location and cover of bare rock). CCA indicated that the spatial distribution of soil nutrients, especially TK, TMg, pH, TCa and OM, has an important impact on tree species composition and distribution, and thus showed a prevalence of soil resource-based niche differentiation among tree species. Our results suggested high spatial variability of soil nutrients contributes to promoting maintenance of species diversity and the stability of karst forest communities.

Aims Soil quality plays an essential role in vegetation restoration in the karst soil ecosystem. Many studies have reported soil quality of different plantations and vegetation successional stages in karst regions, but few have focused on the seasonal dynamics of basic soil properties. Our objectives were to investigate annual dynamics of basic soil properties of different types of plantations and evaluate soil integrated quality index (SQI).
Methods We analyzed the dynamics of soil physical and chemical properties and soil enzyme activities for four sites in Puding County, Guizhou Province, China: Robinia pseudoacacia plantation (RP), Cupressus duclouxiana plantation (CD), R. pseudoacacia-C. duclouxiana mixed plantation (RD) and a non-plantation area (CK). Soil samples were collected in alternate months from September 2009 to September 2010. Soil factors were measured using general methods, and data were analyzed using SPSS 13.0 software.
Important findings Soil physical properties of all three plantations had an advantage over the non-plantation area and were slightly improved within one year. There were significant differences in soil nutrients and soil pH among the four sites (p < 0.01). Soil urease activity in all sites was highest in September and lowest in January. Soil invertase activities were remarkably different among the four sites (p < 0.01). Soil catalase activity exhibited a unimodal peak, and alkaline phosphatase activity had a bimodal peak. Soil polyphenoloxidase activity was lowest in January and very low in RP throughout the study. Moreover, the rank of means of five soil enzyme activities was different among the four sites. The SQI of RP, CD, RD and CK was 0.748, 0.406, 0.590 and 0.315, respectively. In general, all three types of plantations, but especially RP and RD, could improve soil quality after conversion of farmland to forest.

Aims Our objective was to analyze the calcium absorption and distribution characteristics of pteridophyte species, and to determine their adaptation to high calcium.
Methods Eleven pteridophytes were collected from Maolan National Nature Reserve and the surrounding area. We analyzed their calcium absorption and distribution behavior by comparing the calcium content in each organ and the rhizosphere.
Important findings In acidic soil, calcium availability in the rhizosphere of Nephrolepis auriculata was much higher than that of other species. Because of low calcium content in acidic soil, the calcium content of calcifuge was significantly lower than that of exclusive calciphytes. Except for N. auriculata and Parathelypteris glanduligera, the calcium content in various organs of plants that lived in acidic soil were mature leaf > roots > young leaf, and the calcium content in various organs of plants that lived in calcareous soil were roots > mature leaf > young leaf. In addition, calcium content in various organs of Pteris cretica var. nervosa had differences between calcareous and acidic soils. Calcium content of exclusive calciphytes had significant interspecific differences. Results suggested that N. auriculata could meet its calcium needs by enriching and activating calcium in the rhizosphere. The calcium content in plants could be reflected by the calcium supply in the soil. In different soils, the calcium-content differences in various organs might be related to their adaptive behavior towards changes of soil calcium content. The demands for calcium of the five exclusive calciphytes species were disparate. When they encountered high calcium stress, their primary adaptation behaviors differed. Cyrtogonellum fraxinellum, Cyrtomium fortune and Pteris vittata had calciphilious features, but Adiantum capillus-veneris was a low calcium species. Key words calcareous soil;calcium content of plant;exclusive calciphytes;high calcium content adaptation

Aims Drought stress is one of the most important factors limiting the growth of plants in the harsh karst habitats of southwestern China, especially at the seedling establishment stage. Our objective was to elucidate the adaptive strategies against drought stress of native plants with different growth forms.
Methods We investigated leaf water potential, photosynthetic capacity, pigments, osmotic solutes, antioxidant enzymes, and growth of the seedlings of four plant species under four drought intensities. The species were Pyracantha fortuneana (evergreen shrub), Rosa cymosa (deciduous shrub), Cinnamomum bodinieri (evergreen tree), and Platycarya longipes (deciduous tree).
Important findings As drought stress intensified, leaf water potential, photosynthetic capacity, chlorophylls content, biomass increase, leaf mass ratio (LMR), leaf area ratio (LAR) and specific leaf area (SLA) gradually decreased, while thermal dissipation (NPQ), ratio of carotenoids to chlorophylls, malondialdehyde content and root mass ratio (RMR) increased in the four species. Intrinsic water use efficiency (A_n/g_s), content of osmotic solutes and activity of antioxidant enzymes in C. bodinieri and Platycarya longipes increased under mild and/or moderate drought and decreased under severe drought, while A_n/g_s, proline content and superoxide dismutase activity gradually increased in Pyracantha fortuneana and R. cymosa as drought intensified. Under severe drought, Pyracantha fortuneana and R. cymosa showed smaller decreases of predawn water potential and chlorophylls content and maintained higher photosynthetic capacity and larger percent biomass increase than C. bodinieri and Platycarya longipes, due to lower SLA and LAR, higher A_n/g_s and NPQ and higher capacities of osmotic adjustment and antioxidant protection. Under moderate drought, C. bodinieri exhibited small decrease of predawn water potential and higher LMR and LAR than the deciduous species, and maintained unusually high proline accumulation and high activities of antioxidant enzymes. However, the low maximum quantum efficiency of PSII photochemistry and net assimilation rate, the sharp decreases of water potential, LMR, LAR and biomass and the low capacities of osmotic adjustment and antioxidant protection under severe drought indicated C. bodinieri’s weak tolerance. Under well-watered condition, Platycarya longipes with high RMR showed higher LAR, chlorophylls content and biomass increase than the two shrubs. However, in response to drought stress, Platycarya longipes revealed sharp reduction of biomass due to large drought-induced decreases of gas exchange, LAR, LMR and chlorophylls content. It minimized water loss by both stomatal closure and reducing transpiration leaf area through shedding leaves and also reduced light harvesting by pigments breakdown. These results suggested that Pyracantha fortuneana, R. cymosa and C. bodinieri adopted tolerance strategies against drought stress with C. bodinieri having lower tolerance to severe drought, whereas Platycarya longipes was more sensitive to drought stress and employed avoidance strategies.

Aims Our objective was to explore the genetic diversity of arbuscular mycorrhizal fungi (AMF) in karst microhabitat.
Methods We used nested polymerase chain reaction and denaturing gradient gel electrophoresis to study the genetic characteristics of AMF sampled from microhabitats of three different vegetation types in Maolan National Nature Reserve of Guizhou Province.
Important findings The AMF genetic diversities in all three microhabitat types were rich. The highest values of biodiversity index (4.06) and species abundance (68) were found in the shrubland soil surface, and the lowest values (3.16 and 29, respectively) were found in the secondary forest rocky crevice. The average values of biodiversity index and species abundance of the 9 microhabitats studied were 3.67 and 48, respectively. These were much higher than those in some other areas; the possible reasons were the complex karst ecological system structure and high plant species diversity. The AMF genetic diversity of different microhabitat types showed significant differences. The highest similarity index was only 0.45, and this means the spatial heterogeneity of different microhabitat types had significant influence on AMF genetic diversity. Glomus was the dominant genus through the karst area and should be a candidate for screening high ecological restoration strains for karst areas.