Aims Vegetation water content is an important biophysical property of terrestrial vegetation, and its remote estimation can be utilized for real-time monitoring of vegetation drought stress. This paper reviewed and summarized the conception and research progress of four commonly used vegetation water indicators: canopy water content, leaf equivalent water thickness, live fuel moisture content, and relative water content. The advantage and disadvantage of various research methods were evaluated by estimating vegetation water content and identifying the limitation in monitoring vegetation water content using optical hyperspectral remote sensing techniques. Finally, the future research tasks were discussed to address issues on accurate monitoring, early warning and evaluation of vegetation drought stress.

Aims Linear models have been widely used to examine the impacts of climatic factors on plant phenology, although the relationship between phenology and climate could be nonlinear. Based on survival analysis, robust nonlinear models were empirically developed to examine the phenological changes in relation to air temperature and precipitation for the grasslands in China and individual woody plants in Europe.

Methods Three datasets were used in our survival analysis: two datasets of the remotely-sensed vegetation phenology for grasslands in Nei Mongol grasslands and meadows in Qinghai-Xizang Plateau, and a dataset of the phenological observations of individual woody plants in Europe. Monte Carlo simulations were performed to estimate model parameters in our survival analysis.

Important findings The survival analysis appeared to be a powerful tool in modeling the nonlinear changes in green-up date (GUD) to the climatic factors. The analyses showed that both spring temperature and precipitation are significantly correlated with the GUD in the semi-arid grasslands in Nei Mongol. For Qinghai-Xizang Plateau and Europe, the spring temperature seemed highly correlated with GUD, while the correlation was weak with the higher Holdridge aridity index. The survival model predicted that the GUD in the three regions would be advanced by 1-6 days with an increase in temperature of 1 °C. A combined increase in spring temperature and precipitation would lead to nonlinear responses, suggesting the need for developing nonlinear models. Our empirical exercise in this study demonstrated that the survival analysis could offer an alternative tool for predicting plant phenology under the changing climate.

Aims We studied flowering phenology and growth of four typical shrub grass plants (Carex diandra, Ribes procumbens, Ledum palustre, Saussurea neoserrata) with different life histories in the Da Hinggan Ling of northeast China to explore changes of flowering phenology and growth of early succession Taiga forests and to learn about the post-fire succession of the Taiga forests in warmer and drier climate.

Methods Open-top chambers (OTCs) and artificial drainage ditches were used to simulate the warmer and drier climate in the field. After two years of experimental warming and drainage, we recorded the flowering phenology and growth indices of four typical shrub grass plants. Flowering phenology included the first flowering date, peak flowering date, last flowering date, flowering duration and maximum flowering number. The growth indices of plants included height, coverage, frequency and above-ground biomass.

Important findings Our results revealed that: 1) Under experimental warming and drainage treatment, the first flowering dates for Carex diandra and Ribes procumbens were advanced due to early elimination of the temperature limit, which for Saussurea neoserrata were delayed by the water stress. Moreover, the Ledum palustre had longer flowering duration and more followers under the experimental warming and drainage because of the adverse shift in flowering phenology of the earlier flowering plant and the later flowering plant. 2) The Carex diandra, Saussurea neoserrata and Ledum palustre had higher coverage and frequency under experimental warming and drainage, especially in Ledum palustre, while the coverage and frequency of Ribes procumbens were declined. 3) There was no significant interaction effect between the warming and drainage on plant flowering phenology, but the responses of plant growth characteristics to warming were affected by drainage. These results indicated that species respond differently to warmer and drier climate due to different flower functional groups they belong to. The first flowering date of the early flowering plants had been progressed, and that of the late flowering plants was delayed. On the one hand, these changes can change niches in the community and interspecific competition and further alter the composition and structure of the community. On the other hand, these changes could be a way for the community to regulate community phenology to adapt climate change.

Aims Our objectives were to obtain typical plant association types in a 20 hm ² forest dynamic monitoring plot in Mt. Tiantong, and provide methodological references for determining transitional types and identifying typical types in vegetation classification.

Methods We used two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) to remove transitional community and identify typical association types. DCA method was also used to analyze the relationship between the distributions of different plant associations and environmental variables.

Important findings The results showed that the classification of typical plant associations was greatly improved by the removal of transitional communities. The forest was divided into three associations: 1) Viburnum erosum- Ternstroemia gymnanthera/Lithocarpus harlandii + Cyclobalanopsis sessilifolia Association, 2) Daphniphyllum oldhami-Lithocarpus glaber/Schima superba + Castanopsis carlesii Association, and 3) Illicium lanceolatum- Phoebe sheareri/Choerospondias axillaries + Machilus leptophylla Association. The results of DCA revealed the importance of environmental variables (elevation, convexity, slope, and aspect) on spatial distribution of plant associations. Elevation and convexity had significant effects on the distribution of associations, while slope and aspect had weak effects. The results confirmed the high accuracy of the association classification we used.

Aims The aims are to characterize key plant functional traits and their interactions of woody species growing in special and harsh karst habitats, and to explore their potential ways in adapting harsh karst habitats.

Methods A comprehensive survey of nine plant functional traits (including above- and below-ground ones) was conducted in a 100 m × 30 m permanent plot in the Tianlongshan Mountain of Puding County, central Guizhou Province, southwestern China in the summer 2016. Five dominant tree species (Carpinus pubescens, Machilus cavaleriei, Itea yunnanensis, Platycarya strobilacea, Lithocarpus confinis), three shrubs (Zanthoxylum ovalifolium, Stachyurus obovatus, Rhamnus heterophylla) and two vines (Rosa cymosa and Dalbergia hancei) in an evergreen and deciduous broadleaved mixed forest were chosen as target species. Nine traits of leaf, stem, branch and root were investigated and measured. Key features of these nine functional traits of ten woody species were numerically characterized. Traits variations among plant species, life form and leaf phenology group were further investigated. Relationships among key functional traits and between above- and below-ground traits were statistically analyzed.

Important findings (1) Nine traits varied in varying degrees. The maximum and minimum coefficient of interspecific variation were the fine root tissue density (FRTD) and twig dry-matter content (TDMC), 96.47% and 11.67%, respectively. Similarly, the largest and smallest coefficients of intraspecific variation were also FRTD and TDMC, 51.44% and 6.83%, respectively; (2) At the interspecific level, among different species FRTD had no significant difference, but other traits including specific root length (SRL), leaf thickness (LT), leaf area (LA), specific leaf area (SLA), leaf dry-matter content (LDMC), leaf tissue density (LTD), TDMC and twig tissue density (TTD) showed significant differences (p < 0.01). At the intraspecific level, however, SLA showed significant difference, and differences of other traits were not significant. (3) There was a significant correlation between most leaf and branch traits, and SRL vs. SLA were negatively correlated. However, there was no significant correlation among other root traits and leaf and twig traits. In a word, compared to the functional traits in tree species of non-karst evergreen broad-leaved forests in the same latitude, karst woody plants in Puding had a series of functional traits, such as smaller LA, SLA and larger LDMC and LTD and so on, which are beneficial to reducing transpiration and storing nutrient. This may be its main ecological strategy for adapting to arid and poor karst environments.

Aims Litter is an important source of nutrient in forest ecosystems, and its decomposition rate has a significant impact on soil nutrient supply. Previous observations indicated that different leaf falling time resulted in different litter decomposition rates. We found that the leaf falling time of Quercus mongolica was later than that of other tree species, especially in the barren soil. However, it is not yet clear why the leaves of Q. mongolica fall later. We hypothesized that the leaves of Q. mongolica had higher nutrient concentration, and longer time for resorption, which could lead to the later time of leaf falling.

Methods We continuously measured N, P, K, Ca, Mg, Cu, Fe, Mn and Zn concentrations in leaves of three tree species (Q. mongolica, the leaf falling time is the last; Juglans mandshurica, the leaf falling time is the earliest, Acer mono, the leaf falling time is in between Q. mongolica and J. mandshurica) from leaf maturity (August) to litter fall (October) in a montane region of eastern Liaoning Province. We analyzed leaf nutrient concentrations and resorption efficiencies of each species.

Important findings The nutrient concentrations in mature leaves of Q. mongolica are similar to those of other tree species. N, P and K concentrations in the litter of Q. mongolica were significantly lower than those of other species (p < 0.05), and the resorption efficiencies were generally consistent with the leaf falling time. These findings did not support the hypothesis that leaves of Q. mongolica have higher nutrient concentrations than other species. The resorption efficiencies of N, P and K did not influence leaf nutrient concentrations, but were directly related to the biological characteristics of tree species. The leaves of Q. mongolica fall later, which might be due to the high adaptability of Q. mongolica to the barren soil. Although the mature leaves could not accumulate more nutrients from barren soil, they increased the nutrient use efficiency by prolonging the nutrient resorption time. We inferred that leaves with higher nutrient resorption efficiency would fall later, because of greater nutrient storage such as Q. mongolica, which is better adapted to barren soil than other tree species. On the contrary, trees with lower nutrient resorption efficiency generally grow better in the fertile soil, such as J. mandshurica.

Aims The development of ecological agriculture by agroforestry models could improve resource utilization. The Hevea brasiliensis-Alpinia oxyphylla agroforestry system is among the largest agroforestry models in rubber plantation. In this study, we aimed to investigate the physiological strategies that allow Alpinia oxyphylla, a perennial herb widespread under-growing the Hevea brasiliensis, to cope successfully with the environmental factors with the seasonal changes of the tropical monsoon climate.

Methods Gas exchange and light response curve measurements as well as pigment content determinations were performed periodically throughout different seasons on A. oxyphylla growing in the rubber plantation by a portable leaf gas exchange system (LI-6400).

Important findings (1) The diurnal change of the net photosynthetic rate had a V-shaped pattern in March, which decreased to be the lowest at 14:00. The diurnal changes of the P_n in June, September, and December increased to the peak at 10:00 and then began to decline slowly. The daily average and maximum of the net photosynthetic rate during the monsoon season (June and September) were much higher than those in the dry season (March and December), which suggested that A. oxyphylla had the physiological strategy to environmental changes in different seasons. The severe soil moisture deficit inhibits photosynthetic CO₂ assimilation due to the decline of stomatal conductance in March. (2) The light compensation point and dark respiration rate of March generally were higher than those of other seasons (June, September and December), but the maximum net photosynthetic rate and light saturation point were on the contrary. The discrepancies that may be related to the photosynthetic enzymatic activity were restrained by the dry conditions, which caused the occurrence of photoinhibition, the increased respiration, and decreased photosynthetic capacity. (3) The net photosynthetic rate in March was negatively correlated with air temperature, but positively correlated with air humidity. Air temperature and air humidity in combination inhibited photosynthesis of A. oxyphylla in March. However, photosynthetic active radiation was a pivotal factor to photosynthesis of A. oxyphylla in September and December.

Aims Vegetation restoration plays an important role in the accumulation and storage of soil organic carbon (SOC). Our objectives were to investigate the effects of vegetation restoration on SOC and to explain the underlying mechanisms of carbon sequestration during vegetation restoration in the mid-subtropical China.

Methods According to the disturbance intensity and the degree of restoration, we used the space-for-time substitution method by selecting four different types of vegetation communities, composed of Loropetalum chinense-Vaccinium bracteatum-Rhododendron simsii scrub-grass-land (LVR), Loropetalum chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-Loropetalum chinense coniferous-broad leaved mixed forest (PLL), and Lithocarpus glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG) to represent the successional sequence in the secondary forests in Changsha County, Hunan Province, China. Permanent plots were established in each vegetation communities. Soil samples (0-40 cm) were collected and divided into four layers (0-10, 10-20, 20-30 and 30-40 cm). Soil organic carbon concentration (C_SOC) and soil organic carbon density (D_SOC) were measured. The main influencing factors on C_SOC and D_SOC were analyzed with Principal Component Analysis and Stepwise Regressions Analysis.

Important findings 1) Along vegetation restoration, C_SOC and D_SOC increased dramatically. The C_SOC was the highest in LAG, which was 12.5, 9.3 and 4.7 g·kg ^-1 higher than in LVR, LCQ and PLL in 0-40 cm soil depth, increasing by 248.5%, 113.1% and 58.5%, respectively. The increments of D_SOC in LAG at 0-40 cm soil depth were 67.1, 46.1 and 32.5 t C·hm ^-2, and increased by 182.0%, 79.7% and 45.6% compared to D_SOC in LVR, LCQ and PLL, respectively. 2) Correlation analysis showed that C_SOC and D_SOC were strongly and positively correlated with species diversity index, community total biomass, aboveground biomass, root biomass, existing biomass in litter layer, nitrogen (N), phosphorus (P) concentration in litter layer, soil total P, soil available P, soil C/N ratio (except C_SOC), soil C/P ratio, soil N/P ratio and percentage of soil clay (< 0.002 mm), but significantly and negatively correlated with C/N in litter layer (except D_SOC), C/P in litter layer, soil pH and soil bulk density, suggesting that the differences in C_SOC and D_SOC under different vegetation stages were related to both vegetation and soil properties. 3) The results of principal component analysis and stepwise regression analysis revealed that soil C/P, pH, concentration of soil clay (except C_SOC) and C/P in litter layer were the dominant factors affecting C_SOC and D_SOC during vegetation restoration. Among them, soil C/P ratio ranked first. These results indicated that the differences in soil C/P ratio, pH, soil clay concentration and C/P in litter layer were responsible for the changes in SOC during vegetation restoration.