Aims Seasonality is the typical characteristic of plant landscape in Beijing, including seasonal dynamics of plant phenology. We analyzed the seasonal changes in phenology of 120 deciduous trees in Beijing Botanical Garden, with additional efforts on an innovative methodology in studying plant phenology.

Methods Based on the standards of the Chinese Phenological Observation Method, three-level Phenological Code (a, b, and c) was used to recode the phenology data. Our data analysis was performed with “pentad” (5-day period) in 24 Solar Terms. Analytical methods include a frequency distribution method to explore the division of phenophases and their dynamic constitution. The frequency distribution statistics in SPSS 20.0 were applied to explore the temporal dynamics in occurrence time and duration for different types of phenophases.

Important findings We found that: The division of phenological seasons and their phenological constitution as: 6th-19th pentad for Spring, with 54.03% of the whole phenophases that are featured with sprouting, leaf spreading and flowering; 20th-45th pentad for Summer, with 12.95% of phenophases that include conclusions of leaf spreading for all trees, intensive fruiting, fewer flowering, and autumn-leaf scenery in late summer; 46th-59th pentad for Autumn, with 27.19% of the phenophases that are characterized with leaf discoloration and defoliation, some fruiting, and very few flowering; and 60th pentad for Winter, with 0.6% of phenophases that are all constituted with defoliation. The temporal distribution pattern of different kinds of phenophases is as follows. The leaf-unfolding phenophases span from 3rd to 23rd pentad and averagely last for 3.27 pentads, with Sorbaria kirilowii as one of the earliest leaf-unfolding species. The leaf coloration phenophases happen between 40th -63rd pentad, with Tilia mongolica and Armeniaca sibirica as the earliest species to show fall-color leaf. The autumn-leaf duration lasts for 8.2 pentads in average, with Euonymus alatusand Sambucus williamsii as the typical species that show longer leaf duration. The leaf period averagely lasts for 44.2 pentads, with Abelia chinensis, Salix matsudana and Kerria japonica holding the longest leaf time. The flowering-type phenophases happen during 1st-53rd pentad, with 8th-23rd pentad as the best ornamental period, and three species (Chimonanthus praecox, Jasminum nudiflorum and Ulmus pumila) as the earliest blooming species and Elsholtzia stauntonias the last one to bloom. The flowering period lasts for 6.7 pentads in average, with Sorbaria kirilowii, Hibiscus syriacusand Lagerstroemia indica showing the longest flowering time. The fruiting-type phenophases happen between 8th-59th pentad, with Ulmus pumila and Lonicera fragrantissima as the earliest species for fruit maturation. The fruiting duration averagely lasts for 29.0 pentads, and those species that do not lose fruits during the winter and some other species with longer fruit holding period though falling fruits completely in winter such as Viburnum melanocarpum and Physocarpus opulifolius ‘Luteus’ have longer ornamental time of fruit scenery. Compared with a counterpart research in the 1980s, this study reveals that spring in 2017 came earlier by a pentad than that 30 years ago while autumn came later by 3 pentads; additionally, autumn duration shortened by 2 pentads while summer duration prolonged by 4 pentads, resulting in larger differences between the duration of the four seasons.

Aims Leaf size, as one of the easier measured plant morphological traits, reflects response and adaptation of plants to environment and indicates functions and processes of ecosystem. When measuring leaf size (the leaf area, LA) on the field, the common accepted practice considers that the number of leaves picked off is often 10-20. However, what is the optimal number of leaves remains unknown. In this study, we attempt to determine how many leaves should be investigated when the leaf size of a tree is measured.

Methods This study selected two dominant tree species (Schima superba, Ss and Liquidambar formosana, Lf) from a broadleaved evergreen and deciduous mixed forest in Jinhua Mountain of Zhejiang Province, eastern China. On the basis of sampling (>2 500 leaves for each tree) in five classes of the diameter of breast height (DBH) of tree species and at six directions for each individual, variations of LA in the two tree species are statistically analyzed. The optimal number of leaves, which can mostly represent the common leaf size feature, is further investigated.

Important findings Mean LAof the evergreen tree Ss was smaller than that of the deciduous tree Lf. The former was (41.60 ± 10.88) cm ² (16.74-100.80 cm ²) and the latter was (57.65 ± 19.35) cm ² (11.31-129.51 cm ²). LA of Lf was significantly related to the DBH, but LAof Ss was not. LA of both trees in the middle DBH class (15-20 cm) was not significantly different from their means. LA of two trees have no significant correlations with the sampling directions, but LA at the east, west and bottom had no significant relationships with their means. Considering the representativeness and practicality in the field sampling, the priority of selecting leaves can target the bottom direction of middle diameter mature trees. Random sampling analysis indicated that, the optimal number of leaves for tree LA measurement is species specific. The optimal number of leaves for Ss is 40 and for Lf is at least 170, respectively. Therefore, when measuring leaf area in a forest community, the optimal sampling number of leaves should not be limited to 10-20 leaves. Under sufficient labor, material and time, more leaves should be measured.

Aims Our objectives were to investigate differences in nutrient resorption between different plant organs (leaf and branch), among plants with different life spans (one-year old, two-year old and senesced), and under different duration of nitrogen (N) deposition treatments in a Chinese fir (Cunninghamia lanceolata) plantation.

Methods The long-term N deposition experiment was conducted in a 12-year-old fir plantation of subtropical China. N deposition treatment was initiated in January 2004 until now, up-going 14 years. N deposition were designed at 4 levels of 0, 60, 120, and 240 kg·hm ^-2·a ^-1, indicated as N0, N1, N2, and N3, respectively, with 3 replicates for each treatment. The solution of CO(NH₂)₂was sprayed on the forest floor each month. In the study, we measured N and phosphorus (P) concentrations and analyzed the pattern of nutrient resorption of mature and senescing leaves and branches. The different responses of needles N and P resorption after 7- and 14-year N deposition treatments were also compared.

Important findings After 14 years of N deposition, (1) during the senescing process, leaf and branch C, N, and P content gradually decreased with increasing treatment duration, with higher content in leaf than in branch. N content decreased in the order of one-year old green leaf > two-year old green leaf > senescent leaf > one-year old living branch > two-year old living branch > senescent branch, and N3 > N2 > N1 > N0, with C:N showing the opposite trend. Senescent organs had higher C:N, N:P, and C:P than mature living organs. N deposition increased N, N:P, and C:P of mature living organs (except for the two-year old green leaf), while decreased P and C:N. (2) N resorption efficiency (RE_N) and P resorption efficiency (RE_P) of leaves and branches decreased gradually with increasing life span. RE_P was typically higher in leaf and branch than RE_N. Leaf had lower RE_N (28.12%) than branch (30.00%), but higher RE_P (45.82%) than branch (30.42%). A highly significant linear correlation existed between N:P and RE_N:RE_P in leaves and branches. (3) RE_N decreased but RE_P increased with the treatment duration of N deposition. The longer experimental duration (14 years) reduced RE_N by 9.85%, 3.17%, 11.71% under N1, N2, and N3 treatments, respectively, and increased RE_P by 71.98%, 42.25%, 9.60%, respectively, than the shorter treatment duration (7 years). In summary, the responses of essential nutrients resorption efficiency for different plant organs and life span varied with the levels and duration of N deposition treatment. RE_N:RE_P in leaf and branch were mostly driven by N:P of leaf and branch. The results highlight that nutrients resorption is significantly influenced by long-term N deposition.

Aims As an endangered wild species with extremely small populations, Ferrocalamus strictusis narrowly distributed in South Yunnan with a small number of individuals. The survey of population structure and community characteristics of the wild population of F. strictus can facilitate understanding its endangered system and mechanisms and provide preliminary research basis for its protection.

Methods We investigated the community and population structure of F. strictus, including species composition, population density, population survivorship curve and death factors by plot surveying and sampling.

Important findings The community in which population of F. strictus is located in Mojiang has some characteristics of mountain rainforests in terms of appearance and species composition. The population density of F. strictus was 2.04 ind.·m ^-2. The survivorship curve of F. strictus was between Deevey-I and Deevey-II. The net proliferation rate (R₀) of F. strictus population was 1.10, which indicates an expanding population of F. strictus. The death of F. strictusis caused by human logging, natural death, shoot degradation and insects feeding. Among them, artificial cutting accounts for the largest proportion. Ferrocalamus strictus is a species of forest bamboos distributed in the South Asian subtropics, which is a medium-sized bamboo species. Its internode length change suddenly from the base 3-4 nodes. The longest ones exceed 1 m, which ranks at the top of all bamboo species and is closely related to its adaptation to the tropical mountain rainforest environment.

Aims Modelling potential distribution ranges of threatened species is of great significance for their conservation. In this paper, the distribution of potential suitable habitat of Impatiens hainanensis,a limestone-endemic and endangered plant in Hainan Island, was studied to provide scientific basis for their effective in situ conservation and re-introduction of I. hainanensis.

Methods Based on eight occurrence sites and 12 environmental variables, the Maximum Entropy (MaxEnt) algorithm and GIS technology were used to create a model linking the distribution ranges of I. hainanensis with environments. With data on five actual distribution sites and five non-occurrence sites, four model evaluation metrics (area under the receiver operating characteristic curve (AUC), kappa coefficient, true skill statistic (TSS), overall accuracy) were used to evaluate the predictive performance and accuracy of this model.

Important findings The results indicated that the indicative value of all four evaluation metrics were above 0.9, indicating that the MaxEnt model can effectively predict the potential suitable habitats of I. hainanensis.Slope, precipitation of the driest quarter and coefficients of precipitation variation were the three main environmental factors influencing the distribution of I. hainanensis. At present, the most suitable habitat includes western and southern parts of Baisha County, the central and southern parts of Changjiang County, the eastern part of the Dongfang City and northeastern Ledong County, accounting for 1.8% of land area on Hainan Island. Since the potential suitable habitat of I. hainanensis is rare and severely fragmented, the protection of this species is urgent. We suggest to collect the seeds of various geographic populations of I. hainanensis to establish a germplasm resource bank. The most suitable habitat of the species, including Tian’an Village and Jiangbian Village in Dongfang City, northeast of Ledong County (Jiaxi Reserve), should be selected as the priority places for future extensive field surveys and re-introduction.

Aims Fine root decomposition is the major pathway of carbon and nutrient input to the soil in forest ecosystems. However, the patterns and controlling factors of the decomposition of these roots, especially the finest roots, are poorly understood.

Methods Using a root branch-order classification, we separated the first four orders of fine root systems of Pinus koraiensis, Larix gmelinii, Fraxinus mandschurica and Betula platyphylla into two classes: first- and second-?order roots combined into lower-order; third- and fourth-order roots combined into higher-order. We conducted a four-year field litterbag study on decomposition of these four root orders of four temperate tree species in northeast China.

Important findings The results showed that the lower-order and higher-order roots had a decomposition rate constant of 0.342 and 0.461 for Pinus koraiensis, 0.304 and 0.436 for Larix gmelinii, 0.450 and 0.555 for Fraxinus mandschurica, and 0.441 and 0.579 for Betula platyphylla, respectively. We observed slower decay rates in lower-order than in higher-order roots in all four studied tree species. The root decay constants (k) was significantly correlated with both acid-unhydrolyzable fraction (AUF) and total non-structural carbohydrate (TNC). We concluded that slow decomposition of lower-order roots was mainly driven by their high AUF and low TNC concentrations.

Aims Global nitrogen (N) deposition not only alters soil N and phosphorus (P) availability, but also changes their ratio. The levels and ratios of N and P supply and their interaction may simultaneously influence plant seed traits. However, so far there has been no experiments to distinguish these complex impacts on plant seed traits in the field.

Methods A pot experiment with a factorial design of three levels and ratios of N and P supply was conducted in the Nei Mongol grassland to explore the effects of levels and ratios of N and P supply and their interaction on seed traits of Chenopodium glaucum.

Important findings We found that the relative contribution (15%-24%) of N and P supply levels in affecting the N concentrations, P concentrations and germination rates of seeds was larger than that (3%-7%) of N:P supply ratios, whereas seed size was only significantly influenced by N:P. Simultaneously, seed N and P concentrations were impacted by the interaction of N and P supply levels and ratios. At the same N:P, decrease in nutrient supply levels increased seed N concentrations, P concentrations and germination rates. N:P supply ratios only had a significant effect on seed size and germination rates under low nutrient levels. Overall, these results indicate that different seed traits of C. glaucum show different sensitivities to N or P limitations, leading to adaptive and passive responses under different nutrient limitations. This study presents the the first field experiment to distinguish the effects of nutrient supply levels, ratios and their interactions on plant seed traits, which provides a new case study on the influences of global N deposition on future dynamics of plant population and community.