Aims Stand age plays a vital role in carbon (C) stock and its distribution (vegetation, woody debris, litter and soil) within forest ecosystems. Subtropical forests are pivotal in the C cycling of terrestrial ecosystems. In subtropical China, Fagus trees are widely distributed and of great importance. However, the analyses of C storage in chronosequent Fagus forests have not been well performed.

Methods Nine Fagus lucida forests at three succession stages (33, 82 and 208 year-old) were studied in Mt. Yueliang, Guizhou Province, and their C stocks and distributions within the forests were investigated and estimated.

Important findings Ecosystem C stock increased significantly with increasing stand age, which was (186.9 ± 46.0), (265.8 ± 82.3) and (515.1 ± 176.4) Mg·hm^-2 in the 33, 82 and 208 year-old forests, respectively. The increase in the C stock appeared mainly attributed from increase in vegetation C stocks that accounted for 32%-79% of the total C stock. The woody debris and litter carbon stocks also increased significantly with increasing stand age, but accounted for <1% of the total C stock. While soil C stock showed no significant change with increasing stand age, it decreased its contribution to the total C stock (from 67% to 20%). These results confirmed the importance of stand age on C storage and the dynamic reallocations in the subtropical forests. Results from this study also added additional evidences in understanding the significance of disturbance and land use in C accumulation.

Aims Few comparative studies have been conducted on the decomposition of the plant litters from different geographical sources in the same site. We aimed to understand the effect of geographical sources and biochemical traits of peatland plants on litter decomposition.

Methods Along a latitudinal gradient, we collected plant materials from three peatlands, Dajiuhu, Hani and Mangui, to carry out a one-year decomposition experiment with litter bags in Hani Peatland, Changbai Mountains.

Important findings When species identity was not considered, we found that overall initial nitrogen (N) content decreased while initial lignin content, carbon nitrogen ratio (C/N) and lignin/N increased with latitude in the litters from 3 peatlands. Litter decomposition differed with plant functional groups. After one year of decomposition, dry mass loss of both birch and sedge (ca. 50%) was higher than that of peat mosses (ca. 10%). No significant difference was observed in litter dry mass loss among different geographical sources. However, dry mass loss of Sphagnum magellanicum from the middle latitudinal peatland (19%) was higher than that from the high latitudinal site (9%). The factors affecting litter decomposition differed among plant functional groups. Initial total phenolics/N was the important factor to determine the difference in litter dry mass loss among the 3 genera. The initial N content and C/N, and Klason lignin content and total phenolics/N were positively related to litter decomposition of Carex and Sphagnum, respectively. If the decrease in latitude is used to indicate climate warming, to some extent, our study suggests that current climate warming, by changing the plant composition and biochemical traits, may alter litter decomposition and even carbon accumulation in high latitudinal peatlands.

Aims The objective was to explore the differences in rhizosphere effect among different plants in plantation and provide important theoretical basis for understory vegetation management in plantation ecosystem.

Methods We collected bulk and rhizosphere soils of overstory trees and understory shrubs (Loropetalum chinense, Adinandra millettiiand Eurya muricata) in Cunninghamia lanceolata, Pinus massoniana and Pinus elliottiiplantations which were planted in about 1985, at Qianyanzhou Ecological Research Station, Taihe, Jiangxi, to investigate soil pH value, soil nitrogen, carbon and phosphorus content and to access their rhizosphere effects.+++Important findings (1) Most of the chemical properties of rhizosphere soil and bulk soil were significantly different for overstory tree species (p< 0.05), while the differences between bulk soil and rhizosphere soil of understory shrubs were related to understory shrub species. For example, most of the properties were significantly different between bulk and rhizosphere soils for L. chinense, but not for E. muricata. (2) Rhizosphere effects among shrub species were significantly different except for those of nitrate nitrogen (NO₃ ^--N).Specifically,the rhizosphere effects of pH, ammonium nitrogen (NH₄ ⁺-N), dissolved organic carbon (DOC), total nitrogen (TN), total carbon (TC), carbon-nitrogen ratio (C/N), available phosphorus (AP) and total phosphorus (TP) of L. chinense were significantly higher than those of E. muricata.And the rhizosphere effects of TN, TC, C/N and AP of L. chinense were significantly higher than those of A. millettii. No significant differences were found between the rhizosphere effects of A. millettii and those of E. muricata. (3) The rhizosphere effects of C. lanceolata were significantly higher than those of the three understory shrubs. But no significant difference was found between P. massoniana or P. elliottii and L. chinense. While the rhizosphere effects of P. massoniana were significantly higher than those of A. millettii and E. Muricata, and the rhizosphere effects of P. elliottii were significantly higher than those of E. muricata. The results showed that the rhizosphere effects of overstory tree species were higher than those of understory shrubs (especially for E. muricata), indicating overstory tree species have stronger ability to obtain nutrients. But the differences in rhizoshpere effects between overstory trees and understory shrubs varied between shrub species and forest types. Therefore, this study suggested that understory shrub species should be considered according to forest stand type in plantation management in order to provide higher productive and ecological value.

Aims This study was performed to compare the growth and characteristics of nutrient elements at different leaf positions of reed (Phragmites australis) under salinity stress. The adaptive mechanisms by which reeds at a Songnen grassland tolerate salinity stress were determined.

Methods Samples were collected from normal grassland, moderate degraded grassland and severe degraded grassland, respectively. Plant height, shoot dry mass, and nutrient elements at different leaf positions of reeds were measured.

Important findings The Na⁺ content, total salt content and pH value of soil are important factors that determine soil salinity in the Songnen grassland. The degree of soil salinity was aggravated stepwise from the single dominant reed communities to the reed coexisted with Suaeda salsa communities. Height and shoot dry mass decreased with increased salinity. The profiles of 10 key nutrient elements were measured, namely, K, Na, Ca, Mg, Fe, Cu, Zn, Mn, P, and B. Results from the principal component analysis indicated that all samples were distributed within the 95% confidence interval. The results showed that K and P contents decreased with lowered leaf positions; while Na, Ca, and Mg showed the opposite distribution trends. Fe and Cu contents were less in young leaves than in the other leaves, Mn accumulated in the old leaves. However, a large amount of Zn accumulated in the young leaves. No obvious change in B was observed. Thus, salinity stress produced a small effect on the distribution of nutrients in young leaves, but strongly affected the older leaves. Under salinity stress, old leaves accumulated more Na⁺ to protect the young leaves from ion harm. High accumulation of Ca, Mg, Fe, and Cu in mature and old leaves was more beneficial to maintain and protect the function of photosynthesis. The increased K and P contents in the young leaves could provide the necessary nutrition and improve the salinity resistance of reed. This process contributes to the physiological response strategy of reed under salinity stress.

Aims In this study, the patterns of variations in leaf turgor pressure and responses to environmental factors were investigated in Populus tomentosa, in order to provide a theoretical basis for guiding irrigation using leaf turgor pressure as a water stress indicator.

Methods The study was conducted in a two-year-old Populus tomentosaplantation under surface drip irrigation. Leaf patch clamp pressure (P_p) was continuously monitored in treatments of full irrigation (FI) and control (CK). Soil temperature (T_s), soil water potential (Ψ_s), sap flow velocity (V_SF) and meteorological factors were monitored simultaneously. The patterns of variations in leaf turgor pressure and relationships between P_p and environmental factors of P. tomentosa under different water treatments were analyzed.

Important findings The P_p values exhibited a clear pattern of “daytime high and nighttime low” with varying weather conditions, and the width of peak signals in P_p was greatest in sunny days. The positive relationships between normalized leaf patch pressure (ΔP_p) and V_SF fitted a polynomial function under different weather conditions, with R² values ranked in the order of sunny days (0.87) > cloudy days (0.72) > rainy days (0.31). Photosynthetically active radiation (PAR), air temperature (T_a), relative air humidity (RH), and vapor pressure deficiency (VPD) were predominant environmental factors affecting P_p, especially PAR. Hysteresis was found between ΔP_p and different environmental factors, and the size of the hysteresis loop differed between the two irrigation treatments. There were significant differences in the shapes of P_p curves between the irrigation treatments. In conclusion, the variations of leaf turgor pressure were closely related to environmental factors in P. tomentosa, and there was a high degree of synergistic change with the sap flow on sunny days. Therefore, leaf turgor pressure can potentially serve as a diagnostic indicator of water deficit.

Aims Liquidambar formosanais a fast-growing and multipurpose native tree species in China. Our aim is to determine the phenotypic variations, adaption and distribution patterns of seed and fruit characteristics of L. formosana populations.

Methods Data for 10 phenotypic traits of seeds and fruits including fruit diameter, peduncle length, thousand kernel weight, seed length, seed width, seed wing length, seed wing width, seed width ratio, seed wing width ratio, ratio of seed length and seed wing length, were sampled from 36 natural L. formosana populations across China. Analysis of variance (ANOVA), correlation analysis, and regression analysis were used to analyze the phenotypic variations among and within populations.

Important findings Results showed that the mean phenotypic differentiation coefficient was 57.55%, which indicated that the phenotypic variation among populations was the main source of the phenotypic variation in L. formosana. The mean coefficient of variation was 15.83%, ranging from 10.05% to 24.31%, suggesting that the phenotypic variation of seeds and fruits was very plentiful. The coefficient of variation was different among populations. The mean coefficient of variation in Anfu was the highest (16.73%), while that of Jianyang was the lowest (11.48%). The pattern of geographic variation of most seed and fruit phenotypic traits was random. There was no significant correlation between the adjacent populations in phenotypic traits. The mean temperature in January, altitude and latitude played important roles in affecting the phenotypic traits. The length-width ratio of seeds decreased with the increase of altitude, which can be used to infer the altitude of the distribution of a population. Our results provide useful information for the collection of wild resources and the breeding of this economically important species.

Aims Arbuscular mycorrhizal fungi (AMF) can form symbiotic associations with most terrestrial plants to improve plant growth and stress resistance. It has been well demonstrated that AMF can promote plant acquisition of water and enhance plant tolerance to drought. In this study, AMF extraradical hyphae were obtained from in vitro culture of AMF Rhirophagus irregularis with hairy carrot (Daucus carota var. sativa) root to investigate the morphological and physiological changes of hyphae in response to drought stress induced by polyethylene glycol (PEG).

Methods The influence of drought stress on the hyphal morphology was observed by using the field emission-scanning electron microscope-energy dispersive X-ray spectroscopy (FE-SEM-EDS), while H ⁺ and Ca ²⁺ion fluxes through living hyphae were monitored by non-invasive micro-test technique (NMT).

Important findings The results showed that significant H⁺ efflux and Ca²⁺ influx through the tip and side of the extraradical hyphae were detected in response to drought stress induced by PEG for 1 h. Fluorescence probing confirmed that the intracellular pH value and Ca²⁺ concentration of hyphae significantly increased under PEG treatment. The morphology of hyphae changed and the pH value of the growth medium decreased after treatment with PEG for 24 h. The P, Ca, and Fe elements accumulated at the hyphosphere to enhance the nutrient absorption by hyphae. The study confirmed that AMF regulated the transmembrane H⁺ and Ca²⁺ flux to promote the material exchange between hyphae and environment under drought stress. The acidification of the hyphosphere environment potentially promoted the absorption of nutrients and also the signal exchange between AMF and the host plant to enhance plant drought tolerance.

Aims The composition of soil organic carbon has been changed significantly in mangrove ecosystems due to the invasion of Spartina alterniflora in recent years. However, few studies were reported on functional groups of soil organic carbon in the two communities. The object of this study was to understand the differences in soil carbon pool and organic carbon functional group characteristics in mangrove community and S. alterniflora community of Zhangjiang Mangrove Nature Reserve in Fujian Province.

Methods We used the method of “space for time” to study the changes of soil carbon composition following the invasion of S. alterniflora. Three transects were selected from landward to seaward in the wetland of Zhangjiang Mangrove Nature Reserve in Fujian Province, with three sampling sites in each transect: mangrove community (MC), transitional community (TC), and S. alterniflora community (SC). We sampled three plots in each site for replicates. Soil samples from five soil layers at 0-100 cm were collected to analyze the characteristics of total organic carbon (TOC), particulate organic carbon (POC) and dissolve organic carbon (DOC). Nuclear magnetic resonance (NMR) spectroscopy was used to analyze the functional group characteristics for surface (0-15 cm) and deep layers (75-100 cm).

Important findings We found that: (1) soil organic carbon decreased from MC to SC, with TOC and POC following the pattern of MC > TC > SC. However, the DOC did not show a clear trend. (2) The functional groups of soil organic carbon in all vegetation types were mainly alkyl carbon and alkoxy carbon, followed by aromatic carbon and carbonyl carbon. In the surface soil 0-15 cm, the alkyl carbon and alkoxy carbon showed an increasing trend from MC to SC. The aromatic carbon and phenolic carbon decreased from MC to SC. In the deep layer of 75-100 cm soil, however, soil organic carbon composition showed no significant difference among the three communities. (3) In the surface 0-15 cm soil, alkyl carbon/alkoxy carbon showed the following pattern: SC > MC > TC; SC has the least aromaticity; hydrophobic carbon/hydrophilic carbon showed no significant difference; aliphatic carbon/aromatic carbon showed larger values in SC than in MC and TC. At the depth of 75-100 cm, there were no significant differences for all the ratios. In summary, the carbon storage of MC was higher than that of SC. The decomposition rate of soil organic carbon of SC in surface soil layer was higher than that of MC, indicating more complex organic carbon in MC. The deep layer carbon pool was more stable and less affected by vegetation type. The results indicated that S. alterniflora would reduce soil carbon storage after invading mangroves, as well as changing the composition of soil organic carbon functional groups. The molecular structure of soil organic carbon in SC was simpler than MC, and the degree of decomposition was greater in SC than MC.

Aims Stipa tianschanicavar. gobica steppe is mainly distributed on the rocky slopes or rocky hills of desert steppe region, and can also be found in rocky hills or mountains of the typical steppe area eastwardly and some rocky slopes of the desert region westwardly. The main vegetation types of S. tianschanicavar. gobica steppe in China were investigated in this paper, and based on the 115 plot samples, the characteristics of the main desert steppe plant communities from the main vegetation types were quantitatively described. And the results showed that: according to the quadrat data, 272 seed plants belonging to 38 families and 127 genera (including the subspecies, varieties and forms) were recorded in the S. tianschanicavar. gobica steppe of China, among which there were 3 gymnosperm species belonging to 1 families and 1 genera, and 269 angiosperm species belonging to 37 families and 126 genera. The families having more than 10 species were Compositae, Poaceae, Leguminosae, Rosaceae, Liliaceae, Chenopodiaceae and Caryophyllaceae respectively. Hemicryptophyte, with a total of 178 species is the dominant life form in S. tianschanicavar. gobica steppe, which accounted for 65.44% of the total species. As for the ecological type of water, xerophytes was the dominant plants, with a total of 120 species, accounting for 44.12% of all species. East Palaeo-North element areal-type (including 82 species) and Middle Asia element (included the variants) areal-type (including 80 species) were the major floristic elements, containing 30.14% and 29.41% of the total species. The coverage of 0.1%-1% was the dominant level in the cover class distribution of the species, including 63.97% of the total species. The constancy degree of I (0-20%) was the dominant level in the constancy degree distribution of the species in S. tianschanicavar. gobica steppe, containing 94.85% of all the species. In accordance with the classification principle of community-appearance, Form. S. tianschanicavar. gobica was divided into 8 S. tianschanicavar. gobica steppe association groups, and 106 associations were divided from these 8 association groups based on community survey data.