Nuclear cGAS suppresses DNA repair and promotes tumorigenesis.

Accurate repair of DNA double-stranded breaks by homologous recombination preserves genome integrity and inhibits tumorigenesis. Cyclic GMP-AMP synthase (cGAS) is a cytosolic DNA sensor that activates innate immunity by initiating the STING-IRF3-type I IFN signalling cascade1,2. Recognition of ruptured micronuclei by cGAS links genome instability to the innate immune response3,4, but the potential involvement of cGAS in DNA repair remains unknown. Here we demonstrate that cGAS inhibits homologous recombination in mouse and human models. DNA damage induces nuclear translocation of cGAS in a manner that is dependent on importin-α, and the phosphorylation of cGAS at tyrosine 215-mediated by B-lymphoid tyrosine kinase-facilitates the cytosolic retention of cGAS. In the nucleus, cGAS is recruited to double-stranded breaks and interacts with PARP1 via poly(ADP-ribose). The cGAS-PARP1 interaction impedes the formation of the PARP1-Timeless complex, and thereby suppresses homologous recombination. We show that knockdown of cGAS suppresses DNA damage and inhibits tumour growth both in vitro and in vivo. We conclude that nuclear cGAS suppresses homologous-recombination-mediated repair and promotes tumour growth, and that cGAS therefore represents a potential target for cancer prevention and therapy.

Resting-state functional network connectivity underlying conscientiousness in school-aged children.

Conscientiousness is a personality trait that matures from early childhood to late adolescence, yet little is known about its underlying brain mechanisms during this period. To investigate this, our study examined the resting-state functional network connectivity (rsFNC) of 69 school-aged children (mean age = 10.12 years, range = 9-12) using a whole-brain region-of-interest (ROI) based analysis, based on functional magnetic resonance imaging (fMRI). The results indicated a positive association between conscientiousness and the rsFNC between the fronto-parietal network (FPN) and two brain networks: the somatosensory motor-hand network (SMHN) and the auditory network (AN). However, conscientiousness was negatively associated with the rsFNC between FPN and two other networks: the salience network (SN); the default mode network (DMN). Moreover, our results suggest that the FPN may play a hub role in the neural performance of children's conscientiousness. Intrinsic brain networks, particularly those involved in higher-order cognitive functions, impact children's conscientiousness. Therefore, FPN plays an important role in the development of children's personality, providing insight into the neural mechanisms underlying children's personality.

Effects of field soil warming on the growth and physiology of Juglans mandshurica seedlings.

Global climate change will increase surface soil temperature, with consequences on plant seedling growth and population dynamics. In this study, we carried out a field experiment to investigate the effects of 2 ℃ soil warming on the growth and physiological characteristics of 1- and 2-year-old seedlings of a dominant tree species in broadleaved Korean pine forest, Juglans mandshurica. The results showed that soil warming significantly increased basal diameter, root length, total leaf area, leaf dry weight, root dry weight, total biomass, apparent photosynthetic electron transfer rate (ETR), PSⅡ actual photochemical efficiency (ΦPSⅡ), and apparent photosynthetic electrophotochemical quenching coefficient (qP) of 1-year-old seedlings by 18.3%, 66.7%, 94.4%, 105.9%, 95.8%, 37.8%, 89.5%, 100.0%, and 71.4%, respectively. Soil warming significantly increased basal diameter, total leaf area, leaf dry weight, total biomass, leaf superoxide dismutase activity, peroxidase activity, catalase activity and free proline content, ETR, ΦPSⅡ, and qP of 2-year-old seedlings by 12.5%, 180.5%, 97.3%, 42.5%, 23.9%, 20.4%, 14.9%, 20.7%, 66.7%, 283.3% and 284.6%, respectively. There was an interaction between seedling age and soil warming on the root-shoot ratio and the ΦPSⅡ and qP in chlorophyll fluorescence parameters, in that soil warming significantly reduced the root-shoot ratio of 2-year-old seedlings and that the increase of chlorophyll fluorescence parameters of 2-year-old seedlings (4.1-4.6 times) was much higher than that of 1-year-old seedlings (1.5-1.8 times). Soil warming of 2 ℃ was beneficial to the growth of 1- and 2-year-old J. mandshurica seedlings and increased their regeneration potential. In particular, 2-year-old J. mandshurica seedlings responded to soil warming by increasing leaf area, improving leaf photochemical efficiency, and enhancing protective enzyme activity to increase resistance.

Wnt/beta-catenin signaling in embryonic stem cell converted tumor cells.

BACKGROUND: Embryonic stem cells (ESCs) are pluripotent stem cells and can form tumors containing cells from all three germ layers. Similarities between pluripotent stem cells and malignant tumor cells have been identified. The purpose of this study was to obtain ESCs-converted tumor cell lines and to investigate the mechanism of malignancy in pluripotent stem cells. METHODS: Mouse ESCs were subcutaneously injected into nude mice to obtain tumors from which a tumor-like cell line (ECCs1) was established by culturing the cells in chemical-defined N2B27 medium supplied with two small molecular inhibitors CHIR99021 and PD0325901 (2i). The ECCs1 were then subcutaneously injected into nude mice again to obtain tumors from which another tumor-like cells line (ECCs2) was established in the same 2i medium. The malignant degree of ESCs, ECCs1 and ECCs2 was compared and the underlying mechanism involved in the malignancy development of ESCs was examined. RESULTS: The three ESCs, ECCs1 and ECCs2 cell lines were cultured in the same 2i condition and showed some likeness such as Oct4-expression and long-term expansion ability. However, the morphology and the tumor-formation ability of the cell lines were different. We identified that ECCs1 and ECCs2 gradually acquired malignancy. Moreover, Wnt signaling-related genes such as CD133 and ß-catenin expression were up-regulated and Frizzled related protein (FRP) was down-regulated during the tumor development of ESCs. CONCLUSIONS: The two tumor-like cell lines ECCs1 and ECCs2 stand for early malignant development stage of ESCs and the ECCs2 was more malignant than the ECCs1. Moreover, we identified that Wnt/ß-catenin signaling played an important role in the malignancy process of ESCs.

Application of fertilization in changing light adaptability and improving growth of Aralia elata (Miq.) Seem. seedlings under various light conditions in temperate forests.

Non-timber forest plants have always played a significant role in livelihood security by providing valuable non-timber forest products, especially in less-developed countries. Artificial cultivation is a key approach to sustainably develop non-timber forest plants, for which, in-forest planting is vital. Light conditions in forests severely affect in-forest planting, and the growth of many plants may be restricted due to inappropriate light conditions. Thus, to fully and effectively utilize forest spaces with various light environments, fertilization, as an important practice to supply nutrients for promoting plant growth, was selected to mitigate light constraints in forests. Aralia elata (a valuable non-timber forest plant species) was chosen as the subject to explore the effects of fertilization on photosynthetic and morphological adaptation to light and the growth of in-forest planted seedlings by simulating different light environments. The results showed that the effects of fertilization on light adaptability (i.e., photosynthesis and leaf traits) of A. elata seedlings were limited; that is, only the variations in light-saturated photosynthetic net rate (PNmax), specific leaf area (SLA), and chlorophyll (Chl) content of A. elata seedlings between different shade intensities were noticeably affected by fertilization. Fertilization was positive for growth, and a half fertilization treatment (50 g per plot) was optimum for improving the growth of A. elata seedlings under light conditions of 0-75% shade intensities. These results can provide some practical references for the application of fertilization in in-forest planting and management of transplanted non-timber forest plant seedlings under various light conditions in the forests.

Different responses of growth and physiology to warming and reduced precipitation of two co-existing seedlings in a temperate secondary forest.

Warming and precipitation reduction have been concurrent throughout this century in most temperate regions (e.g., Northeast China) and have increased drought risk to the growth, migration, or mortality of tree seedlings. Coexisting tree species with different functional traits in temperate forests may have inconsistent responses to both warming and decreased precipitation, which could result in a species distribution shift and change in community dynamics. Unfortunately, little is known about the growth and physiological responses of coexisting species to the changes in these two meteorological elements. We selected two coexisting species in a temperate secondary forest of Northeast China: Quercus mongolica Fischer ex Ledebour (drought-tolerant species) and Fraxinus mandschurica Rupr. (drought-intolerant species), and performed an experiment under strictly controlled conditions simulating the predicted warming (+2°C, +4°C) and precipitation reduction (-30%) compared with current conditions and analyzed the growth and physiology of seedlings. The results showed that compared with the control, warming (including +2°C and +4°C) increased the specific area weight and total biomass of F. mandschurica seedlings. These were caused by the increases in foliar N content, the activity of the PSII reaction center, and chlorophyll content. A 2°C increase in temperature and reduced precipitation enhanced root biomass of Q. mongolica, resulting from root length increase. To absorb water in drier soil, seedlings of both species had more negative water potential under the interaction between +4°C and precipitation reduction. Our results demonstrate that drought-tolerant species such as Q. mongolica will adapt to the future drier conditions with the co-occurrence of warming and precipitation reduction, while drought-intolerant species will accommodate warmer environments.

The powerful brain: Neural correlates of sense of power and hope.

A sense of power refers to the perception that one can control and influence others' states by providing or withholding valued resources in an asymmetrical way, and which has been associated with greater hope. However, little is known about the neural bases underlying this association. The present study aimed to examine these phenomena in 261 healthy adolescent students by assessing resting-state brain activity (i.e., the amplitude of low-frequency fluctuations, ALFF) and connectivity (i.e., resting-state functional connectivity, RSFC). Whole-brain correlation analyses revealed that higher levels of perceived power were linked with reduced ALFF in the left thalamus and increased RSFC between the left thalamus and left superior temporal gyrus. Mediation analyses further showed that perceived power mediated the influence of the left thalamus activity on hope. Our results remained significant even after controlling for the head motion, age, and gender. Our findings contribute to the neurobiological basis of a sense of power and the neural mechanism underlying the relationship between a sense of power and hope.

Stronger functional network connectivity and social support buffer against negative affect during the COVID-19 outbreak and after the pandemic peak.

Health and financial uncertainties, as well as enforced social distancing, during the COVID-19 pandemic have adversely affected the mental health of people. These impacts are expected to continue even after the pandemic, particularly for those who lack support from family and friends. The salience network (SN), default mode network (DMN), and frontoparietal network (FPN) function in an interconnected manner to support information processing and emotional regulation processes in stressful contexts. In this study, we examined whether functional connectivity of the SN, DMN, and FPN, measured using resting-state functional magnetic resonance imaging before the pandemic, is a neurobiological marker of negative affect (NA) during the COVID-19 pandemic and after its peak in a large sample (N = 496, 360 females); the moderating role of social support in the brain-NA association was also investigated. We found that participants reported an increase in NA during the pandemic compared to before the pandemic, and the NA did not decrease, even after the peak period. People with higher connectivity within the SN and between the SN and the other two networks reported less NA during and after the COVID-19 outbreak peak, and the buffer effect was stronger if their social support was greater. These findings suggest that the functional networks that are responsible for affective processing and executive functioning, as well as the social support from family and friends, play an important role in protecting against NA under stressful and uncontrollable situations.

[Temporal effects of thinning on the composition and growth of regenerated woody plants in Larix kaempferi plantations]. / 间伐对日本落叶松人工林林下更新木本植物组成和生长影响的时间效应.

Understanding the temporal effects of thinning on the composition and growth of regene-rated broadleaved woody species in coniferous plantations can provide profound references for promoting the conversion of monoculture plantations into mixed conifer-broadleaved forests, which could solve the problem that the production and ecological functions of monoculture plantations cannot be balanced. We compared the composition of regenerated woody plant species in Larix kaempferi plantation with short-term (1-3 years), medium-term (4-9 years) and long-term (>9 years) after thinning. Furthermore, we selected three regenerated tree species with higher importance value and reciprocal symbiosis with L. kaempferi, which differed in shade tolerance, including shade-intolerant species Quercus mongolica, intermediate shade-tolerant species Acer mono, and shade-tolerant species Tilia mandschurica. We analyzed the relationships between light conditions (i.e., canopy density) and the growth (i.e., base diameter and height) of those species in L. kaempferi plantation with different terms after thinning. The results showed that 46 species of regene-rated broadleaved woody plants were recorded in thinned plantations. The common and dominant tree in different terms after thinning was A. mono, and the shrub species were Lonicera japonica and Euonymus alatus. With the increasing time after thinning, species richness of regenerated trees decreased, but the ratio of tree to shrub species increased and the intermediate shade-tolerant tree species took the dominant position. The temporal effect of thinning on the growth of three tree species was affected by shade tolerance ability. Basal diameter and height of T. mandschurica were higher than those of Q. mongolica and A. mono. With the increases of time after thinning, basal diameter of T. mandschurica and height of A. mono were more sensitive to light, indicating that there were respectively "a shade tolerance strategy" and "a shade avoidance strategy" to adapt to the post-thinning environment. The effects of thinning on the composition and growth of regenerated broadleaved woody species in L. kaempferi plantations were significantly time-sensitive. When deve-loping thinning measures to promote the regeneration of broadleaved trees in plantations, we should consider to extend the thinning interval appropriately to ensure the growth of broadleaved tree seedlings (e.g., T. mandschurica and A. mono) and accelerate their migration into the canopy layer. This would promote the formation of mixed conifer-broadleaved forests and eventually realize the sustainable development of plantations.

[Functions and applications of Multi-Tower Platform of Qingyuan Forest Ecosystem Research Station of Chinese Academy of Sciences]. / ä¸­å›½ç§‘å­¦é™¢æ¸ åŽŸæ£®æž—ç”Ÿæ€ç³»ç»Ÿè§‚æµ‹ç ”ç©¶ç«™å¡”ç¾¤å¹³å°çš„åŠŸèƒ½å’Œåº”ç”¨.

The relationship between the structure and function of forest ecosystems is the main intere-sts in the research area of forest ecology and management. However, over complex terrains in particular, these studies had been challenged as uneasy tasks due to the limitations in the forest survey and measurement techniques and other supporting technologies. Chinese Academy of Sciences (CAS) funded "Multi-Tower LiDAR/ECFlux Platform for Monitoring the Structure and Function of Secondary Forest Ecosystems" (Multi-Tower Platform, MTP) as a field station network corner-stone research infrastructure project, which was completed by Qingyuan Forest CERN (Chinese Ecosystem Research Network). In a distinctively-bounded and monitored-outlet watershed, the MTP was integrated by light detection and ranging (LiDAR) scanners, eddy covariance (EC) flux instrument systems, whole- and sub-watershed hydrology station network, long-term forest plot arrays, and live data center. Using LiDAR scanning, the MTP can get cloud data for holographic information on canopy structure. The EC-flux instrument system and hydrology station network along with forest plot arrays could ensure the reliability of water and carbon observations over this complex terrain, which allows to verify the studies on flux measurement technologies and methods, as well as to understand the processes of ecohydrology and CO2 exchange between forest ecosystem and the atmosphere. Further, we can also assess the primary ecosystem services, including water conservation and carbon sequestration. All the data from "tower-station" were streamed through wireless network, which would facilitate data monitoring, management, and sharing. There are three tasks of MTP team: 1) defining innovative methods and descriptors to quantify three-dimensional forest structure; 2) developing theories and techniques to measure CO2/H2O fluxes and other trace gases over complex terrains; 3) understanding the relationship between structure and function of forest ecosystems, providing information and rationales for forest management practices to assure broad and sustainable benefits from forests.

Crystal structure of Rv1220c, a SAM-dependent O-methyltransferase from Mycobacterium tuberculosis.

Rv1220c from Mycobacterium tuberculosis is annotated as an O-methyltransferase (MtbOMT). Currently, no structural information is available for this protein. Here, the crystal structure of MtbOMT refined to 2.0 Šresolution is described. The structure reveals the presence of a methyltransferase fold and shows clear electron density for one molecule of S-adenosylmethionine (SAM), which was apparently bound by the protein during its production in Escherichia coli. Although the overall structure of MtbOMT resembles the structures of O-methyltransferases from Cornybacterium glutamicum, Coxiella burnetti and Alfa alfa, differences are observed in the residues that make up the active site. Notably, substitution of Asp by His164 seems to abrogate metal binding by MtbOMT. A putative catalytic His-Asp pair located in the vicinity of SAM is absolutely conserved in MtbOMT homologues from all species of Mycobacterium, suggesting a conserved function for this protein.

Structural Insight into the Activation of PknI Kinase from M. tuberculosis via Dimerization of the Extracellular Sensor Domain.

Protein kinases play central roles in the survival of Mycobacterium tuberculosis within host. Here we report the individual high-resolution crystal structures of the sensor domain (in both monomer and dimer forms) and the kinase domain of PknI, a transmembrane protein member of the serine/threonine protein kinases (STPKs) family. PknI is the first STPK identified whose sensor domain exists in a monomer-dimer equilibrium. Inspection of the two structures of the sensor domain (PknI_SD) revealed conformational changes upon dimerization, with an arm region of critical importance for dimer formation identified. Rapamycin-induced dimerization of unphosphorylated fusions of PknI juxtamembrane and the kinase domain, intended to mimic the dimerization effect presumably imposed by PknI_SD, was observed to be able to activate auto-phosphorylation activity of the kinase domain. In vivo experiments using an M. bovis model suggested PknI functions as a dimer in the regulation of M. tuberculosis growth.

[Forest resources in Qungyuan County of Liaoning, Northeast China: the structure and optimal spatial allocation].

By using RS/GIS techniques and the method of multiple objective grey situation decision, and in considering the forest economic benefits (biomass and stand productivity) and ecological benefits (water and soil conservation) , an optimal spatial allocation of the present forest types in Qingyuan County of Liaoning, Northeast China was approached in this study. After the optimization of spatial allocation, the structural proportions of different forest types in Qingyuan County changed obviously, with the area of coniferous forests reduced from 43% to 23% , the area of broadleaved forests reduced from 51% to 31% , the area of mixed coniferous-broadleaf forests increased from 3% to 43% , and the area of shrubs remained unchanged. As compared with the results before optimization, the biomass, stand productivity, and water conservation function of the forest ecosystem in Qingyuan County after optimization increased by 0.6%, 2.1% , and 31.7%, respectively, and the soil conservation function remained unchanged. It could be concluded that after the optimization of spatial allocation, the forest ecosystem of Qingyuan County could maintain its soil conservation function, and, at the time of keeping higher timber production, fully exert waler conservation function, realizing the maximization of the economic and ecological benefits of the forest ecosystem.

[Effects of light quality on the seed germination of main tree species in a secondary forest ecosystem of Northeast China].

This paper explored the effects of light quality on the seed germination of five dominant tree species (Larix kaempferi, Phellodendron amurense, Acer mono, Fraxinus mandshurica, and Pinus koraiensis) in a secondary forest ecosystem of Northeast China, based on the experiments with the seeds of the five tree species in laboratory and those of the P. koraiensis and L. kaempferi in the field. Four treatments of different light quality were designed in laboratory (taking dark as the control), and three treatments of R/FR (the ratio of red light and far red light intensity) were installed in the field. The laboratory experiment showed that light quality had less effect on the seed germination of L. kaempferi, but the seed germination rates of the other four tree species were significantly different under the treatments of different light quality. P. amurense had the highest seed germination rate under white light, whereas A. mono, F. mandshurica, and P. koraiensis had the highest one under the alternative irradiation with red light and far red light (R-FR-R). In consistence with the results in laboratory, the seed germination rate of P. koraiensis in the field decreased with decreasing R/FR ratio, while that of L. kaempferi was less affected. Under natural condition, the R-FR-R fluctuated with the activity of sun-fleck, and the seed germination patterns of A. mono, F. mandshurica, and P. koraiensis could be the adaptation to the sun-fleck environment in forest stand. The germination of large seeds was significantly affected by light quality.

Seed regeneration potential of canopy gaps at early formation stage in temperate secondary forests, Northeast China.

Promoting the seed regeneration potential of secondary forests undergoing gap disturbances is an important approach for achieving forest restoration and sustainable management. Seedling recruitment from seed banks strongly determines the seed regeneration potential, but the process is poorly understood in the gaps of secondary forests. The objectives of the present study were to evaluate the effects of gap size, seed availability, and environmental conditions on the seed regeneration potential in temperate secondary forests. It was found that gap formation could favor the invasion of more varieties of species in seed banks, but it also could speed up the turnover rate of seed banks leading to lower seed densities. Seeds of the dominant species, Fraxinus rhynchophylla, were transient in soil and there was a minor and discontinuous contribution of the seed bank to its seedling emergence. For Quercus mongolica, emerging seedling number was positively correlated with seed density in gaps (R = 0.32, P<0.01), especially in medium and small gaps (<500 m(2)). Furthermore, under canopies, there was a positive correlation between seedling number and seed density of Acer mono (R = 0.43, P<0.01). Gap formation could promote seedling emergence of two gap-dependent species (i.e., Q. mongolica and A. mono), but the contribution of seed banks to seedlings was below 10% after gap creation. Soil moisture and temperature were the restrictive factors controlling the seedling emergence from seeds in gaps and under canopies, respectively. Thus, the regeneration potential from seed banks is limited after gap formation.

Regeneration of a coastal pine (Pinus thunbergii Parl.) forest 11 years after thinning, Niigata, Japan.

To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1-3 years with densities of 9.9 and 5.1 seedlings m(-2) in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m(-2) in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha(-1) at ages 40-50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.

[Physical and chemical properties of throughfall in main forest types of secondary forest ecosystem in montane regions of eastern Liaoning Province, China].

From July to September 2008, a measurement was made on the physical and chemical properties of bulk precipitation and throughfall in five main forest types, i.e., larch plantation (LP), Fraxinus rhynchophylla stand (FR), mixed forest stand (MF), Korean pine plantation (KP), and Mongolian oak stand (MO), of secondary forest ecosystem in montane regions of eastern Liaoning Province, China. Comparing with bulk precipitation, the throughfall in the five forest types was significantly acidified (P < 0.05), and the acidification degree was in the order of KP > LP > MF > MO > FR. The conductivity and total dissolved solids of the throughfall increased significantly (P < 0.05), and were in the sequence of MO > FR > LP > MF > KP. The dissolved oxygen concentration of the throughfall lowered significantly (P < 0.05), with the rank of KP > MF > FR > MO > LP, while the Cl- concentration increased significantly, ranked as LP > MO > MF > FR > KP. The NO3-concentrations of the throughfall in FR, MO and MF were higher, while those in LP and KP were lower than that of the bulk precipitation.

[Comparison of light characteristics in different size gaps in eastern Liaoning montane secondary forests].

With three different size gaps (G1, 670 m2; G2, 290 m2; and G3, 90 m2) in eastern Liaoning montane secondary forests of China as test objects, and through a continuous measurement of light intensity, the spatiotemporal distribution of photosynthetic photon flux density (PPFD) in the gaps was compared. The results showed that the diurnal variation of PPFD in the gaps was greater at northern than at southern position. The larger the forest gap, the broader the higher PPFD value area, and the more obvious the heterogeneity. As for the monthly variation of PPFD, the maximum PPFD at each position of the gaps appeared at the beginning of growth season (i.e., in April and May), while the minimum PPFD occurred in different months. The maximum PPFD at the eastern and western positions of each gap was basically appeared in the same months, and the PPFD was significantly higher in spring than in summer and autumn (P < 0.05). The mean monthly PPFD at the centers of G1, G2, and G3 was 66.59%, 49.05%, and 30.37% of full sunlight, respectively, and in growth season, the PPFD at gap center was 37.8, 27.9 and 10.3 times higher than that at understory. It was suggested that owing to the different size and shape of forest gap and the effects of landform, the light intensity and its distribution in forest gap were different, being the key factors leading to the heterogeneity of regeneration pattern and the variation of species composition in forest gap.

The role of reproductive phenology, seedling emergence and establishment of perennial Salix gordejevii in active sand dune fields.

BACKGROUND AND AIMS: The function of sexual reproduction of perennials in restoration of vegetation of active dune fields frequently has been underestimated. The objective of this study was to evaluate the role of sexual reproduction of the perennial Salix gordejevii in the revegetation of active dunes. METHODS: Seedling emergence and establishment of S. gordejevii were examined both in controlled experiments (germination at different burial depths with different watering regimes) and in field observations in three dune slacks. The reproductive phenology and soil seed bank of S. gordejevii, the dynamics of soil moisture, the groundwater table and the landform level of three dune slacks were monitored. KEY RESULTS: Seeds of S. gordejevii began maturation on 1 May, and seed dispersal lasted from 8 May to 20 May. Seeds on the soil surface germinated significantly faster than those buried in soil (P<0.05). Seedling emergence was negatively correlated with landform level. When most seedlings emerged, there was a significantly positive correlation between soil moisture and seedling emergence (P<0.01). Rainfall was negatively correlated with seedling emergence. Seedling establishment was significantly and positively correlated with seedling emergence (P<0.05), and 72.3 % of the emergent seedlings were established at the end of the growing season. These results indicated that (a) seeds matured and dispersed before the rainy season; (b) seeds germinated as soon as they contacted a moist surface and relied more on soil moisture than on rainfall; and (c) more seedlings emerged at lower sampling points in dune slacks. CONCLUSIONS: In natural conditions, restoration of active sand dune fields generally commences with revegetation of dune slacks where sexual reproduction of perennials contributes greatly to species encroachment and colonization and hence plays an important role in restoration of active dune fields. Furthermore, aeolian erosion in dune slacks, leading to good soil moisture, facilitates seed germination, seedling emergence and establishment of S. gordejevii.

[Effects of burial on seed germination characteristics of 65 plant species on Horqin semi-arid steppe].

The study on the germination characteristics of newly collected and one year-buried seeds of 65 plant species on Horqin semi-arid steppe showed that after one year's burial, the seeds of 38 plant species still remained their vitality. For the species whose freshly collected seeds had a germination rate higher than 80%, the seed germination rate after burial was decreased, while it was in adverse for those whose freshly collected seeds had a germination rate less than 80%. The effects of burial on seed germination varied with the ecological types of the species (i.e., weed, steppe species, meadow species, and psammophytes). After one year's burial, the germination rate of perennials had no significant increase, but that of annuals increased significantly (P < 0.05). The species with a < 10% difference of germination rate between their freshly collected and one year-buried seeds could be classified into three categories, according to the seed germination pattern, i.e., germination was promoted by burial (e.g. Artemisia halodendron), restrained by burial (e.g. A. sieversiana); and unchanged after burial (e.g. Lappula myosotis).