Global nitrogen (N) deposition has been consistently enhanced and significantly influenced the carbon (C) cycle of forest ecosystem. However, studies on the quantitive response of C sequestration to N deposition in China’s boreal forest ecosystem still remains insufficient. Tree growth is one of important components of C sequestration in forest ecosystem. In order to accurately evaluate the influence of N deposition on C sequestration in China’s boreal forest ecosystem, This study was designed to investigate how N deposition influenced the tree diameter at breast height (DBH) growth of a Larix gmelinii primitive forest.

We carried out a N enrichment experiment in an L. gmelinii primitive forest in Greater Khingan Mountains with four N addition levels (control (0), low N (20 kg N·hm^-2·a^-1), medium N (50 kg N·hm^-2·a^-1) and high N (100 kg N·hm^-2·a^-1)). DBH was measured from 2012-2014 within all treatments.

Medium N and high N additions significantly influenced the relative DBH growth of L. gmelinii, and the influence became more pronounced through time. N deposition significantly affected the DBH growth among different tree height classes: low height class (tree height <16.5 m) did not show significant response to N deposition, while high height class (tree height >16.5 m) showed significantly accelerated growth under medium and high N additions (the relevant DBH growth rate >79.5%), and this acceleration effect decreased as the tree height increased. This study indicated that N addition did enhance the DBH growth of L. gmelinii, but this enhancement mainly affected taller L. gmelinii trees.

Temperature is usually hypothesized to be the primary climate factor limiting tree growth at high elevation. We test this hypothesis by investigating the tree growth and climate factors at treeline ecotone on the southeastern Xizang Plateau.

Tree-ring samples of Picea likiangensis var. balfouriana were collected at treeline ecotone in Kese Village, Bangda Town, Basu County, Xizang. These samples were polished, measured, crossdated, and detrended to produce sequences of tree-ring width indices for each individual sample. Pearson correlation coefficients were calculated among each pair of the individual samples. Correlation between tree-ring sequences and climatic factors (air temperature and precipitation) were also calculated to examine tree-ring responses to air temperature, precipitation.

At the treeline ecotone of P. likiangensis var. balfouriana, air temperature had little effect on tree-ring growth. Precipitation in growing season had a strong effect on tree growth with large variation among individual trees. Our results suggest that temperature sensitivity of tree growth might be over-estimated at treeline ecotone on the southeastern Xizang Plateau.

Exploring variation patterns of C, N, P contents and their ratios of plant vegetative organs along environmental gradient can provide insight on the resource allocation strategy of plants. In order to search the environmental heterogeneity and mechanism of stoichiometry properties of plant vegetative organs (including root, stem and leaf), we investigated the influences of different soil nutrients conditions on the element allocation among plant vegetative organs in the dominant shrub communities along a hydro-thermic gradient across Loess Plateau.

The species compositions and structures of 123 small quadrats (5 m × 5 m) of dominant shrub communities in 41 sites were investigated by standard community sampling method along the declined hydro-thermic conditions from southern Gansu Province to northern Ningxia Hui Autonomous Region and western Gansu. The data about height, coverage and number of the dominant shrub were recorded. At least 369 biological samples of plant vegetative organs (root, stem and leave) of dominant shrubs were collected and their fresh and dry mass were measured, respectively. About 123 soil samples were taken by earth boring auger and ring knife. C, N and P contents of all biological and soil samples were measured after lapping and sieving.

1) Organic matter content (mean concentration of leaf C ((424.11 ± 42.21) mg·g^-1) in Gansu and Ningxia Hui Autonomous Region was relatively low, and nitrogen (mean concentration of leaf N ((23.00 ± 8.09) mg·g^-1) was higher while phosphorous (mean concentration of leaf P ((1.18 ± 0.50) mg·g^-1) was relatively deficient. 2) Along the increasing growing season temperature and declining annual precipitation from southern Gansu to northern Ningxia Hui Autonomous Region and western Gansu, soil nutrients content decreased, and the storage of C, N and P in root, stem and leaf decreased. The shift trends of C:N agreed with the N storage’s shift trends in root and stem while N:P in all organs were contrary to the P storage’s shift trends. Meanwhile, the allocation patterns of C, N and P among vegetative organs among the three regions dominated by shrub communities were much different. 3) In the region with high soil nutrients, the nutrient storage in vegetable organs were similar among different species in the same dominant shrub regions, but in the regions with low soil nutrients, the nutrient storage in vegetable organs displayed high variations. The variations of nutrient storage of vegetable organs for the same shrub communities from different regions were not significant.

Exudation measurements focus exclusively on total exudate carbon (C) fluxes without considering how root-derived nitrogen (N) inputs and variable exudate stoichiometries may influence microbial activity and biogeochemical cycles. As a result, the biogeochemical consequences of exudate stoichiometry for soil C-nutrient couplings and feedbacks to environmental changes remain largely unknown. Our objective is to explore to what extent N availability modifies soil microbial processes and the dynamics of soil carbon pool induced by labile C.

We conducted a 50-day laboratory incubation experiment by addition of simulated exudates varying in C:N to two coniferous forest soils: a natural forest and Picea asperata plantation. The five exudate addition treatments are C alone, N alone, and combinations of C and three N levels (C:N ratio of 10, 50 and 100).

The addition of labile C exudates decreased soil total C for both natural forest and the plantation by stimulating soil organic matter (SOM) mineralization (i.e. greater priming effect), while the addition of N decreased total C. The decreased soil total C induced by exogenous labile C addition was greater in the plantation than that in the natural forest. The influence of exudate additions produced no significant influence on labile and recalcitrant carbon pools at either soil. The addition of labile C exudate decreased the total phospholipid fatty acid (PLFA), actinomycetic, bacterial and fungal PLFA for the natural forest, but increased them in the plantation. Moreover, the microbial community composition (i.e. the value of bacterial PLFA:fungi PLFA) varied greatly among the treatments. These results indicate that both root-derived N inputs and soil N availability co-regulate the direction and magnitude of priming effects on SOM decomposition by controlling the activity and the relative abundance of bacterial and fungal. Our results provide additional evidences toward a robust theoretical foundation for better understanding the ecological consequences of exudate stoichiometry on soil C cycling in forests.

Our objective was to explore the distribution patterns of 20 noxious invasive plants in Hainan Island notified by the National Ministry of Agriculture, and their influences on native plants. We also focused on investigating the traits of six most widely spread invasive plants and plant distributions in seven types of terrestrial ecosystems. Three hypotheses were deployed in this study: (1) the ecological effects of plant invasion were related to the characteristics of invaded ecosystems and successional phases of invaded communities; (2) the invasive plants rather affected certain functional groups than the whole communities; (3) and most invasive plant species tended to colonize frequently disturbed ecosystems, while they were usually excluded by intact forest ecosystems.

The plot survey was conducted to investigate the distributions of the 20 target invasive plants. The appearance frequency of the six most widely spread invasive plants (i.e., Chromolaena odorata, Praxelis clematidea, Mimosa pudica, Wedelia trilobata, Conyza sumatrensis, and Lantana camara) was compared among seven terrestrial ecosystems (i.e., secondary forest, farmland, grassland, abandoned land, plantation, village, and forest edge) to evaluate the invasibility of different ecosystems. The plots invaded by target species were classified, and species richness of native species in these invaded plots was compared using one-way ANOVAS. Relationships between the total coverage of invasive plants and the species richness of native plants were assessed using a linear regression model.

(1) A total of 11 noxious invasive plants were found in Hainan Island, accounting for 55% of the target specie. (2) The target invasive species were mostly distributed in the northeastern and southwestern regions of Hainan Island, less in the southeastern region, and least in the central region. (3) An order of the intensity regarding plant invasiveness was expressed as Praxelis clematidea > Chromolaena odorata > Mimosa pudica > Wedelia trilobata > Lantana camara > Conyza sumatrensis. The appearance frequency of Conyza sumatrensis and Lantana camara showed no significant differences among the surveyed ecosystems, while Praxelis clematidea, Mimosa pudica and Wedelia trilobata had obviously higher appearance frequency in plantations and abandoned lands, in farmlands, and in plantations, respectively. (4) Farmlands, plantations and abandoned lands were the most frequently invaded ecosystems; but forest edges and natural secondary forests appeared to be less vulnerable to plant invasion. (5) The appearance frequency of invasive plants was negatively correlated with plant coverage of the community invaded by the target species. The total coverage of invasive plants and the richness of native plant species showed a positive correlation in grasslands when the coverage was within a certain extent, and a negative correlation both in forest edges and abandoned lands, and no obvious correlation in plantations farmlands and village sites.

Our objective was to analyze the effect of water levels and light intensities on capsule production dynamics of Sphagnum to lay the foundation for further research on its reproductive phenology.

Our selected Sphagnum capillifolium in this study. We set up a simulation experiment within a growth chamber and grew moss communities in polystyrene containers. Water levels and light intensities were altered to create different environmental conditions. Gametophores and capsule production were observed and recorded.

Seta length, shoot height and capsule cracking rate increased when water level increased. Under high light intensities, capsule diameter and capsule cracking rate were higher. Water level and light intensity had an interactive effect on shoot height increment and capsule diameter. Water level and light intensity had no effect on capsule production rate. Increase in both water level and light intensity led to earlier spore release. Reproductive phenology advance can reduce the abortive risk of spores by avoiding detrimental environment conditions such as drought. After capsules dehisced, reproductive shoots were able to accelerate height growth to avoid shading to lay a foundation for further reproduction in the future.

Tribulus terrester is an annual plant commonly found in the suburb of Ürümqi, Xinjiang, China. One fruit of this species is composed of five synaptospermies. This study aims to explore the morphological traits and intermittent germination characteristics of synaptospermy and further investigate the adaptability of its seeds under changing enviroment.

Shape, color and appendage of synaptospermy, and the mass, length of burs, percentage of appendage mass, number of seeds per synaptospermy, were determined; and the vigor, water absorption and germination characteristics of synaptospermies matured at different month were compared in the laboratory.

The synaptospermies became hardened after ripening, with scale-form appendages, and they are significantly different in mass, the percentage of mass of appendage, amount of seeds, vigor, water absorption rate, germination percentage and germination rate. The averages of vigor and germination percentage were increasing and the water absorption rate was decreasing following the order of maturing month in July, August and September. The average of vigor was positively correlated with the ripening time of fruit, as well as germination percentage, while the water absorption rate was negatively correlated with the ripening time of fruit. This suggests that the earlier the fruit ripening, the lower the vigor and germination rate and the higher the water absorption rate. Under the best germination conditions, all synaptospermies matured in September could germinate, whereas only some synaptospermies could germinate if matured in the other two months. Moreover, only those seeds located in the position of the long thorn of one synaptospermy could germinate. Part of the seeds could germinate in the season of ripening; the others retain in the dispersal unit and germinate after several weeks, months or years. This germination behavior was defined as intermittent germination. These results indicate that there is a change of gradient in morphology, vigor and water absorption among fruit ripening in different months and among different synaptospermy of the same fruit. We conclude the variation is a main factor responsible for intermittent germination, which can reduce competition among siblings; based on these strategies, Tribulus terrester can spread the risk of survival and ensure its breeding success.

Syntrichia caninervis, a typical drought-tolerant moss species found worldwide in various semiarid and arid regions, is the dominant species of soil crust mosses in the Gurbantünggüt Desert, which is a temperate northern desert of Central Asia. It appears able to endure frequent and intensive freeze-thaw cycles in the surface soil and maintain physiological functions active even under extreme low temperatures in winter. However, there have been few studies exploring the adaptive strategies of the species during freeze-thaw processes and interpreting well the phenomena. One of the major goals of this study was to investigate physiological regulatory mechanisms of the species when undergoing freezing-thawing periods and relevant antioxidant enzyme activities.

A series of microclimate and soil conditions were continuously monitored in the sampling sites starting from November 2013. The samples of the moss were collected during the early spring of 2014 from February to April and from three microhabitats including the sites under live shrub, under dead shrub and on an open ground. The moss samples were quickly treated in the field for keeping freshness and then brought to laboratory for measurement and analysis. The traits/characteristics that reflect physiological and biochemical activities were measured for analyzing responses of the species to freeze-thaw processes and for comparing the impacts of different habitats, which included water content, concentrations of proline, soluble sugar, soluble protein and malondialdehyde (MDA), as well as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) activities.

The results showed that, during different freeze-thaw periods, microhabitats and their interactions with alternative freeze-thaw processes significantly affect the contents of proline, soluble sugar, soluble protein and MDA in shoots of the species, as well as the enzyme activities of CAT, POD, and SOD. Extreme low temperature and drought caused significantly higher soluble sugar and MDA contents, higher CAT, POD and SOD activities, but lower soluble protein content, in snow covered period (February) and dry period (April) than the snow melting period (March). The existence of live shrub decreased temperature around the bushes during snow melting because of the effect of shade, causing increased contents of soluble sugar and MDA in moss shoots, when compared to those growing in the habitats under dead shrub and on open ground. However, live shrub could provide a moister environment for S. caninervis than dead shrub and exposed ground for the duration of desiccation. As the result, the proline content, soluble sugar content and MDA content of the species under the live shrub canopy were the lowest among the three habitats. Furthermore, the mosses lived on the exposed ground showed the highest antioxidant enzyme activities comparing to those under the dead shrub and living shrub. This may suggest that S. caninervis grown on exposed grounds has developed rather a specific adaptations for a harsher environment condition than that occurred in other two habitats.