Aims The objective was to investigate the respiration rate of snowpack soil in relation to temperature in the alpine tundra community of Sanguisorba sitchensis (= S. stipulata) in the Changbai Mountain, northeastern China.

Methods Soil respiration under different temperatures was measured with an LI-8100 automated CO₂ flux system in the laboratory, and annual respiration was estimated based on current and presumed temperature scenarios.

Important findings Soil temperature under snowpack most of the year was around or over 0 °C, and the variation was less than 20 °C. Estimated respiration rates within 10 cm depth were 307.1 g C·m^-2·a^-1 at 2 036 m elevation and 270.9 g C·m^-2·a^-1 at 2 260 m. Because the snow cover was present for a long period, the length of which increased with elevation, winter respiration accounted for 42.5% at 2 036 m and 49.7% at 2 260 m. Under the scenario that the snow period decreases if annual temperature rises 1 °C, annual respiration would increase by 8% or 0.25 g C·kg^-1·a^-1 (22.65 g C·m^-2·a^-1), but winter respiration would decrease by 0.118 g C·kg^-1·a^-1 (10.81 g C·m^-2·a^-1).

Aims Plant growth and substance allocation are greatly affected by temperature change, and the response modes have been shown to vary for different functional groups (graminoids and forbs). Our main objective was to assess how experimental warming affects growth in different functional groups and how they adapt to experimental warming by different substance allocation and structural adjustment.

Methods We selected three dominant plant species, graminoid Elymus nutans and forbs Rumex acetosa and Potentilla anserina, in an alpine meadow in Northwestern Sichuan, and adapted open-top chambers as passive warming devices to generate an artificially warmed environment. After three years of warming, we measured biomass accumulation and substance allocation of the three species.

Important findings Compared to the control, experimental warming significantly increased SLA (specific leaf area) and biomass accumulation of E. nutans and R. acetosa and significantly decreased SLA and biomass accumulation of P. anserine. Warming significantly increased leaf biomass of R. acetosa, but its root biomass significantly decreased; however, warming significantly decreased leaf biomass and stem biomass of P. anserine and its root biomass significantly increased. Warming significantly increased root C concentration of R. acetosa, but decreased root N concentration. Warming significantly increased the LMR (leaf mass ratio), RMR (root mass ratio) and R/S (shoot/root biomass ratio) of R. acetosa, but its SMR (stem mass ratio) significantly decreased. For P. anserina, warming significantly increased its RMR and R/S, but its SMR and LMR significantly decreased. Warming significantly increased C and N allocation in leaves of R. acetosa, and also significantly increased C allocation in its roots, but C and N allocations in its stem were significantly decreased. For P. anserina, warming significantly decreased C allocation in its leaves, but C and N allocations in its roots were significantly increased.

Aims Our objective is to test whether C and N releases in winter wheat (Triticum aestivum) litter change monotonically or unimodally with soil nutrients in its habitats.

Methods We conducted a growth experiment where winter wheat was subjected to 6-level nutrient regimes and a common garden decomposition experiment. We determined initial C:N ratios of live tissues, biomass loss of litters, C:N ratios of remaining litter, and the amounts of C and N releases. We analyzed correlations between initial C:N ratios and C/N release or between C:N ratios. All data were analyzed with SPSS 13.0 and R 2.9.1.

Important findings Litterfall, initial leaf/root C:N ratios, C:N ratios of remaining litter, and C and N releases changed monotonically along a soil nutrient gradient. Soil nutrients had significant effects on biomass loss of leaves, but not of roots. There were negative correlations between initial leaf/root C:N ratios and C and N releases. Initial leaf/root C:N ratios were strongly and positively correlated with C:N ratios of remaining litter. These findings suggest that (1) increased soil nutrients surrounding winter wheat plants enhance C and N return in litter, thereby being beneficial to its growth, (2) C:N ratios indicate the potential amounts of C and N releases, and (3) decomposition processes decrease C:N ratios in remaining litter.

Aims Tsuga chinensis var. tchekiangensis is a species with a small geographic distribution in the subtropical forests in eastern China. The species has been listed as Chinese national third protective plant. Our objective was to investigate the differences and correlations of metal element contents in plant and forest soil of T. chinensis var. tchekiangensis in different community types in Jiulongshan Nature Reserve, Zhejiang Province, China. Findings will provide a scientific basic for feasible in situ and ex situ conservation of the species.

Methods Forty representative plots (10 m × 10 m) were investigated along different ridges from low to high altitude. The community types of these plots were identified, and the groups of tree relationships were established based on TWINSPAN. Twelve metal elements of root, stem, bark and leaf of T. chinensis var. tchekiangensis samples and forest soil were measured by ICP-AES. Soil factors such as pH, water content, organism content and electrical conductivity were also measured. Differences of metal element contents were analyzed among different community types and organs. The correlation among different metal element contents of T. chinensis var. tchekiangensis and soil nutrient factors were analyzed and compared.

Important findings Based on the investigations and results of TWINSPAN classification, the plots were classified into five communities. Differences among metal element contents of plant and soil in different community types were determined. The contents of plant elements such as K, Ca, Fe, Mg, Ba and Cr were higher in community II and V, and most soil elements were highest in community II. The content of Ca, K, Mg, Fe and Mn were higher in plant, and Al and Fe were higher in soil. The content of metal elements among different organs was different, and their change tendencies and variation degrees were discordant. Enrichment coefficient and correlation analysis showed that the absorption of Mg and Zn, as well as Fe and Al by T. chinensis var. tchekiangensis was similar; however, most plant elements had no correlation with soil elements.

Aims Our objective was to collect tree-ring data of Sabina przewalskii and analyze the effects of elevation and aspect on tree growth.

Methods We collected tree ring samples from four sample sites that differed by elevation and slope aspect on a continuous mountain slope of Hebei Forest Farm in southern Tongde County, eastern Anymaqen Mountains, Qinghai Province. We analyzed relationships among the four tree ring-width chronologies using correlation and Principal Component Analysis (PCA) and made simple correlation function analysis between tree-ring width index and climate factors by Dendro2002 software.

Important findings Tree-ring chronological eigenvalues indicated the upper three sites had similar variation, but differed from the low-elevation chronology. Correlations among chronologies and results of PCA showed there was change along the altitude gradient. Correlations between tree-ring index and mean temperature in current June-August trended to increase, and the upper treeline was mainly determined by mean temperature of current July and August. There were significantly negative correlations between tree-ring index of the low sampling sites and temperature of prior November and current June and significant positive correlations between tree-ring index of the low sampling sites and precipitations of prior August and current May. Compared to the usual situation of tree-growth at lower elevation limits being constrained by precipitation results indicated an enhanced role of temperature and a reduced role of precipitation. Slope aspect played an important role in the growth of S. przewalskii along the elevation gradient.

Aims Our objective was to examine the effects of temperature, soil water content and photosynthesis on soil respiration in Populus and Ulmus pumila planting shelterbelts in China’s Junngar Basin.

Methods Soil respiration was measured during the growing seasons in 2005 and 2006 using an automated CO₂ efflux system (LI-8100). Air temperature (at 50 cm in height) and soil temperature (every 5 cm from 0 to 50 cm depth) were monitored at three points adjacent to the chamber using a digital thermometer (WMY-01C, Huachen Medical Instrument Inc., Shanghai, China) at each site. Gravimetric soil moisture at 0-5, 5-15, 15-30, and 30-50 cm depths at three points were measured using the oven-drying method at 105 °C for 48 h.

Important findings Soil respiration displayed irregular fluctuation of daytime pattern and significant single-peaked curve of seasonal pattern in the two woodlands. Seasonally, soil respiration was characterized by a maximum in July or August and a minimum in October or May, following the change of soil temperature. The rate of soil respiration was significantly higher in Populus woodland than that in U. pumila woodland with mean rates of 3.71 and 1.82 μmol CO₂·m^-2·s^-1in two growing seasons, respectively. Soil respiration was significantly correlated with temperature in exponential equation, but uncorrelated with soil water content in the two woodlands. Soil temperature at 50 and 30 cm depths could explain 78.5% and 64.4% of seasonal variations of soil respiration in Populus woodland and U. pumila woodland, respectively, which confirms the common explanation by temperature and soil water content. The difference in soil respiration between the woodlands was influenced by growth state of trees, photosynthesis and soil salinity. Our results suggested that there was significant seasonal variation of soil respiration in oasis shelterbelts in the arid region and soil temperature was the main regulating factor.

Aims Nocturnal sap flow is a driving force not only for chemical transport and nutrient movement within trees, but also for water recharge caused by diurnal transpiration loss. Therefore, it is both ecologically and physiologically significant for estimating tree and stand transpiration at larger spatial and longer temporal scales. Our objective was to analyze nocturnal sap flow (18:00-5:00 next morning) and its biophysical controls in four tree species (Cedrus deodara, Zelkova schneideriana, Euonymus bungeanus and Metasequoia glyptostroboides) in Laodong Park in Dalian, China.

Methods During June 1-August 31, 2008, we measured sap flow of twelve urban trees of four species and three diameter at breast height (DBH) classes of each species continuously by thermal dissipation probes, soil moisture by ECH2O soil moisture probe and microclimate data by an automatic weather station. SPSS 13.0 was used for statistical analysis of sap flow and environmental factors.

Important findings Nocturnal sap flow was measured in all sampled trees, but varied from 0.44% to 75.96% of total daily water consumption. Nocturnal flow was larger and more active on rainy days than that on sunny ones, to the extent that it equaled or exceeded the diurnal volume. Vapor pressure deficit and wind speed were significantly correlated with nocturnal water movement (R² > 0.6), which could provide an explanation for nocturnal transpiration. Nocturnal sap flow mainly contributed to nocturnal transpiration and water recharge. It peaked before midnight and dropped to nearly zero afterwards. Furthermore, nocturnal sap flow was remarkably correlated with diurnal sap flow (R² = 0.356, p = 0.00) and DBH (R²_Spearman > 0.80), substantiating the important role of specific structural and physiological characteristics. Nocturnal sap flow of individuals accounted for an average of < 14.4% of the total transpiration volume. Total water consumption of a forest ecosystem scaled up by daytime sap flux measurements can be underestimated without integration of nocturnal sap flux.

Aims The Chinese medicinal plant Rehmannia glutinosa has a significant continuous cropping obstacle effect. Our objective was to determine its physio-ecological properties under continuous cropping.

Methods We determined changes in the physio-ecological properties of R. glutinosa under continuous cropping, with the first cropping plants used as the control.

Important findings The continuous cropping obstacle effect on R. glutinosa occurred at the seedling stage. The plasamembrane lipid peroxidation of the plants led to impaired structure and function of plant cells in the 60 days after being planted under continuous cropping. Also, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and chlorophyll content (Chl) of the plants under continuous cropping were significantly lower than those of the control, but the reverse was true for limited stomatal value (L_s). P_n was significantly correlated with G_s and Chl (r = 0.977 and 0.814, respectively). Electron microscopy revealed that changes in mesophyll cell ultrastructure, including chloroplast structure, began at the mid-growth stage under continuous cropping. Therefore, it was suggested that the accumulation of reactive oxygen species (ROS) and free radicals in plant cells, caused by the stressful condition of continuous cropping, resulted in damaged membrane structure, which in turn led to decreased chlorophyll content, closed stomata and reduced photosynthetic capacity and consequently retarded growth of the plants at the seedling stage, i.e., the so-called continuous cropping obstacle effect.

Aims Our objective was to investigate the effects of different water stress levels on yield, N absorption, allocation and utilization in winter wheat cultivars ‘Shijiazhuang 8’ (drought resistant) and ‘Yanmai 20’ (drought sensitive) during different growth durations.

Methods We divided the growing stages of winter wheat into recovering-jointing, jointing-flowering and late filling. Soil water levels based on field capacity were 75%-80% (control, full water supply or well-watered), 65%-70% (light drought stress), 55%-60% (medium drought stress) and 40%-45% (severe drought stress) from winter wheat seeding to maturity and were controlled by irrigation and mobile rain shelters.

Important findings The drought resistant cultivar ‘Shijiazhuang 8’ had a higher grain yield than ‘Yanmai 20’ under drought stress, and medium drought stress in all the three durations can increase winter wheat yield. Drought stress in the jointing-flowering stage has the greatest effects on N assimilation and translocation in winter wheat, the second greatest being in the recovering-jointing stage, while that in late filling stage has few effects. Both medium and severe drought stress during different growth durations will lower the translocation of stored nitrogen before anthesis into grain, as well as N utilization rate and productivity; on the other hand, light drought stress in the recovering-jointing and late filling stages can improve the translocation of stored N into grain as well as N utilization rate and productivity. Under drought stress, N accumulation in grain of drought-resistant ‘Shijia- zhuang 8’ relies more on the retranslocation of stored N before anthesis, while that of ‘Yanmai 20’ relies more on the N accumulation and translocation after anthesis. Considering yield and N translocation of wheat, light drought stress during the recovering-jointing and late filling stages is necessary, as well as sufficient irrigation during jointing-flowering stage, so as to improve N accumulation and partitioning.

Aim Our objective was to test whether the overexpression of the Arabidopsis thaliana tonoplast Na⁺/H⁺ antiporter gene, AtNHX1, can improve salt tolerance in poplar.

Methods Transgenic and wild-type poplar (Populus × euramericana ‘Neva’) were subjected to low salt and high salt treatments. We investigated the effects of NaCl on the transgenic and wild-type poplar by measuring growth parameters, chlorophyll (Chl) and carotenoid (Car) content, net photosynthetic rate (P_n), maximal photochemical efficiency of PSII (F_v/F_m), ion content, leaf malondialdehyde (MDA) and electrolytic leakage after 30 days.

Important findings Compared with the control, the growth of wild-type plants was restrained significantly in the presence of both low salt and high salt. The dry weight of wild-type plants was significantly lower under salt stress than that of control, the dry weight decreased gradually with increasing NaCl concentration and their dry weight under high salt was just 50% of the control. However, the dry weight of transgenic plants in low salt was similar to the control up to the high salt treatment, where their dry weight was 74% of the control. Moreover, the dry weight of transgenic plants was significant higher than that of wild-type in both NaCl treatments, and the discrepancy of dry weight was increased with increasing NaCl concentration. In the presence of NaCl, Chl and Car content of transgenic plants were significantly higher than that of wild-type, and the transgenic plants maintained a remarkably high P_n and F_v/F_m. Although these transgenic plants accumulated more Na⁺ in their roots and leaf tissues under salinity conditions compared with the wild-type plants, they absorbed more K⁺and maintained a higher K⁺/Na⁺ratio. Moreover, these transgenic plants kept a lower MDA and electrolytic leakage level than that of wild-type. These findings indicate that transformation of AtNHX1 gene into poplar can confer plants more tolerance to salinity than wild-type poplar by maintaining better growth, higher Chl and Car content and improved P_n and F_v/F_m. These transgenic plants have potential for further applications in saline soil.

Aims Much research has been carried out on the relationship between forest fire occurrence and weather factors by use of modeling in recent years. However, the data organization used in past research can not satisfy the requirements of models well. Our aims are to determine the regression model that best fits the forest fire data set and provides a new model theory for research on forest fire and its influencing factors in order to forecast lighting fire occurrence.

Methods We used negative binomial (NB) and zero-inflated negative binomial (ZINB) models to describe the relationship between lighting fire occurrence and weather factors in the Daxing’an Mountains for 1980-2005 using SAS 9.1 version and R-Project statistic software and comparing results from these models by use of AIC and Vuong methods.

Important findings Both NB and ZINB models produced results with high significance for each weather factor. Comparison of the two models according to AIC, Vuong and other methods showed that the fitting ability and predictive power of ZINB model are better than those of the NB model. The advantage was also found when we compared the modeling results with Ordinary Least Squares. Then we obtained the best model for the relationship between lighting fire and weather factors.

Seed heteromorphism is the production of seeds of different form or behavior by single individuals. According to the relative position of seeds on the plant, seed heteromorphism can be divided into amphicarpy and heterodiaspory. Seed heteromorphism has been reported in 26 families, 129 genera and 292 species of angiosperms. Most heteromorphic plants studied are annuals, often species in Asteraceae and Chenopodiaceae faced with stochastic environments such as arid, semiarid, desert and saline soil. Seed heteromorphism is generally considered to play an important role in escaping from the negative effect of crowding, reducing sib competition and adapting to environment by following bet-hedging strategy. We review and analyze recent advances in seed heteromorphism research, with emphases on 1) conception and types of seed heteromorphism and the species of the heteromorphic plants, 2) habitats and life types of the heteromorphic plants, 3) ecological characteristics of heteromorphic seeds, 4) theoretical model of seed heteromorphism and 5) ecological significance of seed heteromorphism. In addition, we discuss prospects for further research in this area and suggest 1) species with seed heteromorphism should be investigated and their biological characteristics should be studied and 2) the model plant of seed heteromorphism needs to be selected and ecological, physiological and molecular biological methods should be used to reveal the ontogenetic and molecular controlling mechanisms.

Chromolaena odorata, native to Central and South America, is a worldwide perennial invasive alien weed. It has spread into most of the humid tropical and subtropical regions of Africa, Asia, Oceania and Micronesia. Moreover, C. odorata continues to spread rapidly, posing a serious threat to crops, forestry, indigenous vegetation and biodiversity conservation. It has captured extensive attention because of its serious impacts on environment and socioeconomic development. In order to restrict its range expansion and eliminate its adverse impacts, it is necessary to elucidate the mechanisms underlying successful invasion of C. odorata, for which introduction status and invasion routes should be known. We reviewed the research on this weed, including its biological characteristics, geographic distribution, invasion consequences and control, especially its introductions, invasion routes throughout the world and mechanisms of successful invasion. We presented prospects for research on the ecophysiology and molecular biology of C. odorata, emphasizing that study of the genetic basis of adaptive evolution may facilitate elucidating mechanisms underlying its successful invasion.

Soil respiration is an important issue in research on regional carbon budget and global change. Rainfall, which acts as an important disturbance to soil respiration, leads to large uncertainties in estimating carbon exchange between soil and the atmosphere, especially in arid and semiarid regions. Although significant progress on the response of soil respiration to rainfall has been made, considerable controversies on its mechanism still exist. There are two different mechanisms to interpret the “Birch effect”, which is characterized by a strong soil CO₂ emission soon after a rainfall event: “the substrate supply change mechanism” and “microbial stress mechanism”. We review progress in the study of the response of soil respiration to rainfall and summarize the responses of different components of soil respiration to the changes induced by rainfall, including physical replacement and blockage, substrate supply change, activity change of root system and microbes and changes in the structure and function of the microbial community. We also point out four important aspects to be considered in the future: 1) evaluating the function of “substrate supply change mechanism” and “microbial stress mechanism” to the “Birch effect”, 2) quantifying the response of soil respiration to rainfall based on different components, 3) modeling and estimating the response of soil respiration to rainfall on different temporal and spatial scales, and 4) evaluating the possible effects of N and H⁺ from rainfall on soil respiration.

Aims The karst vegetation in southwestern China, growing in a harsh environment, is a specific ecosystem that can lead to land degradation and rocky desertification under human disturbances. The root biomass (RB) of the karst vegetation is very difficult to measure due to the karst geomorphology and rigorous habitat and is therefore rarely reported. However, RB is a key factor in understanding ecosystem stability in this region and is an indicator of vegetation restoration in different rocky desertification stages. Our objective was to estimate the RB of karst plant communities in each restoration stage in Maolan National Natural Reserve of Guizhou Province, southwestern China.

Methods We investigated 40 plots. The karst vegetation was divided into five restoration stages according to its community physiognomy, dominant species, habitat types, mean tree diameter at breast height (DBH), mean tree height and tree density, as well as disturbances of rocky desertification: herb community, herb-scrub community, scrub-shrub community, sub-climax community and climax community of evergreen-deciduous broadleaved mixed forests. We divided the karst plant communities into rock-dominated and soil-dominated stands. We measured root biomass in different soil layers and in various root diameter classes and estimated it in 10 representative plots using the Specific Sampling Method of Averaged Standard Tree.

Important findings Forward restoration of karst vegetation significantly increases its RB from 2.63 Mg·hm^-2 in rock-stand herb community to 58.15 Mg·hm^-2 in rock-stand climax evergreen-deciduous broadleaved mixed forest (p < 0.001). In the same restoration stage, RB of rock-stands and RB of soil-stands are not significantly different (p > 0.05). Total RB in rock-stand climax and sub-climax communities are higher than that in soil-stand ones, but it is reversed in the other three restoration stages. In the same restoration stage, coarse RB in the rock-stand community is not significantly different from soil-stand community (p > 0.05). The fine and small RB in the soil-stand community is significantly higher than in the rock-stand community (p < 0.05). The biomass ratio of coarse versus total roots in rock-stand and soil-stand communities increases gradually with forward restoration. The RB of rock-stand communities is mainly distributed on the rock surface or in the rock gaps, and has no obvious vertical pattern of distribution. The distribution of RB in soil-stand communities, however, is concentrated in the top 10 cm of the soil. In different soil layers the ratio of coarse to total RB is ca. 80%; it decreases with increasing soil depth.