Aims Our objectives were to consider a new scheme for vegetation regionalization of Northeast China, especially for vegetation in the Songliao Plain, and to illustrate the distribution pattern of vegetation as determined by altitude.
Methods We clustered the sites from Inner Mongolia steppe, east forest and central Songliao Plain with temperature, precipitation, soil types and underground water depth using principle component analysis (PCA). We also analyzed the physiognomy, topography of Northeastern China using GIS, vegetation types and soil types of Songnen Plain.
Important findings The dominant vegetation of Songliao Plain is meadow, an unzonal vegetation type. The Stipa communities, an indicator of the zonal vegetation type, mainly distributed on the second mesa in Songnen Plain, are a sandland vegetation type that is distributed discontinuously among meadow vegetation. Therefore, the vegetation of Songliao Plain should be regionalized as an area of temperate broad-leaved deciduous forest, and the east boundary of temperate steppe region should be moved toward to the west of the Da Hinggan Mountains. The vegetation distribution of Northeast China shows a vertical zonation determined by altitude.

Aims Winter soil respiration is reported to be a significant component of the annual carbon budgets. In order to understand how projected global warming affects winter soil respiration and soil microbial properties, we conducted a warming experiment in a young Pinus armandii plantation during the winter period to assess short-term response of winter soil CO₂ efflux and microbial properties to artificial warming. Methods We used an infrared heater and monitored soil temperature and relative air humidity in November 2009 and analyzed soil respiration, microbial biomass and inorganic nitrogen pools throughout the winter. Important findings The average daily air and soil temperatures were 2.1 and 6.7 ℃ higher in the warmed plots than in the control plots, respectively. Warming declined relative air humidity and soil water content by 15.2% and 7.2%, respectively. Across all measuring dates, simulated warming increased average soil CO₂ efflux by 31.4%. Warming significantly enhanced the soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N) by 23.2% and 22.7%, respectively, but did not affect the ratio of SMB-C to SMB-N, which indicated that elevated temperature tended to accelerate the growth of SMB, but did not change the community structure of SMB. Likewise, warming tended to increase soil inorganic nitrogen pools. Nitrate (NO₃ ^--N) and ammonium (NH₄ ⁺-N) in the warmed soil increased 38.5% and 12.3%, respectively, compared with control soil. Results indicate that winter soil respiration, microbial activities and nutrient mineralization in the coniferous forest soils could be sensitive to future global warming.

Aims Our objective is to investigate the impact of salinity on decomposition of Kandelia candel leaf litter.
Methods Four laboratory treatments with different salinities (0, 10‰, 25‰ and 35‰ salinity, representing fresh water and low, medium and high salinity treatments, respectively) were set up to simulate tidal conditions for leaf litter decomposition. We analyzed dry weight, nitrogen (N) and phosphorus (P) contents, their release rates and energy loss of leaf litter at different decomposition stages under these four treatments.
Important findings Percentage weight loss and mean rate of decomposition (MRD) in high salinity treatment were significantly lower than in fresh water and low salinity treatments. Theoretical time required for 50% loss of dry weight of leaf litter was highest in high salinity treatment. Salinity significantly affected the dynamic variation of N and P in leaf detritus. The N release rate of leaf detritus tended to increase with higher salinity, resulting in lowest N content in the high salinity treatment. During the first week, fresh water and the low salinity treatment were found to accelerate the release of P, but P content was lower under medium and high salinity than other treatments. The caloric values of leaf detritus were significantly higher in fresh water and low salinity treatments than in the high salinity treatment; however, no significant difference was found in percentage energy loss during decomposition under different salinities.

Aims Our objectives were to: 1) compare the advantages and disadvantages of the root order and diameter classes in the description of root morphology characteristics and 2) explore the inherent connection between them.
Methods We excavated 2-year-old Pinus tabulaeformis seedling roots in Zhouzhi County, Shaanxi Province, China. Individual roots were dissected according to the branching order, starting from the distal end of the root system that was numbered as the first order and then increasing sequentially with each branch from the first order roots to higher order ones. Following dissection, fine root samples were scanned by the Win-RHIZO system to analyze root length, specific root length, specific root surface area, diameter and tips. Fine root samples were then oven-dried at 65 °C to a constant weight to determine weight.
Important findings Six root orders were included, with diameters that ranged from 0.169 to 3.877 mm. The summed length and surface area of the first three orders accounted for 78.77% and 62.72% of the totals, respectively. The specific root length and specific root area of the first three orders are 1.3-3.0 times and 1.0-1.5 times that of as the other orders. Based on diameter classes of ≤0.5, 0.5-1.0, 1.0-1.5 and 1.5-2.0 mm, most root diameters of P. tabulaeformis seedling were <1.5 mm. The summed length and surface area of this diameter range accounted for 93.76% and 84.35% of the totals, respectively. The specific root length and specific root area of roots <1.5 mm in diameter were 3.0-7.0 times and 1.5-3.0 times as large as roots >1.5 mm. For the exponential relationship between root orders and diameters and based on diameters’ maximum ratio reflecting root orders, a new diameter classification was proposed: ≤0.4, 0.4-0.8, 0.8-1.3 and 1.3-2.0 mm. As a result, the above intervals might represent the I, II, III, IV and V root orders in number of root tip of 93.22%, 86.37%, 75.96%, 70.47% and 76.67%, root length of 89.34%-70.83%, root area of 86.01%-76.12% and root volume of 87.73%-76.12%. Therefore, we identified a relationship between root diameter classification and root order, and it is possible to reflect root orders through logical division of the root diameter classes.

Aims The two primary limiting factors for biological activities in desert ecosystems are nitrogen and water. Our study, which examined their combined effects, can provide insight into the responses of arid ecosystems to global climate change. We selected two typical annual desert plants, Malcolmia africana and Bassia hyssopifolia to determine the combined effects of nitrogen deposition and drought stress on their growth and photosynthetic physiological responses.
Methods Three levels of N addition (0, 0.18 and 0.72 g N·m ^-2·week ^-1) and two soil watering regimes (60%-70% and 30%-40% of field capacity) were randomly provided in order to simulate nitrogen deposition and drought stress. Changes in plant growth and photosynthetic physiological traits were measured shortly before flowering.
Important findings N supply and drought stress significantly affected growth of both species. With the enhancement of N supply, we found an increase in growth parameters (including root length, root weight, leaf number, leaf area, total biomass and shoot/root (S/R)). At the same N level, increased drought stress could counteract the positive effects of N supply on plant growth. Increased N, however, could also alleviate the negative effects caused by drought stress. With the increasing N addition, we also observed increase of physiological indices (net photosynthetic rate, content of chlorophyll and soluble protein). Malcolmia africana was more sensitive to N supply and drought stress than B. hyssopifolia. The different responses of the two species may due to their different biological characteristics, such as life form. The results indicated that N and water pulses in spring in this desert would be beneficial to the growth and productivity of M. africana and B. hyssopifolia, especially for aboveground parts. Moreover, N deposition could partially alleviate the negative effects caused by drought stress during the severe dry season.

Aims Flooding disturbance can change the species composition of plant communities. Field investigation showed that annual herbs were an important part of the natural vegetation of the water-level-fluctuating zone (WLFZ) in the Three Gorges Reservoir, but there are few studies on the effects of flooding on annual plants. Annual, which reproduce from seeds, usually grow fast and can rapidly rehabilitate areas. Our objective is to determine the effects of water submergence on the germination of seeds of annuals, with regard to possible use of annual plants in vegetation restoration of WLFZ in the Three Gorges area.
Methods Seeds of four annuals, Echinochloa crusgali, Setaria pumila, Digitaria sanguinalis and Arthraxon hispidus, were collected in autumn 2008 in Wushan County of Chongqing Municipality. Seeds for control (CK) were kept in envelopes; seeds for water submergence treatments were buried in soil in plastic containers and water was poured into the containers to maintain a water layer on the soil surface. We used six different durations of water submergence, 30, 75, 115, 155, 195 and 240 days, to match water level operation of the Three Gorges Reservoir. After treatments ended, seeds were separated from soil by water flushing and filtering with gauze. The treated seeds were incubated in pots filled with soil watered daily. Three replicates of 50 seeds per sample were used for each treatment. Germinated seeds were counted daily until the end of germination.
Important findings Water submergence significantly affected seed germination rate and germination course of all four annuals. Germination rates first increased and then decreased with increased duration of submergence. Germination rates with short-time submergence treatments were significantly higher than CK. Submergence can break seed dormancy and increase the rate of seed germination. Submergence also accelerated the course of germination. Short-time submergence treatments increased germination indices significantly greater than in CK, and the germination periods were shorter, but long-time submergence had little effect on the course of seed germination. Overall, the germination rates of all treatments of all annuals were > 40%. Therefore, these four annuals are useful in vegetation restoration of WLFZ in the Three Gorges Reservoir.

Aims Crop coefficients are the key parameters in calculating crop evapotranspiration. There are few reference values for crop coefficients of natural grass in FAO irrigation and drainage papers. Our aim was to define crop coefficients under different water conditions for typical steppe in Inner Mongolia based on actual observation data so as to accurately calculate the water demand and actual evapotranspiration.
Methods Data were collected from field experiments at Xilinhot (44°08′03 N, 116°19′43 E, elevation 990 m), Inner Mongolia in 2008, and meteorological data from 26 years were obtained from four stations. Using the water balance equation, we calculated crop coefficients of typical steppe using statistical analyses and developed the standard crop coefficients of typical steppe and simulated equations through comparison and validation with recommend values by FAO. We established a climatic correction method for the standard crop coefficients and a correction method of crop coefficients under water stress.
Important findings Standard crop coefficient values of typical steppe were fitted with trinomial using days after return of the green period of grass and accumulated temperature (≥0 °C), with correlation coefficients >0.94. Crop coefficients of typical steppe were described as an exponential equation with relative leaf area index (LAI) and relative plant cover. Average value of standard crop coefficient of typical steppe for the growing season was 0.60, and the maximum value was 1.02. Typical values of crop coefficients in different growing stages were 0.40 for initial stage, 0.93 for medium stage and 0.80 for later stage, and threshold ranges of three growing stages were 0.35-0.45 for initial stage, 0.85-1.00 for medium stage and 0.70-0.90 for later stage. Compared with measured data from a lysimeter, the simulated values for 10 days of evapotranspiration indicated an average relative error of 20%-24% for whole growing season, and <10% for the active growing stage. The method and results defined here are applicable to typical steppe in Inner Mongolia.

Aims Our objective was to determine the effects of supplemental irrigation on water consumption characteristics and dry matter accumulation and distribution in different spike-type wheat cultivars under field conditions based on testing soil moisture.
Methods We conducted a field experiment using medium-spike (‘Shannong 15’) and large-spike (‘Shannong 8355’) cultivars. Three irrigation treatments were designed based on the contents of relative soil moisture at jointing and anthesis stages: 65% and 60% (treatment W0), 70% and 70% (W1), and 70% and 70% (delaying irrigation 8 d after the designated stages mentioned above; W2).
Important findings Grain yield in treatment W0 was the lowest in both cultivars. In ‘Shannong 15’, there was no significant difference between W1 and W2, whereas in ‘Shannong 8355’, W1 had higher grain yield than W2. Water use efficiency (WUE) and irrigation water use efficiency (IWUE) of W1 were significantly higher than those of W2 in both cultivars. Under W1, grain yield of ‘Shannong 15’ was lower than that of ‘Shannong 8355’, but IWUE was the opposite. There was no significant difference between ‘Shannong 15’ and ‘Shannong 8355’ in WUE. Under W2, grain yield, WUE and IWUE had no significant differences. The lowest total water consumption amount (TWCA) was obtained in W0 in both cultivars. In ‘Shannong 15’, W1 had lower TWCA than that of W2, while there was no significant difference in ‘Shannong 8355’ between the two treatments. Soil water consumption amount and its ratio to TWCA in W1 were significantly higher than those in W2 in both cultivars. Under W1 condition, TWCA and the ratio of irrigation amount to that in ‘Shannong 15’ were significantly lower than those in ‘Shannong 8355’, but the ratio of soil water consumption amount to TWCA was the opposite. Under W2, there was no significant difference between TWCA and the ratio of soil water consumption amount to it. Dry matter accumulation at maturity of W1 was significantly higher than that in other treatments in both cultivars, and it was significantly lower for W1 and W2 in ‘Shannong 15’ than in ‘Shannong 8355’. Treatment W1 increased dry matter accumulation amount after anthesis and its contribution to grains in ‘Shannong 8355’, but it did not change significantly in ‘Shannong 15’. Dry matter translocation after anthesis, its ratio and contribution to grains of W1 and W2 in ‘Shannong 15’ were significantly higher than those in ‘Shannong 8355’, while dry matter accumulation after anthesis and its contribution to grains were the opposite. In wheat production under conditions similar to this study, the optimal irrigation treatment in both cultivars was W1.

Aims The degree of specificity of mycorrhizal association in tropical orchids has been controversial for many years. Our objective is to address this issue.
Methods Twenty-two endophyte fungal strains isolated from the roots of wild temperate terrestrial orchids were inoculated with the seeds, protocorms and seedlings of tropical epiphytic orchid species Doritis pulcherrima in flasks. Transverse sections of roots were observed by microscope.
Important findings After 20-weeks cultivation, only the fungal strains Cf1 and Mm1 caused swelling of the embryo, and nine caused differentiation of the protocorms into leaves or roots. The other fungal strains were pathogenic or had no function in seed germination and protocorm differentiation. In the seedling-fungi symbiotic treatment, the survival rate of the seedlings reached 100% and 11 of 22 fungal strains significantly enhanced the seedling growth. The fungal strain Mm1 had the most significant effect on increasing fresh mass of seedling. The existence of pelotons in the cortex of the roots of the protocorms and seedlings indicated successful infection. The effects of 22 endophyte fungal strains on seed germination, protocorm development and seedling growth of D. pulcherrima showed that the endophyte fungi did not enhance seed germination but were associated with the protocorms and seedlings; However, no one fungus was associated with all three key stages simultaneously. Our study suggested that the degree of specificity of tropical epiphyte orchids is influenced by the development stages of the plant.

Aims Our objective was to investigate the light-adaptive physiological mechanism of maize on shading stress after anthesis, in order to provide theory behind evidence for high and stable yield in summer maize.
Methods In a field experiment, we used common corn (Zea mays) (TY2) to analyze changes of photosynthetic performance, chlorophyll fluorescence parameters, xanthin circle and light partition in maize in the process of shading and recovery stages under (a) shading 55% (+S) 1-20 d after pollination and (b) natural illumination in field condition (-S).
Important findings The net photosynthetic rate and light saturation point of ear leaves declined rapidly, because the chlorophyll content, soluble protein content and PEPCase and RuBPCase activities in ear leaves markedly decreased after shading. Under shading, the maximal photochemical efficiency (F_v/F_m) and the actual photochemical efficiency (Φ_PSII) significantly declined, but non-photochemistry quenching (NPQ) increased. The Φ_PSII of ear leaves increased in early recovery, which indicated that the sudden exposure to natural light significantly enhanced the photosynthetic electron transport rate, according with its photosynthetic rate and carbon metabolism activity of maize ear leaves. After shading, the size of xanthin circle sink in ear leaves was not significantly different, but the de-epoxidation state of xanthin circle (A + Z)/(V + A + Z) increased after shading. The distribution of light energy in photochemical reaction was lower, but the antenna dissipation rate of light energy increased significantly. On the other hand, the dissipation of excess light energy in the recovery process mainly depended on non-photochemical reactions. The PSII primary photochemistry activity of maize decreased under after shading and recovery in early stage, which limited electron supply of photosynthetic carbon metabolism and re- strained the photosynthesis. Then the energy dissipation mostly relied on the xanthin circle increased. The light protective mechanism of maize leaves improved in adaptation to the natural light, and photosynthetic capability gradually recovered after illumination switch.

Aims Malus hupehensis var. pingyiensis with strong ability for apomixes is unique to China and is tolerant of waterlogged conditions and salt. There is little difference among its seedlings because of apomixes. Malus hupehensis var. pingyiensis is widely used as stocks of apple cultivars and ornamental apples and has important applied value in apple production and research. Our objective was to determine the response characteristic of cells and mitochondria in M. hupehensis var. pingyiensis roots under high saline conditions.
Methods Pot seedlings with at least seven mature leaves were used in this experiment. In order to avoid irreversible damage to roots caused by sudden exposure to high level saline condition, we first used a weak saline solution (0.051 mol·L ^-1 NaCl) to water seedlings every two days, for a total of three times. Then strong saline solution (0.085 mol·L ^-1 NaCl) was used to water seedlings. Tap water was used for control seedlings. H₂O₂ content, membrane potential of mitochondria (Δψm), ATP content, terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL) and caspase3/7 activity were determined every two days from the third day of 0.085 mol·L ^-1 NaCl treatment, altogether five times.
Important findings Δψm of roots declined slowly in the first six days of 0.085 mol·L ^-1 NaCl treatment and thereafter declined rapidly. The H₂O₂ content in mitochondria decreased slowly in the first six days and then accumulated quickly. ATP content in roots remained constant during the treatment of 0.085 mol·L ^-1 NaCl, but was low compared with that in control seedlings. The results of TUNEL assay showed that root paraffin slices displayed distinct positive-reaction spots that became more numerous in the root paraffin slice of the ninth day. Caspase3/7 activity was examined with a detection kit; it remained at a low level for the first six days of 0.085 mol·L ^-1 NaCl treatment, and thereafter increased sharply. Results indicated that programmed cell death could be induced in roots of M. hupehensis var. pingyiensis by 0.085 mol·L ^-1 NaCl treatment, and this was closely related to the change of mitochondrial characteristics.

Aims In addition to producing energy, mitochondria in fine roots play a dual role in oxidative stress, being both reactive oxygen species (ROS) producers and integrators of the cell antioxidant defense systems. Structural integrity of mitochondria is the fundamental guarantee for producing ATP in fine roots. Therefore, our objective was to observe mitochondrial structural and functional changes in Fraxinus mandshurica fine roots of different colors under drought stress to better relate different-colored fine roots with different functions and to develop a theoretical basis for judging fine root death according to root color.
Methods We observed the number, distribution and structure of mitochondria in different-colored fine roots cortical parenchyma cells of F. mandshurica by electric microscopy. Mitochondrial respiratory control ratio (RCR) and phosphorus oxygen ratio were measured by oxygen electrode. The malondialdehyde (MDA) content, membrane permeability and H₂O₂ concentration were studied by UV spectrophotometer.
Important findings Compared with the control, there were no significant differences of mitochondrial shape, structure or distribution under drought stress in white and yellow roots’ cortical parenchyma cells. However, there were fewer mitochondria in brown fine roots under drought stress, and their membranes had disintegrated and disappeared to a different degree. The normal breathing coupling of mitochondrial membrane role in fine-root mitochondria was disturbed significantly under drought stress. The value of RCR and P/O were significantly lower than that of the control (p < 0.05). With deepened fine-root color, mitochondrial RCR and P/O value decreased gradually, white roots > yellow roots > brown roots. The H₂O₂ content, mitochondrial membrane permeability and MDA content in different-colored fine roots mitochondria under drought stress were significantly higher than the control (p < 0.05). Values increased markedly with deepened color.

Aims Our aims are to compare the photosynthetic and fluorescence characteristics in different species in Paeonia sect. Paeonia and to determine how these species fit different circumstances in photosynthesis. This information will be important in protecting and using these wild resources.
Methods The LI-6400 Portable Photosynthesis System was used to determine diurnal photosynthetic changes, light-response curves and CO₂-response curves of different species in sect. Paeonia under good growth conditions. The OS5-FL modulated chlorophyll fluorometer was used to determine their chlorophyll fluorescence characteristics. The light-response curves and CO₂-response curves were simulated with modified rectangular and nonrectangular hyperbolic models.
Important findings We found an obvious difference between photosynthetic rates of species in sect. Paeonia. The simulated result with modified rectangular hyperbolic model is more consistent with the result determined than the other model. The index of light-response curves and CO₂-response curves differ among species. Paeonia veitchii, P. anomala, P. mairei, P. anomala var. intermedia and P. lactiflora have the characteristic of “siesta”, but it is not obvious in P. lactiflora var. trichocarpa. The index of chlorophyll fluorescence characteristics reflects the photosynthetic characteristics. The photosynthetic characteristics of P. lactiflora and P. lactiflora var. trichocarpa embody their strong adaptability.

There has been considerable progress in understanding plant nutrient foraging plasticity in the past three decades, resulting in better comprehension of belowground ecology. However, studies of mycorrhizal plasticity, an important aspect of plant nutrient foraging plasticity, are mostly limited in conceptual development due to methodology restrictions. Without understanding mycorrhizal plasticity, the comprehension of plant root plasticity is incomplete. The rapid development of mycorrhizal biology, especially the involvement of molecular biology approaches, lends the possibility of in-depth study of mycorrhizal plasticity. We focus on ectomycorrhizal plasticity with a brief introduction to basic ectomycorrhizal biology. Few studies have focused on mycorrhizal plasticity specifically, and they have yielded only scattered implications, mostly morphological. Studies on physiological plasticity have been basically absent. Development of study approaches in ectomycorrhizae lends great promise for research on mycorrhizal plasticity. The complexity of ectomycorrhizal foraging plasticity determines the complexity of research and questions to be answered. We address expected directions and questions in ectomycorrhizal foraging plasticity.