Aims The responses of plant roots to soil heterogeneity and the interactive effects among plant roots have been important research topics in recent years. Most studies have focused on annual plant species and conducted experiments in controlled greenhouse conditions. Few comprehensive studies have been carried out on the response of perennial plant roots to soil heterogeneity and competition. Our objective is to investigate the responses and adaptive strategies of root-system growth of the perennial plant Alhagi sparsifolia to nutrient heterogeneity and competition.
Methods We used sheep feces as nutrient patches to form soil heterogeneity and planted A. sparsifolia in glass pools. Seedlings received one of six factorial combinations of soil heterogeneity (uniform, patch-center and patch-edge) and competition treatments (alone versus with competition). We excavated whole plants and analyzed their root biomass, root respiration, root system architecture and other related characteristics in each treatment after 100 days.
Important findings Roots of A. sparsifolia grow in the direction where soil space is abundant under no plant competition, even though nutrient patches are present on the opposite side. Roots of A. sparsifolia also grow in the direction where soil space is abundant under plant competition, but neighboring plants limited the development of focal plants, resulting in significantly reduced root and shoot biomass (p < 0.01). Nutrient patches promote the growth of plant roots. The growth of A. sparsifolia roots needs both nutrients and soil space, and space is more important than nutrients. If neighbors are present, plant roots first occupy the space where competitors exist.

Aims Deficient water resources in the lower reaches of Tarim River of China impose constraints on the growth and survival of planted seedlings of Tamarix ramosissima. Our objective was to study root morphology and growth of T. ramosissima seedlings to provide suggestions for rehabilitating degraded desert riparian forest.
Methods We investigated root growth, biomass production of the seedlings under two irrigation treatments, i.e., layered-side irrigation and above-ground irrigation, and three watering levels, i.e., high water level (W1, 50 L∙ tree ^-1), medium water level (W2, 25 L∙tree ^-1) and low water level (W3, 12.5 L∙tree ^-1).
Important findings Layered side-irrigation significantly increased fine root length (0.5 mm < d < 2 mm), fine root surface area, coarse root biomass (d > 2 mm), below- and above-ground biomass and root depth compared with above-ground irrigation. Root length and biomass with layered side-irrigation and W1 increased significantly (p < 0.05). Total fine root (d < 2 mm) specific root length (SRL) with layered side-irrigation increased significantly with the increase in watering level, and above-ground irrigation caused insignificant differences in the SRL between W1, W2 and W3. The root/shoot ratio (R/S) in the layered side-irrigation treatment was less than that in the above-ground irrigation treatment. Our results suggest that the layered side-irrigation caused more rapid and greater root elongation, as well as root biomass production in T. ramosissima seedlings. This may benefit seedling survival in the early growing stage.

Aims Soil water in the root zone is a direct water source for desert phreatophytes; however, the significance of soil water for desert phreatophytes has been ignored. Instead, research has focused on the relationship between groundwater and desert phreatophytes. Our objectives were to explore spatial and temporal changes in soil water content in the root zone of Tamarix ramosissima, analyze the significance of soil water to the shrub and reveal root hydraulic lift phenomenon and its ecological effects.
Methods Soil volumetric water content was measured every half hour during the booming growth period of T. ramosissima by frequency domain capacitance sensors. The sensors were located at soil depths of 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 m.
Important findings The soil water profile can be divided into three layers: shallow relatively wet layer (0.2-1.7 m), middle relatively dry layer (1.7-2.7 m), and deep available water layer. In the shallow relatively wet layer, the soil water content showed obvious diurnal variation, decreased in daytime and increased at night. At the same time, no similar variation of soil water content in the other two layers was observed. Concurrent measurement and comparison of the plant stem water potential and the soil water potential in the shallow relatively wet layer suggested that a positive water potential gradient in root-soil interface would exist at night, which is the physical basis of water efflux from root to soil. The root hydraulic lift of T. ramosissima is the main reason that the shallow soil layer was relatively wet under the arid climate. Further root sampling determined that fine roots in the shallow soil layer were greatly developed, which indicated that the hydraulically lifted water maintained the development of shallow fine roots and ensured root activity. The great development of shallow roots is a probable explanation for the sand-fixation function of T. ramosissima. It was estimated that the percentage of hydraulically lifted water to the daily evapotranspiration in T. ramosissima stand was about 5%-8%. Water from the deep layer accounted for most water consumption of T. ramosissima, which is jointly controlled by soil texture, root uptake and the groundwater table.

Aims Our objective was to examine the effects of global warming inducing environmental and biological changes on soil respiration of desert steppe.
Methods We used infrared heaters to carry out the interactive simulation of warming and increasing precipitation in a desert steppe of Inner Mongolia from June to September 2011. Our experimental design was set up with two temperature levels (control and warming) and three precipitation treatments (control, 15% and 30% increase of the average precipitation during 1987-2007), using a complete randomized block arrangement. Soil respiration rate was measured by a LI-8100 carbon flux system in these six different treatments. We analyzed the relationships between soil respiration and environmental factors, aboveground biomass, and belowground biomass at different soil layers (0-10, 10-20 and 0-20 cm).
Important findings Soil respiration in the desert steppe reached its peak value in the middle of the growing season. The average soil respiration rate of the desert steppe from July to August was 1.35 μmol CO₂·m ^-2·s ^-1. The soil respiration rate was 2.08 and 0.63 μmol CO₂·m ^-2·s ^-1 in July and August, respectively. Increasing soil moisture and temperature significantly influenced daily soil respiration, but their interaction had no significant effect on soil respiration. Soil moisture had greater impact on monthly soil respiration than soil temperature. Soil respiration rate showed a power function relationship with belowground biomass at different soil depths. The belowground biomass at 0-10 cm soil was the major part of the belowground biomass and could explain more variation of soil respiration rate (79.2%) than that at 10-20 cm (31.6%). Under the future climatic changes scenarios, soil moisture was a principal environmental factor affecting plant biomass, while belowground biomass was a major biological factor controlling soil respiration in the desert steppe. Soil moisture might control the heterogeneity of soil respiration by influencing the distribution of belowground biomass at different soil depths.

Aims Suaeda salsa is a typical species in coastal wetlands, and understanding change in its stoichiometric characteristics would help to assess its health status and target conservation efforts. We investigated which nutrient factor restricts its growth and proposed theories for protecting and managing coastal wetland by comparing the C, N and P stoichiometric characteristics of S. salsa in different growth periods.
Methods We collected S. salsa leaves in different growth phases from June to November 2010 in Yancheng coastal wetlands, Jiangsu Province. The C, N and P contents of the leaves were measured. Data were analyzed by correlation analysis between N content and C:N and P content and C:P. N content and P content were also analyzed.
Important findings Leaf C content of S. salsa had significant differences among three different growth phases, with the lowest in the growth phase and the highest in the decline phase. Leaf N content in the decline phase is significantly lower than in the mature and growth phases, and no significant difference of leaf P content was found. C:N and C:P were gradually increasing in the growth period while N:P showed a gradually decreasing trend. Correlation analysis indicated that C:N and C:P were negatively correlated with corresponding N, P content in three different phases. N content was positively linearly correlated with P content, indicating consistent demand of N and P by S. salsa. Furthermore, N is a restrictive factor for S. salsa in coastal wetlands during its growth and development.

Aims Our objective was to investigate the effects of different light intensities on leaf morphology, photosynthetic capacity, heat dissipation and antioxidant enzyme activities in seedlings of Alnus formosana and A. cremastogyne from a hilly region near Lingyan Mountain in northwestern Sichuan Province in China. We also discuss photosynthetic acclimation and photoprotection strategies in seedlings of the two species --Methods-- Three light regimes of 100%, 56.2% and 12.5% of natural light were simulated to match forest openings, forest gaps and forest canopies, respectively. After more than three months, we measured the parameters of gas exchange, including maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), intercellular CO₂ concentration (C_i), fluorescent non-photochemical quenching (NPQ), maximum efficiency of PSII photochemistry (F_v/F_m) and light use efficiency (LUE), using a LI-6400 in seedling leaves. We also determined pigment contents per unit leaf area, lamina mass per unit area (LMA) and activity of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase). --Important findings-- LMA, carotenoid content (Cars), ratio of carotenoid to total chlorophyll (Car/Chl) and activities of superoxide dismutase, catalase and ascorbate peroxidase in leaves increased with the increase of light intensities. P_max, LSP, LCP and NPQ tended to increase, while the chlorophyll content (Chl) and LUE decreased. However, the C_i decreased with the increase of P_n, G_s and stomatal limitation value (L_s). We speculated that non-stomatal limitation was the main factor that inhibited P_n. Seedlings of the two alder species could acclimate to different light regimes in this study through changing of physiological and morphological traits. Under all light regimes, diurnal photoinhibition of photosynthesis, as judged by F_v/F_m, was significantly more severe in A. cremastogyne than in A. formosana. The acclimation capacity to high light regime was stronger in A. formosana than in A. cremastogyne. With the increase of light intensities, P_max and antioxidant enzyme activities increased significantly, but not NPQ in A. formosana. The opposite trends occurred in A. cremastogyne. At the same light intensity, thermal dissipation was much lower, but P_max was much higher in A. formosana than in A. cremastogyne. These results indicated that A. formosana seedlings might adapt resistance to photoinhibition through improving the use of solar energy by higher P_max and antioxidant enzyme system, while A. cremastogyne seedling avoided photoinhibition mainly through converting excess light energy to heat energy in the form of non-radiative dissipation through the antenna system.

Aims Integrated research on the effect of N supply on successive levels from leaf to canopy would be helpful to improve the field N management in winter wheat production areas in China.
Methods Field experiments were conducted under 5 N levels: 0, 70, 140, 210 and 280 kg N·hm ^-2. Four levels of productivity were measured: leaf photosynthetic rate (A_leaf) and canopy photosynthetic rate (A_canopy) measured at the stages of booting, flowering and grain-filling, crop growth rate (CGR) measured during the stages of setting-flowering and flowering-ripening and grain yield (GY) measured at the stage of harvesting.
Important findings Results show that A_leaf, A_canopy and CGR have increasing patterns at all stages when N supply increases from 0 to 210 kg N·hm ^-2. When N supply increases from 210 to 280 kg N·hm ^-2, GY has no significant variation; however, the A_leaf and A_canopy during the grain-filling stage and the CGR during the flowering-ripening stage decrease. These results indicate that: 1) excessive N supply of 280 kg N·hm ^-2 can decrease the productivity of winter wheat over leaf, canopy and biomass levels and inhibit GY increasing; 2) the negative effect of excessive N supply is readily demonstrated during the stage of grain-filling; and 3) A_canopy is more capable of detecting the negative effect of excessive N supply than A_leaf, CGR and GY.

Aims Our objectives were to reveal differences in physiological characteristics, photosynthesis, ultrastructure of root tip cell and grain Zinc (Zn) accumulation in different varieties of rape under different Zn treatments.
Methods Pot experiments were carried out. Zn treatments were 0, 1.0, 5.0, 10.0 and 20.0 mg·kg ^-1, and five varieties of rape were ‘Luopingjincaizi’ (Brassica juncea), ‘Erniuwei’ (B. juncea), ‘Liyangkucai’ (B. juncea), ‘Nantonghuangyoucai’ (B. chinensis) and ‘H33’ (B. napus). All experiments were performed in triplicate, and pots were arranged in a completely randomized design inside a greenhouse.
Important findings The dry weights of roots, leaf, straw, grain and plant, physiological characteristics and concentration and accumulation of Zn significantly differed among the different varieties and Zn treatments. The activities of antioxidant enzymes, net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and dry weights of plant, straw, leaf and grain increased at Zn ≤ 5.0 mg·kg ^-1. The highest yields of grain for the five varieties were all observed in the 5.0 mg·kg ^-1 Zn treatment and were 37.7%, 23.4%, 29.5%, 82.6% and 18.0% greater than the control, respectively. Ultrastructural damage was found in the root-tip cells for ‘Luopingjincaizi’, ‘Erniuwei’, ‘Nantonghuangyoucai’ and ‘Liyangkucai’ in the presence of 20.0 mg·kg ^-1 Zn and included mitochondria inflation, cell-wall thickening, nucleus atrophy and decreased contents of nucleus, while unaltered structure of the root-tip cells was observed in ‘H33’. Grain Zn accumulation for the five varieties increased at Zn ≤ 5.0 mg·kg ^-1, and decreased at Zn > 5.0 mg·kg ^-1. Highest concentration and accumulation of Zn in grains were observed in ‘Erniuwei’ at 5.0 and 10.0 mg·kg ^-1 Zn (172.34 mg·kg ^-1, 2.932 mg·pot ^-1 and 164.10 mg·kg ^-1, 2.575 mg·pot ^-1) treatment, respectively.

Aims Our purpose was to demonstrate the potential of using airborne laser to estimate biomass components of temperate forest. The airborne Lidar data and field data of concomitant plots were used in a forest of the Northeastern China.
Methods A set of biomass components, i.e., leaf biomass, branch biomass, trunk biomass, aboveground biomass and belowground biomass, were calculated from field data using species-specific allometric equations. Canopy height indices and density indices were calculated from Lidar point cloud data. The height indices evaluated included maximum height of all points, mean height of all points, quadratic mean height (square root of the mean squared height of each Lidar point) as well as height percentiles. Canopy density indices were computed as the proportions of laser points above each percentile height to total number of points. Then statistical models between these biomass components from field data and Lidar indices were built. Stepwise regression was used for variable selection and the maximum coefficient of determination (R ²) improvement variable selection techniques were applied to select the ALS-derived variables to be included in the models. The least squares method was used generally and repeated until all the independent variables of the regression equation were accord with the requirements of entering models.
Important findings There were good correlations between biomass components and Lidar indices. The R ²was >0.6 for all the biomass components when we put all three types of forest (i.e., needle-leaved, broad-leaved and mixed) together. Needle-leaved forest had best estimation followed by broad-leaved and mixed forests when we built separate models for the three types of forest. This estimation capability is better when the regression models are built for different forest types.

Aims Our objective was to integrate vegetation survey data, remotely sensed data and environmental data based on generalized additive model to map vegetation and investigate whether coupling remotely sensed data and environmental data could improve the performance of generalized additive model.
Methods Altitude, slope, nearest distance to coastline, nearest distance to the Yellow River and spectral variables were selected as predictive variables. Generalized additive model was employed to describe the relation between the vegetation and predictive variables. Deviance (D ²) was employed to test the goodness of curve fitting, and a probability map of each vegetation type produced by the fitted generalized additive model was assessed by cross-validation of receiver operating characteristic (ROC). Vegetation type of each grid cell was determined according to the maps of probability. We validated the final predicted vegetation type map by comparing the predicted vegetation type map with vegetation survey data.
Important findings Results indicated that integrating field sampling, digital elevation model and remotely sensed data based on generalized additive model was feasible to map vegetation. Coupling environmental variables and spectral variables improved the performance of generalized additive model. Prediction accuracy varied according to the plant community type, and plant community with dense cover was better predicted than sparse plant community. The selected generalized additive models for each vegetation type indicated that both environmental variables and spectral variables were important factors for predicting vegetation distribution. Drop contribution calculation indicated that the contribution of the same predictive variable for different vegetation types was different. This can be explained by the different spectral and environmental characteristics of vegetation types. The contribution of each predictive variable for the same vegetation type varied according to the modeling scene. This might be explained by the coupling effects of environmental variables and spectral variables.

Plants have developed sophisticated defense systems during their long-time interaction with insects. About three decades ago, it was found that insect-damaged plants can prime their neighbors to express defense proteins, and this phenomenon was called “plant-plant communication”. A series of studies have focused on this topic since then. Results indicate that green-leaf volatiles and terpenes are the main chemicals emitted from the infested plant to the healthy neighbor plants, while direct and indirect defenses of the neighbors may both be regulated. An important consensus about plant-plant communication mechanisms until now is that the volatile organic chemicals do not induce resistance directly, but sensitize the receiver plant for augmented response to subsequent damages, which is called “priming”. However, the molecular mechanism of this phenomenon is unclear. We used Arabidopsis thaliana genome arrays and mutants to examine the molecular mechanisms of plant-plant communication. Our results indicate that several volatiles are effective signals, and the active volatiles are correlated with their emission rhythms to achieve the optimum effect. The ethylene pathway is indispensable for sensing the induction signal in the early phase of induction, while Jasmonic acid signal can amplify the effects. As the mechanisms of plant-plant communication become clearer, future research may focus on the origin and evolution of this phenomenon.