Aims At larger scales, the elevational gradient interacts with the redistribution of water and soil solutes to determine regional vegetation pattern, especially in regions with small variation in elevation. However, little is known about the processes of water redistribution in coastal ecosystems. Our objective is to test if water redistribution affects vegetation pattern at large scales in a coastal ecosystem in the Yellow River Delta using an integrated remote sensing and GIS method.

Methods One-way ANOVA was employed to test whether normalized difference vegetation index (NDVI) is significantly different among four major plant communities. Correlations between NDVI and topographic indexes were identified by the Spearman non-parametrical method. Moran’sI coefficients were also calculated for all selected variables.

Important findings NDVI was highly different among the four communities, as determined by differences in habitat structure of coastal plants. Correlations between NDVI and elevation were highly significant at all scales, which may closely associate with the groundwater depth at smaller scales and with water redistribution at larger scales. At the 750 m grain scale, the correlation coefficients between topographic wetness index and slope were highly significant and the Moran’sI coefficient increased abruptly, indicating water redistribution at this scale. Topographical factors affect the vegetation pattern via scale-dependent adjustment and control on soil moisture and salinity. At small scales, topographic factors regulate soil water and salinity through evaporation from the soil surface. At large scales, topographic factors redistribute the soil water and salinity through runoff and the groundwater system.

Aim Vegetation and environmental degeneration from global change and intensive human activities are among the most serious problems on the Loess Plateau of China. Our objective was to study the trend in vegetation cover and its relationship with dominant environmental factors to provide a basis for ecological restoration and regional assessment on the Loess Plateau.

Methods We analyzed the temporal and spatial changes of vegetation cover and its relationship with rainfall in the Jinghe Watershed using the GIMMS-NDVI time series data and rainfall data for 1982-2003.

Important findings Annual NDVI slightly increased during the study period and varied spatially. Vegetation cover increased 69.2%, of which the 16.61% of the study area in the middle-west and lower reach of the watershed had a significant increase of vegetation cover. NDVI strongly decreased in the upper reach and the surrounding area, which accounts for 1.65% the whole watershed.NDVI was highly correlated with precipitation, and annual NDVI and annual rainfall had logarithmic distributions. There was a one-month lag of monthly NDVIafter rainfall in the growing season. Rain use efficiency (RUE) decreased during the study period, which indicated lack of improvement of the land situation. Our finding that RUE decreased with increased precipitation contrasts with previous research.

Aims The “Three-River Headwaters” Region, as the headwaters of important rivers and an area sensitive to global climate change, has become a recent research focus. Our objective is to model and assess the spatial-temporal pattern of net primary production ( NPP) and its control mechanisms.

Methods We applied the GLOPEM-CEVSA model, which has been validated with carbon flux observation in forest, grassland and cropland. The main inputs are spatially interpolated meteorological data and fraction of photosynthetically active radiation absorbed by vegetation canopy, using 1 km resolution of the Advanced Very High Resolution Radiometer of the National Oceanic and Atmospheric Administration in 1988-2004.

Important findings Modeled NPP ranged from 36.13 gC·m^-2·a^-1 for desert to 267.90 gC·m^-2·a^-1 for forest, and the mean was 143.17 gC·m^-2·a^-1. Spatially, NPP decreased from southeast to northwest, as influenced by geography and climate. Variability of NPP was the largest in desert (41.75%), was similar for cropland (25.93%), grassland (22.31%) and wetland (24.72%) and was the smallest in forest (20.79%). During 1988-2004, NPP increased at the rate of 7.8-28.8 gC·m^-2 per 10 years in the western area, but decreased 13.1-42.8 gC·m^-2 per 10 years in the central and eastern areas. At 99 and 95% significance levels, the area with NPP increasing (regression slope b > 0) was 13.43% and 20.34%, respectively, of the whole area, and mainly distributed in the western region, while the area with NPP decreasing (b < 0) was 0.75% and 3.77%, respectively, of the whole area and distributed in the central and western areas and was more concentrated near the main rivers at higher significance levels. Increases of NPP in the western area may have been affected by increasing temperature and precipitation, while central and eastern areas may have been impacted by human activities, especially along the Yangtze, Yellow and other rivers with intensive human habitation and where the warmer and drier climate has led to more serious grassland degradation. The effects of human activities on NPP were not analyzed because data on human activity were unavailable and spatial interpolation of the impact is difficult.

Aims Solar radiation can affect net ecosystem exchange (NEE) of carbon dioxide of forests, because cloud cover alters solar radiation, which in turn alters other environmental factors such as temperature and vapor pressure deficit. Our objective was to analyze the effects of these changes on NEE of broadleaved-Korean pine (Pinus koraiensis) mixed forest in Changbai Mountain.

Methods Our analysis was based on 30-min flux data and routine meteorology data for mid-growing season (June to August) for 2003-2006.

Important findings Cloud cover significantly increased NEE. The light-saturated maximum photosynthetic rate was enhanced 34%, 25%, 4% and 11% on cloudy days compared with clear days in the four years of study. Relative irradiance and clearness index (k_t) were important in quantifying the effects of cloud cover, cloud shape and cloud thickness on solar radiation. When k_twas about 0.5, NEE reached its maximum. When the relative irradiance was over the critical relative irradiance of 37%, NEE was enhanced; maximum NEE occurred at about 75%. Enhancement ofNEE was ascribed to increased canopy assimilation and decreased above-ground respiration, which resulted from increased diffuse radiation and decreased air temperature and vapor pressure deficit with increased cloudiness.

Aims Forest ecosystems are important carbon pools of the global terrestrial ecosystem and play a key role in sequestrating and reserving greenhouse gases. Our objectives were to quantify the carbon stock of different forest ecosystems in the subalpine coniferous forest in western Sichuan Province (SCFS) and identify short-term carbon sequestration potential.

Methods We investigated the forests of Wanglang National Natural Reserve, located in Pingwu County, Sichuan Province. Five similar altitude and slope ecosystems dominated byBetula platyphylla(BF), Betula spp. and Abies faxoniana(MF),Abies faxoniana (FF), Picea purpurea(SF) and Sabina saltuaria(CF) were selected to quantify ecosystem carbon stock and its allocation. We sampled eight replicate plots in each ecosystem. All plants in each plot were surveyed and sorted into three groups: tree layer (DBH ≥5 cm), understory ( DBH <5 cm), and herb layer. We surveyed the carbon stock of the tree layer using standard tree sampling methods, in which biomass and carbon stock of three newly up-rooted trees were measured. Carbon stock of understory, herb, ground cover (including litter, lichens and coarse woody debris <2 cm diameter) and soil was measured by destructive sampling.

Important findings Soil organism carbon (SOC) decreased significantly with increased soil depth (p<0.01). Carbon stock contributions of ground cover were similar (3%-4% of the total). The tree layer had the largest plant carbon pool, and root carbon reached 13%-19% of plant carbon. The main carbon stock was in plants in SF and FF and in soil in MF, BF and CF. Ecosystem carbon stock was SF (729.92±43.49) > FF (618.86±53.97) > MF (353.88±21.76) > BF (247.79±17.15) > CF (244.52±18.70) 10³ kgC·hm^-2, and the difference was significant (p<0.05). Plant recent carbon stock potentials were 2.97, 3.80, 5.15, 3.33 and 4.84 10³ kgC·hm^-2·a^-1, respectively. Therefore, the SCFS could play a key role in CO₂sequestration. This provides insight into forest carbon sequestration capacity and, hence, into understanding global carbon balance.

Aims Our objectives were to investigate phenotypic variation of Picea balfouriana in 12 natural populations and to discuss the relationship between phenotypic variation of the natural population and different distribution areas.

Methods We investigated 12 phenotypic traits for 360 individuals in 12 natural populations of P. balfourianafrom Ganzi Tibetan Autonomous Prefecture in Sichuan Province of China and used nested analysis, correlation analysis, cluster analysis, variance analysis and multi-comparison to analyze results.

Important findings There were significant differences in phenotypic variation among and within populations. The mean phenotypic differentiation coefficient (VST) among populations was 36.53%, which was less than that of within populations (63.47%). TheVST of cone, needle, seed scale and seed wing were 47.15%, 31.93%, 21.89% and 45.14%, respectively. In different individuals within populations, the coefficients of variation (CV) for four phenotypic traits (cone, needle, seed scale and seed wing) were 12.56%, 22.16%, 12.61% and 16.53%, respectively. The traits stability of cone were higher than that of other traits. The cone length, cone width, needle length and seed scale length were the most important phenotypic traits that were easy to measure in P. balfouriana. The traits variation of natural populations were affected mainly by longitude (such as cone and needle) and latitude (such as seed scale and seed wing) in spatial distribution. The 12 populations of P. balfouriana investigated could be divided into three groups according to the cluster analysis.

Aims Our objective was to develop theory for design and reestablishment of high-generation seed orchard by discussing the relationships between pollen dispersal distances and genetic composition of seed orchard progeny under open- and control-pollinated situations.

Methods Open- and control-pollinated seeds were collected from two maternal trees. Microsatellites markers (SSRs) were used in paternity analysis. A total of 281 progenies were analyzed, of which the paternity could be accurately identified for just 126. Paternity inference was conducted using CERVUS software.

Important findings Analysis of open-pollinated seeds of two clones, Nos.11 and 24, showed the effective dispersal distance of pollen is within 30 m and the longest dispersal distance is 85 m. 11.1%-12.8% of pollen-father comes within a radius of 10 m from the seed tree, 37.0%-40.4% within 10-20 m and 17.2%-22.2% within a radius of 20-30 m. In order to discover the key factor to selection fertilization, the paternity analysis of control-pollinated seeds for two clones, Nos.11 and 24, was estimated too. Four clones. Nos. 50, 7, 25 and 33, applied 50.62% and 61.54% pollen to control-pollinated seeds collected from two mother trees, but the reason is not yet clear. We analyzed the influence of pollen size, weight and vigor on selection fertilization, but no significant correlation was found. We suggested detailed study of influence of pollen-tube growth rate on selection fertilization.

Aims It is not clear if plants respond phenologically to global warming in desert area, and if they do, what is the pattern of the change? We analyzed phenological data observed from 18 tree species for up to 34 years in the Minqin Desert Botanical Garden. Our objectives were to determine the relationships between plant phenology and air temperature change in the Minqin Desert area.

Methods The trend lines for change in temperature and phonology were linear, the correlation between temperature and phenology was expressed by a relationship coefficient and the significance of the relationship coefficient was examined by the t-test.

Important findings The effect of the prior month’s temperature on phenology was less than that of the current month’s temperature, but more than that of the annual mean temperature. The temperature increase in spring was more obvious in the study area than other parts of the region, which was likely the reason that the local spring phenology had a relatively large advance. The change in plant phenology, particularly in the desert, was not only a response to climate change, but also an adaptation to climate change.

Aims Inter-specific interactions in plant communities can be characterized by their spatial relationships. Because these interactions are usually asymmetrical, i.e., one species exerts more influences on the other, asymmetric spatial patterns should be expected. Our objective was to study how species spatially adapt to arid conditions in four typical arid communities that differed in growth-form composition (tree-grass, shrub-grass, shrub-semishrub and forb-grass).

Methods We selected four representative arid plant communities near Sand Lake in Xidatan, Pingluo County, Ningxia Hui Autonomous Region and measured the position, height and crown diameter of each individual in a 30 m × 30 m plot in each community. We applied the bivariate Ripley’s K function in spatial association analysis and developed a new method named pattern control analysis (PCA) for investigating asymmetric spatial relationships. PCA was derived from the assumption that the controlled species should be distributed around the controlling species regularly at a specific scale. Two simulated community patterns were used to test the new method.

Important findings In communities ofElaeagnus angustifolia-Achnatherum splendens (EA), Nitraria tangutorum-A. splendens (NA) and A. splendens-Sophora alopecuroides (AS), significant positive spatial associations were detected between the dominant species (at scales of 0-15 m, 0-7.5 m and 0-7 m, respectively), and species pairs with positive spatial association significantly differed with each other in growth form. In the community of Reaumuria soongorica-Kalidium foliatum (RK), negative spatial association was detected (at the scale of <15 m) between the two dominant species, which are similar in growth form. Pattern control analysis showed a relationship between the dominant species in the three communities with positive spatial associations at scales of 0-6.5 m, 0-0.65 m and 0-1.5 m in EA, NA and AS, respectively. The pattern-controlling species in each community are larger in size and produced better developed microhabitats. However, no such relationship was detected between the dominant species of similar growth form and comparable microhabitats in RK. Results indicate that certain spatial relationships, especially pattern-controlling relationships, might be mechanisms for adaptation within plant communities. This might help in understanding inter-specific interactions within plant communities.

Aims The objective was to introduce a simplified method called nested regression for quick establishment of allometric models for tree biomass.

Methods Main branches at all orders were used as basic sample units. The biomass of a branch was obtained by summing that of its sub-branches or sub-main branches, either observed or estimated. Thus the span of branch diameter for the equation was extended. The branch was dissected into main braches, and a main branch is the axis of a branch at any order. Biomass equations were established for main branches, branches and individual trees, progressively. By summing the values of main braches, the biomass of a branch in a higher order was obtained.

Important findings Because of data nesting, i.e., small branches were encompassed in their upper-order branches, the measured sample was reduced to a minimum, making the method time- and cost-effective. Satisfactory accuracy of predicted values was shown by testing with observed data.

Aims Caragana tibetica is commonly found in the ecotone between desert steppe and desert of the Inner Mongolian Plateau. It is often used as an indicator species in vegetation regionalization. Due to its dwarf shrub characteristics C. tibetica can easily initiate nebkha (dune) formation in sand-covered habitats. The objective of the present study is to understand C. tibetica ecological adaptability by investigating soil heterogeneity of C. tibetica community.

Methods Nebkhas formed by C. tibetica were classified into three size groups. Small and medium nebkhas corresponded to a development stage, and large nebkhas represented a stable stage. Soil organic mater (SOM), total phosphorus (TP) and water content (W_m) were measured at the top each nebkha, in the middle of the nebkha slope, in the interspace between nebkhas, and under the nebkhas. We then also averaged these properties for each nebkha (mean of top and middle samples).

Important findings Average content of SOM, TP and W_m of nebkhas and the soil underlying them increased with nebkha age. For large and medium nebkhas and the soil underlying them these properties were higher than that in the interspaces between them. Average SOM of small nebkhas was higher than that in the interspace between them. However,average TP and W_m of the soil underlying small nebkhas were lower than in the interspace. At the top and middle of nebkhas of all sizes, SOM and TP first increased and then decreased vertically while W_m decreased gradually. Plant residues content captured by C. tibetica nebkhas increased gradually with nebkha development stage. We conclude that the “fertility island effect” formed inside and below nebkhas increases as nebkhas develop. At the same time, we found that spatial heterogeneity of SOM,TP and W_m is high.

Aims We studied the physiological and ecological characteristics of Salsola collina and S. arbuscula in order to provide a theoretical basis for understanding their physiological and ecological mechanisms of adaptation to their habitats.

Methods We chose representative plants and collected mature leaves for anatomical structure analysis, measured leaf gas exchange parameters under natural conditions in their mixed community and compared drought structures and photosynthetic characteristics of the two species.

Important findings Salsola collina leaves had epidermal hairs and more developed water storage parenchyma. Salsola arbuscula leaves had thicker cuticles with a layer of hypodermal cells under them, and the palisade cells were longer and arranged more densely. The net photosynthetic rate of S. collina was significantly higher than that of S. arbuscula, with daily mean values of 21.5 and 15.7 μmol CO₂·m^-2·s^-1, respectively. The transpiration rate of S. collina was also higher than S. arbuscula, with daily mean values of 14.9 and 10.2 mmol·m^-2·s^-1, respectively. The daily mean values of water use efficiency of S. collina and S. arbuscula were 1.39 and 1.53 μmol CO₂·mmol^-1H₂O, respectively; especially at 14:00, they were 1.61 and 2.30 μmol CO₂·mmol^-1H₂O, respectively,S. arbuscula was 42% higher than S. collina approximately. The light compensation point and CO₂ compensation point of S. collina were lower and its light saturation point and photo-quantum efficiency were higher than S. arbuscula. These findings indicate that the drought structures of the two species are different, and S. arbuscula has more desert plant features. In the community suitable for the growth of both species, the photosynthetic capacity of S. collina was stronger than S. arbuscula, and the water use efficiency of S. arbuscula was higher.

Aims Pyrola dahurica, an indicator of mixed conifer-broadleaved forest, is an important medicinal species in northeastern China. Our objective is to explore the mechanism of cold hardiness for this evergreen species during winter seasons.

Methods We studied changes in Malondialdehyde (MDA), cell membrane relative conductivity and the activities of peroxidase (POD) and superoxide dismutase (SOD) in the leaves of P. dahurica during two periods (November to December 2005 and March to April 2006) in Maoershan, Harbin, China.

Important findings Safe hibernation of P. dahurica depends on two critical periods, early stage of snow cover (ESSC: November to December in 2005) and late stage of snow cover (LSSC: March to April in 2006). ESSC extends from the beginning of snow cover to the peak of snow cover, and LSSC extends from the early to late stage of snow thaw. MDA content, cell membrane relative conductivity, and SOD and POD activity increased during the period of snow accumulation. Entering the peak period of snow cover, these same factors decreased as the temperature became higher and more constant under the snow. In the early stage of snow thaw in spring (March 1 to 15), temperature decreased and the MDA content increased, cell membrane relative conductivity increased to a higher level than in the period of snow accumulation and SOD and POD activities increased but were lower than in the period of snow accumulation. During the late stage of snow thaw (middle March), MDA content, relative conductivity of cell membrane and SOD and POD activity decreased.

Aims Lobelia chinensis(Campanulaceae), a perennial herbaceous creeper that grows mainly on riverbanks or wet farmland in central and southern China, is characterized by stamen fusion. The anthers of its five stamens are fused tightly into a tube in which the stigma and style are packed, and the filaments are also fused at the upper parts, forming a column-like structure surrounding the pistil. The objective was to elucidate the adaptive significance of this growth pattern, the floral syndrome and breeding system using anatomical analyses, pollination surveys and bag experiments.

Methods Flowers were observed at different developmental stages to determine the growth patterns of each floral part, especially morphologies of sexual organs, dichogamy and numbers of pollen grains and ovules, and their possible changes in spatial position and morphology. Pollination surveys were conducted to find the primary floral visitors. Bag experiments were conducted to determine self-compatibility, autogamy and apomixy. These studies would reveal the breeding system.

Important findings Flower diameter was >1 cm. The lower parts of perianth were fused into an open tube. The stigma and style were enclosed in the anther tube and the united parts of filaments. The flower was protandrous, and the pollen grains were released into the anther tube and dropped on the stigma surface. Growth of the style sent the stigma out of the anther tube 1 or 2 days after opening and then it became receptive. The main floral visitors were ants, hoverflies and flies. The pollen-ovule ratio (P/O) was <100, suggesting facultative autogamy, but the outcrossing index suggested the breeding system is outcrossing with partial self-compatibility and a pollinator is needed. Bag experiments indicated no apomixy and no spontaneous autogamy, but self-compatibility. The species largely outcrossed but suffered pollen limitation in field. The low P/O in this stamen-fused species might be due to the higher siring probability of individual pollen grains resulting from the accumulation and collective pollination of pollen, a similar mechanism to pollen aggregation such as pollinia, tetrads and viscin threads. The correlation of stamen fusion with perianth tube, dichogamy and low pollen-ovule ratio in this and other anther-fused species suggested that these floral traits probably formed a floral syndrome adaptive for small pollinators.

Aims The Yangtze River Estuary (YRE) is a complex aquatic system, and large environmental gradients and complicated hydrological conditions make the vertical pattern of chlorophyll a perplexing. Our aims are to 1) describe the vertical profile of chlorophyll a and 2) analyze the environmental factors impacting the vertical pattern.

Methods Four seasonal, multidisciplinary cruises were carried out from September 2005 to May 2006 in YRE and its adjacent waters. Chlorophyll a concentration was determined fluorometrically (Parsons et al., 1984) by means of Turner Fluorometry Model 10 (Turner Designs Inc.). Seawater temperature and salinity were measured in situ by YSI 6100 probes (Y. S. I., Inc.). Nitrate, phosphate and silicate were analyzed spectrophotometricly (Valderrama, 1981).

Important findings Chlorophyll a concentration was the highest in spring and lowest in winter. High chlorophyll a occurred in the low-salinity area or the salinity front. In upper estuary and adjacent sea, chlorophyll a concentration showed slight vertical fluctuations, due to sufficient vertical water exchange. In the plume zone characteristic of water stratification, chlorophyll a was much more concentrated in the upper water column. Skeletonema costatum determined the vertical profile of phytoplankton cell abundance, which correlated well with that of chlorophyll a. Ample nutrients from the water of the Yangtze River stimulated the growth of phytoplankton; nevertheless, low nutrients and weak solar radiation in high-salinity seawater restrained the accumulation of phytoplankton biomass.

Aims Our objective was to study the relationships between the distribution of Crofton weed (Eupatorium adenophorum) seeds in soil and the destiny of seedlings in order to help prevent the continued spread and to control the weed.

Methods We collected soil seed banks of Crofton weed in orchards and grazed and ungrazed shrublands (a gradient of decreased disturbance) in Panzhihua Prefecture, Sichuan Province, China, to determine seed distribution patterns in the soil. We also tested the effects of sowing depth and light intensity on seedling recruitment and establishment.

Important findings In orchard and grazed and ungrazed shrublands, the proportion of the seed bank in deeper layers of the soil was 56.44%, 46.96% and 24.86% (p=0.006), respectively. Therefore, the greater the disturbance, the higher the percentage of seeds deeper in the soil. Seeds of Crofton weed planted at 0, 1 and 5 cm depths of soil germinated at rates of 64.67%, 22.67% and 13.33%, respectively, revealing germination rates decrease with soil depth. The mortality of seedlings germinated from 0, 1 and 5 cm depths were 27.95%, 0 and 0, respectively, showing that seedlings germinated from the seeds on the surface have higher mortality. Mortality of seedlings that grew under three different light intensities (full light, half-shade and all shade) were 72.15%, 30.38% and 4.87%, respectively, indicating that shade can reduce mortality (p=0.00) and sunlight might be an important factor in seedling mortality. These results imply that disturbance from human activities could favor seeds lying in deeper layers of the soil seed bank by enabling these seeds to have higher efficiency of seedling establishment despite a lower germination rate. Therefore, human activities can promote the invasion of Crofton weed and limit control of the invasion.

Aims Pot experiments were conducted to investigate effects of water deficit and duration of the deficit (0, 15, 36 and 14 days recovery) on four hybrid Populus: 15-29 (P. trichocarpa × P. deltoids), DN-2 (P. deltoids × P. nigra), DN-14274 (P. deltoids × P. nigra) and R-270 (P. deltoids × P. nigra). Our objective was to examine the responses of Populus plants to soil water deficit by analyzing eco-physiological, morphological, and growth characteristics, as well as several parameters of plant performance.

Methods Seedlings were exposed to four treatments: 100%, 70%, 50% and 30% of soil field water capacity (treatments T1-T4, respectively).

Important findings The four hybrids were sensitive to water deficit. All developed physiological adaptive mechanisms as well as configurational strategies to cope with water shortages to different degrees by closing stomata and reducing leaf number and leaf area to regulate water loss, by depressing net photosynthetic rate (P_n), transpiration rate (T_r) and leaf water potential (ψ) to enhance water use efficiency (WUE), or by changing allocation of biomass productivity (B_p). Under water stress, R-270 only decreased its leaf dry weight but the other three hybrids decreased their dry weight of leaf, stem and root. With declining soil moisture, root/shoot of 15-29 and R-270 increased, implying the roots obtained more carbohydrates, which favors water absorption. Carbon isotope composition (δ¹³) of DN-2 was significantly positively correlated to WUE, but δ¹³ of R-270 was significantly negatively correlated to WUE. P_n, stomatal conductance (G_s), T_r,ψ, biomass and canopy areas of the seedlings in T1 and T2 are higher than those in T3 and T4, suggesting that the four hybrids can obtain high production in arid areas under sufficient-moderate irrigation. LowerP_n, G_s, T_r,ψ, biomass, canopy areas and higher WUE of the seedling in T3 and T4 indicate that the four hybrids can develop survival strategies under water stress, but biomass production was negatively affected. Clone 15-29 and R-270 showed a stronger adaptive response than DN-2 and DN-14274 under water stress, implying they have greater drought-resistance ability.

Aims Soil depth and fertilizer application affect soil biological properties. A few studies in China have focused on the influence of soil depth and long-term fertilizer application on microbial activity. Our objective was to study changes in microbial activity in different soil layers under 28-year fertilizer treatments in wheat (Triticum aestivum) field soil to provide basic data on microbial activity and structure and function of farmland ecosystems.

Methods In 1978, six different treatments were established in the Gaoping Agricultural Experimental Station in Pingliang, Gansu Province of China for an experiment on long-term fertilization and wheat-maize rotation. We chose two treatments, no fertilizer application treatment (CK) and mineral fertilizer plus manure application treatment (MNP). The amount of fertilizer per year was 75 000 kg∙hm^-2 manure, 90 kg∙hm^-2 N, and 75 kg∙hm^-2 P. Five soil layers were sampled in both treatments: 5-15, 15-20, 25-30, 35-40 and 45-50 cm. The microbial activity of the different soil layers and the effect of fertilizer on its vertical distribution were determined with microcalorimetry. All experiments were repeated three times. Analysis was done using integrative method combining correlation and component analyses in SPSS.

Important findings With an increase of soil depth, the number of bacteria colonies decreased. This was negatively correlated with P_t values, which indicates time from the growth of microbes to the peak. Thermal power-time curves changed from steep to flat and from regular to irregular, shoulders were shorter and peak height lower. The microbial growth rate constant µand the peak height P_hvalues in different soil layers also varied significantly, and both decreased with increased soil depth. There were different kinds of curve shapes in CK and MNP, particularly in the former two layers of soil samples. Curves of MNP were steeper than for CK, and their shoulders before the peak were significantly much shorter. The P_h and μ values of MNP were greater than for CK, and the P_tvalues of MNP were less than for CK.

Aim Our objective was to study effects of nitrogen on drought resistance in terms of changes in root development and activity of water-stressed cotton plants.

Methods We studied short-term water stress using pot experiments by withholding water for eight days and then watering for ten days at Nanjing Agricultural University in 2005 and 2006. Cotton plants were grown at three nitrogen levels (0, 240 and 480 kg N·hm^-2).

Important findings Soil relative water content decreased with increasing N supply during the soil water stress period, while dry matter production and N accumulation increased. The root/shoot ratio and root-N/ shoot-N ratio increased with water stress and were smallest at 240 kg N·hm^-2. Application of N increased the activities of peroxidase (POD) and catalase (CAT) of roots, but decreased superoxide dismutase (SOD) activity during water stress as well as during recovery. Malondialdehyde (MDA) content significantly (p<0.05) increased and was smallest in the 240 kg N·hm^-2 treatment during water stress. On the 10th day after soil watering, MDA content at 240 kg N·hm^-2was similar to that at 480 kg N·hm^-2, but was less than that at 0 kg N·hm^-2. Root vigor, which was adversely affected by water stress, was highest at 240kg N·hm^-2. After soil watering, N application promoted root vigor. Trends of net photosynthetic rate were the same as those of root vigor during water stress. These results suggest that appropriate N supply (240 kg N·hm^-2 in this investigation) may contribute to drought resistance of cotton plants by adjusting the antioxidant enzyme activities of roots, decreasing lipid peroxidation and boosting root vigor during water stress; however, excessive N supply (480 kg N·hm^-2) had a deleterious effect on plant drought resistance.

Volatilization of nitrogenous compounds from above-ground plant parts is an important pathway for nitrogen losses and also an effective approach for increasing atmospheric NH₃ and N₂O. Therefore, the study of nitrogen losses from above-ground plant parts is meaningful for both atmospheric environment and nitrogen use efficiency in agriculture. We review research progress on various forms of volatilization of nitrogenous compounds (NH₃, NO, NO₂, N₂O and N₂) and their mechanisms. The main factor for volatilization of nitrogenous compounds was imbalance between active nitrogen accumulation and assimilation in plants. Active nitrogen accumulation in plants can result from light density, temperature, water, fertilizer, air conditions, plant physiological disease, aging and other factors, but whether nitrogen losses occurred from above-ground plant parts is also significantly related to partial pressure of gaseous nitrogenous compounds between intercellular spaces and the atmosphere—the various forms of nitrogenous compounds compensation point. NH₃ and N₂O are the main forms of nitrogenous compounds lost from above-ground plant parts, and the main nitrogen losses occurred in late stages of growth, but the responses of different forms of volatilized nitrogenous compounds to stages of growth are not identical. We summarize the mechanism of volatilization of nitrogenous compounds and indicate key problems that need to resolved: 1) the relationship among different forms of nitrogenous compounds losses and the mechanism are not fully explained by present research, particularly the mechanism of enzyme-catalyzed coordination; 2) the exchange of nitrogenous compounds (including absorption and release) and its mechanism is not entirely clear, so it is difficult to assess nitrogen losses from above-ground plant parts; 3) present research implied that the senescence of plants resulted in a increase in volatilization of nitrogenous compounds, but its physiological mechanism is unclear; and 4) there is no technique to reduce losses of nitrogenous compounds from above-ground plant parts; therefore, volatilization of nitrogenous compounds from N fertilization can not be controlled and nitrogen use efficiency in agriculture can not be promoted by such control.