Aims In arid and semiarid regions, precipitation is the most important water source for plants. Our objective was to investigate the water-use strategies of two dominant desert plants along a precipitation gradient in northwestern China.

Methods We determined stable hydrogen and oxygen isotope compositions of the stem water from Artemisia ordosicaand Nitraria tangutorum and potential water sources (rain water, groundwater and soil water) at three study sites with different annual precipitation (Hanggin Banner and Dengkou County of Inner Mongolia Autonomous Region and Minqin County of Gansu Province). The IsoSource model was then used to calculate probable contributions of potential water sources to total plant water uptake. We also determined foliar carbon isotope ratios and free proline contents of both species to indicate water use efficiency and osmotic-adjustment ability.

Important findings At the Hanggin Banner site (highest annual precipitation), both species obtained the highest proportion of water from shallow soil water and A. ordosicatook up water mostly from the 0-50 cm soil layer. However, they depended mainly on deep soil water or groundwater at the Dengkou and Minqin sites with lower annual precipitation. The water use efficiency of both species decreased with increasing annual precipitation. There was a positive correlation between carbon isotope ratio and free proline content in A. ordosica. These results suggest that desert plants can adjust their capabilities for up-take from different water sources and other physiological properties with variation in natural precipitation, but the strategies are species-specific.

Aims Our purpose was to study the effects of deposition of nitrogen (N) on plant carbon (C), N, phosphorus (P), N and P nutrient resorption efficiencies, C : N : P stoichiometry and their internal relations on Stipa bungeanaof Loess Plateau natural grassland.

Methods Deposition of N was simulated by N fertilization at four levels. Changes of C, N and P contents were detected, and C : N : P and the N and P nutrient resorption efficiencies were estimated for S. bungeana.

Important findings The C and N contents of leaves and N and P contents of standing litter increased significantly with N addition. However, the P content of leaves and C content of standing litter did not response to N addition. The N and P resorption efficiencies of S.bungeana decreased significantly with N addition. When there was no N addition, N and P resorption efficiencies were highest (60.35% and 71.75%, respectively). Meanwhile, the P resorption efficiency was greater than that of N in same treatment. The C : N ofS. bungeana decreased gradually with N addition, but the N : P and C : P increased with N addition. Values of the N : P were 18.25-29.01. The results showed the Loess Plateau natural grassland was mainly limited by P, and the strength of P limitation was enhanced with N deposition. Higher N and P resorption efficiencies were an important strategy for S. bungeana to survive soil infertility.

Aims Changes in atmospheric nitrogen (N) and precipitation are two important aspects of global climate change. They have altered biogeochemical cycling in ecosystems and are expected to affect plant nutrient use strategy and litter decomposition.

Methods We used three pot experiments, i.e., N addition (0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0 and 128.0 g N∙m^-2), phosphorus (P) addition (same levels) and water addition (3 600, 3 900, 4 500, 5 100, 6 000, 7 200, 9 000, 12 000, 18 000 and 36 000 mL∙pot^-1), to study N and P concentrations and C : N and C : P in senescing leaves of Leymus chinensis.

Important findingsN addition increased N concentration and decreased C : N, but did not significantly affect P concentration and C : P. P addition increased N and P concentrations and decreased C : N and C : P. Water addition decreased N and P concentrations and increased C : N and C : P. Therefore, changes in N, P and water availabilities affect litter decomposition quality and have effects on nutrient cycling in the plant-soil ecosystem.

Aims Our objective was to construct and use a Ryel model to quantify hydraulic redistribution of Populus euphratica, a species in desert riparian vegetation.

Methods We constructed a Ryel model to estimate the amount of net water redistribution under the canopy of P. euphratica. We based the model on data from studies measuring the shape and distribution of roots under the canopy of P. euphratica and observing values for volumetric water contents (θ_s), saturated hydraulic conductivity (K_s), maximum radial soil-root conductance of the entire active root system for water (C_RT), soil water potential (ψ_i) and residual volumetric water contents (θ_r) in five soil layers. We used this model to make a short-term simulation of root hydraulic redistribution in different seasons.

Important findings Hydraulic redistribution under the canopy of P. euphratica reached a maximum at 2:30 am. The amount of net water redistribution under the canopy decreased and moved towards the underlying soil with changes in the growing season. In June, hydraulic redistribution mainly occurred in the 0-40 cm soil layer, the maximum amount of redistribution was 0.022 0 cm and the total at night was up to 0.111 0 cm. In August, hydraulic redistribution mainly occurred in the 10-70 cm soil layer, the maximum amount of redistribution was 0.006 5 cm and the total at night was up to 0.018 4 cm. In October, hydraulic redistribution mainly occurred in the 70-100 cm soil layer, the maximum amount of redistribution was 0.003 9 cm and the total at night was up to 0.008 6 cm.

Aims A new drought-resistance farming technology of double ridges and furrows mulched with plastic film and furrow planting (PMF) is widely applied on rain-fed agriculture in the middle and eastern part of Gansu Province, China, to increase crop yield and water use efficiency. However, its impacts on seasonal and annual soil water dynamics are not well understood. Our objectives were to (a) investigate seasonal and annual changes in soil water content, corn yield and water use efficiency of different mulching methods and (b) evaluate the ecological impact of PMF on rain-fed cropland in semi-arid areas.

Methods We studied three treatments: PMF, whole field surface sand mulching and flat planting (SM) and uncovered and flat planting (CK). Using oven-drying and neutron-probe methods, we observed soil water in the 0-200 cm layer from 2009 to 2010.

Important findings PMF could improve soil water storage in the 0-200 cm layer significantly before corn jointing and improve corn development in the early growth period. With corn growth, there was a significant difference in water consumption among the three treatments in the sequence PMF > SM > CK. Conversely, the sequence of change of soil water storage was CK > SM > PMF. Under the same precipitation, soil water restoration depth of PMF was deepest and CK was shallowest (in the 0-200 cm soil layer). The quantity and depth of soil water consumption increased with increases of corn planting years in PMF treatment, e.g., depth of water consumption deepened from 20-120 cm to 120-200 cm from 2009 to 2010. After two years of continuous cropping of corn, soil water content in the 40-120 cm layer was <9.0% in all three treatments, the soil water content of PMF treatment decreased to 7.9% (which is close to the wilting coefficient of 7.2%) and corn development depended on rainfall in the growing season. This indicates that continuous corn cropping with PMF would result in a dry soil layer in semiarid areas. Water consumption, corn yield and water use efficiency were highest in PMF treatment, but lowest in CK in both years. Therefore, PMF could improve corn yield significantly, but continuous cropping may result in significant reduction of soil water storage and was disadvantageous to sustainable development capacity of cropland.

AimsArtemisia wellbyi, A. younghusbandii and Sophora moorcroftiana are the major psammophyte populations on the aeolian desertified land in the riparian ecotone of the middle reaches of the Yarlung Zangbo River. Our objectives were to determine how spatial scales are related to population patterns and how species spatially adapt to semi-arid conditions in the riparian ecotone, as well as to provide theoretical foundation for vegetation restoration on sand dunes in the study area.

Methods We selected four representative plant communities under different habitat conditions in the riparian ecotone, measured the position, height and crown diameter of each individual in a 20 m × 30 m plot and studied the population structure, spatial distribution and association of these psammophyte populations using point pattern analysis.

Important findings The population structure of A. wellbyi on semi-exposed sandy gravel land and semi-fixed sandy land is that of a growing population, while A. younghusbandii and S. moorcroftiana on fixed sandy land both have the structure of a declining population. Artemisia wellbyi and A. younghusbandii both have a clumped distribution at different scales, while the distribution pattern of S. moorcroftiana changed from clumped to random to clumped to random as the scale increased. Spatial distribution is mainly determined by the smaller size classes, while fluctuations or changes of population distribution are mainly determined by the larger size classes. There is a scale effect among the studied populations, and positive spatial association occurs mainly at certain scales. Spatial association is often affected by plant size and environmental heterogeneity. The spatial association of A. wellbyi and S. moorcroftiana on semi-exposed sandy gravel land or semi-fixed sandy land changes from independent to positive to independent to positive. The spatial association of A. wellbyi and Oxytropis sericopetala on semi-exposed sandy gravel land changes from positive to independent to positive to independent to negative, and that of A. younghusbandiiand S. moorcroftiana changes from positive to independent. The degree of aggregation weakens with increasing plant size. The smaller size class has a clumped distribution, and the larger has a random distribution or random and clumped. The positive spatial association between different size classes of the same species appears to weaken when the difference of plant size becomes greater and even changes into negative spatial association, while the spatial association of various size classes at a smaller scale often is positive or independent.

Aims Our objectives were to determine the feasibility of estimating nitrogen content in fresh and dry wheat leaves using near-infrared (NIR) spectroscopy and chemometrics and to establish the near-infrared model for estimating nitrogen content in wheat leaves in order to lay a foundation for wheat nitrogen management.

Methods We conducted three field experiments with different years, wheat varieties and nitrogen rates and determined time-course near-infrared absorbance spectroscopy and total nitrogen content from fresh and dry wheat leaves. The methods of partial least squares (PLS), back-propagation neural network (BPNN) and wavelet neural network (WNN) were used to establish the calibration models, and a dataset selected at random was used to evaluate the established models.

Important findings Near infrared calibration models based on PLS, BPNN and WNN could be used to estimate nitrogen content in wheat leaves with high precision and stable performance, especially WNN. The validation results showed that the root mean square errors of prediction (RMSEP) for the power model are 0.147, 0.101 and 0.094, respectively, while those for the fresh leaves model are 0.216, 0.175 and 0.169, respectively. The correlation coefficients (R²) for all models are >0.84. Therefore, near-infrared spectrometry can be an efficient method to estimate the nitrogen nutrition of crops.

Aim Estimating regional variation in vegetation phenology from time-series remote sensing data is important in global climate change studies. However, there are few studies on vegetation phenology for the Qinghai-Tibet Plateau and most are based on field records of stations.

Methods We utilized the dynamic threshold method to explore vegetation phenological metrics (greenup date, length of season and senescence date) of typical grassland in the Northern Tibetan Plateau. We used time-series TERRA/MODIS EVI data for 2001-2010 reconstructed by the asymmetric Gaussian function fitting method to analyze spatial pattern and differentiation of vegetation phenology and its inter-annual variation and to examine the relationship between phenological variation and climate changes.

Important findings The spatial pattern of date of vegetation greenup was embodied by transition from southeast to northwest and vertical zonation in the mountainous topography of the southeast. The vegetation greenup date in approximately sixty percent of the northern Tibetan Plateau had advanced, especially in high mountains. Inter- annual variation of vegetation senescence date was not obvious, and most of the region had natural inter-annual fluctuations. The variation of growing season length is influenced by greenup and senescence dates, but was chiefly affected by advanced greenup date lengthening the growing season. Among the four different climatic zones in the study area, the mountain and valley Nagqu sub-arctic and sub-humid zone and the southern Qinghai sub-arctic and semi-arid zone had the most apparent advanced greenup date and prolonged growing season. Based on measured data from weather stations, increased temperature appears to be a critical factor contributing to earlier greenup and prolonged growing season; however, the relationship between precipitation fluctuations and phenological variation was unclear.

Aims A pot experiment to examine the effects of clonal integration on growth of the stoloniferous herb Centella asiaticasuffering from heterogeneous heavy metal Cd²⁺stress was conducted to address two questions: (1) does clonal integration alleviate the negative effects on growth of clonal plants suffering from heterogeneous heavy metal stress; and (2) do the ramets growing in unfavorable microhabitats incur increased photosynthetic efficiency in the connected ramets?

Methods Relatively young, distal ramets of C. asiatica were assigned to normal or Cd²⁺ stressed soil, and the stolon connections between the relatively old proximal ramets and the young distal ramets were either severed or left intact. The net photosynthetic rate (P_n), chlorophyll fluorescence (maximum quantum yield of PSII, F_v/F_m) and chlorophyll contents of distal ramets and P_n of proximal ramets were measured. The growth performance of distal and proximal ramets was investigated at the end of the experiment.

Important findings Cd²⁺stress treatment significantly decreased the P_n, F_v/F_m, chlorophyll contents and growth of distal ramets. Clonal integration significantly alleviated the negative effect of Cd²⁺stress to distal ramets in terms of P_n, F_v/F_m, chlorophyll contents and biomass of distal ramets. There was no significant cost to the connected proximal ramets, and clonal integration did not incur increased photosynthetic efficiency in the proximal ramets. In addition, clonal integration significantly decreased root to shoot ratio of distal ramets suffering from Cd²⁺stress, and reduced the uptake of the heavy metal. Petiole length of proximal and distal ramets was not significantly affected by stolon severing and Cd²⁺stress. It is suggested that clonal integration may enhance growth of clonal plants suffering from heterogeneous heavy metal stress.

Plants are a key biological component in the controlled ecological life support system at low atmospheric pressure. Both total pressure and partial pressure (of oxygen, carbon dioxide, etc.) are reduced at low atmospheric pressure. Plants can complete their life cycle (from seed to seed) at low pressure, but their course of development is different from that at normal pressure, in adapting to changed atmospheric conditions. We summarized the effects of low pressure on seed germination, morphology, leaf structure, growth characteristics, nutrient uptake, plant nutrition, gas exchange and ethylene release. In addition, we summarized signal transmission and gene express induced by low pressure and discussed the latest research advances on growth characteristics and adapting mechanisms of plants at low atmospheric pressure. We also suggested future emphases and directions of study of plants at low atmospheric pressure.

An encyclopedia of Chinese vegetation is going to be compiled as a series of books, and comments are sought to revise the “Vegetation Classification System of China” (VCSC). These require several key decisions. First, the principle of VCSC proposed by Vegetation of China (1980) that “the higher rank of classification unit would be based on the physiognomy of vegetation, while the middle and lower rank emphasized on species composition and community structure” should be maintained because it is corresponding with the current trends of international vegetation classifications. Second, VCSC should classify Chinese vegetation to be compatible with global vegetation classification, so that the terms and concepts will be widely accepted internationally. Third, “Association”, a fundamental classification unit described by the series of books of Chinese vegetation, should be defined and used consistently, so that misunderstandings between northern and southern associations can be avoided. Fourth, the hierarchy in the classification of vegetation generally should be rigid, but different ranks remain open and flexible, i.e., upper-level units can be supplemented to meet future needs. A draft of the VCSC (from class to vegetation type) is proposed in this paper.