Lin XW Zhang ZH Wang SP et al.. Response of ecosystem respiration to warming and grazing during the growing seasons in the alpine meadow on the Tibetan plateau. Agricultural and Forest Meteorology 2011 151(7): 792-802. (IF 3.2238 农林科学， 一区）

Abstract

    Intensive studies reveal that there is much uncertainty regarding how ecosystem and soil respiration will respond to warming and grazing especially in the alpine meadow ecosystem. We conducted a first of its kind field-manipulative warming and grazing experiment in an alpine meadow on the Tibetan plateau to determine the effects of warming and grazing on ecosystem and soil respiration for 3-years from 2006 to 2008. Generally warming and grazing did not affect seasonal average ecosystem respiration (Re) and there was no interaction between grazing and warming. However they significantly affected the Re early in the growing season and by the end of the growing season. Warming significantly increased seasonal average soil respiration (Rs) by 9.2% whereas the difference mainly resulted from data gathered early in the growing season before June 2007. Positive correlations between soil temperature and Re and Rs were observed and soil temperature explained 63-83% of seasonal Re variations during the 3-year study and 19-34% of Rs variations in 2007. Seasonal Re in 2008 and Rs in 2007 were slightly negatively correlated to soil moisture but interannual average Re decreased with a decrease in precipitation for all treatments. Warming and grazing reduced the Q(10) value of Re in 2007 and 2008 but did not affect the Q(10) value of Rs. The Q(10) values of Rs were much lower than the Q(10) values of Re in 2007. These results suggest that grazing may reduce the temperature sensitivity of Re and that Re was mainly controlled by soil temperature rather than moisture which varied with timescale in the alpine meadow.

Tang JL McDonald S Peng XH et al.. Modelling Cryptosporidium oocysts transport in small ungauged agricultural catchments. Water Research 2011 45(12): 3665-3680. (IF 4.546 环境科学，二区Top）

Abstract

    Cryptosporidium is an environmentally robust pathogen that has caused severe waterborne disease outbreaks worldwide. The main source of zoonotic Cryptosporidium parvum oocysts in human drinking water is likely to be from farm animals via catchment pathways with water as the main transport vector. The vast majority of small agricultural catchments are ungauged therefore it is difficult to use a process model to predict and understand the mechanisms and activities that regulate the risk of surface water contamination from agricultural areas. For this study two ungauged agricultural catchments in Ireland were used to model Cryptosporidium oocyst transport using SWAT2005 on a daily basis with reference data from adjacent catchment gauging stations. The results indicated that SWAT2005 could simulate stream flow with good agreement between prediction and observation on a monthly basis (R² from 0.94 to 0.83 and E (efficiency) from 0.92 to 0.66) but Cryptosporidium oocyst concentration results were less reliable (R² from 0.20 to 0.37 P < 0.05; with poor E −0.37 to −2.57). A sensitivity analysis using independent parameter perturbation indicated that temperature was the most important parameter regulating oocyst transport in the study catchments and that the timing of manure application relative to the occurrence of water runoff event was critical. The results also showed that grazing management had little influence on predicted oocyst transport while fields fertilized with manure were the key critical source areas for microbial contaminations in the study catchments. It was concluded that the approach presented could be used to assist with understanding the epidemiology of waterborne cryptosporidiosis outbreaks and to improve catchment management for the safety of the general public health.

Zhu TB Zhang JB Cai ZC. The contribution of nitrogen transformation processes to total N(2)O emissions from soils used for intensive vegetable cultivation. Plant and Soil 2011 343(1-2): 313-327. (IF 2.773 农林科学，一区）

Abstract

    The rapid expansion of intensively farmed vegetable fields has substantially contributed to the total N₂O emissions from croplands in China. However to date the mechanisms underlying this phenomenon have not been completely understood. To quantify the contributions of autotrophic nitrification heterotrophic nitrification and denitrification to N₂O production from the intensive vegetable fields and to identify the affecting factors a ¹⁵N tracing experiment was conducted using five soil samples collected from adjacent fields used for rice-wheat rotation system (WF) or for consecutive vegetable cultivation (VF) for 0.5 (VF1) 6 (VF2) 8 (VF3) and 10 (VF4) years. Soil was incubated under 50% water holding capacity (WHC) at 25°C for 96 h after being labeled with ¹⁵NH₄NO₃ or NH₄¹⁵NO₃. The average N₂O emission rate was 24.2 ng N kg⁻¹ h⁻¹ in WF soil but it ranged from 69.6 to 507 ng N kg⁻¹ h⁻¹ in VF soils. Autotrophic nitrification heterotrophic nitrification and denitrification accounted for 0.3–31.4% 25.4–54.4% and 22.5–57.7% of the N₂O emissions respectively. When vegetable soils were moderately acidified (pH 6.2 to  ≥ 5.7) the increased N₂O emissions resulted from the increase of both the gross autotrophic and heterotrophic nitrification rates and the N₂O product ratio of autotrophic nitrification. However once severe acidification occurred (as in VF4 pH ≤ 4.3) and salt stress increased both autotrophic and heterotrophic nitrification rates were inhibited to levels similar to those of WF soil. The enhanced N₂O product ratios of heterotrophic nitrification (4.84‰) autotrophic nitrification (0.93‰) and denitrification processes were the most important factors explaining high N₂O emission in VF4 soil. Data from this study showed that various soil conditions (e.g. soil salinity and concentration of NO₃^– or NH₄⁺) could also significantly affect the sources and rates of N₂O emission.

Wang HY Shen QH Zhou JM et al.. Plants use alternative strategies to utilize nonexchangeable potassium in minerals. Plant and Soil 2011 343(1-2): 209-220. (IF 2.773 农林科学，一区）

Abstract

    Plant species differ in their capacity to use nonexchangeable potassium (NEK) in soils. In this study two typical plants with high K use efficiency ryegrass and grain amaranth were compared with regard to their capacity to use K from five K-bearing minerals. Biomass relative yield and K uptake data indicated that ryegrass was much more efficient than grain amaranth at using NEK in minerals. Root exudates of grain amaranth collected under hydroponic culture contained considerable amounts of oxalic and citric acids while these acids were not detected in ryegrass root exudates. Compared with grain amaranth the kinetic parameters of K uptake by ryegrass roots were characterized by a significantly higher K uptake rate (V_max) and a significantly lower C_min the minimum external K concentration at which K is taken up. The dynamic release of NEK from minerals in various solutions showed that the release rate of NEK was largely K-concentration dependent and some thresholds of K concentration prevented further NEK release from minerals. The K thresholds were related to mineral type and increased in the presence of Ca²⁺ or Na⁺ in solutions. The positive effect of H⁺ (20 mmol L⁻¹) on NEK release was also mainly attributed to elevating the thresholds of K concentration rather than to the effects of weathering. The results indicated that the main mechanism by which plant species efficiently use NEK in minerals was to the capacity of plants to absorb K at low concentrations. The lower the C_min for the root K uptake the higher the expected NEK use efficiency of the plant.

Huang P Zhang JB Zhu AN et al.. Atmospheric deposition as an important nitrogen load to a typical agroecosystem in the Huang-Huai-Hai Plain. 1. Measurement and preliminary results. Atmospheric Environment 2011 45(20): 3400-3405. (IF 3.226 环境科学，二区Top）

Abstract

    Atmospheric nitrogen (N) deposition has been widely considered as an important N input into agroecosystems but its measurement involves considerable uncertainties with various methods. In this study a field sampler with distilled water as a surrogate surface was developed and trialed for the collection of dry and wet N deposition. The direct measuring results were compared with the value calculated by the N mass balance method (crop N uptake from plots receiving no N fertilizers of the long-term fertilization experiment in the monitoring station). The results indicated that exposure durations of 3–5 days and water volumes of 2000–2800 ml were tested to be suitable to collect dry N deposition while water volumes of less than 1000 ml and sampling conducted immediately after rain event were found to be appropriate for wet N collection under the present experimental conditions. The monitoring work was conducted from June 2008 to May 2009 and annual N deposition totaled up to 40.32 kg N ha⁻¹ of which dry deposition accounted for 62.45%. NH₄–N was the dominant species in N deposition and contributed 62.68% and 66.00% to wet and dry deposition respectively. Organic N (O-N) was found to make greater contributions than NO₃–N in both dry and wet depositions. Total N deposition was parallel to the results estimated by the method of mass N balance from the long-term experiment as 45.6 kg N ha⁻¹. These results provide helpful knowledge to elucidate the N deposition scenario of a typical agroecosystem and can be of great importance for the calculation of fertilizer recommendations in the Huang-Huai-Hai Plain.

Kopittke PM Kinraide TB Wang P et al.. Pb Rhizotoxicities in Cowpea (Vigna unguiculata) as Related to Ion Activities at Root-Cell Plasma Membrane Surface. Environmental Science & Technology 2011 45(11): 4966-4973. (IF 4.827 环境科学，二区Top）

Abstract

    Cations such as Ca and Mg are generally thought to alleviate toxicities of trace metals through site-specific competition (as incorporated in the biotic ligand model BLM). Short-term experiments were conducted with cowpea (Vigna unguiculata L. Walp.) seedlings in simple nutrient solutions to examine the alleviation of Cu and Pb toxicities by Al Ca H Mg and Na. For Cu the cations depolarized the plasma membrane (PM) and reduced the negativity of ψ₀^o (electrical potential at the outer surface of the PM) and thereby decreased {Cu²⁺}₀^o (activity of Cu²⁺ at the outer surface of the PM). For Pb root elongation was generally better correlated to the activity of Pb²⁺ in the bulk solution than to {Pb²⁺}₀^o. However we propose that the addition of cations resulted in a decrease in {Pb²⁺}₀^o but a simultaneous increase in the rate of Pb uptake (due to an increase in the negativity of E_msurf the difference in potential between the inner and outer surfaces of the PM) thus offsetting the decrease in {Pb²⁺}₀^o. In addition Ca was found to alleviate Pb toxicity through a specific effect. Although our data do not preclude site-specific competition (as incorporated in the BLM) we suggest that electrostatic effects have an important role.

Zhang YP Wang F Yang XL et al.. Extracellular polymeric substances enhanced mass transfer of polycyclic aromatic hydrocarbons in the two-liquid-phase system for biodegradation. Applied Microbiology And Biotechnology 2011 90(3): 1063-1071. (IF 3.242 农林科学，一区）

Abstract

    The objective was to elucidate the role of extracellular polymeric substances (EPS) in biodegradation of polycyclic aromatic hydrocarbons in two-liquid-phase system (TLPs). Therefore biodegradation of phenanthrene (PHE) was conducted in a typical TLPs—silicone oil–water—with PHE-degrading bacteria capable of producing EPS Sphingobium sp. PHE3 and Micrococcus sp. PHE9. The results showed that the presence of both strains enhanced mass transfer of PHE from silicone oil to water and that biodegradation of PHE mainly occurred at the interfaces. The ratios of tightly bound (TB) proteins to TB polysaccharides kept almost constant whereas the ratios of loosely bound (LB) proteins to LB polysaccharides increased during the biodegradation. Furthermore polysaccharides led to increased PHE solubility in the bulk water which resulted in an increased PHE mass transfer. Both LB-EPS and TB-EPS (proteins and polysaccharides) correlated with PHE mass transfer in silicone oil indicating that both proteins and polysaccharides favored bacterial uptake of PHE at the interfaces. It could be concluded that EPS could facilitate microbial degradation of PHE in the TLPs.

Liu HH Cai XY Wang Y et al.. Adsorption mechanism-based screening of cyclodextrin polymers for adsorption and separation of pesticides from water. Water Research 2011 45(11): 3499-3511. (IF 4.546 环境科学，二区Top）

Abstract

    A rational screening of cyclodextrin-based polymer (CDP) in terms of the relationship between adsorption potential and adsorbent-adsorbate was investigated to adsorb and separate pesticides from water. Seven spherical porous CDPs were prepared with onefold or composite cyclodextrin(s) as complex and epichlorohydrin as cross-linking reagent. The adsorption kinetics and isotherms of the polymers toward a mixture of ten distinct pesticides clearly demonstrate that the adsorbents with a homogeneous open network structure can absorb pesticides via multiple adsorption interactions such as CD inclusion loading into swelling water and physical adsorption on network. The multivariate regression analysis distinguishes the quantitative contributions of polymer properties to its adsorption potential among which CD content swelling capacity and pore size appear to be major influencing factors. Consequently a facile mixture of three CDPs (i.e. β-CDP RM-CDP and HP-CDP) was screened to obtain above prerequisite properties. The multiplex polymer could superiorly separate the pesticides at environmentally relevant levels from water.