基于InVEST模型的渭河流域干支流生态系统服务时空演变特征分析

渭河作为黄河的最大支流,是生态保护建成区重点之一,对其生态系统服务研究有利于实现流域内高质量发展和生态保护之间的平衡关系,保持流域生态系统服务功能,促进流域生态系统恢复。基于InVEST模型分析渭河流域2000—2018年5期土地利用和干支流生态系统服务时空动态变化,采用相关性分析水源涵养、土壤保持和生物多样性之间的权衡和协同。结果表明:19年间,研究区土地利用情况主要以耕地、草地和林地为主,占总面积的95%以上。流域内水源涵养呈现"先上升后下降"趋势,平均栅格单元产水量542.9 mm,渭河流域干流水源涵养量最高,为6.88×10~8 m~3,其次为北洛河和泾河流域,分别为3.36×10~8,5.04×10~8 m~3。土壤保持呈斑块状分布,流域整体土壤侵蚀状况为微度侵蚀,且渭河流域干流实际土壤侵蚀量总量最高为6.67×10~8 t,其次为北洛河和泾河流域,分别为6.22×10~8,3.13×10~8 t。生物多样性表现为生境质量高区集中分布在生态较好的森林生态保护区,人类活动较为密集地区生境质量较差。研究期间,渭河流域水源涵养与土壤保持、生态质量之间为高度协同关系,其他生态系统服务不显著,不同的土地利用类型对生态系统服务之间权衡和协同贡献值不一致。     

干旱内陆河流域生态系统服务空间权衡与协同作用分析

为了测度生态系统服务的空间权衡/协同关系,该文以干旱内陆河流域典型地区嘉峪关-酒泉地区为研究区,对其2000年和2010年食物供给、碳储存、水源涵养和土壤保持4种生态系统服务物质量进行定量测算.利用相关分析法和空间热点制图等方法,分析了生态系统服务时空变化,从县域尺度和区域尺度上分析了生态系统服务之间的权衡协同关系,识别了某种服务的物质量或价值量极高的热点区.结果表明:研究区单位面积食物供给的高值区分布在中东部的肃州区及嘉峪关市,碳储存表现为东部及南部较高的分布格局;土壤保持在2000年和2010年变化不大,呈现出从西到东逐渐增大的分布趋势;单位面积水源涵养值由2000年的0.40mm/(m2·a)提高到2010年的0.99mm/(m2·a).县域尺度上,各种生态系统服务之间大多为协同关系,其中食物-碳和水源-碳之间的协同程度较高;区域尺度上,食物供给和土壤保持、水源涵养和土壤保持生态系统服务间存在此消彼长的权衡关系.4种生态系统服务的值均未超过各自平均值的0类服务区和只有1种生态系统服务的值超过其所对应平均值的1类服务区分别占总面积的58.50%和25.20%.该研究结果可为制定差别化的区域发展与生态保护双赢政策提供科学参考.     

基于改进的InVEST模型的韶关市生态系统服务功能时空变化特征及影响因素

基于改进的InVEST模型,评估了1990—2017年4个时期韶关市生态系统水源涵养、水土保持、生物多样性、碳储存服务功能时空演变趋势,并通过地理探测器方法分析了影响服务功能时空变化特征的主要因素。结果表明:(1)研究区单位面积水源涵养、水土保持量均呈先上升后下降趋势,分别以2000年、2010年达到最高,主要是由于年际气象条件的影响;生境质量、碳储存则受土地利用变化影响,呈逐年下降趋势。(2) 1990—2017年4个时期生态系统服务低值区主要分布在区内韶关中心城区及南雄、翁源、乐昌盆地区域,高值区则各有差异,水源涵养高值区分布在研究区南部,与区域降水量南高北低的趋势一致;水土保持高值区集中分布在乐昌—乳源县中部的大东山、始兴仁化县交界处的瑶岭,与区域地形一致;生物多样性、碳储存高值区分布与土地利用类型较高一致性。随着韶关中心城区及各县城区的扩张,以各城区为中心的生态系统服务功能低值区范围持续扩大。(3)水源涵养量空间异质性主要受土地利用类型、降水量影响,生境质量、碳储存主要由土地利用类型、坡度、海拔影响,土壤保持量则受各因素影响相对均等。除土壤保持量外,土地利用类型对生态系统服务功能空间异质性的影响显著大于其他因素。(4)气象因素在很大程度上决定了生态系统服务功能的年际差异,土地利用类型则是影响其空间分布的主要因素。     

大理河流域退耕还林工程对生态系统服务功能的影响

以大理河流域为研究区,应用InVEST生态系统服务功能评估模型,结合1980年、1985年、1990年、1995年、2000年、2005年、2010年该流域的土地利用/土地覆被资料,定量评价了退耕还林工程对碳储量、土壤保持和水源涵养生态服务功能的影响。结果表明:(1)研究区30年间土地利用/土地覆被情况变化显著,其中林地和建设用地面积分别增加了31.52,0.65km~2,耕地、草地和水域的面积分别减少了2.49,27.32,2.36km~2;(2)研究区30年间碳储量值略有增加,不同土地利用类型碳储存能力从大到小的排序分别为林地草地耕地;(3)研究区30年间土壤保持量整体上以增加为主,耕地土壤保持能力明显低于林地和草地;(4)研究区30年间水源涵养量略有减少,不同土地利用/土地覆被类型的水源涵养量各有不同,且与当年降雨量关系密切。本研究通过对大理河流域生态系统服务功能进行评估,获得了研究区退耕还林工程的生态效果,可以为日后生态规划提供科学依据。     

农牧交错带禁牧草地生态系统服务空间权衡与协同关系

为明确农牧交错带禁牧草地生态系统主要服务间的相互作用关系,以宁夏盐池县草地为研究对象,借助本地化的InVEST模型,对禁牧以来(2000-2015年)草地碳储存、水源涵养、土壤保持3项关键服务进行精准测度,明确其时空变化特征,以此为基础,通过逐像元相关系数法对3种服务间的权衡作用进行定量可视化表达,分析乡镇尺度各服务间的空间权衡与协同关系。结果表明:1)禁牧以来,草地生态系统碳储存、水源涵养和土壤保持功能显著增加,但增加过程存在一个显著的"N"型波动,碳储存总量及单位面积均值由217.46万t、5.78t/hm~2增加到263.12万t、6.19 t/hm~2;水源涵养总量及单位面积均值由2 884万t、76.69 t/hm~2增加到6 118万t、143.92 t/hm~2;土壤保持总量及单位面积均值由1 383万t、36.78 t/hm~2增加到3 474万t、81.71 t/hm~2。碳储存功能与草地覆被关系密切,年际波动小、增长稳定,水源涵养和土壤保持功能受降水和地形显著影响,年际波动大、空间差异显著。2)草地土壤保持与水源涵养功能呈显著的空间协同关系(面积占86.34%),碳储存与水源涵养功能关系复杂,空间权衡与协同关系不显著(面积分别占47.66%和52.34%),碳储存与土壤保持功能呈空间协同关系(面积占69.55%)。通过定量可视化评估草地生态系统各服务间的空间权衡与协同关系,可为草地生态系统优化提供科学依据,为草地资源管理提供参考。     

泾河流域生态系统服务权衡/协同关系的尺度异质性研究

[目的]探究泾河流域生态系统服务权衡/协同关系的尺度异质性,阐明权衡/协同关系在子流域尺度发生变化的主要原因,为黄土高原地区的生态保护和高质量发展提供科学参考。[方法]利用SWAT模型、CASA模型、InVEST模型等量化粮食供给、土壤保持、产水、固碳、生境质量5种生态系统服务,并采用空间相关性统计方法从全流域和子流域两个尺度上进行生态系统服务及两两之间权衡/协同关系的尺度异质性研究。[结果](1)泾河流域粮食供给服务在流域东南部较强;土壤保持服务在流域北部、中部较弱,在西南部、东南部较强;产水服务在流域西部、南部以及东南部较强,在北部、东北部及东部地区较弱;固碳服务流域南部强于北部,东部强于西部;生境质量以中值区和高值区为主,其高值区主要分布在流域东部、东南部及西部,低值区主要分布在建设用地。(2)从全流域尺度来看,粮食产量和土壤保持、产水量、NPP和生境质量以权衡关系为主;土壤保持和产水量、NPP和生境质量以协同关系为主;产水量和NPP是协同关系为主,和生境质量是权衡关系为主;NPP和生境质量是以协同关系为主。(3)泾河流域生态系统服务之间的权衡/协同关系在部分子流域发生改变,土地...     

陇东黄土高原农田生态系统服务及其权衡协同关系

陇东黄土高原是中国农耕文明发祥地之一,探究其农田生态系统服务及其权衡协同关系对于维持农田生态系统多功能性,促进耕地保护、保障粮食安全具有重要价值。为了厘清其农田生态系统服务之间的权衡协同关系,该研究基于社会经济与资源环境数据,运用降水贮存量法、通用土壤流失方程、InVEST 等6种生态系统服务评估模型,测算2020年农田生态系统供给服务（食物供给）、调节服务（水源涵养、碳固存）、支持服务（土壤保持、生境维持）和文化服务（美学景观）的物理量,并采用皮尔逊相关系数、双变量莫兰指数,分别识别供给服务与其他3类服务之间的权衡协同关系、各项服务之间关系的空间异质性。结果表明：1）研究区农田生态系统食物供给、水源涵养、碳固存、土壤保持服务物质量分别为4.61×10⁶ t、2.45×10⁸ m³、2.94×10⁶ t、6.61×10⁹ t,生境质量服务均值为0.26;供给服务与文化服务均呈“东西高、中北低”的分布格局,调节服务与支持服务则呈“带状”分布格局。2）研究区农田生态系统供给服务与调节、支持、文化服务之间以及食物供给服务与水源涵养、碳固存、土壤保持、生境维持、美学景观服务之间均表现为不同程度的协同关系。3） 研究区农田生态系统4类服务之间、各项子服务之间的权衡协同关系均具有空间自相关性,空间异质性显著。各项服务之间的协同关系“组团”出现在陇东中北部地区,聚集性较明显;各项服务之间的权衡关系则零散分布,聚集性不明显。因此,应全力维持陇东黄土高原农田生态系统多功能性,实施分区管理策略,充分发挥农田生态系统各类服务的协同效应,整体提升农田生态系统服务功能（特别是食物供给服务）,巩固新时代“陇东粮仓”地位。     

喀斯特地区退耕还林工程下生态系统服务变化与关系分析

为了给新形势下退耕还林工程的实施提供科学的理论依据,以贵州省安顺市普定县为研究区域,借助生态系统服务和交易的估价权衡模型(InVEST)测度了普定县1990年、2000年、2010年、2017年的土壤保持、产水量、碳储存和生境质量4项服务。结果表明:(1)产水量、碳储量、土壤保持和生境质量服务在3个时段生态系统服务变化指数(ESCI)的结果各不相同,如持平和倍增。增益及损失范围在空间分布上不相同,同种生态系统服务在不同的时间段上分布也不相同。(2) 4种主导生态系统服务的分布格局也显示出显著的空间差别:土壤保持主导服务主要分布在山地林地地区;产水量主导服务主要分布在山地林地、建设用地及裸地;碳储量主导服务主要分布在林区;生境质量主导服务分布在水域、林地、草地和耕地。(3)普定县土壤保持与碳储存服务、土壤保持与生境质量服务、碳储存与生境质量都存在明显的协同关系;土壤保持与产水量存在较好的协同关系。(4)普定县4类及3类生态系统服务热点区主要分布在林地和草地地区,且随着退耕还林(草)政策的全面开展,4类及3类热点区面积逐年增加;0类和1类服务热点区主要分布在普定县的建设用地、裸地及耕地地区。     

湖南省多尺度生态系统服务供需关系及影响因素

[目的]分析生态系统服务供需分布格局及主要驱动因素,为区域生态保护实践、生态环境改善提供科学参考。[方法]借助InVEST模型、ArcGIS等工具,评估湖南省2000—2020年粮食生产、碳固持、水源涵养、土壤保持以及生境质量共5项生态系统服务供需量,分析其时空演变规律和空间匹配关系,在网格尺度和县域尺度运用最优参数地理探测器模型探究影响生态系统服务供需比的驱动因子。[结果](1)湖南省生态系统服务供给总量均大于需求总量,碳固持服务和生境质量服务供给量以及水源涵养服务需求量下降,其他生态系统服务供需量均上升。(2)湖南省各项生态系统服务供需分布、供需比集聚特征以及供需空间匹配空间异质性明显。(3)两种尺度生态系统服务供需比主导因子有一定差异,社会经济因子在县域尺度上的影响较网格尺度更为显著;土地利用因子与其他因子的交互作用对生态系统服务供需比空间分异解释力较高。[结论]不同尺度生态系统服务供需矛盾突出,未来各级政府应制定更加精确的生态管理措施,并以此为基础促进区域土地合理利用,最终达到区域绿色发展的目标。     

2000-2015年黄土高原生态系统水源涵养、土壤保持和NPP服务的时空分布与权衡/协同关系

生态系统服务评估决定区域可持续发展,对人类福祉至关重要。以黄土高原为研究区域,基于CASA、InVEST和RUSLE模型,结合土地利用类型、归一化植被指数、气象等数据,分析了2000年、2005年、2010年和2015年的NPP、土壤保持和水源涵养3项关键生态系统服务的时空分布特征,识别了3种生态系统服务的热点区,并基于相关系数法分析了黄土高原地区和不同气候区(干旱气候区、半干旱气候区、高原气候区、半湿润气候区)不同生态系统服务间的权衡/协同关系。结果表明:(1)2000—2015年,黄土高原地区的土地利用类型变化剧烈,其中林地(2.8%)和建设用地(43.1%)显著增加,耕地(-2.7%)明显减少;(2)2000—2015年,净初级生产力(NPP)、产水量和土壤保持均呈现增长趋势,分别增加14.1%,5.3%和101.3%;(3)黄土高原的4类热点区(非热点区、一类热点区、二类热点区、三类热点区)所占面积变化不显著,分布具有明显的地带性,从西北到东南依次为非热点区、一类热点区、二类热点区和三类热点区;(4)在整个黄土高原地区,土壤保持与NPP、水源涵养之间为协同关系,NPP与水源涵养为权衡关系;在4个气候区,NPP与土壤保持之间的权衡/协同关系与黄土高原地区一致,但土壤保持和水源涵养在半干旱气候区和半湿润气候区呈权衡关系,NPP与水源涵养在高原气候区和半湿润气候区为协同关系。为促进区域生态系统可持续管理,应在土地规划过程中考虑生态系统服务之间的相互关系,尽可能减少权衡,增加协同。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.