模拟氮沉降对干旱半干旱温带草原土壤细菌群落结构的影响

随着社会经济发展,活性氮源随人为活动逐年递增,导致氮沉降相应增加,由此带来的生态环境问题也日益严重.本研究基于细菌16S rRNA基因高通量测序技术,分析长期人工模拟氮沉降氮输入量为0、1、4、8、32 g·(m~2·a)~(-1)对干旱半干旱区草原土壤微生物群落结构的影响.结果表明,模拟氮沉降7 a增加了土壤中可利用氮含量,引起草原土壤酸化.高通量测序结果表明,细菌OTU(operational taxonomy unit)数量随氮输入量的增加呈现增加的趋势,高氮处理[8 g·(m~2·a)~(-1)和32g·(m~2·a)~(-1)]显著高于低氮和对照处理;细菌α多样性指数呈现先增加后降低的趋势.不同氮输入水平下土壤细菌群落结构差异显著,且与土壤p H和氮的有效性显著相关.不同细菌相对丰度在纲的水平对氮输入的响应趋势不同.氮的长期大量输入可直接或间接通过改变土壤性状而影响草地土壤细菌群落结构和多样性.     

不同退化程度羊草草原碳收支对模拟氮沉降变化的响应

2009~2010年,选择内蒙古温带典型草原区2个不同退化程度羊草群落为研究对象,利用小区模拟控制试验,设置0g·(m2·a)-1(CK)、10 g·(m2·a)-1(MN)这2个氮处理水平,模拟研究了大气氮沉降水平变化对植物净初级生产力(NPP),土壤呼吸(Rs)以及整个群落碳收支(NEE)的定量影响,比较了不同退化程度草地群落NEE对等量氮添加的响应差异.结果表明,对于轻度退化羊草草原(样地A),MN处理生长季平均地上生物量(AGB)两年分别比CK增加21.5%及46.8%,而对于中度退化羊草草原(样地B),氮添加在2009年降低了植物AGB及地上NPP(ANPP),在2010年则表现为正效应;两年氮添加均增加了样地A与样地B的根系生物量(BGB)以及样地B的地下NPP(BNPP),但降低了2010年样地A的BNPP;氮输入增加并未明显改变Rs的时间变化规律.与CK处理相比,样地A的MN处理两年土壤微生物呼吸年累积通量较CK分别增加了14.6%与25.7%,而样地B则分别降低了10.4%与11.3%;样地A与样地B两年均表现为大气的碳汇,碳汇强度(以碳计)分别为59.22 g·(m2·a)-1与166.68 g·(m2·a)-1以及83.27 g·(m2·a)-1与117.47 g·(m2·a)-1.相对于CK,样地A两年碳汇增加量分别为15.79 g·(m2·a)-1与82.94 g·(m2·a)-1,样地B分别为74.54 g·(m2·a)-1与101.23 g·(m2·a)-1,单位氮输入量在初始氮水平低的草地群落能获得更大的增汇效应.     

塔里木沙漠石油公路风沙危害

为了给沙漠石油公路防沙工程设计和未业公路养护提供科学依据,综合野外观测及风洞模拟实验资料,分析了塔里木沙漠石油公路风沙危害的形成,建立了风沙危害程度的评价模式,从而得出公路沿线的风沙危害具有如下时空分布规律：（１）在时间上,风沙危害主要集中于春、夏季节（４－９月）,其中４月份最强;（２）在空间上,愈向沙漠深入,风沙危害愈烈,风沙危害程度指数的理论估算值与风沙现象观测记录相吻合。     

沙漠环境特点及其对工程装备的影响

介绍了国内典型沙漠环境的特点,分析了其对工程装备的主要影响和危害,从装备论证、研制、设计定型和使用等全寿命周期提出了增强工程装备沙漠环境适应性所需要采取的措施。     

降雨变化对荒漠草原植物群落多样性与土壤C:N:P生态化学计量特征的影响

研究降雨格局变化对植物群落多样性、土壤C：N：P生态化学计量特征的影响,以及关键土壤因子与植物群落多样性间的关系,对于荒漠草原植物群落多样性的保护具有重要意义.本文以黄土高原西部荒漠草原为研究对象,通过3 a野外降雨控制试验（减少40%降雨、减少20%降雨、自然降雨、增加20%降雨和增加40%降雨）,探讨干湿年份下降雨变化对植物群落多样性及其土壤C：N：P生态化学计量特征的影响,以及降雨变化下土壤C：N：P生态化学计量特征及关键土壤因子与植物群落多样性的关系.结果表明,在正常年份与偏干年份（2013年与2015年）,Patrick丰富度和Shannon-Wiener多样性指数分别以减雨20%处理显著低于对照和增雨40%处理,在偏湿年份（2014年）,Patrick丰富度和Shannon-Wiener多样性指数对降雨处理无显著差异.在正常年份与偏干年份,随降雨量的增加土壤有机碳（SOC）、全氮（TN）、全磷（TP）、碳氮比（C：N）、碳磷比（C：P）和氮磷比（N：P）呈降低趋势,其中,C：N显著降低;在偏湿年份,随降雨量增加土壤SOC、TN、C：P和N：P呈上升趋势.在正常年份,降雨处理对土壤含水量影响不显著,导致土壤含水量对植物群落影响有限,SOC、TN、N：P、C：N和微生物量氮（MBN）对植物群落多样性的影响更为突出;在偏湿年份,年降雨量丰富,降雨量增加导致土壤养分上升,水分不是限制植物生长的最重要因素,土壤含水量、土壤养分与生态化学计量特征共同调节和控制着植物群落多样性;在偏干年份,降雨处理对土壤含水影响显著,且降雨量增加导致土壤养分流失较多,因此,土壤含水量成为影响植物群落多样性的最主要因素.由此可知,在不同干湿年份,植物群落多样性与土壤C：N：P生态化学计量特征对降雨变化的响应不同;土壤C：N：P对植物群落多样性的影响也不同,本文的研究结果旨在为未来降雨变化下荒漠草原的保护与管理提供一定的理论依据.     

An integrated ecosystem service assessment in an artificial desert oasis of northwestern China

Spatially explicit integrated assessment of ecosystem services is a new and important research field in landscape ecology. The objective of this paper was to develop an integrated process-based modeling method to simulate changes in multiple ecosystem services in 2000–2009 at pixel and regional scales in the Zhangye oasis of northwestern China. Six ecosystem service indicators were selected and quantified using process-based models, including net primary production (NPP), grain production, net oxygen production (NOP), carbon sequestration (CS), water conservation, and soil conservation. Analytical results were as follows: (1) At the oasis scale, NPP, NOP, CS, water conservation, and soil conservation decreased from 2000 to 2009, whereas grain production increased. (2) At the pixel scale, the spatial changes in NPP were similar to those in NOP and CS, but changes in grain production showed the opposite pattern. Water conservation and soil conservation showed somewhat unintuitive spatial patterns. (3) The impact of land-use forms on ecosystem services showed that grazing and township construction both had negative impacts on all services, but that nature conservation and wetland development had positive impacts on all services. This research showed that the integrated modeling can be proposed as an environmental decision-making tool in similar case studies.     

Applying Satellite Imagery to Triage Assessment of Ecosystem Health

Considerable evidence documents that certain changes in vegetation and soils result in irreversibly degraded rangeland ecosystems. We used Advanced Very High Resolution Radiometer (AVHRR) imagery to develop calibration patterns of change in the Normalized Difference Vegetation Index (NDVI) over the growing season for selected sites for which we had ground data and historical data characterizing these sites as irreversibly degraded. We used the NDVI curves for these training sites to classify and map the irreversibly degraded rangelands in southern New Mexico. We composited images into four year blocks: 1988–1991, 1989–1992, and 1990–1993. The overlap in pixels classified as irreversibly degraded ranged from 42.6% to 84.3% in year block comparisons. Quantitative data on vegetation composition and cover were collected at 13 sites within a small portion of the study area. Wide coverage reconnaissance of boundaries between vegetation types was also conducted for comparisons with year block maps. The year block 1988–1991 provided the most accurate delineation of degraded areas. The rangelands of southern New Mexico experienced above average precipitation from 1990–1993. The above average precipitation resulted in spatially variable productivity of ephemeral weedy plants on the training sites and degraded rangelands which resulted in much smaller areas classified as irreversibly degraded. We selected imagery for a single year, 1989, which was characterized by the absence of spring annual plant production in order to eliminate the confounding effect of reflectance from annual weeds. That image analysis classified more than 20% of the rangelands as irreversibly degraded because areas with shrub-grass mosaic were included in the degraded classification. The single year image included more than double the area classified as irreversibly degraded by the year blocks. AVHRR imagery can be used to make triage assessments of irreversibly degraded rangeland but such assessment requires understanding productivity patterns and variability across the landscapes of the region and careful selection of the years from which imagery is chosen.     

Effects of Human Trampling on Populations of Soil Fauna in the McMurdo Dry Valleys,Antarctica

Abstract: Antarctic ecosystems are often considered nearly pristine because levels of anthropogenic disturbance are extremely low there. Nevertheless, over recent decades there has been a rapid increase in the number of people, researchers and tourists, visiting Antarctica. We evaluated, over 10 years, the direct impact of foot traffic on the abundance of soil animals and soil properties in Taylor Valley within the McMurdo Dry Valleys region of Antarctica. We compared soils from minimally disturbed areas with soils from nearby paths that received intermediate and high levels of human foot traffic (i.e., up to approximately 80 passes per year). The nematodes Scottnema lindsayae and Eudorylaimus sp. were the most commonly found animal species, whereas rotifers and tardigrades were found only occasionally. On the highly trampled footpaths, abundance of S. lindsayae and Eudorylaimus sp. was up to 52 and 76% lower, respectively, than in untrampled areas. Moreover, reduction in S. lindsayae abundance was more pronounced after 10 years than 2 years and in the surface soil than in the deeper soil, presumably because of the longer period of disturbance and the greater level of physical disturbance experienced by the surface soil. The ratio of living to dead Eudorylaimus sp. also declined with increased trampling intensity, which is indicative of increased mortality or reduced fecundity. At one site there was evidence that high levels of trampling reduced soil CO₂ fluxes, which is related to total biological activity in the soil. Our results show that even low levels of human traffic can significantly affect soil biota in this ecosystem and may alter ecosystem processes, such as carbon cycling. Consequently, management and conservation plans for Antarctic soils should consider the high sensitivity of soil fauna to physical disturbance as human presence in this ecosystem increases.     

水氮控制对荒漠草原中小型土壤动物的影响

为了解模拟氮沉降和降雨变化对短花针茅荒漠草原中小型土壤动物的影响,本试验设计主区为自然降雨（CK）、增雨30%（W）和减雨30%（R）3个水分处理,副区为0（N0）,30（N30）,50（N50）和100（N100） kg/（hm²·a）4个氮素处理共12个处理.研究表明：在相同的水分处理中随着氮浓度的不断增高,表层土壤中中小型土壤动物的个体密度呈先上升后下降趋势.W-N30处理下中小型土壤动物个体密度高于其他处理（P<0.05）,类群数随着氮浓度升高呈下降趋势,减雨与过量施氮对表层土壤中中小型土壤动物个体密度具有抑制作用.短花针茅荒漠草原中小型土壤动物在土层中具有明显的表聚特性.另外,冗余分析（RDA）表明,研究区内中小型土壤动物的优势类群与常见类群受环境因子影响较显著,土壤pH值、温度、含水量、有机质和植物全C、全N、C/N对中小型土壤动物个体密度影响均较大,但短期内对类群数的影响不显著.当短花针茅荒漠草原面临全球变化时,随着氮沉降量逐渐增加,表层土壤中中小型土壤动物个体密度先逐渐增加,当达到不同水分条件下氮浓度阈值时,则对表层土壤中中小型土壤动物产生抑制作用.     

荒漠生态环境监测指标体系初探

讨论了建立荒漠生态环境监测指标体系应遵循的五个原则,并提出初步的荒漠生态环境监测指标体系,将指标体系分为三个部分:(1)荒漠环境指标;(2)荒漠生物指标;(3)社会经济指标.