河西走廊植物群落特征及其与气候的关系初探

对河西走廊荒漠植物的群落类型、盖度、密度、重要值、地上生物量等进行了调查,收集整理各区域的气候资料,对它们的关系进行了初步研究。结果显示:(1)物种种类组成、总密度与海拔、经度呈正相关,与纬度呈负相关,在走廊的东南→西北方向上呈递减趋势。(2)在活动积温(>10℃)>3 200℃的荒漠地区,灌木(包括半灌木)在群落中占有绝对优势,其重要值可达到100;当活动积温在3 000℃左右时,群落往往是一些过渡类型,或以草本为优势种、以半灌木或灌木为伴生种,或以半灌木为优势种、以多年生草本为伴生种。(3)在年降水量110 mm以上的荒漠地区,植物群落生活型主要为半灌木或多年生草本;在年降水量110 mm以下的地区,生活型主要为小灌木或一年生草本;在年降水量小于50 mm的极端干旱地区,只有在雨季时有一年生草本生长。表明荒漠生态系统植被稀疏,生物量小,对气候因子,特别是降水变化敏感,对其保育显得尤为重要。     

Spatio-temporal characteristics of vegetation water use efficiency and their relationships with climatic factors in alpine and subalpine area of southwestern China

水分利用效率(WUE)是深入理解生态系统水碳循环及其耦合关系的重要指标。为了揭示气候变化背景下区域尺度不同植被类型的响应和适应特征, 对中国西南高山亚高山地区2000-2014年的9种植被类型的WUE时空特征及其影响因素进行探究。该研究基于MODIS总初级生产力(GPP)、蒸散发(ET)数据和气象数据, 估算西南高山亚高山区植被WUE, 采用趋势分析及相关分析等方法, 分析了研究区植被WUE与气温、降水及海拔的关系。主要结果: (1)西南高山亚高山区2000-2014年植被WUE多年均值为0.95 g·m^-2·mm^-1, 整体呈显著增加趋势, 增速为0.011 g·m^-2·mm^-1·a^-1; 空间上WUE呈东南高西北低的分布, 85.84%区域的WUE呈增加趋势。(2)西南高山亚高山区各植被类型WUE多年均值表现为常绿针叶林>稀树草原>常绿阔叶林>有林草原>农田>落叶阔叶林>混交林>郁闭灌丛>草地; 时间上, 各植被类型WUE均呈上升趋势。(3)西南高山亚高山区89.56%区域的WUE与气温正相关, 92.54%区域的WUE与降水量负相关; 各植被类型中, 草地WUE与气温的相关性最高, 有林草原WUE与降水量的相关性最高。(4)西南高山亚高山区典型的地带性顶极植被常绿针叶林的WUE具有较强的海拔适应性及应对气候变化的能力。     

近60年秦岭山地旱涝变化规律

随着极端气候变化,山地灾害频发。基于秦岭山地32个气象站点的实测数据,以标准化降水蒸散指数(SPEI)为旱涝量化指标,研究了过去60年秦岭山地旱涝时空变化特征、频率、周期等变化规律,结果表明：(1)1960—2019年,秦岭山地年SPEI指数以0.124/10a的速度下降,其中,90.23%的面积呈显著下降趋势,1.96%的面积呈显著上升趋势,并在1990年发生干旱突变;秦岭北坡的干旱化趋势大于南坡,且高海拔地区干旱化更为明显。(2)突变前秦岭山地湿润比例平均值为36.94%,突变后下降为18.19%;干旱比例由突变前的17.64%急剧上升到突变后的38.19%;突变前30年秦岭山地极端干旱事件、严重干旱事件极少发生,发生频率几乎为0;突变后30年严重干旱和极端干旱事件发生频率增加,秦岭南北坡极端湿润和严重湿润事件近乎销声匿迹。(3)整体上,太阳黑子与秦岭山地旱涝变化以显著负相关关系为主;ENSO事件对秦岭山地的旱涝变化影响较大,在La Nina年易发生洪涝事件,在El Ni1o年易发生干旱事件;在不同时域范围内,海表温度距平(SSTA)对秦岭山地旱涝变化的影响不同：1990年以前,S...     

火烧强度对中亚热带人工造林初期土壤呼吸的影响

在热带和亚热带森林中,火烧是一种清理采伐迹地的有效管理措施。尽管许多研究表明,火烧刺激了土壤的碳排放,但对亚热带火强度对土壤呼吸的影响还缺乏了解。在中亚热带米槠常绿阔叶次生林采伐迹地上,设置高火烧强度（HF）、低火烧强度（LF）炼山造林处理,利用LI-8100对造林初期（2012年3月-2012年12月）土壤呼吸进行测定,同时监测观测期土壤温度、含水量以及降雨量等气象因子,分析不同火烧强度对中亚热带造林初期土壤呼吸及排放量的影响,同时探讨影响土壤呼吸变化的主要因素。结果表明：（1）观测期间不同火烧强度对土壤呼吸的影响呈现出明显的时间变化特征：与对照（CT）相比,土壤呼吸在火烧后2个月以内显著增加（P<0.05）,HF和LF分别增加76.3%和55.3%;在火烧后2-5个月内三种处理间没有显著差异（P>0.05）;但之后,火烧处理土壤呼吸显著低于CT （P<0.05）,HF和LF分别降低40%和32.6%;在观测期间火烧处理没有导致土壤CO₂累计排放量的增加。（2）火烧处理下,仅HF处理中土壤呼吸与土壤温度显著相关（P<0.05）,但拟合决定系数较低。（3）单次降水事件会导致火烧处理下土壤呼吸的增加,而对照无明显增加;但连续性降水事件中,降雨早期促进土壤呼吸,而后期呈现出抑制作用。     

微生物水泥相关酶的研究进展

微生物诱导碳酸钙沉积(microbial induced calcium carbonate precipitation,MICP)是微生物通过新陈代谢在其周围微环境中形成碳酸钙沉积的一种自然现象,根据其原理目前研发出了“微生物水泥”。因其具有绿色环保、经济高效的特点,已成为生物、土木、环境等领域的研究热点。文中就与微生物水泥密切相关的关键酶——脲酶、碳酸酐酶的研究进展进行了系统综述,主要包括两种酶的基因、蛋白结构、调控机制、工程菌的构建以及脲酶与碳酸酐酶在MICP过程中的协同关系等,并对MICP未来的发展作出展望。在现有研究基础上,借助生物信息学、合成生物学等前沿技术,开发能适应广泛环境、高性能的生物水泥,这将开启MICP研究的一个新阶段。     

近20年内蒙古鄂托克旗草地降水利用效率时空演变的驱动力量化

降水利用效率(PUE)是评价干旱半干旱地区草地生产力与降水关系的有效指标。为进一步探究气候变化和人类活动对草地PUE的驱动机理,本研究采用改进的CASA模型估算了2001—2020年鄂托克旗草地净初级生产力(NPP),结合同期降水量的空间插值数据获取了研究区草地PUE,利用简单线性回归和分段线性回归分析了PUE的时空演变特征及其空间格局对6类气候因子的响应,并引入基于偏导数的量化分析方法定量评估了气候变化和人类活动对PUE动态的相对贡献。结果表明: 鄂托克旗草地PUE多年均值为0.748 g C·m^-2·mm^-1,年际波动呈显著下降趋势,下降速率为0.014 g C·m^-2·mm^-1·a^-1;PUE在空间上西低东高,沿气温、降水、相对湿度、日照时数和ET₀的增长梯度呈显著的单峰分段线性模式,而沿风速梯度表现为先快后慢的持续显著增长模式;研究区94.3%的草地表现为PUE衰减态势,且有43.6%为严重衰减,这一突出问题是气候变化和人类活动共同作用导致的,二者的贡献分别为-1.162×10^-2和-0.240×10^-2 g C·m^-2·mm^-1·a^-1,而气候变化是首要驱动力,其中降水是关键气候驱动因子。     

荒漠短命植物地上和地下生产力对极端干旱和降水的响应

在古尔班通古特沙漠南缘沙垄4个坡位和坡向,设置减少65%和增加65%生长季降水量以模拟极端干旱和极端降水事件,研究极端干旱和极端降水事件对沙垄不同坡位和坡向短命植物层片生产力的影响。结果表明: 极端干旱使地上净初级生产力和地下净初级生产力分别显著降低48.8%和13.7%,极端降水使地上净初级生产力和地下净初级生产力分别显著增加37.9%和23.2%。地上净初级生产力对极端干旱和极端降水的敏感性(0.26和0.21 g·m^-2·mm^-1)显著强于地下净初级生产力的敏感性(0.02和0.03 g·m^-2·mm^-1)。沙垄东坡地上净初级生产力(24.22 g·m^-2)和地下净初级生产力(5.77 g·m^-2)与西坡相比显著增大29.7%和71.7%,而地上净初级生产力和地下净初级生产力对降水变化的敏感性在不同坡位和坡向之间差异不显著。     

Comparison of microbially induced calcium carbonate precipitation eligibility using sporosarcina pasteurii and bacillus licheniformis on two different sands

The use of biological means for ground improvement have become popular, which generally works through the process called microbially-induced calcium carbonate precipitation (MICP). Many studies indicate successful application of MICP based improvement with multiple bacteria and on several soils. Given the proven performance of MICP, this study aims to examine the MICP process by comparing the calcium carbonate precipitation ability of widely studied bacteria, i.e., Sporosarcina pasteurii and relatively under-recognized bacteria, i.e., Bacillus licheniformis to outline the formation success. For this purpose, two different sands were tested for observing precipitation behavior using a series of syringe tests. Furthermore, the effect of concentration and inclusion of calcium chloride for nutrition of bacteria, saturation with water, and hybrid use of two bacteria were investigated in some tests for diversification. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were used for the interpretation of results. Results indicated that Sporosarcina pasteurii had performed superior over Bacillus licheniformis when achieving calcium carbonate precipitation in tests for both sands. In addition, many intriguing SEM images contributed to the literature of MICP monitoring, highlighting the effects of the variables investigated.     

Microbially Induced Calcite Precipitation for Seepage Control in Sandy Soil

Microbially induced calcite precipitation (MICP) can reduce the permeability of soil by reducing the pore volumes. A MICP-based soil improvement method to control water leakage in irrigation channels and reservoirs built on sandy soil grounds is presented in this article. Using this method, a low-permeable hard crust can be formed at the soil surfaces. An experimental study was carried out to evaluate the effect of this method. Sandy soil samples were treated using four different schemes, namely, (1) surface spray, (2) surface spray with the addition of fibers, (3) surface spray and bulk stabilization, and (4) immersion stabilization. By applying around 2.6?L treatment liquid (consisting of ureolytic bacteria, 0.5?mol/L calcium chloride and 0.5?mol/L urea) to the top 2-cm thick soil, the seepage rates of the samples treated by the four different schemes could be reduced by up to 379 times. The conversion rates of calcium source in the tests were up to 89.7%. The results showed that a method of treating the soil in bulk before the formation of a crust on top of the soil layer was effective in reducing the seepage rates. After the bio-treatment, the formed low-permeable hard crust layer was 10 to 20?mm thick with a calcite content higher than 5%. Below the hard crusts, the calcite content was less than 5% and the soil was not properly cemented. Using the mercury intrusion test, it was found that both pore volumes and pore sizes of the bio-treated soil reduced significantly as compared with the untreated soil. Penetration tests using a flat-bottom penetrometer were used to assess the mechanical behavior of the bio-treated soil. The results indicated that the penetration resistance of the bio-treated soil layer was much higher than that of the untreated soil.     

Increased rainfall variability and reduced rainfall amount decreases soil CO2 flux in a grassland ecosystem

Predicted climate changes in the US Central Plains include altered precipitation regimes with increased occurrence of growing season droughts and higher frequencies of extreme rainfall events. Changes in the amounts and timing of rainfall events will likely affect ecosystem processes, including those that control C cycling and storage. Soil carbon dioxide (CO₂) flux is an important component of C cycling in terrestrial ecosystems, and is strongly influenced by climate. While many studies have assessed the influence of soil water content on soil CO₂ flux, few have included experimental manipulation of rainfall amounts in intact ecosystems, and we know of no studies that have explicitly addressed the influence of the timing of rainfall events. In order to determine the responses of soil CO₂ flux to altered rainfall timing and amounts, we manipulated rainfall inputs to plots of native tallgrass prairie (Konza Prairie, Kansas, USA) over four growing seasons (1998–2001). Specifically, we altered the amounts and/or timing of growing season rainfall in a factorial combination that included two levels of rainfall amount (100% or 70% of naturally occurring rainfall quantity) and two temporal patterns of rain events (ambient timing or a 50% increase in length of dry intervals between events). The size of individual rain events in the altered timing treatment was adjusted so that the quantity of total growing season rainfall in the ambient and altered timing treatments was the same (i.e. fewer, but larger rainfall events characterized the altered timing treatment). Seasonal mean soil CO₂ flux decreased by 8% under reduced rainfall amounts, by 13% under altered rainfall timing, and by 20% when both were combined (P<0.01). These changes in soil CO₂ flux were consistent with observed changes in plant productivity, which was also reduced by both reduced rainfall quantity and altered rainfall timing. Soil CO₂ flux was related to both soil temperature and soil water content in regression analyses; together they explained as much as 64% of the variability in CO₂ flux across dates under ambient rainfall timing, but only 38–48% of the variability under altered rainfall timing, suggesting that other factors (e.g. substrate availability, plant or microbial stress) may limit CO₂ flux under a climate regime that includes fewer, larger rainfall events. An analysis of the temperature sensitivity of soil CO₂ flux indicated that temperature had a reduced effect (lower correlation and lower Q₁₀ values) under the reduced quantity and altered timing treatments. Recognition that changes in the timing of rainfall events may be as, or more, important than changes in rainfall amount in affecting soil CO₂ flux and other components of the carbon cycle highlights the complex nature of ecosystem responses to climate change in North American grasslands.