花棒茎流对降雨的响应

干旱半干旱区植物生理过程的水分响应依赖于降雨强度和频率,研究典型沙生植物对降雨的响应有助于预测未来气候条件下荒漠生态系统的结构和功能变化.2012和2013年花棒生长季,在宁夏盐池采用包裹式茎流仪对花棒茎流进行连续观测,分析茎流在晴天和雨天的变化特征及其对不同降雨事件的响应.结果表明: 雨天的花棒日茎流量低于晴天.晴天,茎流日变化呈“几”字型宽峰曲线,与太阳辐射和相对湿度呈正相关;雨天,茎流日变化呈多峰曲线或者一直处于极低状态,与太阳辐射和空气温度呈正相关.降雨不仅可以通过影响当天太阳辐射、空气温度、饱和蒸汽压差和相对湿度影响花棒茎流通量,还通过调控土壤含水量影响降雨后的茎流通量.降雨量<20 mm时,降雨前后茎流通量差异不显著;降雨量>20 mm时,降雨后的茎流通量比降雨前有显著提高.高土壤含水量不仅能够提高茎流通量,并且能够提高茎流通量对太阳辐射、饱和水汽压差和空气温度的响应敏感性.     

Strain improvement of <Emphasis Type="Italic">Sporosarcina pasteurii</Emphasis> for enhanced urease and calcite production

Phenotypic mutants of Sporosarcina pasteurii (previously known as Bacillus pasteurii) (MTCC 1761) were developed by UV irradiation to test their ability to enhance urease activity and calcite production. Among the mutants, Bp M-3 was found to be more efficient compared to other mutants and wild-type strain. It produced the highest urease activity and calcite production compared to other isolates. The production of extracellular polymeric substances and biofilm was also higher in this mutant than other isolates. Microbial sand plugging results showed the highest calcite precipitation by Bp M-3 mutant. Scanning electron micrography, energy-dispersive X-ray and X-ray diffraction analyses evidenced the direct involvement of bacteria in CaCO₃ precipitation. This study suggests that calcite production by the mutant through biomineralization processes is highly effective and may provide a useful strategy as a sealing agent for filling the gaps or cracks and fissures in any construction structures.     

Isolation of clean and PCR-amplifiable DNA fromAnthurium andreanum

A DNA extraction procedure that does not require hazardous materials, such as CTAB, phenols, or liquid nitrogen, was optimized forAnthurium andreanum, a plant rich in polysaccharides and polyphenolics. Three DNA isolation techniques were tested. The modified Rowhani protocol (1983), with slight modifications, was found to yield up to milligrams of DNA suitable for RAPD from spathe and leaf tissues. High-quality DNA was obtained readily from spathe tissues, while a spermine precipitation step was found to be essential when DNA was extracted from the leaf tissues.     

泾河流域植被覆盖动态变化特征及其与降雨的关系

植被退化是全球环境变化研究的一个重点问题,植被状况是环境评估的重要指标.利用8km分辨率的NOAA-AVHRR/NDVI时间序列数据,对位于黄土高原的泾河流域1982～2003年植被特征及变化状况进行系统分析,并在此基础上评估降雨与流域植被的相互关系.研究主要利用了变化斜率法、主成分分析法和相关分析法,得到如下结论:过去22a来流域植被NDVI均值波幅和变化都很小,变化较显著的区域集中在流域上游和流域边缘的山区.变化斜率分析得出了类似的结论,气候变化以及人类活动导致的土地利用改变可能是影响在流域不同地区植被状态变化的主要原因.对NDVI时间序列的主成分分析发现PC1和PC2与植被覆盖和气候密切联系,PC3和PC4与流域汛期洪水有关,PC5和PC6体现了人类活动的影响.流域的NDVI与降雨显示了良好的相关性,降雨与NDVI相关性的阈值可能在550mm或更高.     

梭梭(Haloxylon ammodendron)生理与个体用水策略对降水改变的响应

随着全球变化的加剧,降水改变正导致荒漠生态系统中植物用水策略的适应性变化;对降水变化响应的种间差异性影响着荒漠植物群落组成。研究将生理生态与个体形态尺度相结合,调查中亚荒漠关键种梭梭Haloxylon ammodendron对降水变化导致的自然生境中水分条件改变的响应与适应。实验于2005年生长期开展,在古尔班通古特沙漠南缘原始盐生旱生荒漠中设置3个降水梯度（自然、双倍和无降水）;观测并比较不同降水条件下光合作用、蒸腾作用、叶水势、水分利用效率、地上生物量累积和根系分布的变化。结果表明,梭梭主要利用降水形成的浅层土壤水维持生存;有效的形态调节和较强的气孔控制是其维持光合能力以及适应降水变化的主要机制;降水增多对其产生正效应,预示着梭梭可能在未来种间竞争和群落演替中占有优势。     

Pine needle growth and fine structure after prolonged acid rain treatment in the subarctic

The growth and morphology of Scots pine needles were studied in a long-term acid rain experiment in the far north of Finnish Lapland. Pine trees 5 m tall of age 50–70 years were exposed, by spraying the foliage and soil from a height of 2 m, to either clean water (IC) or acidified water over the period 1985–1992, the acidification site being divided into sub-areas in which the precipitation contained two levels of either sulphuric (Sm, Sh) or nitric (Nm, Nh) acid, or both (SNm, SNh). The treatments with medium and high sulphate-S over eight consecutive years yielded a total sulphur deposition of 3·4 and 17·1 gm⁻², respectively, and those with medium and high nitrate-N a total nitrogen deposition of 1·1 and 5·9 g m⁻². Needles were collected for light and electron microscopy, growth measurements and morphometry. Growth in branch height had decreased by about 40% after 6 years of SNm or SNh treatment, and needle growth by 15% in the SNh trees as compared with the irrigated control trees (IC), although decreases were statistically significant only with respect to the non-irrigated control trees (DC). Growth of branches and needles was slightly better in the Nh treatment than in the IC group. The areas of the whole needle, the mesophyll and the phloem decreased in response to SNh treatment as compared with IC or DC, and a statistically significant decrease of about 30–40% was seen in the area of the xylem in comparison with DC. Cellular damage was observed following the acid treatments, especially with a high acid load. The damage was manifested in collapse of the cellular compartments, increases in lipid accumulations and swelling or disorganization of the protoplast. Increased vacuolization of the cytoplasm, plasmalemma irregularities and chilling-type damage to the mitochondria were also observed.     

Hair of grazing cattle provides an integrated measure of the effects of site conditions and interannual weather variability on δ13C of temperate humid grassland

The carbon isotope composition (δ¹³C) of C3 ecosystems is sensitive to water availability, and provides important information for the assessment of terrestrial carbon (C) sink/source activity. Here, we report the effects of plant available soil water (PAW) on community ¹³C signatures of temperate humid grassland. The 5‐year study was conducted on pastures exhibiting a large range of PAW capacity that were located on two site types: peat and mineral soils. The data set included the centennial drought year 2003, and data from wet years (2000 and 2002). Seasonal variation of PAW was modeled using PAW capacity of each pasture, precipitation inputs and evapotranspiration estimates. Community ¹³C signatures were derived from the δ¹³C of vegetation and segments of tail switch hair of cattle grown while grazing pastures. Hair ¹³C signatures provided an assimilation‐weighted ¹³C signal that integrated both spatial (paddock‐scale) and temporal (grazing season) variation of ¹³C signatures on a pasture. The δ¹³C of hair and vegetation increased with decreasing modeled PAW in the same way on mineral and peat soils. But, at a given PAW, the δ¹³C of hair was 2.6‰ less negative than that of vegetation, reflecting the diet‐hair isotopic shift. Furthermore, the δ¹³C of hair and vegetation on peat soil pastures was 0.5‰ more negative than on pastures situated on mineral soil. This may have resulted from a ～10 ppm CO₂ enrichment of canopy air derived from ongoing peat mineralization. Community‐scale season‐mean ¹³C discrimination (Δ) exhibited a saturation‐type response towards season‐mean modeled PAW (r²=0.78), and ranged between 19.8‰ on soils with low PAW capacity during the drought year of 2003, and 21.4‰ on soils with high PAW capacity in a wet year. This indicated relatively small variation in season‐mean assimilation‐weighted p_i/p_a (0.68–0.75) between contrasting sites and years. However, this range is similar to that reported in other studies, which encompass the range from subtropical arid to humid temperate grassland. Furthermore, the tight relationship between season‐mean Δ and modeled mean PAW suggests that PAW may be used as proxy for Δ.     

CO2浓度倍增、高氮沉降和高降雨对南亚热带人工模拟森林生态系统土壤呼吸的影响

 土壤呼吸响应全球气候变化对全球C循环具有重要作用。应用大型开顶箱(Open-top chamber, OTC)人工控制手段, 研究了大气CO₂浓度倍增、高氮沉降和高降雨处理对南亚热带人工森林生态系统土壤呼吸的影响。结果表明: 对照箱、CO₂浓度倍增处理以及高氮沉降处理下土壤呼吸速率都具有明显的季节变化, 雨季(4~9月)的土壤呼吸速率显著高于旱季(10月至次年3月) (p<0.001); 但高降雨处理下无明显的季节差异(p>0.05)。CO₂浓度倍增能显著提高土壤呼吸速率(p<0.05), 其他处理则变化不大。大气CO₂浓度倍增、高氮沉降、高降雨处理和对照箱的土壤呼吸年通量分别为4 241.7、3 400.8、3 432.0和3 308.4 g CO₂·m^–2·a^–1。但在不同季节, 各种处理对土壤呼吸的影响是不同的。在雨季, 大气CO₂浓度倍增和高氮沉降的土壤呼吸速率显著提高(p<0.05), 其他处理无显著变化; 而在旱季, 高降雨的土壤呼吸速率显著高于对照箱(p<0.05), 氮沉降处理则抑制土壤呼吸作用(p<0.05)。各处理的土壤呼吸速率与地下5 cm土壤温度之间具有显著的指数关系(p<0.001); 当土壤湿度低于15%时, 各处理的土壤呼吸速率与地下5 cm土壤湿度具有显著的线性关系(p<0.001)。     

不同降水条件下沙鞭种群非生殖株丛空间格局分析

植物空间分布格局是物种自身生物学特性与环境因素共同作用的结果,非生殖株丛空间分布格局能够揭示物种无性繁殖与种群扩张过程对异质生境的生态学适应机制。利用基于完全随机、泊松聚块和嵌套双聚块模型的点格局方法和群落学调查,分析了沙鞭(Psammochloa villosa)种群非生殖株丛空间分布格局,探讨了空间格局对降水梯度的响应和适应过程。结果表明：(1)聚集分布是沙鞭种群非生殖株丛的主要类型。在89 mm/a、107.8 mm/a、117.4 mm/a、186 mm/a、191.1 mm/a、363 mm/a降水梯度上聚集尺度分别为3—126 cm、9—200 cm、9—129 cm、6—77 cm、2—95 cm、2—96 cm;(2)基于完全随机模型的空间分布格局对降水的响应规律显著,整体表现为随干旱程度加剧,沙鞭种群非生殖株丛聚集尺度从2—96 cm下降至6—77 cm;(3)在107.8 mm/a、117.4 mm/a、191.1 mm/a、363 mm/a降水梯度上,基于泊松聚块模型的空间分布格局分别在15—19 cm、2—6 cm、2—4 cm、9—25 cm尺度正向偏离泊松聚...     

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。