Performance of trichlorfon degradation by a novel <Emphasis Type="Italic">Bacillus tequilensis</Emphasis> strain PA F-3 and its proposed biodegradation pathway

The novel trichlorfon (TCF)-degrading bacterium PA F-3, identified as Bacillus tequilensis, was isolated from pesticide-polluted soils by using an effective screening and domesticating procedure. The TCF biodegradation pathways of PA F-3 were also systematically elucidated. As revealed by high-performance liquid chromatography, the TCF residues in the mineral salt medium demonstrated that PA F-3 can utilize TCF as its sole carbon source and reach the highest degradation of 71.1 % at an initial TCF concentration of 200 mg/L within 5 days. The TCF degradation conditions were optimized using response surface methodology as follows: temperature, 28 °C; inoculum amount, 4 %; and initial TCF concentration, 125 mg/L. Biodegradation treatments supplemented with exogenous carbon sources and yeast extract markedly increased the microbial dry weights and TCF-degrading performance of PA F-3, respectively. Meanwhile, five metabolic products of TCF were identified through gas chromatography/mass spectrometry, and a biodegradation pathway was proposed. Results indicated that deoxidation and dehydration (including the cleavage of the P–C phosphonate bond and the C–O bond) were the preferred metabolic reactions of TCF in this TCF-degrading bacterium.     

Changes in seasonal precipitation distribution but not annual amount affect litter decomposition in a secondary tropical forest

In the tropics of South China, climate change induced more rainfall events in the wet season in the last decades. Moreover, there will be more frequently spring drought in the future. However, knowledge on how litter decomposition rate would respond to these seasonal precipitation changes is still limited. In the present study, we conducted a precipitation manipulation experiment in a tropical forest. First, we applied a 60% rainfall exclusion in April and May to defer the onset of wet season and added the same amount of water in October and November to mimic a deferred wet season (DW); second, we increased as much as 25% mean annual precipitation into plots in July and August to simulate a wetter wet season (WW). Five single‐species litters, with their carbon to nitrogen ratio ranged from 27 to 49, and a mixed litter were used to explore how the precipitation change treatments would affect litter decomposition rate. The interaction between precipitation changes and litter species was not significant. The DW treatment marginally accelerated litter decomposition across six litter types. Detailed analysis showed that DW increased litter decomposition rate in the periods of January to March and October to December, when soil moisture was increased by the water addition in the dry season. In contrast, WW did not significantly affect litter decomposition rate, which was consistent with the unchanged soil moisture pattern. In conclusion, the study indicated that regardless of litter types or litter quality, the projected deferred wet season would increase litter decomposition rate, whereas the wetter wet season would not affect litter decomposition rate in the tropical forests. This study improves our knowledge of how tropical forest carbon cycling in response to precipitation change.     

祁连山北麓高原鼢鼠栖息地选择要素

Studying the habitat characteristics and habitat selection of the plateau zokor in different grassland types is very important to understand the function and position of the zokor in these grassland ecosystems. We selected the plateau zokor inhabiting in the alpine meadow, alpine shrub meadow and alpine grassland located in northern Qilian Mountain to describe habitatcharacteristics and study its habitat selection by dividing five plots in each grassland according to the zokor’s mounds densities, which can be regarded as relative population density of zokors. We investigated soil compaction, soil moisture, soil temperature, soil pH, as well as plant community structure in each plot of three grassland types. One-Way ANOVAs showed that there were significant differences in vegetation and soil among the three grassland types. Soil compaction, soil temperature, and total plant species number in alpine meadow were the highest (P<0.05), soil moisture and total vegetation coverage in alpine shrub meadow were the highest (P<0.05), soil pH in alpine grassland was the highest (P<0.05). Correlation analysis showed that soil compaction was negatively correlated with the relative population density of the zokor (P<0.05). Stepwise linear regression analysis showed that the plateau zokor preferred habitat with lower compaction, richer forbs in alpine meadow, lower compaction in alpine shrub meadow, and lower compaction, higher soil moisture, richer sedges in alpine grassland. In the three grassland types, we found that the soil compaction was the key factor of habitat selection of the plateau zokor and food resources was the secondary factor.     

Effects of sheep urine on growth characteristics of different life form plants in a Chinese steppe grassland

The effects of sheep urine deposition volume (0, 1, 2 or 4 L/m²) and deposition stage of plant growth (vegetative or reproductive) on the number and size of tillers/branches and the biomass of Stipa bungeana, Artemisia capillaries and Lespedeza davurica in a Chinese steppe grassland were determined. The results indicate that the response of the three plant species to sheep urine deposition differs, and is influenced by both urine deposition volume and deposition stage of plant growth. Urine deposition had a short-term scorch effect on grassland plants, which mainly occurred in the inner zone of urine patches. Urine application had a long-term positive effect on S. bungeana and a long-term negative effect on A. capillaries and L. davurica, which lasted at least two years and decreased with decrease in urine deposition volume. All species growing in the inner zone of urine patches were scorched by sheep urine deposition, some species in the marginal zone of patches were also scorched, while no species were scorched in the outer zones. The reproductive and vegetative stages of A. capillaries and the reproductive stages of S. bungeana and L. davurica were sensitive to sheep urine deposition.     

不同改良剂对珊瑚砂理化性质和氮素固持的影响

高碱环境和土壤养分的匮乏严重限制了我国热带珊瑚岛土壤环境下植物的生长适应能力,因此,珊瑚砂改良对促进珊瑚岛植被恢复,维持珊瑚岛生态环境可持续健康发展具有重要意义。该研究通过室内土柱模拟试验,对比了同一梯度下4种常用土壤改良材料(蛭石、珍珠岩、生物炭和钙基膨润土)对珊瑚砂理化性质、氮素淋溶以及总氮含量的影响。结果表明,与对照(CK)相比,施用生物炭使珊瑚砂pH显著降低1.4%,钙基膨润土、生物炭和蛭石能够显著提高珊瑚砂的阳离子交换量至CK的24.21、10.43和9.43倍。同时,施用生物炭、钙基膨润土和蛭石并不能降低以硝态氮形式为主的氮素淋失,但是能显著减少其他途径的氮素损失,从而达到促进珊瑚砂氮素固持的效果,3种改良剂施用下的珊瑚砂总氮损失相较于CK分别降低了40.92%、27.32%和25.09%。因此,施用生物炭、钙基膨润土和蛭石均能有效提高珊瑚砂土壤质量,对改良珊瑚砂和热带珊瑚岛植被恢复具有重要意义,其中生物炭的改良效果最为显著,是改良珊瑚砂的理想材料。     

窄行匀播对晚播冬小麦群体环境、个体性状和物质生产的影响

为了明确行距和行内种子分布形式对华北平原晚播冬小麦群体生长的影响,以济麦22为试验材料,在晚播条件下设置3种行距(10、15、20 cm)和2种行内种子分布形式[随机分布(R)和均匀分布(A)]处理,考察了不同处理冬小麦的冠层结构与环境特征、个体性状、生物量累积及产量性能。结果表明:在相同播种量下较小行距比较大行距、种子均匀分布比非均匀分布群体叶面积较大,冠层下部漏光较少,温度较低且相对湿度较高;缩小行距或增加行内种子分布均匀度使群体内个体间植株性状差异缩小,穗层分布趋向均匀,花后物质积累量增加,穗粒重增加,最终产量提高。10 cm行距的产量高于15 cm行距、显著高于20 cm行距;在15 cm和20 cm行距下植株均匀分布处理产量显著高于非均匀分布处理的产量。综合研究认为,窄行匀播是华北平原干旱缺水地区提高晚播小麦群体产量的有效措施。     

青藏高原火绒草斑块群落空间格局分析

以青藏高原两种生境(阴坡和阶地)和4个斑块大小等级水平(等级1:0.2—0.6m2,G1;等级2:0.6—2 m2,G2;等级3:2—3.6 m2,G3和等级4:3.6—8.6 m2,G4)的火绒草(Leontopodium nanum)群落为对象,利用幂乘方法则,分析了其种群和群落空间异质性和群落物种多样性特征,明晰了优势种、亚优势种、伴生种和偶见种对其植被分布格局的影响。结果表明:各火绒草斑块的群落空间分布格局均呈集群分布,植物种的随机出现频率和实际出现频率的方差对数值与其幂乘方法吻合性较高(R2﹥0.8),幂乘方法能对火绒草斑块植被空间分布格局进行客观分析。优势种火绒草和线叶嵩草(Kobresia capillifolia),亚优势种球花蒿(Artemisia smithii)和珠芽蓼(Polygonum viviparum)等的相对空间异质性(ε)高于群落的空间异质性(δC),位于直线y=0上方,使群落趋于集群分布;伴生种西北针茅(Stipa krylovii)、瑞香狼毒(Stellera chamaejasme)和苔草(Carex sp)等的ε与群落的δC类似,位于直线y=0附近,它们维持群落自身空间分布状态;偶见种的ε低于群落的δC,位于直线y=0下方,降低群落的集群分布。随火绒草斑块等级水平的增加,群落物种数呈增加,丰富度指数DGI呈降低变化。一般火绒草斑块的δc和βw为阶地﹥阴坡,DGI为阶地﹤阴坡;两种生境下,植物种组成的相似性G1斑块较低,G2—G4斑块较高。火绒草斑块的群落分布格局主要由优势种和亚优势种及偶见种的ε决定。     

黄土丘陵沟壑区三种豆科人工草地的植被与土壤特征

在黄土高原丘陵沟壑区以 4龄苜蓿 (Medicago sativa)、沙打旺 (Astragalus adsurgens)和甘草 (Giycyrrhiza uralensis)单播人工草地为材料 ,人工牧草、杂草和土壤 3方面研究了其生产性能和生态特性。在相同的管理条件下 ,沙打旺种群高度平均高于苜蓿 33.8% ,是甘草的 6 .2倍 ;苜蓿的密度分别是甘草和沙打旺的 5 .9倍和 2 .6倍 ;沙打旺盖度最大 ,苜蓿次之 ,甘草最小。三种牧草的地上生物量及其占群落生物量的比例依次是苜蓿 >沙打旺 >甘草 ;苜蓿种群生物量占群落的比例接近沙打旺 ,二者远高于甘草。甘草人工草地的杂草种数、杂草生物量及其生物量占群落的比例均最大。0～ 10 0 cm土层内三种人工草地的地下生物量依次为甘草 >苜蓿 >沙打旺。 0～ 10 0 cm土层内营养物质含量 :全 P,苜蓿 >甘草 >沙打旺 ;全 N,苜蓿与甘草接近 ,高于沙打旺 ;速效 P、速效 N都是甘草最高 ;有机质含量 ,苜蓿接近甘草、高于沙打旺。讨论了管理措施与人工草地的关系 ,加大投入是维持人工草地群落稳定的前提之一     

畜尿排泄特征及其对草地植被和家畜选择采食的作用

综述了畜尿特征及其对草地植被和家畜选择采食的作用.畜尿主要成分为尿素,尿斑N浓度一般为20～80 g N/m2.家畜排尿量和尿斑大小与家畜种类、饮水次数和放牧季节有关.畜尿空间分布表现为数量和浓度的不同,常呈线形函数形式随机分布于家畜采食路线周围,尿斑中心与边缘的尿N浓度差别很大.通常,畜尿对草地植物的影响限于尿斑区域,约为尿斑面积的2倍,作用时间可持续6～12个月;对草地植物生长具长期促进和短期灼烧作用,其效应大小与尿N浓度和施尿时期有关.一般畜尿促进禾草生长,抑制豆科草的生长和固氮作用.尿斑处植物的N成分比非施尿斑块高,植物吸收的N量随家畜年排泄N不同而异,尿排泄对植物生长的正效应发生于≤250 kg N/(hm2·a)情况下.畜尿排泄增加草地植物多度、丰富度和群落多样性,并受放牧、培育措施的影响.不同植物对畜尿的响应不同,放牧家畜对尿斑不同植物的选食性和补偿性生长差异,是引起和维持草地异质性的重要因素之一.放牧家畜具优先选食和反复采食尿斑植物或高营养斑块的特点,亦经常在远离高营养植被斑块的地方采食.具体草地管理与生产实践中,可通过在草地采食不足的地方设置饮水点、补饲料及搭荫棚等措施,提高家畜对整个草地的利用,以降低家畜对尿排泄物密集区高N植被斑块的过度采食.