黄河三角洲地区刺槐白蜡人工混交林枯落物分解的林龄差异

为研究黄河三角洲不同林龄刺槐白蜡混交林枯落物分解,选取7,12,21,30年生的刺槐白蜡人工混交林,采用分解袋法研究了为期2年的枯落物分解。结果表明:(1)混交林枯落物分解系数为0.44~0.60,大小顺序为30a21a12a7a;半分解周期为1.15~1.58年,分解周期为4.96~6.83年,两者大小顺序为7a12a21a30a。(2)枯落物分解速率与初始N含量显著正相关,与初始C/N值显著负相关;4个林龄混交林枯落物初始N含量之间差异显著,12,21年生混交林枯落物初始C/N值差异不显著,但它们与7,30年生混交林枯落物初始C/N值差异显著(P0.05)。(3)枯落物分解速率与土壤有机质含量呈显著正相关,与土壤碱解氮含量呈显著正相关;4个林龄混交林土壤有机质、碱解氮含量差异显著(P0.05)。综上,随着林龄的增加,枯落物初始N含量升高,初始C/N值降低,混交林枯落物分解速度加快。     

Snow cover and soil moisture controls of freeze–thaw-related soil gas fluxes from a typical semi-arid grassland soil: a laboratory experiment

In situ field measurements as well as targeted laboratory studies have shown that freeze–thaw cycles (FTCs) affect soil trace gas fluxes. However, most of past laboratory studies adjusted soil moisture before soil freezing, thereby neglecting that snow cover or water from melting snow may modify effects of FTCs on soil trace gas fluxes. In the present laboratory study with a typical semi-arid grassland soil, three different soil moisture levels (32 %, 41 %, and 50 % WFPS) were established (a) prior to soil freezing or (b) by adding fresh snow to the soil surface after freezing to simulate field conditions and the effect of the melting snow on CO₂, CH₄, and N₂O fluxes during FTCs more realistically. Our results showed that adjusting soil moisture by watering before soil freezing resulted in significantly different cumulative fluxes of CH₄, CO₂, and N₂O throughout three FTCs as compared to the snow cover treatment, especially at a relatively high soil moisture level of 50 % WFPS. An increase of N₂O emissions was observed during thawing for both treatments. However, in the watering treatment, this increase was highest in the first thawing cycle and decreased in successive cycles, while in the snow cover treatment, a repetition of the FTCs resulted in a further increase of N₂O emissions. These differences might be partly due to the different soil water dynamics during FTCs in the two treatments. CO₂ emissions were a function of soil moisture, with emissions being largest at 50 % WFPS and smallest at 32 % WFPS. The largest N₂O emissions were observed at WFPS values around 50 %, whereas there were only small or negligible N₂O emissions from soil with relatively low soil water content, which indicates that a threshold value of soil moisture might exist that triggers N₂O peaks during thawing.     

不同螯色罗氏沼虾形态性状对体质量的影响

运用通径分析方法,研究了2种螯色、不同性别的6月龄罗氏沼虾(Macrobrachium rosenbergii)(深蓝螯色雌虾、深蓝螯色雄虾、浅黄螯色雌虾、浅黄螯色雄虾)的22个形态性状对体质量的决定效应,得到相关系数、通径系数和决定系数,并进行了多元回归分析。结果表明,蓝雌组6个性状、蓝雄组8个性状、黄雌组7个性状、黄雄组6个性状与体质量的相关系数达到极显著水平(P0.01)。综合考虑相关系数、通径系数大小和可操作性后认为,深蓝螯色雌虾的育种目标性状首选指标是第1腹节宽,深蓝螯色雄虾、浅黄螯色雌虾和雄虾的首选指标均为全长。     

A retrospective analysis on changes in sediment flux in the Mississippi River system: trends,driving forces,and implications

Journal of Soils and Sediments - The Mississippi River is the largest river in the USA and one of the most regulated rivers in the world. Understanding fluvial sediment flux changes in the...     

The multi-scale spatial variance of soil moisture in the semi-arid Loess Plateau of China

Purpose  

An understanding of soil moisture heterogeneity across spatial scales has been considered to be critical to eco-hydrological research and particularly important for vegetation restoration in semi-arid areas. This study aimed to investigate the spatial variance of deep soil moisture at multiple scales in the semi-arid Loess Plateau of China. The relative importance of the related factors and the dominant driver of soil desiccation were especially discussed.     

有机肥与化肥配施对松花菜花球营养品质和挥发性物质的影响

以松花菜品种力禾青梗100天为材料,设置CK1(不施肥)、CK2(常规施肥)、T1(平衡施肥)、T2(平衡施肥+3 000 kg·hm^-2生物有机肥)、T3(平衡施肥+6 000 kg·hm^-2生物有机肥)和T4(平衡施肥+12 000 kg·hm^-2生物有机肥)6个处理,研究不同处理对松花菜花球营养品质和挥发性物质数量与含量的影响。结果表明:相比CK2,生物有机肥配施化肥(T2~T4处理)有助于提高松花菜花球营养物质含量和挥发性物质的数量与含量。与CK2相比,T3处理下松花菜花球的维生素C含量显著(P<0.05)提高17.6%;T2和T3处理下松花菜花球中的Ca含量分别显著(P<0.05)提高14.3%和36.8%。T2、T3、T4处理下松花菜花球中的挥发性物质数量分别比CK2增加8、12、13种,酮类物质含量较CK2分别增加3.4、2.9和7.1倍。另外,与CK2相比,T2和T3处理下松花菜花球中具有青香、果香和花香味的特征性挥发性物质种类和含量增加。基于营养品质指标和挥发性物质指标的主成分分析综合评价结果显示,6个处理的得分从高到低依次为T3>T2>T4>CK2>T1>CK1。在本试验条件下,较常规施肥化肥减量30%的平衡施肥方案配施6 000 kg·hm^-2生物有机肥处理下松花菜花球的综合品质最优。     

中国旱灾的地理分布特征与灾情分析

本文以农业灾害统计资料为基础,较系统地分析和探讨建国以来各阶段、各地区的旱灾状况及灾情的波动特征,旱灾和灾情的区域分异特征。分析旱灾对我国粮食产量的影响,提出减灾对策。     

Soil erosion and its control in the loess plateau of China

Abstract. The loess plateau in China is the most developed region of loess in the world in terms of extent, thickness and depositional sequence. It is also the region with the most serious soil erosion in the world. This paper reviews the factors and reasons for soil erosion in this area. The loess is prone to vertical cleavage and its surface soils are soft and loose. Rainstorms are frequent with intense rain concentrated during the summer. Irrational land use and exploitive management have been carried out for thousands of years and express themselves through the loss of grassland and natural forests. Finally, some soil conservation schemes for use in the loess plateau are suggested.