Impact of salt stress on the features and activities of root system for three desert halophyte species in their seedling stage

Linkage between belowground and aboveground sections of ecological system is mainly depending on root system. But root system is the parts of plant that people less understand. The absorption function of root system is closely related to their morphology and activity. Moreover root system can interact with the environmental stress under the adverse situation, and adjust its system to take adaptation responses in morphology and physiology to strengthen its survival chance. This research is focused on three desert halophyte species of H. ammodendron (C.A.Mey.) Bge., S. physophora Pall., and S. nitraria Pall. under solution culture, to study the differences of their root system morphology and activity in the seedling stage under varying salt concentration conditions. The study results show that: A certain salt concentration can promote development of these three halophytes; but rather high salt concentration will restrain their growth, in particular inhibit the root system development. Under the same salt concentration condition, S. nitraria Pall. grows fast and accumulates the largest amount of biomass. Under relatively low salt concentration, the length of axial root and the total length of root system of these three halophyte species are all increased; and compared to the checking samples, S. physophora Pall. occupies the top place of root system growth, but the high salt concentration will restrain the increase of total root length; among them, the impact intensity on S. physophora Pall. is lighter than to H. ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. is lighter; the salinity does not bring distinct influence on the average diameter of root system of these three plant species, but trends to reducing the size; under the solution culture conditions, the middle and lower parts of the axial root of H. ammodendron (C.A.Mey.) Bge. and S. physophora Pall. are rather equally distributed, but the central zone of S. nitraria Pall. root system is more significantly increased than the upper and lower zones; salt concentration does not bring significant impact on the root system spatial distribution of each species. The root activity of the three plants is increased along with the increase of the salt concentration. When the salt concentration is low, the root activity is not significantly increased; but when the salt concentration is high, the root activity is increased significantly. The experimental results show that the saline tolerance capacity of H. ammodendron (C.A.Mey.) Bge. is lower than the other two species, and the capacity of S. physophora Pall. ranks the top place.     

Patterns of shrub species richness and abundance in relation to environmental factors on the Alxa Plateau: Prerequisites for conserving shrub diversity in extreme arid desert regions

Shrub species are considered the dominant plants in arid desert ecosystems, unlike in semiarid steppe zones or in grassland ecosystems. On the Alxa Plateau, northern China, sparse vegetation with cover ranging from 15% to 30% is characterized mainly by multifarious shrubs because herbaceous species are strongly restricted by the extreme drought climate, wind erosion, overgrazing and sand burial. Patterns in shrub species richness and species abundance in relation to environmental conditions were examined by DCA (detrended correspondence analysis) and interpreted by a biplot. The relationships between species diversity and environmental factors were examined using regression analyses. Our results show that the distributions of the shrub species in response to environmental conditions can be grouped into four ecological types, corresponding with the biological traits of the shrubs and their responses to the gradients of soil texture and soil water content. Patterns in species richness and species abundance were mainly determined by the deeper soil water content, instead of the soil texture as hypothesized by numerous studies in semiarid grasslands. With exception of the deeper soil water content, soil organic matter and total N content were positively correlated with species abundance, while pH was negatively correlated with it. These findings imply that it is vital for current shrub diversity conservation to reduce agricultural water use in the middle reaches of the Heihe River, which supplies water for the lower reaches in the western parts of the plateau, and to reduce the amount of groundwater exploitation and urban and oasis water use, to increase the water supply from Helan Mountain to the eastern desert of the Alxa Plateau. Supported by National Key Technology R & D Program (Grant Nos. 2007BAD46B03, 2006BAD26B0201) and National Natural Science Foundation of China (Gant No. 40825001)     

镍添加对水鳖(Hydrocharis dubia)叶片镍和营养元素含量以及氧化胁迫和抗氧化系统的影响

采用营养液水培的方法,研究不同镍(Ni)添加浓度(0、0.05、0.10、0.15、0.20 mmol/L)对水鳖(Hydrocharis dubia)叶片中Ni元素积累、营养元素(Ca、Mg、K、Fe和Mn)含量、氧化胁迫和抗氧化系统的影响.结果显示:(1)叶片中Ni含量以浓度依赖的方式增加;(2)叶片中营养元素含量(Ca、Mg、K、Fe、Mn)也受影响,其中Ca、Mg含量随Ni浓度增加而显著上升;K含量随Ni浓度增加有所升高,但不显著;Mn含量虽在较大Ni浓度时有所下降,但处理组始终高于对照组;而Fe含量则随Ni浓度增加而下降;(3)Ni胁迫诱导了明显的氧化胁迫,主要表现为:O·-2产生速率以及过氧化氢和丙二醛含量显著升高,可溶性蛋白以及光合色素含量明显下降;(4)随着Ni浓度的升高,过氧化物酶活性逐渐升高,过氧化氢酶活性呈下降趋势,超氧化物歧化酶活性在Ni添加浓度为0.05 mmol/L时出现短暂升高随后下降;维生素E和黄酮含量随Ni浓度增加呈缓慢上升趋势;还原型谷胱甘肽未发生明显变化,非蛋白巯基和植物络合素含量均表现为先升后降的趋势;总抗氧化能力随Ni浓度升高先增强后减弱.由此可见,Ni添加引起水鳖叶片中Ni元素的累积和营养元素含量变化,同时产生明显的氧化胁迫,打破了抗氧化系统的平衡.