To understand the variations of the metabolic function of soil G+ and G- bacteria on the mobile sand dune of Horqin sandy land after the establishment of sand-fixing Caragana microphylla plantation, Biolog-GN2 and GP2 microplate tests were conducted to study the functional diversity of carbon sources metabolism of soil G+ and G- bacteria in the 9-, 16-, and 26-year-old C. microphylla plantations, with the mobile sand dune and natural C. microphylla community as the controls. The establishment of C. microphylla plantation on the mobile sand dune resulted in a gradual increase of the functional diversity of carbon sources metabolism of soil G- bacteria, and their Shannon index and evenness index for the 0- to 26-year-old plantations increased from 3.85 to 4.17 and from 0.85 to 0.94, respectively. As for G+ bacteria, their Shannon index and evenness index had a significant decrease first (P0.05), and then increased gradually with the increasing age of C. microphylla plantation. The carbon source types (carbohydrates, carboxylic carbons, amphiphilic compounds, polymers, amines, and amino acids) metabolized by soil G+ and G- bacteria increased with plantation age. The utilization patterns of carbon sources by the soil G+ and G- bacteria in 26-year-old C. microphylla plantation were similar to that in natural C. microphylla community.
The coast of Jiangsu Province is famous for its radial sandbanks offshore.Dynamic changes of tidal creeks are difficult to survey for complex,quick-changing terrain.Medial axis methods of tidal creeks are the focus of this paper.The concept of medial axis in mathematics,as well as voronoi diagram(V diagram) in GIS for its special properties,was introduced and discussed,.Points in every edge of V diagram have the shortest distance to adjacent edges of polygon.Thus,medial axis extraction is converted to V diagram generation.Remote Sensing Medial Axis method(RSMA method) is presented because it is quick and convenient for survey,much better than previous traditional visual interpretation methods.Using the RSMA method,five main tidal creeks in the area were extracted and studied based on four TM images from 1988,1995,2003 and 2008.The results showed that:(1) for analysis on main tidal creeks in different time,RSMA method revealed the dynamic evolution quickly and accurately;(2) during the last 20 years,Xiyang deep trough had the greatest changes as the west coast retreated back and the east extended east;while the rest four tidal creeks moved in the north-south direction periodically and went straight gradually.Therefore,study on the evolution of tidal creeks has great significance for monitoring the dynamic changes of tidal fiat,development and utilization of coastal zone and the construction of coastal engineering.
In an arid region, water shortage limits agricultural development, and worse, soil salinization is accompanied by soil moisture drought. In this region, hydraulic lift occurs due to the drying upper layer caused by high precipitation and the wet lower layer. Hydraulic lift is defined as water redistribution from wetter, deeper soil layers to drier, shallower soil layers near the soil surface through the plant roots. To examine the effects of water and salt stresses on tomato yield and fruit quality under the condition of hydraulic lift, a 2year experiment was conducted. Different water and salt treatments were designed, including three water levels (W1, W2 and W3 indicating soil moisture contents of 60%–70%, 50%–60% and 40%–50% of the field capacity, respectively) and four salt levels (S0, S1, S2 and S3 indicating NaCl addition of 0%, 0.2%, 0.4% and 0.6% of the dry soil weight, respectively) of the upper pot, and water and salt levels of control treatment (CK) were W1 and S0, respectively. The yield under other treatments significantly decreased by 4.59%–58.39% and 5.12%–62.96% in 2018 and 2019, respectively, compared with that under CK, and the yield under W1S1 treatment had no significance with that under CK in 2018. The firmest fruit quality was observed in the plant under W3S1 treatment, and the percentage increases were 28.67% and 28.89% in both years compared with that under CK. Water, salt stress and their interactions had significant effects on tomato taste quality and vitamin C. Tomato taste quality and vitamin C decreased under the W3 and S3 treatments. In both years, the total magnitudes of hydraulic lift during the entire growth period were higher under the W1S2 treatment (65.20% and 76.06%, respectively) than that under CK. Whereas yield and total magnitudes of hydraulic lift were significantly both correlated with single fruit weight, single fruit volume, fruit shape index and taste qualities, no correlations were observed between hydraulic lift and yield. Mild waterdeficit and salt stresses could improve tomato quality with negligible yield loss, and hydraulic lift had positive effects on fruit quality. Principal component analysis revealed that the combination of W1 and S1 treatments increased fruit quality and total hydraulic lift magnitudes with an acceptable yield decline. These results are important for tomato production in arid saline-alkali region where hydraulic lift is positively corelated with fruit quality and famers may consider this trait to resist drought and soil salinization. Future studies focusing on the effects of the internal mechanisms of hydraulic lift caused by changes in sap flow on tomato quality and yield are warranted.
Expansins are cell wall (CW) proteins that mediate the CW loosening and regulate salt tolerance in a positive or negative way. The transcription of Populus trichocarpa expansin A6 (PtEXPA6) was downregulated upon prolonged duration of salt stress (48 h) after a transient increase induced by NaCl (100 mM). The role of PtEXPA6 in salt tolerance was determined by transferring the PtEXPA6 gene into the hybrid species Populus alba × P. tremula var. glandulosa clone 84K (84K) and Populus tremula × P. alba INRA '717-1B4' (717-1B4). The PtEXPA6-transgenic poplars of 84K and 717-1B4 showed a greater reduction in photosynthesis, stem height and diameter growth under salt stress and a reduced capacity for ROS scavenging by antioxidant enzymes, which is associated with excessive Na+ accumulation in roots and shoots. NMT flux recordings showed that the radial translocation of Na+ salt into the root xylem and real-time Na+ translocation from roots to leaves were greater in PtEXPA6-transgenic poplars than in wild-type poplars. Analysis of comparative contractility and comparative extensibility of intact root tips indicated that PtEXPA6 increased the CW loosening in the transgenic poplars of 84K and 717-1B4. Noteworthy, the PtEXPA6-promoted CW loosening was shown to facilitate radial and longitudinal transport of Na+ in transgenic poplars. We conclude that overexpression of PtEXPA6 leads to CW loosening that facilitates radial translocation of Na+ into the root xylem and subsequent Na+ translocation from roots to leaves, resulting in excessive Na+ accumulation and consequently reduced salt tolerance in transgenic poplars.
Germination and hydroponic experiments are performed on rice seeds growing in soils treated with Cd stress, with rice seeds of the same variety that is not treated with Cd stress as a control, to study the effects of Cd stress on quality of rice seeds. The results have shown that: (1) Cd stress reduces the thousand grain weight of rice seeds, and higher Cd content means lower thousand grain weight; (2) The germination vigor and germination percentage of rice seeds under Cd stress as well as their I±-amylase activity and I²-amylase activity are all lower than those of the control. They decreases as the Cd stress increases; (3) For rice seeds under Cd stress, the height, fresh and dry weight of seedlings, as well as the chlorophyll content, photosynthetic rate and content of soluble protein of their leaves are all lower than those of the control. This indicates that Cd stress has certain effects on the germination and growth of the rice seeds.
This paper analyzes the principles and shortages of the calculation methods for channel storage volume which are commonly used,i.e.slice method,sediment-transport method and topographic method.Using the underwater terrain maps from 1973 to 2002,the paper creates DEM,then analyzes the precision,calculates the channel storage volume,and intersects different data,finds the change of channel storage volume and visualizes the change of underwater terrain,and comes into the following conclusions:(1)Precision of the DEM built based on chart data is very well,and the mean square error in 1982 is only 0.78 m;(2)During 1973-2002,the channel storage volume of the North Channel is enlarged,and the scouring volume is 1.60×108 m3;During 1982-1987,the channel storage volume is reduced,and siltation occur in the channel;(3) The riverbed of the North Channel is unstable and changing.The stream makes sand remove and subside,and floods play an important role in the North Channel evolution.
Revegetation by planting shrubs on moving sand dunes is widely used to control desertification in arid/semi-arid areas. The soil including microbial community can gradually be improved along with plantation development. The purposes of this study were (1) to investigate the responses of microbial communities involved in the mineralization of soil organic phosphorus (OP) and dissolution of inorganic P (IOP) in the development of sand-fixating plantation and (2) to discuss the interactions between P turnover microbial communities and soil properties. We assessed the compositions of soil phoD gene (one of the Pho regulons encoding alkaline phosphomonoesterases) and gcd gene (encoding glucose dehydrogenase) in microbial community by using high-throughput Illumina MiSeq sequencing in a chronosequence of Caragana microphylla plantations (0-, 10-, 20-, and 37-year plantations and a native C. microphylla shrub forest) in Horqin Sandy Land, Northeast China. Soil properties including soil nutrients, enzymatic activity, and P fractions were also determined. The abundance of phoD and gcd genes linearly increased with the plantation age. However, the diversity of soil phoD microbes was more abundant than that of gcd. The phoD gene abundance and the fractions of total OP and IOP were positively correlated with the activity of phosphomonoesterase. Actinobacteria and Streptomycetaceae were the dominant phoD taxa, while Proteobacteria and Rhizobiaceae were the dominant gcd taxa. Plantation development facilitated the progressive successions of soil phoD and gcd communities resulting from the increase in the abundance of dominant taxa. Total soil N, NH4-N, and available K were the main factors affecting the structures of phoD and gcd communities, while pH was not significantly influencing factor in such arid and nutrient-poor sandy soil. Many phoD or gcd OTUs were classified into Rhizobium and Bradyrhizobium, suggesting the coupling relationship between soil P turnover and N fixation.
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