Soil water regimes and water extraction patterns under two semi-arid shrub (Atriplex spp.) communities

Soil water regimes and water extraction patterns estimated over a period of two years are described for two plantation communities of semi-arid shrubs, Atriplex vesicaria Hew. ex Benth. and A. nummularia Lindl., growing on the same soil type under identical climatological conditions near Deniliquin, New South Wales. In spite of poor water flow properties of the soil, surface run-off was negligible.About 90% of the extractable water was stored in the top (45 cm) soil layer. Both species withstood exceedingly low water potentials, although A, vesicaria reduced soil water to a much lower water potential than did A. nummularia. Water potentials at depths below 60 cm were always – 15 bars and remained constant. Water extracted beyond –15 bars amounted to 41% more than the water available within conventionally accepted water potential limits (between –0.3 to – 15 bars). During Slimmer, the plant water potential of A. vesicaria fell to much lower values than that of A. nummularia. Relationships between relative leaf water content and plant water potential differed between the two species, and the suggestion is made that at low plant water potential, leaf targidity of A. vesicaria would be higher, and thus this species would have a higher tolerance to desiccation. On a yearly, half-yearly and even a quarterly basis, evapotranspiration (FT) of the two communities did not differ. Fortnightly FT rates were similar during winter but during early summer, the initial ET rate of A. vesicaria was higher than that of A. nummularia; A, nummularia can therefore conserve water for later use. These differences in water extraction patterns and evapotranspiration were associated with differential rooting characteristics and probably differential stomatal functioning. The relationships between fortnightly ET/FO (ratio of actual evapotranspiration to that from a Class A pan) and profile water content, for both communities, were linear but different.     

Role of phloem sap quality and exudation characteristics on performance of pea aphid grown on lucerne genotypes

The phloem sap of two lucerne (Medicago sativa L.) genotypes inducing differences in pea aphid,Acyrthosiphon pisum Harris (Homoptera: Aphididae) performances (weight, fecundity, survival), was collected by stylectomy (radio frequency microcautery). Sugars and amino acids were assayed. No significant difference in their concentrations could be established between genotypes. It is thus unlikely that a substantial part of the varietal resistance of these lucerne genotypes to pea aphid could be related to the content in sugars or amino acids. The same conclusion was drawn for the sugar/amino acid ratio. The amino acid profiles were globally similar. They nevertheless allowed a discrimination between the two genotypes on a few amino acids (alanine, leucine, isoleucine, arginine, ornithine) only. Moreover, the degree of resistance can be related neither to GABA concentration, nor to that of sulfur amino acids, because these constituants were either absent, or in trace amounts, whatever the lucerne genotype taken into account. Stylectomy parameters revealed some interesting differences in the sap exudation of the two genotypes. Average volume of exudation by stylet and average duration of exudation were respective 2.8 and 2.3 times higher in the susceptible genotype. These results suggest a reduced flow of phloem sap, after puncturing of the sieve-tubes by the aphid stylets on the resistant genotype; this could result in a greater difficulty in phloem sap ingestion by aphids settled on the resistant genotype and thus in suboptimal performances.     

Partitioning the parameters of stony soils,important in moisture determinations into their constituents

Partitioning the parameters of stony soils in order to express their water content on a volumetric basis, into their pure stone and pure soil constituents, is an important step towards understanding the behavior of such nonhomogeneous systems.The equations derived are exact mathematical identities. Their applications are discussed.Contribution from Agricultural Research Organization, Volcani Center, Bet Dagan, Israel. Serial No. 226-E.     

Soil water dynamics and vegetation patterns in a semiarid grassland

Long-term (1985–1992) dynamics and spatial variations in soil water below the evaporative zone were evaluated for a shortgrass steppe with a low and variable precipitation regime. Each of a sandy loam, clay loam, and two sandy clay loam sites comprised a toposequence with upland, midslope and lowland positions. Soil water was monitored at 15 cm intervals providing estimates covering 22.5 to 97.5 cm depths.Soil water throughout the profile was highest in the clay loam site and lowest in the sandy loam site. However, stored soil water did not vary systematically among slope positions. Total vegetation cover was highest on the lowland in two sites, but was greatest on the midslope position in the other two. Total vegetation cover was greatest on the CL site, which was the wettest in terms of soil water. Soil water depletion was related to the depth-distribution of roots. There was an inverse relationship between aboveground production and soil water content of the 30, 45 and 60 cm layers during the growth period. Root distributions through the profile did not, however, vary with soil texture or with different soil water profiles controlled by texture. The less variable water content of deeper soil layers is a resource which potentially buffers the impact of pronounced variability in precipitation and thus contributes to vegetation stability of the shortgrass community.     

Observations on root hair production by lucerne,maize and perennial ryegrass grown in a sandy loam

Summary Root hair production by young plants of lucerne, maize and perennial ryegrass grown in a sandy loam was assessed by examining roots growing at a soil-glass interface. Results are given for the percentage frequency distribution of root hair lengths and the numbers of root hairs produced per mm root. The mean lengths of root hairs observed on lucerne, maize and perennial ryegrass roots were 0.35, 0.90 and 1.12 mm respectively. Lucerne produced an average of 105 root hairs per mm of root, whereas maize produced 161 and perennial ryegrass produced 88. The total length of root hairs per mm length of root was estimated to be 37, 146 and 99 mm for lucerne, maize and perennial ryegrass resp. Letcombe Laboratory     

Effect of inoculation on element uptake by plants grown on saline soils

A relationship between inoculation and elemental uptake ofMedicago sativa inoculated withRhizobia meliloti (isolated from a saline area) was found. The plant uptake of the elements with atomic number between 19 and 42 was significantly higher in plants grown on inoculated soils, with the exception of molybdenum. Preliminary evidence shows that the concentration of some elements was affected by inoculation.     

黄土塬区不同土地利用方式下深层土壤水分变化特征

利用长期定位监测数据,对陕西省长武黄土塬区裸地、高产农田、苜蓿草地和苹果林地下0—15 m黄土剖面土壤水分环境进行了研究。结果表明,不同土地利用方式下,干湿交替层内土壤水分具有明显季节性波动变化特征,但其深度范围有别。裸地、高产农田、苜蓿草地和苹果林地分别约为0—5 m,0—4 m,0—2 m和0—3.5 m。干湿交替层以下深层土壤水分状况主要受土地利用方式的影响,其影响大小依次为苜蓿草地苹果林地高产农田裸地,各土地利用方式下表现出不同的时间变化特征。黄土塬区土壤水量平衡计算中土层厚度大小的确定非常重要,这不仅与土地利用方式相关,也与林草植被的生长阶段相联。裸地和高产农田土层厚度选择不宜小于5 m和4 m;未形成深厚稳定土壤干层的苜蓿草地和苹果林地,土层厚度选择不宜小于15 m和10 m;对于已经形成稳定土壤干层的林草地来说,进行年尺度的水量平衡分析时,其计算深度可取降水入渗深度。研究可从土壤水资源的保持及利用的角度上服务于黄土塬区旱作农业的持续发展和土地利用方式的优化配置。     

Expression patterns of three genes in the stem of lucerne (Medicago sativa)

We have identified three stem abundantly expressed genes in lucerne (alfalfa, Medicago sativa). A cDNA library, constructed from lucerne stem polyadenylated RNA, was screened by differential hybridization. From this screening, cDNA clones that correspond to genes which are preferentially, or specifically, expressed in the stem were isolated. MsaS1 encodes an unidentified protein, MsaS2 encodes an S-adenosyl-homocysteine hydrolase and MsaS3 encodes an extensin-like protein. Northern blot analysis of RNA isolated from individual stem internodes indicated that the three corresponding genes show differing developmental patterns of expression. The expression of MsaS1 was confined to the youngest stem tissue and may be regulated by sucrose. In stem tissue the level of RNA for the three genes decreased in response to wounding. Tissue print hybridization analysis was used to localize the expression of the genes to the xylem side of vascular bundles in lucerne stems.     

Accumulation of magnetic nanoparticles in plants grown on soils of Apsheron peninsula

The disclosure of magnetic nanoparticles in five plant species growing in Apsheron peninsula have been detected by the EPR method. The EPR spectra of these nanoparticles proved to be similar to those of synthesized magnetic nanoparticles. The result demonstrated that plants are capable of absorbing magnetic nanoparticles from the soil. The accumulation of nanoparticles in plants is confirmed by the presence of a broad EPR signal whose maximum position of the low-field component changes from g = 2.38 and halfwidth of the signal of 32 mT at room temperature to g = 2.71 and 50-55 mT at 80 K. The intensity of the broad EPR signal for plants grown in radioactively contaminated areas (170-220 mkR per h) was substantially lower compared with plants grown on clean soil. The parameters of the broad EPR signal and its dependence on the temperature of recording were identical with those for synthetic magnetic nanoparticles. The photosynthetic activity and changes in the genome of irradiated plants by the analysis of PCR products were studied.     

Accumulation of magnetic nanoparticles in plants grown on soils of Apsheron peninsula

Magnetic nanoparticles in five plant species growing on the Apsheron peninsula have been detected by the EPR method. The EPR spectra of these nanoparticles proved to be similar to those of synthesized magnetic nanoparticles. The result demonstrated that plants are capable of absorbing magnetic nanoparticles from the soil. The accumulation of nanoparticles in plants is confirmed by the presence of a broad EPR signal whose maximum position of the low-field component changes from g = 2.38 and half-width of the signal of 32 mT at room temperature to g = 2.71 and 50–55 mT at 80 K. The intensity of the broad EPR signal for plants grown in radioactively contaminated areas (170‐220 μR/h) was substantially lower compared with plants grown on clean soil. The parameters of the broad EPR signal and its dependence on the temperature of recording were identical with those for synthetic magnetic nanoparticles. The photosynthetic activity and changes in the genome of irradiated plants by the analysis of PCR products were studied.     

Availability of fluoride to plants grown in contaminated soils

Two pot experiments were carried out to study uptake of fluoride (F) in clover and grasses from soil. Fluoride concentrations in t Trifolium repens (white clover) and t Lolium multiflorium (ryegrass) were highly correlated with the amounts of H₂O– and 0.01 t M CaCl₂–extractable F in soil when increasing amounts of NaF were added to two uncontaminated soils (r=0.95–0.98, t p<0.001). The amounts of H₂O– or 0.01 t M CaCl₂–extractable F did not explain the F concentrations to a similar extent in t Agrostis capillaris (common bent) grown in 12 soils (Cambic Arenosols) collected from areas around the Al smelters at Å: rdal and Sunndal in Western Norway (r=0.68–0.78). This may be due to variation in soil pH and other soil properties in the 12 soils. Soil extraction with 1 t M HCl did not estimate plant–available F in the soil as well as extraction with H₂O or 0.01 t M CaCl₂. Fluoride and Al concentrations in the plant material were positively correlated in most cases. Fluoride and Ca concentrations in the plant material were negatively correlated in the first experiment. No consistent effects were found on the K or Mg concentrations in the plant material. The F accumulation in clover was higher than in the grasses. The uptake from soil by grasses was relatively low compared to the possible uptake from air around the Al smelters. The uptake of F in common bent did not exceed the recommended limit for F contents in pasture grass (30 mg kg^–1) from soil with 0.5–28 mg F(H₂O) kg^–1 soil. The concentration in ryegrass was about 50 mg F kg^–1 when grown in a highly polluted soil (28 mg F(H₂O) kg^–1 soil). Concentrations in clover exceeded 30 mg F kg^–1 even in moderately polluted soil (1.3–7 mg F(H₂O) kg^–1 soil). Liming resulted in slightly lower F concentrations in the plant material.     

直接从土壤中提取DNA的方法

研究微生物的多样性 ,即微生物的种类和数量的多少是评价土壤质量的重要指标。由于土壤微生物种类繁多 ,数量巨大 ,加上土壤中 99%的种类难以通过传统的平板分离技术来进行培养[1],人们必须借助其他技术来解决。近年发展的非培养技术 ,如ＢＩＯＬＯＧ微量板分析技术[2 ]、细胞壁磷脂酸分析技术[3]和分子生物学方法[4 - 6 ],克服了培养的环节 ,对微生物生态学研究产生极大的推动作用。其中分子生物学是应用最广、最有发展潜力的技术。它的主要步骤是通过直接提取土壤中的ＤＮＡ ,经纯化处理后 ,利用合适的引物扩增 1 6ＳｒＲＮＡ基因 ,通过分…     

Nutritional composition of water hyacinths grown on domestic sewage

A nutrient analysis of water hyacinths grown in sewage wastewaters was conducted. Crude protein averaged 32.9% dry weight in the leaves, where it was most concentrated. The amino acid content of water hyacinth leaves was found to compare favorably with that of soybean and cottonseed meal. The vitamin and mineral content of dried water hyacinths met or exceeded the FAO recommended daily allowance, in many cases. It is concluded that in favorable climatic zones, water hyacinths grown in enriched mediums, such as sewage lagoons, could potentially serve as a substantial dietary supplement or nutrient source.     

Influence of soil heterogeneity on water regime and yields of lucerne,sugar beet and wheat

Lucerne plants in the first crop year as well as plants of spring wheat from different sites of the respective experimental plots showed differences in sap exudation from detopped roots or from stumps of the main shoots, reflecting differences in properties of the soil profile. The differences in sap exudation were observed at a time when the plants did not show any visible differences in water availability. Differences in the water potential deficit of the leaf blades of lucerne plants in the second crop year and of sugar beet plants, related to differences in soil profile properties, were observed in another series of experiments. Sugar beet plants showed a higher physiological lability than lucerne plants. The sites characterized by unfavourable plant-water-relations usually gave lower yields. The coefficients of variability for the yields of lucerne fresh matter from irrigated plots were three times lower than those for yields from plots without irrigation, influenced by soil heterogeneity.     

Seasonal water use patterns of woody species growing on the continuous dolostone outcrops and nearby thin soils in subtropical China

In karst regions, forests often grow on bedrock outcrops, however the water sources used by the forest vegetation are not known. This study aimed at investigating whether there were seasonal shifts (dry/wet season) of water sources for plants growing on the continuous dolostone outcrops, and comparing their differences with those growing on nearby thin soils in karst areas of southwest China. Rainwater, soil water within 0–30 cm depths, spring water (as a reflection of local deep water sources) and plant xylem water were sampled in March (late dry season) and July (mid rainy season) 2009, respectively. A direct inference approach and the IsoSource mixing model were used to estimate the contributions of different sources to the plant xylem water. On the outcrops, the deciduous tree species Radermachera sinica mainly used deep water sources during the dry season and a mixture of rainwater and deep water sources during the wet season. By contrast, the deciduous small shrub Alchornea trewioides largely relied on recent rainwater during both dry and wet seasons. Three non-deciduous species (Sterculia euosma, Schefflera octophylla and Ficus orthoneura) appear to rely on deep water sources during the wet seasons. In nearby thin soils, R. sinica mainly utilized deep water in the dry season and a mixture of soil water and deep water in the wet season. A. trewioides relied on the same water sources (rainwater-derived soil water) in the different seasons. The above results indicate that inter-specific differences in rooting patterns and leaf phenologies may lead to the differences in the sources of water used by coexisting plant species in karst regions.     

The role of water lichens in the biogeochemical processes in the Lake Baikal stony littoral

Water crustose lichens of g. Verrucaria (V. scabra Vězda, V. rheitrophyla Zsch., V. maura Wahlenb. in Ach., and V. hydrela Ach.) and water foliose lichen Collema ramenskii Elenk. were studied in the stony littoral of the western coast of Lake Baikal in 2002–2006. Their densities were highest at depths of 1.5 to 2 m; 95–100% of rock fragments collected from the depths of 1.5–2.2 m were covered by plentiful crustose thalli of Verrucaria spp. Lichens make a large contribute to the destruction of the stony ground in the shallow-water zone. Unlike water, foliose and crustose lichens concentrate Ti, La, Ce, Y, Mn, and Th. Thalli of Collema ramenskii differ from Verrucaria species in their ability to accumulate Zn, Co, and Ni. Compared to the bottom sediments, all the studied water lichen species concentrate Zn, while Collema ramenskiiconcentrate Zn and Mo.