A Simple Method for Quantitative Estimation of Rhizosphere pH along Root Axes through Visualization

Abstract

Rhizosphere pH is known to be strongly influenced by nitrogen sources and plant species. We have evaluated whether the exposure of the shoot to light affects the pH changes in the rhizosphere of legumes and cereals in the presence of different forms of nitrogen (ammonium, nitrate or both). The pH changes in the rhizosphere were quantified as apparent proton fluxes by image analysis of agar gel containing a pH indicator, in which the root was embedded. In the presence of ammonium or ammonium nitrate, the rhizosphere was alkalized under dark conditions and acidified under light conditions in both cowpea and sorghum. This implied that, in the presence of ammonium, acidification of the rhizosphere is induced by exposure of shoot to light. In the presence of nitrate, both plants alkalized their rhizospheres in the dark, whereas in the light cowpea acidified its rhizosphere although sorghum alkalized it. Light-induced acidification, in the presence of nitrate, was also found in chickpea and adzuki bean, but not in maize. We found, that a particular part of the root axis strongly acidifies the rhizosphere in response to the exposure of shoot to light, especially in legumes. We conclude that rhizosphere pH is strongly affected by the light conditions encountered by the shoot, and the pH changes in response to the light locally along the root axis.     

Hydrogen Stable Isotope Analysis of Water Acquisition Ability of Deep Roots and Hydraulic Lift in Sixteen Food Crop Species

Abstract

Deep root penetration, which allows access to deep soil water and hydraulic lift, may help plants to overcome drought stress. The aim of this study was to evaluate the ability of sixteen food crop species to take up water from deep soil layers and the extent of hydraulic lift by the use of deuterated water. Plants were grown in pots consisting of two loose soil layers separated by a hardpan and a Vaseline layer. The lower (deep) layers were always kept wet (32%; ψ = –5 kPa), while soil moisture in the upper (topsoil) ones was adjusted to 25% (ψ = –7 kPa) and 12% (ψ = –120 kPa) in the well-watered and drought treatments, respectively. The deuterium labeling of the deep soil water provided evidence that wheat, Job’s tears, finger millet, soybean, barnyard millet, rice, and rye (in decreasing order of D₂O increments) extracted more water from the deep layers under drought than well-watered in topsoil. These species showed significantly greater hydraulic lift under drought, except for soybean. Most of these species also showed increased root length density in deep soil layers and sustained high photosynthetic rates under drought. In contrast, pigeon pea, cowpea, common millet, pearl millet, foxtail millet, maize, barley, and oat did not show a significant increment in either deep-water uptake or hydraulic lift under drought. In summary, increased extraction of deep soil water under drought was closely related with the magnitude of hydraulic lift.     

Tillage effects on maize yield in a Colombian savanna oxisol: Soil organic matter and P fractions

Soil organic matter (SOM) and phosphorus (P) fractions play a key role in sustaining the productivity of acid-savanna oxisols and are greatly influenced by tillage practices. In 1993, a long-term experiment on sustainable crop rotation and ley farming systems was initiated on a Colombian acid-savanna oxisol to test the effects of grain legumes, green manures, intercrops and leys as possible components that could increase the stability of systems involving annual cereal crops. Five agropastoral treatments (maize monoculture—MMO, maize–soybean rotation—MRT, maize–soybean green manure rotation—MGM, native savanna control—NSC and maize-agropastoral rotation—MAP) under two tillage systems (no till-NT and minimum tillage-MT) were investigated. The effects of NT and MT on SOM and P fractions as well as maize grain yield under the five agropastoral treatments were evaluated. Results showed that soil total C, N and P were generally better under no-till as compared to minimum-tilled soils. While P fractions were also generally higher under no-till treatments, SOM fractions did not show any specific trend. Seven years after establishment of the long-term ley farming experiment (5 years of conventional tillage followed by 2 years alternative tillage systems), MT resulted into moderately higher maize grain yields as compared to NT. The MGM rotation treatment had significantly higher values of maize yield under both tillage systems (4.2 Mg) compared to the NSC (2.3 Mg ha⁻¹). Results from this study indicate that the rotational systems (maize–soybean green manure and maize-pastures) improved the soil conditions to implement the no-till or minimum tillage systems on Colombian savanna oxisol.     

中山人工草地共生固氮和尿素的去向

试验结果表明，亚热带中山草地施入75kg／ha15N－尿素能明显提高鸭茅产草量，其N％的增加显著高于多年生黑麦草；豆科牧草的N％不受施氮的影响。但是，巴东红三叶的固氮活性因尿素的施入而显著降低，胡依阿白三叶则无明显变化。前者固定空气氮量占植株地上部全氮量的81．95～93．24％，后者为56．64～69．84％。草场中生长10年以上的红三叶固氮百分率为91．82±7．65％，白三叶为54．74±12．34％。15N－尿素施入50天内豆禾牧草混播植株吸收利用36．02％，土壤残留46．79％，仅有17．18％的尿素损失；而混播禾本科牧草分别为28．44％、34．29％和37．20％。表明豆禾牧草混播显著优于禾本科牧草混播。在施入少量化合态氮素的情况下，禾本科牧草主要吸收土壤氮素，其吸收量占植株全氮的62．41～72．87％，豆科牧草则主要依靠共生固氮满足其生长和繁殖所需。     

扁穗牛鞭草的他感作用研究

扁穗牛鞭草是我国南方重要的饲草来源,但在与豆科牧草混播时却难以成功,因为它具有较强的竞争能力和对其他植物的排斥作用。本研究通过牛鞭草根、茎、叶浸出液对豆科牧草种子发芽率和发芽势的影响,以寻找能与扁穗牛鞭草混播的草种,以提高牧草的产量和质量。试验结果表明,牛鞭草的根浸出液对所有试验豆科牧草种子(川引拉丁诺白三叶、Dory红三叶,Cherokee红三叶、巫溪红三叶、箭三叶)均有抑制作用,而茎、叶浸出液对豆科牧草种子的抑制作用不明显。     

沙坡头地区豆科植物共生固氮资源初步研究

对沙坡头地区引进和野生的１９属５１种豆科植物的结瘤固氮状况进行了调查，除花生，三刺皂荚，铃铛刺３属３种外，其余４８种均能自然结瘤，种的结瘤率为９４．１％，其中２７种为Ａｌｌｅｎ文献中未记载的结瘤豆科植物。根瘤形态大多数圆形，棒状域指状，形态较为规则，白色黄色者居多，乙炔还原活力测定表明，２４．６％为无效根瘤，不同种豆科植物根瘤的乙炔还原活力相差不大，一般活力都较低，乙炔还原活力小于１μｍｏｌＣ２Ｈ     

一种新的蒺藜苜蓿遗传杂交方法

遗传杂交技术是开展遗传研究的基本工具,也是研究基因功能的必要手段之一。虽然对豆科模式植物蒺藜苜蓿(Medicago truncatula)的研究愈来愈多,但其遗传杂交技术因难度较高而只被研究蒺藜苜蓿比较悠久的科研团体掌握。为了便于更多实验室能够掌握该项技术,本文在已报道的蒺藜苜蓿杂交方法的基础上提出了一种新的杂交技术。研究内容包括蒺藜苜蓿的花果发育周期、花解剖结构、不同发育时期花的花药发育、遗传杂交程序、母本花的选择标准以及杂交鉴定等。本研究所提出的蒺藜苜蓿杂交方法与已有其它杂交方法相比,具有操作难度低、杂交后无需特殊护理措施、杂交成功率高等特点。     

Potential of sun hemp residue to provide potato with adequate nitrogen

Sun hemp (Crotalaria juncea L.) residue as a proper nitrogen (N) source for a potato crop (Solanum tuberosum L.) was investigated. Leaf nutritional indices (LNI), i.e, SPAD (SPAD-502, Minolta, Japan), total chlorophyll (CHLT), and N-total content, and their validity to predict tuber yield and N recovery were estimated. Moreover, comparison with mineral N fertilization was conducted. The estimated variables exhibited linear increase patterns to sun hemp N rates. Moreover, correlation coefficients between LNI and yield components were significant. Comparison of sun hemp N-amounts with mineral nitrogen showed lower SPAD values, similar CHLT, N-total, and N recovery. However, the elevated application produced superior yields to mineral one. Sun hemp residue incorporation prior to potato accounted for adequate N supply. Additionally, LNI are appropriate tools to determine potato N status and enable yield prognoses.     

磷胁迫下豆科作物的基因调控

磷胁迫是全球耕地面临的共性问题.自然资源的局限限制了磷肥的生产,因此植物如何高效利用磷素已经成为研究热点.从基因调控的角度,包括磷胁迫诱导的EST、磷胁迫响应的转录因子、磷胁迫响应的MICRORNA以及植物激素等,综述了植物高效吸收利用磷素的机制.     

Grazing behaviour,intake and performance of dairy ewes with restricted access time to berseem clover (Trifolium alexandrinum L.) pasture

The effects of restricted access time to pasture (2, 4 or 6 h d^?1; 2H, 4H or 6H) on ingestive behaviour and performance were assessed on four occasions per target grazing day (D1, initial day; D4, intermediate day; and D7, final day) in dairy ewes rotationally grazing berseem clover with a 7‐day grazing period and a 21‐day recovery period. A randomized block design with two replicates per treatment was used. All ewes were supplemented daily with 700 g per head of concentrates and 700 g per head of ryegrass‐based hay. Pasture subplot and animal group data were analysed by a factorial model including access time (AT), grazing day (D) and their interaction as fixed factors. Sward height decreased from D1 (P < 0·001) and green leaf mass from D4 (P < 0·001) onwards during the grazing period. Grazing time as a proportion of AT was higher in 2H than in 4H and 6H ewes on D1 and D4 but not on D7 (P < 0·05 for AT × D). Herbage intake rate was higher in 2H than in 4H and 6H ewes (P < 0·001). Herbage and total intakes were higher in 4H and 6H than in 2H ewes (P < 0·001), with herbage intake varying non‐linearly during the grazing period (P < 0·05). Milk yield was higher in 4H and 6H than in 2H ewes (P < 0·01). To conclude, despite the evidence of compensatory behaviour, restricting access time to 2 h d^?1 constrained intake and performance of dairy ewes rotationally grazing berseem clover.