Genetic and demographic responses of fragmented Acacia dealbata (Mimosaceae) populations in southeastern Australia

Genetic and demographic studies of fragmented populations of common plant species often reveal negative impacts that are likely to constrain persistence. Examining species that are broadly representative of functional groups within fragmented landscapes is one approach to providing a better understanding of how these processes will influence vegetation persistence. Acacias are a significant component of the Australian flora, with Acacia dealbata being a common and representative species of fragmented landscapes across New South Wales. Previous reproductive assessments of fragmented A. dealbata populations indicated significant constraints for small populations through low reproductive output mediated by fertilisation success. This study examined genetic diversity, mating system, and progeny growth parameters of the seed crops produced by these populations to assess whether further constraints to persistence could be detected. Spatially explicit simulation studies were also conducted to assess the persistence likelihood of fragmented populations. Landscape parameters such as population size and plant density were useful predictors for some of the genetic and demographic responses, but a poor response signal was generally observed. Strong evidence for a self-incompatibility mechanism was observed in A. dealbata and is likely to be the major driver of population persistence. Self-incompatibility in small populations limits mate availability and eliminates inbred progeny early in the reproductive cycle leading to poor reproductive output. The simulation data provides further evidence that mate limitation in smaller populations (<200 plants and 40 S alleles) constrains reproductive output and persistence. These data indicate that introducing new germplasm to smaller populations can dramatically improve their persistence likelihood.     

Reduced seed production, inbreeding, and pollen shortage in a small population of a threatened tree, Magnolia stellata

We investigated how genetic factors and pollen shortage affect seed production in a small population of Magnolia stellata, a threatened insect-pollinated tree. We used microsatellite and manual pollination techniques, and compared a small population to a large one. Compared to the large population, the small population showed low allelic variation and had an F_IS significantly greater than 0 in adults, indicating that genetic deterioration, including genetic drift and inbreeding, may have occurred in adults. Manual self-pollination lowered seed production relative to manual cross-pollination to a different extent between populations: δ (the magnitude of inbreeding depression due to self-fertilization) was lower in the small population than in the large population. However, under natural pollination, the estimated embryo mortality rates after ovules self-fertilized were similar between the two populations because the primary selfing rate was higher in the small population. The ovule mortality rate due to pollen shortage and that due to factors independent of pollen shortage and selfing were both approximately 10% higher in the small population, suggesting that pollen transfer may have decreased and genetic deterioration effects may have increased in that population. These factors reduced seed production in the small population (female reproductive success = 0.3%) compared to the large population (2.6%). Our results suggest that seed production in the small population of M. stellata is strictly limited by elevated pollen shortage, selfing, and genetic deterioration in adults, which accelerate the risk of extinction.     

Effects of phenolic acids on seed germination and seedling growth in soil

Summary It is commonly assumed that the adverse effect of plant residues on crop yields is largely or partly due to phytotoxic compounds leached from these residues or produced by their decomposition. There has been substantial support for the hypothesis that the phytotoxic compounds responsible for reduced crop yields are phenolic acids such as p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid. To test the validity of this hypothesis, we studied the effects of nine phenolic acids (caffeic acid, chlorogenic acid, p-coumaric acid, ellagic acid, ferulic acid, gallic acid, p-hydroxybenzoic acid, syringic acid, and vanillic acid) on (1) seed germination of corn (Zea mays L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) on germination paper and soil, (2) seedling growth of alfalfa, oats, sorghum, and wheat on germination paper and soil, and (3) early plant growth of corn, barley, oats, rye, sorghum, and wheat in soil. The results showed that although the phenolic acids tested affected germination and seedling growth on germination paper, they had no effect on seed germination, seedling growth, or early plant growth in soil even when the amounts applied were much greater than the amounts detected in soil. We conclude that the adverse effect of plant residues on crop yields is not due to phenolic acids derived from these residues.     

Reproductive biology and conservation implications of three endangered snapdragon species (Antirrhinum, Plantaginaceae)

About 32% of Antirrhinum species are considered to be endangered; however, no field studies have focused on their reproductive biology. In this work, several aspects of the reproductive biology (flowering phenology, floral biology, breeding system) and potential limits on seed quantity and quality (pollen limitation, inbreeding depression) were studied in natural populations of three endangered species of the genus (Antirrhinum charidemi, Antirrhinum subbaeticum, Antirrhinum valentinum). Results disclose that all three species need insect visitors for seed production since fruit set after autonomous self-pollination was lower than under hand cross-pollination. A. charidemi and A. valentinum were mainly self-incompatible, whereas A. subbaeticum was self-compatible but herkogamous. Supplementary pollination in open-pollinated flowers only increased fruit set and seed set relative to controls in a given population of A. valentinum. Preliminary data on inbreeding depression at early life-cycle stages of the self-compatible A. subbaeticum revealed that the cumulative level was low. Despite the three species being closely related and sharing many ecological characteristics, they show different mating systems, and different factors limit seed quantity and quality. Thus, caution should be taken when making a common conservation plan for a group of closely related taxa.     

Inbreeding and small population size reduce seed set in a threatened and fragmented plant species, Lupinus sulphureus ssp. kincaidii (Fabaceae)

Willamette Valley upland prairie in western Oregon, USA, has been reduced to less than 1% of its original historic range following European settlement in the 1850s. Lupinus sulphureus ssp. kincaidii (Kincaid's lupine), a threatened species and the primary larval host plant of the endangered Icaricia icarioides fenderi (Fender's blue butterfly), was historically a panmictic metapopulation. Habitat fragmentation may be causing many of the Kincaid's lupine colonies to display typical symptoms of inbreeding depression, such as low seed production. Hand outcrosses on bagged inflorescences significantly increased seed set and seed fitness compared to open pollination and within-colony pollen treatments. Natural seed set was positively correlated with an increase in the number of Kincaid's lupine patches, suggesting that population size limits seed set. An increase in fruit set was positively correlated with Kincaid's lupine raceme number, raceme density, and the number of lupine patches, demonstrating that floral display and population size increase pollinator service. Restoration of Kincaid's lupine populations should consider measures that lessen the effects of inbreeding depression, especially in small, isolated populations, for the long-term persistence of the species.     

锗对植物影响的研究进展

锗是良好的半导体材料,且具有清除自由基、抗衰老抗氧化等生物活性,在电子工业和医学领域应用广泛。目前在植物上的研究主要集中在提高植物品质,促进植物生长及对植物毒害等方面。本文综述了锗及其化合物的理化性质、起源与分布特征,分析了锗在影响植物生长方面的生理生化机制。锗具有清除自由基的电子结构,能改变土壤中酶活性和微生物,改变植物对营养元素的吸收和利用、影响植物光合作用、改变植物的抗氧化系统等。适宜剂量的锗能促进种子萌发,有效控制藻类生长,提高作物的品质。锗积累过多,影响生理代谢,抑制植物生长,产生毒害。锗在种子萌发、植物生长方面的研究与应用,为探索锗在调节植物生长、生理生态等方面的作用提供理论基础,为植物吸收利用锗,减少锗污染方面提供理论参考。     

Sodium,calcium and magnesium ratios in soils of NW Victoria,Australia may restrict root growth and crop production

Fifty-six sites throughout the Wimmera region of Victoria were sampled to 1 m depth, and 1:5 extracts analysed for pH, conductivity and cation content. The relationship between conductivity measured in saturated extracts and 1:5 extracts at five sites was used to calculate cation concentrations expected if saturated extracts had been prepared. Soils were generally alkaline and cations at depth were dominated by sodium. The ratio of sodium to calcium varied from <2.6 (10% of samples) to >85.5 (10%) to a maximum of 247.1. It exceeded 12.8 in 40% of samples, and exceeded 45.6 in 20% of samples, levels which are likely to reduce root growth and ability of roots to exclude sodium. Higher ratios were associated with depth, pH and conductivity. The ratio of magnesium to calcium exceeded 1 in 80% of samples, 2 in 55% of samples, 3 in 30% of samples and the maximum measured was a ratio of 7.6, suggesting plant growth may be reduced. The issues of extrapolating from experiments in solution culture to soil, and errors likely in using 1:5 extracts are discussed.     

Seed priming in nanoparticles of water treatment residual can increase the germination and growth of cucumber seedling under salinity stress

Abstract

A laboratory experiment was carried out to evaluate the impact of the nanoparticles of water treatment residuals (nWTRs) and salt stress on germination and growth parameters of cucumber seedling. The interaction between three nWTRs treatments (0, 500, and 1000 mgL^?1) nWTRs and five saline solution (fresh water: sea water) treatments had 0.70, 2, 3, 6, and 11?dSm^?1 were studied. The results revealed that increasing salinity levels significantly reduced the percentage of germination (GP) for the primed seeds treated in fresh water and nWTRs. The GP reduction was higher in seeds primed in fresh water compared to which primed in nWTRs. Salt stress negatively affected radicle length of cucumber seedling for both priming treatments. However, this impact was more pronounced for the primed seeds treated in fresh water than which treated in nWTRs at high salinity stress. Priming in nWTRs significantly decreased the root radius of cucumber seedlings, and the1000 mgL^?1 priming treatment obtained a lowest value of radicle radius. Increasing salt concentration in culture medium reduced total biomass of cucumber seedling, however for the primed seeds treated in nWTRs, the total biomass was increased in comparison with which treated in fresh water. Salt tolerance and vigor indices were significantly (p?<?0.01) affected by salinity levels, nWTRs treatments and their interaction. It can be concluded that nWTRs are ameliorating materials for plant growth under salt stress conditions.     

Effects of nitric oxide and nitrogen on seedling emergence,ion accumulation,and seedling growth under salinity in the euhalophyte Suaeda salsa

Recently nitric oxide (NO) has emerged as a key signal molecule in plants. However, little is known about the role of NO in the salt tolerance of halophytes. Effects of the NO donors sodium nitroprusside (SNP) and nitrate (NO ) on growth and ion accumulation in the euhalophyte Suaeda salsa under salinity were investigated in the present study. The results showed that higher SNP supply increased seedling emergence, but SNP had no effect on shoot growth and the concentrations of Na⁺, K⁺, Cl^–, and NO . Higher NO had no effect on seedling emergence of the species. Shoot Cl^– decreased, but NO₃^– increased markedly, with a higher NO supply. The decrease in the estimated contribution of Cl^– to the osmotic potential was compensated for by an increase in that of NO . It appears that NO plays an important osmotic role in S. salsa under high salinity with a higher NO supply, and this trait may increase salt tolerance of the species under high salinity.     

Effect of the presence of nectar feeders on the breeding success of Salvia mexicana and Salvia fulgens in a suburban park near México City

The use of nectar feeders has grown a lot as a result of people wanting to attract hummingbirds to their gardens. This has caused an increment in the density and diversity of these birds in urban and suburban habitats. The feeders not only represent a bonanza resource for hummingbirds but they can also result in reduced visitation to native plants. We experimentally assessed the effect of placing nectar feeders in the vicinity of two native plant species in a suburban area of Mexico City. The plants with feeders showed a reduced visitation rate and in one case (Salvia fulgens) produced fewer seeds than the controls. Salvia mexicana was not only visited by hummingbirds but it was also by bees that were not attracted to the feeders, probably resulting in the lack of effect on this plant. Native plants in urban and suburban habitats can be threatened by reduced visitation rates and reduced seed sets resulting from the use of feeders.     

Root growth,nutrient uptake and yield of soybean cultivars grown in the field

Abstract

Soybean (Glycine max L. Merr.) cultivars differ in their root morphology and their nutrient uptake capabilities. The relation between root growth, P and K uptake, and grain yield was investigated using eight cultivars grown in the field on Raub (Aquic Argiudoll) silt loam which received 49 kg P/ha and 93 kg K/ha. Hobbit (maturity group III, determinate) was among the highest in grain yield, P and K uptakes, and root system length. However, this cultivar was intermediate in its relative efficiency to utilize P and K to produce grain yield; among the most efficient cultivars were Asgrow 3127 (maturity group II) and Williams‐79 (maturity group III). The hay cultivar, Wilson‐6, was the least efficient. It was concluded that even though grain yield was correlated with nutrient uptake, selection for higher yields was not necessarily a selection for higher efficiency in utilization of fertilizer for grain production.     

水稻育秧生产线秧盘播种量智能调控装置设计与试验

水稻工厂化育秧过程中,秧盘播种量的精准控制能有效保证育秧质量。为解决水稻工厂化育秧中秧盘播种量调控操作繁琐和效率低等问题,该研究研究设计了一种水稻育秧生产线秧盘播种量智能调控装置,该系统以STM32F429微处理器为控制核心,利用双漫反射光电传感器检测连续输送秧盘的准确到达位置,设计了秧盘质量称量机构,建立了常规稻和杂交稻芽种秧盘播种量与排种轮电机转速（频率）的关系模型,基于统计分析、信息反馈技术与秧盘播种量变化规律模型,实现不同水稻品种秧盘播种量的智能精准调控。试验结果表明,在500盘/h的生产效率下,装置的平均检测精度为94.84%,经调控后的杂交稻秧盘播种量的平均变异系数为2.5%,常规稻秧盘播种量的平均变异系数为4.04%。所设计的水稻育秧生产线智能调控装置具有较高的播种量检测精度,满足当前育秧播种量调控的使用要求,对提高水稻秧盘育秧播种生产线智能化水平、保证秧苗质量具有实际应用价值。     

Isozyme diversity and analysis of the mating system of the wild rice Oryza latifolia Desv. in Costa Rica

Oryza latifolia is the most abundant and widespread wild relative of rice in the lowlands of Costa Rica. It also has the most diverse morphology. However, little is known about the genetic diversity and mating system of this allotetraploid species. Genetic analyses of nine populations from different life zones from the Pacific and Atlantic slopes were performed using six isozyme loci. Differences in genetic variability were observed among populations, of which Palo Verde and Santa Rosa were the most diverse. Most Atlantic populations clustered together, and a similar result was obtained with the Pacific populations. High levels of interpopulation diversity were observed while most populations were monomorphic for at least one genotype, suggesting little genetic flow within populations. Even in polymorphic populations no variation was observed within progeny groups, combined with Hardy-Weinberg disequilibria in most populations, commonly observed in autogamous species or in species with clonal reproduction. However, the high frequency of heterozygous-like patterns may suggest that the reproductive system of O. latifolia might be more complex. Future research may explain the genetic patterns as well as the reproductive biology of this species. The knowledge of the genetic diversity and mating system of O. latifolia could contribute to the implementation of genetic resource conservation strategies and gene flow analyses, as well as of breeding programs for rice improvement.     

Effects of drought stress on the seedling growth,development, and metabolic activity in different cultivars of canola

ABSTRACT

The comparative effects of drought stress on seed performance, growth parameters, free proline content, lipid peroxidation, and several antioxidative enzymes activities were studied in both cultivars of Brassica napus L. Drought stress increased mean germination rate and mean of day germination in both cultivars, and its effect was more pronounced in RGS003. The length and dry weight of root increased significantly in both cultivars under drought. RGS003 was more tolerant and obtained more biomass under drought than that of Sarigol. Proline content and pyrroline-5-carboxylate synthetase expression increased in Sarigol under drought. Measurement of malondialdehyde content in seedlings showed that lipid peroxidation was lower in RGS003 than in Sarigol. Antioxidant enzyme activities showed different trends in the two cultivars under drought stress but were higher in RGS003 than in Sarigol. These results suggest that RGS003 is better protected against drought-induced oxidative damage. Lipoxygenase activity only induced under water deficit condition in RGS003. Changes of respiratory enzymes activities of RGS003 subjected to drought stress showed a pattern different with Sarigol. Drought stress induced aconitase activity in RGS003, but it reduced fumarase and succinate dehydrogenase activity in Sarigol. This study showed that RGS003 exhibits a better protection mechanism against oxidative damage and RGS003 is more drought-tolerant than Sarigol possibly by maintaining and/or increasing growth parameters, antioxidant enzyme activities, and respiratory enzymes activities.     

The influence of two agricultural biostimulants on nitrogen transformations, microbial activity, and plant growth in soil microcosms

The influence of two experimental soil treatments, Z93 and W91, on nitrogen transformations, microbial activity and plant growth was investigated in soil microcosms. These compounds are commercially marketed fermentation products (Agspectrum) that are sold to be added to field soils in small amounts to promote nitrogen and other nutrient uptake by crops in USA. In laboratory microcosm experiments, soils were amended with finely ground alfalfa-leaves or wheat straw, or left unamended, in an attempt to alter patterns of soil nitrogen mineralization and immobilization. Soils were treated in the microcosms with Z93 and W91 at rates equivalent to the recommended field application rates, that range from 0.2 to 1.1 l ha⁻¹, (0.005-0.03 μl g⁻¹ soil). We measured their effects on soil microbial activity (substrate-induced respiration (SIR), dehydrogenase activity (DHA) and acid phosphatase activity (PHOS)), soil nitrogen pools (microbial biomass N, mineral N, dissolved organic N), and transformations (net N mineralization and nitrification, ¹⁵N dilution of the mineral N pool, and accumulation of mineral N on ion-exchange resins), and on wheat plant germination and growth (shoot and root biomass, shoot length, N uptake and ¹⁵N enrichment of shoot tissues), for up to 56 days after treatment. To follow the movement of nitrogen from inorganic fertilizer into plant biomass we used a ¹⁵N isotopic tracer. Most of the soil and plant responses to treatment with Z93 or W91 differed according to the type of organic amendment that was used. Soil treatment with either Z93 or W91 influenced phosphatase activity strongly but did not have much effect on SIR or DHA. Both chemicals altered the rates of decomposition and mineralization of organic materials in the soil, which was evidenced by significant increases in the rates of the decomposition of buried wheat straw, and by the acceleration of net, rates of N mineralization, relative to those of the controls. Soil nitrate availability increased at the end of the experiment in response to both chemical treatments. In alfalfa-amended soils, the final plant biomass was decreased significantly by treatment with W91. Increased plant growth and N-use efficiency in straw-amended soil, resulting from treatments with Z93 or W91, was linked to increased rates of N mineralization from indigenous soil organic materials. This supports the marketing of these compounds as promoters of N uptake at these low dosage inputs.     

Effects of bacterial inoculant biofertilizers on growth,yield and nutrition of rice in Australia

Inoculant biofertilizer application increased fertilizer nitrogen (N) use efficiency in Vietnam in some previous field experiments. Similar results may be obtained in Australia. With this view in mind, a greenhouse experiment and two field experiments were conducted using a Vietnamese inoculant biofertilizer (BioGro) and several other plant growth promoting (PGP) bacteria. In the greenhouse trial, bacterial inoculations increased shoot and root weights of rice plants significantly. In the field experiments, particularly with Rhizobium leguminosarum, similar effects including significant differences in nitrogen uptake in vegetative matter were observed at the panicle initiation (PI) stage. However, these effects were not significant on grain yield at harvest and it is concluded that the much longer period of growth for Australian rice may allow compensation between treatments. Re-inoculation of plants at the PI stage, and lower application rates of N fertilizer in at least two splits are suggested for future field experiments.     

Location of roosts of the lesser long-eared bat Nyctophilus geoffroyi and Gould's wattled bat Chalinolobus gouldii in a fragmented landscape in south-eastern Australia

The location of roosts of two species of vespertilionid bats, the lesser long-eared bat (Nyctophilus geoffroyi) and Gould’s wattled bat (Chalinolobus gouldii), was investigated in a remnant vegetation-farmland mosaic and adjacent floodplain forest in south-eastern Australia. A total of 45 individuals of N. geoffroyi and 27 C. gouldii were fitted with radio transmitters, which resulted in the location of 139 and 89 roosts respectively. Selection of roosting habitat showed both inter- and intra-specific differences. At the landscape level, locations of roosts used by male and female N. geoffroyi differed markedly. Most males roosted in the farmland mosaic within 3 km (mean 1.9±2.9 km) of where they were captured while foraging in remnant vegetation. In contrast, roost sites of females were predominantly in the floodplain forest, 6-12 km from their capture site in farmland (mean for all females, 6.7±2.9 km). All maternity roosts were in the extensive floodplain forest, 4-10 km from foraging areas. Distances moved by this species were greater than previously recorded and further than predicted by flight morphology. Most C. gouldii roosted in the floodplain forest, 4-10 km from their capture site (6.9±1.6 km). Within the floodplain forest, both species roosted in areas that had higher densities of hollow-bearing trees than generally available; dead hollow-bearing trees for N. geoffroyi and large, live trees for C. gouldii. The scale of movements undertaken by these species means that they can obtain resources from multiple landscape elements. Both species used different habitats for roosting and foraging despite the energetic costs of commuting relatively large distances. Conservation of bat populations in rural environments needs to be considered at the landscape scale, with particular attention to identifying landscape elements that provide key resources.     

Migration,colonization and seedling growth of rhizobia with matrine treatment in alfalfa (Medicago sativa L.)

Purpose: The purposes of this study were to determine the effect of matrine on the migration and the colonization dynamics of the two fluorescent-tagged rhizobia in Gannong No.5 alfalfa (Medicago sativa L. Gannong No. 5) tissues, and also to determine the effect of the combination treatments on alfalfa seedlings’ growth.

Materials and methods: 0, 100, 200, 300 and 400 mg L^?1 matrine levels were added into two cyan fluorescent protein (CFP)-tagged rhizobia; Ensifer meliloti LZgn5f (gn5f) and Ensifer meliloti 12531f (12531f), respectively; and drenched the alfalfa root with the inoculants. Then the migration and colonization of the two rhizobia in alfalfa on D7, D14, D21 and D28, and subsequently seedling growth were investigated.

Results: The results showed that the optimum matrine level enhanced the colonization of both fluorescent-tagged rhizobia in alfalfa roots and the highest colonization densities of log 6.31 cfu g^?1 and log 5.87 cfu g^?1 were achieved by adding 300 mg L^?1 matrine into 12531f and adding 100 mg L^?1 matrine into gn5f, respectively. They could migrate to the aerial tissues and most colonize stems through the application of adding 300 mg L^?1 matrine into 12531f and 100 mg L^?1 matrine into gn5f, respectively. No fluorescent-tagged rhizobia were detected in the control treatment. Alfalfa seedling growth parameters like leaf chlorophyll content, seedling growth rate, root length, seedling biomass and total N percentage also increased the most when 300 mg L^?1 matrine was added into 12531f and 100 mg L^?1 matrine added into gn5f treatments.

Conclusions: Our results suggest that 300 mg L^?1 matrine added into 12531f and 100 mg L^?1 matrine added into gn5f might be exploited to promote the colonization of rhizobia in alfalfa tissue and positively impact growth and yield, indicating possible benefits for plant cultivation.     

Effect of nitrogen and potassium fertilizer on growth,herbage and oil yield of irrigated palmarosa (Cymbopogon martinii [roxb.] wats. var. motia burk) in a semi-arid tropical climate

The world's agricultural production is increasing by 1 to 2 per cent annually and has been enough to satisfy the growing world population's need for food. Breeding, fertilisation and crop protection have decidedly contributed to that progress in productivity. But since the 1960s, agriculture has been more and more conceived by the public as an environment-contaminating industry. The public is concerned about water contamination with nitrate as a result of the use of fertilisers, and about harmful effects of chemical plant protection products on soil, water, air, animals and wild plants. The public discussion has not remained without consequences. Sustainability of development has become a central political objective in all spheres of social life, and in all world regions. Sustainable development concerns economic, ecological as well as social objectives, and is also the guideline for a renovation of agriculture. Any concepts and strategies integrating environmental aspects into agricultural production are linked with the objective of sustainable development. Discussion on sustainable agriculture has become more concrete on the basis of the Brundtland Report and Agenda 21 , as well as the various follow-up meetings of the 1992 Conference of Rio. Although efforts towards sustainable development in agriculture encounter widespread scepticism, clear progress is to be noted since that discussion has intensified. Farmers have paid more attention to new farming practices. Environmental aspects now play an important role when extension services advise farmers on fertilisation and crop protection. Research has contributed essentially to the change in agriculture towards sustainable production. Sustainability in agriculture has also been expressed in new legal regulations. Principles of good professional practice in applying fertilisers, as it is required by the Fertilisers Act from the year 1989, have been spelled out more clearly in a legal regulation issued on 26 January 1996 (Federal Law Gazette part I of 06 February 1996, p. 118). Principles of good professional practice in crop protection were published in Bundesanzeiger (Federal Gazette) No. 220 a of 21 November 1998. Principles of integrated crop protection were first discussed by representatives of agriculture, environment protection offices and researchers at a workshop at Biologische Bundesanstalt für Land- und Forstwirtschaft (BBA, Federal Biological Research Centre for Agriculture and Forestry) in Kleinmachnow on 23° March 2000. The debate on sustainability centres around the aspects of economic and social efficiency of measures taken, and their effects on the environment. The following article deals with some basic aspects of efficiency on the one hand, and effects/emission on the environment on the other, of fertilisers and crop protection products as important input factors in agriculture. Crop husbandry always is an interference with nature. The Lüneburger Heide cropping region is a memorial of ecologically out-dated land management. Today, sustainable and at the same time efficient agriculture can only be realised with modern methods based on sound knowledge. This includes mineral fertilisation and chemical crop protection. Cropping permanently draws nutrients from the soil-plant system. They have to be refilled by fertilisation. If no fertilising measures are taken at all, the humus layer of the soil declines and soil degrades. The decline in fertility will result in yield losses of between 70 and 90%. In contrast, combination of organic and mineral fertilisers has continually added to soil fertility. This is reflected in the humus content of the soil, which is by about a quarter higher than it was a hundred years ago. Farmers resorting solely to mineral fertilisation produce yields lower by 5-10% than those combining mineral and organic fertilisers. If only organic fertilisers are used, this may reduce yields by between 10 and 40%, depending on the site. Unwanted side-effects of fertilisation (such as leaching of nitrates) may be reduced to a tolerable level by precise input of nutrients, improved methods such as precise fertiliser input depending on the condition of certain field patches, and by integrated crop protection, which relies on synergetic effects of various measures. Germany has for these reasons witnessed a relaxation of environmental pressure from excessive nutrient input. If crop protection measures were abandoned, pests and diseases would reduce yields by between 40 and 80 per cent. Our own trials about energy input-output proportions have shown a ratio of 1:4.6 with use of fertilisers (100kg N/ha), and a ratio of 1:8.6 with use of fertiliser and chemical plant protection products. The risk potential of modern chemical plant protection products has permanently decreased over the past few decades and is generally about one tenth of the values of 15 years ago. Integrated crop protection, which combines various methods of crop protection and reduces the use of chemical crop protection products to a necessary minimum, is the "optimal solution for the future" and "contributes to the sustainability of agriculture", as it is said in the Agenda 21 programme adopted by the 1992 environmental conference in Rio.     

供氮水平对芦荟幼苗生长、硝酸盐和次生代谢产物含量的影响

采用温室砂培试验研究了不同氮素水平(5.0、7.5、10.01、5.01、7.5.mmol/L)对二年生库拉索芦荟生长和蒽醌、芦荟甙等次生代谢产物及硝酸盐含量的影响。结果表明,供氮水平由5.0.mmol/L增加到10.0.mmol/L,库拉索芦荟地上部产量和总生物量显著增加,继续提高氮水平芦荟地上部产量和总生物量没有显著增加;芦荟根干重及其根冠比则随着氮水平的增加而下降;叶片和根系的硝酸盐含量则随施氮浓度的提高呈增加趋势。供氮浓度从5.0mmol/L增加到10.0.mmol/L时,叶片的维生素C(Vc)含量显著增加,继续提高供氮水平,叶片Vc含量则明显下降;蒽醌含量则随施氮水平的上升而不断增大,但施氮10.0、15.0、17.5.mmol/L的处理间没有显著性差异。芦荟甙含量变化趋势和Vc含量相似,以施氮10.0.mmol/L为最高,其含量分别是其它处理的1.4、1.2、1.4、1.3倍。由此可见,芦荟在供氮10.0.mmol/L时能够获得较高的产量和蒽醌含量,较低的硝酸盐含量和高的Vc和芦荟甙含量,表明适宜的供氮水平是芦荟高产优质的保证。