Cereal cyst nematode effects on wheat water use,and on root and shoot growth

Wheat (Triticum aestivum L.) is grown in many arid regions using fallow management whereby no crop is grown in alternate cropping seasons. Although fallowing is important in increasing the availability of water and nitrogen to crops in many environments, experiments in Israel revealed that water carryover from the fallow season for wheat production was rare. This paper examines the possibility that improved water use, and improved root and shoot growth, result from soil sanitation of cereal cyst nematode (CCN, Heterodera avenae Woll.) in the fallow season. Pot experiments in controlled environments revealed a dramatic, negative effect of various populations of CCN on wheat root growth. The decrease in root growth was associated with decreased shoot growth and decreased rates of transpiration. Mechanical pruning of roots mimicked the effects of CCN infestation indicating that root pruning is probably the primary damage of CCN. In the field, dry weight yields of wheat were maintained even in continuous wheat management when a soil biocide was used to control CCN. It is proposed that the success of the fallow management is based on the fact that CCN cysts hatch in wet soil during rainy periods of the fallow year but fail to produce a new generation of cysts because no host plants are present.     

Yield and nitrogen concentration of above- and below-ground biomasses of red clover cultivars in pure stands and in mixtures with three grass species in northern Europe

Three red clover (Trifolium pratense) varieties differing in productivity and winter hardiness, Jokioinen, Betty and Ilte, were sown in a 2‐year (2003–2004) pot experiment in pure stands and mixtures with the grasses, timothy (Phleum pratense), tall fescue (Festuca arundinacea) and meadow fescue (Festuca pratensis). Grass growth dominated until fertilizer‐N, applied when the stands were sown, was depleted. Timothy was the least competitive of the grass species. Red clover variety Ilte produced the highest dry‐matter (DM) yields. Variety Betty yielded less, but allocated as much biomass to the root and stubble (soil‐bound) fraction as variety Ilte. Variety Jokioinen allocated least to the soil‐bound fraction. While the root structure and the starch concentration of the crown‐root area were similar in all varieties, the high ratio of soil‐bound: harvested fractions could be a key to the higher winter survival and higher DM yields of Betty under field conditions. At the end of the experiment, 3–5 g N pot^?1 (49–81 g m^?2) had been harvested and 0·7–1·5 g N pot^?1 (11–24 g m^?2) was left in the soil‐bound fraction, amounts depending on the red clover variety and grass mixture, with pure clover stands containing the highest N amounts. Because of the high N concentrations in the biomass of red clover, the proportion of red clover and conditions prevailing during canopy and root death in mixed stands are crucial for N mineralization and incorporation into new growth.     

Effects of cutting frequency on plant production, N-uptake and N2 fixation in above- and below-ground plant biomass of perennial ryegrass–white clover swards

Nitrogen (N), accumulating in stubble, stolons and roots, is an important component in N balances in perennial ryegrass–white clover swards, and the effects of cutting frequency on the biomass of above‐ and below‐harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N₂ fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range of 3000–7000 kg DM ha^?1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height but the different weather conditions between years had less effect on stubble and, in particular, biomass of roots. The biomass of roots of white clover was significantly lower than that of roots of perennial ryegrass and remained at a relatively constant level (200–500 kg DM ha^?1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2400 kg DM ha^?1 in the year of establishment to 10 200 kg DM ha^?1 in the infrequent cutting treatment and 6650 kg DM ha^?1 in the frequent cutting treatment by the end of the experiment, giving shoot:root ratios of 4·7–16·6 and 0·5–1·6 for white clover and perennial ryegrass respectively. Annual N₂ fixation was in the range of 28–214 kg N ha^?1, and the proportion of N fixed in stolons and roots was on average 0·28. However, as weather conditions affect the harvested DM production and the shoot:root ratio, care must be taken when estimating total N₂ fixation based on an assumed or fixed shoot:root ratio.     

Effect of season and cutting frequency on root and shoot competition between Festuca pratensis and Dactylis glomerata

Abstract Plant competition strongly affects the species composition of managed grassland. To identify relevant processes, Festuca pratensis (Huds.) and Dactylis glomerata (L.) were grown as monocultures or mixtures in boxes placed in the field for two seasons and subjected to two cutting frequencies. Root and shoot competition effects were separated using soil and aerial partitions. Shoot competition was analysed by measuring the vertical distribution of the leaf area and root competition by analysing the absorption of tracers. Values of relative yield indicated that the two grasses fully competed for the same limiting resources under the experimental conditions. The competitive ability of F. pratensis was lower during both years relative to D. glomerata. This was mainly related to its consistently lower shoot competitive ability, which was associated with less leaf area in the upper layers of the canopy and shorter leaves. Root competitive ability of F. pratensis changed with season. It was similar to that of D. glomerata during spring and autumn, but less during summer. The lower root competitive ability in summer might be due to the lower root activity of F. pratensis, measured as rubidium (Rb) and strontium (Sr) absorption in July, 0·1 and 0·2 m below the ground. Cutting frequency did not greatly influence the relative importance of root and shoot competition during the first growing season. However, under infrequent defoliation, the competitive ability of F. pratensis decreased markedly in full competition during the second growing season. These results suggest that distinct differences in the canopy structure and root activity of different plant species can affect the relative importance of root and shoot competition during the season.     

Effects of sulphur dioxide and nitrogen dioxide on shoot and root growth of Kennebec and Russet Burbank potato plants

The effects of sulphur dioxide (SO₂) and nitrogen dioxide (NO₂), singly and in combination, on the shoot and root growth of two potato cultivars sensitive to these pollutant gases were determined using rooted cuttings in controlled conditions. Plants were exposed to 0.11 ppm SO₂ and/or 0.11 ppm NO₂ for 24 hours a day for 7 or 14 days. Kennebec plants had significantly lower root fresh and dry weights after 7 days in the mixture treatments and lower root fresh weight in the NO₂ treatment. Russet Burbank plants were more sensitive to SO₂ and NO₂ than Kennebec. Russet Burbank plants had significantly reduced leaf area, and leaf, stem, and root fresh and dry weights after 7 and 14 days of mixture treatment, and the leaf to root dry weight ratio was higher than in control plants. The combination treatment and SO₂ alone resulted in visible injury on leaves of both cultivars. Changes in tissue water concentration, decreased specific leaf area and decreased root growth suggested that SO₂ and NO₂ altered plant water status and interfered with partitioning of dry matter from the leaves to other plant parts.     

Precision tillage effects on potato root and tuber production

American Journal of Potato Research - Impedance to the extension of potato roots in a high-strength soil was reduced by chiseling with a subsoil shank directly in the center of the potato bed...     

The importance of water-soluble carbohydrate reserves on regrowth and root growth of Lolium perenne (L.)

This glasshouse study aimed to determine the relative importance of water-soluble carbohydrates (WSC) and current photosynthate on root and top regrowth of perennial ryegrass (Lolium perenne L.). Individual plants were arranged in one of two miniswards (Experiments 1 and 2) and underwent varying defoliation frequencies designed to obtain a gradient of WSC content at the final harvest of each treatment (H₁), when all treatments were defoliated. In Experiment 1, the plants were defoliated either three times at the one new leaf per tiller stage of regrowth (treatment 3 × 1), once at the two-leaf and again at the one-leaf stage (treatment 2, 1), once at the one-leaf and again at the two-leaf stage (treatment 1, 2) or once only at the three-leaf stage (treatment 1 × 3), up to H₁. Leaf and root growth and other parameters were assessed over 6 d after H₁ in sunlight, and over a 4-week period in darkness, and related to initial plant WSC content. In Experiment 2, plant defoliation treatments were: 3 × 1, 1, 2 or 1 × 3. Leaf regrowth was assessed for 36 d until the plants had three fully expanded new leaves per tiller. Leaf regrowth in both experiments was significantly related to stubble WSC (below 50 mm height). In Experiment 1, plants were almost fully reliant upon plant reserves for the first 3 d of regrowth, with reliance decreasing up to 6 d. When regrowth of plants was compared after 1 week in light or in darkness, it was estimated that one-third of leaf regrowth was due to plant WSC reserves and the remainder due to photosynthesis. However, the capacity to photosynthesize and to grow roots after H₁ was also significantly related to stubble WSC content. In Experiment 2, there was a significant difference (P<0·01) between defoliation treatments on leaf dry matter (DM) yield at 12 d (×1 leaf tiller^?1) of regrowth, and this was, as in Experiment 1, significantly positively related to WSC content in the stubble. However, after 36 d of regrowth, DM yield of plants defoliated at 2 or 3 leaves tiller^?1 up to H₁ were similar, and both were significantly higher (P<0·01) than regrowth of plants defoliated at the one-leaf stage. After defoliation, the period of reliance on WSC reserves may be substantially increased in situations of shading (canopy competition or cloud cover) or if the new regrowth shoot is removed by regrazing.     

Effect of lowering the root/shoot ratio by pruning roots on water use efficiency and grain yield of winter wheat

A pot and a field experiment were conducted to assess the effects of root/shoot ratio (R/S) on the water use efficiency (WUE) and grain yield of winter wheat. The R/S was regulated by pruning the roots during the stem elongation stage, resulting in reduced root systems of the plants. At the heading stage, the root dry weight of root-pruned plants was less than that of intact-root plants, but their R/S was similar to that of intact-root plants under both experimental conditions. After tiller pruning, the R/S of root-pruned plants was significantly lower than that of intact-root plants (p < 0.05). Root pruning reduced the rate of leaf transpiration and lowered the number of tillers per plant (p < 0.05) during the vegetative stage. As a result, root-pruned wheat showed reduced water use when compared to intact-root plants before heading (p < 0.05). At anthesis, there was no significant difference in transpiration between plants with intact roots and those with pruned roots in the pots. However, under field conditions, transpiration of root-pruned plants was significantly higher than that of intact-root plants at anthesis. Additionally, at anthesis root-pruned plants had a higher rate of leaf photosynthesis and lower rate of root respiration, which resulted in a significantly higher grain yield at maturity when compared to plants with intact roots. Under both experimental conditions, there were no significant differences in shoot dry weight per plant between root-pruned and intact-root plants grown in monoculture. When root-pruned plants were grown with intact-root plants, the root-pruned wheat was less productive and had a lower relative shoot dry weight (0.78 and 0.86, respectively) than the intact-root plants (1.24 and 1.16, respectively). These results suggest that plants with pruned roots had a lower ability to compete and to acquire and use the same resources in the mixture when compared with intact-root plants. Root pruning improved the WUE of winter wheat under both experimental conditions. This suggests that appropriate management for the root system/tillers in wheat crops can be used to increase grain yield and water use efficiency. Specifically, lowering the R/S improved the grain yield and WUE of winter wheat significantly by lowering its competitive ability and improving root efficiency. Therefore, drought-resistance breeding to improve the grain yield and WUE, at least for wheat, should be made by targeted selection of less competitive progeny with a small R/S for cultivation in arid and semiarid areas.     

Grazing cycle length and silage supplementation: effects on the performance of lactating ewes with twin lambs

Masham ewes, stocked at 20 ewes ha⁻¹, reared twins at pasture in 1979 and 1980 and were rotationally grazed around six paddocks. There were three lengths of grazing cycle (18, 30 or 42 d) and the ewes at pasture were either offered silage ad libitum (S) for 8 weeks of lactation or they were not supplemented with silage (N). By feeding silage, S ewes and lambs moved into greater herbage masses (3735 u. 3390 kg organic matter (OM) ha⁻¹), but there was little effect on net herbage accumulation (10.5 v. 10.0 t OM ha⁻¹) and herbage intakes per ewe were similar (2.31 v . 2.27 kg OM d⁻¹) over the 7-month grazing season. During the period of silage supplementation, total intake was 19% higher for S than N ewes, lamb growth rates were slightly higher (280 v . 273 g d⁻¹) and the ewes lost less weight (−78 v −96 g d⁻¹).
For 18-, 30- and 42-d grazing cycles respectively the herbage masses before grazing were 2825, 3620 and 4240 kg OM ha⁻¹; net herbage accumulations were 9.8, 10.4 and 10.6 t OM ha⁻¹; mean daily herbage intakes by each unit (ewe+lambs) were 2.22, 2.35 and 2.30 kg OM and lamb growth rates from birth to weaning at 20 weeks were 205, 204 and 204 g d⁻¹.
Frequent grazing of relatively light herbage masses or infrequent defoliation of heavier herbage masses made little difference to sward or animal performance. It is concluded that, at this stocking rate, different grazing cycles of 18, 30 or 42 d do not affect the performance of lactating ewes.     

广佳安对油菜芽苗根系形态结构及生理指标的影响

为研究除草剂广佳安对油菜根系的影响,以甘蓝型油菜陕油16和白菜型油菜白杂一号为材料,用室内水培法研究了不同浓度广佳安对2个油菜品种芽苗根系生长发育的影响。结果表明,广佳安明显抑制油菜根系生长,随着处理浓度的增加抑制作用增大;广佳安使油菜芽苗主根长度、根干重及根冠比都下降,根毛和侧根长度缩短,根毛密度减小,且扭曲、变形,交错缠绕,分布不均匀。芽苗所测根系的MDA含量、过氧化物酶(POD)及过氧化氢酶(CAT)的活性都随广佳安处理浓度的增加而增大,超氧化物歧化酶(SOD)表现为先增高后降低的趋势。广佳安胁迫使根尖膨胀变粗,根冠由尖锥形变为近圆弧形,在较高浓度下,表皮细胞排列不整齐,甚至部分缺失;皮层薄壁组织细胞层数减少、细胞液泡化程度增高,细胞边缘皱褶溃烂。2个油菜品种相比,白杂一号对广佳安的耐药性较陕油16强。     

Effects of light, hydropriming and abiotic stress on seed germination, and shoot and root growth of pyrethrum (Tanacetum cinerariifolium)

Poor germination and seedling establishment are major problems in arid and semi-arid environments, and these characteristics are considered to be important factors in later plant growth and yield. Laboratory experiments were conducted on freshly harvested pyrethrum (Tanacetum cinerariifolium) seeds to investigate the effects of light (influenced by the seeding method) and seed hydropriming on germination, and shoot and root growth at 25 °C. Exposure to light could reduce germination from 52% to 22% and increase the mean germination time (MGT) from 7 to 12 days. The responses of hydroprimed and unprimed seeds to salt and drought stress were determined at osmotic potentials of 0 (distilled water), −0.3, −0.6, −0.9, −1.2 MPa in NaCl and PEG6000. Seed germination and seedling growth were inhibited by increasing salt and drought stress. The germination percentage of unprimed seeds was reduced from 52% to 16% in −1.2 MPa NaCl, and no seeds germinated at osmotic potentials ≤−0.9 MPa PEG. Both shoot and root growth were inhibited at osmotic potentials ≤−0.9 MPa NaCl and ≤−0.6 MPa PEG. Hydropriming shortened the delay of MGT at all osmotic potentials, and improved the germination percentage in distilled water (from 52% to 59%) and resistance to salt stress with nearly double germination (from 16% to 29%) at the highest salt concentration. When non-germinated seeds were transferred to distilled water after 20 days of incubation in total up to 12-15% of NaCl and 25-27% of PEG stressed seeds did not recover. These results show that the inhibition of the germination and seedling growth at the same osmotic potential of NaCl and PEG resulted from drought stress rather than salt toxicity, and that hydropriming is an effective tool to improve the quality of pyrethrum seeds.     

Effects of shoot,root and stolon temperature on the development of the potato (Solanum tuberosum L.) plant. II. Development of stolons

Summary Cultivars Bintje and Désirée were grown in a multi-compartment set-up, which allowed different shoot, root and stolon temperatures, to study the effects of temperature around different plant organs on the development of stolons. A high root temperature induced orthotropic stolon growth in cv. Bintje. Stolon number was not affected when temperature was increased in one compartment only, but high root temperature combined with high stolon temperature or high air temperature reduced stolon number. For ‘Bintje’, branching of stolons and their dry-matter yield were enhanced by a high temperature in each compartment, but combining high air temperature with another temperature increase was detrimental. Stolon initiation was less synchronized when plants were exposed to both high air temperature and high stolon temperature. The hormonal regulation of stolon formation and the effects of temperature on the hormonal balances involved are discussed.     

Effects of shoot,root and stolon temperature on the development of the potato (Solanum tuberosum L.) plant. III. Development of tubers

Summary The cultivars Bintje and Désirée were growth with their shoots, roots and stolons at different temperatures, to study the effects on tuber development. More tuber sites were initiated in ‘Bintje’ when the air, root or stolon temperature was increased but a combined increase of air and root temperature greatly reduced the number of sites. In contrast, each temperature increase reduced the number of tuber sites in ‘Désirée’ but an increase in temperature in one compartment usually increased the number of tubers set. The relative tuber set was enhanced by a combination of high stolon temperature and low root temperature. Especially an increase in air temperature reduced tuber yield and tuber dry-matter content, but increasing stolon temperature had the largest effects on the induction of second growth. Stolon and tuber development, dry-matter partitioning and initiation of second growth responded differently to variation in temperature around different plant parts suggesting that these processes are affected by different regulation mechanisms.     

Associative effects between fresh perennial ryegrass and white clover on dynamics of intake and digestion in sheep

The aim of this study was to determine the associative effects between fresh perennial ryegrass and fresh white clover on intake and digestion in sheep. Five proportions of ryegrass and white clover, ranging from 0 to 1 in 0·25 increments (DM basis), were allocated to two groups of five sheep according to a replicated 5 × 5 Latin square design, and intake behaviour and digestive parameters including methane (CH₄) emissions were measured. Feeding behaviour was affected through increased forage intake when the proportion of white clover was increased, and there were positive associative effects on intake, eating time and eating rate during the main meals consumed immediately after feed was given. These effects seemed to be related to a greater motivation to eat, rather to more efficient digestion, as no difference on DM digestibility (average 766 g kg^?1) was detected. There were no differences in CH₄ yield (average 18·1 g kg^?1 DM intake) among the treatments. The optimal proportion of white clover fed with ryegrass to optimize intake and digestion was between 0·25 and 0·50. These results indicate that mixing perennial ryegrass and white clover positively affects forage intake in sheep and their motivation to eat.     

Effects of shoot,root and stolon temperature on the development of the potato (Solanum tuberosum L.) plant. I. Development of the haulm

Summary Cultivars Bintje and Désirée were grown in a set-up that allowed temperatures of the shoot, root, and stolon environments to be separately varied. Shoot and root temperatures were either low, 18°C, or high, 28°C. Stolon temperatures were either ‘normal’, i.e. allowed to equilibrate at an ambient that depended on the temperatures of the shoot and root compartments, or ‘in-creased’ by fixed supplementary heating units in the stolon chambers. Haulm longevity was increased by the combination high shoot temperature and low root temperature, but greatly decreased by high shoot temperature combined with high root temperature. The increased stolon temperature also advanced senescence. The number of branches per stem (and thereby the number of leaves) was increased by an increase in stolon temperature, but the interaction with air temperature was significant. A high root temperature reduced the number of leaves significantly. The effects on stem yield were complex; several interactions proved significant. The total drymatter yield was affected by all single factors except shoot temperature.     

Coppicing experiments on the spread and control of cocoa swollen shoot virus in Ghana

A coppicing technique was used to assess the incidence of latent and missed infection around 76 outbreaks of cocoa swollen shoot disease found during routine surveys of cocoa farms in Ghana. When all apparently healthy trees were coppiced within at least 27 m of trees found with symptoms, some failed to regenerate, with overall mortalities of 15% and 19% in progenies of Upper Amazon and West African Amelonado parentage, respectively. Many of the regenerating shoots developed stem and/or leaf symptoms of swollen shoot disease within 3 years of coppicing. There were great differences between sites, with overall incidences of infection of 21% and 16% in the Amazon and Amelonado plantings, respectively. The infections revealed by coppicing were not usually grouped closely around trees originally found with symptoms. Gradients of infection were seldom evident and the overall incidence of infection within 3 m of the initial outbreak areas (17%) was little greater than that beyond (14%). The original inspections of the standing trees detected only c. 12% and 18% of all the infected trees present at the Amazon and Amelonado sites, respectively. These results emphasize the limitations of routine inspections in determining the true incidence of infection. They have an important bearing on the conduct and effectiveness of the eradication measures adopted in Ghana and are discussed in relation to the future policy for limiting spread.     

The effects of living mulches and weed cover on the dynamics of foliage- and soil-arthropod communities in three crop systems

The effects of vegetation background in the form of living mulches and weed cover on the population dynamics of foliage and soil arthropods were studied in corn, tomato and cauliflower crop systems in California. In Davis (Central Valley site) herbivores (especially aphids and lygaeids) were more abundant in the weed cover than in the clover mulch, whereas leafhoppers were most common in the clover mulch. Higher numbers of natural enemies were observed in the clover plots. Significantly more ground predators (Carabidae, Staphylinidae, spiders) were caught in pitfalls placed in the weedy and clover plots, than in the clean cultivated plots. In Albany (Coastal area), specialized herbivore (cabbage aphids and flea-beetles) densities were significantly reduced in plots with additional vegetation cover. It is not clear if this reduction was due to plant diversity or density effects, to the effects of natural enemies or to the lower quality of plants in the weedy and mulched plots, as crop growth and yields were drastically reduced in these plots at both sites. Further agronomic work is warranted to minimize the competitive effects of legume covers on crops, so that the entomological advantages reported here can be used in a practical way.     

Interacting effects of yak dung deposition and litter quality on litter mass loss and nitrogen dynamics in Tibetan alpine grassland

The effects of grazing‐induced dung deposition on plant growth and soil attributes are well established, but little is known about dung effects on litter decomposition. Here, we tested effects of yak dung on litter decomposition and nutrient content in a Tibetan alpine meadow. We incubated litter of four common alpine meadow species using litter bags in the field. Two low‐quality species (Kobresia capillifolia and Elymus nutans) with low nitrogen (N), high C/N and Lignin/N, and two high‐quality species, (Saussurea nigrescens and Thermopsis lanceolata) were incubated in monoculture with and without dung addition. Mass loss of leaf litter, fibre fraction (cellulose, hemi‐cellulose and lignin), N and phosphorus (P) were measured after 6, 12 and 18 months of incubation in the field. Dung addition significantly increased decomposition constants for low‐quality litter species, but not for high‐quality litter species. Dung addition promoted cellulose and hemi‐cellulose loss, but lignin loss was not affected by dung addition, except after 12 months for high‐quality litter species. Dung reduced N immobilization after 6 months and did not affect subsequent release in low‐quality litter species, and promoted N release after 6 and 12 months in high‐quality litter species. Regardless of litter quality, dung increased P release after 6 and 12 months. Our results suggest grazing‐induced dung deposition may accelerate C and nutrient turnover, primarily through increasing the mass loss of low‐quality litter, P release from litter and N release from high‐quality litter. The mechanisms underlying the effects of dung deposition need to be clarified in future studies.     

The effects of spatial and temporal heterogeneity on the population dynamics of four animal species in a Danish landscape

Background  

Variation in carrying capacity and population return rates is generally ignored in traditional studies of population dynamics. Variation is hard to study in the field because of difficulties controlling the environment in order to obtain statistical replicates, and because of the scale and expense of experimenting on populations. There may also be ethical issues. To circumvent these problems we used detailed simulations of the simultaneous behaviours of interacting animals in an accurate facsimile of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of skylarks Alauda arvensis, voles Microtus agrestis, a ground beetle Bembidion lampros and a linyphiid spider Erigone atra. This allows us to quantify and evaluate the importance of spatial and temporal heterogeneity on the population dynamics of the four species.