Influence of initial levels of carbohydrates, fructans, nitrogen, and soluble proteins on regrowth of Lolium perenne L. cv. Bravo following defoliation

An experiment was designed to evaluate the role of N and C reserves on regrowth of Lolium perenne cv. Bravo following defoliation. By using two nitrogen fertilization levels together with three photoperiodic conditions, plants with variable contents of water-soluble carbohydrates (43-216 mg g^-1 DW in stubble) and contrasting amounts of nitrogen (7-49 mg g^-1 DW) were obtained. Plants were severely defoliated and regrowth was followed for 28 d under the same environmental conditions. The yield of leaf dry matter at the end of the regrowth period was not related to the initial level of carbohydrate reserves. However, levels of fructan in leaf sheaths and in elongating leaf bases strongly influenced the shoot yield during the first 2 d following defoliation. Fructan exohydrolase activity increased 2-3-fold in sheaths and 3.5-5-fold in elongation leaf bases, suggesting that not only fructans from sheaths but also fructans from immature cells may be used as substrates for growth. In contrast, no direct relationship was found between shoot production and nitrogen or soluble protein accumulation in source organs during early regrowth. A significant correlation existed with the initial amount of soluble proteins in sheaths and in elongating leaf bases after only 6 d of regrowth.     

Effects of temperature and nitrogen supply on the growth of timothy (Phleutn pratense L.)

Timothy was grown in controlled environments with day/night temperatures of 18.5/10° C. and 29.5/21° C, with and without extra nitrogen. High temperatures hastened all stages of development after inflorescence initiation. Anthesis occurred after 48 days when N was added and after 52 days without N. Anthesis did not occur until after 68 days at the lower temperatures, with or without N. Largest yields of leaves, stems and stubble were produced at all growth stages at the lower temperatures with N. This treatment gave the highest crop growth rate, which increased almost linearly with time. The lower temperatures with N gave many more and longer stems and more inflorescences than any other treatment. With N and high temperatures, there was no increase in crop growth rate after inflorescence emergence. Temperature had little effect on growth when no N was provided. With no added N, crop growth rate was retarded and increased very little after inflorescence initiation. Herbage produced at high temperatures had the lower percentages of water-soluble carbohydrates and digestible dry matter, but had the higher percentages of most minerals. N increased the percentage content of most minerals. Weights of stubble and of water-soluble carbohydrates in the stubble, and the numbers of stem bases and tillers, were larger at the lower temperatures, and were usually larger with added N in both temperature regimes. Nitrogen decreased the percentage content of carbohydrates in the stubble. Large haplocorms were produced at the low temperatures, but none developed at the high temperatures, indicating less carbohydrate storage. The results partly explain the vigorous growth of timothy in the cool, temperate regions of Europe and North America, and the small dry matter production, lower nutritional value of the herbage, and lack of persistence in the warm southern regions where rainfall is adequate.     

Effects of leaf zeatin and zeatin riboside induced by different clipping heights on the regrowth capacity of ryegrass

The effect of clipping height on ryegrass regrowth was investigated by examining the roles of several plant hormones. Our study consisted of three treatment conditions: (1) darkness over whole plants, (2) darkness only over stubble leaf sheaths, and (3) light over whole plants. Results showed that under darkness over whole plant, low stubble height resulted in low leaf regrowth biomass. Similar leaf regrowth biomass was observed under conditions of darkness only over stubble leaf sheaths as well as light over whole plants. Each unit weight of stubble at different clipping heights has relatively similar potential of providing stored organic substance for leaf regrowth. Therefore, regrowth index, calculated as newly grown leaf biomass divided by unit stubble weight, was used to evaluate regrowth capacity at different clipping heights under minimal influence of organic substances stored in stubbles. Under light over whole plants and single clipping, low stubble height and high stubble height with root thinning resulted in low leaf biomass and high regrowth index. On the other hand, under light over whole plants and frequent clipping high leaf biomass and regrowth index were observed in high stubble height. In addition, we found that leaf zeatin and zeatin riboside (Z + ZR) affected ryegrass regrowth and that roots regulated leaf Z + ZR concentration. Thus, our results indicate that root-derived cytokinin concentration in leaves influences ryegrass regrowth at different clipping heights.     

Specific and constitutive expression of oxalate oxidase during the ageing of leaf sheaths of ryegrass stubble

Changes in the activity of oxalate oxidase (OxO) and of the concentrations of oxalate and H₂O₂ were investigated during the ageing of leaf sheaths of ryegrass (Lolium perenne L.) stubble. The accumulation of H₂O₂ during ageing coincides with the increases of both oxalate level and OxO activity. Western and Northern blot analyses using protein and RNA extracts of the different categories of leaf sheaths suggested that OxO gene expression, as well as Ca-oxalate synthesis, are crucial events of ageing for leaf sheaths. Immunocytochemistry experiments have revealed that OxO, which is an extracellular enzyme, is nearly always present in the parenchymatous cells surrounding the vascular bundles and in the cells of the lower epidermis. Overall, results suggest that in ryegrass that synthesizes both Ca-oxalate and OxO, the production of H₂O₂ and Ca²⁺ during ageing of stubble might be involved in the constitutive defences against pathogens, thus allowing the phloem mobilization of nutrient reserves from the leaf sheaths towards elongating leaf bases of ryegrass.     

Mobilization of fructan reserves and changes in enzyme activities in wheat stems correlate with water stress during kernel filling

Triticum aestivum (wheat) plants grown at a daynight temperature of 1813 °C from anthesis were held as well watered controls, or subject to either a mild (large pot volume) or a more severe (small pot volume) water stress by withholding water from the time of anthesis. Extracts from the peduncle (enclosed by the flag leaf sheath) and the penultimate internode were prepared to determine the activities of fructan exohydrolase and acid invertase and to assess the level of hexose sugars, sucrose and fructans. Measurements were made of ear and individual grain weights and stem fresh weight and dry weight. Plant water relations at the time of each sampling were determined as the flag leaf water potential and the water content of individual organs. Water stress resulted in a shorter duration of kernel filling, smaller kernels at maturity and an earlier loss of stem weight. There was an increase in stem fructose and a fall in fructan level that preceded the loss of dry matter associated with water stress. Coincident with the early fall in fructan content under water stress there was a rise in both fructan exohydrolase and acid invertase in the internodes of stressed plants. This correlation suggests that the conversion of fructans to fructose might have resulted from enzyme induction associated with water stress, but as this conversion occurs before the major export of reserves from the stem it might be only indirectly related to changes in the demand for reserves.     

Carbohydrate storage and use in an alpine population of the perennial herb, Oxytropis sericea

I tested hypotheses for ecological roles of storage carbohydrates in perennating organs (roots and branches) of alpine Oxytropis sericea, a leguminous herb. In naturally growing plants, total nonstructural carbohydrates achieved their maximal concentration in the fall, declined during winter, and reached minimal levels immediately after growth initiation in the spring. Experimental manipulation of carbon sink-source relations through shading of leaves of reproductive plants revealed that the normally unused portion of these carbohydrates is largely available for withdrawal. In another experiment, plants subjected to carbohydrate depletion through shading suffered decreased leaf growth after winter dormancy and had a lower probability of flowering and decreased inflorescence biomass. The dependence of reproductive growth on stored carbohydrates, however, was limited to its initial stages, because accumulation of storage carbohydrates occurred simultaneously with inflorescence expansion, flowering, and fruiting. Moreover, the whole-plant photosynthetic rate, estimated from gas exchange measurements also peaked at the time of inflorescence growth. To address whether stored reserves allow compensatory regrowth following defoliation, plants were subjected to experimental removal of leaves and inflorescences. Defoliated O. sericea partly regrew the lost leaves but withdrawal of stored carbohydrates was limited. Similarly, in a second defoliation experiment where infructescences were left intact, the plants used little stored carbohydrate and only partly compensated for fruit growth. However, carbohydrate accumulation was negatively affected by defoliation. While the ecological importance of stored nonstructural carbohydrates cannot be attributed to any function in isolation, winter respiration, leaf regrowth after winter, and early reproductive growth in O. sericea all depend to a significant extent on stored reserves. Maintaining a large storage pool may protect these functions in years when carbon status is less favorable than during this study. Received: 13 May 1998 / Accepted: 24 November 1998     

Interaction of carbon and nitrogen metabolism in the productivity of maize

Five maize (Zea mays L.) hybrids, FS854, B73 × Mo17, B84 × Mo17, B73 × B77, and P3382, grown under field conditions, were sampled at intervals during the grain-filling period. Plants were subdivided into stalks (including sheaths), leaves, and kernels. These parts were assayed for dry weight, reduced nitrogen, and extractable nonstructural carbohydrates. The duration and rates of net nitrate reduction and photosynthesis were approximated by the changes over time in the accumulation of reduced nitrogen and dry weight by the plant (total, above ground), respectively.

Data on the accumulation of reduced nitrogen and dry weight by the plant show that decreases in nitrate reduction preceded (in time and extent for four of the hybrids and in extent for FS854) decreases or cessation of photosynthesis. FS854 continued to accumulate reduced nitrogen and dry matter throughout the grain-filling period.

The patterns of change in stalk carbohydrate and reduced nitrogen during the early stages of ear development show the stalk serves as a storage reservoir and that these reserves were remobilized during the final stages of grain development. The marked increase and maintenance of dry weight and carbohydrate content of stalks until 34 days after anthesis, shows the capacity of the leaves to produce photosynthate through the first half of the grain-filling period exceeds the needs of the ear and/or the transport system. In contrast, stalk nitrogen content shows a slight increase up to 12 days after anthesis and decreases continually thereafter. Leaf nitrogen was lost continuously throughout grain development. The potential capacity of the plant to supply newly reduced nitrogen was inadequate to support initiation and early development of the kernels without remobilization of vegetative nitrogen. Of the two hybrids having delayed leaf senescence, FS854 with its initially higher concentration and content of reduced nitrogen in the stalk, initiated and developed a bigger ear than P3382, which had lower levels of stalk nitrogen.

Three of the five hybrids had `near linear' rates of accumulation of kernel dry weight, whereas none of the hybrids had linear rates of gain in kernel nitrogen. All hybrids had maximum or near maximum rates of gain of kernel nitrogen between 26 and 34 days after anthesis and a marked reduction (41-52%) of rates in the following sampling interval. These decreases are concurrent with decreases in rates of nitrate reduction (nitrogen accumulation) by the whole plant for four of the hybrids and with decreases in remobilization of nitrogen from the vegetation of FS854. Data for the ratio of rates of accumulation of dry weight/reduced nitrogen by the kernels versus time after anthesis, show that the accumulation of dry weight and reduced nitrogen are independent of each other. The variations in the ratio values appear best related to variations in the availability of nitrogen from the vegetation.

     

苜蓿与沙打旺苗期生长和水分利用对土壤水分变化的反应

通过室内生长箱内盆栽实验,比较了苜蓿和沙打旺苗期的根冠生长和水分利用对种土壤水分环境变化的响应和差异.结果表明,充分供水下苜蓿和沙打旺苗期生物量和蒸腾效率均最高,苜蓿均显著高于沙打旺.土壤水分减少后苜蓿苗期生物量和蒸腾效率下降幅度均大于沙打旺.从低水到阶段低水处理后土壤水分逐渐降低和降低后再复水到低水处理,苜蓿和沙打旺的生物量分别较持续低水处理显著减少47.8%和27.9%.旱后复水后苜蓿根冠比和单位根量耗水量较显著增加,蒸腾效率显著下降; 沙打旺根冠比显著下降,单位根量耗水量和蒸腾效率变化不显著.     

控制降水梯度对荒漠草原优势植物叶功能性状及土壤养分的影响

探究植物叶功能性状随降水梯度的变化规律,对揭示干旱区优势植物对环境变化的响应和适应策略至关重要。以盐池荒漠草原为研究对象,采用遮雨棚和喷灌系统控制降水梯度,分析了优势植物蒙古冰草（Agropyron mongolicum）、短花针茅（Stipa breviflora）及达乌里胡枝子（Lespedeza davurica）叶功能性状变异,以及土壤水分、养分和微生物特性与响应性状间的相关关系。结果表明：HW（增水50%）处理下3个植物LA（叶面积）、LDMC（干物质含量）显著增大,LW处理（减水50%）下短花针茅和达乌里胡枝子LA、LDMC显著减小,降水处理对短花针茅和达乌里胡枝子SLA（比叶面积）影响不显著,LW处理显著提高了蒙古冰草SLA;LW处理显著提高了蒙古冰草和短花针茅LNC（叶氮含量）和LPC（叶磷含量）;HW显著降低了土壤C、N含量,LW和HW均显著减少了真菌数量,而放线菌数量、微生物生物量C、N显著增加;3种优势植物LA均与土壤水分显著正相关,蒙古冰草和短花针茅通过提高SLA、LNC及LNP来适应干旱生境,蒙古冰草和短花针茅LNC及LNP是表征土壤P、微生物生物量有效性的关键指标,达乌里胡枝子通过自我调节养分利用策略来适应C、N、P含量和微生物活性较低的生境,从而决定其在群落中的优势地位。     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.): Susceptibility of proximal and distal parts of leaves from different stalk positions on intact and topped field plants in relation to free amino nitrogen and carbohydrate content*

The area covered by visible mycelium of E. cichoracearum on the upper surface of leaves 4, 8, 12 and 16 of tobacco plants in field plots in Rhodesia was expressed as percentages of the proximal and distal halves at weekly intervals. Free amino nitrogen and carbohydrate in discs from proximal and distal halves of the same leaves were analysed when each leaf was expanding rapidly and was not infected, and several weeks later, when the rate of expansion had slowed down and there was slight infection. On two other occasions, similar leaf discs were inoculated with conidia, to measure the percentage germination and hyphal length from individual conidia after incubation for 2–3 days at constant temperature and humidity; duplicate discs were chemically analysed. Leaves were not susceptible until at least 6 weeks after they had emerged from the bud. Soluble carbohydrate increased and free amino nitrogen decreased during the change from resistance to susceptibility. Proximal parts of leaves were usually infected first; they initially contained less amino nitrogen and soluble carbohydrate than distal parts. All parts of the leaf seemed to be equally susceptible later, when there were no differences in their amino nitrogen or soluble carbohydrate. Upper leaves of intact plants had more natural infection than those from corresponding leaves from topped plants. More conidia germinated on discs from them and produced longer hyphae. The discs from intact plants contained less free amino nitrogen and more soluble carbohydrate than those from topped plants. The accuracy of visual assessments of susceptibility was, generally, confirmed by measurements of percentage germination and length of hyphae from individual conidia on leaf discs. Regressions of hyphal length on leaf composition showed that susceptibility was apparently related inversely to free amino nitrogen and water content and directly to insoluble carbohydrate per unit dry matter.     

Growth,water and nutrient status of plants in relation to patterns of variations in concentrations of dry matter and nutrient elements in base-to-top leaves

Summary Patterns of variations in dry matter concentrations in tomato plants reflected production and translocation of dry matter, implying the possibility of controlling and regulating growth and development of plants by use of dry matter concentration as a useful parameter.Dry matter concentrations, analogous to nutrient concentrations, varied depending on growth conditions, and on type, age and position of plant organs.Interpretation of patterns of variations in contents and concentrations of leaf dry matter in plants, grown under widely different conditions, agreed with the source/sink hypothesis.High water applications were associated with high dry matter concentrations in upper leaves of young pot plants with low sink capacity and with low dry matter concentrations in leaves of older, trough-grown plants with high sink capacity.Accumulation of dry matter in upper leaves of plants is suggested to be associated with development of secondary sinks and, accumulation of dry matter in lateral shoots is considered as a possible explanation of apical dominance.Water regime and transpiration influenced distribution of contents of dry and fresh matter and of absorbed nutrient elements. Redistribution was influenced by water regime.The term, distribution is in the following used in connection with not only absolute values (contents) but also relative values (concentrations).     

Influence of Sink-Source Interaction on Dry Matter Production in Tomato

Sink-source ratio in tomato was manipulated, in six glasshouseexperiments, by fruit pruning (trusses pruned to two to sevenfruits immediately after fruit set of each truss), truss pruning(removal of every other truss at anthesis) and truss pruningin plants with two shoots. Periodic destructive harvest wereconducted for about 100 d after flowering of the first truss.Dry matter production was not influenced by sink-source ratio,whereas dry matter distribution between fruits and vegetativeparts was greatly affected. The fraction of dry matter distributedto the fruits at the end of the fruit pruning experiments (F_fruits)could be described accurately as a saturation-type functionof number of fruits retained per truss (N_f): F_fruits = 0.660(l-e^-0.341N_f). Specific leaf area and internode length decreasedand plant leaf area increased when sink-source ratio was reduced.Removal of every other truss at anthesis did reduce dry matterpartitioning into the fruits, but it did not influence internodelength. Plant development (number of visible leaves at the endof the experiments) was not influenced by sink-source ratio.In four experiments some plants were pruned to one fruit pertruss. Final dry matter production was 8-24% lower for theseplants, compared with plants with more than one fruit per truss.This was, at least party, the result of less light interceptionby these plants, which had strongly curled leaves pointing downwards. Results indicate that effects of sink demand on dry matter productionper unit of intercepted radiation and probably on leaf photosyntheticrate in commercial tomato production can be ignored.Copyright1995, 1999 Academic Press Dry matter production, feedback control, glasshouse, growth analysis, Lycopersicon esculentum, pruning, sink demand, sink-source ratio, tomato     

Effects of a stay-green mutation on plant nitrogen relations in Lolium perenne during N starvation and after defoliation

The stay-green mutation of the nuclear gene sid results in inhibition of chlorophyll degradation during leaf senescence in grasses, reducing N remobilization from senescing leaves. Effects on growth of Lolium perenne L. were investigated during N starvation (over 18 d) and after severe defoliation, when leaf growth depends on the remobilization of internal N. Rates of dry mater production, partitioning between shoots and roots, and re-partitioning of N from shoots to roots were very similar in stay-green and normal plants under N starvation. Km and Vmax for net uptake of NH4+ were also similar for both genotypes, and Vmax increased with the duration of N deprivation. The mutation had little effect on recovery of leaf growth following severe defoliation, but stay-green plants recommenced NO3- and K+ uptake 1 d later than normal plants. Import of remobilized N into new leaves was generally similar in both lines. However, stay-green plants remobilized less N from stubble compared with normal plants. It was concluded that the sid locus stay-green mutation has no significant adverse effect on the growth of L perenne during N starvation, or recovery from severe defoliation when plants are grown under an optimal regime of NO3- supply both before and after defoliation. The absence of any effect on leaf dry matter production implies that the difference in foliar N availability attributable to this mutation has little bearing on productivity, at least in the short to medium term.     

Dry matter economy and reproduction of a temperate forest spring geophyte, Allium ursinum

For a natural population of Allium ursinum age states are defined on the basis of morphological criteria Differences in the dry matter economy of these age states illustrate the underlying life history
Most seeds rest several years m dormancy after maturity It takes on average more than 6 yr until juvenile plants attain the dry matter threshold level for the production of an inflorescence Flowering plants divert 41% of their dry matter gain during spring to reproductive parts (7% to the seeds) Since flowering plants show a marked negative annual dry matter balance, c 81% of them are not able to flower again the next year
At the same expense of carbon reserves the formation of daughter bulbs results in a considerably higher number of new ramets than the production of seeds Nevertheless, the investment in seed production is extraordinarily high in relation to other woodland perennials This might be explained by the lack of an effective dispersal of the daughter bulbs By vegetative propagation dense groups of adult ramets develop, which will finally undergo mutual shading     

Sexual behavior of dwarf and normal genotypes in divergent growth lines of chickens

Comparisons of several reproductive factors were made among dwarf, heterozygous and normal chickens in lines selected for high (HW) and low (LW) juvenile body weight. Semen concentration was significantly greater in the HW than in the LW line, and was greater for the normals than for the heterozygous or dwarf males. HW males had a significantly lower percentage of normal spermatozoa than the LW males, while there were no differences among dwarf genotypes. Fertility, as measured by A.I., was higher for LW than for HW females, whereas there were no differences among male genotypes. Mating behavior of males was measured in flocks where the pullets were of the same genotype, and where several genotypes were intermingled. The number of courts, mounts, treads, completed matings and crouches elicited was less for HW than for LW males. Although morphological and behavioral pre-mating barriers among populations were not complete, there was a tendency toward preferential mating between dwarf genotypes within the LW line which resulted in a male genotype-female genotype interaction. Matings among other genotypes were random, with an expression of passive dominance of males over females.     

Partitioning of Dry Matter and the Deposition and Use of Stem Reserves in a Semi-dwarf Wheat Crop

An experiment was carried out within a crop of spring wheat(cv. Condor) to examine dry matter partitioning between thedeveloping stem and ear, and to estimate the magnitude of carbonstored in the stem both before and after anthesis, and the subsequentutilization of these reserves during grain growth. The amount of reserve laid down and mobilized was estimatedfrom analysis of data for changes in masses of stem and leaffrom frequent harvests. The rate of change of the dry mass ofthe individual plant organs was expressed as a proportion ofthe rate of change of the total dry mass of the large culm.This value was called the Allocation Ratio (AR). It was assumedthat assimilate was transferred directly from the stem intothe growing ear, and not into other organs. This paper providesevidence for the idea that the stem intemodes of wheat are ableto accumulate and subsequently mobilize a dry matter reserve.The accumulation and subsequent mobilization of fructans inthe stem was demonstrated using ascending thinlayer chromatography.On a dry matter basis the large culms of the wheat crop accumulatedall of their stem reserves after anthesis (0–41 g perlarge culm; 98·4 g m^–1). After adjusting the lossof mass by 33% to allow for respiration, it was concluded thatpost-anthesis stem reserves may have contributed at least 21%of the final grain yield of this crop. Triticum aestivum L., semi-dwarf spring wheat, dry matter partitioning, stem reserves, fructans     

Cassava Response to Water Deficit in Deep Pots: Root and Shoot Growth, ABA, and Carbohydrate Reserves in Stems, Leaves and Storage Roots

Cassava (Manihot esculenta, Crantz) is an important staple crop for tropical climates worldwide, including drought-prone environments where it is valued for its reliable yield. The extent to which stress tolerance involves regulation of growth and carbon balance aided by remobilization of carbohydrate from various plant parts was investigated. Plants were grown in 1-meter high pots to permit observation of deep rooting while they were subjected to four soil water regimes over a 30-d period. Transpiration declined abruptly in conjunction with leaf ABA accumulation and severe leaf abscission. In water stressed plants, growth of all plant parts decreased substantially; however, a basal rate of leaf growth continued to provide some new leaves, and although growth of fibrous lateral roots was reduced, main root elongation to deeper regions was only modestly decreased by stress. In leaf blades and petioles, sugars were the predominant form of nonstructural carbohydrate and about one third was in starch; these reserves were depleted rapidly during stress. In contrast, stems and storage roots maintained relatively high starch concentrations and contents per organ until final harvest. Stems gradually lost starch and had sufficient reserves to serve as a prolonged source of remobilized carbohydrate during stress. The amount of starch stored in stems represented about 35 % of the reserve carbohydrate in the plant at the onset of water stress (T₀), and 6 % of total plant dry mass. We suggest that this pool of carbohydrate reserves is important in sustaining meristems, growing organs, and respiring organs during a prolonged stress and providing reserves for regrowth upon resumed rainfall.     

平茬高度对中国沙棘萌枝能力及非结构性碳水化合物积累与分配的影响

为探讨中国沙棘(Hippophae rhamnoides ssp.sinensis)伐桩萌枝的养分投资与分配机制,以陕西省定边县15a中国沙棘人工林为研究对象,设置不平茬(对照)和平茬高度0、10、20 cm处理,分析伐桩萌枝能力、非结构性碳水化合物(NSC)对平茬高度的响应规律及其因果关系.结果显示:(1)随平茬高度...     

施氮对半湿润农田生态系统不同冬小麦品种灌浆期物质转移的影响

在年均降水量632 mm的黄土高原南部半湿润红油土上,以NR9405、9430、偃师9号、小偃6号、陕229、西农2208、矮丰3号和商188为供试材料,进行大田试验,研究在不施氮和施氮(90 kg.hm-2)条件下不同品种冬小麦灌浆特性及物质转移效率。结果表明,冬小麦干物质生产及物质转移效率共同受品种和氮肥的影响。开花期老叶、茎鞘和成熟期茎鞘、籽粒干重间存在显著差异。施氮对开花期、成熟期地上部各部位干重均有明显的促进作用。各部位干物质转移量、转移效率和转移量对籽粒的贡献率既与品种有关,也与施氮有关;氮肥的影响又因品种不同而异。干物质转移量、转移效率和转移干物质对籽粒的贡献率在8个供试品种中,最高的是NR9405,最低的是偃师9号,除NR9405和西农2208籽粒中50%以上干物质来自于开花前贮存光合产物的再转移外,其余6个品种籽粒中50%以上的干物质来自于开花后新合成的同化产物。干物质转移量对籽粒的贡献率以穗轴+颖壳部位最低,且多数处理为负值,以茎秆为最大,叶片居中。从总体看,干物质转移量、干物质转移率和干物质转移量对粒重的贡献率在不同品种之间的差异大于施氮处理间的差异,施氮后降低了干物质向籽粒中的转移。     

Distribution of alfalfa weevil (Coleoptera: Curculionidae) larvae among postcutting locations

A field study was conducted in 1996 and 1997 to determine survival and spatial patterns of alfalfa weevil, Hypera postica (Gyllenhal), larvae within and between windrows of swathed alfalfa, Medicago sativa L., forage as dry matter concentration increased. After harvest, the percentage of live weevil larvae residing in swathed forage decreased as swath dry matter percentage increased. Conversely, larval populations in stubble between windrows increased with increasing swath dry matter. Larval populations in stubble under windrowed forage increased slightly as windrowed forage dry matter increased. Applications of these results for the development of alfalfa harvest systems for improved cultural control of alfalfa weevil are discussed.