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1.
Abstract Defoliation by goats (leaves plus shoots) during the growing phenophases resulted in a considerable stimulation of leaf and shoot growth relative to non‐defoliated plants. The response differed considerably depending on the intensity and phenophase of defoliation. Plants were most susceptible to defoliation and young shoot removal during the spring flush when carbohydrate levels were at their lowest. During the rest of the growing season carbohydrate levels were high. At these times moderate to heavy (50 % to 75 % leaf removal) defoliations resulted in the greatest leaf and shoot growth. In contrast, the initial and continuing impact of avian and insect consumption of leaves only reduced leaf and shoot production. The stimulatory effect of defoliation in one season carried through the dormant season to the following growing season. Defoliations during the dormant season did not have any positive or negative impact on plants relative to non‐defoliated plants. Leaf and shoot material removed when the plants were growing, was replaced within weeks of defoliation. 相似文献
2.
W.R. Teague 《African Journal of Range and Forage Science》2013,30(3):132-138
Acacia karroo trees were defoliated by goats at two intensities and four frequencies; 2, 4, 8 and 12‐weekly. Leaf accumulation and carbohydrate reserve levels were compared to a non‐defoliated control, and to plants (defoliation controls) which were defoliated for the first time that season each time a frequency treatment was defoliated. These plants are activated by defoliation in such a manner that successive defoliations can result in this activation being additive. There is clearly a defoliation level below which they are not activated. Activation appears to be negated to a degree by defoliations at 2 and 4‐weekly frequencies, relative to the 8‐weekly defoliation frequency. The 12‐weekly frequency at heavy defoliation produced less than the same defoliation at 8‐weekly frequency. The 2‐weekly frequency treatments produced as much leaf as the 4 and 12‐weekly defoliations at the same defoliation intensity. The more frequently plants were defoliated, the more carbohydrate reserves dropped. However, plants adjusted to cope with very frequent defoliations. There was no connection between leaf accumulation and carbohydrate reserve levels following the different frequencies and intensities of defoliation. 相似文献
3.
W.R. Teague 《African Journal of Range and Forage Science》2013,30(4):223-226
Abstract A field study was conducted with Acacia karroo plants to determine changes in relative photosynthetic rates, the extent of carbohydrate reserve depletion and the rate reserves take to recover, following defoliation by goats at different intensities and phenophases, at a “wet” and a “dry” site. The rate of photosynthesis of fully expanded leaves increased markedly following defoliation. Light defoliation increased photosynthetic rate the most. Total non‐structural carbohydrate levels dropped significantly after defoliation. The magnitude of decrease was directly related to the intensity of defoliation. Following the heavy defoliations, recovery of carbohydrate levels was much faster than after the light defoliations. Rates of recovery were also faster following defoliation in the second half of the growing season, than in the first half. However, the plants that had been heavily defoliated in the second half of the growing season had not fully recovered carbohydrate levels before leaf fall in late autumn. Moisture stress had very little effect on carbohydrate levels in comparison with the defoliation treatments. 相似文献
4.
W.R. Teague 《African Journal of Range and Forage Science》2013,30(4):225-229
The response of Acacia karroo trees to defoliation of either the upper or lower canopy only, was compared experimentally with that of plants whose whole canopies had been defoliated at a range of defoliation levels. These plants were very sensitive to defoliation of the upper canopy. A 100% defoliation of the upper canopy only, resulted in the same amount of growth as 100% defoliation of the whole canopy. This was considerably less than the growth of plants defoliated overall, at 25% and 50% leaf removal. In contrast, defoliating the bottom half of the canopy only, stimulated growth in the whole canopy to the same degree as defoliation of the whole canopy at 25–50%. The increases of growth were due largely to increased growth in the top half of the canopy. Plants were very sensitive to defoliation in the early‐flush phenophase. This probably masked the positive effects of the partial defoliations applied at this phenophase. 相似文献
5.
Eragrostis curvula in pots was cut every 2, 3, 4, 6, or 12 weeks, for 12 weeks. Regrowth and the recovery of total available carbohydrates (TAC) in the next 7 weeks was measured weekly. The regrowth (dry‐matter yield) of tops was progressively less with increasing frequency of defoliation. After the defoliation period the root weights decreased in the more lenient treatments, The crowns did not show this marked initial decrease, but increased steadily in weight. Immediately after the last defoliation, the TAC content of the roots and crowns decreased significantly, and it was not restored to the level observed at the last cut until the third week after defoliation. A comparison of average relative growth rates of tops revealed that during the first three weeks after the last defoliation the highest values were obtained from plants defoliated least frequently. For this period there was a significant correlation between average grwoth rate and reserve status. The results indicate that the plants drew on their carbohydrate reserves for at least a short period during regrowth. 相似文献
6.
C. Chirara P.G.H. Frost V.E.E. Gwarazimba 《African Journal of Range and Forage Science》2013,30(1-2):41-47
Abstract Two experiments were conducted, one in the field and the other in the greenhouse, to investigate the effects of the intensity and frequency of grass defoliation on the survival and growth of Acacia karroo seedlings. In the greenhouse, seedlings growing with heavily clipped grasses had higher biomass production than those competing with moderately clipped grasses. Root/shoot ratios were higher in treatments with undipped grasses. There was a negative relationship between grass root production and A. karroo biomass production. The field experiment was carried out in two paddocks, one previously heavily‐grazed and the other lightly‐grazed. Grazing in both paddocks was simulated by artificial defoliation. Generally more A. karroo seedlings emerged under lightly defoliated treatments. Clipping frequency had a strong effect (P=0.066) on the survival of emerged seedlings during the wet season. There were no differences in survival rate at the end of the dry season. Though grass defoliation was shown to enhance seedling growth under controlled conditions, no evidence was found to suggest that seedling establishment during the first year is influenced by the intensity of grass defoliation. 相似文献
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Root proliferation is important in determining root foraging capability of rangeland grasses to unpredictable soil-nutrient pulses. However, root proliferation responses are often confounded by the inherent relative growth rate (RGR) of the particular species being compared. Additionally, inherent biomass allocation to roots (R:S ratio) can be associated with root RGR, hence likely influencing root foraging responses. The influence of relative growth rate and biomass allocation patterns on the speed and efficiency of root foraging responses at the critical seeding stage was examined in two important perennial rangeland grasses that occur widely in the Great Basin Region of the United States (Whitmar bluebunch wheatgrass [Pseudoroegneria spicata {Pursh} Löve] and Hycrest crested wheatgrass [Agropyron desertorum {Fisch. ex Link} Schult. × A. cristatum L. Gaert.]) as well as in the widespread exotic invasive annual grass, cheatgrass (Bromus tectorum L.). Greenhouse-grown seedlings were exposed to four nutrient regimes: uniform–low, uniform–high, soil-nutrient pulse, soil-nutrient depletion, and to either no clipping or clipping (80% removal of standing shoot biomass). Hycrest was the only species that exhibited root proliferation responses to the short-lived nutrient pulse, and this response occurred through root elongation rather than initiation of lateral root branches. Overall, defoliation inhibited proliferation-based root responses to a larger extent than topological-based root responses. Defoliated plants of Hycrest interrupted root development (topological index did not change) following shoot defoliation compared to undefoliated plants. In contrast, root topological developmental patterns were the same for defoliated and undefoliated plants of Whitmar, whereas cheatgrass exhibited an intermediate response between Whitmar and Hycrest. Our results suggest that inherent biomass allocation to roots contributes to enhanced capabilities of proliferation-based root responses. 相似文献
8.
The second youngest fully‐expanded leaf on the main tiller of vegetative Themeda triandra plants was exposed to 14CO2. Thereafter, quantitative analysis of partitioning, storage and remobilization after defoliation of 14C‐labclled assimilate was conducted in serially‐harvested plants over a 27‐day period. In undefoliatcd plants, 50% of assimilated 14C was ultimately lost through respiration, while that remaining in the plant reached its final destination within two days of assimilation. A small, but significant, portion of assimilated 14C was invested into long‐term storage in roots and stem bases. These reserves were remobilized after defoliation, and a portion of the remobilized 14C was incorporated into new growth. Partially‐defoliated plants regrew more rapidly than totally‐defoliated plants, but they both made equal demands on 14C reserves. Reserve depletion took place from both roots and stem bases. 相似文献
9.
J. H. Visser 《African Journal of Range and Forage Science》2013,30(1):41-48
A pot experiment was conducted in the glasshouse to determine the effect of three heights of cut on translocation of 14C‐labelled assimilates in Eragrostis curvula cv Ermelo. Autoradiographs revealed that to produce regrowth plants defoliated to a height of 7,5 cm did not draw on their reserves significantly and that both new growth and stubble were able to maintain a continuous supply of assimilates to the roots after defoliation. In contrast, in plants defoliated to 2,5 cm all assimilates were retained in the labelled tiller to sustain new growth. Results from plants defoliated to 5,0 cm revealed the same patterns as for plants defoliated to 7,5 cm, although it was clear that smaller amounts had been translocated. These results indicate the practical importance of not defoliating E. curvula too low. 相似文献
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外来植物对草地生态系统的入侵会导致草地生物多样性降低、植被生产力下降、生态环境日趋恶化等严重后果,要想有效防治草地入侵植物,深入了解其生理生态特性十分关键。根据国内外利用刈割这一常规管理方法控制草地入侵植物的现状,对草地入侵植物响应枝叶去除处理的模式与机理相关研究展开综述,并得出以下主要结论:(1)草地入侵植物倾向于利用补偿性光合作用模式保证和提高其光合作用能力;(2)通过快速的茎叶再生机制来补偿光合器官和地上生物量的损失;(3)改变土壤微生物群落结构使其更有利于入侵植物的生长;(4)入侵植物利用高效和多样化的资源分配策略促进再生;(5)入侵植物将更多能量优先分配到繁殖器官以维持种群稳定;(6)草地入侵植物在不同发育阶段对枝叶去除的耐受性差异较大。并且,本研究对刈割控制草地入侵植物的优势与不足进行了简要分析,并提出了三点防治草地入侵植物的具体建议。此外,建议在今后的相关研究中,研究者应重点考虑草地入侵植物响应枝叶去除的分子机理,以及放牧草地入侵植物对全球变化的响应机制,以巩固与拓展科学高效防治草地入侵植物的理论基础。 相似文献
11.
由于一些侵染性病害的影响,浙江省主要梨产区早期落叶现象严重,严重影响了砂梨产业的发展。通过对浙江省杭州市商业梨园主栽品种的田间调查发现,不同品种对病菌的抵抗能力不同。园黄为黑斑病的易感品种,但对炭疽病的的抗性较强;黄花和翠冠较抗黑斑病,但黄花炭疽病的发病率较高;三个品种的锈病发病率没有显著差异。病菌侵染和落叶时间的相关性分析表明：病菌侵染后翠冠和园黄落叶较黄花早;受黑斑病菌侵染的叶片最易脱落,而梨炭疽病菌和梨锈病菌不易引起落叶,仅在后期形成穿孔。总体上园黄早期落叶现象最为严重。受梨黑斑病菌侵染后,叶片诱导POD活性的增加来抵御病原菌的侵染。 相似文献
12.
R. E. Altona 《African Journal of Range and Forage Science》2013,30(1):19-23
In intact plants C14‐assimilates were translocated from the treated leaf on the primary tiller to young leaves on that tiller, to secondary tillers, and also to the roots. Plants defoliated after labelling revealed movement of materials from the storage organs to all the new leaves. Here these materials were used as a respiratory substrate and for the production of structural materials. Although initially after defoliation new leaves retained all their assimilates, presumably for their own growth, assimilates were soon translocated from these leaves to the roots. 相似文献
13.
W.R. Teague 《African Journal of Range and Forage Science》2013,30(4):230-235
Patterns of browse selection by Boer goats in a representative Acacia karroo community in the eastern Cape were studied. The rate of intake of browse was positively related to the leaf mass per unit length of the shoot. The ease of harvesting leaf material, as determined by the height off the ground, modified the rate of intake. Generally, following browsing, tannin levels increased significantly and in vitro digestibility decreased significantly. These changes in tannin content and digestibility differed in magnitude according to the plant size and age of the shoot and leaf. Generally, the leaf and shoot intake was negatively related to tannin content and positively related to digestibility, thus influencing patterns of selection for different plant parts and size classes of A. karroo. However, some of the results are contradictory. 相似文献
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Our objective was to determine the short-term response of bluebunch wheatgrass and medusahead to defoliation of wheatgrass designed to stimulate regrowth through tillering. We hypothesized that defoliating bluebunch wheatgrass by 20% at the 3 to 3.5 leaf stage followed by a 50% defoliation at peak standing crop would increase its tillering and biomass production. Consequently, we expected a reduction of the density and biomass of medusahead over that of bluebunch wheatgrass defoliated 50% at peak standing crop. Treatments included four initial medusahead densities (200, 333, 444, 600 plants · m-2) created by hand-pulling and three defoliation regimes factorially arranged (12 treatment combinations) in a randomized complete-block design and replicated four times at two sites. In 2006 and 2007, defoliation was accomplished by hand-clipping bluebunch wheatgrass 1) by 50% once at peak standing crop (late June); 2) by 20% at the 3 to 3.5 leaf stage, then again to 50% at peak standing crop (mid May, late June); or 3) plants were not clipped. Density was sampled in 2006 and 2007, and biomass was harvested only at Star Mountain (near Riverside, Oregon) in 2007 because Warm Springs (near Drewsey, Oregon) was burned by a wildfire before final 2007 data could be collected. In 2006, no treatments applied at either site detectably altered the number of tillers produced by bluebunch wheatgrass nor did they affect bluebunch wheatgrass density or biomass in 2007 at Star Mountain. Changes in medusahead density were not detected in 2006, but this annual invasive grass increased in density and biomass in 2007 at Star Mountain in plots receiving two defoliations. The relatively short growing period caused by summer drought and the relative intolerance of bluebunch wheatgrass to grazing make the twice-over grazing an unlikely practice for arid rangelands in the western United States. In fact, it could possibly increase the risk of annual grass invasion. 相似文献
16.
J.E. Danckwerts A.J. Aucamp L.P. Du Toit 《African Journal of Range and Forage Science》2013,30(3):9-14
Abstract Marked populations of Themeda triandra tillers were sequentially sampled at fortnightly intervals under normal conditions and without moisture stress respectively, covering a period from tiller initiation through to senescence after flowering. Parameters recorded were height of shoot apex, tiller mass, leaf area, leaf number, secondary tiller development and premature tiller mortality. Tillers of irrigated plants had a significantly higher mass, more elevated shoot apices, and produced a greater total number of leaves than those of non‐irrigated plants. Fewer unstressed tillers senesced prematurely than those experiencing moisture stress. 相似文献
17.
Abstract A field study was conducted to describe the growth patterns of A. karroo at different levels of water stress in different edaphic situations. Shoots are heterophyllous and are formed by free growth. The degree of development of a shoot, relative to others in the canopy, is governed by branch and position in the canopy. At least six phenological phases were identified in the annual growth cycle. The pattern of growth and the phenological cycle are not changed by water stress. Initiation, emergence and development of shoots and leaves are governed by how favourable environmental conditions are. If there is little shoot growth early in the season, these plants can partially compensate by producing more leaf per unit of shoot if environmental conditions improve. Leaf and shoot growth at the beginning of the season took place only if there was sufficient moisture available, and if the minimum temperature had risen above a threshold amount. Where there was insufficient soil moisture, no growth was observed before rains had fallen. The growth strategy of A. karroo differs markedly from that of broadleaved African savanna tree species. Growth in A. karroo is dominated by current growing conditions, rather than those of the previous season. They are able to make opportunistic growth at any time. Soil depth had a marked influence on plant growth, presumably due to a larger available nutrient and moisture pool. 相似文献
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Jerry D. Volesky Walter H. Schacht Ann E. Koehler Erin Blankenship Patrick E. Reece 《Strength and Conditioning Journal》2011,64(5):506-513
Root growth is important to the competitive ability of plants, and understanding how herbage defoliation affects root growth has implications for development of management strategies. Objectives were to determine the effects of defoliation intensity and frequency on root characteristics and herbage production of slender wheatgrass (Elymus trachycaulus [Link.] Shinners), Nebraska sedge (Carex nebrascensis C. Dewey), and “Steadfast” birdsfoot trefoil (Lotus corniculatus L.). Plants of each species were transplanted into containers that had been placed in the ground at wet meadow field sites the prior year. There were eight replications of a control and five defoliation treatments, which were combinations of different frequencies (two or five times) and intensities (light or heavy) and haying. Treatments were applied for a single growing season, and aboveground biomass was collected. Containers were extracted in October, and plant crowns, rhizomes, and roots were separated from the soil. Defoliation treatment did not affect total root weight, length, and surface area of Nebraska sedge or birdsfoot trefoil (P>0.10). Slender wheatgrass total root weight was less when defoliated five times (4.46 g·container?1) than when defoliated twice (6.62 g·container?1) during the growing season. More frequent defoliation of slender wheatgrass also reduced length (20%) and surface area (21%) compared to less frequent defoliation. However, defoliation frequency did not affect aboveground biomass. Defoliation intensity did not affect aboveground production or root characteristics of the three species. Abundant soil moisture in meadows likely buffers negative effects of defoliation. For all species, two defoliation events (e.g., haying followed by grazing) does not appear to negatively affect root growth and herbage production. 相似文献
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放牧活动是包含牧食折损、枝叶去除、唾液沉积等多个过程的融合,而觅食者分泌的唾液对牧草具有潜在影响。本试验选择外源无机盐与硫胺素处理作为试验组,以去离子水与羊唾液处理为参考对照,并将4种溶液涂抹作用于不同枝叶去除水平的紫花苜蓿截面处,探究植食性动物(羊)唾液中的无机盐与硫胺素是否对紫花苜蓿的再生性产生影响,分析枝叶去除与羊唾液是如何诱导植物的补偿再生,同时探寻紫花苜蓿从形态与生理上对无机盐和硫胺素的差异响应。试验结果表明,1)与单一的枝叶去除处理相比,在羊唾液的催化作用下,枝叶去除后的紫花苜蓿再生能力明显提高,其中硫胺素是羊唾液中的有效成分;2)相对于外源无机盐,硫胺素对枝叶去除紫花苜蓿牧草有更为显著的正效应,紫花苜蓿地上累积生物量显著增加,茎叶比差异也达到了4.3~7.9倍;在80%枝叶去除水平下,总分蘖数大约是无机盐组的1.56倍;3)不同处理下紫花苜蓿的生理指标差异性不均一。在各项处理中,紫花苜蓿的叶绿素含量值都接近49.3 mg/g;在20%枝叶去除水平下,清水与羊唾液处理均促进根系可溶性糖含量大幅度增加;对于无机盐组,POD活性随着枝叶去除水平呈递增变化,而硫胺素处理没有引起POD活性的改变。通过本研究,期望进一步了解紫花苜蓿响应放牧的内在机制,为改善人工草地现状和提高牧草的农业效益提供参考,同时也为放牧生态学的发展提供理论支持。 相似文献