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1.
An experiment was carried out in which simulated swards of ryegrass (cv. S23) were grown in boxes. In the first instance the swards were cut at weekly intervals to maintain five levels of leaf area index (LAI) from LAI 1 to 4–5 in simulation of continuous grazing. Measurements were made of growth, senescence and net growth rate and of net canopy photosynthesis at constant irradiance. The results showed that the swards adapted to the defoliation regimes mainly by changes in tiller population density and pseudostem length. When the swards had equilibrated to the cutting regime growth rate increased with LAI but, since tiller density and the partitioning of growth between herbage harvested and that lost by sensecence also changed with LAI, net growth rate was constant over the LAI range 2–4·5. Maximum weight of herbage harvested was obtained between LAI 2 and 3.
After 10 weeks of weekly cutting all the swards were cut back to LAI 1 and allowed to regrow. Growth rate showed almost no response to the previous culling treatments. The relationship of net canopy photosynthesis to LAI was linear for the frequently defoliated swards and curvilinear for regrowing swards. The reasons for this difference were examined. 相似文献
After 10 weeks of weekly cutting all the swards were cut back to LAI 1 and allowed to regrow. Growth rate showed almost no response to the previous culling treatments. The relationship of net canopy photosynthesis to LAI was linear for the frequently defoliated swards and curvilinear for regrowing swards. The reasons for this difference were examined. 相似文献
2.
The relationship between net canopy photosynthesis (Pnc) measured at 400 J m−2 s-1 and leaf area index (LAI) was determined on ryegrass-dominant swards over a range of her bage masses in five grazing experiments. In three experiments the swards were continuously stocked either by sheep or by cattle to maintain a number of herbage heights and hence LAI values. In two experiments the swards were intermittently grazed with 21 -d regrowth intervals. On the continuously stocked swards measurements were made over nine periods each of 7 to 21 d in length. On the intermittently grazed swards measurements were made over six periods while the herbage was being grazed down from a high to a low LAI and over three periods during the regrowth phase.
On all the swards where measurements were made while grazing was in progress, the relation of Pnc to LAI was linear. The photosynthetic rate was greater on the continuously grazed than on the intermittently grazed swards up to LAI 35 and in two experiments to LAI 5. The relationship of Pnc to LAI of swards in the regrowth phase was predominantly curvilinear and such that over much of the LAI range they had a greater photosynthetic potential than the same swards being grazed down from high to low mass. Daily rates of CO2 uptake and growth in the field were calculated for one continuously stocked experiment. Both were linearly related to LAI in the range LAI 2–4·5. The agronomic implications of the results are discussed. 相似文献
On all the swards where measurements were made while grazing was in progress, the relation of Pnc to LAI was linear. The photosynthetic rate was greater on the continuously grazed than on the intermittently grazed swards up to LAI 35 and in two experiments to LAI 5. The relationship of Pnc to LAI of swards in the regrowth phase was predominantly curvilinear and such that over much of the LAI range they had a greater photosynthetic potential than the same swards being grazed down from high to low mass. Daily rates of CO
3.
The long-term influence of sward height from April to July (Phase 1) and from July to early October (Phase 2) on total herbage and white clover production was measured over four years (1988–1991) as herbage accumulation. A subsidiary experiment to determine the influence of leaf area index (LAI) on gross canopy photosynthesis was conducted to aid interpretation of growth from herbage accumulation data. Target sward heights in 0·5 ha plots in two blocks were 5,7 or 9 cm in Phase 1 and 7 or 9 cm in Phase 2, although mean actual heights per phase were slightly higher. Net herbage accumulation (NHA) was measured within mobile exclosure areas over successive two-week intervals. Gross photosynthesis was measured in circular turves removed from the trial area representing a range of LAIs with an at least reasonable clover content. Despite wide differences in mean sward height and herbage mass, NHA and net clover accumulation for a given phase were not generally affected by treatments. Positive effects of grazing at 5 cm in Phase 1 on NHA and clover accumulation later in the year, and of grazing at 7 cm in Phase 2 on NHA in the following spring were sometimes apparent. Gross canopy photosynthesis (g CO2 m?2 h?1) at 1500 μE m?2 s?1 and 18–21°C was linearly related to LAI described by 1·003 + 1·165 LAI over the LAI range 0·7 to 4·5. Total herbage and clover growth, interpreted from NHA by a previously described model, was predicted to be marginally lower in shorter swards. Similarity in NHA and clover accumulation between treatments was considered to be because of lower senescene and decomposition, and a higher proportion of new tissue being assigned to lamina growth, despite lower LAI and gross photosynthesis in the shorter swards. It was concluded that stocking intensity in swards continuously stocked with cattle did not have a strong influence on net total herbage and clover growth. 相似文献
4.
Leaf age structure and canopy photosynthesis in rotationally and continuously grazed swards 总被引：2，自引：0，他引：2
The leafage structure of ryegrass canopies and its role in canopy photosynthesis were compared under continuous and rotational grazing by sheep. Under continuous grazing, an increase in the intensity of grazing increased the proportion (by leaf area) of young leaves in the sward. A mechanistic mathematical model was used to demonstrate how this may have arisen, even though it would largely have been the young leaves that were eaten.
However, the observations do not confirm the hypothesis that continuously grazed swards have a characteristically greater proportion of young leaves, and so a greater photosynthetic potential, than rotationally grazed ones. The proportion of young leaves increased during regrowth following severe rotational grazing (residual LAI < 05) and the photosynthetic potential of the canopy became greater than under continuous grazing.
A model of canopy photosynthesis was used to demonstrate that the observed difference in the proportion of young leaves alone was unlikely to account for all the differences in canopy photosynthesis between managements, and further differences in canopy structure were evaluated. Despite the delay in the restoration of leaf area following severe grazing in a rotation, the total photosynthetic uptake of a system involving some 12–13 days regrowth and 3 days grazing exceeded that of a well-utilized continuously grazed sward. Re growths of longer duration led to progressively greater total photosynthetic uptake, though this was not considered synonymous with greater yield. 相似文献
However, the observations do not confirm the hypothesis that continuously grazed swards have a characteristically greater proportion of young leaves, and so a greater photosynthetic potential, than rotationally grazed ones. The proportion of young leaves increased during regrowth following severe rotational grazing (residual LAI < 05) and the photosynthetic potential of the canopy became greater than under continuous grazing.
A model of canopy photosynthesis was used to demonstrate that the observed difference in the proportion of young leaves alone was unlikely to account for all the differences in canopy photosynthesis between managements, and further differences in canopy structure were evaluated. Despite the delay in the restoration of leaf area following severe grazing in a rotation, the total photosynthetic uptake of a system involving some 12–13 days regrowth and 3 days grazing exceeded that of a well-utilized continuously grazed sward. Re growths of longer duration led to progressively greater total photosynthetic uptake, though this was not considered synonymous with greater yield. 相似文献
5.
Net photosynthesis per unit area of ground surface was determined at saturating light energy levels in Dactylis glonwrata swards over a wide range of leaf area indices (LAI). The relationship between net photosynthesis and LAI was influenced by the particular defoliation regime to which the sward was subjected. In most instances net photosynthesis and LAI were linearly related, with defoliation regime influencing both the slope and intercept of the regression. However, a defoliation regime which left leaves below 3 inches (7.5 cm) resulted in a curvilinear relation. The net photosynthesis-LAI relationships were compared with the DM production of the swards on which they were obtained. Differences in these relationships did not entirely explain the differences in sward yield. The significance of these findings is discussed with reference to the theories of light interception and pasture growth. 相似文献
6.
不同覆膜方式对春玉米超高产群体冠层垂直结构的影响 总被引：10，自引：4，他引：6
在不同覆膜方式下对春玉米超高产田的冠层垂直结构与产量进行了系统研究。结果表明：行间覆膜可使春玉米超高产群体的植株叶片功能期延长、LAI和LAD增大、Pn和叶绿素提高,冠层内光分布均匀合理,能截获更多的光合有效辐射量,透光率增大,避免下层叶片早衰,提高光合能力,获得更大产量。不同覆膜处理在冠层各层中对叶片功能期、LAI、LAD、Pn、光合有效辐射量及透光率均表现为行间覆膜>行上覆膜>不覆膜,这一规律与各处理对产量的影响一致。 相似文献
7.
在PVC管栽和大田条件下,采用裂区试验设计,主区为玉米自交系、裂区为水分处理,测定玉米冠层光合和产量等指标。结果表明,与对照(CK)相比,干旱胁迫(WS)处理下冠层叶色值(SPAD)、光合速率(Pn)、蒸腾速率(Tr)和叶面积指数(LAI)均呈下降趋势,耐旱性较强的黄早四(HZS)平均降幅小于耐旱性较弱的CML58,其SPAD和LAI的降幅较高期(R3)出现早于CML58(R5);干旱胁迫后,水分利用效率(WUE)呈升高趋势,HZS平均升幅高于CML58。HZS的SPAD、Pn、Tr、WUE、LAI、单株粒重、收获指数和群体产量均高于CML58。与CK相比,WS处理下HZS群体产量平均降幅低于CML58。综上,耐旱性较强的玉米自交系冠层光合参数对生殖生长期干旱胁迫响应相对滞后,可在干旱胁迫后维持相对较高的光合性能、水分利用效率和叶面积指数,促进植株干物质转化与子粒建成,最终获得较高产量。 相似文献
8.
为了解冬小麦不同冠层叶片光合和蒸腾作用特征以及随水分条件的变化规律,通过田间试验,以冬小麦京冬22为试验材料,设置0 mm（T0）、220 mm（T1）、280 mm（T2）3种水分处理,比较分析了冬小麦不同冠层叶片净光合速率、蒸腾速率及水分利用效率对光合有效辐射和灌溉响应的差异。结果表明,三种水分处理下,冬小麦不同冠层叶片的蒸腾速率和光合速率随光合有效辐射的增加而增加,随后趋于平缓。不同冠层叶片蒸腾速率、光合速率对光合有效辐射的响应表现为上层>中层>下层;不同冠层叶片WUE对光合有效辐射的响应表现为上中层>下层。光合有效辐射相同时,灌水处理（T1和T2）的叶片光合蒸腾速率均高于不灌水处理（T0）。T1、T2处理下,叶片光合速率对光合有效辐射响应在整个生育期内表现为灌浆期>抽穗期>成熟期>拔节期,蒸腾速率对光合有效辐射响应在整个生育期内表现为抽穗期>灌浆期>拔节期>成熟期;T0处理下,叶片光合速率对光合有效辐射响应在整个生育期内表现为灌浆期>拔节期>抽穗期>成熟期,蒸腾速率对光合有效辐射响应在冬小麦整个生育期内表现不显著。因此,在进行小麦叶片到单株光合蒸腾尺度拓展估算时,应考虑冠层位置和水分条件对拓展结果的影响。 相似文献
9.
Canopy height and N affect herbage accumulation and the relative contribution of leaf categories to photosynthesis of grazed brachiariagrass pastures 
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下载免费PDF全文 J. I. Yasuoka C. G. S. Pedreira V. J. da Silva M. P. Alonso L. S. da Silva F. J. Gomes 《Grass and Forage Science》2018,73(1):183-192
The effects of three canopy heights (10, 25 and 40 cm) and two N rates (50 and 250 kg ha?1 year?1) on herbage accumulation (HA), participation of leaf categories in the leaf area index (LAI) and photosynthesis of grazed “Mulato II” brachiariagrass (Brachiaria brizantha × B. decumbens × B. ruziziensis) were investigated during two summer growing seasons in Piracicaba, São Paulo, Brazil. The HA and LAI increased linearly from 8560 to 13600 kg DM ha?1 year?1 and 2.3 to 5.5 m2 m?2, respectively, as canopy height increased. Mulato II brachiariagrass maintained at 10 cm canopy height showed greater proportion of young leaves, but was less productive than taller canopies. Taller canopies had greater proportion of mature leaves in the LAI as well as greater photosynthesis. The greater N rate contributed to increased LAI, leaf and canopy photosynthesis rates and HA but did not affect the LAI composition. The total leaf area is more important to HA than the proportion of young leaves in the LAI, as taller canopies were more productive, suggesting that maintaining Mulato II brachiariagrass at 25 or 40 cm is advantageous for this grass. 相似文献
10.
Measurements of sward surface height and of the ratio of light at 660 and 730 nm reflected from a pasture canopy were correlated with measurements of leaf area index (LAI) and herbage mass of two ryegrass dominant swards. Both pastures were continuously stocked by sheep to maintain a range of sward heights from 2 to 6 cm corresponding approximately to LAI 2 to 5.
Sward height appeared to be linearly related to both LAI and herbage mass, whereas 660/730 reflectance displayed a non-linear relationship with both parameters. The accuracy of prediction by the two methods over the range LAI 1 to 3 or herbage mass 700 to 1800 kg DM ha-1 was very similar. However, reflectance measurements could not be used above about LAI 3–4 and to this extent were less useful. Nevertheless, reflectance measurements have a potential advantage in their ability to sample large areas of pasture very quickly. 相似文献
Sward height appeared to be linearly related to both LAI and herbage mass, whereas 660/730 reflectance displayed a non-linear relationship with both parameters. The accuracy of prediction by the two methods over the range LAI 1 to 3 or herbage mass 700 to 1800 kg DM ha
11.
Changes in contribution of white clover to canopy structure in perennial ryegrass/white clover swards in response to N fertilizer 总被引：1，自引：0，他引：1
Twelve plots were laid down on an existing perennial ryegrass/white clover sward, one plot in each of six replicated blocks receiving 100 kg N ha−1 (100N) and one plot receiving no N (0N). Biomass, canopy development (stratified cuts and point quadrat records at 2–4-week intervals) and changes in stolon population density were recorded during one 8-week regrowth period (25 July–23 September) to investigate the likely causes of N effects on white clover in mixed swards.
Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.
While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer. 相似文献
Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.
While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer. 相似文献
12.
花生叶面积系数（ＬＡＩ）、群体净光合速率和群体呼吸速率分别在播后８２、９０和９０９５天达到高峰。ＬＡＩ与群体净光合速率的关系可分为播后８２天前的相关和其后的非相关阶段。ＬＡＩ与群体呼吸速率在播后５０天前同步增长；５０—８２天ＬＡＩ增加快，群体呼吸速率增加慢；８２９０天ＬＡＩ逐渐下降．群体呼吸速率迅速增加；９８天后同步下降四个阶段。群体净光合速率与群体呼吸速率的关系可分为播后５０天期间同步增长；５０—８０天关系不明显和９８天后同步下降的三个阶段。在不同生育时期，群体呼吸速率一天中均呈单峰曲线变化。群体净光合速率因品种而异，在苗期，海花１号一天中呈双峰曲线变化，并有严重午休现象，鲁花１１号则呈偏峰型。播种３０天后，两品种的群体净光合速率一天中均呈单峰曲线变化，１２∶００时达到高峰，早上６∶００７∶００时前、晚１７∶３０－１９∶００时后为负值。 相似文献
13.
DRY MATTER PRODUCTION AND LIGHT INTERCEPTION OF CROP SURFACES 总被引：1，自引：0，他引：1
The growth curves of closed grassland swards obtained during the growing seasons of six successive years were compared with each other and with theoretical growth rates calculated by de Wit's method and based on the mean light energy input data for the same years. The form of the growth curve consisted of a period with a constant rate, lasting for 6–7 weeks in May-June, then rapidly shortening to 3 weeks in August-September, after which there was a rather abrupt change to zero values. A comparison with theoretical values showed that a period of constant growth rate was possible, because the promoting influence of increasing LAI counteracted the effect of increasing respiration. Before the longest day this period was lengthened by an increasing daylength; thereafter the reverse was found. There is no ready explanation for the sudden decline to zero values. This is thought to be associated with changes in the rate of photosynthesis. 相似文献
14.
为探究小麦叶面积指数(LAI)的空间分布及与不同光质透光率间的关系,通过三年田间试验,设置不同品种、氮肥水平和灌水次数,测定分析了小麦拔节期至灌浆后期冠层不同空间层次的透射光及叶面积指数(LAI),并对不同光质透光率与LAI间进行回归分析。结果表明,小麦LAI随生育时期的推进呈单峰动态变化,最高值出现在抽穗-开花期,且随灌水和施氮水平的增加而增大;光合有效辐射(PAR)透光率随生育时期呈先降后升趋势,且随灌水和施氮水平的增加而减小。LAI与PAR透光率均存在时空异质性,叶面积的垂直分布直接影响冠层内光分布。水氮处理对植株上层LAI影响较小,而对下层影响较大;40 cm处透光率递变明显,低水高氮以及高水低氮处理对透光率递减的影响较大。不同光质透光率均随冠层高度的下降均出现不同程度消减,透光率与向下累积LAI间均呈显著指数相关,相关性由强到弱依次为红边、蓝光、光合有效辐射(PAR)、绿光、近红外和红光。经回归分析,红边和蓝光透光率与LAI的定量关系表现较好,拟合性均优于PAR,尤其是红边透光率(R2=0.749),因此可以利用红边透光率建立模型,以监测小麦冠层LAI。 相似文献
15.
A study was made to determine the effects of grazing to a height of 1 in. when the swards reached heights of 3 and 9 in. on the dry matter production, LAI, tillering and rate of leaf production of new and old tillers in the spring–summer and autumn–winter seasons of 3 pasture species growing in association with white and red clovers. In both seasons the herbage yield under 9–1 management was higher than that under 3–1 and was significantly greater in the spring-summer season. Differences in DM production between cocksfoot, tall fescue and Ariki ryegrass failed to reach significance.
Light utilization under the 2 management systems was considered to be inefficient. In the autumn-winter period there was a linear relationship between the LAI and DM production in all treatments.
The rate of leaf production per tiller was significantly higher in cocksfoot than in ryegrass and tall fescue in both seasons.
New tillers had a significantly higher rate of leaf production than old tillers in the spring-summer period, but not in autumn-winter. The numbers of grass tillers and rooted nodes of clover were significantly higher under 3–1 than under 9–1 and were influenced by season. 相似文献
Light utilization under the 2 management systems was considered to be inefficient. In the autumn-winter period there was a linear relationship between the LAI and DM production in all treatments.
The rate of leaf production per tiller was significantly higher in cocksfoot than in ryegrass and tall fescue in both seasons.
New tillers had a significantly higher rate of leaf production than old tillers in the spring-summer period, but not in autumn-winter. The numbers of grass tillers and rooted nodes of clover were significantly higher under 3–1 than under 9–1 and were influenced by season. 相似文献
16.
大豆不同群体叶面积与光强垂直分布初步分析 总被引：14，自引：2，他引：14
亚有限类型和无限类型大豆品种（品系）叶面积指数（ＬＡＩ）在结荚期均达到最大值，至鼓粒期亚有限类型回落明显，无限类型仍维持较高值。结荚或鼓粒期ＬＡＩ分布为下层比例最低，亚有限类型上层比例大、无限类型中层比例大。开花期光照分布主要集中于上层、中层较弱、下层更弱，亚有限类型冠层上部光强低于无限类型。按叶片自然生长姿态将冠层分成上、中、下三部分，ＬＡＩ累加值自上而下递增，冠层中光分布依次衰减。叶面积大小是 相似文献
17.
《Field Crops Research》1999,63(1):63-77
Non-uniform canopy N distributions have been reported to result in substantially higher canopy photosynthesis over short periods of time compared to a uniform distribution. Canopy N distribution profiles were observed in five spring wheat cultivars grown in the field under optimum management conditions at two planting dates. A curvi-linear relationship of maximum leaf photosynthesis (Am) with leaf N was established. The impact of canopy N profile on growth was assessed with the crop growth simulation model SUCROS, adjusted for this purpose. The calculated growth with the observed profiles did not exceed the growth calculated with the standard version of SUCROS. A uniform canopy N profile with observed upper leaf N had little effect, because photosynthesis deep in the canopy is almost entirely determined by radiation intensity. A uniform profile based on average canopy leaf N underestimated growth. No major differences in response to canopy N profiles became apparent among cultivars. Increase in biomass production through increased leaf N was found to depend strongly on the curvature of the Am-leaf N relationship. Responses appeared particularly sensitive to changes in initial light-use efficiency. It is concluded that determination of total canopy LAI and upper leaf N suffices for growth estimation. 相似文献
18.
Summary The growth and duration of crop leaf area determines the amount of solar radiation intercepted by the canopy and therefore
influences the extent of photosynthesis, evaporation, transpiration and final dry matter yield. The objective of this study
was to develop cultivar specific relationships to estimate the daily leaf area index (LAI) for the potato crop (Solanum tuberosum L.) that included the effects of available soil water. The model is divided into three LAI growth stages, the durations of
which are partially related to potato heat units (PHU). The LAI in the first stage is estimated from a cultivar specific leaf
area-based radiation use efficiency index with a soil water reduction factor. The second stage involves the maintenance of
a constant LAI with the duration related to both PHU and a soil water index that can accelerate senescence. The final stage
includes a decrease in the LAI from a maximum to zero in response to a cultivar specific PHU accumulation.
Model simulations compared favourably with independent LAI measurements obtained with a LI-COR plant canopy analyzer over
two seasons. 相似文献
19.
In a recent paper by Anslow it was concluded that there was no significant relationship between Leaf-area Index, light interception and growth rate in a perennial ryegrass sward. The author further concluded that higher growth rates would not be obtained by attention to this relationship. The data presented by Anslow are re-examined in this paper and the results of the analysis showed that: (a) recovery growth of the swards followed a sigmoid pattern of growth, (b) at low values of LAI growth rate was low and maximum growth rate was attained when most of the visible light was intercepted by leaves, and (c) the relationship between yield and LAI was linear, indicating that leaf-area increase after defoliation also followed a sigmoid pattern. These results are discussed in relation to Anslow's interpretation. 相似文献
20.
本试验探讨了甜菜不同密度处理条件下群体各叶层光合速率的变化,生理、生态因子的变化及其各叶层对群体光合作用的贡献。结果表明：不同叶层对整个冠层群体光合作用贡献明显不同,叶丛形成期是中层＞下层＞上层,块根增长期以后则是上层＞中层＞下层。密度过大的处理,中、后期群体光合速率的下降主要与群体中、下位叶层光合速率下降有关,其叶片气孔阻力、相对光照强度和叶面积指数均与低密度处理有明显差异。 相似文献