施氮量对测墒补灌小麦冠层不同层次光截获和干物质分布的影响

以大穗型小麦品种‘山农23’为材料,在大田拔节期和开花期土壤相对含水量分别补灌至70%和65%的条件下,设置4个施氮水平0 (N₀)、180 (N₁)、240 (N₂)和300 kg·hm^-2 (N₃),研究施氮量对小麦冠层不同层次光合有效辐射(PAR)截获和干物质分布的影响.结果表明: N₂处理开花期群体总茎数、开花后10、20和30 d的叶面积指数、开花后20 d冠层上层和中层及冠层总的PAR截获率和截获量显著高于N₀和N₁,施氮量增加至N₃,上述指标无显著增加.N₂处理成熟期各层次营养器官干物质积累量显著高于N₀和N₁,籽粒干物质积累量和植株总干物质积累量比N₀分别高36.7%和35.4%,比N₁分别高9.5%和10.2%,与N₃处理无显著差异.各层次营养器官干物质积累量、籽粒干物质积累量和植株总干物质积累量与上层和中层PAR截获率呈显著正相关,与下层PAR截获率无显著相关;各层次营养器官干物质积累量与籽粒干物质积累量均呈显著正相关.施氮量为240 kg·hm^-2的N₂处理是本试验条件下的最优处理.     

河套地区小麦/玉米套作群体光能瞬时传输的数学模拟

作物间套作群体冠层中叶片水平向和垂向分布的不均匀性给其光能截获的连续测定带来了很大困难.为了量化小麦/玉米套作群体不同生长阶段的光能吸收,本文建立了模拟该套作群体光合有效辐射(PAR)瞬时传输的几何模型,并用大田实测值对模型进行验证.结果表明:几何模型可有效地模拟小麦/玉米套作群体冠层底部的PAR强度.小麦/玉米6∶2套作(I62)群体模型估算结果与实测值的线性回归方程的决定系数为0.947,小麦/玉米12∶4套作(I124)群体模拟结果与实测值的线性回归方程的决定系数为0.950.2012和2013年I62套作群体截获的PAR分别为1061.4和924.3 MJ·m-2,在所有处理中最高.2012年I62和I124套作群体相对于单作的PAR截获比率分别为1.29和1.19,2013年I62和I124套作群体相对于单作的PAR截获比率分别为1.21和1.16.     

水稻冠层光截获、光能利用与产量的关系

以两优培九和武香粳14号水稻品种为材料,在不同栽插密度和施氮水平下进行2年田间试验,研究水稻冠层光合有效辐射(PAR)截获率、光能利用率与水稻产量的关系.结果表明:分蘖期至成熟期,各处理水稻冠层平均PAR反射率为3.45％,其中,分蘖期至抽穗期的冠层反射PAR占冠层总PAR损失的10.90％,显著小于抽穗期至成熟期的22.06％.分蘖期至成熟期的冠层PAR转化率随栽插密度的增加而减少,随施氮量的增加而增大;分蘖期至抽穗期的冠层PAR转化率高于抽穗期至成熟期.在分蘖期至成熟期,冠层PAR利用率随栽插密度和施氮量的增加而增大,各处理中两优培九的平均PAR利用率(1.83 g· MJ-1)显著高于武香粳14(1.42 g·MJ-1);武香粳14因生育期较长,分蘖期至成熟期的入射PAR及中、高栽插密度处理的PAR截获量均高于两优培九.水稻不同生长阶段冠层PAR截获率和利用率与产量呈显著正相关,PAR转化率与产量也呈正相关,但相关性不显著.因此,在保持较高PAR截获率的基础上提高冠层PAR转化率,进而提高冠层PAR利用率,有利于水稻高产.     

秸秆覆盖和灌溉对冬小麦农田光能利用率的影响

研究了秸秆覆盖和灌溉对冬小麦农田光能利用率的影响.结果表明,秸秆覆盖降低了冬小麦的基本苗、分蘖数及生育前期的叶面积指数,但到生育后期,覆盖处理的叶面积指数反而升高.覆盖和灌溉降低了光合有效辐射（PAR）的底层透射率和冠层反射率,使PAR总截获率升高.覆盖和灌溉主要增加了40～60 cm高度的PAR截获率.覆盖处理籽粒光能利用率降低,茎叶光能利用率和总光能利用率升高.     

水稻冠层光截获、光能利用与产量的关系

以两优培九和武香粳14号水稻品种为材料,在不同栽插密度和施氮水平下进行2年田间试验,研究水稻冠层光合有效辐射(PAR)截获率、光能利用率与水稻产量的关系.结果表明： 分蘖期至成熟期,各处理水稻冠层平均PAR反射率为3.45%,其中,分蘖期至抽穗期的冠层反射PAR占冠层总PAR损失的10.90%,显著小于抽穗期至成熟期的22.06%.分蘖期至成熟期的冠层PAR转化率随栽插密度的增加而减少,随施氮量的增加而增大;分蘖期至抽穗期的冠层PAR转化率高于抽穗期至成熟期.在分蘖期至成熟期,冠层PAR利用率随栽插密度和施氮量的增加而增大,各处理中两优培九的平均PAR利用率(1.83 g·MJ^-1)显著高于武香粳14(1.42 g·MJ^-1);武香粳14因生育期较长,分蘖期至成熟期的入射PAR及中、高栽插密度处理的PAR截获量均高于两优培九.水稻不同生长阶段冠层PAR截获率和利用率与产量呈显著正相关,PAR转化率与产量也呈正相关,但相关性不显著.因此,在保持较高PAR截获率的基础上提高冠层PAR转化率,进而提高冠层PAR利用率,有利于水稻高产.     

不同穗型小麦光能利用和旗叶13C同化物分配特性及对补灌水平的响应

为明确不同穗型小麦冠层光能利用和¹³C同化物分配特性的差异及对补灌水平的响应,以中穗型品种‘青农2号’和‘济麦22’、大穗型品种‘山农23’和‘山农30’为材料,设置3个水分处理:小麦全生育期不灌水(W₀)、节水灌溉(W₁,拔节期和开花期0～40 cm土层土壤相对含水量分别补灌至65%和70%)和充分灌溉(W₂,拔节期和开花期0～40 cm土层土壤相对含水量分别补灌至85%和90%),研究了不同处理对两种穗型小麦冠层光能利用和旗叶¹³C同化物分配特性的影响.结果表明:W₁处理两种穗型小麦品种开花后2、11、20和31 d的叶面积指数、冠层PAR截获率和利用率均显著高于W₀处理,再增加灌水至W₂处理,上述各指标无显著变化.¹³C示踪表明,济麦22和山农23的W₁旗叶¹³C同化物在籽粒中的分配量比W₀分别高159.34和171.1 g·hm^-2,分配比例分别高6.5%和6.5%,与W₂无显著差异;两种穗型品种W₁的籽粒产量亦显著高于W₀,与W₂无显著差异.不同穗型品种比较,节水灌溉条件下中穗型品种在开花后2和11 d、大穗型品种在开花后20和31 d具有较高的冠层光合有效辐射(PAR)截获和利用能力;中穗型品种济麦22旗叶¹³C同化物在籽粒的分配量和分配比例比大穗型品种山农23分别低6.8%和2.7%.     

行距和播种量对冬小麦冠层光合有效辐射垂直分布、生物量和籽粒产量的影响

为明确行距和播种量对冬小麦冠层光合有效辐射(PAR)垂直分布、生物量和籽粒产量的影响,在不增加水肥等投入的基础上,设置等行距(R₁,20 cm+20 cm)、宽窄行(R₂,12 cm+12 cm+12 cm+24 cm)两种行距方式和低(D₁,120 kg·hm^-2)、中(D₂,157.5 kg·hm^-2)、高(D₃,195 kg·hm^-2)3个播种量水平,分析不同处理组合下冬小麦主要生育时期冠层PAR的截获率及利用率、群体光合能力、生物量和产量差异。结果表明: 冬小麦冠层总PAR截获率、上层PAR截获率均表现为R₁行距显著大于R₂,而中层和下层PAR截获率则表现为R₂大于R₁,且在中层差异显著;从小麦开花至成熟期,相同播种量下R₂行距光合势(LAD)、群体光合速率(CAP)、PAR转化率和利用率都显著高于R₁,并以R₂D₂处理最大;冬小麦的群体生物量(BA)和不同层次叶片生物量(BL)均表现为随播种量增加而增加,但单株生物量(BP)则相反。在同一播种量下,BA、BL和BP均在开花期之后表现为R₂行距高于R₁,其中,BA、BP在成熟期行距间差异显著,中层和下层BL在D₂、D₃播种量下行距间差异显著;不同处理组合间冬小麦的穗数、穗粒数、千粒重、籽粒产量分别以R₂D₃、R₂D₁、R₂D₁、R₂D₂最大,其中,R₂行距下千粒重、穗粒数和籽粒产量显著大于R₁。综上,改变行距可以改善小麦冠层中下层PAR的截获量,增强冬小麦单株和群体光合能力、光合有效辐射的利用及转化效率,提高生物量和籽粒产量。在冬小麦高产栽培中,应重视通过优化田间结构,塑造麦田理想的群体光合结构,以充分利用单位土地面积上光照资源,挖掘作物自身的光合生产潜力,达到高产高效的目的。在本试验条件下,以R₂D₂配置群体光合能力、光合有效辐射利用率和产量最佳。     

群体分布和灌溉对冬小麦农田光能利用的影响

于2006-2008年进行冬小麦田间试验,设置行距×株距分别为：7 cm×7 cm（A）、14 cm×3.5 cm（B）、24.5cm×2 cm（C）、49 cm×1 cm（D）4种群体分布方式,每种分布方式设4种灌溉处理：整个生育期内不灌溉,灌拔节水,灌拔节和抽穗水,灌拔节、抽穗和灌浆水（每次灌水量相同,均为0.60 m³）,研究在同一群体密度(2.04×10⁶ 株·hm^-2)下不同群体分布和灌溉对冬小麦光能利用状况的影响及其在生产中的利用价值.结果表明：A、B处理的群体分蘖数和叶面积指数（LAI）显著高于C、D处理;随着行距的加大,光合有效辐射（PAR）透射率逐渐增多,而PAR截获率呈下降趋势;增加灌溉可提高冬小麦群体单茎数和LAI,降低PAR透射率,从而明显提高了PAR总截获率.冠层内PAR截获率表现为上强下弱的趋势,相对均匀的群体分布和所有灌溉处理均显著增加了冠层40 cm以上的PAR截获率.冬小麦光能利用率（RUE）随行距增大而逐渐降低,其中,A、B、C、D处理总RUE两年的均值分别为1.24%、1.27%、1.21%和1.06%,B处理较C、D处理分别提高了5.21%和19.56%,差异显著.群体分布相对均匀的A、B处理可显著改善冬小麦群体结构和PAR截获状况,有利于充分利用光能;所有灌溉处理也可影响群体结构,进而明显提高作物的RUE.     

抽雄期前后大风倒伏对夏玉米生长及产量的影响

利用2013年8月1日河南省南阳地区夏玉米大风倒伏灾害的调查数据,分析抽雄期前后不同类型倒伏对夏玉米生长及产量形成的影响,研究不同品种的抗倒性差异和适播期.调查对象为5个播期的浚单20和3个播期的郑单958,倒伏类型划分为根斜、根倒、茎折和折断4种.研究表明： 各品种及播期均于抽雄前～抽雄后15 d倒伏率较高.浚单20各播期的总倒伏率为86.0%～98.5%,郑单958各播期的总倒伏率为60.0%～76.4%,且播种越早的播期总倒伏率越低.浚单20倒伏发生时,播期Ⅱ～Ⅴ的夏玉米生育时期接近抽雄,以根倒类型为主,倒伏率为53.0%～84.3%,已过抽雄期的播期Ⅰ夏玉米以茎折倒伏为主,倒伏率为37.5%.倒伏发生后干物质积累显著降低,各倒伏类型对干物质积累的影响总体表现为茎折>根倒>根斜,播种越晚的总干物质积累越少.倒伏对干物质分配比例影响表现为叶片和茎杆干物质比例增大,果穗干物质比例减少.根倒和茎折两种倒伏类型使穗长显著变短,穗粗显著变细,穗粒数显著减少,抽雄后发生倒伏也会使百粒重显著降低;而根斜倒伏类型对各性状的影响均不显著.倒伏后产量损失严重,不同倒伏类型中茎折类型减产最多,浚单20和郑单958平均减产率分别为74.2%和68.7%,尤其是茎折发生在抽雄之前难以形成产量;其次是根倒,平均减产率分别为46.3%和46.5%;根斜产量损失最小,平均分别为8.4%和13.2%.大风倒伏灾害后,浚单20产量平均为4959.9 kg·hm^-2,产量随播期的推迟而减少;郑单958平均为6026.1 kg·hm^-2,随播期变化不明显.总体上,郑单958品种抗倒性好于浚单20.     

定向种植对夏玉米群体内光环境及叶片光合性能的影响

为改善玉米群体内光环境,进一步提高玉米单株光合能力以获得高产,本研究以郑单958为试验材料,通过设置种子定向入土方式,研究了定向有序种植条件下群体内光分布特征,以及单株玉米穗位叶花后光合性能,并借助快速叶绿素荧光动力学曲线分析了与叶片光合性能有密切联系的光系统Ⅱ(PSⅡ)的性能特征.结果表明:叶片不同朝向显著改变夏玉米群体内穗位叶处光合有效辐射截获量,朝南处理(S)平均比朝北处理(N)高271.8%.不同朝向的叶片对高光与弱光的利用能力差异显著,朝南处理饱和光强下净光合速率(Pn)显著升高,表明其高光强利用能力显著提升;而朝北处理(N)表观量子效率(α)则随生育期推进显著增加,有利于叶片适应长期弱光环境.生育前期朝南处理PSⅡ电子供体侧和受体侧性能显著提高,进而改善了PSⅡ反应中心性能(PIABS)和荧光光化学淬灭系数(ψo),电子在电子传递链中转移效率(φEo)的提高增强了电子由PSⅡ向光系统Ⅰ(PSⅠ)的传递性能.生育前期叶片性能呈现出朝南>朝东>朝西>朝北的趋势.但成熟末期朝南处理对强光的利用效率显著降低,朝北处理在生育后期表现出较强的弱光利用能力,表观量子效率显著升高,花后40dPn与PSⅡ性能均表现为朝北>朝西>朝东>朝南的趋势.总体上,朝南与朝东处理群体内光环境改善显著,群体穗位层截获光合有效辐射较多,光合能力和干物质生产能力增强,有利于夏玉米产量提高.     

Characterisation, prediction and relationships between different wavebands of solar radiation transmitted in the understorey of even-aged oak (Quercus petraea, Q. robur) stands

Solar radiation transmission in forest stands affects many processes, including biomass and diversity of understorey vegetation and tree seedling regeneration (growth and morphogenesis). However, understorey light availability is not easy for forest managers or scientists to measure. Therefore, different models have been developed to predict light transmission in forest stands according to tree or stand structure. However, these models are generally too complex to be used operationally. This paper reports the assessment of light transmission according to stand parameters commonly measured by foresters in inventories. We measured transmittance in 29 even-aged oak stands in France for various wavebands, total solar radiation (TSR, 300–3000 nm), PAR (400–700 nm), red (R, 660 nm) and far-red (FR, 730 nm), and demonstrated that transmittance in a given waveband can be predicted from the measurement of another waveband. The R:FR ratio can be predicted according to TSR or PAR transmittance, but the opposite is also true; PAR or TSR transmittance can be predicted from the R:FR ratio. Transmittance variability was characterised, and the variation coefficient ranged from 5 to 45% with a trend to increase with tree density. By analogy to Beer–Lambert's law, we established that mean daily transmittance for the different wavebands can be assessed according to stand basal area and stand age with good accuracy (R ²>0.74). Results are discussed in comparison with other models based on the principle of parsimony.     

Daylight spectra (400–740 nm) beneath sunny,blue skies in Tasmania,and the effect of a forest canopy

Abstract The photosynthetically active radiation (PAR) incident on a horizontal surface at an open mountain site is positively correlated with solar altitude for sunny, blue sky conditions. The proportion of red light in PAR decreases with increasing solar altitude, while that of blue increases. These results are consistent with the wavelength dependency of Rayleigh and Mie scattering. The ratio of near infrared radiation to PAR decreases with increasing solar altitude towards solar noon and with decreasing solar altitude towards sunset. Thus surface reflection seems to be an important part of the light climate. The relative transmission of daylight through a forest canopy to a horizontal surface is not correlated with solar altitude for sunny, blue sky conditions at a mountain site. The amount of diffuse daylight is negatively correlated with per cent canopy interception, and the amount of direct sunlight is negatively correlated with per cent solar track interception. Daylength is negatively correlated with both canopy and solar track interceptions. The proportion of red light in PAR increases with increasing solar altitude, while that of blue decreases. These results are opposite those for the open site and are due to the spatial patterns of canopy obstruction of the sky vault, and of the spectral quality of daylight across the sky. The ratio of near infrared radiation to PAR in shadelight increases with increasing canopy interception due to the selective scattering properties of the canopy. The ratio for shadelight is positively correlated with the ratio for sunflecks.     

UV-B and PAR in single and mixed canopies grown under different UV-B exclusions in the field

The purpose of this study was to investigate whether differences in canopy architecture due to the investigated species (planophile versus erectophile, single versus mixed canopies) or to UV-B effects on plant morphology, lead to differences in UV-B and UV-B/PAR doses within canopies.The development of a very small (10 mm diameter) UV-B and PAR sensor on a long 5 mm wide stick allowed us to measure the penetration of UV-B and PAR in single and mixed canopies of the grass Dactylis glomerata and white clover, Trifolium repens. The plants were grown in greenhouses covered with different thicknesses (3 and 5 mm) of UV-transmittant plexi (12 and 18% UV-B exclusion).For clover, a planophile vegetation, radiation penetration was very low for both UV-B and PAR. UV-B penetration was much less than for PAR, resulting in low UV-B/PAR ratio's within the canopy. This is explained by the low UV-B transmittance of the leaves (<0.1 %) in combination with the planophile leaves.In the grass species, both UV-B and PAR penetrated much deeper into the canopy due to the erectophile structure. The difference between UV-B and PAR penetration was generally quite small except in very tall canopies.The mixed species canopies showed results comparable to the clover canopies. Due to the strongly increased grass growth in these plots, light penetration was generally much lower than in the single species cultures. The increased growth of grass in these mixed plots could be linked to the lower UV-B/PAR dose they received.In plots grown under the higher UV-B level there was a relative decrease in UV-B/PAR ratio within the canopy for both species, compared to canopies from the lower UV-B greenhouses. This could not be explained by changes in leaf angle or biomass, but might be linked to the increase in leaf transmittance of PAR.     

Growth of Lettuce, Onion, and Red Beet. 1. Growth Analysis, Light Interception, and Radiation Use Efficiency

A field experiment was carried out to analyse the growth oflettuce, onion and red beet in terms of: (a) canopy architecture,radiation interception and absorption; (b) efficiency of conversionof absorbed radiation into biomass; and (c) dry matter partitioning.Growth analysis, total solar radiation interception, PAR interceptionand absorption by the crop canopy, ground cover, maintenancerespiration of onion bulbs and red beet storage roots were measured.Models for different leaf angle distribution and ground coverwere used to simulate light transmission by the crop canopy. The three crops are shown to have contrasting growth patternsfrom both a morphological and a physiological point of view.Lettuce showed very high light interception and growth afterthe early growth stages but, throughout the growth cycle, thisleafy crop showed the lowest radiation use efficiency due tothe respirational cost of the high leaf area. Onion showed alower early relative growth rate than lettuce and red beet.This was due partly to the low light interception per unit leafarea in the later stages of growth and partly to the low initialradiation use efficiency compared with the other two crops.On the other hand, thanks to more uniform distribution of theradiation inside the canopy, to the earlier termination of leafdevelopment and to the very low level of bulb respiration, onionshowed high radiation use efficiency and was able to producea large amount of dry matter. Red beet leaf posture and canopystructure resulted in high light interception and absorption.Its radiation use efficiency was lower than that of onion, partlyperhaps because of the more adverse distribution of the interceptedradiation fluxes within the canopy and partly because of thehigh respiration cost of a continuous dry-matter allocationto the leaves. However, this crop can accumulate a very largeamount of dry matter as leaf blade development and storage rootgrowth can both continue almost indefinitely, providing continuouslyavailable sinks. Ground cover gave a good estimate of the PAR interception onlyat low values of light interception but, in general, it underestimatedPAR interception in all three crops. Ratios between attenuationcoefficients established by considering PAR or total solar radiationand LAI or ground cover were calculated. Lettuce,Lactuca sativa L. var.crispa ; onion,Allium cepa L.; red beet; Beta vulgaris L. var.conditiva ; growth analysis; light interception and absorption; canopy architecture; ground cover; radiation use efficiency; maintenance respiration rate; dry matter distribution     

玉米雄穗颜色QTL分析

雄穗是玉米的重要生殖器官,不同品种间玉米的雄穗外观差异明显。对玉米雄穗的颜色进行遗传分析和QTL定位,筛选与雄穗颜色紧密连锁的分子标记,可以作为玉米的品种保护和品种鉴别的有用工具。同时,紫色雄穗中花色苷类色素含量较高,与玉米雄穗的抗虫性密切相关。本研究利用一个黑玉米自交系SDM为共同父本,分别与白玉米自交系木6和黄玉米自交系Mo17杂交,构建2个相关F2∶3群体,分别命名为MuS(木6×SDM)和MoS(Mo17×SDM),在云南和重庆两个不同的环境中种植,对玉米花药颜色(COAn)和花药护颖颜色(COCa)2个性状进行QTL定位。结果表明:玉米花药和花药护颖的颜色均为数量性状,受主效基因和微效基因共同控制。2个群体在2个环境中共检测到7个与花药颜色相关的QTL,位于第2、3、6和10染色体上,其中位于第10染色体标记区间umc1196a-IDP8526内的QTL在重庆和云南同时表达,对表型的贡献率分别为23.17%和19.98%;2个群体在2个环境中共检测到9个与花药护颖颜色相关的QTL,位于第3、6、9和10染色体上,其中3个QTL为环境钝感QTL(在2个环境中均表达,且至少在1个环境中贡献率大于10%),分别位于第6染色体标记区间umc1979-umc1796、mmc0523-umc2006内和第10染色体标记区间umc1196a-umc2043内,对表型的贡献率为10.69%～59.30%。2个群体检测到的主效QTL的位置和效应高度一致,且控制花药颜色和花药护颖颜色2个性状的主效QTL有连锁分布的现象,主要表现在bins 6.04处的标记mmc0523和bins 10.04处的标记IDP8526附近。位于第6和第10染色体上的在不同环境和遗传背景下稳定的QTL可以作为进一步精细定位的靶位点,也可以为玉米雄穗颜色的分子标记辅助选择提供有价值的参考。     

Effect of the change of leaf angle arrangement on productivity of maize (Zea mays L.) stands

Leaf angles, frequency distribution of leaf area inclinations, leaf area index, amount of intercepted radiation, biological, vegetative and grain yields and grain yield proportion of biological yield were determined in maize stands of two population densities, 55 555 plants ha^?1 (S ₁), and 80 000 plants ha^?1 (S ₂). Also the effect of the artificial change of leaf angle upon these indices was studied. We classified normal maize stand (N) as the interstage between a planophile and a plagiophile type of canopy, that with artificially changed leaf angle (V) as an erectophile type of canopy. The relative interception of the incoming radiation in the variantsV S ₁ andV S ₂ was lower than in the variantsN S ₁ andN S ₂. The variantsV in comparison with variants N increased grain yield and biological yield.     

Stem tilting in the inter‐tropical cactus Echinocactus platyacanthus: an adaptive solution to the trade‐off between radiation acquisition and temperature control

While plants require radiation for photosynthesis, radiation in warm deserts can have detrimental effects from high temperatures. This dilemma may be solved through plant morphological attributes. In cold deserts, stem tilting keeps reproductive organs warm by increasing radiation interception at the cost of decreased annual light interception. Conversely, little is known about stem tilting in warm deserts. We hypothesised that stem tilting in Echinocactus platyacanthus prevents high temperatures near the apex, where reproduction occurs. The study was conducted in the warm, inter‐tropical portion of the Chihuahuan Desert, Mexico. We found that cacti preferentially tilted towards the south, which reduced temperatures of reproductive organs during the hot season, but increased total annual near‐apex PAR interception. Tilting also maximised reproduction, a likely consequence of temperature control but perhaps also of the difficulty in translocating photosynthates in cacti; therefore, annual energy acquisition near floral meristems may be largely allocated to reproduction. Unlike plants of higher latitudes, in inter‐tropical deserts sunlight at noon comes either from the north or the south, depending on the season, and thus stem tilting may more strongly affect total annual radiation received in different portions of the stem. Inter‐tropical cacti can synchronise reproduction with irradiance peaks if flowering occurs in a specific (north or south) portion of the stem; also, they effectively solve the conflict between maximising annual PAR interception and minimising temperature at the hottest time of day. Notably, the two inter‐tropical cacti in which stem tilting has been studied successfully solve this conflict.