剔除土壤背景的棉花水分胁迫无人机热红外遥感诊断

剔除无人机热红外影像中的土壤背景是提高作物水分诊断精度的有效途径,但也是热红外图像处理的难点问题。本文以不同水分处理的花铃期棉花为研究对象,分别在09:00、13:00和17:00等3个时刻,连续5 d采集无人机高分辨率热红外影像,并采用二值化Ostu算法和Canny边缘检测算法对热红外图像进行掩膜处理,实现对土壤背景的剔除,然后分别计算二值化Ostu算法、Canny边缘检测算法和包含土壤背景下的3种棉花水分胁迫指数(Crop water stress index,CWSI),最后建立不同时刻下3种CWSI与棉花叶片气孔导度Gs的关系模型。研究结果表明,应用Canny边缘检测算法可有效剔除热红外影像中的土壤背景,剔除土壤背景后的温度直方图呈单峰的偏态分布;3种处理方法获得的作物水分胁迫指数CWSI中,Canny边缘检测算法的CWSI最小,二值化Ostu算法的CWSI较高,包含土壤背景的CWSI最大;采用Canny边缘检测算法剔除土壤背景后的CWSI与棉花叶片气孔导度Gs的决定系数R2达到0.84,Ostu算法的结果次之,包含土壤背景的最差。本研究可为无人机热红外遥感监测作物水分状况提供参考。     

‘富士’苹果不套袋与套袋密度对树体光合特性的影响

为进一步探讨不套袋与套袋对苹果品质影响的机理,以8年生‘富士’苹果（‘天红2号’/‘M26’/八棱海棠）为试验材料,共设5个套袋密度处理（不套袋、套袋1/3的果实、套袋1/2的果实、套袋2/3的果实、套袋所有果实）,所用果袋为小林果袋（双层纸袋,内红外棕）,研究不同套袋密度对果实套袋前（6月19日）、套袋后2天（6月21日）、套袋中（8月22日和9月27日）、摘袋后2天（10月9日）和采收后1天（11月3日）苹果叶片光合特性的影响。结果表明,套袋不仅降低了苹果树冠层内的光照强度,而且显著降低了叶片的光合速率,而随着套袋密度的增加,苹果树冠层内的净光合速率显著降低,尤其是在8月和9月。5个处理的冠层光强、气孔导度、叶绿素含量、类胡萝卜素含量和叶片比重的变化与净光合速率的变化基本一致,说明果实套袋导致叶片光合性能下降。套袋苹果光合速率的降低是由气孔导度的降低引起的,这可能与光照强度降低有关;而在9月光合速率的降低还可能与高温弱光,套袋苹果叶片出现非气孔限制有关。     

不同天气条件下田间大豆光合作用日变化的研究

田间大豆叶片光合速率的日变化进程和光合午休的有无、轻重,在不同天气条件下表现不同,并无固定模式。高湿的晴天,没有光合午休,气孔因素和叶肉因素对光合的限制都很小;高湿适温的多云天气,光合速率主要受光强制约,光强高时,光合速率受气孔因素限制,光强低时,受叶肉因素限制;低湿高温的晴天,常有午休出现,光合速率的中午降低,主要是气孔因素限制的结果,有时也出现叶肉因素限制。诱发气孔限制的生理生态因子,首先是空气相对湿度（RH）和叶片、大气间水汽压差（VPD）,其次是叶温（LT）和叶片相对含水量（RWC）。     

亚精胺对提高玉米幼苗抗旱机理的研究

以掖单４号玉米幼苗为材料，用０．５Ｍｐａ的ＰＥＧ—６００进行人工模拟水分胁迫，同时叶面喷施１ｍＭ亚精胺（ｓｐｄ），研究了在水分胁迫条件下亚精胺对玉米幼苗中保护酶系、光合强度以及气孔阻力的影响。结果表明，亚精胺处理大大提高玉米幼苗中ＳＯＤ、ＰＯＤ的活性以及光合强度，适当减小气孔阻力，故亚精胺可以提高玉米幼苗的抗旱性。     

香港润楠属植物叶表皮形态及分类学意义

利用光学显微镜和扫描电镜观察了11种香港润楠属（Machilus Nees)植物叶表皮。在香港润楠属植物中，大多数种类的叶表皮均具有单细胞表皮毛，其气孔复合体均为平列型，保卫细胞两侧或一侧有1个副卫细胞；叶上表皮细胞的形态有较大的差异，主要有3种类型：垂周面平直、浅波状和深波状。叶表皮角质突起饰物的形态也有差异，根据表皮角质突起物的形态可划分出有2种类型。这些表皮特征有助于识别一些在外部形态较相近种类。     

栓皮栎对CO2增长的生理生态响应

通过对 5 0年生栓皮栎天然次生林叶片的活体测定 ,研究了CO2 浓度增长对栓皮栎林光合生理生态特性的影响 .结果如下 :CO2 浓度为 80 0 μmolCO2 ·mol- 1 时栓皮栎叶片的净光合速率比在正常大气CO2 条件下提高 42 .5 3 % ,同时光补偿点降低 ,光饱和点提高 ,光量子效率提高 ;CO2 浓度为 80 0 μmolCO2 ·mol- 1 时 ,栓皮栎净光合速率的日变化为单峰曲线 ,而CO2 浓度为40 0 μmolCO2 mol- 1 时 ,净光合作用的日变化为双峰曲线 ;CO2 浓度倍增 ,栓皮栎叶片的气孔导度 ,蒸腾速率和暗呼吸速率降低 ,水分利用效率显著提高 .栓皮栎叶片对CO2 增长的反应 ,对其生长是有利的 ,对全球CO2 浓度增长起到反馈调节作用 .     

在CO2浓度加富条件下马尾松针叶的生理生态响应

研究了在3种不同CO2浓度(360 μmol·mol-1、800 μmol·mol-1、1 200 μmol·mol-1)下马尾松针叶的净光合速率、蒸腾速率、气孔导度、水分利用效率的变化.结果表明:在当前CO2(360 μmol·mol-1)浓度下,当光强为1 000 μmol·m-2·s-1时,净光合速率、蒸腾速率、气孔导度分别为3.46 μmol·m-2·s-1、0.273 mmol·m-2·s-1、0.0254 mmol·m-2·s-1,针叶的光饱和点和光补偿点分别为:(1 800±2) μmol·m-2·s-1和(24±2) μmol·m-2·s-1.当CO2加富到1 200 μmol·mol-1时,针叶的光饱和点降低了200 μmol·m-2·s-1,而光补偿点增加了4 μmol·m-2·s-1.在光照强度为50～2 000 μmol·m-2·s-1的条件下,不同CO2浓度下的水分利用率平均值分别为:1 200 μmol·mol-1浓度下的19.163 μmol·mmol-1,800 μmol·mol-1浓度下的12.912 μmol·mmol-1,360 μmol·mol-1浓度下的11.192 μmol·mmol-1.短期的CO2加富降低了植物叶片的蒸腾速率、气孔导度,而植物的水分利用效率则上升.     

紫茎泽兰叶片气体交换的气孔调节特性:对其入侵能力的意义

紫茎泽兰是一个典型的外来入侵植物.利用便携式光合测定系统,对分布于四川省凉山州德昌市郊(27°28′36"N,102°12′28″E)的紫茎泽兰的气体交换特性进行测定,并与本地8个伴生种和其他12个分布于我国不同地区和日本的入侵种和本地种进行比较.目的是探讨气孔调节在日变化过程和长期干旱与湿润生境上的差异及其对紫茎泽兰入侵能力的影响.研究发现紫茎泽兰光合午休现象明显,气孔调节和非气孔调节共同控制了紫茎泽兰的光合日进程模式,而以气孔调节最为重要.非气孔调节主要是通过羧化效率的降低,从而影响表观量子效率或其他光合过程来实现的,而气孔调节主要是通过降低胞间CO2浓度,提高气孔限制值来实现的,这与其他种的差异不大.经过长期的野外不同湿度环境适应后,气孔调节出现了一定的弹性变化.在气孔导度相差不大的情况下,土壤有机质、土壤pH值和土壤有效氮含量差异不明显,湿生生境的光合速率和蒸腾速率显著高于干生生境,并导致了叶片含氮量显著提高.气孔在调节紫茎泽兰水分利用效率方面有别于所测定的其他20种植物,在湿生生境下随气孔导度下降,水分利用效率下降,而在干生生境下则显著升高.因此,紫茎泽兰同时兼有"省水"植物和"费水"植物的双重特点,这一灵活水分利用特点保证了它在不利环境中的生存和有利环境中的扩展,对于其在侵入区的生长发育有一定的意义.     

Water relations of Eucalyptus nitens × Eucalyptus grandis: is there interclonal variation in response to experimentally imposed water stress?

This study tested the hypothesis that water stress increases the hydraulic efficiency of Eucalyptus nitens × E. grandis saplings as a result of osmotic and elastic adjustments. Eucalyptus nitens × E. grandis clones (NH00, NH58, NH69 and NH70) were potted in coarse river sand supplemented with a slow-release fertiliser, drip-irrigated four times daily and exposed to full sunlight for eight months. Thereafter, irrigation was withheld twice for seven consecutive days from half of the saplings of each clone, with a seven-day recovery period (regular irrigation) in-between. Relative soil moisture content did not correlate with stomatal conductance (g_s) at pre-dawn and at midday. Leaves of plants subjected to the water-stress treatment wilted in 7 d, and the reduction in g_s was significant at midday with no significant differences between clones. Stomatal conductance and all traits derived from pressure-volume graphs (e.g. osmotic potential at full turgor) were constant in the control treatment. There were no clear patterns in osmotic and elastic adjustments in both treatments. Root hydraulic conductance was constant between treatments and clones. However, water stress reduced shoot hydraulic conductance and stem hydraulic conductivity with significant interclonal effects. Plant biomass, leaf area and leaf weight ratio were significantly lower in the water-stressed plants, but there were no differences between the clones. In conclusion, the water-stress treatment did not introduce significant differences in stomatal conductance and tissue-water relations of Eucalyptus nitens × E. grandis clones. Interclonal variation in water-stress response was found in shoot hydraulic traits, and clone NH58 may be more suitable for planting across sites prone to moderate water stress.     

Quality assessment of three warm-season turfgrasses growing in different substrate depths on shallow green roof systems

In an effort to increase the accessibility and functionality of shallow green roof systems, the ability of warm-season grasses to provide acceptable growth needs to be further investigated. In the current study, which was conducted during 2011 and 2012, three warm-season grasses (hybrid bermudagrass, Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy ‘MiniVerde’; seashore paspalum, Paspalum vaginatum Swartz ‘Platinum TE’ and zoysiagrass, Zoysia japonica Steud. ‘Zenith’) were established in outdoor lysimeters. The lysimeters were equipped with all necessary green roof layers placed below a coarse-textured substrate that comprised pumice, thermally treated attapulgite clay, peat, compost and zeolite. Half of the lysimeters had a substrate depth of 15 cm, while the other half had a substrate depth of 7.5 cm. Irrigation was applied at crop evapotranspiration (ET_c). Measurements included determination of substrate moisture content, green turf cover (GTC) and leaf stomatal resistance. Significant differences were observed in the values of GTC among the three turfgrass species and the two substrate depths. Zoysiagrass exhibited the best adaptation at the lower depths of shallow green roof systems. At 15 cm substrate depth, zoysiagrass managed to sustain green coverage for the two study periods. In addition, it was the only turfgrass species that managed to perform well at the substrate depth of 7.5 cm. Seashore paspalum exhibited limited green cover at both substrate depths, while hybrid bermudagrass could provide acceptable green coverage only at 15 cm substrate depth.