Phenotypic plasticity in response to light in the coffee tree

Phenotypic plasticity to light availability was examined at the leaf level in field-grown coffee trees (Coffea arabica). This species has been traditionally considered as shade-demanding, although it performs well without shade and even out-yields shaded coffee. Specifically, we focused our attention on the morpho-anatomical plasticity, the balance between light capture and excess light energy dissipation, as well as on physiological traits associated with carbon gain. A wide natural light gradient, i.e., a diurnal intercepted photon irradiance differing by a factor of 25 between the deepest shade leaves and the more exposed leaves in the canopy, was explored. Responses of most traits to light were non-linear, revealing the classic leaf sun vs. leaf shade dichotomy (e.g., compared with sun leaves, shade leaves had a lower stomatal density, a thinner palisade mesophyll, a higher specific leaf area, an improved light capture, a lower respiration rate, a lower light compensating point and a limited capacity for photoprotection). The light-saturated rates of net photosynthesis were higher in sunlit than in shade leaves, although sun leaves were not efficient enough to use the extra light supply. However, sun leaves showed well-developed photoprotection mechanisms in comparison to shade leaves, which proved sufficient for avoiding photoinhibition. Specifically, a higher non-photochemical quenching coefficient was found in parallel to increases in: (i) zeaxanthin pools, (ii) de-epoxidation state of the xanthophyll cycle, and (iii) activities of some antioxidant enzymes. Intracanopy plasticity depended on the suite of traits considered, and was high for some physiological traits associated with photoprotection and maintenance of a positive carbon balance under low light, but low for most morpho-anatomical features. Our data largely explain the successful cultivation of the coffee tree in both exposed and shade environments, although with a poor resource-use efficiency in high light.     

热带雨林冠层树种绒毛番龙眼两种发育阶段叶片的光抑制

 通过测定西双版纳热带雨林冠层树种绒毛番龙眼(Pometia tomentosa)完全伸展嫩叶和成熟叶的叶片解剖、生理特征和雨季晴天自然条件下叶绿素a荧光以及午间强光对部分保护酶活性和膜脂过氧化作用的影响,探讨了两种不同发育阶段叶片光合作用的光抑制与强光和温度的关系。结果表明：绒毛番龙眼全展嫩叶和成熟叶表现出明显的解剖和生理特征差异。与全展嫩叶相比,成熟叶的叶片较厚、叶绿素含量高、气孔导度大、羧化效率高、最大净光合速率和光饱和点高,而气孔密度和保卫细胞长度没有显著差别。在雨季晴天自然条件下,午间最高光强可达2 200 μmol·m-2·s-1以上,最高叶温比气温高7～8 ℃,而成熟叶片的最高温度比全展嫩叶高1.5～2 ℃。上午随光强的增大,两种叶片的非光化学猝灭系数（NPQ）增大,PSⅡ原初光化学效率(Fv/Fm)、实际光化学效率［(Fm′_Fs)/Fm′］逐渐减小,在15∶30左右达最小。下午随着光强的减弱,Fv/Fm逐渐恢复,在傍晚基本恢复到清晨值。初始荧光(F0)在一天中变化很小。这表明绒毛番龙眼叶片光抑制是非辐射能量耗散增加引起的保护光合机构免受光破坏的保护性反应,而非光破坏。全展嫩叶比成熟叶有较低的光化学效率和非辐射耗散能力,对强光和高温处理的敏感性也较强,但在自然条件下一天中的光抑制程度与成熟叶没有显著差别。田间午间强光导致两种叶片的保护酶活性(超氧化物歧化酶,SOD;抗坏血酸过氧化物酶,APX)升高,而H2O2含量变化较小。其中,全展嫩叶的保护酶活性高,丙二醛(MDA)含量低。这表明自然条件下,与成熟叶相比,绒毛番龙眼全展嫩叶通过较低的光能利用效率、较低的叶温和高的保护酶活性减轻了强光高温的光抑制程度。     

紫苏叶精油化学成分分析研究

用GC -MS对紫苏叶精油进行分析鉴定 ,结果表明 :紫苏叶精油中主要化学成份为甲基紫苏酮 ,其质量分数为 5 7.5 1%。     

Does the photosynthetic light‐acclimation need change in leaf anatomy?

There is a strong correlation between leaf thickness and the light‐saturated rate of photosynthesis per unit leaf area (P_max). However, when leaves are exposed to higher light intensities after maturation, P_max often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase P_max, the change in anatomical and physiological characteristics of mature leaves of Chenopodium album, which was transferred from low to high light condition, were examined. When compared with leaves subjected to low light continuously (LL leaves), the leaves transferred from low to high light (LH leaves) significantly increased P_max. The transfer also increased the area of chloroplasts facing the intercellular space (S_c) and maintained a strong correlation between P_max and S_c. The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase P_max when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in P_max to the level in HH leaves. Thus leaf thickness determines an upper limit of P_max of leaves subjected to a change from low to high light conditions. Shade leaves would only increase P_max when they have open space to accommodate chloroplasts which elongate after light conditions improve.     

Decomposition of leaves of huisache (Acacia tortuoso) and mesquite (Prosopis spp) in soil of the central highlands of Mexico

In the central highlands of Mexico, mesquite (Prosopis spp) and huisache (Acacia tortuoso), N₂ fixing trees or shrubs, dominate the vegetation and are used in an alley cropping system to prevent erosion and restore soil fertility. We investigated how much the leaves of both trees contribute to dynamics of carbon (C) and nitrogen (N) in soil by adding leaves of both species to soil sampled under the canopy of mesquite and huisache, outside their canopy and from fields cultivated with maize at three different sites and monitoring microbial biomass C, production of carbon dioxide (CO₂), and dynamics of inorganic N (ammonium and nitrate) in an aerobic incubation. The soluble fraction and N content of the mesquite leaves were larger than in the huisache leaves, but lignin and polyphenol content were lower. Evolution of CO₂ increased 2.7-times when mesquite and 2.4-times when huisache leaves were added to soil. During all stages of decomposition and in all treatments, C mineralization of leaves from mesquite was greater than from huisache leaves. Mesquite leaves induced an increase in mineral N of 25.6 mg N kg^–1 soil after 56 days and those of huisache 9.8 mg N kg^–1. Twenty-six percent of N from mesquite leaves and 11% of huisache was mineralized, if no priming effect was considered. Nitrogen release from the leaves was greater when the soil organic matter content was lower. It was found that soil under the canopy of mesquite and huisache effectively accumulated organic material, micro-organisms and valuable nutrients. In an alley cropping system huisache might be a better choice than mesquite as huisache grows faster than mesquite and sheds its leaves twice a year while mesquite only once, although the amount of N mineralized was larger from mesquite leaves than from those of huisache.     

温度对绿豆离体叶片光合作用的影响

绿豆离体叶片分别经25、30、35、40、45、50、55℃处理60 min后,发现净光合速率和光系统Ⅱ的最大量子效率(Fv/Fm)当温度分别高于35和40℃时明显下降;细胞间隙CO2浓度的变化趋势与净光合速率的基本相反.因此认为,Fv/Fm比净光合速率(Pn)更能耐受高温;气孔因素不是各种温度处理中净光合速率升高或降低的主要原因.     

Predicting leaf traits of herbaceous species from their spectral characteristics

Trait predictions from leaf spectral properties are mainly applied to tree species, while herbaceous systems received little attention in this topic. Whether similar trait–spectrum relations can be derived for herbaceous plants that differ strongly in growing strategy and environmental constraints is therefore unknown. We used partial least squares regression to relate key traits to leaf spectra (reflectance, transmittance, and absorbance) for 35 herbaceous species, sampled from a wide range of environmental conditions. Specific Leaf Area and nutrient‐related traits (N and P content) were poorly predicted from any spectrum, although N prediction improved when expressed on a per area basis (mg/m² leaf surface) instead of mass basis (mg/g dry matter). Leaf dry matter content was moderately to good correlated with spectra. We explain our results by the range of environmental constraints encountered by herbaceous species; both N and P limitations as well as a range of light and water availabilities occurred. This weakened the relation between the measured response traits and the leaf constituents that are truly responsible for leaf spectral behavior. Indeed, N predictions improve considering solely upper or under canopy species. Therefore, trait predictions in herbaceous systems should focus on traits relating to dry matter content and the true, underlying drivers of spectral properties.     

一个玉米旱敏感突变体的遗传分析与基因定位

玉米干旱胁迫相关突变体在发掘玉米耐旱关键基因研究中具有重要利用价值。在玉米自交系综31的田间扩繁过程中,发现一个玉米干旱胁迫敏感的自然突变体,该突变体在轻度干旱条件下叶片发生卷曲,严重干旱时叶尖变黄,衰老坏死。遗传分析表明突变性状受1对主效单基因控制,表现为隐性遗传,将突变基因命名为DS。利用B73与突变体ds组配F2分离群体,以干旱条件下叶片是否卷曲为指标,将DS基因初定位在第3号染色体SSR标记umc1772和umc2158之间,物理距离为5 Mb。以上研究结果为该基因的克隆及功能分析奠定了基础。     

Interfacial Effects of Superhydrophobic Plant Surfaces： A Review

Nature is a huge gallery of art involving nearly perfect structures and properties over the millions of years of development. Many plants and animals show water-repellent properties with fine micro-structures, such as lotus leaf, water skipper and wings of butterfly. Inspired by these special surfaces, the artificial superhydrophobic surfaces have attracted wide attention in both basic research and industrial applications. The wetting properties of superhydrophobic surfaces in nature are affected by the chemical compositions and the surface topographies. So it is possible to realize the biomimetic superhydrophobic surfaces by tuning their surface roughness and surface free energy correspondingly. This review briefly introduces the physical-chemical basis of superhydrophobic plant surfaces in nature to explain how the superhydrophobicity of plant surfaces can be applied to different biomimetic functional materials with relevance to technological applications. Then, three classical effects of natural surfaces are classified： lotus effect, salvinia effect, and petal effect, and the promising strategies to fabricate biomimetic su- perhydrophobic materials are highlighted. Finally, the prospects and challenges of this area in the future are proposed.