ALA对遮荫条件下西瓜幼苗强光抑制的保护效应

以遮荫生长的盆栽西瓜幼苗为材料,研究了100mg/L5-氨基乙酰丙酸(5-aminolevulinic acid,ALA)处理对暗适应叶片转入强光下叶绿素荧光特性的影响.结果显示,遮荫能显著提高暗适应叶片的Fo,降低Fv/Fm和Fv/Fo;正常光照下生长的植株叶片暗适应后转入1500μmol·m-2·s-1作用光强下5min的ΦPSⅡ、qP和Pc分别为0.176、0.399和0.180,约为600μmol·m-2·s-1作用光强下的62%、72%和64%;而遮荫下生长的幼苗叶片暗适应后转入1500μmol·m-2·s-1作用光强下的ΦPSⅡ、qP和Pc分别为0.089、0.301和0.089,仅为600μmol·m-2·s-1作用光强的40%、66%和40%;遮荫还显著降低西瓜叶片暗适应后转入强光1500μmol·m-2·s-1的PCR和qL,同时提高L(PFD).ALA处理能提高遮荫西瓜幼苗叶片PCR、Pc、qL和Hd等荧光参数,降低Ex、ΦNO和L(PFD);SOD活性抑制剂DDC处理降低PCR、Pc、qL和Hd等荧光参数,而ALA处理可以逆转DDC的抑制效应;ALA处理能提高西瓜幼苗叶片SOD、POD和APX活性.研究发现,遮荫导致西瓜幼苗光抑制程度加重,ALA通过增强PSⅠ附近SOD等抗氧化酶活性,促进水-水循环,增加热耗散,减轻光抑制,提高西瓜幼苗叶片的光化学效率,从而对强光下的光合作用起到保护作用.     

两种生物型芦苇胚性悬浮培养物对渗透胁迫的生理响应 Ⅱ．抗氧化酶类活性的变化

渗透胁迫处理下,沙丘芦苇和沼泽芦苇培养细胞的H2O2含量变化不大,MDA含量随时间延长而降低。抗氧化酶中,沙丘芦苇的SOD、CAT、POD和APx的活力均显著高于沼津芦苇,显示出比沼泽芦苇更强的ROS清除能力。胁迫初期（0．5h-1d)沙丘芦苇细胞中主要表现出SOD、CAT活力的提高,胁迫2d后4种酶活力均明显被诱导。两种生态型芦苇的PEG适应性培养物APx及SOD酶活力显著提高,POD活性仅沼泽芦苇中升高。提示SOD、CAT主要参与沙丘芦苇在渗透胁迫下的短期响应,而APx与长期响应有关。     

Testing for local adaptation in Avena barbata: a classic example of ecotypic divergence

Forty years ago, Robert Allard and colleagues documented that the slender wild oat, Avena barbata , occurred in California as two multi-locus allozyme genotypes, associated with mesic and xeric habitats. This is arguably the first example of ecotypes identified by molecular techniques. Despite widespread citation, however, the inference of local adaptation of these ecotypes rested primarily on the allozyme pattern. This study tests for local adaptation of these ecotypes using reciprocal transplant and quantitative trait locus (QTL) mapping techniques. Both ecotypes and 188 recombinant inbred lines (RILs) derived from a cross between them were grown in common garden plots established at two sites representative of the environments in which the ecotypes were first described. Across four growing seasons at each site, three observations consistently emerged. First, despite significant genotype by environment interaction, the mesic ecotype consistently showed higher lifetime reproductive success across all years and sites. Second, the RILs showed no evidence of a trade-off in performance across sites or years, and fitness was positively correlated across environments. Third, at QTL affecting lifetime reproductive success, selection favoured the same allele in all environments. None of these observations are consistent with local adaptation but suggest that a single genotype is selectively favoured at both moist and dry sites. I propose an alternative hypothesis that A. barbata may be an example of contemporary evolution – whereby the favoured genotype is spreading and increasing in frequency – rather than local adaptation.     

Species Identity and Water Availability Determine Establishment Success Under the Canopy of Retama sphaerocarpa Shrubs in a Dry Environment

Seedling establishment in harsh environments is often enhanced by the proximity of adult shrubs. This information has been used in restoration work by placing seedlings of species being restored under the canopy of some shrubs. However, monitoring this process is often restricted to a single species, and comparisons with practices that protect planted seedlings against harsh conditions are scant. Similarly, few studies have supplied seedlings with water in the summer to observe the effects of water availability on the interaction. We compared sapling survival of three woody species (Olea europaea, Pistacia lentiscus, and Ziziphus lotus) under the leguminous shrub Retama sphaerocarpa and in gaps covered with piled branches that mimicked a shrub canopy. After 3 years, survival of saplings planted under Retama differed depending on species identity and water supply. Survival of Olea saplings placed under Retama shrubs was twice that under piled branches if not watered (35 ± 8 vs. 17 ± 2 %, respectively), whereas survival of saplings under Retama, if watered, was less (48 ± 11 vs. 68 ± 8%, respectively). Retama shrubs had a negative effect on Ziziphus; most saplings died under its canopy, whereas survival in piled branches ranged 10–54%. Pistacia was neither facilitated nor outcompeted by Retama. Facilitation of Olea by Retama shrubs was more apparent under dry conditions where watering increased competition and decreased facilitation. Overall, we conclude that Retama shrubs can help dry land restoration to a greater extent than artificial shade for Olea when not watered. The critical role played by water supply in determining nursing success rates warrants further study.     

Impact of shade on the spatial distribution of Sahlbergella singularis in traditional cocoa agroforests

• 1 Shade management is commonly considered to be an effective pest management strategy for cocoa mirids, yet shade management recommendations are not based on extensive knowledge of the mirid ecology in traditional cocoa agroforests.
• 2 The main objectives of the present study were an assessment of the impact of shade on the spatial distribution of mirid populations and thus the evaluation of shade management strategies.
• 3 Mirid densities were measured and shade was characterized for three plots located in three different agroecological zones in the Centre region of Cameroon. Mirid densities generally followed a negative binomial law. Geostatistical procedures were used to characterize spatial distribution of mirid density. Light conditions were assessed using hemispherical photography.
• 4 Populations of Sahlbergella singularis were highly aggregated in the plots. Semivariance analysis and kriging visualized the spatial dependence of mirid densities. Clearly distinguishable mirid pockets of 20–30 adjacent infested cocoa trees were identified in two of the three plots.
• 5 The high diversity of shade tree species and the large variability in density and size of shade trees resulted in a considerable heterogeneity of plot light conditions. Percentage transmitted light varied in the range 9.4–80.1% in the most heterogeneous plot.
• 6 For two of the three plots, mirid pockets were aggregated in those areas where light transmission was highest. In the third plot, relatively high mirid densities and the presence of an alternative host resulted in a more homogeneous distribution. The importance of these findings for improved mirid control is discussed.

     

Effects of an experimental drought on the functioning of a cacao agroforestry system,Sulawesi, Indonesia

Agroforestry systems may play a critical role in reducing the vulnerability of farmers' livelihood to droughts as tree‐based systems provide several mechanisms that can mitigate the impacts from extreme weather events. Here, we use a replicated throughfall reduction experiment to study the drought response of a cacao/Gliricidia stand over a 13‐month period. Soil water content was successfully reduced down to a soil depth of at least 2.5 m. Contrary to our expectations we measured only relatively small nonsignificant changes in cacao (?11%) and Gliricidia (?12%) sap flux densities, cacao leaf litterfall (+8%), Gliricidia leaf litterfall (?2%), soil carbon dioxide efflux (?14%), and cacao yield (?10%) during roof closure. However, cacao bean yield in roof plots was substantially lower (?45%) compared with control plots during the main harvest following the period when soil water content was lowest. This indicates that cacao bean yield was more sensitive to drought than other ecosystem functions. We found evidence in this agroforest that there is complementary use of soil water resources through vertical partitioning of water uptake between cacao and Gliricidia. This, in combination with acclimation may have helped cacao trees to cope with the induced drought. Cacao agroforests may thus play an important role as a drought‐tolerant land use in those (sub‐) tropical regions where the frequency and severity of droughts is projected to increase.     

骆驼刺在不同遮阴下的水分状况变化及其生理响应

为了研究骆驼刺(Alhagi sparsifolia)在不同遮阴环境下的生理适应性, 以塔克拉玛干沙漠南缘策勒绿洲外围骆驼刺为试验材料, 设置正常光照、中度遮阴(70%自然光)、重度遮阴(30%自然光) 3种光照环境, 观测了遮阴90天后土壤含水率, 骆驼刺水势、气孔导度(G_s)、叶形态、叶绿素(Chl)含量、脯氨酸(Pro)含量、丙二醛(MDA)含量、可溶性糖含量等在不同遮阴条件下的变化特征。结果显示: 随着遮阴强度的增大, 土壤含水率, 骆驼刺水势、G_s、比叶面积、Chl含量、类胡萝卜素含量有一定程度的增加; 骆驼刺叶片厚度、Pro含量、MDA含量、可溶性糖含量以及Chl a/Chl b有不同幅度的减少。结果表明: 一段时间内适度的遮阴在一定程度上降温增湿, 能够改善骆驼刺的生境, 从而避免高温强光和低水势对植物造成的伤害, 促进植物的生长, 但长期遮阴对植物的生长不利。因此建议通过短期的遮阴, 特别是在温度较高、光照较强的夏季正午前后对骆驼刺进行遮阴处理, 以达到对骆驼刺的逆境防护, 促进骆驼刺的生长。     

Plasticity in seedling morphology,biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit

• Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle‐leaved) and observed tolerance to shade, when growing in two contrasting light treatments – open (about 20% of full sunlight) and shade (about 5% of full sunlight).
• We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments.
• Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) – leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area‐based rates of light‐saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade.
• We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle‐leaved conifers in response to shade. However, an expectation of higher plasticity in shade‐intolerant species than in shade‐tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.

     

Shade tolerance and herbivory are associated with RGR of tree species via different functional traits

• Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade‐off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth‐related functional traits.
• Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth‐related functional traits and (i) species’ shade‐tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth‐related functional traits.
• We found that RGR was associated negatively with shade‐tolerance and positively with herbivory rate. However, herbivory rate and shade‐tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (A_max) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade‐tolerance was strongly related to A_max and to a lesser extent to leaf mass ratio (LMR) and dark respiration (R_d), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content.
• The effects of low light on RGR would be mediated by A_max, while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource‐uptake functional traits.

     

Morphophysiological,ultrastructural, and nutritional changes induced by Cu toxicity in young Erythrina fusca plants

Erythrina fusca is an important legume used for shade cover in cacao plantations in Brazil. Cacao plantations receive large quantities of copper (Cu)-containing agrochemicals, mainly for control of diseases. Therefore, Cu toxicity was investigated in seedlings grown in hydroponics with increasing concentrations of Cu (0.005–32 mg L^?1) in a greenhouse. Ultrastructural analyses showed cell plasmolysis in the root cortical area and changes in thylakoid membranes at 8 mg Cu L^?1 and higher. There were changes in epicuticular wax deposition on the leaf surface at the 16 and 32 mg Cu L^?1 treatments. Leaf gas exchanges were highly affected 24 hours after application of treatments beginning at 8 mg Cu L^?1 and higher Cu concentrations. Chemical analyses showed that Cu content in E. fusca roots increased as Cu concentration in the nutrient solution increased, whereas the shoot did not show significant changes. It is also observed that excess Cu interfered with Zn, Fe, Mn, Mg, K, P, and Ca content in the different E. fusca organs. Investigation of Cu toxicity symptoms focusing on morphophysiological, ultrastructural, gas exchange, and nutritional changes would be useful to alleviate Cu toxicity in E. fusca under field conditions, an important agroforestry species in cacao plantation.