中国顶丝藻科新记录Ⅲ

继续报导中国顶丝藻科新记录6种。渐尖旋体藻Audouinella attenuata,球状旋体藻A.globosa,纤细旋体藻A.gracilis,无柄旋体藻A.hypneae,偏枝旋体藻A.secundata,连续旋体藻A.seriata。     

Priming and filtering of antiherbivore defences among Nicotiana attenuata plants connected by mycorrhizal networks

Arbuscular mycorrhizal fungi (AMF) establish symbiotic associations with a majority of terrestrial plants to form underground common mycorrhizal networks (CMNs) that connect neighbouring plants. Because Nicotiana attenuata plants do not respond to herbivory‐elicited volatiles from neighbours, we used this ecological model system to evaluate if CMNs function in interplant transmission of herbivory‐elicited responses. A mesocosm system was designed to establish and remove CMNs linking N. attenuata plants to examine the herbivory‐elicited metabolic and hormone responses in CMNs‐connected “receiver” plants after the elicitation of “donor” plants by wounding (W) treated with Manduca sexta larval oral secretions (OS). AMF colonization increased constitutive jasmonate (JA and JA‐Ile) levels in N. attenuata roots but did not affect well‐characterized JAs‐regulated defensive metabolites in systemic leaves. Interestingly, larger JAs bursts, and higher levels of several amino acids and particular sectors of hydroxygeranyllinalool diterpene glycoside metabolism were elevated in the leaves of W + OS‐elicited “receivers” with CMN connections with “donors” that had been W + OS‐elicited 6 hr previously. Our results demonstrate that AMF colonization alone does not enhance systemic defence responses but that sectors of systemic responses in leaves can be primed by CMNs, suggesting that CMNs can transmit and even filter defence signalling among connected plants.     

Restoration impacts on fuels and fire potential in a dryland tropical ecosystem dominated by the invasive grass Megathyrsus maximus

Ecological restoration often attempts to promote native species while managing for disturbances such as fire and non‐native invasions. The goal of this research was to investigate whether restoration of a non‐native, invasive Megathyrsus maximus (guinea grass) tropical grassland could simultaneously promote native species and reduce fire potential. Megathyrsus maximus was suppressed with herbicide, and three suites of native species—each including the same groundcover and shrub, and one of three tree species—were outplanted in a randomized, complete block design that also included herbicide control (herbicide with no outplantings) and untreated control treatments. Fuels were quantified 27 months after outplanting, and potential fire behavior (rate of spread and flame length) was modeled with BehavePlus. Compared with untreated controls, native outplant treatments reduced M. maximus cover by 76–91% and M. maximus live and dead fuel loads by greater than 92 and 68%, respectively. Despite reductions in M. maximus fuels, neither treatment‐level (grass + native) total fuel loads and fuel moistures, nor modeled fire behavior differed between outplant treatments and controls. The best performing native woody species (Dodonaea viscosa) had significantly lower average individual plant live fuel moisture (84%) than M. maximus (156%) or other native woody outplant species (201–328%), highlighting the need for careful species selection. These results demonstrate that restoring native species to degraded tropical dry forests is possible, but that ecological restoration will not necessarily alter the potential for fire, at least in the short term, making selection of species with beneficial fuel properties and active fire management critical components of ongoing restoration.     

车桑子幼苗生物量分配与叶性状对氮磷浓度的响应差异

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

Trichomes as dangerous lollipops: Do lizards also use caterpillar body and frass odor to optimize their foraging?

When attacked by herbivores, plants produce toxic secondary metabolites that function as direct defenses, as well as indirect defenses that attract and reward predators of the offending herbivores. These indirect defenses include both nutritive rewards such as extra floral nectar, as well as informational rewards, such as the production and release of volatile compounds that betray the location of feeding herbivores to predators. Herbivory of Nicotiana attenuata by the tobacco hornworm (Manduca larvae) alters the volatile profiles of both the plant and larval headspace. Herbivory-elicited specific changes in the volatile profiles are detected by arthropod predators of Manduca larvae. The known predators that perceive volatile cues induced by Manduca herbivory of N. attenuata are insects that target Manduca at early developmental stages, when the larvae are still small; large, late-instar larvae may have outgrown these predation risks. However, here we offer evidence that branched chain aliphatic acids derived from the digestion of plant O-acyl sugars from trichomes may betray Manduca larvae to lizard predators during late developmental stages as well.     

Effect of a saprophytic fungus on the growth and the lead uptake, translocation and immobilization in Dodonaea viscosa

Phytoremediation is a feasible alternative to remediate soils polluted with toxic elements, which can be enhanced by manipulating plant-microbe interactions. Regarding this, free-living saprophytic fungi that interact beneficially with roots have been scarcely studied. Thus, the aim of this study was to assess the effect of a saprophytic fungus, Lewia sp., on the plant growth and the ability of Dodonaea viscosa to phytoaccumulate or phytostabilize soluble and insoluble sources of lead in a solid support. The growth of D. viscosa was influenced by both Pb and Lewia sp. While seedlings exposed to Pb showed a decrease in biomass production, in seedlings grown without Pb the biomass was stimulated by Lewia sp. The fungus strongly stimulated the weight-to-length ratio in roots. Regardless of the treatment, D. viscosa accumulated 4.4-6.5 times more Pb in roots than in shoots, conducting to low translocation factors (< 0.2). The presence of Lewia sp. significantly improved Pb accumulation, achieving high bioconcentration factors (> 22), which was attributed to an increased bioavailability and uptake of Pb due to the fungus. This study demonstrated that Lewia sp. could improve Pb-phytostabilization by D. viscosa in soils polluted with soluble and insoluble forms of Pb.     

Allocation of nitrogen to an inducible defense and seed production in Nicotiana attenuata

Resource-based tradeoffs in the allocation of a limiting resource are commonly invoked to explain negative correlations between growth and defense in plants, but critical examinations of these tradeoffs are lacking. To rigorously quantify tradeoffs in a common currency, we grew Nicotiana attenuata plants in individual hydroponic chambers, induced nicotine production by treating roots with methyl jasmonate (MJ) and standardized leaf puncturing, and used ¹⁵N to determine whether nitrogen-based tradeoffs among nicotine production, growth, and seed production could be detected. Plants were treated with a range of MJ quantities (5, 45 or 250 μg plant^?1) to effect a physiologically realistic range of changes in endogenous jasmonic acid levels and increases in nicotine production and accumulation; MJ treatments were applied to the roots to target JA-induced nicotine production, since nicotine biosynthesis is restricted to the roots. Leaf puncturing and 5 μg MJ treatments increased de novo nicotine synthesis and whole-plant (WP) nicotine pools by 93 and 66%, while 250 μg MJ treatments increased these values 3.1 and 2.5-fold. At these high rates of nicotine production, plants incorporated 5.7% of current nitrogen uptake and 6.0% of their WP nitrogen pools into nicotine. The ¹⁵N-labeled nicotine pools were stable or increased for the duration of vegetative growth, indicating that the N-nicotine was not metabolized and re-used for growth. Plants with elevated nicotine production grew more slowly and the differences in plant biomass gain between MJ-treated plants and controls were linearly related to the differences in nicotine accumulation. Despite the reductions in rosette-stage growth associated with nicotine production, estimates of lifetime fitness (cumulative lifetime seed production, mass/seed, seed viability) were not affected by any treatment. Only two treatments (leaf puncturing and 250 μg MJ) increased the allocations of ¹⁵N acquired at the time of induction to seed production. On average, plants used only 14.9% of their WP nitrogen pool for seed production, indicating that either the nitrogen requirements for seed production or the reproductive effort of these hydroponically-grown plants are low. To determine if seed production is strongly influenced by the amount of vegetative biomass attained before reproduction, the experiment was repeated with plants that had 44% of their leaf area (or 29% of their WP biomass) removed before MJ treatments with a removal technique that minimized the nicotine response. MJ treatments of these plants dramatically increased nicotine production and accumulation, but these plants also suffered no measurable fitness consequences from either the leaf removal or MJ treatments. We conclude that when N. attenuata plants are grown in these individual hydroponic chambers, their allocation to reproduction is sufficiently buffered to obscure the large increases in nitrogen allocations to an inducible defense. To determine whether soil-grown plants are similarly buffered, we grew two genotypes of plants in the high-nutrient soil from a 1-year-old burn in a piñyon-juniper forest (the plants' natural habitat) and in low-nutrient soil from an adjacent unburned area, and induced nicotine production in half of the plants with a 500 μg root MJ treatment. Plants grown in burned soils had an estimated lifetime fitness that was on average 2.8-fold greater than that of plants grown in unburned soils. MJ treatment reduced fitness estimates by 43% and 71% in the burned and unburned soils, respectively. We conclude that while hydroponic culture allows one to rigorously quantitate nitrogen allocation to growth, reproduction and defense, the allocation patterns of plants grown in hydroponic culture differ from those of plants grown in soil. Under hydroponic conditions, plants have low reproductive allocations and reproductive-defense tradeoffs are not detected. Reproductive-defense tradeoffs are readily discernible in soil-grown plants, but under these growing conditions, the nitrogen-basis for the tradeoff is difficult to quantify.     

Identification and characterization of the water gap in the physically dormant seeds of Dodonaea petiolaris: a first report for Sapindaceae

Background and Aims

The Sapindaceae is one of 17 plant families in which seed dormancy is caused by a water-impermeable seed or fruit coat (physical dormancy, PY). However, until now the water gap in Sapindaceae had not been identified. The primary aim of this study was to identify the water gap in Dodonaea petiolaris (Sapindaceae) seeds and to describe its basic morphology and anatomy.

Methods

Seed fill, viability, water-uptake (imbibition) and other characteristics were assessed for D. petiolaris seeds. The location and structure of the water gap were investigated using a blocking experiment, time series photography, scanning electron microscopy and light microscopy. Dodonaea petiolaris seeds with PY also were assessed for loss of PY at four ecologically significant temperatures under moist and dry conditions. Seeds of three other species of Sapindaceae were examined for presence of a water gap.

Key Results

The water gap in D. petiolaris seeds was identified as a small plug in the seed coat adjacent to the hilum and opposite the area where the radicle emerges. The plug was dislodged (i.e. water gap opened = dormancy break) by dipping seeds in boiling water for 2·5 min or by incubating seeds on a moist substrate at 20/35 °C for 24 weeks. Layers of cells in the plug, including palisade and subpalisade, are similar to those in the rest of the seed coat. The same kind of water gap was found in three other species of Sapindaceae, Diplopeltis huegelii, Distichostemon hispidulus and Dodonaea aptera.

Conclusions

Following dormancy break (opening of water gap), initial uptake of water by the seed occurs only through the water gap. Thus, the plug must be dislodged before the otherwise intact seed can germinate. The anatomy of the plug is similar to water gaps in some of the other plant families with PY.     

Using nutritional indices to study LOX3-dependent insect resistance

Induced resistance to biotic attackers is thought to be mediated by responses elicited by jasmonic acid (JA), a subset of which are lipoxygenase 3 (LOX3) dependent. To understand the importance of LOX3-mediated insect resistance, we analysed the performance of Manduca sexta larvae on wild-type (WT) and on isogenic Nicotiana attenuata plants silenced in NaLOX3 expression and JA signalling, and we used Waldbauer nutritional indices to measure the pre- and post-ingestive effects. LOX3-mediated defenses reduced larval growth, consumption and frass production. These defenses reduced how efficiently late-instar larvae converted digested food to body mass (ECD). In contrast, LOX3-mediated defenses decreased approximate digestibility (AD) in early instar larvae without affecting the ECD and total food consumption. Larvae of all instars feeding on defended WT plants behaviourally compensate for their reduced body mass by consuming more food per unit of body mass gain. We suggest that larvae feeding on plants silenced in NaLOX3 expression (as-lox) initially increase their AD, which in turn enables them to consume more food in the later stages and consequently, to increase their ECD and efficiency of conversion of ingested food (ECI). We conclude that N. attenuata's oxylipin-mediated defenses are important for resisting attack from M. sexta larvae, and that Waldbauer nutritional assays reveal behavioural and physiological counter responses of insects to these plant defenses.