Positive Effects of Plant Genotypic and Species Diversity on Anti-Herbivore Defenses in a Tropical Tree Species

Despite increasing evidence that plant intra- and inter-specific diversity increases primary productivity, and that such effect may in turn cascade up to influence herbivores, there is little information about plant diversity effects on plant anti-herbivore defenses, the relative importance of different sources of plant diversity, and the mechanisms for such effects. For example, increased plant growth at high diversity may lead to reduced investment in defenses via growth-defense trade-offs. Alternatively, positive effects of plant diversity on plant growth may lead to increased herbivore abundance which in turn leads to a greater investment in plant defenses. The magnitude of trait variation underlying diversity effects is usually greater among species than among genotypes within a given species, so plant species diversity effects on resource use by producers as well as on higher trophic levels should be stronger than genotypic diversity effects. Here we compared the relative importance of plant genotypic and species diversity on anti-herbivore defenses and whether such effects are mediated indirectly via diversity effects on plant growth and/or herbivore damage. To this end, we performed a large-scale field experiment where we manipulated genotypic diversity of big-leaf mahogany (Swietenia macrophylla) and tree species diversity, and measured effects on mahogany growth, damage by the stem-boring specialist caterpillar Hypsipyla grandella, and defensive traits (polyphenolics and condensed tannins in stem and leaves). We found that both forms of plant diversity had positive effects on stem (but not leaf) defenses. However, neither source of diversity influenced mahogany growth, and diversity effects on defenses were not mediated by either growth-defense trade-offs or changes in stem-borer damage. Although the mechanism(s) of diversity effects on plant defenses are yet to be determined, our study is one of the few to test for and show producer diversity effects on plant chemical defenses.     

FT及其同源基因在植物发育调控中的多功能效应

FT是植物开花调控途径的重要整合因子和调控开花的关键基因之一,也是植物可传导开花物质“成花素”的编码基因.FT蛋白是成花素的必需组分,FT mRNA是成花素的潜在组分;FT及其同源基因不仅参与株龄影响及逆境诱导的开花,还参与营养生长、器官形态建成、源库关系和器官脱落调控.该文对近年来国内外有关FT及其同源基因在植物发育调控中的多种功能效应及作用方式进行综述.     

Airborne Induction and Priming of Plant Defenses against a Bacterial Pathogen

Herbivore-induced plant volatiles affect the systemic response of plants to local damage and hence represent potential plant hormones. These signals can also lead to “plant-plant communication,” a defense induction in yet undamaged plants growing close to damaged neighbors. We observed this phenomenon in the context of disease resistance. Lima bean (Phaseolus lunatus) plants in a natural population became more resistant against a bacterial pathogen, Pseudomonas syringae pv syringae, when located close to conspecific neighbors in which systemic acquired resistance to pathogens had been chemically induced with benzothiadiazole (BTH). Airborne disease resistance induction could also be triggered biologically by infection with avirulent P. syringae. Challenge inoculation after exposure to induced and noninduced plants revealed that the air coming from induced plants mainly primed resistance, since expression of PATHOGENESIS-RELATED PROTEIN2 (PR-2) was significantly stronger in exposed than in nonexposed individuals when the plants were subsequently challenged by P. syringae. Among others, the plant-derived volatile nonanal was present in the headspace of BTH-treated plants and significantly enhanced PR-2 expression in the exposed plants, resulting in reduced symptom appearance. Negative effects on growth of BTH-treated plants, which usually occur as a consequence of the high costs of direct resistance induction, were not observed in volatile organic compound-exposed plants. Volatile-mediated priming appears to be a highly attractive means for the tailoring of systemic acquired resistance against plant pathogens.Plants respond to attack by pathogens or herbivores with extensive changes in gene expression that lead to induced resistance phenomena (Karban and Baldwin, 1997); various traits are then expressed de novo or at much higher intensities, which reduce or prevent further tissue damage. As both pathogens and herbivores can spread from the initial site of attack to other organs, such plant responses are often not restricted to the damaged tissue but are expressed systemically, in yet undamaged organs. Three plant hormones playing central roles in the long-distance signaling that underlies this systemic response to local attack are jasmonic acid (JA), ethylene, and salicylic acid (SA). SA and JA, in particular, are transported themselves or in the form of derivatives within the plant in order to elicit systemic responses (Truman et al., 2007; Wasternack, 2007; Heil and Ton, 2008).Recent studies have revealed that long-distance signaling is not only caused by molecules that are transported in the vascular system; signals can also be volatile compounds that move in the headspace outside the plant (Heil and Ton, 2008). In particular, green-leaf volatiles and other herbivore-induced volatile organic compounds (VOCs) can mediate the systemic response of plants to local herbivore damage (Karban et al., 2006; Frost et al., 2007; Heil and Silva Bueno, 2007). Since such VOCs move freely in the air, they may also affect neighboring plants and then mediate the phenomenon of “plant-plant communication,” which has been found in taxonomically unrelated plants such as Arabidopsis (Arabidopsis thaliana), alder (Alnus glutinosa), corn (Zea mays), lima bean (Phaseolus lunatus), maple (Acer saccharum), sagebrush (Artemisia tridentata), and wild tobacco (Nicotiana attenuata; Baldwin and Schultz, 1983; Rhoades, 1983; Tscharntke et al., 2001; Engelberth et al., 2004; Heil and Kost, 2006; Karban et al., 2006; Paschold et al., 2006; Heil and Silva Bueno, 2007; Ton et al., 2007; Godard et al., 2008).Plant-plant communication via VOCs thus appears to be a common phenomenon in herbivore resistance, and similar volatile compounds can also mediate the beneficial effects that are caused by plant growth-promoting rhizobacteria (Ryu et al., 2003, 2004b). Furthermore, exposure to VOCs such as trans-2-hexenal, cis-3-hexenal, or cis-3-hexenol enhanced resistance of Arabidopsis against the fungal pathogen Botrytis cinerea (Kishimoto et al., 2005), which indicates that VOCs may also induce disease resistance. However, the wound response, the induction of VOCs, the effects of plant growth-promoting rhizobacteria, and even the resistance to necrotrophic pathogens such as B. cinerea and Alternaria brassiccicola are mediated via JA signaling (Wasternack and Parthier, 1997; Pieterse et al., 1998; Schilmiller and Howe, 2005; Francia et al., 2007; Heil, 2008; Heil and Ton, 2008). In contrast, systemic acquired resistance (SAR) to biotrophic pathogens in many plant species is mediated by SA signaling, which increases the expression of phytoalexins and of several PATHOGENESIS-RELATED (PR) proteins (van Loon, 1997; Hammerschmidt and Smith-Becker, 1999; Durrant and Dong, 2004) and which usually is thought to act as an antagonist to JA signaling (Maleck et al., 2000; Pieterse and Dicke, 2007; Korneef and Pieterse, 2008). The volatile derivative of SA, methyl salicylate (MeSA), has been proposed as the most likely systemic signal (Park et al., 2007). In tobacco (Nicotiana tabacum), MeSA is converted back to SA, which then forms the active resistance-inducing compound (Kumar and Klessig, 2003; Forouhar et al., 2005). This mechanism might underlie the resistance induction in tobacco plants that were exposed to high MeSA concentrations (Shulaev et al., 1997). In a study on the role of MeSA as a mobile signal, Park and coworkers (2007), however, only found evidence for the vascular transport of this compound.We used lima bean to investigate whether plant-plant signaling can also affect SAR to biotrophic bacterial pathogens. Plants were exposed to the VOCs emitted from neighbors that had been treated with the chemical SAR elicitor benzothiadiazole [BTH; benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester] or that had been induced biologically, and resulting changes in resistance were monitored at the phenotypic and gene expression levels. A common phenomenon involved in disease resistance is priming, which prepares the plant to respond more rapidly and/or effectively to subsequent attack (van Hulten et al., 2006; Bruce et al., 2007; Goellner and Conrath, 2008) but which comes at much lower costs than direct resistance induction (Heil and Baldwin, 2002; Walters and Boyle, 2005; Walters and Heil, 2007). Therefore, we investigated whether VOCs also can prime resistance to pathogens by first exposing plants to VOCs coming from directly induced plants and then challenging them with Pseudomonas syringae pv syringae. Finally, VOCs released from induced plants were analyzed, and the most likely candidates were evaluated for their effect on expression of the resistance marker gene PR-2 in order to understand the chemical nature of the signal.     

Pre‐Patch Experience Affects the Egg Distribution Pattern in a Polyembryonic Parasitoid of Moth Egg Batches

According to foraging theory, female parasitoids should alter their host choice in response to cues that indicate a limitation of resources. We tested whether females of the polyembryonic parasitoid Ageniaspis fuscicollis (Hymenoptera: Encyrtidae), which attack egg batches of small ermine moths (Lepidoptera: Yponomeutidae), would alter their host acceptance pattern in response to different pre‐patch experience. We kept females of the parasitoid prior to a patch visit under different conditions, which should indicate different levels of competition for hosts. With increased competition as pre‐patch experience, females laid more eggs per host egg and self‐superparasitized more often, and the resultant egg distributions showed a trend from more regular distributions to increasingly Poisson and aggregated distributions. Consequently, females with a pre‐patch experience that would indicate low competition for hosts had the most even egg distributions. We conclude that pre‐patch experience of competitors may lead to a significant change of mutual interference patterns in egg‐laying A. fuscicollis wasps.     

Genetic Diversity and Host Alternation of the Egg Parasitoid Ooencyrtus pityocampae between the Pine Processionary Moth and the Caper Bug

The increased use of molecular tools for species identification in recent decades revealed that each of many apparently generalist parasitoids are actually a complex of morphologically similar congeners, most of which have a rather narrow host range. Ooencyrtus pityocampae (OP), an important egg parasitoid of the pine processionary moth (PPM), is considered a generalist parasitoid. OP emerges from PPM eggs after winter hibernation, mainly in spring and early summer, long before the eggs of the next PPM generation occurs. The occurrence of OP in eggs of the variegated caper bug (CB) Stenozygum coloratum in spring and summer suggests that OP populations alternate seasonally between PPM and CB. However, the identity of OP population on CB eggs seemed uncertain; unlike OP-PPM populations, the former displayed apparently high male/female ratios and lack of attraction to the PPM sex pheromone. We studied the molecular identities of the two populations since the morphological identification of the genus Ooencyrtus, and OP in particular, is difficult. Sequencing of COI and ITS2 DNA fragments and AFLP analysis of individuals from both hosts revealed no apparent differences between the OP-PPM and the OP-CB populations for both the Israeli and the Turkish OPs, which therefore supported the possibility of host alternation. Sequencing data extended our knowledge of the genetic structure of OP populations in the Mediterranean area, and revealed clear separation between East and West Mediterranean populations. The overall level of genetic diversity was rather small, with the Israeli population much less diverse than all others; possible explanations for this finding are discussed. The findings support the possibility of utilizing the CB and other hosts for enhancing biological control of the PPM.     

Effects of Bacillus thuringiensis on Adults of Cotesia plutellae (Hymenoptera: Braconidae), a Parasitoid of the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

To complement existing information on the mortality of larvae of the wasp Cotesia plutellae attacking moth caterpillars infected with Bacillus thuringiensis (Bt) we tested the direct and indirect effects of the bacterium on adult wasp longevity and oviposition behaviour. In one experiment with female parasitoids, mean longevity (SEM) was not significantly different between females exposed to Bt (1.98 +/- 0.08 days) and those not exposed (2.18 +/- 0.13 days). In a second experiment with both males and females, Bt treatment did not significantly effect either male or female parasitoids exposed to Bt. To observe the possible effects of Bt on oviposition behaviour of C. plutellae each of 10 females were given five larvae that had been treated with Bt and five untreated larvae at the same time. All parasitoids were observed to make oviposition attempts in both untreated and treated larvae. Upon dissection of the host larvae, one or more C. plutellae eggs were found in each of the larvae in which a parasitoid attempted oviposition. There was no effect of Bt treatment on parasitoid oviposition. The mean number of ovipositions in treated larvae (4.3 +/- 0.3) was not significantly different from untreated larvae (4.7 +/- 0.2).     

Hydrostatic Pressure and Temperature Effects on the Membranes of a Seasonally Migrating Marine Copepod

Marine planktonic copepods of the order Calanoida are central to the ecology and productivity of high latitude ecosystems, representing the interface between primary producers and fish. These animals typically undertake a seasonal vertical migration into the deep sea, where they remain dormant for periods of between three and nine months. Descending copepods are subject to low temperatures and increased hydrostatic pressures. Nothing is known about how these organisms adapt their membranes to these environmental stressors. We collected copepods (Calanoides acutus) from the Southern Ocean at depth horizons ranging from surface waters down to 1000 m. Temperature and/or pressure both had significant, additive effects on the overall composition of the membrane phospholipid fatty acids (PLFAs) in C. acutus. The most prominent constituent of the PLFAs, the polyunsaturated fatty acid docosahexanoic acid [DHA – 22:6(n-3)], was affected by a significant interaction between temperature and pressure. This moiety increased with pressure, with the rate of increase being greater at colder temperatures. We suggest that DHA is key to the physiological adaptations of vertically migrating zooplankton, most likely because the biophysical properties of this compound are suited to maintaining membrane order in the cold, high pressure conditions that persist in the deep sea. As copepods cannot synthesise DHA and do not feed during dormancy, sufficient DHA must be accumulated through ingestion before migration is initiated. Climate-driven changes in the timing and abundance of the flagellated microplankton that supply DHA to copepods have major implications for the capacity of these animals to undertake their seasonal life cycle successfully.     

Dissociation of Puberty and Adolescent Social Development in a Seasonally Breeding Species

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Development of New Multilocus Variable Number of Tandem Repeat Analysis (MLVA) for Listeria innocua and Its Application in a Food Processing Plant

Listeria innocua is an important hygiene indicator bacterium in food industries because it behaves similar to Listeria monocytogenes, which is pathogenic to humans. PFGE is often used to characterize bacterial strains and to track contamination source. However, because PFGE is an expensive, complicated, time-consuming protocol, and poses difficulty in data sharing, development of a new typing method is necessary. MLVA is a technique that identifies bacterial strains on the basis of the number of tandem repeats present in the genome varies depending on the strains. MLVA has gained attention due to its high reproducibility and ease of data sharing. In this study, we developed a MLVA protocol to assess L. innocua and evaluated it by tracking the contamination source of L. innocua in an actual food manufacturing factory by typing the bacterial strains isolated from the factory. Three VNTR regions of the L. innocua genome were chosen for use in the MLVA. The number of repeat units in each VNTR region was calculated based on the results of PCR product analysis using capillary electrophoresis (CE). The calculated number of repetitions was compared with the results of the gene sequence analysis to demonstrate the accuracy of the CE repeat number analysis. The developed technique was evaluated using 60 L. innocua strains isolated from a food factory. These 60 strains were classified into 11 patterns using MLVA. Many of the strains were classified into ST-6, revealing that this MLVA strain type can contaminate each manufacturing process in the factory. The MLVA protocol developed in this study for L. innocua allowed rapid and easy analysis through the use of CE. This technique was found to be very useful in hygiene control in factories because it allowed us to track contamination sources and provided information regarding whether the bacteria were present in the factories.     

Searching Speed of Trichogramma minutum and Its Potential as a Measure of Parasitoid Quality

Searching speed has been proposed as a quality criterion for the prediction of field efficacy of mass-reared Trichogramma spp. The searching speed, walking speed, and activity of female T. minutum Riley were measured using an automated video tracking system. Two- and 3-day-old thelytokous females searched twice as fast as 1-day-old females, whereas the searching speed of a strain of arrhenotokous females was similar at all ages. When reared on Actebia fennica Tauscher, the resulting wide variation in wasp size was not related to searching speed or walking speed. Both strains of T. minutum searched faster later in the day. In a second laboratory experiment, the proportion of hosts parasitized, the proportion of hosts accepted, and searching speeds of parasitoids were measured simultaneously for groups of females of both strains. Percentage parasitism was related to host acceptance but not searching speed. Searching speed was unrelated to the estimated number of host contacts. These results suggest that searching speed is not a useful measure of parasitoid efficacy for T. minutum.     

Building Development and Roads: Implications for the Distribution of Stone Curlews across the Brecks

Background

Substantial new housing and infrastructure development planned within England has the potential to conflict with the nature conservation interests of protected sites. The Breckland area of eastern England (the Brecks) is designated as a Special Protection Area for a number of bird species, including the stone curlew (for which it holds more than 60% of the UK total population). We explore the effect of buildings and roads on the spatial distribution of stone curlew nests across the Brecks in order to inform strategic development plans to avoid adverse effects on such European protected sites.

Methodology

Using data across all years (and subsets of years) over the period 1988-2006 but restricted to habitat areas of arable land with suitable soils, we assessed nest density in relation to the distances to nearest settlements and to major roads. Measures of the local density of nearby buildings, roads and traffic levels were assessed using normal kernel distance-weighting functions. Quasi-Poisson generalised linear mixed models allowing for spatial auto-correlation were fitted.

Results

Significantly lower densities of stone curlew nests were found at distances up to 1500m from settlements, and distances up to 1000m or more from major (trunk) roads. The best fitting models involved optimally distance-weighted variables for the extent of nearby buildings and the trunk road traffic levels.

Significance

The results and predictions from this study of past data suggests there is cause for concern that future housing development and associated road infrastructure within the Breckland area could have negative impacts on the nesting stone curlew population. Given the strict legal protection afforded to the SPA the planning and conservation bodies have subsequently agreed precautionary restrictions on building development within the distances identified and used the modelling predictions to agree mitigation measures for proposed trunk road developments.     

Diastereoselective Synthesis of a Lilac Aldehyde Isomer and Its Electrophysiological Detection by a Moth

The monoterpene lilac aldehyde (=2‐(5‐ethenyl‐5‐methyloxolan‐2‐yl)propanal) is a widespread flower scent. Lilac aldehyde is emitted in high amounts from nocturnal plant species, and it is highly attractive to nocturnal moth pollinators, such as Hadena bicruris, the pollinating seed predator of Silene latifolia. Lilac aldehyde possesses three stereogenic centers and can occur in eight stereoisomers which induce different antennal responses in H. bicruris. The distribution pattern of stereoisomers differs among plant species, and if H. bicruris has different receptors for detecting different isomers, it may use these differences to discriminate flowers of S. latifolia hosts from flowers of non‐host plants. To investigate the question whether the moths have in their antennae one olfactory receptor or several different receptors for the detection of the single lilac aldehyde isomers, (2S,2′S,5′S)‐lilac aldehyde was diastereoselectively synthesized. (2S,2′S,5′S)‐Lilac aldehyde and its isomeric mixture were tested electrophysiologically on antennae of H. bicruris. The results displayed antennal responses, which are characteristic for a single receptor that detects the different lilac aldehyde isomers.     

奥氮平诱导大鼠肥胖及其机制研究

目的建立奥氮平诱导的肥胖大鼠模型,并探讨其诱导肥胖的发生机制。方法 SD雌性大鼠20只,随机分为对照组和模型组,模型组大鼠每日黑暗时相前1h灌胃奥氮平(1.2mg/kg),对照组给予等容量蒸馏水。每周称体重1次,测饮水饮食量2次。给药7周时,利用SMART video-tracking system测定大鼠白天和黑暗时相的自主活动,然后处理大鼠,测体长,计算Lee's指数,称脂肪湿重,计算脂肪系数,采用高效液相色谱-电化学检测(HPLC-ECD)法测定大鼠下丘脑神经递质,用ELISA试剂盒测定血清瘦素(leptin)、脂联素(adiponectin,ADP)水平。结果模型组大鼠造模第2周至第7周时体重均明显高于对照组(P0.05或P0.01),饮食量明显增加(P0.01),黑暗时相平均速度、路程明显减少(P0.05),Lee's指数、脂肪湿重、脂肪系数明显升高(P0.05或P0.01),下丘脑5-HT、DA、DOPAC含量明显升高(P0.01或P0.05),血清leptin含量明显升高(P0.01),ADP含量明显降低(P0.01)。结论奥氮平(1.2mg/kg)增加动物摄食量,减少活动量而引起肥胖,此作用与下丘脑神经递质、瘦素和脂联素的调节有着密切联系。     

Fungal Assemblages Associated with Roots of Halophytic and Non-halophytic Plant Species Vary Differentially Along a Salinity Gradient

Structure of fungal communities is known to be influenced by host plants and environmental conditions. However, in most cases, the dynamics of these variation patterns are poorly understood. In this work, we compared richness, diversity, and composition between assemblages of endophytic and rhizospheric fungi associated to roots of two plants with different lifestyles: the halophyte Inula crithmoides and the non-halophyte I. viscosa (syn. Dittrichia viscosa L.), along a spatially short salinity gradient. Roots and rhizospheric soil from these plants were collected at three points between a salt marsh and a sand dune, and fungi were isolated and characterized by ITS rDNA sequencing. Isolates were classified in a total of 90 operational taxonomic units (OTUs), belonging to 17 fungal orders within Ascomycota and Basidiomycota. Species composition of endophytic and soil communities significantly differed across samples. Endophyte communities of I. crithmoides and I. viscosa were only similar in the intermediate zone between the salt marsh and the dune, and while the latter displayed a single, generalist association of endophytes, I. crithmoides harbored different assemblages along the gradient, adapted to the specific soil conditions. In the lower salt marsh, root assemblages were strongly dominated by a single dark septate sterile fungus, also prevalent in other neighboring salt marshes. Interestingly, although its occurrence was positively correlated to soil salinity, in vitro assays revealed a strong inhibition of its growth by salts. Our results suggest that host lifestyle and soil characteristics have a strong effect on endophytic fungi and that environmental stress may entail tight plant-fungus relationships for adaptation to unfavorable conditions.     

植物花粉S基因及其应用研究进展

自交不亲和性(self-incompatibility)研究是探讨植物遗传机制和植物育种的重要基础.在显花植物中,配子体自交不亲和由花柱S基因S-RNase和花粉S基因两个基因控制,这两个基因都具有较高的多态性和序列多样性的特征.花粉自交不亲和性是由花粉特异表达的F-box基因控制,命名为SFB(S haplotype-specific F-box protein)基因,并认为它就是花粉S基因的首选.就SFB基因的克隆、结构特点和作用机理以及应用予以综述.     

植物生物钟及其调控生长发育的研究进展

作为植物细胞内部的授时机制, 生物钟系统主要包括信号输入、核心振荡器和信号输出3个主要部分。该系统通过感受外界光照和温度等环境因子的昼夜周期性变化动态, 协调植物生长发育、代谢与生理反应, 赋予植物对生存环境的适应性。植物生物钟系统的核心振荡器通过多层级调控复杂的下游信号转导网络来参与调节植物生长发育及对生物与非生物胁迫的适应性。该文概述了近年来生物钟核心振荡器及其调控植物生长发育过程诸方面的研究进展, 并初步提出了植物时间生物学研究领域一些亟待解决的科学问题, 以期为生物钟领域的研究成果在作物分子育种方面的利用提供理论借鉴。     

Organic Carbon Composition and Oxygen Metabolism across a Gradient of Seasonally Inundated Limesink and Riparian Wetlands in the Southeast Coastal Plain,USA

A set of three relatively pristine seasonally inundated limesink wetlands and one riparian wetland was studied over a 4–6 month long inundation period in 2001. Patterns in organic matter properties and oxygen consumption in the water column followed a previously documented ecological gradient based on soil composition, vegetation type, and canopy cover. The full canopy, cypress-gum swamp had the highest mean concentrations of dissolved organic carbon (DOC; 26.2 mg/l) and dissolved lignin (sum 6; 299 μg/l) with lower concentrations observed in the partial canopy, cypress savanna (22.0 mg/l DOC; 252 μg/l sum 6) and the open marsh savanna (20.6 mg/l DOC; 135 μg/l sum 6), respectively. During the inundation period, DOC increased in concentration, dissolved lignin decreased, and δ¹³C shifted to more positive values which collectively indicate a large reduction in the percentage of aromatic carbon during the inundation period. All wetlands had very high concentrations of organic matter, yet microbial oxygen consumption was almost always stimulated by the addition of glucose rather than inorganic nutrients. Stimulation by glucose suggests that there were very small pools of highly bioavailable forms of DOC in the wetlands. A larger pool of moderately bioavailable organic matter had the capacity to sustain microbial oxygen consumption rates under dark conditions for at least 15 d. During the inundation period, the cypress-gum swamp had the lowest average rates of whole water oxygen consumption (1.0 μM/h) with increasing rates observed in the cypress savanna (1.3 μM/h), marsh savanna (1.6 μM/h), and riparian wetland (1.9 μM/h), respectively. The lignin compositional fingerprint varied across the gradient of limesink wetlands, and was useful for identifying different sources of vascular plant-derived DOM. Vascular plant production, algal production, microbial respiration, and UV degradation are all important drivers of DOM cycling, and the consistencies observed in this initial assessment of seasonally inundated limesink wetlands suggest they vary in predictable ways across the ecological gradient.     

Short and Long-Term Soil Moisture Effects of Liana Removal in a Seasonally Moist Tropical Forest

Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increasing in the neotropics. Lianas can compete intensely with trees for above- and belowground resources, including water. As tropical forests experience longer and more intense dry seasons, competition for water is likely to intensify. However, we lack an understanding of how liana abundance affects soil moisture and hence competition with trees for water in tropical forests. To address this critical knowledge gap, we conducted a large-scale liana removal experiment in a seasonal tropical moist forest in central Panama. We monitored shallow and deep soil moisture over the course of three years to assess the effects of lianas in eight 0.64 ha removal plots and eight control plots. Liana removal caused short-term effects in surface soils. Surface soils (10 cm depth) in removal plots dried more slowly during dry periods and accumulated water more slowly after rainfall events. These effects disappeared within four months of the removal treatment. In deeper soils (40 cm depth), liana removal resulted in a multi-year trend towards 5–25% higher soil moisture during the dry seasons with the largest significant effects occurring in the dry season of the third year following treatment. Liana removal did not affect surface soil temperature. Multiple and mutually occurring mechanisms may be responsible for the effects of liana removal on soil moisture, including competition with trees, and altered microclimate, and soil structure. These results indicate that lianas influence hydrologic processes, which may affect tree community dynamics and forest carbon cycling.     

Plant Quantity Affects Development and Survival of a Gregarious Insect Herbivore and Its Endoparasitoid Wasp

Virtually all studies of plant-herbivore-natural enemy interactions focus on plant quality as the major constraint on development and survival. However, for many gregarious feeding insect herbivores that feed on small or ephemeral plants, the quantity of resources is much more limiting, yet this area has received virtually no attention. Here, in both lab and semi-field experiments using tents containing variably sized clusters of food plants, we studied the effects of periodic food deprivation in a tri-trophic system where quantitative constraints are profoundly important on insect performance. The large cabbage white Pieris brassicae, is a specialist herbivore of relatively small wild brassicaceous plants that grow in variable densities, with black mustard (Brassica nigra) being one of the most important. Larvae of P. brassicae are in turn attacked by a specialist endoparasitoid wasp, Cotesia glomerata. Increasing the length of food deprivation of newly molted final instar caterpillars significantly decreased herbivore and parasitoid survival and biomass, but shortened their development time. Moreover, the ability of caterpillars to recover when provided with food again was correlated with the length of the food deprivation period. In outdoor tents with natural vegetation, we created conditions similar to those faced by P. brassicae in nature by manipulating plant density. Low densities of B. nigra lead to potential starvation of P. brassicae broods and their parasitoids, replicating nutritional conditions of the lab experiments. The ability of both unparasitized and parasitized caterpillars to find corner plants was similar but decreased with central plant density. Survival of both the herbivore and parasitoid increased with plant density and was higher for unparasitized than for parasitized caterpillars. Our results, in comparison with previous studies, reveal that quantitative constraints are far more important that qualitative constraints on the performance of gregarious insect herbivores and their gregarious parasitoids in nature.