Quantitative trait loci for key defensive compounds affecting herbivory of eucalypts in Australia

* Formylated phloroglucinols (FPCs) are key defensive compounds that influence herbivory by mammals and arthropods in eucalypts. However, the genetic architecture underlying variation in their levels remains poorly understood. * Quantitative trait loci (QTL) analysis for the concentrations of two major FPCs, sideroxylonal A and macrocarpal G, was conducted using juvenile leaves from 112 clonally duplicated progenies from an outcross F2 of Eucalyptus globulus. * Two unlinked QTL were located for macrocarpal, while another unlinked QTL was located for sideroxylonal. The sideroxylonal QTL collocated with one for total sideroxylonal previously reported using adult Eucalyptus nitens foliage, providing independent validation in a different evolutionary lineage and a different ontogenetic stage. * Given the potential widespread occurrence of these QTL, their ontogenetic stability, and their impact on a range of dependent herbivores, it is possible that they have extended phenotypic effects in the Australian forest landscape.     

Influence of fire severity on the regeneration,recruitment and distribution of eucalypts in the Cotter River Catchment,Australian Capital Territory

Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre‐fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.     

The effect of fire on nutrients in a pine forest soil

The effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986. In comparison with the adjacent unburned forest, total nitrogen decreased by 25% but available forms of nitrogen were much higher. In burned and unburned soils there was a similar trend to increase and decrease in NH ₄ ⁺ −N, However, while (NO ₂ ⁻ +NO ₃ ⁻ −N decreased in the unburned soil it rose rapidly in the burned ash soil. Total phosphorus increased by 300% after the fire but decreased again 2 months later. Also water-soluble P increased up to November and then decreased to the levels of the unburned soils. The same was true for electrical conductivity and pH, increasing immediately after the fire and then leveling off again. This increase in nutrient levels in the “ash soil” was reflected in the striking increase in shoot and root biomass and in the content of N, P, Mg, K, Ca, Zn and Fe in wheat and clover plants grown in pots in these soils. These nutrient levels were much higher in the wheat plants, which also produced 12 times more seeds in the “ash soil.” It seems that fire in these pine forests causes a short-term flush of the mineral elements in the upper “ash soil” layer which is reverted gradually via the herbaceous post-fire to the ecosystem.     

Lack of fire and insect herbivory constrain recruitment in a rare legume from Western Australia

We investigated factors influencing recruitment in the rare endemic shrub Acacia insolita subsp. recurva (Fabaceae) from the heavily cleared south‐west of Western Australia. We examined annual seed production over 4 years, including the impact of herbivory on reproductive output. Conversion of bud to fruit was low (overall 0.02%). The lack of significant difference in canopy dimensions between caged and uncaged plants suggested that vertebrate herbivore grazing was negligible, but invertebrate predation had a negative impact on seed production (loss of >80% of fruiting potential). Soil cores determined the presence of soil‐stored seeds and an experimental burn confirmed that plants are fire‐killed and can regenerate from the seed bank. This seed reserve was found to contain <5 seeds m^?2, and both freshly collected seeds and seeds retrieved from the soil had high viability (99% vs. 91%) when subjected to a germination test. Seedling recruitment 29 months post‐fire resulted in a ratio of three seedlings for every adult killed by fire. We also compared reproductive success in this rare Acacia with its common conspecific and although the rare species produced more flowers, the success of flowering did not translate into better fruit set. We conclude that insect damage to reproductive branchlets and lack of appropriate disturbance are major factors constraining recruitment. Active site management may be required for the continued persistence of this fire‐dependent legume.     

Plasticity of leaf traits and insect herbivory in Solanum incanum L. (Solanaceae) in Nguruman, SW Kenya

Plasticity of leaf traits of Solanum incanum was evaluated by comparing its expression in three sites differing in soil moisture (dry, intermediate, humid) in Nguruman, SW Kenya. Leaf size and shape, and leaf traits related to defence against herbivores, varied significantly among sites. The relationship between leaf traits showing among-site variation and insect herbivory was evaluated at a within-site scale. Leaf thickness was correlated with the level of foliar herbivory by a flea beetle ( Epitrix sp.). This correlation was negative at the dry site and positive at the humid site. No relationship was found at the intermediate site. Interestingly, leaf thickness and toughness were positively and significantly correlated at the dry site, but not elsewhere. Finally, overall patterns of herbivory by the flea beetle and unidentified defoliators differed among sites. The importance of scale when evaluating plant plasticity is discussed.     

No detectable impacts of frequent burning on foliar C and N or insect herbivory in an Australian eucalypt forest

Question: What is the effect of frequent low intensity prescribed fire on foliar nutrients and insect herbivory in an Australian eucalypt forest? Location: Lorne State Forest (Bulls Ground Frequent Burning Study), mid‐north coast, New South Wales, Australia. Methods: Eighteen independent sites were studied representing three experimental fire regimes: fire exclusion (at least 45 years), frequently burnt (every 3 years for 35 years) and fire exclusion followed by the recent introduction of frequent burning (two fires in 6 years). Mature leaves were collected from the canopy of Eucalyptus pilularis trees at each site and analysed for nutrients and damage by invertebrate herbivores. Results: Almost 75% of all leaves showed some signs of leaf damage. The frequency of past fires had no effect on carbon and nitrogen content of canopy leaves. These results were consistent with assessments of herbivore damage where no significant differences were found in the amount of invertebrate herbivory damage to leaves across fire treatments. Conclusions: This eucalypt forest displayed a high degree of resilience to both frequent burning and fire exclusion as determined by foliar nutrients and damage by insect herbivores. Fire frequency had no detectable ecological impact on this aspect of forest health.     

Impact of feral water buffalo and fire on growth and survival of mature savanna trees: An experimental field study in Kakadu National Park,northern Australia

Abstract The impact of feral Asian water buffalo (Bubalus bubalis) and season of fire on growth and survival of mature trees was monitored over 8 years in the eucalypt savannas of Kakadu National Park. Permanently marked plots were paired on either side of a 25‐km‐long buffalo‐proof fence at three locations on an elevational gradient, from ridge‐top to the edge of a floodplain; buffalo were removed from one side of the fence. All 750 trees ≥ 1.4 m height were permanently marked; survival and diameter of each tree was measured annually; 26 species were grouped into four eco‐taxonomic groups. The buffalo experiment was maintained for 7 years; trees were monitored an additional year. Fires were excluded from all sites the first 3 years, allowed to occur opportunistically for 4 years and excluded for the final year. Fires were of two main types: low‐intensity early dry season and high‐intensity late dry season. Growth rates of trees were size‐specific and positively related to diameters as exponential functions; trees grew slowest on the two ends of the gradient. Eucalypt mortality rates were 1.5 and 3 times lower than those of pantropics and of arborescent monocots, respectively, but the relative advantage was lost with fires or buffalo grazing. Without buffalo grazing, ground level biomass was 5–8 t ha^?1 compared with 2–3 t ha^?1, within 3 years. In buffalo‐absent plots, trees grew significantly slower on the dry ridge and slope, and had higher mortality across the entire gradient, compared with trees in buffalo‐present plots. At the floodplain margin, mortality of small palms was higher in buffalo‐present sites, most likely due to associated heavy infestations of weeds. Low‐intensity fires produced tree growth and mortality values similar to no‐fire, in general, but, like buffalo, provided a ‘fertilization’ effect for Eucalyptus miniata and Eucalyptus tetrodonta, increasing growth in all size classes. High‐intensity fires reduced growth and increased mortality of all functional groups, especially the smallest and largest (>35 cm d.b.h.) trees. When buffalo and fires were excluded in the final year, there were no differences in growth or mortality between paired sites across the environmental gradient. After 8 years, the total numbers of trees in buffalo‐absent plots were only 80% of the number in buffalo‐present plots, due to relatively greater recruitment of new trees in buffalo‐present plots; fire‐sensitive pantropics were particularly disadvantaged. Since the removal of buffalo is disadvantageous, at least over the first years, to savanna tree growth and survival due to a rebound effect of the ground‐level vegetation and subsequent changes in fire‐vegetation interactions, process‐orientated management aimed at reducing fuel loads and competitive pressure may be required in order to return the system to a previous state. The ‘footprint’ of 30 years of heavy grazing by buffalo has implications for the interpretation of previous studies on fire‐vegetation dynamics and for current research on vegetation change in these savannas.     

Effects of fire on sandhill herbs: nutrients, mycorrhizae, and biomass allocation

Differences in growth responses, tissue and soil inorganic nutrients, and mycorrhizal relationships of four herbaceous species were studied on burned and unburned sandhill sites in south-central Florida, USA. Three species, (Aristida stricta, Liatris tenuifolia var. laevigata, and Pityopsis graminifolia) responded positively to conditions following the burn by increased vegetative growth and flowering. The fourth species, Balduina angustifolia, is a fire-sensitive biennial and its first-year rosettes were, with an occasional exception, unable to survive or resprout following fire. Availability of all soil inorganic nutrients examined (Ca, K, Mg, and P) was low, as were total nitrogen, soil organic matter, and pH. There was a slight nutrient pulse of phosphorus into the soil following burning. For two species (Aristida and Liatris), shoot tissue concentrations of several inorganic nutrients (especially N and P) were higher on the burned site than the unburned site following burning. These differences generally dissipated over time since burning. The high concentration of tissue nutrients postburn followed by a decline on the burned site may result from rapid nutrient uptake after fire and dilution of this concentration following restoration of plant mass. Despite low levels of soil inorganic nutrients, including phosphorus, mycotrophy was absent or weakly developed among the herbaceous species examined, except for the tap-rooted Balduina angustifolia. Colonization of host plants by vesicular mycorrhizal fungi was unaffected by burning. Mycorrhizal inoculum potentials of sandhill soil were extremely low, varying seasonally from (mean +/- 1 SE) 0.3 +/- 0.2 to 3.8 +/- 0.7%.     

Biotic and abiotic consequences of differences in leaf structure

Both within and between species, leaves of plants display wide ranges in structural features. These features include: gross investments of carbon and nitrogen substrates (e.g. leaf mass per unit area); stomatal density, distribution between adaxial and abaxial surfaces, and aperture; internal and external optical scattering structures; defensive structures, such as trichomes and spines; and defensive compounds, including UV screens, antifeedants, toxins, and silica abrasives. I offer a synthesis of selected publications, including some of my own. A unifying theme is the adaptive value of expressing certain structural features, posed as metabolic costs and benefits, for (1) competitive acquisition and use of abiotic resources (such as water, light and nitrogen) and (2) regulation of biotic interactions, particularly fungal attack and herbivory. Both acclimatory responses in one plant and adaptations over evolutionary time scales are covered where possible. The ubiquity of trade-offs in function is a recurrent theme; this helps to explain diversity in solutions to the same environmental challenges but poses problems for investigators to uncover numerous important trade-offs. I offer some suggestions for research, such as on the need for models that integrate biotic and abiotic effects (these must be highly focused), and some speculations, such as on the intensity of selection pressures for these structures.     

Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park,South Africa

Aim s: The long-term effects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics. We present results from one of the longest running (>44 years) fire experiments in savannas, the experimental burn plots (EBPs), which is located in the Kruger National Park (South Africa) and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall (450–700 mm) and soil fertility.Methods: Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method, once prior to initiation of the experiment (1954) and again after 44–47 years. Different combinations of three fire frequency (1-, 2- and 3-year return intervals) and five season (before the first spring rains, after the first spring rains, mid-summer, late summer and autumn) treatments, as well as a fire exclusion treatment, were applied at the plot level (~7 ha each), with each treatment (n = 12 total) replicated four times at each of the four sites (n = 192 plots total). The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site.Important Findings: Over the 44+ years duration of the experiment, fires were consistently more intense on sites with higher mean annual rainfall (>570 mm), whereas fires were not as intense or consistent for sites with lower and more variable rainfall (<510 mm) and potentially higher herbivory due to greater soil fertility. Because the plots were open to grazing, the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites. As a consequence, fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites. For the high-rainfall sites, frequent dry season fires (1- to 3-year return intervals) resulted in high grass richness, evenness and diversity, whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses. Overall, the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients, with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.     

Processing of leaf litter in a northern jarrah forest stream,Western Australia: I. Seasonal differences

Seasonal differences in the processing of jarrah (Eucalyptus marginata) leaves were examined in a small forest stream of the Darling Range, Western Australia. Processing rates in both summer and winter were very low, placing this species in the slow category (k < 0.005) of Petersen & Cummins (1974).Macroinvertebrates did not contribute to the processing of jarrah leaves during summer and autumn, coincident with the period of peak litter fall. The low quality of detritus entering the streams, and possibly some adverse interactions with the physical and chemical environment, inhibits processing during the summer months. As a consequence, a significant proportion of the coarse-particle detritus entering these streams may be exported unprocessed at the onset of high winter flows.In contrast with previous studies, jarrah leaves were processed at a faster rate during winter than summer. This seasonal difference can, in part, be attributed to the increased density and proportion of shredders at this time. Despite this, the processing of jarrah leaves during winter was very slow and must reflect the poor quality of this detritus as food for invertebrate consumers.     

Influence of leaf herbivory,root herbivory,and pollination on plant performance in Cucurbita moschata

Abstract 1. Plants experience herbivory on many different tissues that can affect reproduction directly by damaging tissues and decreasing resource availability, or indirectly via interactions with other species such as pollinators. 2. This study investigated the combined effects of leaf herbivory, root herbivory, and pollination on subsequent damage, pollinator preference, and plant performance in a field experiment using butternut squash (Cucurbita moschata). Leaf and root herbivory were manipulated using adult and larval striped cucumber beetles (Acalymma vittatum F.), a cucurbit specialist. 3. Leaf herbivory reduced subsequent pistillate floral damage and powdery mildew (Sphaerotheca fuliginea) infection. In spite of these induced defences, the overall effect of leaf herbivory on plant reproduction was negative. Leaf herbivory reduced staminate flower production, fruit number, and seed weight. In contrast, root herbivory had a minimal impact on plant reproduction. 4. Neither leaf nor root herbivory altered pollinator visitation or floral traits, suggesting that reductions in plant performance from herbivory were as a result of direct rather than indirect effects. In addition, no measured aspect of reproduction was pollen limited. 5. Our study reveals that although leaf herbivory by the striped cucumber beetle can protect against subsequent damage, this protection was not enough to prevent the negative impacts on plant performance.     

Carbon,fire and seed addition favour native over exotic species in a grassy woodland

Cumberland Plain grassy woodland in western Sydney has been reduced to less than 12% of its pre‐settlement distribution; efforts to restore it on cleared and grazed sites within its former distribution have met with mixed success. Elevated soil nitrate levels, coupled with propagule and establishment limitation, have been identified as barriers to restoration in other grasslands. Our study used a factorial combination of carbon addition, fire and native seed addition to test whether these barriers operated on a former Cumberland plain woodland site dominated by exotic perennial grasses. Replicate field plots were established in November 2004; fire plots were burnt in December 2004; carbon was then added as sugar every 3 months until September 2005; and seeds of five native grasses were added in January 2005. Carbon addition significantly reduced soil nitrate, the effect appearing in October 2005. Carbon addition and fire each reduced the total abundance of exotics; when combined, they halved the abundance of the two dominant exotic grasses. Total abundance of native species responded positively to carbon and seed addition, but significant responses to carbon were not detected for individual species. Abundance of two native grasses responded positively to fire; after treatment the native proportion of total abundance rose from 26% on controls to 44–65% on carbon and/or fire plots. Exotic species richness was decreased independently by carbon addition and fire. Native species richness was increased independently by fire and seed addition. All five native grasses established sporadically, but only on carbon and/or fire plots. The three treatments each significantly and independently affected species composition, which showed the greatest change when all three were applied. The three treatments collectively increased the proportion of natives in measures of both plant abundance and species richness. The study confirmed that elevated soil nitrate, plus propagule and recruitment limitation are barriers to restoring this grassy woodland on cleared and grazed sites.     

Environment,not phylogeny,drives herbivory and leaf attributes in trees from two contrasting forest formations of the Brazilian Atlantic Forest

ABSTRACT

Background

The degree of herbivory in plants can be related to leaf traits, which are, in turn, determined by phylogeny and environment.     

Changes in photosynthesis,xanthophyll cycle,and sugar accumulation in two North Australia tropical species differing in leaf angles

Two tropical species of North Australia, Acacia crassicarpa and Eucalyptus pellita, have similar leaf size and leaf structure but different leaf angles. A. crassicarpa with near vertical leaf angle directly reduced photon absorption and leaf temperature (T _l) and had relatively high photosynthetic activity (P _max) and low xanthophyll cycle activity. In contrast, E. pellita with a small leaf angle exhibited high T _l, low P _max, and high activity of xanthophyll cycle which was useful for the dissipation of excessive energy and reduction of photoinhibition. In the dry season, contents of soluble sugars including pinitol, sucrose, fructose, and glucose in A. crassicarpa increased whereas larger amounts of only fructose and glucose were accumulated in E. pellita. Different sugar accumulation may be involved in osmotic adjustment of leaves during water stress that makes photosynthesis more efficient. The leaf angle may be critical for developing different protective mechanisms in these two tropical tree species that ensure optimal growth in the high irradiance and drought stress environment in North Australia.     

Post‐fire resprouting responses of native and exotic grasses from Cumberland Plain Woodland (Sydney,Australia) under elevated carbon dioxide

This study investigated the effect of elevated CO₂ on the post‐fire resprouting response of a grassland system of perennial grass species of Cumberland Plain Woodland. Plants were grown in mixtures in natural soil in mesocosms, each containing three exotic grasses (Nassella neesiana, Chloris gayana, Eragrostis curvula) and three native grasses (Themeda australis, Microlaena stipoides, Chloris ventricosa) under elevated (700 ppm) and ambient (385 ppm) CO₂ conditions. Resprouting response after fire at the community‐ and species‐level was assessed. There was no difference in community‐level biomass between CO₂ treatments; however, exotic species made up a larger proportion of the community biomass under all treatments. There were species‐level responses to elevated CO₂ but no significant interactions found between CO₂ and burning or plant status. Two exotic grasses (N. neesiana and E. curvula, a C₃ and a C₄ species respectively), and one native grass (M. stipoides, a C₃ species) significantly increased in biomass, and a native C₄ grass (C. ventricosa) significantly decreased in biomass under elevated CO₂. These results suggest that although overall productivity of this community may not change with increases in CO₂ and fire frequency, the community composition may alter due to differential species responses.     

浙江天童常绿阔叶林石栎叶片昆虫取食状类型和取食强度研究

在浙江天童常绿阔叶林中随机选择10株石栎（Lithocarpus glaber）大树,每株选择冠层向阳枝条2枝,取其所有成熟叶片（2332片）对昆虫取食状类型和取食强度进行了分析。结果表明,石栎叶片昆虫取食状类型多样,计有15种,但出现频度有很大不同;顶食状和缘食状的频度分别在30％以上;切叶状、连续小孔状和大孔状的频度在10％～30％：小孔状、阴面食状、叶中脉、泡状的频度在6．4％～1．5％;其余6种类型的频度〈1％。对叶片的危害程度取决于取食面积和频度,顶食状等3种类型频度高、取食面积大,对叶片的危害重;而阴面食状等11种类型取食面积较小,频度低,对叶片的危害较小;连续小孔状尽管取食频度高,但取食面积小,对叶片的危害也小。连续小孔状和切叶状之间存在显著正相关,但连续小孔食状与阴面食状之间,切叶状、连续小孔食状与小孔食状之间则存显著负相关,其它取食状之间均没有显著相关性,反映出不同昆虫类型的取食生态位关系。石栎叶片昆虫取食率为13．6％,介于温带森林和热带森林之间;但石栎叶片的昆虫取食频率64％,小于辽东栎,可能是由于防御机制上的差异所至;此外,石栎叶片昆虫取食强度还受到植株本身因素和小生境等因素的影响。     

Similar breakdown rates and benthic macroinvertebrate assemblages on native and Eucalyptus globulus leaf litter in Californian streams

1. Eucalyptus globulus, a tree species planted worldwide in many riparian zones, has been reported to affect benthic macroinvertebrates negatively. Although there is no consensus about the effects of Eucalyptus on aquatic macrobenthos, its removal is sometimes proposed as a means of ecological restoration. 2. We combined the sampling of macroinvertebrates with measurement of the colonisation of leaf packs in mesh bags, to examine the effects of riparian Eucalyptus and its litter on benthic macroinvertebrates in three small streams in California, U.S.A. Each stream included one reach bordered by Eucalyptus (E‐site) and a second bordered by native vegetation (N‐site). 3. The macrobenthos was sampled and two sets of litter bags were deployed at each site: one set with Eucalyptus litter (Euc‐bags) and one with mixed native tree litter (Nat‐bags) containing Quercus, Umbellularia, Acer and Alnus. Bags were exposed for 28, 56 and 90 days and this experiment was repeated in the autumn, winter and spring to account for effects of changing stream flow and insect phenology. 4. Litter input (average dry mass: 950 g m^?2 year^?1 in E‐sites versus 669 g m^?2 year^?1 in N‐sites) was similar, although in‐stream litter composition differed between E‐ and N‐sites. Litter broke down at similar rates in Euc‐bags and Nat‐bags (0.0193 day^?1 versus 0.0134 day^?1), perhaps reflecting the refractory nature of some of the leaves of the native trees (Quercus agrifolia). 5. Summary metrics for macroinvertebrates (taxon richness, Shannon diversity, pollution tolerance index) did not differ significantly between the E and N sites, or between Euc‐bags and Nat‐bags. No effect of exposure time or site was detected by ordination of the taxa sampled. However, distinct seasonal ordination clusters were observed in winter, spring and autumn, and one of the three streams formed a separate cluster. 6. The presence of Eucalyptus was less important in explaining the taxonomic composition of the macrobenthos than either ‘season’ or ‘stream’. Similarly, these same two factors (but not litter species) also helped explain the variation in leaf breakdown. We conclude that patches of riparian Eucalyptus and its litter have little effect on stream macrobenthos in this region.