Visual, semi-quantitative assessments allow accurate estimates of leafminer population densities: an example comparing image processing and visual evaluation of damage by the horse chestnut leafminer Cameraria ohridella (Lep., Gracillariidae)

Abstract: Qualitative or semi-quantitative visual assessments are most often used for estimating population size of herbivorous insects. The precision of these estimates, however, is often difficult to establish. A 'simulation game' with the horse chestnut leafminer, Cameraria ohridella Deschka & Dimic (Lep., Gracillariidae) shows that visual, semi-quantitative assessments can provide accurate information. Damaged areas of 411 horse chestnut leaves collected in 100 sites were closely related to mine numbers despite some variability in mine and leaf size ( R ² = 0.915; n  = 411; P < 0.001). On the basis of this relationship, two methods of population assessment are compared: (i) digital image processing of leaf damage and (ii) visual assessment using a damage key reflecting the relative infested area on each leaf (0, 0%; 1, 0–2%; 2, 2–5%; 3, 5–10%; 4, 10–25%; 5, 25–50%; 6, 50–75%; 7, 75–100%). Both methods used to estimate damage presented a similar, close relationship to the 'real' numbers of mines ( R ² = 0.858; n  = 777; P < 0.001 for image processing and R ² = 0.905; n  = 777; P < 0.001 for visual assessment). The potential of using visual assessments as an accurate and fast method in situ at the tree scale is discussed.     

Dynamics of carbohydrates in the embryo axes of horse chestnut seeds during their transition from dormancy to germination

It was shown that the content of carbohydrates and their composition in embryo axes of horse chestnut seeds changed as seeds acquired a capability of dormancy release and germination. Sucrose prevailed among carbohydrates, comprising to 150–160 mg/g dry wt. During the first half of the seed imbibition time, oligosaccharides, namely raffinose and stachyose, degraded, whereas the contents of glucose and fructose were very low. The second half of the imbibition period (until radicle protrusion) was characterized by a cessation of oligosaccharide breakdown and accumulation of monosaccharides. Carbohydrate balance showed that the contribution of oligosaccharide breakdown to sucrose and monosaccharide accumulation was rather small, and monosaccharides accumulated mostly at the expense of sucrose gradually coming from cotyledons during imbibition. The trend of carbohydrate metabolism in imbibing axial organs was similar during the entire period of a seed dormancy release in the course of stratification. A readiness for the commencement of these processes during the entire dormancy period implies that carbohydrate conversions in embryo axes are not a trigger for a dormancy release. Monosaccharide accumulation in embryo axes before radicle protrusion produces an increase in the osmotic pressure, as compared to that provided by sucrose, by approximately 20%. Recalcitrance of the horse chestnut seeds is discussed in relation to the role of carbohydrates and other endogenous osmotica in the establishment of osmotic properties.     

Cellulase activity on decomposing leaf litter in microcosms

In this paper, we describe cellulase and cellobiose dehydrogenase (CBDH) dynamics in relation to incubation time, mass loss and chemical composition of decomposing deciduous leaf litter. Cellulose disappearance from litter coincided with periods of maximum cellulase activity. CBDH activity peaked later in decomposition after cellulase activity had declined. Enzyme activity patterns differed among litter types when expressed on the basis of decomposition time or cumulative mass loss. The patterns converged when expressed on the basis of chemical composition as indexed by the fraction of cellulose in the lignocellulose complex. We present a three-stage model of decomposition based on temporal changes in cellulase activities and coincident changes in litter chemical composition.     

毛竹凋落叶组成对叶凋落物分解的影响

毛竹混交林具有较高的生产力和较好的生态功能,可能与混合凋落物的养分归还特征有关。本研究采用凋落物分解袋法对不同混合比例毛竹凋落叶分解特征进行了为期1年的研究,共设置5个处理,分别为Ⅰ(毛竹纯叶)、Ⅱ(毛竹、楠木叶比例为8:2);Ⅲ(毛竹、杉木叶比例8:2)、Ⅳ(毛竹、楠木叶比例5:5)和Ⅴ(毛竹、杉木叶比例5:5)。结果表明,不同处理凋落物分解速率符合Olson指数分解模型,R2均高于0.92。5个处理分解系数的排列顺序为Ⅱ>Ⅰ>Ⅲ>Ⅴ>Ⅳ,分别为0.68、0.66、0.58、0.55和0.49。处理Ⅰ和Ⅱ的分解速度显著高于其他处理,说明并非所有类型毛竹混合凋落叶均会促进凋落物分解,只有合适的比例和树种会促进凋落物分解。其中,竹阔混合凋落叶的分解速度高于竹针混合凋落叶的分解速度,竹阔混交可能更有利于竹林持续生产力的维持。N、P、K3种元素养分释放模式不同,N元素表现为净富集与净释放交替出现;P元素在经过4个月的快速富集后,4—5个月有短暂的净释放过程,其后呈富集状态;K元素浓度先升高后降低,在放置的前3个月净释放,随后呈富集状态。竹林凋落叶的养分含量对凋落物养分归还有重要影响,尤其是C/N和P可能作为竹林凋落...     

Variable effects of air-drying on leaching losses from tree leaf litter

Leaching of soluble substances may be an important first step in leaf litter decomposition in small streams, but recent research has suggested that large leaching losses (up to 30% of initial mass in 48 h) may be an artifact created by using air-dried leaves in decomposition experiments. In laboratory experiments, we compared 3 d leaching losses from freshly fallen and air-dried senescent leaves of 27 tree species from different regions across Canada. Air-dried leaves from all species leached measurable amounts of original mass (3.6–32.8% dry mass), but leaching losses from fresh leaves (0–35%) were detectable in all but two species. Air-drying increased leaching losses in many species, but in others it reduced leaching losses or had no measurable effect. Results for leaves of the same species collected in different regions or in different years were generally similar, but species within the same genus often behaved very differently. Neither moisture content (fresh or air-dried), leaf thickness, nor cuticle thickness proved of any value as predictors of leaching losses or the effect of air-drying. The propensity of autumn-fallen leaves to leach, whether fresh or air-dried, appears to be a property of the individual tree species.     

浅埋对三倍体毛白杨落叶分解的影响

凋落物分解在森林生态系统养分循环及能量流动中具有十分重要的作用,为实现三倍体毛白杨纸浆林养分的科学管理,加快落叶分解,采用网袋法研究了2、4、6年生3个不同年龄的林分落叶在浅埋条件下的分解情况.结果表明:与在地表分解相比,浅埋显著促进了三倍体毛白杨落叶的分解,1年的分解率显著提高,分别为落叶在地表年分解率的130％、194％和186％;浅埋落叶分解50％所需天数分别只有地表的58％、39％和38％,而分解95％所需的天数分别只有地表的60％、38％和36％;浅埋对不同年龄林分落叶的促进程度不同.     

UV-B辐射对杉木凋落叶分解的影响

采用分解袋法对自然和UV-B辐射滤减环境下的杉木凋落叶进行分解试验.结果表明:与对照相比,UV-B辐射滤减处理使杉木凋落叶的分解速率降低了69.6%(P<0.001),凋落叶中氮、磷和木质素的相对含量分别增加150%、83.3%和13.8%,抑制了钾和碳的释放.木质素光降解在杉木凋落叶分解过程中的作用不明显.UV-B辐射可以加快杉木凋落叶的分解,促进氮、磷、钾和碳的释放,以及杉木林凋落物层的营养周转速度,增加地表的碳通量,对杉木林的碳源或碳汇功能具有潜在的影响.     

Effects of burial on leaf litter quality,microbial conditioning and palatability to three shredder taxa

Summary 1. Heterotrophic microorganisms are crucial for mineralising leaf litter and rendering it more palatable to leaf‐shredding invertebrates. A substantial part of leaf litter entering running waters may be buried in the streambed and thus be exposed to the constraining conditions prevailing in the hyporheic zone. The fate of this buried organic matter and particularly the role of microbial conditioning in this habitat remain largely unexplored. 2. The aim of this study was to determine how the location of leaf litter within the streambed (i.e. at the surface or buried), as well as the leaf litter burial history, may affect the leaf‐associated aquatic hyphomycete communities and therefore leaf consumption by invertebrate detritivores. We tested the hypotheses that (i) burial of leaf litter would result in lower decomposition rates associated with changes in microbial assemblages compared with leaf litter at the surface and (ii) altered microbial conditioning of buried leaf litter would lead to decreased quality and palatability to their consumers, translating into lower growth rates of detritivores. 3. These hypotheses were tested experimentally in a second‐order stream where leaf‐associated microbial communities, as well as leaf litter decomposition rates, elemental composition and toughness, were compared across controlled treatments differing by their location within the streambed. We examined the effects of the diverse conditioning treatments on decaying leaf palatability to consumers through feeding trials on three shredder taxa including a freshwater amphipod, of which we also determined the growth rate. 4. Microbial leaf litter decomposition, fungal biomass and sporulation rates were reduced when leaf litter was buried in the hyporheic zone. While the total species richness of fungal assemblages was similar among treatments, the composition of fungal assemblages was affected by leaf litter burial in sediment. 5. Leaf litter burial markedly affected the food quality (especially P content) of leaf material, probably due to the changes in microbial conditioning. Leaf litter palatability to shredders was highest for leaves exposed at the sediment surface and tended to be negatively related to leaf litter toughness and C/P ratio. In addition, burial of leaf litter led to lower amphipod growth rates, which were positively correlated with leaf litter P content. 6. These results emphasise the importance of leaf colonisation by aquatic fungi in the hyporheic zone of headwater streams, where fungal conditioning of leaf litter appears particularly critical for nutrient and energy transfer to higher trophic levels.     

Trophic cascading effects of predatory fish on leaf litter processing in a Japanese stream

A manipulative field experiment to test for trophic cascading effects of predatory fish on detritus processing by benthic invertebrates was performed in stream channels running through a wetland forest in northern Japan. To control for fish effects on benthic invertebrates, two simple treatments (fish-present and fish-absent) were established for 4 weeks, with two common predatory fish, rainbow trout (Oncorhynchus mykiss) and freshwater sculpin (Cottus nozawae), being introduced into and excluded from stream cages. At the end of experiment, the biomass of the dominant detritivore, an amphipod (Jesogammarus jezoensis), was significantly less in the fish-present treatment (0.56 g m^–2 in dry mass on average) than that in the fish-absent treatment (1.32 g m^–2), there being no significant treatment effect evident for the second-dominant detritivore, coleopteran larvae (Optioservus kubotai). The loss of oak leaves (Quercus crispla) from litter bags in the fish-present treatment (0.31 g week^–1 in dry mass on average) was significantly less than in the fish-absent treatment (0.54 g week^–1). Predator-induced lower biomass and likely lowered foraging activities of the J. jezoensis were responsible for the suppression of litter processing efficiency. In contrast, the standing crop of fine particulate organic matter did not differ significantly between the treatments. The experimental results revealed that the predatory fish had an indirect but significant effect on leaf litter processing in the stream.     

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.     

UV‐B effect on Quercus robur leaf litter decomposition persists over four years

The effects of elevated UV‐B (280–315 nm) radiation on the long‐term decomposition of Quercus robur leaf litter were assessed at an outdoor facility in the UK by exposing saplings to elevated UV‐B radiation (corresponding to a 30% increase above the ambient level of erythemally weighted UV‐B, equivalent to that resulting from a c. 18% reduction in ozone column) under arrays of cellulose diacetate‐filtered fluorescent UV‐B lamps that also produced UV‐A radiation (315–400 nm). Saplings were also exposed to elevated UV‐A radiation alone under arrays of polyester‐filtered fluorescent lamps and to ambient solar radiation under arrays of nonenergized lamps. After 8 months of irradiation, abscised leaves were placed into litter bags and allowed to decompose in the litter layer of a mixed deciduous woodland for 4.08 years. The dry weight loss of leaf litter from saplings irradiated with elevated UV‐B and UV‐A radiation during growth was 17% greater than that of leaf litter irradiated with elevated UV‐A radiation alone. Annual fractional weight loss of litter (k), and the estimated time taken for 95% of material to decay (3/k) were respectively increased and decreased by 27% for leaf litter exposed during growth to elevated UV‐B and UV‐A radiation, relative to that exposed to UV‐A alone. The present data corroborate those from a previous study indicating that UV‐B radiation applied during growth accelerates the subsequent decomposition of Q. robur leaf litter in soil, but indicate that this effect persists for over four years after abscission.     

The effects of shredding invertebrates on the transfer of organic carbon from littoral leaf litter to water-column bacteria

Leaf litter can be of great importance for the productivity of small oligotrophic lakes surrounded by deciduous forests. Feeding invertebrate shredders produce particulate organic leftovers, but their feeding also enhances the release of dissolved organic carbon (DOC). We tested whether invertebrate-mediated DOC release affects the production of heterotrophic water-column bacteria. Submersed leaves were incubated in microcosms with and without shredders; and DOC, absorbance, bacterial abundance and bacterial production in the water column were monitored. We also measured dry weight of the organic particles (FPOC, fine particulate organic carbon, leaf residues and shredders). Total leaf-litter carbon decreased by nearly 80% in the presence of shredders, and on average 56% of the initial leaf carbon ended up as FPOC after 126 days of incubation. Without shredders FPOC production was almost zero, and 72% of the added leaf carbon could be retrieved as leaves when the experiment ended. Both these figures include the rapid release of DOC during the first week of leaf incubation in the lake water (equivalent to 16–19% of total added leaf carbon). Although bacterial production in the water was several times higher in treatments with shredders, bacterial consumption of leaf-derived DOC from shredding was obviously of minor importance in the total carbon budget. This result suggests, although shredders have a strong impact on transformation of leaves to FPOC, they do not greatly enhance the initial rate of mineralization of the leaf-derived detritus.     

Using experimental manipulation to assess the roles of leaf litter in the functioning of forest ecosystems

The widespread use of forest litter as animal bedding in central Europe for many centuries gave rise to the first litter manipulation studies, and their results demonstrated that litter and its decomposition are a vital part of ecosystem function. Litter plays two major roles in forest ecosystems: firstly, litterfall is an inherent part of nutrient and carbon cycling, and secondly, litter forms a protective layer on the soil surface that also regulates microclimatic conditions. By reviewing 152 years of litter manipulation experiments, I show that the effects of manipulating litter stem from changes in one, or both, of these two functions, and interactions between the variables influenced by the accumulation of litter can result in feedback mechanisms that may intensify treatment effects or mask responses, making the interpretation of results difficult.Long-term litter removal increased soil bulk density, overland flow, erosion, and temperature fluctuations and upset the soil water balance, causing lower soil water content during dry periods. Soil pH increased or decreased in response to manipulation treatments depending on forest type and initial soil pH, but it is unclear why there was no uniform response. Long-term litter harvesting severely depleted the forests of nutrients. Decreases in the concentrations of available P, Ca, Mg, and K in the soil occurred after only three to five years. The decline in soil N occurred over longer periods of time, and the relative loss was greater in soils with high initial nitrogen concentration. Tree growth declined with long-term litter removal, probably due to lower nutrient availability. Litter manipulation also added or removed large amounts of carbon thereby affecting microbial communities and altering soil respiration rates.Litter manipulation experiments have shown that litter cover acts as a physical barrier to the shoot emergence of small-seeded species; further, the microclimate maintained by the litter layer may be favourable to herbivores and pathogens and is important in determining later seedling survival and performance. Litter manipulation altered the competitive outcomes between tree seedlings and forbs, thereby influencing species composition and diversity; changes in the species composition of understorey vegetation following treatments occurred fairly rapidly. By decreasing substrate availability and altering the microclimate, litter removal changed fungal species composition and diversity and led to a decline in populations of soil fauna. However, litter addition did not provoke a corresponding increase in the abundance or diversity of fungi or soil fauna.Large-scale long-term studies are still needed in order to investigate the interactions between the many variables affected by litter, especially in tropical and boreal forests, which have received little attention. Litter manipulation treatments present an opportunity to assess the effects of increasing primary production in forest ecosystems; specific research aims include assessing the effects of changes in litter inputs on the carbon and nutrient cycles, decomposition processes, and the turnover of organic matter.     

Interactive effects of pH and leaf litter on a shredder, the scirtid beetle, Helodes pulchella, inhabiting tree-holes

1. Scirtid beetles (Coleoptera: Scirtidae) are common inhabitants of water-filled treeholes and interact with other detritivores in a processing chain commensalism. The strength of the commensalism is determined by resource quantity and the organisms involved have different tolerances to low pH. To determine the effects and interactions of resource quantity and pH on one of these leaf-shredding scirtid beetles, Helodes pulchella (Guerin), leaf litter and pH were varied independently in experimental microcosms which mimic treehole habitats.
2. Helodes pulchella growth was affected by both resources and pH in two similar experiments conducted in different years. Scirtid larvae grew more slowly in low resource treatments and also grew more slowly in low pH treatments. Scirtid survival was not affected by pH, but was lower in high resource microcosms in the 1997 experiment. Consumption of leaf litter was much higher in high resource microcosms, even though not all leaf litter was consumed in low leaf litter treatments.
3. Thus, water chemistry and leaf litter quantity could have strong effects on resource availability through effects on these beetle facilitators, in turn affecting other insects living in these detritus-based communities.     

巨桉凋落叶分解对菊苣生长及光合特性的影响

采用盆栽试验,研究了巨桉凋落叶分解初期对菊苣幼苗生长和光合生理特性的影响.试验设置A₁(30 g·pot^-1)、A₂(60 g·pot^-1)、A₃(90 g·pot^-1)和对照（CK）4个凋落叶水平,将各处理的凋落叶分别与12 kg土壤混合后装盆,播种菊苣.待A₃处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标.结果表明：巨桉凋落叶分解初期明显抑制了菊苣生物量积累、叶面积的增加及光合色素的合成,且随着凋落叶施入量的增加抑制作用加大;菊苣叶片胞间CO₂浓度增加,而净光合速率、气孔导度和蒸腾速率均显著低于对照;随土壤中凋落叶含量的增加,除CO₂补偿点呈增加趋势外,其他光响应和CO₂响应的特征参数都呈明显下降趋势,并与对照差异显著.巨桉凋落叶分解过程中,其化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长.     

川西亚高山森林凋落物分解初期土壤动物对红桦凋落叶质量损失的贡献

2010年10月26日-2011年4月18日在川西亚高山地区季节性冻融期间,选择典型的红桦-岷江冷杉林,采用凋落物分解袋法调查了不同网孔(0.02、0.125、1和3 mm)凋落物分解袋内的凋落物质量损失,分析微型、中型和大型土壤动物对红桦凋落叶分解的贡献.结果表明:在季节性冻融期间,0.02、0.125、1和3 mm分解袋内的红桦凋落叶质量损失率分别为11.8％、13.2％、15.4％和19.5％,不同体径土壤动物对红桦凋落叶质量损失的贡献率为39.5％;不同孔径凋落物袋内土壤动物的类群和个体相对密度与凋落叶的质量损失率的变化趋势相对一致.在季节性冻融的初期、深冻期和融化期,不同土壤动物对红桦凋落叶质量损失的贡献率为大型土壤动物(22.7％)＞中型土壤动物(11.9％)＞微型土壤动物(7.9％).季节性冻融期间土壤动物活动是影响川西亚高山森林凋落物分解的重要因素之一.     

巨桉凋落叶分解初期对菊苣生长和光合特性的影响

采用盆栽试验,于2010年3-5月在四川农业大学教学科研园区内研究了巨桉凋落叶分解初期对受体植物菊苣幼苗生长和光合特性的影响.试验设置CK (0 g·pot-1)、A1(30 g·pot-1)、A2(60 g·pot-1)和A3 (90 g·pot-1)4个凋落叶施用水平,将各处理的凋落叶分别与12 kg土壤混合后装盆,播种菊苣,分别在播种30、45、60和75 d测定菊苣生长指标,待凋落叶量的最高处理组A3植株第3片真叶完全展开后,测定菊苣叶片的光合生理指标.结果表明:在各测定时间下,不同巨桉凋落叶施用水平的菊苣生物量积累和叶面积增长受到显著抑制;在凋落叶分解初期,菊苣幼苗叶片光合色素合成受到明显抑制,且随着凋落叶施用量增加抑制作用加大,各处理幼苗的光合速率日变化均呈午休双峰型曲线,气孔导度和水分利用效率的变化趋势与净光合速率相同,日光合总量表现为CK＞A1 ＞A2 ＞A3.经GC-MS定期检测,凋落叶中有33种小分子化合物随着凋落叶的分解而逐步释放,以具有化感作用的萜类物质为主.