木兰科常绿与落叶物种叶片构建策略的差异

为探究木兰科(Magnoliaceae)常绿与落叶物种叶片构建的生理生态策略,选取黄山木兰(Yulaniacylindrica)、玉兰(Y.denudata)和鸡公山玉兰(Y. jigongshanensis) 3种落叶物种,以及荷花玉兰(Magnolia grandiflora)、含笑花(Michelia figo)、石碌含笑(M. shiluensis) 3种常绿物种,对其叶片构建成本和叶片寿命相关的性状进行比较。结果表明,木兰科3落叶种的单位叶片面积成本(CCarea)显著低于3常绿种,但落叶和常绿物种的叶片质量成本(CCmass)差异不显著。落叶物种的叶氮、磷含量(Nmass,Pmass)和比叶面积(SLA)均显著高于常绿物种,而叶片寿命(LLS)显著低于常绿物种。CCarea与LLS呈显著正相关,Nmass、Pmass和SLA均与LLS呈显著负相关。这说明木兰科玉兰属落叶物种单位面积叶片构建成本小于常绿物种;落叶物种叶片寿命短,但采取低成本构建策略,提高比叶面积获得更多光资源,增加营养积累,也揭示了玉兰属落叶物种适应北亚热带较短的生长季和较低水热条件的生理生态策略。     

Water relations of indigenous versus exotic tree species,growing at the same site in a tropical montane forest in southern Ethiopia

The objective of the study was to compare the water relations of two indigenous [Podocarpus falcatus (Thunb.) Endl., Croton macrostachys Hochst. ex. Del.] and two exotic tree species (Eucalyptus globulus Labille., Cupressus lusitanica Miller) growing in the same location in the montane Munessa State Forest, southern Ethiopia. Stem flow was measured with Granier type thermal dissipation probes. Sap flux, normalized per unit sapwood area, and the total sapwood areas of the particular trees were used to estimate daily transpiration. Maximum daily transpiration values (60 kg water) were recorded for Croton when at full foliage. After shedding most of its leaves in the dry season transpiration was reduced to 8 kg per day. Eucalyptus had the next highest transpiration (55 kg), in this case at the peak of the dry season. It transpired 4–5 times more than Podocarpus and Cupressus trees of similar size. Maximum stem flux density was tree-size dependent only in Croton. Diurnal patterns of stem flux indicated that Croton, Eucalyptus and Podocarpus, in contrast to Cupressus, responded more directly to light than to atmospheric water pressure deficit. At high VPD (>1.0 kPa) stem flux reached a plateau in Croton and Podocarpus indicating stomatal limitation. Per unit leaf area Croton had the highest and Podocarpus and Cupressus the lowest daily transpiration rates. In summary, the pioneer tree Croton had the lowest and Podocarpus the highest water use efficiency. The contribution of the study to the understanding of the role of each tree species in the hydrology of the natural forest and the plantations is discussed.     

Weak relationships between leaf phenology and isohydric and anisohydric behavior in lowland wet tropical forest trees

Wet tropical forest trees display a wide range of leaf phenology dynamics. However, the interrelation between deciduousness, water status, and leaf and stem characteristics have been poorly investigated compared with dry forests. We studied wet forest trees to answer the following questions: (1) do water regulation modes (iso/anisohydric behavior) of evergreen species differ from those found in deciduous species? (2) Does leaf water potential (Ψ_L) influences leaffall and emergence dynamics? (3) Are leaf and stem characteristics consistent across evergreen and deciduous trees? We evaluated vegetative phenology, Ψ_L, and leaf and stem characteristics of six evergreen and three deciduous species monthly for 2 yr. Species exhibited different leaffall and emergence dynamics, as well as different water regulation modes, independent of their deciduousness. Thus, the relationship between leaf phenology and water regulation behaviors appears to be a species‐specific property rather than a functional group attribute. Ψ_L had no direct influence on the dynamics of leaffall and/or emergence, indicating that this process is not modulated by water availability alone. Individual groups of evergreen and deciduous species could not be identified using principal component analysis (PCA), but a decoupling was observed in the leaf and stem economics spectra. The lack of an interrelation between deciduousness and iso/anisohydry, as well as the independence of leaf and stem trade‐offs, emphasizes that more systematic measurements of vegetative phenology and ecophysiological characteristics are necessary to advance our knowledge of leaf habit and water regulation behaviors based on the functional traits of wet forest plants.     

Daily and seasonal courses of gas exchange and niche partitioning among coexisting tree species in a tropical montane forest

We investigated the seasonal gas exchange patterns of three different functional types of tropical afromontane trees, namely Podocarpus falcatus (Thunb.) Mirb. (evergreen gymnosperm), Prunus africana (Hook. f.) Kalkm. (broad-leaf evergreen), and Croton macrostachyus Hochst. ex Del. (broad-leaf deciduous) which grow side-by-side in the Munessa forest, southern Central Ethiopia. The hypothesis is that the trees can make different use of the environmental conditions which change seasonally and also from year to year. These changes can be understood as fluctuating niches, the utilization of which allows coexistence through balanced carbon gain. In this study, light and moisture were considered the two main fluctuating niches. Porometry was used to measure the daily and seasonal responses of the leaves to environmental variables under dry and wet season conditions in the course of the climatically differing years 2009 and 2010. Correlations of the patterns of these responses were analyzed by regression analysis. From daily integrated rates of irradiation, photosynthesis and transpiration, light and water use efficiencies of photosynthetic carbon gain and their mutual interdependences were determined. Except an extended dry season in 2009 when C. macrostachyus had shed its foliage, all three species continued photosynthetic net CO₂ uptake concomitant with transpiration at all seasons, although at varying rates. Ecophysiological performance of P. falcatus leaves is mainly light-driven and responds relatively little to a change in moisture conditions. Its carbon and water relations are striving for stability rather than flexibility. As of a typically subdominant species of the forest, P. africana leaves can efficiently use low light intensities but suffer from photoinhibition at full light. Their performance, showing more dynamic response to the environment than P. falcatus, P. africana appears driven more by moisture than by light. Compared to the two evergreens C. macrostachyus exhibited the highest flexibility in its leaves’ physiological responses to environmental conditions, in particular to the light climate which is additionally potentiated by the fast turnover of its foliage. This species optimizes its carbon gain during the wet season and during the early dry period when cloud cover is minimal. Our findings thus reveal that elasticity of the response to fluctuating environmental conditions is an additional aspect in the assessment of the utilization of temporally fluctuating niches by adult tree individuals.     

Leaf habit does not predict leaf functional traits in cerrado woody species

Plant species with a high leaf life span (LLS) commonly have a low specific leaf area (SLA), leaf nitrogen per unit mass (N), and phosphorous concentration (P), whereas species with low LLS have a high SLA, N and P. However, LLS tends to be longer in species growing in low-nutrient soils and, therefore, differences in LLS and other leaf traits may not be consistent with a plant classification according to leaf habit. Here we investigated whether leaf habit is consistent with leaf economic spectrum trade-offs in cerrado (a Neotropical savanna) woody species. We analyzed the SLA, N and P of 125 woody species with a distinct leaf habit (deciduous, semideciduous, brevideciduous or evergreen). We also gathered data on the LLS (33 species), maximum net photosynthesis per leaf area (A_area, 56 species) and per leaf mass (A_mass, 31 species), comprising the most extensive database analyzed so far for the cerrado. Differences among leaf habit groups were tested using generalized linear mixed models and ANOVA. We did not find differences in SLA and N among species with a distinct leaf habit, but deciduous species had a higher leaf P concentration than evergreens. Species did not differ in LLS and A_mass, but A_area varied among groups. Semideciduous species had higher A_area values than deciduous and brevideciduous species, but all other groups had similar A_area values. Because of the small difference in the LLS, SLA, leaf N, leaf P and maximum net photosynthesis, we argue that deciduous, brevideciduous, semideciduous and evergreen species may not constitute different functional groups in cerrado woody species.     

Acclimation responses of mature Abies amabilis sun foliage to shading

This paper addresses two main questions. First, can evergreen foliage that has been structurally determined as sun foliage acclimate physiologically when it is shaded? Second, is this acclimation independent of the foliage ageing process and source-sink relations? To investigate these questions, a shading and debudding experiment was established using paired branches on opengrown Abies amabilis trees. For each tree, one branch was either shaded, debudded, or both, from before budbreak until the end of summer, while the other branch functioned as a control. Foliage samples were measured both prior to and during treatment for photosynthesis at light saturation (A _max), dark respiration, nitrogen content, chlorophyll content, chlorophyll-to-nitrogen ratio and chlorophyll a:b ratio. All age classes of foliage responded similarly during the treatment, although pre-treatment values differed between age classes. Within 1 month after the treatment began, A _max was lower in shaded foliage and remained lower throughout the treatment period. For debudded branches, A _max was lower than the controls only during active shoot elongation. At the end of the treatments in September, A _max in shade-treated sun foliage matched the rates in the true shade-formed foliage, but nitrogen remained significantly higher. By 1.5 months after treatment, chlorophyll content in shaded foliage was higher than in controls, and the chlorophyll a:b ratio was lower for the shaded foliage. On debudded branches, chlorophyll content and chlorophyll a:b ratio were similar to the values in control samples. Shading lowered the rate of nitrogen accumulation within a branch, while removing debudding decreased the amount of sequestered N that was exported from the older foliage to supply new growth. By September, chlorophyll content in shade-treated foliage was higher than that in the control sun foliage or in true shade foliage. The chlorophyll increase as a result of shading was unexpected. However, the chlorophyll-to-nitrogen ratio was identical for the shade-treated sun foliage and the true shade foliage while being significantly lower than the control sun foliage. It appears that acclimation to shading in mature foliage involves a reallocation of nitrogen within the leaf into thylakoid proteins. A redistribution of resources (nitrogen) among leaves is secondary and appears to function on a slower time scale than reallocation within the leaf. Thus, A. amabilis foliage that is structurally determined as sun foliage can acclimate to shade within a few months; this process is most likely independent of ageing and is only slightly affected by source-sink relations within a branch.     

Foliage phenols and nitrogen in relation to growth,insect damage,and ability to recover after defoliation,in the mountain birch Betula pubescens ssp tortuosa

We studied growth of the mountain birch, and the role of foliage phenols, nitrogen, and variance in the timing of bud burst, as potential defensive characters, in Finnish Lapland in 1975–1979. Annual and local variation both in phenol and nitrogen concentration of foliage were significant. Individual trees retained their position in the foliage and nitrogen distribution of the population in successive years, as well as in the order of leaf flush in spring. Growth of twigs, mature leaf size, and ability of trees to recover in the year following artificial defoliation correlated positively with the sum of degree days in the previous growing season. Foliage nitrogen correlated negatively with foliage phenols in within-site comparisons. Twig growth correlated negatively with foliage phenols, particularly in growing seasons following cool summers, but did not correlate with foliage nitrogen. Birches flushing early did not grow more than birches flushing late. Between-site differences in foliage phenol content were mainly determined by abiotic conditions, like temperature and nutrient availability. In a between-site comparison insect chewing marks in leaves correlated positively with foliage phenols as well as with nitrogen; intensity of invertebrate predation presumably explained variable herbivory between the sites. In a within-site comparison trees with the highest foliage phenol content had few herbivores only at the site with the highest average phenol level.     

Quercus pubescens and its hemiparasite Loranthus europaeus: nutrient dynamics of leaves and twigs

Despite a long history of observations of the hemiparasitic plant, mistletoe, the mechanism of mineral movement from the host to the mistletoe is still not fully understood. In this article, we focused on the leaf development and nutrient dynamics of Loranthus europaeus and the host tree, Quercus pubescens. The nitrogen, potassium and calcium contents of leaves, current-year twigs and 1-year-old twigs were analysed. The timing of the leaf development differed between species. Leaf expansion occurred in the first 23 and 136?days, and leaf senescence took 78 and 24?days for Quercus and Loranthus, respectively. The similar nitrogen concentrations per unit leaf area may indicate that both species have the same assimilation rate. The differences in nutrient accumulation seem to support the hypothesis that nitrogen is the limiting nutrient in the transpiration stream. Larger differences in the nutrient dynamics between species were revealed in the accumulation potassium and calcium. Nutrients seemed to be transferred passively through the xylem sap between Loranthus and Quercus as we found a strong correlation between the calcium and potassium concentrations within the species and between the species. There was no correlation in the case of 1-year-old twigs, possibly due to the relatively small amount of nutrients incorporated into 1-year-old twigs and the fact that nutrient translocation occurs according the needs of the physiologically more active leaves and current-year-old twigs.     

Spatial and temporal variations in photosynthetic capacity of a temperate deciduous-evergreen forest

Key message

The understory evergreen trees showed maximal photosynthetic capacity in winter, while the overstory deciduous trees showed this capacity in spring. The time lag in productive ecophysiologically active periods between deciduous overstory and evergreen understory trees in a common temperate forest was clearly related to the amount of overstory foliage.

Abstract

In temperate forests, where deciduous canopy trees and evergreen understory trees coexist, understory trees experience great variation in incident radiation corresponding to canopy dynamics represented by leaf-fall and leaf-out. It is generally thought that changes in the light environment affect understory plants’ ecophysiological traits. Thus, to project and estimate annual energy, water, and carbon exchange between forests and the atmosphere, it is necessary to investigate seasonal variation in the ecophysiological activities of both evergreen trees in the understory and deciduous trees that make up the canopy/overstory. We conducted leaf-scale gas-exchange measurements and nitrogen content analyses for six tree species along their heights throughout a complete year. Photosynthetic capacity as represented by the maximum carboxylation rate (V _cmax25) and photosynthetic nitrogen use efficiency (PNUE) of deciduous canopy trees peaked immediately after leaf-out in late May, declined and stabilised during the mid-growing season, and drastically decreased just before leaf-fall. On the other hand, the timing of lowest V _cmax25 and PNUE for evergreen understory trees coincided with that of the highest values for canopy trees. Furthermore, understory trees’ highest values appeared just before canopy tree leaf-out, when incident radiation in the understory was highest. This implies that failing to consider seasonal variation in leaf ecophysiological traits for both canopy and understory trees could lead to serious errors in estimating ecosystem productivity and energy balance for temperate forests.

     

Understanding changes in black (Picea mariana) and white spruce (Picea glauca) foliage biomass and leaf area characteristics

Key message

Growth conditions related to inter-tree competition greatly influence black and white spruce foliage biomass and projected leaf area characteristics.

Abstract

Foliage characteristics such as biomass and area are important among other reasons because they can be related to tree growth. Despite their economic and ecologic importance, equations to characterize foliage biomass and projected area of black (Picea mariana (Miller) BSP) and white (Picea glauca (Moench) Voss) spruces are sparse. Total foliage biomass and projected leaf area, foliage biomass and leaf area density, and relative vertical distribution of black and white spruces foliage biomass and leaf area were modelled with linear and nonlinear mixed effect models. A total of 65 white spruces and 57 black spruces were destructively sampled at four different locations in Alberta, Québec, and Ontario, Canada. Our results show that for each species, total tree foliage biomass and projected leaf area is proportional to stem diameter, total height, and crown length. The addition of crown length in the equations improved the precision of the predictions of total foliage biomass for both species and diminishes greatly the site level random effect. An increase in DBH for black spruce and in the DBH to total height ratio for white spruce skewed the relative vertical foliage biomass distribution toward the base of the living crown. According to our results, growth conditions or tree development stage influence both foliage biomass and leaf area characteristics of black and white spruces. Our results emphasize the importance of inter-tree competition on foliage biomass characteristics.     

The phenology of leaf quality and its within‐canopy variation is essential for accurate modeling of photosynthesis in tropical evergreen forests

Leaf quantity (i.e., canopy leaf area index, LAI), quality (i.e., per‐area photosynthetic capacity), and longevity all influence the photosynthetic seasonality of tropical evergreen forests. However, these components of tropical leaf phenology are poorly represented in most terrestrial biosphere models (TBMs). Here, we explored alternative options for the representation of leaf phenology effects in TBMs that employ the Farquahar, von Caemmerer & Berry (FvCB) representation of CO₂ assimilation. We developed a two‐fraction leaf (sun and shade), two‐layer canopy (upper and lower) photosynthesis model to evaluate different modeling approaches and assessed three components of phenological variations (i.e., leaf quantity, quality, and within‐canopy variation in leaf longevity). Our model was driven by the prescribed seasonality of leaf quantity and quality derived from ground‐based measurements within an Amazonian evergreen forest. Modeled photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its vertical distribution within the canopy, with markedly more sensitivity to upper canopy leaf quality. This is because light absorption in tropical canopies is near maximal for the entire year, implying that seasonal changes in LAI have little impact on total canopy light absorption; and because leaf quality has a greater effect on photosynthesis of sunlit leaves than light limited, shade leaves and sunlit foliage are more abundant in the upper canopy. Our two‐fraction leaf, two‐layer canopy model, which accounted for all three phenological components, was able to simulate photosynthetic seasonality, explaining ~90% of the average seasonal variation in eddy covariance‐derived CO₂ assimilation. This work identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs that utilize the FvCB model of CO₂ assimilation and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.     

Periodicity of leaf growth and leaf dry mass changes in the evergreen and deciduous species of Southern Assam,India

The study described patterns of leaf dry mass change, leaf mass per area (LMA), relative growth rate and leaf life span (LL) for 14 evergreen and 7 deciduous species of a tropical forest of Southern Assam, India. Leaf expansion in both the groups was, in general, completed before June (i.e. well before the onset of monsoon rains). Although leaf dry mass during leaf initiation phase was significantly higher (P < 0.01) in evergreen species than in deciduous species, at the time of full leaf expansion, average leaf dry mass relative to the peak leaf dry mass, realised by the evergreen species was lower (66 %) than for deciduous species (76 %). Leaf dry mass increase in both groups continued after leaf full expansion. Evergreen species had a longer leaf dry mass steady phase than deciduous species (2–6 vs 2–3 months). Average LMA of mature leaves for evergreen species (77.43 g m^?2) was significantly greater than that of deciduous species (48.43 g m^?2). LL ranged from 165 days in Gmelina arborea (deciduous) to 509 days in Dipterocarpus turbinatus (evergreen). LMA was correlated positively with LL, indicating that evergreen species with higher leaf construction cost retain leaves for longer period to pay back. The average leaf dry mass loss before leaf shedding was greater (P < 0.01) for deciduous species (30.29 %) than for evergreen species (18.31 %). Although the cost of leaf construction in deciduous species was lower than for evergreen species, they replace leaves at a faster rate. Deciduous species perhaps compensate the cost involved in faster leaf replacement through higher reabsorption of dry mass during senescence, which they remobilise to initiate growth in the following spring when soil resources remain limiting.     

Global quantification of contrasting leaf life span strategies for deciduous and evergreen species in response to environmental conditions

Aim Species with deciduous and evergreen leaf habits typically differ in leaf life span (LLS). Yet quantification of the response of LLS, within each habit, to key environmental conditions is surprisingly lacking. The aim of this study is to quantify LLS strategies of the two leaf habits under varying temperature, moisture and nutrient conditions, using a global database. We hypothesize that deciduous LLS reflects the length of the growing season, avoiding unfavourable conditions regardless of the cause. Evergreen species adjust to unfavourable periods and amortize lower net carbon gains over several growing seasons, with increasing LLS associated with increasingly short favourable versus unfavourable season lengths. Location Global. Methods Data on LLS and environmental variables were compiled from global datasets for 189 deciduous and 506 evergreen species across 83 study locations. Individual and combined effects of measures of seasonality of temperature, water and nutrient availability on length of the growing season and on LLS were quantified using linear mixed models. The best models for predicting LLS were obtained using Akaike's information criterion (AIC) and ΔAIC. Results The LLS of deciduous and evergreen species showed opposite responses to changes in environmental conditions. Under unfavourable conditions, deciduous LLS decreases while evergreen LLS increases. A measure of temperature alone was the best predictor of the growing season. The LLS of deciduous species was independent of environmental conditions after expressing LLS in relation to the number of growing seasons. Evergreen species, on the other hand, adjusted to unfavourable conditions by increasing LLS up to four growing seasons. Contrary to expectations, variation in LLS was best explained solely by temperature, instead of by combined measures of temperature, moisture and nutrient availability. Shifts in the photosynthesis to respiration balance might provide a physiological explanation. Main conclusions Temperature, and not drought or nutrient availability, is the primary driver of contrasting responses of LLS for different leaf habit types.     

Relationship between intake of tannin-containing tropical tree forage,PEG supplementation,and salivary haze development in hair sheep and goats

The objective of this study was to estimate the relationship between tannin binding salivary protein (TBSP) and condensed tannins (CT) intake in hair sheep and creole goats. Foliage was obtained from trees with different levels of CT content; animals were offered foliage ad libitum, with or without polyethylene glycol (PEG). Saliva haze development (SHD) was evaluated as evidence for TBSP. PEG consumption did not affect dry matter intake (DMI) (P > 0.05). Lignin (R = −0.714, P < 0.001) and Crude Protein (CP) (R = 0.622, P < 0.001) contents had a stronger association with DMI than CT (R = 0.622, P < 0.011) in sheep; no significant association was found in goats. The positive relationship between tannin intake and SHD (P < 0.05) was not confirmed after PEG supplementation in sheep (P > 0.09), but remained significant for goats (P < 0.01), except for those fed Lysiloma latisiliquum (P = 0.07). Foliage lignin or CP contents are better predictors of foliage intake than CT. Sheep and goats fed with tropical tree forages containing different levels of tannins exhibited differences in intake behavior; moreover, individual variations in TBSP expression helps explaining foliage DMI.     

Variability,repeatability, character correlation and path coefficient analyses in yellow yam

Summary Phenotypic variances, genetic coefficients of variation, repeatability, expected genetic advance, correlation coefficients and path coefficients were estimated for seven agronomic traits in yellow yam. Plant leafiness, leaf virus infection, number of tubers per hill and tuber yield showed higher expected genetic advances associated with higher repeatability. Positive and highly significant correlations of tuber yield with plant leafiness, shoot height and vine dry weight were observed. Correlations of time to vine emergence and leaf virus infection with yield were negative. Path analysis showed that leaf virus infection had a large negative direct as well as indirect effect on yield. Based on these studies, it is suggested that resistance to leaf virus infection, as expressed by foliage vigour, is the chief criterion for selecting high yielding plant types in yellow yam.     

Caterpillar assemblages on Chusquea bamboos in southern Ecuador: abundance,guild structure,and the influence of host plant quality

1. Information on the guild structure of foliage‐associated tropical insects is scarce, especially as caterpillars are mostly considered only as herbivores feeding on living leaves. However, many caterpillar species display alternative trophic associations, feeding on dead or withered leaves or epiphylls (‘non‐herbivores’). 2. To determine the contribution of these non‐herbivores, caterpillar communities associated with Chusquea Kunth (Poaceae) in the Andes of southern Ecuador were investigated. Caterpillars were collected at two elevation levels (montane rainforest ～2000 m and elfin forest at ～3000 m a.s.l.) and assigned to three feeding guilds (strict herbivores, non‐herbivores, and switchers) based on feeding trials. Foliage quality and leaf area were recorded to test for their influence on guild composition and caterpillar density. 3. Three hundred and eighty‐nine individuals belonging to 175 Lepidoptera species associated with Chusquea bamboos were found. The species richness of caterpillars was similarly high at both elevation levels but varied between feeding guilds. Approximately half (46.5%) displayed an alternative feeding association, i.e. were non‐herbivores (31.1%) or switchers (15.4%). 4. Caterpillar density was nearly two‐fold higher in the elfin forest, but only strict herbivores and switchers increased significantly with elevation. Leaf area positively influenced the density of strict herbivores and switchers; foliage quality only affected strict herbivores. The density of non‐herbivores did not differ significantly between the forest types and was not related to leaf area or foliage quality. 5. The present study underpins that non‐herbivores make up a considerable fraction of caterpillar communities in tropical mountain ecosystems and demonstrates that elevation, foliage quality and available plant biomass further shape feeding guild composition.     

Foliage Density of Branches and Distribution of Plant‐Dwelling Spiders1

We compared the abundance of foliage‐living spiders among seven widespread plant species comprising a gradient of levels of structural complexity in a tropical savannah‐like region in southeastern Brazil. Spider abundance among plant species was positively related to the foliage density of their branches. A field experiment using artificial branches was carried out to isolate foliage density effects on spider abundance, thus controlling both biomass and texture effects. Artificial branches were attached to branches of three plant species with similar foliage density, Baccharis dracunculifolia, Diplusodon virgatus, and Microlicia fasciculata. Two treatments were set up: artificial branches with higher foliage density attracted more spiders than those with lower foliage density. The guild structure of hunting spiders was compared among vegetative branches of three plant species with different levels of foliage density: B. dracunculifolia, D. virgatus, and Bidens gardneri. Stalker, and ambusher spiders were more abundant on branches of B. dracunculifolia, which had the highest foliage density. Foliage‐runners constituted the dominant guild on D. virgatus and B. gardneri, which have lower foliage density branches. Our results suggest that branch architecture is the most important factor determining the abundance of plant‐dwelling spiders in the study area independently of branch biomass, leaf surface area or texture.     

Variability in water use efficiency at the leaf level among Mediterranean plants with different growth forms

Assessing natural variability of leaf water use efficiency in plants adapted to extreme conditions of the Mediterranean climate represents an important step in the evaluation of the usefulness of some plant ecophysiological traits under water stress. Eleven Mediterranean species naturally inhabiting the Balearic Islands and corresponding to different growth forms (herbs, semi-deciduous shrubs, woody evergreen shrubs and woody evergreen semi-shrubs) were subject to progressive soil water depletion. Leaf intrinsic water use efficiency was measured by gas exchange at four different degrees of water stress. Under well watered conditions, differences in leaf intrinsic water use efficiency (A _N/g _s) among growth forms were limited to woody evergreen semi-shrubs, which presented the highest values. Under water stress conditions, differences became more evident, with a trend for an increase in A _N/g _s from woody evergreen shrubs, through semi-deciduous shrubs and herbaceous to woody evergreen semi-shrubs. The observed variation in A _N/g _s correlated with several physiological (leaf water potential, soil to leaf hydraulic conductance and stomatal conductance) and morphological (stomatal density) parameters, displaying a general relationship for all growth forms. This suggests that the capacity for withstanding water limitation is adaptive for all Mediterranean species. However, when A _N/g _s was related to leaf mass area, this relationship was not generally applicable, and depended on growth forms, suggesting that different growth forms display specific morphological adjustments in response to water shortage.     

Foliage-canopy structure and height distribution of woody species in climax forests

The correlation between foliage-canopy structure and vertical woody species distribution was examined in seven climax forests ranging from alpine tree limit to tropical rain forest. Foliage density was measured by two-dimensional canopy tomography using photographs. Both foliage density and the vertical species density (the number of woody species having a maximum height within a vertical 1 m) were high in the upper canopy of warm-temperate and subtropical forests, but they were high at lower stratums in the tropical rain forest. Two variables correlated significantly despite the differences in foliage-canopy structures. In contrast to evergreen broad-leaved forests, a clear correlation could not be detected in northern cool-temperate and sub-alpine forests. A possible reason for species convergence in the foliage dense stratum is that species with maximum height in that stratum may be able to survive in the stratum due to symmetrical crown-to-crown interaction. If the maximum height of dwarf species is less than the foliage dense stratum, it may be difficult to survive in the community. The lack of correlation in northern forests may be due to poor canopy tree flora and a mixture of different life forms (non-sprouting trees and sprouting shrubs).     

Nitrogen addition drives convergence of leaf litter decomposition rates between <Emphasis Type="Italic">Flaveria bidentis</Emphasis> and native plant

Evidence is growing that invasive species can change decomposition rates and associated nutrient cycling within an ecosystem by changing the quality of the litter entering a system. However, the relative contribution of their distinct litter types to carbon turnover is less understood, especially in the context of enhanced N deposition. The objective of this study was to investigate the whole-plant responses of an invasive plant Flaveria bidentis in litter decay to simulated N eutrophication. A 1-year study was conducted to assess if N enhancement influenced decomposition and nutrient dynamics of litters from foliage, fine roots and twigs of F. bidentis compared to co-occurring native species Setaria viridis. N fertilization significantly decreased the decomposition rate of the foliage of the invasive F. bidentis by more than 25% relative to the water control, but had relatively minor effects on decomposition of its twigs and fine root litter or leaf litter from the native species. Collectively, decomposition rates of foliar litters of the invasive and native species become convergent over time in the presence of N addition. Moreover, net N loss was predominately influenced by litter species, followed by the litter type, while N addition had little effect on net N loss. Our study showed that the variation in litter decomposition was much greater between litter types of the invasive F. bidentis than between different plant species under the N addition and that the litter of invasive species with higher inherent decomposability did not always decompose more rapidly than the litter of native species in response to predicted N deposition enhancement.