Seasonal variation in insect abundance among three Australian rain forests,with particular reference to phytophagous types

Monthly sweep net and light trap samples were used to examine seasonal changes in the abundance of insects in subtropical, warm and cool temperate rain forest in New South Wales. Maximum insect abundance, especially of phytophages, coincided with leaf flushing in the canopy trees. Cool temperate insect numbers were highest during the month just following the beech leaf flush, a rapid and synchronous growth event. Conversely, numbers of subtropical insects fluctuated over a longer period, in a pattern similar to the continuous growth of leaves that occurred throughout spring and summer there. The warm temperate was intermediate in its vegetation growth phenology and insect patterns. Rainforest insect abundance varied both temporally and spatially.     

Dependence of Asian honeybee on deciduous woody plants for pollen resource during spring to mid‐summer in northern Japan

Apis cerana japonica Radoszkowski, endemic to Japan, is known to be one of the most important pollinators for wild plants and crops, such as buckwheat, in cool to warm temperate Japan. To determine the degree of dependence of A. cerana japonica on forest resources, we analyzed pollen brought back to nests in a typical “Satoyama” landscape with relatively high deciduous forest coverage in northern Japan. We divided the landscape elements of the study area into three types: deciduous forest, conifer plantation and open land according to landcover digital data, and each pollen taxon was assigned to one of these three types of landscape elements. We collected total pollen loads of 15.75 g (total of colonies A and B) in May (spring), 1.57 g (total of colonies A and C) in June (early summer), 19.03 g (total of colonies A, B and C) in July (mid‐summer) and 45.61 g (total of colonies A, B and D) in September (autumn). Deciduous forests are the most important foraging habitats for A. cerana japonica in the “Satoyama” landscape especially from spring to mid‐summer when mass flowering of tall trees and shrubs species provides rich floral resources for developing bee colonies. On the other hand, the bees frequently foraged from herbaceous plant species in autumn when flowering of tree species reduces and herbaceous plant species have flowering peaks. In turn, the bees provide pollination services to a number of wild flowers blooming in various forest layers ranging from the canopy to the understory layer.     

Fruiting and flushing phenology in Asian tropical and temperate forests: implications for primate ecology

In order to understand the ecological adaptations of primates to survive in temperate forests, we need to know the general patterns of plant phenology in temperate and tropical forests. Comparative analyses have been employed to investigate general trends in the seasonality and abundance of fruit and young leaves in tropical and temperate forests. Previous studies have shown that (1) fruit fall biomass in temperate forest is lower than in tropical forest, (2) non-fleshy species, in particular acorns, comprise the majority of the fruit biomass in temperate forest, (3) the duration of the fruiting season is shorter in temperate forest, and (4) the fruiting peak occurs in autumn in most temperate forests. Through our comparative analyses of the fruiting and flushing phenology between Asian temperate and tropical forests, we revealed that (1) fruiting is more annually periodic (the pattern in one year is similar to that seen in the next year) in temperate forest in terms of the number of fruiting species or trees, (2) there is no consistent difference in interannual variations in fruiting between temperate and tropical forests, although some oak-dominated temperate forests exhibit extremely large interannual variations in fruiting, (3) the timing of the flushing peak is predictable (in spring and early summer), and (4) the duration of the flushing season is shorter. The flushing season in temperate forests (17–28 % of that in tropical forests) was quite limited, even compared to the fruiting season (68 %). These results imply that temperate primates need to survive a long period of scarcity of young leaves and fruits, but the timing is predictable. Therefore, a dependence on low-quality foods, such as mature leaves, buds, bark, and lichens, would be indispensable for temperate primates. Due to the high predictability of the timing of fruiting and flushing in temperate forests, fat accumulation during the fruit-abundant period and fat metabolization during the subsequent fruit-scarce period can be an effective strategy to survive the lean period (winter).     

Temperate tree expansion into adjacent boreal forest patches facilitated by warmer temperatures

Temperate and boreal forests are forecast to change in composition and shift spatially in response to climate change. Local‐scale expansions and contractions are most likely observable near species range limits, and as trees are long‐lived, initial shifts are likely to be detected in the understory regeneration layers. We examined understory relative abundance patterns of naturally regenerated temperate and boreal tree species in two size classes, seedlings and saplings, and across two spatial scales, local stand‐scale ecotones (tens of meters) and the regional temperate–boreal transition zone (?250 km) in central North America, to explore indications of climate‐mediated shifts in regeneration performance. We also tested for the presence of strong environmental gradients across local ecotones that might inhibit species expansion. Results showed that tree regeneration patterns across ecotones varied by species and size class, and varied across the regional summer temperature gradient. Temperate tree species regeneration has established across local ecotones into boreal forest patches and this process was facilitated by warmer temperatures. Conversely, boreal conifer regeneration exhibited negative responses to the regional temperature gradient and only displayed high abundance at the boreal end of local ecotones at cool northern sites. The filtering effects of temperature also increased with individual size for both boreal and temperate understory stems. Observed regeneration patterns and the minor environmental gradients measured across local ecotones failed to support the idea that there were strong barriers to potential temperate tree expansion into boreal forest patches. Detectable responses, consistently in the directions predicted for both temperate and boreal species, indicate that summer temperature is likely an important driver of natural tree regeneration in forests across the temperate–boreal transition zone. Regeneration patterns point toward temperate expansion and reduced but continued boreal presence in the near‐future, resulting in local and regional expansions of mixed temperate‐boreal forests.     

From observations to experiments in phenology research: investigating climate change impacts on trees and shrubs using dormant twigs

Background and Aims Climate change is advancing the leaf-out times of many plant species and mostly extending the growing season in temperate ecosystems. Laboratory experiments using twig cuttings from woody plant species present an affordable, easily replicated approach to investigate the relative importance of factors such as winter chilling, photoperiod, spring warming and frost tolerance on the leafing-out times of plant communities. This Viewpoint article demonstrates how the results of these experiments deepen our understanding beyond what is possible via analyses of remote sensing and field observation data, and can be used to improve climate change forecasts of shifts in phenology, ecosystem processes and ecological interactions.Scope The twig method involves cutting dormant twigs from trees, shrubs and vines on a single date or at intervals over the course of the winter and early spring, placing them in containers of water in controlled environments, and regularly recording leaf-out, flowering or other phenomena. Prior to or following leaf-out or flowering, twigs may be assigned to treatment groups for experiments involving temperature, photoperiod, frost, humidity and more. Recent studies using these methods have shown that winter chilling requirements and spring warming strongly affect leaf-out and flowering times of temperate trees and shrubs, whereas photoperiod requirements are less important than previously thought for most species. Invasive plant species have weaker winter chilling requirements than native species in temperate ecosystems, and species that leaf-out early in the season have greater frost tolerance than later leafing species.Conclusions This methodology could be extended to investigate additional drivers of leaf-out phenology, leaf senescence in the autumn, and other phenomena, and could be a useful tool for education and outreach. Additional ecosystems, such as boreal, southern hemisphere and sub-tropical forests, could also be investigated using dormant twigs to determine the drivers of leaf-out times and how these ecosystems will be affected by climate change.     

Beta-diversity of lepidopteran larval communities in a Japanese temperate forest: effects of phenology and tree species

The specialization of herbivores among tree species is poorly understood despite its fundamental importance as a factor regulating diversity. To examine the effect of tree species on larval community structure, the larval communities in 10 temperate deciduous tree species that differed in leaf emergence pattern (flush- vs. intermediate-type) were seasonally surveyed. The newly developed soft, nitrogen-rich leaves of all species became tough and nitrogen-poor as the season progressed. Following the changes in leaf quality, two distinct seasonal lepidopteran larval communities emerged, with a marked turnover in early July. The beta diversity, or dissimilarity, of species composition in the larval communities among tree species was higher in summer than in spring. These results imply that the lepidopteran larval communities as a whole were supported by alpha diversity in spring and by beta diversity in summer, demonstrating that the plant diversity of this forest could support a caterpillar community. We examined the importance of spatio-temporal variations in leaf quality within and among tree species in promoting herbivore diversity, although other factors, such as tree species phylogeny and predators, may also have a large effect on lepidopteran larval communities.     

Seasonal patterns in species richness of herbivores: Macrolepidopteran larvae on Finnish deciduous trees

Abstract. 1. The seasonal distribution of macrolepidopteran species richness on Finnish deciduous trees vaned from positively skewed (peak in spring) to negatively skewed (peak in autumn).
2. The skewness values of species richness had a significant negative correlation ( r = - 0.98) with the duration of the seasonal shoot-growth period of the tree species.
3. Trees which complete their shoot growth early in the season ( Quercus type) produce new leaves only during spring, while trees whose shoot growth continues to autumn ( Populus type) do so throughout the summer.
4. Consequently, there is a difference in the number of available resources in the late summer foliage of different tree species, Trees ceasing leaf production early such as oak ( Quercus robur ) and bird cherry ( Prunus padus ) have one major resource type (mature leaves) in late-season foliage while trees like birches and alders have two Ooung and mature leaves).
5. Because young leaves formed late in the season are preferred to mature ones by some species of herbivores and because other species prefer mature leaves at the same time, the species richness of Populus-type trees is higher later in the season than the species richness of Quercus-type of trees, which have just one type of resource available.     

Radial growth response of trees to seasonal soil humidity in a subtropical forest

Tree growth is the most important factor in determining the carbon sequestration processes of forest ecosystems. However, the growth phenology (seasonal growth pattern) and responses of tree growth to climatic variables vary considerably among different species, especially between deciduous and evergreen species. Thus, it is crucial to explore the seasonal growth patterns of different tree species in relation to climate to better understand the responses of tree physiology to climate changes, especially in mixed-species forest stands. In this study, we monitored the daily basal area increments of 220 individuals belonging to 15 common broadleaved tree species, nine deciduous and six evergreen species, in mixed-species experimental stands in subtropical China and analysed the relationships between radial stem growth and seasonal climate at a high-temporal resolution. We fitted daily increments of stem diameters with four frequently used nonlinear models and chose the best model for each species. The results showed that the evergreen trees grew faster than the deciduous trees, both annually and within the growing season. The tested nonlinear models (Korf, Weibull, logistic and Gompertz) produced good fits for the growth patterns of all species. Overall, the evergreen species began stem growth earlier and finished later during the growing season than that of the deciduous species. Within the growing season, the radial growth of trees in mixed stands containing both types of species was strongly positively correlated with humidity. In spring, increases in both temperature and moisture increased the daily relative basal area increment of all species. Maximum growth rates occurred when the soil water content reached its highest level and gradually decreased when the soil water content decreased. In summer, high temperatures combined with low amounts of precipitation led to heat-induced summer drought, to which the evergreen trees appeared to be more tolerant than the deciduous trees, which was reflected in the reduced stem growth of the latter. These results indicate the different climate-dependent seasonal growth strategies of evergreen and deciduous trees related to the trade-off described by the leaf economics spectrum, i.e., short-lived leaves with higher assimilation rates in deciduous and longer-lived leaves with a greater drought tolerance in evergreen species.     

Comparison between phenological and aerobiological patterns of some arboreal species of Mar del Plata (Argentina)

An atmospheric pollen survey and a periodical quantitative check of the flowering phases of trees were performed during 1993. Most of specific flowering seasons lasted from 4 to 8 weeks. October is the month with the highest number of species in bloom. Anemophylous species flower mainly in coincidence with the relatively low temperatures of late winter and early spring, while the enthomophylous ones correlate with the high temperatures of late spring and summer. The anemophylous ‘community’ follow a sigmoid pattern with respect to both the flowering development and the cumulative pollen concentration. Agreement between floral phenophases and pollen counts were evaluated for 14 genera (27 species). Pollen data of anemophylous species coincide fairly well with the phenological behaviour. Particular features must be taken into account to interpret this relationship.     

Why does Viola hondoensis (Violaceae) shed its winter leaves in spring?

? Premise of the study: Viola hondoensis is a perennial herb that inhabits the understory of temperate, deciduous forests. It is an evergreen plant with a leaf life span that is shorter than a year. Its summer leaves are produced in spring and shed in autumn; winter leaves are produced in autumn and shed in spring. Here we asked why the plant sheds its winter leaves in spring, though climate conditions improve from spring to summer. We proposed four hypotheses for the cause of shedding: (1) changes in seasonal environment such as day length or air temperature, (2) shading by canopy deciduous trees, (3) self-shading by taller summer leaves, and (4) competition for nutrients between summer and winter leaves. ? Methods: To test these hypotheses, we manipulated the environment of winter leaves: (1) plants were transplanted to the open site where there was no shading by canopy trees. (2) Petioles of summer leaves were anchored to the soil surface to avoid shading of winter leaves. (3) Sink organs were removed to eliminate nutrient competition. ? Key results: Longevity of winter leaves was extended when shading by summer leaves was eliminated and when sink organs were removed, but not when plants were transplanted to the open site. ? Conclusion: We conclude that the relative difference in light availability between summer and winter leaves is a critical factor for regulation of leaf shedding, consistent with the theory of maximization of the whole-plant photosynthesis.     

Different flowering phenology of alien invasive species in Spain: evidence for the use of an empty temporal niche?

Flowering phenology is an important and poorly understood plant trait that may possibly be related to the invasiveness potential of alien species. The present work evaluates whether flowering time of invasive alien species is a key trait to overcome the climatic filters operating in continental Mediterranean ecosystems of Spain (characterised by summer drought and low temperatures in winter). We conducted comparisons between the flowering phenology of the invasive species in their native range and in Spain, and between flowering phenology of 91 coexisting invasive–native species pairs. For the alien species, geographical change from the native to the invaded region did not result in shifts in the start and the length of the flowering period. Overall, climatic conditions in the native range of species selected for a flowering pattern is maintained after translocation of the species to another region. Flowering of tropical and temperate invasive alien species peaked in summer, which contrasts with the spring flowering of native and invasive alien species of Mediterranean climate origin. By exploiting this new temporal niche, these invasive alien species native to tropical and temperate regions benefit from reduced competition with natives for abiotic and biotic resources. We suggest that human-mediated actions have reduced the strength of the summer drought filter in particular microhabitats, permitting the invasion of many summer-flowering aliens.     

Browse on mahoe and kamahi leaf-fall as a trigger for possum control

Introduced brushtail possums (Trichosurus vulpecula) are controlled over large parts of New Zealand to protect canopy trees. The condition of canopy trees is one of the cues used to trigger possum control, but selecting an indicator of canopy tree condition is difficult because many factors unrelated to possum browsing can affect canopy condition, and indices based on canopy scoring may not always quickly detect real changes in possum herbivory. We therefore investigated the usefulness of the percentage of fallen mahoe (Melicytus ramiflorus) and kamahi (Weinmannia racemosa) leaves browsed by possums (‘fallen-leaf browse’ or ‘FLB’) as a trigger for control aimed at protecting these tree species. We collected leaves falling from kamahi and mahoe trees every two months for two years at two study areas in the central North Island, one with initially high possum abundance (Oriuwaka) and the other with low possum abundance (Otupaka). We classified each of 92 384 leaves as either not-browsed, possum-browsed or insect-browsed. There was a strong and similar seasonal pattern in the mean number of fallen leaves per tree for both mahoe and kamahi at both study areas; fewest leaves fell in winter, and the most leaves fell in spring and early summer. Mahoe and kamahi FLB exhibited a similar seasonal pattern at both areas, being lowest in winter and highest in spring and early summer. FLB for both mahoe and kamahi declined following control of possums to low densities at Oriuwaka. The proportion of fallen mahoe and kamahi leaves browsed by possums was small compared with those browsed by insects or not browsed. We show that spring/early summer (i.e. September–December) is the best period for sampling FLB and that the mean FLB can be estimated with a CV of 20% if one trap is randomly placed under the canopy of each of 24 randomly located trees. However, CVs were much larger in other seasons and when possum abundance was low. We consider FLB to be a sensible trigger for initiating possum control when the objective of control is to protect canopy trees, but further work is needed to determine the relationships between possum abundance, FLB, canopy condition, and key tree demographic rates.     

A season- and gap-detection mechanism regulates seed germination of two temperate forest pioneers

The survival of seedlings in temperate climate habitats depends on both temporal and spatial factors. The interaction between an internal seed dormancy mechanism and the ruling environmental conditions allows accurate cueing of germination. We analysed how environmental signals interact in seeds of temperate forest pioneer species, increasing the seed's chances of germinating in the right place at the right time. Digitalis purpurea and Scrophularia nodosa are two small-seeded herbaceous species that typically grow in vegetation gaps in European temperate forests. Seeds of both species are partially dormant at the time of dispersal in summer. This primary dormancy is released in autumn and early winter, resulting in a minimal level of physiological dormancy by late winter and early spring. We observed that physiological dormancy was induced again in seeds exhumed in late spring and in summer. Experiments in laboratory conditions revealed that primary dormancy in seeds of S nodosa was broken by cold stratification, whereas primary dormancy in D. purpurea seeds was broken by both a cold and a warm stratification. The two species differed in their response to the tested gap-detection signals, as light was the most important factor stimulating germination of D. purpurea, and seeds of S. nodosa germinated best when subjected to daily fluctuating temperatures. This study clearly indicates that the ability to germinate in response to gap-detection signals changes seasonally in temperate forest pioneers. Additionally, seeds of both species responded differently to these environmental signals, probably reflecting differences in the regeneration niche.     

Microclimatic Changes Induced by Ecological Restoration of Ponderosa Pine Forests in Northern Arizona

Restoration of ponderosa pine ecosystems results in altered stand structure, potentially affecting microclimatic conditions and habitat quality for forest organisms. This research focuses on microclimatic changes resulting from forest and landscape structural alterations caused by restoration treatments in southwestern ponderosa pine forests. Three microclimate variables—light intensity, air temperature, and vapor pressure deficit (VPD)—were monitored over two field seasons. Differences in microclimate between the treated forest and the surrounding untreated forest were measured, and microclimatic gradients across the structural edge between these two forest types were quantified. Restoration treatments increased sunlight penetration to the forest floor but did not significantly impact ambient air temperature or VPD. Mean values for air temperature and VPD did not differ significantly between treatments, although temperature and vapor pressure deficit did exhibit a trend in the morning; both variables were higher at the structural edge and in the treated forest during morning hours. Significant edge gradients were detected for air temperature and VPD in the morning and evening, increasing from the structural edge into the untreated forest. Our results show that microclimatic effects of these restoration treatments are generally modest, but the changes are more prominent at specific locations and during certain times of day. Because even modest changes in microclimate have the potential to impact a range of key ecological processes, microclimatic effects should be considered when forest restoration treatments at the landscape scale are being planned and implemented.     

Flowering phenology and reproduction of a forest understorey plant species in response to the local environment

Temperate forest understorey plants are subjected to a strong seasonality in their optimal growing conditions. In winter and early spring, low temperatures are suboptimal for plant growth while light becomes limited later in spring season. We can thus expect that differences in plant phenology in relation to spatiotemporal environmental variation will lead to differences in reproductive output, and hence selection. We specifically studied whether early flowering, a paradoxical pattern that is observed in many plant species, is an adaptive strategy, and whether selection for early flowering was confounded with selection for flower duration or was attributable to environmental variables. We used Geum urbanum as a study species to investigate the effect of relevant environmental factors on the species’ flowering phenology and the consequences for plant reproductive output. We monitored the phenology of four to six plants in each of ten locations in a temperate deciduous forest (Belgium). We first quantified variation in flowering time within individuals and related this temporal variation to individual flower reproductive output. Then, we studied inter-individual variation here-in and linked this to reproduction at the plant level, hence studying the selection differential. We found that flowering within individual plants of Geum urbanum was spread over a long period from June to October. Reproductive output of individual flowers, measured as total seed mass per flower, declined during the season. We found no indication for selection for early flowering but rather for longer flower duration. Larger plants had an earlier flowering onset and a higher seed mass, which suggests that these factors covary and are condition dependent. None of the studied environmental variables could explain plant size, although soil pH and to a lesser extent light availability had a positive direct effect on seed mass per plant. Finally, we suggest that the high intra-individual variation in flowering time, which might be a risk spreading strategy of the plant in the presence of seed predation, limits the potential for selection on flowering phenology.

     

Seasonal changes in foliar macronutrients (N,P, K,Ca and Mg) inEucalyptus saligna Sm. andE. wandoo Blakely growing in rehabilitated bauxite mine soils of the Darling Range,Western Australia

Summary Seasonal changes in the foliar concentration of macronutrients (N, P, K, Ca and Mg) in sapling trees ofEucalyptus saligna Sm. andE. wandoo Blakely growing in rehabilitated bauxite mined areas in the Darling Range of Western Australia are described. Foliar N concentration decreased with age of the fully expanded leaf tissue. Leaf N concentrations were also high when rates of litter decomposition were expected to be high during the period of early spring. The greatest foliar N difference between trees growing in good soil conditions and those from poorer soil conditions also occurred during this period. Levels of P in leaves were highest in young developing leaves but once the leaves reached full size, no seasonal trend in P concentration was observed. Foliar K was lower during the winter and probably related to the period of maximum leaching by precipitation. High foliar K during summer, however, could be related to the role of K in lowering cellular water potential. Leaf Ca was highest during early sping. Low mobility of cellular Ca during the cool portion of the year was indicated. Foliar Mg showed a weak pattern of decreasing concentration with leaf age. The best season for sampling for these broadleafed evergreen species to provide information on plant nutrient status appears to be in spring.     

Bud Structure and Shoot Architecture of Canopy and Understorey Evergreen Broad-leaved Trees at their Northern Limit in East Asia

The morphology of winter buds, shoot growth and branching architecturewas studied in evergreen broad-leaved trees of subtropical/warm-temperaterain forests of southern and central Japan. Winter buds werecategorized into three types based on external morphology anddevelopmental processes: naked, hypsophyllary and scaled buds.Each shoot tip with intermittent growth was covered with a smallnumber of immature leaves or hypsophylls when growth ceased.Hypsophylls protect the apical meristem during its resting period,hence we termed them hypsophyllary buds. In trees with nakedbuds, immature leaves resumed their growth and developed tomature leaves the following spring; thus these trees had nospecial organs to cover shoot tips during winter. In trees withhypsophyllary buds, some hypsophylls covering the shoot tipsthrough the year were shed without further growth when new shootsstarted to grow in the spring. In trees with scaled buds, newlygrowing shoots had hypsophyllary buds at their tips in spring.After the completion of stem elongation, the buds were replacedby scaled buds (often covered with more than 30 scales) in summer.These scaled buds grew during autumn and winter until a newflush of growth the following spring. The three bud types correspondedto forest stratification in the northern-limit forest: the nakedbuds of Rubiaceae and Myrsinaceae in the ground layer; the hypsophyllarybuds of various families (e.g. Symplocaceae, Myrsinaceae) inthe understorey; and the scaled buds of Fagaceae and Lauraceaein the forest canopy. The position and activity of buds on abranch were reflected in the architectural patterns of the treesin different layers of the forest. The scaled-bud trees hadwell-protected, abundant axillary buds and are probably suitedto survive in the forest canopy (with frequent disturbances),whereas the single terminal bud of hypsophyllary-bud trees cansurvive in the less disturbed, resource-limited understoreyof the forest.Copyright 1998 Annals of Botany Company Bud structural type; bud formation; bud growth; shoot elongation; shoot-growth cycle; branching architecture; forest stratification.     

Temperature alone does not explain phenological variation of diverse temperate plants under experimental warming

Anthropogenic climate change has altered temperate forest phenology, but how these trends will play out in the future is controversial. We measured the effect of experimental warming of 0.6–5.0 °C on the phenology of a diverse suite of 11 plant species in the deciduous forest understory (Duke Forest, North Carolina, USA) in a relatively warm year (2011) and a colder year (2013). Our primary goal was to dissect how temperature affects timing of spring budburst, flowering, and autumn leaf coloring for functional groups with different growth habits, phenological niches, and xylem anatomy. Warming advanced budburst of six deciduous woody species by 5–15 days and delayed leaf coloring by 18–21 days, resulting in an extension of the growing season by as much as 20–29 days. Spring temperature accumulation was strongly correlated with budburst date, but temperature alone cannot explain the diverse budburst responses observed among plant functional types. Ring‐porous trees showed a consistent temperature response pattern across years, suggesting these species are sensitive to photoperiod. Conversely, diffuse‐porous species responded differently between years, suggesting winter chilling may be more important in regulating budburst. Budburst of the ring‐porous Quercus alba responded nonlinearly to warming, suggesting evolutionary constraints may limit changes in phenology, and therefore productivity, in the future. Warming caused a divergence in flowering times among species in the forest community, resulting in a longer flowering season by 10‐16 days. Temperature was a good predictor of flowering for only four of the seven species studied here. Observations of interannual temperature variability overpredicted flowering responses in spring‐blooming species, relative to our warming experiment, and did not consistently predict even the direction of flowering shifts. Experiments that push temperatures beyond historic variation are indispensable for improving predictions of future changes in phenology.     

全球森林土壤微生物生物量碳氮磷化学计量的季节动态

土壤微生物生物量在森林生态系统中充当具有生物活性的养分积累和储存库。土壤微生物转化有机质为植物提供可利用养分, 与植物的相互作用维系着陆地生态系统的生态功能。同时, 土壤微生物也与植物争夺营养元素, 在季节交替过程和植物的生长周期中呈现出复杂的互利-竞争关系。综合全球数据对温带、亚热带和热带森林土壤微生物生物量碳(C)、氮(N)、磷(P)含量及其化学计量比值的季节动态进行分析, 发现温带和亚热带森林的土壤微生物生物量C、N、P含量均呈现夏季低、冬季高的格局。热带森林四季的土壤微生物生物量C、N、P含量都低于温带和亚热带森林, 且热带森林土壤微生物生物量C含量、N含量在秋季相对最低, 土壤微生物生物量P含量四季都相对恒定。温带森林的土壤微生物生物量C:N在春季显著高于其他两个森林类型; 热带森林的土壤微生物生物量C:N在秋季显著高于其他2个森林类型。温带森林土壤微生物生物量N:P和C:P在四季都保持相对恒定, 而热带森林土壤微生物生物量N:P和C:P在夏季高于其他3个季节。阔叶树的土壤微生物生物量C含量、N含量、N:P、C:P在四季都显著高于针叶树; 而针叶树的土壤微生物生物量P含量在四季都显著高于阔叶树。在春季和冬季时, 土壤微生物生物量C:N在阔叶树和针叶树之间都没有显著差异; 但是在夏季和秋季, 针叶树的土壤微生物生物量C:N显著高于阔叶树。对于土壤微生物生物量的变化来说, 森林类型是主要的显著影响因子, 季节不是显著影响因子, 暗示土壤微生物生物量的季节波动是随着植物其内在固有的周期变化而变化。植物和土壤微生物密切作用表现出来的对养分的不同步吸收是保留养分和维持生态功能的一种权衡机制。     

The resource balance of Milium effusum with emphasis on environmental resource supply

Summary Growth of the broad-leaved graminoid Milium effusum, occurring in shady deciduous forests, was matched with periods of high light influx through the tree canopy in spring and autumn. Fertile shoots grew faster than sterile shoots. Leaves on flowering shoots were fully developed when the budbreak started on the trees, whereas nonflowering shoots had fully developed leaves when the tree canopy closed. Leaf concentrations of N and P were high (6.1 and 0.74% respectively) in spring but decreased as the leaves expanded. Maximum pool sizes of N and P in whole tillers were reached about one month after the onset of spring growth, whereas maximum spring pools of K, Mg, and Ca were timed with peak biomass about one month later. The leaves lost nutrients during summer when no growth took place. Since leaching losses were negligible, nutrients were probably allocated from the leaves to support root growth. Autumn reallocation to winter stores was low. The pattern of growth and nutrient use suggests that light availability, i.e., the resource in relatively lowest supply, regulates the investment of the resource in highest supply, i.e., nutrients. This is consistent with previously reported observations on Eriophorum vaginatum, a graminoid of low nutrient — high light environments. This species utilizes nutrients efficiently at the expense of less efficient acquisition of carbon. We suggest that selection for efficient utilization of the resource in lowest relative supply has been a strong driving force behind the physiological adaptation of both species to their environments.