湘南典型次生林粗木质残体生物量、碳储量和养分特征

对九龙江森林公园次生常绿阔叶林粗木质残体(CWD)进行量化研究,了解亚热带典型次生林CWD的本底数据。以九龙江森林公园典型天然次生林中的6个20m×20m的标准样地为对象,调查并分析样地内不同分解等级CWD的生物量、碳储量和养分特征变化。九龙江森林公园亚热带典型次生林的CWD储量在2.8—30.4t/hm~2之间,碳储量在6.10—6.75t/hm~2之间,大量营养元素(N、P、K、 Ca、 Mg)含量相对稳定,化学计量变化不显著,微量营养元素中Pb与Cd元素含量随着分解等级的增加而增加。九龙江森林公园亚热带典型次生林的CWD储量在亚热带常绿阔叶林中处于中等水平,CWD主要以分解中后期的倒木为主,反映出该次生林处于中幼龄林阶段,具有较高的碳储量,养分含量相对稳定,并表现出Pb与Cd在CWD中积累的现象,在中度分解和重度分解的CWD中Pb含量分别增加了62.65%和69.88%,Cd含量则分别增加了33.33%和100%,其内在机理有待进一步深入研究。研究结果有助于进一步了解CWD如何参与森林生态系统养分循环、重金属积累等生态过程,比较不同林分干扰历史下CWD储量、分布及养分特征的异质性...     

Effects of woody plant species richness on mammal species richness in southern Africa

Aim To determine the relationship between the species richness of woody plants and that of mammals after accounting for the effect of environmental variables. Location Southern Africa, including Namibia, South Africa, Lesotho, Swaziland, Botswana, Zimbabwe, and part of Mozambique. Methods We used a comprehensive dataset including the species richness of mammals and of woody plants and environmental variables for 118 quadrats (each of 25,000 km²) across southern Africa, and used structural equation models (SEMs) and spatial regressions to examine the relationship between the species richness of woody plants and of mammal trophic guilds (herbivores, insectivores, carni/omnivores) and habitat guilds (aquatic/fossorial, ground‐living, climbers, aerial), after controlling for environment. We compared the results of SEMs with those of single‐predictor regressions (without controlling for environment) and of spatial regressions (controlling for both environment and residual spatial autocorrelation). Results The geographical variation of mammal species richness in southern Africa was strongly and positively related to that of woody plant species richness, and this relationship held for most mammal guilds even when the influence of environment and spatial autocorrelation had been accounted for. However, the effect of woody plant species richness on the richness of aquatic/fossorial species almost disappeared after controlling for environment, suggesting that the congruence in species richness patterns between these two groups results from similar responses to the same environmental variables. For many mammal guilds, the relative role of environmental predictors as measured by standardized partial regression coefficients changed depending on whether non‐spatial single‐predictor regressions, non‐spatial SEMs, or spatial regressions were used. Main conclusions Woody plants are important determinants of the species richness of most mammal guilds in southern Africa, even when controlling for environment and residual spatial autocorrelation. Environmental correlates with animal species richness as measured by simple correlations or single‐predictor regressions might not always reflect direct effects; they might, at least to some degree, result from indirect effects via woody plants. Interpretations of the strength of the effect of environmental variables on mammal species richness in southern Africa depend largely on whether spatial or non‐spatial models are used. We therefore stress the need for caution when interpreting environmental ‘effects’ on broad‐scale patterns of species richness if spatial and non‐spatial methods yield contrasting results.     

Mycorrhiza formation and nutrient concentration in leeks (Allium porrum) in relation to previous crop and cover crop management on high P soils

An improved integration of mycorrhizas may increase the sustainability in plant production. Two strategies for increasing the soil inoculum potential of mycorrhizal fungi were investigated in field experiments with leeks: Pre-cropping with mycorrhizal main crops and pre-establishment of mycorrhizal cover crops. Experiments on soils with moderate to high P content (26–50 mg kg^–1 bicarbonate-extractable P) showed that the previous crop influenced mycorrhiza formation, uptake of P, Zn, and Cu, and early growth of leek seedlings. A cover crop of black medic, established the previous autumn, increased the colonization of leek roots by mycorrhizal fungi. During early growth stages, this increase was 45–95% relative to no cover crop. However, cover cropping did not significantly increase nutrient concentration or growth. These variables were not influenced by the time of cover crop incorporation or tillage treatments. Differences in colonization, nutrient uptake and plant growth diminished during the growing period and at the final harvest date, the effects on plant production disappeared. High soil P level or high soil inoculum level was most likely responsible for the limited response of increased mycorrhiza formation on plant growth and nutrient concentrations.     

Linking post-fire regenerative strategy and leaf nutrient content in Mediterranean woody plants

We explored differences in leaf nutrient contents between species from Mediterranean shrublands with the ability to resprout after disturbances such as fire (resprouters) and others without this capacity (non-resprouters). Since it is to be expected that resprouting capacity is related to a more conservative use of nutrients, we hypothesize that resprouter and non-resprouter species will differ in their leaf nutrient concentrations.We measured the following leaf traits: leaf carbon content (LCC), leaf nitrogen content, leaf phosphorous content (LPC), leaf potassium content, leaf calcium content (LCaC), leaf magnesium content and leaf sodium content, in 30 woody species coexisting in a coastal shrubland. We also considered the influence of species’ taxonomic affiliation in our analysis.Non-resprouters had higher LPC and LCaC than resprouter species, and lower LCC, which could be related to their cell and life-history properties. This study also suggests that non-resprouter species have more P in their leaves and are less limited by P than resprouter species.Overall, the differences in leaf nutrient contents suggest that shifts in the proportion of resprouter and non-resprouter species resulting from changes in the fire regime may have effects on the functional properties of the ecosystem.     

Mammal community structure in relation to disturbance and resource gradients in southern Africa

The arrangements of mammals differ along environmental gradients, such as of disturbance and resources. We examined how mammal community composition in the Kalahari, Botswana, varied in relation to disturbance and resource gradients. We predicted that livestock-keeping villages are disturbances and pans are resources for wildlife, that the responses of mammals to disturbance and resources depend on their functional types and that increased disturbance over time has reduced the numbers and distributions of wildlife. The methods involved road-side counts of mammals >0.2 kg and trapping of small mammals, <0.2 kg. The disturbance gradient was more important than the resource gradient for explaining the distribution of mammals >0.2 kg. Communities in low disturbance-high resource areas were most diverse regarding species and functional types. Small mammal species richness and abundances were unaffected by villages, but increased with distance from pans. Villages were particularly deterring to large wild herbivores, functionally similar to livestock. Most large wild herbivores had decreased since 1975–1983. We conclude that large and medium-sized mammals are highly affected by large-scale disturbance gradients, while small mammals are most dependent on small-scale variation in resources, probably shelter and food. Increased disturbance over time leads to decreasing ranges and numbers of the large wild herbivores.     

Manganese content of mustard leaves in relation to iron and major nutrient supply

Summary In a study of manganese uptake by mustard plants in nutrient culture, the Mn/Fe, P/Fe, and K/Ca ratios in the leaves have been shown to vary in the same way with change in iron concentration of the medium. Copper shows similar inverse changes with iron. The metabolic significance of these ratios is discussed.     

Glomalin content of forest soils in relation to fire frequency and landscape position

Low-intensity, dormant season fires were frequent and widespread in oak-hickory ( Quercus-Carya) forests of eastern North America until widespread fire suppression began in the mid-1900s. To assess how reintroduction of fire into such ecosystems might affect the activity of arbuscular mycorrhizal (AM) fungi and, thereby, predict the long-term responses of plants and soils to fire, we analyzed the content of the immunoreactive fractions of the AM-fungus-specific glycoprotein glomalin in soils taken in 1994 and 2000 from three forested watersheds in southern Ohio, USA. One watershed remained unburned, one was burned annually from 1996-1999 and one was burned twice, in 1996 and 1999. In addition, to account for the strong landscape-scale gradients of microclimate and soil that typify these watersheds, we stratified each watershed-scale treatment area into three microclimatic zones (=landscape positions) using a GIS-based integrated moisture index (IMI). In the unburned control, the concentrations of immunoreactive, easily-extractable glomalin (IREEG) and immunoreactive total glomalin (IRTG) did not change significantly over the 6-year interval between sampling times, either overall or within any of the three IMI classes. IRTG content was greatest in the mesic landscape positions and lowest in the relatively xeric landscape positions, but IREEG did not vary among landscape positions. Neither IREEG nor IRTG contents were affected by fire, nor were there significant interactions between fire and landscape position in glomalin content. Both correlation and regression analyses demonstrated significant linkages between soil glomalin content, the density/diversity of herbaceous plants, and soil N availability. Despite significant effects of fires on soil N availability and root growth, we resolved no effect of fire on AM fungal activity at this spatial scale.     

Secondary metabolites in Cladina stellaris in relation to reindeer grazing and thallus nutrient content

We analysed concentrations of phenols and key macro-nutrients in a dominant mat-forming lichen, Cladina stellaris, in dry heath forests subjected to heavy reindeer grazing in Finnish Lapland. Lichen samples were collected in the beginning of two growth seasons from six to eight sites with old reindeer exclosures that served as control plots within sites. The concentration of perlatolic acid in lichen apices (top 10 mm) was higher in grazed plots than in control ones, whereas usnic acid did not seem to respond unequivocally to grazing. Moreover, there was a strong negative relationship between nitrogen and phenolic content of Cladina stellaris in intact plots but this relationship was absent in grazed ones. Changes in nitrogen and phosphorus contents caused by reindeer grazing were not correlated with changes in the level of phenolics in lichen thalli. The present result demonstrated that the carbon-nutrient balance (CNB) hypothesis may well explain some of the variation in lichen phenolic content but is not sufficient for explaining changes caused by reindeer grazing. We hypothesized that physical changes in the lichen microenvironment induced by reindeer have more profound impact on lichen phenolic content than alterations in thallus nutrient content.     

Trends in woody vegetation cover in the Kruger National Park, South Africa, between 1940 and 1998

Changes in the cover and density of shrubs and trees were assessed from aerial photographs (1940, 1974 and 1998) as well as from fixed-point photographs taken in 1984 and 1996 in the Kruger National Park, South Africa. Woody cover (trees and shrubs combined) increased by 12% on granite substrates but decreased by 64% on basalt substrates over the past 58 years. Both these figures are expressed in terms of the initial values, respectively. The density of the large tree component of woody vegetation decreased on both substrates. Woody vegetation cover declined as fire return periods became shorter, but the relationship was weak. The increases in woody plant density and cover on granite are thought to be the result of decreased competition from grasses, which in turn is a result of overgrazing by wild herbivores whose numbers have been kept high through the provision of surface water. These effects were not seen on the relatively nutrient-rich basalts, where grasses can recover rapidly even after heavy grazing. The decline in overall woody cover on basalts is interpreted as a result of regular, short-interval prescribed burning over the past 40 years, while the universal decline in large trees seems to result from an interaction between regular, frequent fires and utilization by elephants. The implications for management are discussed.     

Root-induced increases in soil pH and nutrient availability to field-grown cereals and legumes on acid sandy soils of Sudano-Sahelian West Africa

A field experiment with millet (Pennisetum glaucum L.), sorghum [Sorghum bicolor (L.) Moench], cowpea (Vigna unguiculata L.) and groundnut (Arachnis hypogeae L.) was conducted on severely P-deficient acid sandy soils of Niger, Mali and Burkina Faso to measure changes in pH and nutrient availability as affected by distance from the root surface and by mineral fertiliser application. Treatments included three rates of phosphorus (P) and four levels of nitrogen (N) application. Bulk, rhizosphere and rhizoplane soils were sampled at 35, 45 and 75 DAS in 1997 and at 55 and 65 DAS in 1998. Regardless of the cropping system and level of mineral fertiliser applied, soil pH consistently increased between 0.7 and two units from the bulk soil to the rhizoplane of millet. Similar pH gradients were observed in cowpea, but pH changes were much smaller in sorghum with a difference of only 0.3 units. Shifts in pH led to large increases in nutrient availability close to the roots. Compared with the bulk soil, available P in the rhizoplane was between 190 and 270% higher for P-Bray and between 360 and 600% higher for P-water. Exchangeable calcium (Ca) and magnesium (Mg) levels were also higher in the millet rhizoplane than in the bulk soil, whereas exchangeable aluminium (Al) levels decreased with increasing pH close to the root surface. The results suggest an important role of root-induced pH increases for crops to cope with acidity-induced nutrient deficiency and Al stress of soils in the Sudano-Sahelian zone of West Africa. This revised version was published online in June 2006 with corrections to the Cover Date.     

Climate and woody plant diversity in southern Africa: relationships at species, genus and family levels

Woody plant richness across southern Africa was analysed and related to climate–based water–energy dynamics. The analyses, which were based on an equal–area grid system, were undertaken at the genus and family levels and compared with results previously obtained at the species level. In all cases– climate accounts for most of the variation in richness (74–79%,). with richness being a linear function of liquid water and a parabolic function of energy. There is some variation in the particulars of climate's relationship to richness between the three taxonomic levels considered. But, the overall similarity of the outcomes at all three taxonomic levels supports the view that independent and predictable geographic variation in water-energy dynamics exerts a first-order control on the realised distributional ranges, and thus richness, of surviving and evolving taxa.     

Flowering cycles of woody bamboos native to southern South America

Neotropical woody bamboos range from northern Mexico to southern Argentina and Chile. The most interesting aspect of bamboo biology is their flowering habit. The species that are the most intriguing are those that manifest a cyclic pattern of gregarious flowering after long vegetative periods. The flowering cycle has been described in very few species. The goal was to identify mass flowering events of woody bamboo species native to Argentina and neighboring areas, and to estimate the flowering cycle of each species. Sixteen species were surveyed: Chusquea culeou, C. deficiens, C. lorentziana, C. montana, C. quila, C. ramosissima, C. tenella, C. valdiviensis; Colanthelia rhizantha; Guadua chacoensis, G. paraguayana, G. trinii; Merostachys clausenii, M. multiramea, Rhipidocladum neumannii and R. racemiflorum. To reconstruct flowering dates, information from literature and herbarium collections was consulted and more than 990 records were gathered. Flowering cycles were estimated by recording the intervals between reported flowering events. Evidence of regular flowering cycles of ca. 30 years was found for most of the species considered. There is a remarkable concentration of flowering cycles about multiples of 15–16 years. Flowering synchrony among different species of woody bamboos was recorded for the first time in South America.     

The challenge of interpreting primate diets: mangabey foraging on Blighia unijugata fruit in relation to changing nutrient content

Primates often make foraging selections that are not apparent. For example, they may eagerly consume a particular plant part and species in some instances, but reject it at other times. Blighia unijugata (Baker) fruit is one of the most frequently eaten foods of mangabeys (Lophocebus albigena) in Lwamunda Forest Reserve, Uganda; however, its use varies strikingly depending on the fruit's developmental stage. We conducted feeding observations to investigate the nutritional criteria that mangabeys may have used for the consumption of specific fruit parts by conducting analysis of fruit parts eaten and rejected at different developmental stages. When seeds had low condensed tannins, mangabeys ate them, but seeds were rejected when tannin levels increased. In the first five stages of fruit development, tannin levels in arils declined and the frequency of consumption of the aril increased. Although fat content in seeds increased with maturity, it did not appear to influence seed consumption, but fat content was related to frequency of consumption of the aril. Considering that primates are often making food selections among many species/part combinations, our results illustrate the value of using nutritional analyses to understand foraging decisions. Furthermore, they demonstrate how very specific trade‐offs between consumption of critical nutrients and antifeedants can drive which foods and parts are eaten.     

Determinants of woody encroachment and cover in African savannas

Savanna ecosystems are an integral part of the African landscape and sustain the livelihoods of millions of people. Woody encroachment in savannas is a widespread phenomenon but its causes are widely debated. We review the extensive literature on woody encroachment to help improve understanding of the possible causes and to highlight where and how future scientific efforts to fully understand these causes should be focused. Rainfall is the most important determinant of maximum woody cover across Africa, but fire and herbivory interact to reduce woody cover below the maximum at many locations. We postulate that woody encroachment is most likely driven by CO₂ enrichment and propose a two-system conceptual framework, whereby mechanisms of woody encroachment differ depending on whether the savanna is a wet or dry system. In dry savannas, the increased water-use efficiency in plants relaxes precipitation-driven constraints and increases woody growth. In wet savannas, the increase of carbon allocation to tree roots results in faster recovery rates after disturbance and a greater likelihood of reaching sexual maturity. Our proposed framework can be tested using a mixture of experimental and earth observational techniques. At a local level, changes in precipitation, burning regimes or herbivory could be driving woody encroachment, but are unlikely to be the explanation of this continent-wide phenomenon.     

Influence of woody debris on nutrient retention in catastrophically disturbed streams

The role of woody debris in nutrient cycling was investigated in two catastrophically disturbed streams in the Pacific Northwest that had been subjected to large inputs of wood. One study site in each catchment had all woody debris removed (take section), while the debris in the other study site was left intact (leave section). Nitrate, phosphate and chloride (a conservative tracer) were released in each section and nutrient retention was monitored at downstream stations. Phosphate was removed from solution more than nitrate, probably due to the high N : P ratio in the stream water. However, there were no major differences in nutrient retention between the take and leave sections. In contrast, experiments in recirculating chambers showed that woody debris and cobbles exhibited higher nitrate and phosphate uptake per unit surface area than sand/gravel or fine particulate organic matter. The high uptake rates of woody debris and cobbles may be related to their suitability for colonization by heterotrophic microorganisms and algae. Wood may not influence nutrient retention significantly at the reach level because of its low surface area relative to other substrates. However, wood may be very important at small spatial scales because of its high uptake activity.     

Spontaneous development of urban woody vegetation on differing soils

The general aim of the study was to follow the development of spontaneous woody vegetation on man-made urban habitats in Berlin, Germany. In spring 1968, the vegetation was removed completely in five groups of plots, which had been filled with five different transferred soil material in 1928. The spontaneous vegetation was monitored annually from 1968 to 2006. Especially, the development of shrubs and trees was followed. In addition the growth of the most important herbaceous species, Solidago canadensis, was investigated.

The soils varied from moderately rich sandy soils to rich sandy or loamy soils. On the two sandy soils S. canadensis developed poorly. Tree species dominated (>50% of total cover) on these plots after 14–18 years. On the soils rich in nutrients, S. canadensis developed strongly. Tree species did not dominate there before 21–25 years. The diversity of woody species increased over time and reached 33 species altogether. Indigenous Acer, Quercus and Betula species prevailed. Alien species, typical for urban ruderal sites, were rare.

The results support the idea of establishing urban woodlands by spontaneous succession as a cheap way to develop near-natural plant communities rich in species.     

Biomass distribution of two subalpine dwarf‐shrubs in relation to soil moisture and nutrient content

Question: Do soil water content and/or soil nitrogen (N) content and/or soil phosphorus (P) content affect the biomass of Vaccinium myrtillus and V. vitis‐idaea in a sub‐alpine heath? Location: Dolomites, northern Italy, 1800 m a.s.l. Methods: We determined above‐ground and below‐ground biomass of the shrubs at three sites, each on a different substrate type. At each site, we determined soil N‐ and P‐contents. We also determined leaf water potential (Psi;₁), N‐ and P‐concentrations in plant tissues and litter, as well as δ¹³C and δ¹⁵N in mature leaves. Results: V. myrtillus biomass was highest at the silicate site, V. vitis‐idaea biomass was highest at the carbonate site. Both shrubs had low biomass at the peat site, possibly due to a toxic effect of waterlogging in wet soils. For both species, pre‐dawn Psi;₁ indicated optimal hydration and midday Psi;₁ did not show any sign of water stress. Water use efficiency (WUE) did not differ among sites for any species. Whole‐plant nutrient concentrations showed that, with increasing biomass, N was diluted in V. myrtillus tissues while P was diluted in V. vitis‐idaea tissues. Foliar N‐concentration was higher overall for V. myrtillus. Foliar P‐concentration in V. myrtillus peaked at the silicate site. Foliar N : P ratios suggested that V. myrtillus was primarily P‐limited and V. vitis‐idaea primarily N‐limited. Conclusions: Water content affected the distribution of the two shrubs in a similar way, higher P‐availability in the soil enhanced V. myrtillus rather than V. vitis‐idaea.