Soil-surface carbon dioxide efflux and microbial biomass in relation to tree density 13 years after a stand replacing fire in a lodgepole pine ecosystem

The effects of fire on soil‐surface carbon dioxide (CO₂) efflux, F_S, and microbial biomass carbon, C_mic, were studied in a wildland setting by examining 13‐year‐old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha^?1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (～110‐year‐old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season F_S increased with tree density in young stands (1.0 µmol CO₂ m^?2 s^?1 in low‐density stands, 1.8 µmol CO₂ m^?2 s^?1 in moderate‐density stands and 2.1 µmol CO₂ m^?2 s^?1 in high‐density stands) and with stand age (2.7 µmol CO₂ m^?2 s^?1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g^?1 dry soil over the growing season; C_mic was significantly greater in mature stands (0.5–0.8 mg C g^?1 dry soil). Soil‐surface CO₂ efflux in young stands was correlated with biotic variables (above‐ground, below‐ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below‐ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but C_mic pools and overall F_S rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of F_S and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.     

Roosting Requirements of Two Frugivorous Bats (Sturnira lilium and Arbiteus intermedius) in Fragmented Neotropical Forest1

As tropical forest fragmentation accelerates, scientists are concerned with the loss of species, particularly those that play important ecological roles. Because bats play a vital role as the primary seed dispersers in cleared areas, maintaining healthy bat populations is critical to natural forest regeneration. Observations of foraging bats suggest that many Neotropical fruit‐eating species have fairly general habitat requirements and can forage in many different kinds of disturbed vegetation; however, their roosting requirements may be quite different. To test whether or not general foraging requirements are matched by equally broad roosting requirements, we used radiotelemetry to locate roost sites of two common frugivorous bat species (Sturnira lilium and Artibeus intermedius) in a fragmented forest in southeastern Mexico. Sturnira lilium roosted inside tree cavities and selected large‐diameter roost trees in remnant patches of mature forest. Fewer than 2 percent of trees surveyed had a mean diameter equal to or greater than roost trees used by . S. lilium, Artibeus intermedius roosted externally on branches and vines and under palm leaves and selected roost trees of much smaller diameter. Compared to random trees, roost trees chosen by A. intermedius were closer to neighboring taller trees and also closer in height to these trees. Such trees likely provide cryptic roosts beneath multiple overlapping crowns, with sufficient shelter from predators and the elements. While males of A. intermedius generally roosted alone in small trees within secondary forest, females roosted in small groups in larger trees within mature forest and commuted more than three times farther than males to reach their roost sites. Loss of mature forest could impair the ability of frugivorous bats to locate suitable roost sites. This could have a negative impact on bat populations, which in turn could decrease forest regeneration in impacted areas.     

Dynamic properties of the advertisement calls of gray tree frogs: patterns of variability and female choice

We assessed the potential for several acoustic properties ofthe advertisement calls of male gray tree frogs to affect relativemating success by relating patterns of variation in these propertiesto minimum differences required to elicit female choice. Dynamicproperties (pulse number, PN; call rate, CR; and duty cycle,DC, the ratio of call duration to call period) varied much morewithin bouts of calling than a static property (dominant frequency,DF) but nevertheless exhibited significant between male variationin three of four breeding seasons. Many multiply recorded malesconsistently produced calls with values substantially aboveor below mean values of males recorded on the same nights. Nightlyranges of variation in PN and CR were often greater than theminimum differences required to elicit female preferences inthe laboratory. In most experiments, females chose high-PN orfast-CR calls over low-PN or slow-CR alternatives, respectively,even if the preferred stimuli were farther away or 6-10 dB lowerin sound pressure level (SPL), provided that differences inPN or CR were 100%. Consistent with these results, females didnot always choose the closer of two calling males in the field.Nightly ranges of variation in DF rarely equaled the minimumdifference required to elicit SPL independent preferences. Femalespreferred a stimulus of high-PN and slow-CR over an alternativeof low-PN or fast-CR with the same acoustic on-time; in twoexperiments, females chose calls of high-PN over low-PN alternativeseven though the playback of the high-PN call was interruptedand the low-PN call was broadcast continuously. Thus, femalepreferences were not merely based on the total time of acousticstimulation. Responses of females tested twice in the same experimentsuggest that phenotypic variation in preference was limitedin our study populations.     

Actin distribution in somatic embryos and embryogenic protoplasts of white spruce (Picea glauca)

Summary Examination of unfixed immature somatic embryos of white spruce (Picea glauca) with fluorescent rhodamine-labeled phalloidin revealed an extensive network of fine actin microfilaments (MFs) in the embryonal region which were not detected in specimens fixed with formaldehyde. Transition cells linking the embryonal region and suspensor cells contained fine MFs as well as bundles of MFs. The large, highly vacuolated suspensor cells were characterized by actin MF cables only. Treatment of embryos with cytochalasin B (CB) removed the fine MFs from the embryonal region and transition cells, but many MF cables in suspensor cells were resistant. Full recovery from CB treatment was observed in most somatic embryos. Embryogenic protoplasts capable of regenerating to somatic embryos in culture were released from only the embryonal region of somatic embryos. Both uninucleate and multinucleate embryogenic protoplasts retained the extensive network of fine actin MFs. In contrast, protoplasts derived from vacuolated suspensor cells and vacuolated free-floating cells contained thick MF bundles and were not embryogenic. Distinct MF cages enclosed nuclei in multinucleate protoplasts and may be responsible for preventing nuclear fusion. Microspectrophotometric analyses showed that the DNA contents of embryonal cells in the embryo and embryogenic protoplasts were similar and characteristic of rapidly dividing cell populations. However, transition and suspensor cells which released nonembryogenic protoplasts appeared to be arrested in G₁, and suspensor cells showed signs of DNA degradation.     

In vitro micropropagation of the macarronesian evergreen treePersea indica (L.) K. Spreng

Summary Shoot propagation ofPersea indica (L.) K. Spreng was achieved using seedling axillary buds cultured on MS (Murashige and Skoog, 1962) medium with 1 mg/l (2.8 μM) N⁶-benzyladenine (BA). Forty percent of the obtained shoots did not elongate, but showed bud proliferation, which was maximal (three axillary buds per shoot) at the end of the seventh subculture. Sixty percent of the shoots elongated, did not show bud proliferation, and formed calluses at their base. Successful rooting (84.6%) was achieved dipping the base of each elongated shoot in 3 g/l (16.11 mM) indolebutyric acid (IBA) for 1–2 s, and transferring to half strength MS medium without growth regulators. These shoots presented an acclimatization success of 100%. Results suggest that micropropagated elongated shoots ofP. indica can be adequately used in reforestation programs.     

南亚热带森林几种乔木种子萌发和幼苗生长观察

本文对香椿（Ｔｏｏｎａｓｉｎｅｎｓｉｓ（Ａ．Ｊｕｓｓ．）Ｒｏｅｍ．）、木蝴蝶（Ｏｒｏｘｙｌｕｍｉｎｄｉｃｕｍ（Ｌ．）Ｖｅｎｔ．）、扁斗青冈（ＱｕｅｒｃｕｓｈｕｉＣｈｕｎ）、泡桐（Ｐａｕｌｏｗｎｉａｆｏｒｔｕｎｅｉ（Ｓｅｅｍ．）Ｈｅｍｓｌ）罗浮柿（ＤｉｏｓｐｙｒｏｓｍｏｒｒｉｓｉａｎａＨａｎｃｅ）、枳（ＢｅｒｃｈｅｍｉａｄｕｌｃｉｓＴｈｕｎｂ．）等南亚热带森林乔木种子萌发和幼苗生长进行观察．香椿、扁斗青冈、罗浮柿种子在轻阴（５５％光）条件下萌发率最高,分别为７０％、９０％、３０％,木蝴蝶种子在重阴（３８％光）条件下萌发率最高,为８０％,枳种子在光照条件下萌发率最高,为１５％．阳性树种香椿、木蝴蝶、泡桐、枳幼苗生长速度较快,属速生型树种,其幼苗在光照条件下生长速度最快,森林中树种扁斗青冈、罗浮柿幼苗生长速度较慢,属慢生型树种,其幼苗在轻阴条件下生长较好．随着施肥量的增加,幼苗生长速度明显提高．     

Global extent,development and economic impact of acid soils

Acid soils occupy approximately 30% or 3950 m ha of the world's ice free land area and occur mainly in two global belts where they have developed under udic or ustic moisture regimes. The northern belt (cold and temperate climate) is dominated by Spodosols, Alfisols, Inceptisols and Histosols and the southern tropical belt consists largely of Ultisols and Oxisols.Sixty-seven percent of the acid soils support forests and woodlands and approximately 18% are covered by savanna, prairie and steppe vegetation. Only 4.5% (179 m ha) of the acid soil area is used for arable crops. A further 33 m ha is utilized for perennial tropical crops. The value of the annual production in these areas is approximately US$ 129 billion. Value of products from forests, woodlands and permanent pastures on acid soils is difficult to evaluate.Forests of the tropics and wetlands have an invaluable role in global, regional and local ecosystem balance and a protective role for flora, fauna and water resources. While acid soils in the northern belt are increasingly protected and reafforested, the destructive exploitation of timber and abusive modern shifting cultivation have contributed to the loss of >250 million ha of tropical forest during the second half of this century leaving vast areas of anthropic savannas on heavily eroded and degraded acid soils.The authors believe that attempts to develop acid soils for agriculture and agroforestry in the tropics should concentrate on these deforested and abandoned areas of degraded acid soils. However, this will be difficult without significant initial investment and adequate technology. A three step development approach is suggested, which could help prevent or halt the annual destruction of >5 mill. ha tropical forests by untraditional shifting cultivators. It would help to protect the fragile natural ecosystems on tropical acid soils now considered to be indispensable for the future life on earth.     

Nitrogen fixation in Faidherbia albida,Acacia raddiana,Acacia senegal and Acacia seyal estimated using the 15N isotope dilution technique

A pot experiment was conducted in a greenhouse using the ¹⁵N isotope dilution method and two reference plants, Parkia biglobosa and Tamarindus indica to estimate nitrogen fixed in four Acacia species: A raddiana, A. senegal, A. seyal and Faidherbia albida (synonym Acacia albida). For the reference plants, the ¹⁵N enrichments in leaves, stems and roots were similar. With the fixing plants, leaves and stems had similar ¹⁵N enrichments; they were higher than the ¹⁵N enrichment of roots. The amounts of nitrogen fixed at 5 months after planting were similar using either reference plant. Estimates of the percentage of N derived from fixation (%Ndfa) for the above ground parts, in contrast to %Ndfa in roots, were similar to those for the whole plant. However, none of the individual plant parts estimated accurately total N fixed in the whole plant, and excluding the roots resulted in at least 30% underestimation of the amounts of N fixed. Between species, differences in N₂ fixation were observed, both for %Ndfa and total N fixed. For %Ndfa, the best were A. seyal (average, 63%) and A. raddiana (average, 62%), being at least twice the %Ndfa in A. senegal and F. albida. Because of its very high N content, A. seyal was clearly the best in total N fixed, fixing 1.62 g N plant^–1 compared to an average of 0.48 g N plant^–1 for the other Acacia species. Our results show the wide variability existing between Acacia species in terms of both %Ndfa and total N fixed: A. seyal was classified as having a high N₂ fixing potential (NFP) while the other Acacia species had a low NFP.     

Expression of ferredoxin-dependent glutamate synthase in dark-grown pine seedlings

Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark.