In this study we examined changes of leaf antomy in ten deciduous broad-leaved tree species according to changes in growth light conditions. The ten species are common to Japanese warm-temperate forests, cool-temperate forests and subalpine forests. In all tree species the palisade tissue changed markedly according to changes in light conditions. Six tree species showed a change in thickness of the palisade tissue that was directly proportional to the change in the relative photosynthetic photon flux density. It was judged that the six tree species changed the thickness of their palisade tissue readily according to shading. In four tree species, the thickness of the palisade tissue changed to a constant value according to the change in relative photosynthetic photon flux density. It was judged that in these four species the thickness of the palisade tissue did not change readily with shading. Those tree species which had thick palisade tissue tended to change the thickness of the palisade tissu readily according to shading, whereas such a change did not occur readily in those species which had thin palisade tissue. Only two species showed marked changes in the number of cell layers of the palisade tissue in respose to growth light conditions. Eight tree species responded to light conditions by changing the vertical length of the palisade tissue cells.
Decomposition of fresh leaves of deciduous trees and colonization by macroinvertebrate shredders were studied in a mountain stream in Nagano Prefecture, central Japan. Decomposition experiments were carried out from late June to mid August ("summer experiment") and from early October to late November ("autumn experiment") in 1998. Two types of litter bag (9-mm mesh and 0.4-mm mesh) were used in these experiments to examine the role of shredders in leaf decomposition. Decomposition rates (ks) of fresh leaves calculated using an exponential decay model were faster (k=0.0073-0.0935) than most of the known rates for senescent leaves. The fresh leaves were subjected to a higher degree of microbial and shredder processing because of their lower C/N ratio. Decomposition rates in the summer experiment were higher than in the autumn experiment for both types of mesh bag. Decomposing activities of microbes and/or small shredders would have been higher in the summer experiment, when the C/N ratio of the leaves was lower and the stream temperature was higher. In the early stage of decomposition during the summer experiment, the biomass of shredders colonizing the coarse mesh bags was very large, due to colonization by many large, mature caddisfly larvae (i. e. Pseudostenophylax and Goerodes), while significant effects of mesh size on leaf decomposition were detected. These results suggest that in streams during early summer, when several shredder species are often at a mature stage even though coarse organic detritus is limited, input of high-quality fresh leaves is an important food resource for these shredders.
The effect of high-salinity seawater on gray mangrove, Avicennia marina (Forsk.) Vierh, vegetation growing along desert coasts of the United Arab Emirates was analyzed by ecological observation. Gray mangroves in swamps were severely affected by seawater with salinity between 41.5 ‰ and 80.2 ‰. They normally grew in seawater with salinity below 50 ‰, and dwarf stands resulted as the salinity increased to above 50 ‰. The number of seedlings surviving in highly saline swamps was markedly lower than that in swamps of low salinity. Salt tolerance experiments showed that seeds could not survive in seawater with a salinity higher than 55 ‰. However, seeds were able to survive up to 80 ‰ salinity when only the lower part of cotyledons including the radicle were placed in seawater. These seeds absorb high-salinity seawater through their roots, and cotyledons remove the harmful salts from the seawater through a desalination system. When the seedlings grown in coastal seawater (40 ‰) were transplanted into high-salinity seawater, the survival of seedlings decreased in 60 ‰ seawater, and seedlings were unable to survive in 80 ‰ seawater due to dehydration through their roots. These results show that different levels of salt tolerance exist between cotyledons and roots of gray mangrove, and that the level of salt tolerance in roots is high when seeds germinate in high-salinity seawater. This salt tolerance of seeds shows that they can grow in sand when the seawater salinity is below 50 ‰. When the salinity exceeds 50 ‰, seeds should be laid on the sand surface to attain a high germination ratio.
Colonies of many tropical polistine wasp species have multiple queens. However, recent studies have shown that effective queens comprise only one to a few individuals at the stage of the colony cycle when new reproductives are produced (cyclical oligogyny). The present article addresses the following three issues which are still unresolved : (1) There is a paucity of evidence for cyclical oligogyny even in some species having huge colonies of more than ten thousand workers and several thousand queens. (2) Coexistence of multiple egg-layers in Ropalidia rufoplagiata may be explained by ideas other than the cyclical oligogyny-kin selection hypothesis. (3) As the number of queens per colony is large throughout all stages of the colony cycle of some tropical species, if cyclical oligogyny prevails, it is necessary to demonstrate mechanisms which inhibit the production of reproductives by queens other than one or a few effective queen(s). However, there has been no clear evidence of such inhibition. In addition, the role of relief of queens during a colony cycle must be studied in relation to maintenance of eusociality, despite low intracolony relatedness.