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201.
202.
The ecological differences between ‘shrubs’ and ‘trees’ are surprisingly poorly understood and clear ecological definitions of these two constructs do not exist. It is not clear whether a shrub is simply a small tree or whether shrubs represent a distinct life‐history strategy. This question is of special interest in African savannas, where shrubs and trees often co‐dominate, but are often treated uniformly as ‘woody plants’ even though the tree to shrub ratio is an important determinant of ecosystem functioning. In this study we use data from a long‐term fire experiment, together with a trait‐based approach to test (i) if woody species usually classified as shrubs or trees in African savanna differ in key traits related to disturbance and resource use; and (ii) if these differences justify the interpretation of the two growth forms as distinct life‐history strategies. We measured for 22 of the most common woody plant species of a South African savanna 27 plant traits related to plant architecture, life‐history, leaf characteristics, photosynthesis and resprouting capacity. Furthermore we evaluated their performance during a long‐term fire experiment. We found that woody plants authors call (i) shrubs; (ii) shrubs sometimes small trees; and (3) trees responded differently to long‐term fire treatments. We additionally found significant differences in architecture, diameter‐height‐allometry, foliage density, resprouting vigour after fire, minimum fruiting height and foliar δ13C between these three woody plant types. We interpret these findings as evidence for at least two different life‐history‐strategies: an avoidance/adaptation strategy for shrubs (early reproduction + adaptation to minor disturbance) and an escape strategy for trees (promoted investment in height growth + delayed reproduction). 相似文献
203.
Review of elevated atmospheric CO2 effects on agro-ecosystems: residue decomposition processes and soil C storage 总被引:15,自引:0,他引:15
A series of studies using major crops (cotton [Gossypium hirsutum L.], wheat [Triticum aestivum L.], grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.]) were reviewed to examine the impact of elevated atmospheric CO2 on crop residue decomposition within agro-ecosystems. Experiments evaluated utilized plant and soil material collected from
CO2 study sites using Free Air CO2 Enrichment (FACE) and open top chambers (OTC). A incubation study of FACE residue revealed that CO2-induced changes in cotton residue composition could alter decomposition processes, with a decrease in N mineralization observed
with FACE, which was dependent on plant organ and soil series. Incubation studies utilizing plant material grown in OTC considered
CO2-induced changes in relation to quantity and quality of crop residue for two species, soybean and grain sorghum. As with cotton,
N mineralization was reduced with elevated CO2 in both species, however, difference in both quantity and quality of residue impacted patterns of C mineralization. Over
the short-term (14 d), little difference was observed for CO2 treatments in soybean, but C mineralization was reduced with elevated CO2 in grain sorghum. For longer incubation periods (60 d), a significant reduction in CO2-C mineralized per g of residue added was observed with the elevated atmospheric CO2 treatment in both crop species. Results from incubation studies agreed with those from the OTC field observations for both
measurements of short-term CO2 efflux following spring tillage and the cumulative effect of elevated CO2 (> 2 years) in this study. Observations from field and laboratory studies indicate that with elevated atmospheric CO2, the rate of plant residue decomposition may be limited by N and the release of N from decomposing plant material may be
slowed. This indicates that understanding N cycling as affected by elevated CO2 is fundamental to understanding the potential for soil C storage on a global scale.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
204.
经调查鉴定,云南普洱市有菝葜属植物18种,其中菝葜、小叶菝葜、光叶菝葜(土茯苓)分布较广。介绍了它们的地理分布等,为普洱市菝葜属植物资源的综合利用和深入研究提供一定的依据。 相似文献
205.
Ecological restoration typically focuses on promoting vegetation recovery in degraded habitat or reintroducing endangered animals to enhance their regional or global persistence. Here, we argue that attention should also be devoted to vertebrate reintroductions in overhunted but floristically intact tropical forests in order to prevent insidious regime shifts in these systems. Growing evidence suggests that tropical forests deprived of seed‐dispersing animals exhibit replacement of fleshy fruiting trees by species with abiotic seed dispersal. Left unchecked, this process could eventually render the forest uninhabitable by frugivores through reduced density and diversity of their food plants. In tropical areas where hunting can be controlled, we contend that frugivore reintroduction, regulation of wild fruit harvest by humans, and outplanting of native fruiting trees should be deployed as management tools long before the systems are in need of traditional habitat restoration. 相似文献
206.
Deborah Ann Roach 《Genetica》1993,91(1-3):53-64
Senescence is a decline in age-specific survival and reproduction with advancing age. Studies of evolutionary plant senescence are designed to explain this decline in life history components within the context of natural selection. A review of studies of plant demography reveals senescent declines in both annual and perennial plants, but also suggests that there are some plant species which may not be expected to show senescence. Thus, future comparative studies of closely related species, with and without senescence, should be possible. The assumptions of the major evolutionary theories of senescence are evaluated for their validity with respect to plants. Different plant species violate one or more of the assumptions of the theories, yet the consequences of violating these assumptions have never been investigated. Whereas, to date, evolutionary senescence has been studied only indirectly in plants, it is concluded that plants provide good experimental systems for clarifying our understanding of senescence in natural populations. 相似文献
207.
208.
采用4℃反复浸提、离心、硫酸铵沉淀、DEAE—Sepharose Fast Flow离子交换柱层析,从紫球藻(Porphyridium cruentum Naegeli)冻干粉中分离纯化藻红蛋白,分离纯度达到4.85,总收率51.9%;经羟基磷灰石柱层析纯化,藻红蛋白纯度达到5.10,总收率34.0%,聚丙烯酰胺凝胶电泳显示1条带。所分离纯化的藻红蛋白含有3个亚基(α、β、γ),在可见光区545nm和560nm处有2个吸收峰,在498nm处有1个吸收肩峰。实验结果说明所分离纯化的藻红蛋白纯度符合要求。 相似文献
209.
Summary. Ginkgo biloba and the cycads are the only extant seed plants with motile sperm cells. However, there has been no immunocytochemical characterization
of these gametes to determine if they share characteristics with the flagellated sperm found in bryophytes and pteridophytes
or might give clues as to the relationships to nonflagellated sperm in all other seed plants. To determine characteristics
of proteins associated with the motility apparatus in these motile sperm, we probed thin sections of developing spermatogenous
cells of Ginkgo biloba with antibodies to acetylated and tyrosinated tubulin and monoclonal antibodies that recognize mammalian centrosomes and
centrin. The blepharoplast that occurs as a precursor to the motility apparatus consists of an amorphous core, pitted with
cavities containing microtubules and a surface studded with probasal bodies. The probasal bodies and microtubules within the
blepharoplast cavities are labeled with antibodies specific to acetylated tubulin. Positive but weak reactions of the blepharoplast
core occur with the centrosomereactive antibodies MPM-2 and C-9. Reactions to centrin antibodies are negative at this developmental
stage. From this pre-motility apparatus structure, an assemblage of about 1000 flagella and associated structures arises as
the precursor to the motility apparatus for the sperm. The flagellar apparatus consists of a three-layered multilayered structure
that subtends a layer of spline microtubules, a zone of amorphous material similar to that in the blepharoplast, and the flagellar
band. Centrin antibodies react strongly with the multilayered structure, the transition zone of the flagella, and fibrillar
material near the flagellar base at the surface of the amorphous material. Both the spline microtubules and all of the tubules
in the flagella react strongly with the antibodies to acetylated tubulin. These localizations are consistent with the localizations
of these components in pteridophyte and bryophyte spermatogenous cells, although the blepharoplast material surrounding and
connecting flagellar bases does not occur in the seedless (nonseed) land plants. These data indicate that despite the large
size of ginkgo gametes and the taxonomic separation between pteridophytes and Ginkgo biloba, similar proteins in gametes of both groups perform similar functions and are therefore homologous among these plants. Moreover,
the presence of acetylated tubulin in bands of microtubules may be a characteristic shared with more derived non-flagellated
sperm of other conifers and angiosperms.
Correspondence and reprints: Southern Weed Science Research Unit, USDA Agricultural Research Service, P.O. Box 350, Stoneville,
MS 38776, U.S.A. 相似文献
210.
cDNA-AFLP技术及其在植物基因表达研究中的应用 总被引:1,自引:0,他引:1
cDNA-AFLP技术是一种新的研究基因表达的技术,具有重复性好、稳定、可靠的特点,可对生物体转录组进行全面、系统的分析,广泛应用于基因表达特性研究、植物遗传标记分析和分离植物基因等方面.近年来随着技术的不断进步,设备的不断改进,许多新的研究方法不断的产生,该技术取得了迅速的发展.本文就cDNA-AFLP技术的原理、技术特点及其在植物基因表达研究中的应用进行了综述. 相似文献