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991.
为实现基因工程菌Bacillus subtilis WSHB06-07生产角质酶的高产,在3L发酵罐中考察了不同初糖浓度对菌体生长和产酶的影响,并在选择38 g/L初始蔗糖浓度的基础上,进行碳源的分批流加和恒速流加,结果表明发酵16 h开始流加碳源,采用总补糖量60g/L,蔗糖平均流速为4g/(L·h)的恒速补料方式,角质酶酶活在31h可达到最大545.87U/ml,比分批发酵酶活提高67.8%,并获得较高的角质酶生产强度,满足工业化生产要求。 相似文献
992.
993.
放牧强度对草甸草原生产力和多样性的影响 总被引:11,自引:2,他引:9
采用比较样地法研究了不同放牧强度对羊草草甸草原群落多样性和生产力的影响。结果表明:α多样性指数随放牧强度的增加表现为先增加后降低的趋势,其值在轻度放牧区最大,支持了"中度干扰理论";β多样性指数随放牧强度的增加而变大;不同放牧强度的草地植物种类相似性变差、草地地上净初级生产力与Alatalo均匀度指数具有显著的线性相关性(P0.05);放牧和气候对草地地上净初级生产力均有较大的影响,但二者的互作效应不显著(P0.05);不放牧不能持续维持草地的健康状况,但健康的草地状况可以有效地缓冲放牧和气候干扰,并能够维持较高的草地生产力和生物多样性。 相似文献
994.
Most strictly protected areas world-wide have been established in former commercial forests, but there is little evidence that this strongly advocated tool of conservation has had positive effects on endangered species in the short run of decades. One of the major reasons for the failure of habitat improvement in most of these reserves is a lack of natural disturbance. Consequently, only a few studies of species recovery in protected areas after natural disturbance are available. We demonstrate how natural dynamics in the oldest national park in Germany allows the area-wide recovery of the rare wood-inhabiting fungus Antrodiella citrinella. Our analyses showed that an increase of dead wood at >134-224 m(3)ha(-1), amounts known from primeval forests, allowed the fungus, which has barely survived as 'living dead' in two remnants of pristine forests, to spread from this small relict populations to the whole national park, within a radius of more than 30 km. Our result demonstrate that natural disturbance, even in former commercial forests, allowed the recovery of this rare species and fully supports the use of passive management in protected areas, even if natural dynamics often evokes debates on salvage logging. 相似文献
995.
Coarse woody debris (CWD) is generally considered as dead woody materials in various stages of decomposition,including sound and rotting logs,snags,and large branches.CWD is an important functional and structural component of forested ecosystems and plays an important role in nutrient cycling,long-term carbon storage,tree regeneration,and maintenance of heterogeneous environmental and biological diversity.However,the definition and classification of CWD have been the subject of a long debate in forest ecology.CWD has not been precisely defined.Recently,with the rapid development of landscape ecology in CWD,the USDA Forest Service and the Long Term Ecological Research (LTER)have provided a standardized definition and classification for CWD,which makes data comparison in landscape scale possible.Important characteristics of their definition include:(1) a minimum diameter (or an equivalent crosssection) of CWD≥10 cm at the widest point (the woody debris with a diameter from 1 to 10 cm should be defined as fine woody debris,and the rest is litterfall);and (2) sound and rotting logs,snags,stumps,and large branches (located above the soil),and coarse root debris (larger than 1 cm in diameter).This classification has greatly facilitated CWD studies.Therefore,it has been widely applied in some countries (particularly in North America).However,this classification has long been a source of confusion for forest ecologists in China.Furthermore,different definitions and criteria are still adopted in individual studies,which makes the interpretation and generalization of their work difficult.This article reviewed recent progress in classifying CWD,with an emphasis on introducing the classification system of the USDA Forest Service and the LTER.It is expected that this review will help facilitate the development of standardized definition and classification suitable to forest ecosystems in China. 相似文献
996.
Soil Temperature, Not Aboveground Plant Productivity, Best Predicts Intra-Annual Variations of Soil Respiration in Central Iowa Grasslands 总被引:2,自引:0,他引:2
Soil respiration (RSOIL) is the second largest carbon flux between terrestrial systems and the atmosphere, with a magnitude 10 times greater than
anthropogenic carbon dioxide production. Therefore, it is important that we understand, and be able to predict, how RSOIL responds to climate change. Although a positive, significant temperature effect on RSOIL has long been recognized, recent studies emphasize the overriding importance of current photosynthesis in controlling RSOIL. We tested the hypothesis that model inclusion of intra-annual variations in aboveground net primary productivity (ANPP)
significantly improves RSOIL estimates over predictions based on soil temperature alone. We also evaluated the possibility that canopy production is less
directly linked to RSOIL, by testing the hypothesis that intersite differences in RSOIL correlate more strongly with root biomass than with ANPP. We tested these hypotheses by measuring RSOIL, ANPP, and root biomass at four Iowa grasslands that differed in aboveground growth phenology and productivity. Among all
sites, intra-annual variations in RSOIL were most strongly related to soil temperature (R
2 = 0.89), not ANPP (R
2 = 0.53). All sites responded identically to changes in soil temperature (site-by-temperature P = 0.53), but inconsistently to variation in aboveground dynamics (site-by-canopy P < 0.0001). Incorporating canopy dynamics into temperature-based predictive models improved model R
2 by a maximum of 0.01. Among-site differences in RSOIL were related to root biomass (P < 0.001) but not ANPP (P = 0.34). We found no useful linkage between canopy characteristics and intra-annual or site-specific RSOIL predictions, perhaps because shoot and root dynamics were not consistently linked through time or among sites. 相似文献
997.
Akinori Yamada Tetsushi Inoue Decha Wiwatwitaya Moriya Ohkuma Toshiaki Kudo Atsuko Sugimoto 《Ecosystems》2006,9(1):75-83
Nitrogen (N) fixed by termites was evaluated as a N input to decomposition processes in two tropical forests, a dry deciduous
forest (DDF) and the neighboring dry evergreen forest (DEF), Thailand. A diverse group of termite species were assayed by
acetylene reduction method and only the wood/litter-feeding termites were found to fix N. More intensive samplings of two
abundant species, Microcerotermes crassus and Globitermes sulphureus, were done across several seasons, suggesting N fixation rates of 0.21 and 0.28 kg ha−1 y−1 by termites in the DDF and DEF, respectively. Also, estimates of asymbiotic N fixation rates were 0.75 and 3.95 kg ha−1 y−1. N fixed by termites and by asymbiotic fixers is directly supplied to decomposers breaking down dead plant material and could
be a major source of their N. N fixed by termites was 7–22% of that fixed by termites and asymbiotic fixers. Although N fixed
by termites is a small input compared to other inputs, this N is likely important for decomposition processes. 相似文献
998.
We examined potential large-scale controls over the distribution of arbuscular mycorrhizal (AM) fungi and their host plants.
Specifically, we tested the hypothesis that AM fungi should be more prevalent in biomes where nutrients are primarily present
in mineral, and not organic, forms. Values of percentage root length colonized (%RLC) by AM fungi, AM abundance, and host
plant availability were compiled or calculated from published studies to determine biome-level means. Altogether, 151 geographic
locations and nine biomes were represented. Percent RLC differed marginally significantly among biomes and was greatest in
savannas. AM abundance (defined as total standing root length colonized by AM fungi) varied 63-fold, with lowest values in
boreal forests and highest values in temperate grasslands. Biomes did not differ significantly in the percentage of plant
species that host AM fungi, averaging 75%. Contrary to the hypothesis, %RLC, AM abundance, and host plant availability were
not related to the size, influx, or turnover rate of soil organic matter pools. Instead, AM abundance was positively correlated
with standing stocks of fine roots. The global pool of AM biomass within roots might approach 1.4 Pg dry weight. We note that
regions harboring the largest stocks of AM fungi are also particularly vulnerable to anthropogenic nitrogen deposition, which
could potentially alter global distributions of AM fungi in the near future. 相似文献
999.
Detailed knowledge of the relationship between plant diversity and productivity is critical for advancing our understanding of ecosystem functioning and for achieving success in habitat restoration efforts. However, effects and interactions of diversity, succession and biotic invasions on productivity remain elusive. We studied newly established communities in relation to preexisting homogeneous vegetation invaded by exotic plants in the northern Great Plains, USA, at four study sites for 3 years. We observed variant diversity–productivity relationships for the seeded communities (generally positive monotonic at three sites and non-monotonic at the other site) but no relationships for the resident community or the seeded and resident communities combined at all sites and all years. Community richness was enhanced by seeding additional species but productivity was not. The optimal diversity (as indicated by maximum productivity) changed among sites and as the community developed. The findings shed new light on ecosystem functioning of biodiversity under different conditions and have important implications for restoration. 相似文献
1000.
为揭示海河流域植被净初级生产力(net primary productivity, NPP)时空变化特征及其时空异质性驱动机制,该文基于MOD17A3HGF数据集,综合自然和人为两方面的影响因素,利用变异系数、趋势分析、相关分析、Hurst指数以及地理探测器等,分析2000—2020年海河流域植被NPP时空格局演变特征和定量识别驱动因素及其影响力。结果表明:(1)时间上,2000—2020年海河流域植被NPP整体呈显著上升趋势,增速为1.73 Tg C·a-1,年均NPP为326.75 g C·m-2·a-1,其中针叶林、阔叶林、灌丛、草地和农用地的NPP多年均值分别为313.59、385.28、353.03、320.12、295.22 g C·m-2·a-1。(2)空间上,植被NPP高值区集中于西北部山区,低值区集中于东南部平原区;NPP整体情况稳定,变异系数均值为0.17;未来变化趋势呈反持续性,植被NPP可能下降。(3)植被NPP与气温呈负相关,与降水呈正相关,降水为主要... 相似文献