森林的水土保持作用

森林生物群落拦蓄洪水作用很大,素有“绿色水库”之美誉。据测算,原始林、天然林、人工针叶林截流降水的能力分别为每公顷33.04吨、32.35吨、28.35吨。森林具有的减少洪峰并延迟洪峰到来时间的功能可以有效遏制或减轻山洪暴发和对土壤的冲击。据测定,

Effects of experimental warming on soil microbial communities in two contrasting subalpine forest ecosystems,eastern Tibetan Plateau,China

Soil microbial communities are primarily regulated by environmental temperature. Our study investigated the effects of global warming on soil microbial community composition as measured via phospholipid fatty acid （PLFA） analysis and soil chemical characteristics in relation to soil depth in a dragon spruce plantation and a spruce-fir-dominated natural forestin the Eastern Tibetan Plateau. Opentop chambers were utilized to increase the soil and air temperature. Soil samples were collected from the o-10 cm, 10-20cm, and 20-30 cm layers after a 4-year warming. Our results showed that the soil microbial community and the contents of TC （Total carbon）, TN （Total nitrogen）. NO3-. and NH4＋ responded differently to warming in the two contrasting forests, especially at the 0-10 cm soil depth. Warming increased soil microbial biomass at the 0-20 cm depth of soil in natural forest but reduced it at the o-lo cm depth ofsoil in the plantation. In contrast, the TC and TN contents were reduced in most soil layers of a natural forest but increased in all of the soil layers of the plantation under warming conditions. This result suggested that the effects of warming on soil microbial community and soil C and N pools would differ according to soil depth and forest types; thus, the two contrasting forests would under go differing changes following the future climate warming in this region.

Natural regeneration dynamics of three dry deciduous forest species in Chacocente Wildlife Reserve, Nicaragua

A study was conducted to examine the natural regeneration of three dry forest species, Lysiloma divaricatum （Jacq.）, Tabebuia ochracea （Cham.） and Lonchocarpus minimiflorus （Donn. Sin.） over a three-year period and to analyze heterogeneity of regeneration in relationship to topographic slope and incidence of light in Chacocente Wildlife Reserve in Nicaragua. Permanent sample plots were established in 2001, and all individuals with height as low as 10 cm and diameter as large as 10 cm were recorded for three consecutive years from 2001 to 2003. The results show that the density of naturally regenerated individuals varied significantly among species, as well as over time. L. minimiflorus and T. ochracea had higher densities compared with L. divaricatum, and the net change in population density was slightly positive for T. ochracea only. Regeneration was more abundant in the gentle and steep slopes under partial exposure of the crown to sunlight, thus resulting in aggregated pattern of distribution, especially for L. minimiflorus and T. ochracea. We concluded that natural regeneration alone is not sufficient to maintain the desired number of stocks of these species, and an immediate restoration measure should be taken to assist the natural regeneration process.

Key microorganisms mediate soil carbon-climate feedbacks in forest ecosystems

Soil microorganisms are known to significantly contribute to climate change through soil carbon(C)cycle feedbacks.However,it is challenging to incorporate these feedbacks into predictions of future patterns of terrestrial C cycling,largely because of the vast diversity of soil microorganisms and their responses to environmental conditions.Here,we show that the composition of the bacterial community can provide information about the microbial community-level thermal response(MCTR),which drives ecosystemscale soil C-climate feedbacks.The dominant taxa from 169 sites representing a gradient from tropical to boreal forest mainly belonged to the phyla Actinobacteria and Acidobacteria.Moreover,we show that the MCTR in warm biomes and acidic soils was linked primarily to bacteria,whereas the MCTR in cold biomes and alkaline soils was primarily associated with fungi.Our results provide strong empirical evidence of linkages between microbial composition and the MCTR across a wide range of forests,and suggest the importance of specific microorganisms in regulating soil C-climate feedbacks.

Assessing Threats and Setting Conservation Priorities for Plant Species between Forest and Meadow Ecotone in Sanjiangyuan Nature Reserve, China

In order to understand the pattern and status of plant species in the forest-meadow ecotonein Sanjiangyuan Nature Reserve, this study was undertaken through expert consultation, literaturesurvey and fieldwork in various parts of the ecotone during 2002-2004. Based on 3 important systems,i.e. threatened status, genetic loss effect and use value, the list of threatened and prioritized plants wasestablished. In this paper, the threatened coefficient was defined as the criteria of category for threatenedplants, the conservation priorities coefficient summed by threatened coefficient, genetic coefficient anduse value coefficient was defined as the criteria of prioritized plants. In addition, 10 indicators toevaluate threatened grading and conservation priorities sequence were included in the 3 importantsystems. The weights of 3 systems and 10 indicators were given through expert consultation andanalytic hierarchy process. Ten indicators were given scores based on the subcriteria, respectively, andall the scores of the 3 systems were summed up for each species, then contrasted to the criteria ofthreatened grading and conservation priorities for plant species. The status of endangerment andconservation priorities of plant species were analyzed, and the results showed that the number ofendangered species was 2, vulnerable species 37, near threatened species 140, safe species 767; the firstconcern category had 4 species, the second concern category 18, the third concern category 150 and theleast concern category 774.