上黄村草地生态系统能流和物流的初步研究

上黄村草地土壤生态系统能量投入主要是动力投入,无营养物质投入。人工草地能量产出占总能量产出的50％以上,而面积仅占总面积的20％～52％；草地能量投入具有起伏性,产出具有波动性。草地土壤生态系统营养物质移出是草地土壤肥力退化的根本原因,无营养物质投入的人工草地更加剧了营养物质的迁出及土壤肥力的退化。

Effects of grassland amelioration on terrestrial ecosystem nutrients:a case study in Jianou Niukenglong Grassland Ecosystem Experimental Station, Fujian Province

This paper studies the effects of land cover changes on distributions andcirculations of nutrients in a terrestrial ecosystem, taking Jianou Niukenglong Grassland EcosystemExperimental Station as a case study. During a two year experiment from 1994 to 1996, the land covertypes were changed from desert slopeland to grasslands, in particular, Chamaecristarotundifolia(pers) green + Pasdum thunbergii and Glycine max var. + Pasalum thunbergii. In order tostudy land cover change effects on nutrients in the terrestrial ecosystem, we selected organicmaterials (OMs), nitrogen (N), phosphorus (P), potassium (K) and aluminum (Al) to study theirchanges in total soil nutrient concentrations, nutrient reserves in soil, distributions andreservations of nutrients in distinct grassland communities and overall nutrient contents reservedin terrestrial ecosystem, and their circulation with land cover change. The experimental resultsindicate that with the increase of vegetation coverage, the total concentrations of N, P and K growrapidly in the soil, but that of Al decreases markedly. The increases of the total concentrations ofN, P and K were mainly the consequences of changes of the factors that affect soil evolution, e.g.,soil moisture, and changes of soil evolution processes, e.g., weathering rate and the decrease ofsoil erosion. These changes were caused by land coverage growth from desert slopeland to grassland.With the change of the land cover types and the increase of land coverage, the activity of Alaccelerated as well, and the vertical penetration and lateral penetration of Al have been increased.Therefore, the loss of Al within the experimental terrestrial ecosystem was inevitable, and thetotal concentration and reserve of Al in soil have become smaller and smaller, in spite of thegrowth of grass absorbing some amounts of Al. The Al reserve has increased in vegetation, but it hasdeclined in total terrestrial ecosystem. Land cover change also affects the circulations ofnutrients in the terrestrial ecosystem and for the purpose of study on nutrient circulations, wechoose to study plant absorption, litter and reservation of nutrients to establish an index toindicate the situations of nutrient circulations within terrestrial ecosystems. The results indicatethat in the two land cover types (two grassland ecosystems), the sequence of nutrient circulationindices are N > K > P > Al in Chamaecrista rotundifolia(pers) green + Pasalum thunbergii and P > N >K > Al in Glycine max var. + Pasalum thunbergii. On the basis of the study, we can conclude thatland cover change affects both distributions and circulations in the terrestrial ecosystem, and thatdifferent changes have distinct influences on distributions and circulations. Some nutrients wereaffected differently in some contents.

Comparing Ecological Functions of Eastern and Southern Slopes of a Rangeland Ecosystem in Chaharbagh Region, Golestan Province, Iran

Getting aware of one kind of soil surface attributs is very important. Assessment of important attributes of soil and vegetation can help us to be aware of rangeland potential and help us to determine its situation. The goal of this research is to determine some plant and soil indicators of hilly winter rangelands of Eastern and Southern slopes of Chaharbagh region in Golestan province. By considering plant cover and soil surface attributes, it used the SSCC （soil surface classification） method to assess soil surface attributes. The length and width of ecological patches were measured in the forms of lichen, lichen-Grass, forbs, shrub and bare soil inter patches with litter. Also in this research, it measured the 11 soil surface parameters. These parameters are belonging to three main soil attributes stability, infiltration and nutrient cycles. These three indicators were measured in east and west of Eastern and Southern slopes of this ecosystem and showed significance differences （p 〈 0.05） in shrub, forbs and lichen-grass. In southern and especially in west aspect, these indicators in shrub were more than Eastern. But, in lossy hill of Eastern, lichen-grass patch is more significant. The most important ecological indicators of east landscapes of this region are forbs and lichen-grass.

Belowground Tritrophic Food Chain Modulates Soil Respiration in Grasslands

Edaphic biota significantly affects several essential ecological functions such as C-storage, nutrient turnover, and productivity.However, it is not completely understood how belowground animal contribution to these functions changes in grasslands subject to different land use types. A microcosm experiment was carried out to test the effect of a tritrophic food chain on CO_2 release from grassland soils. Soil was collected from three differently managed grassland systems(meadow, pasture, and mown pasture) located in three distinct German regions that cover a north-south gradient of approximately 500 km. The tritrophic food chain comprised natural edaphic microflora, nematodes, and predatory gamasid mites. The experimental design involved a full factorial combination of the presence and absence of nematodes and gamasid mites. Nematodes significantly increased the CO_2 emissions in most treatments,but the extent of this effect varied with land use type. The fact that grazing by nematodes stimulated the metabolic activity of the edaphic microflora over a wide range of grassland soils highlighted the critical impact of the microfauna on ecosystem services associated with soil organic matter dynamics. Gamasids slightly amplified the effect of nematodes on microbial metabolic activity,but only in the pastures. This effect was most probably due to the control of nematode abundance. The fact that gamasid addition also augmented the impact of environmental conditions on nematode-induced modulation of soil respiration highlighted the need for including land use differences while evaluating soil fauna contribution to soil processes. To conclude, the differential response of the investigated tritrophic food chain to different grassland management systems suggests that adverse effects of land use intensification on important soil processes such as atmospheric C-release could potentially be reduced by using management methods that preserve essential features of the belowground food web.

Microbial Biomass Dynamics in a Tropical Agroecosystem： Influence of Herbicide and Soil Amendments

The influences of herbicide alone and in combination with the soil amendments with contrasting resource qualities on dynamics of soil microbial biomass C （MBC）, N （MBN）, and P （MBP） were studied through two annual cycles in rice-wheat-summer fallow crop sequence in a tropical dryland agroecosystem. The experiment included application of herbicide （butachlor） alone or in combination with various soil amendments having equivalent amount of N in the forms of chemical fertilizer, wheat straw, Sesbania aculeata, and farm yard manure （FYM）. Soil microbial biomass showed distinct temporal variations in both crop cycles, decreased from vegetative to grain-forming stage, and then increased to maximum at crop maturity stage. Soil MBC was the highest in herbicide ＋ Sesbania aculeata treatment followed by herbicide ＋ FYM, herbicide ＋ wheat straw, herbicide ＋ chemical fertilizer, and herbicide alone treatments in decreasing order during the rice-growing period. During wheat-growing period and summer fallow, soil MBC attained maximum for herbicide ＋ wheat straw treatment whereas herbicide ＋ FYM, herbicide ＋ Sesbania, and herbicide ＋ chemical fertilizer treatments showed similar levels. The overall trend of soil MBN was similar to those of soil MBC and MBP except that soil MBN was higher in herbicide ＋ chemical fertilizer treatment over the herbicide ＋ wheat straw treatment during rice-growing period. In spite of the addition of equivalent amount of N through exogenous soil amendments in combination with the herbicide, soil microbial biomass responded differentially to the treatments. The resource quality of the amendments had more pronounced impact on the dynamics of soil microbial biomass, which may have implications for long-term sustainability of rainfed agroecosystems in dry tropics.