Effects of plant diversity on soil microbes.doc

vol.10 no.3 肖辉林等：植物多样性对土壤微生物的影响 241article id：1008-181x (2001) 03-0238-04effects of plant diversity on soil microbesxiao hui-lin1, zheng xi-jian2( 1: guangdong institute of eco-environmental and soil sciences, guangzhou 510650, china;2: guangzhou station of environmental monitoring, guangzhou 510030, china )abstract: ecosystem processes are strongly affected by biodiversity. changes in ecosystem processes may themselves lead to a decline in biodiversity and thus to further reductions in ecosystem function. plant species richness and plant functional diversity have a positive influence on overall catabolic activity and catabolic diversity of soil bacterial community. catabolic activity and catabolic diversity of soil bacteria increased linearly with the logarithm of plant species number and with the number of plant functional groups. these effects may have been caused by an increased diversity and quantity of material and energy flows to the soil. they may also have been mediated by increased diversity of soil microhabitats via a stimulation of the soil fauna. a reduction in plant biomass caused by a loss in plant diversity is expected to have strong effects on the decomposer community: microbial biomass is likely to decrease, because organic carbon sources limit soil microbial activity in most terrestrial ecosystems. key words: plant diversity; soil microbes; ecosystemclc number: q16; s154.36 document code: a植物多样性对土壤微生物的影响肖辉林1，郑习健2（1：广东省生态环境与土壤研究所，广东 广州510650；2：广州市环境监测中心站，广东 广州 510030）摘要：生物多样性强烈地影响生态系统的过程。生态系统过程的变化可导致生物多样性衰减并因此导致生态系统功能衰退。植物种丰度和植物功能多样性对土壤细菌群落的代谢活性和代谢多样性有成正比的影响。土壤细菌的代谢活性和代谢多样性随植物种数量的对数和植物功能组的数量而直线上升。其原因可能是由植被流入土壤的物质和能量的多样性和数量的增加，也可能是由土壤动物区系起作用的土壤微生境的多样性的增加造成的。由于植物多样性的丧失所引起的植物生物量的减少对分解者群落有强烈的影响：微生物生物量将可能减少，因为在大多数陆地生态系统中，有机碳源限制着土壤微生物的活性。关键词：植物多样性；土壤微生物；生态系统中图分类号：q16; s154.36 文献标识码：abiodiversity or biological diversity, is defined as the variety of species and the variability of living organisms, their habitats and the biological ecosystems, encompassing the ecological and evolutionary processes of the natural environment. biodiversity is the wealth of species ecosystems and ecological processes that help make possible the economic and environmental systems. mankind depends on earths biodiversity for food, fiber, medicines and new products. the loss of biodiversity is one of the major threats to the worlds ecosystems in the 21st century. ecosystem processes are strongly affected by biodiversity, but the functional relationship between the two depends on the system considered1, 2. in all cases, however, processes must be maintained so that the ecosystem can continue to exist in either a constant or a changing environment. functional redundancy of similar species may stabilize ecosystem processes during occasional species extinctions3, but this ability appears to be limited4. changes in ecosystem processes may themselves lead to a decline in biodiversity and thus to further reductions in ecosystem function. terrestrial ecologists has always given at least some thought to the chemistry and physical structure of the soil. but only recently have they begun to understand that soil biodiversity is a crucial factor in regulating how ecosystems function. over the past few years, ecologists have realized that many of the most important interactions between plants take place below ground, particularly in the third of the worlds soils that are poor in nutrients. in such soils, the dynamic interactions between plant roots, animals and microbial processes seem to determine what grows where and how. as ecologists have begun to pick up their shovels, they have been faced with a huge challenge: a single cubic metre of temperate grassland soil contains thousands of species of microorganisms and invertebrates whose identities and activities are largely unknown. there is ecology that is as complex as any of the community and ecosystem ecology that has been studied above ground.studies5 show that plant species richness and plant functional diversity have a positive influence on overall catabolic activity and catabolic diversity of the culturable bacterial community in the bulk soil in an experimental grassland ecosystem. although these bacterial represent only a small fraction of taxa present in the soil, there are a useful indicator group for measuring the effects of the autotrophic plant components on the bacterial decomposers in such a system. the increased oxidation of the c sources supplied reflects an increased bacterial density6 while the increase in catabolic diversity reflects the use of different carbon-oxidation pathways and therefore functional diversity7. it is unlikely that a single genotype or low-level taxonomic unit could express so much plasticity in c-source utilization, and this functional diversity is therefore probably related to taxonomic diversity68. however, plants show redundancy among taxa within functional groups, and a similar situation may exist within bacterial communities, so that functional diversity would provide a minimum estimate of taxonomic diversity. catabolic activity and catabolic diversity of culturable soil bacteria increased linearly with the logarithm of plant species number and with the number of plant functional groups5. these effects may have been caused by an increased diversity and quantity of material and energy flows to the soil. they may also have been mediated by increased diversity of soil microhabitats via a stimulation of the soil fauna. earthworms are decomposes of dead plant material. they and other macrofauna mix organic material in the soil, reduce the size of the detritus particles and made them available to microbes. micro- and mesofauna feed on microbes and thereby increase microbial turnover and plant nutrient availability. a reduction in plant biomass caused by a loss in plant diversity is expected to have strong effects on the decomposer community: microbial biomass is likely to decrease, because organic carbon sources limit soil microbial activity in most terrestrial ecosystems9. when changes in biodiversity affect primary production, there may be associated subsequent effects on soil heterotrophic organisms and decomposition due to this change in biomass.the diversities of different trophic levels may be expected to be linked if one level is limiting the other in a bottom-up10 or top-down process. higher plant diversity may have influenced the soil bacteria by increasing the diversity of litter, the heterogeneity of soil microhabitats, or energy and material flows from the vegetation to the soil. the density of earthworms increased by 63% across the range of diversities11, suggesting that effects of plant diversity on bacterial activity were probably mediated to some extent by increased heterogeneity of soil microhabitats. above-ground biomass increased with increasing plant species richness11 and enhanced flow to the soil may well also have contributed to the positive effect on bacteria. experimental results show a positive influence of plant diversity on c-source utilization patterns in soil samples and thus on the activity and functional diversity of culturable bacteria in the bulk soil6. the relationship may be a mutual one in that plants may also profit from diverse soil bacterial communities, e.g. mediated by better nutrient mineralization, growth stimulation, and enhanced antibiosis to pathogens12, 13. mutural relationships between plant and soil organismic diversity have also been suggested for the plant-arbuscular mycorrhizal system. mycorrhizal fungi grow through the soil, colonizing the roots of various plants and sometimes forming links between them. in the case of trees colonized by ectomycorrhizal fungi - which surround but do not grow into plant roots - carbon can be transferred from one tree to another through the fungi. arbuscular mycorrhizae, which actually grow into the roots, forming intimate connections with their cells, influence the diversity and productivity of plants in the soil they inhabit and protect them from pathogens. they also release a glycoprotein that affects the physical structure of the soil, seeming to boost its stability14. but the structure and dynamics of these fungal communities are only just beginning to be uncovered. they are exceptionally important and exceptionally poorly understood. differences in the allocation of carbon in grass species significantly affects bacteria and bacteria-feeding nematodes in the rhizosphere15. large differences in nitrogen mineralization occurred in initial identical soils after 3 years of growth of monocultures of different perennial grass species16 due to differences in the quality and quantity of plant litter17. a diverse mix of litter can affect decay rates, although measurements of mixed-species litter decomposition18 have yielded inconsistent results. in some studies, responses of decomposition rates are idiosyncratic, with both synergistic and antagonistic effects of litter diversity19, 20. other studies showed no significant effects in decay rates when litter of species was mixed together as compared to monospecific litter21, 22. finally, food supply over the season is more variable in communities with low plant species richness because different phonologies of species overlap less in time23. a reduction in plant species richness can therefore have considerable effects on the decomposer subsystem, via (a) effects on plant biomass production, (b) effects of differences in chemical composition of plant debris, or (c), via the timing of debris provision. in most agro-ecosystems, microbial growth is limited by input of fresh organic carbon and hence plant-biomass production24. a sensitive measure for short-term responses to c inputs into soil is the microbial biomass supported per unit of total organic soil carbon cmic/corg ratio25. this ratio also significantly decreased with a decrease in plant species richness or plant biomass, which may be an early indicator for a longer-term decline in soil organic matter of low-diversity mixtures. this is in accordance with the assumption that primary production largely controls soil organic matter as is embodied in ecosystem carbon models. wardle and nicholson20 showed that soil microbial biomass is primarily set by plant biomass production, but is also influenced by the identity and number of plant species present. a decrease in plant species richness may therefore affect microbes directly. one reason could be a decrease in resource heterogeneity. christie et al.26, 27 found less microbial biomass when lolium perenne and plantago lanceolata, were grown separately as compared to growing together. decomposer communities changed when mixed species litter assemblages were provided (irrespective of total n inputs in foliar litter), although the direction of changes remained unpredictable21. another way in which diversity could directly affect decomposers is through the spatial and temporal provision of substrate, which may have been much more patchy in low compared with high species diversity and therefore could have contributed the lower microbial biomass per unit of soil28. in addition to effects mediated by greater plant biomass with increasing plant species richness, the mixed diet was also beneficial for microbes. references:1 schlpfer f, schmid b. ecosystem effects of biodiversity: a classification of hypotheses and cross-system exploration of empirical results j. ecological applications, 1999, 9: 893-912. 2 schlpfer f, schmid b, seidl i. expert estimates about effects of biodiversity on ecosystem processes and services j. oikos, 1999, 84: 346-352. 3 baskin y. ecologists dare to ask: how much does diversity matter? j. science, 1994, 264: 202-203. 4 tilman d, downing j a. biodiversity and stability in grasslands j. nature, 1994, 367: 363-365. 5 stephan a, meyer a h, schmid b. plant diversity affects culturable soil bacteria in experimental grassland communities j. j ecol, 2000, 22: 988-998.6 haack s k, garchow h, klug m j, et al. analysis of factors affecting the accuracy, reproducibility, and interpretation of microbial community carbon source utilization patterns j. applied and environmental microbiology, 1995, 61: 1458-1468. 7 vres l, torsvik v. microbial diversity and community structure in two different agricultural soil communities j. microbial ecology, 1998, 36: 303-315. 8 baath e, diaz ravina m, frostegard a, et al. effect of metal-rich sludge amendments on the soil microbial community j. applied and environmental microbiology, 1998, 64: 238-245.9 van de geijn s c, van veen j a. implications of invreased carbon dioxide levels for carbon input and turnover in soils j. vegetation, 1993, 104/105: 283-292. 10 brown v k, southwood t r e. trophic diversity, niche breadth and generation times of exopterygote insects in a secondary succession j. oecologia, 1983, 56: 220-225. 11 spehn e m, joshi j, schmid b, et al. plant diversity effects on soil heterotrophic activity in experimental grassland ecosystems j. plant and soil, 2000, 224: 217-230.12 grayston s j, campbell c d. functional biodiversity of microbial communities in the rhizospheres of hybrid larch (larix eurolepis) and sitka spruce (picea sithensis) j. tree physiology, 1996, 16: 1031-1038. 13 kim k y, jordan d, mcdonald g a. enterobacter agglomerans, phosphate solubilizing bacteria, and microbial activity in soil: effect of carbon sources j. soil biology and biochemistry, 1998, 30: 995-1003. 14 wright s f, upadhyaya a. extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi j. soil sci, 1996, 161: 575-586. 15 griffiths b s, welschen r, von arendonk j j c m, et al. the effect of nitrate-nitrogen on bacteria and the bacterial feeding fauna in the rhizosphere of different grass species j. oecologia, 1992, 91: 253-259. 16 wedin d a, tilman d. species effects on nitrogen cycling: a test with perennial grass j. oecologia, 1990, 84: 433-441. 17 wedin d, pastor j. nitrogen mineralization dynamics in grass monocultures j. oecologia, 1993, 96: 186-192. 18 jenkinson d s, fox r h, rayner j h. interactions between fertilizer nitrogen and soil nitrogen-the so-called priming effect j. j soil sci, 1985, 36: 425-444. 19 wardle d a, bonner k i, nicholson k s. biodiversity and plant litter: experimental evidence which does not support the riew that