| The relationship between biodiversity and ecosystem function is a hot and difficult problem in the field of ecological research, but a lot of studies are mainly concentrated on the research of grassland ecosystems, aquatic ecosystems and farmland ecosystem, because the means of research is inadequate, studies of forest ecosystem are relatively seldom, as compared with those ecosystems. Subalpine coniferous forests located in eastern edge of Qinghai-Tibet Plateau and the upper area of Yangtze River, it played an important and irreplaceable role in biodiversity conservation, water conservation and the global carbon cycle. Meanwhile, subalpine coniferous forests have some characteristics, for example, the hierarchical structure is clear and species richness is relatively simple, the law of update and succession is clearer; the type of structure and function is more various and so on. Those characteristics provide an ideal natural laboratory for the study of the composition of forest species and variations of forest ecosystems function and the process as affected by diversity change. A large number of studies have shown that the process is closely related to soil biodiversity, vegetation and ecosystems, interaction relationship of soil biological communities and vegetation determine ecosystem processes, the soil ecosystem is likely a bridge which makes biodiversity contact with ecosystem function. Above all, spruce artificial pure forest and mixed forest which were planted in1988were studied in this paper, the effects of plant diversity on soil microbes, soil enzyme activity, litter decomposition though field positioning observation and woodland means of control experiments and the influence of plant diversity on soil ecological process. Those results would enrich theoretical studies of the forest ecosystem biodiversity and ecosystem function, and provide basic data for restoration and reconstruction of subalpine degraded forest ecosystems. The main findings are as follows:1. Effects of plant diversity on soil faunaDifferent types of stand showed differences of the structure and spatial and temporal distribution of soil animal community. There are7197soil animals in Picea asperata pure plantation(not including protozoa, the same below); there are8831soil animals in Picea asperata mixed plantation. The number, density, biomass and diversity index of soil animal group of Picea asperata mixed plantation were higher than Picea asperata pure plantation. Among them, the number, density, biomass and diversity indices of macro-fauna have a significant or very significant difference. The quantities of saprophagous and predatory soil fauna in Picea asperata mixed plantation are higher than Picea asperata pure plantation, but the quantities of phytophagous soil animals are less than Picea asperata pure plantation. The ratio of A/C was effected by latitude and altitude, to some extent, reflect the characteristics of the distribution of soil animals in different zones; it is related to the heterogeneity of habitat, the degree of interference and diversity of plant communities in the same zone. The ratio of A/C of Picea asperata pure plantation was0.87, Picea asperata mixed plantation wasl.59and is about1.83times former. Soil protozoa density of Picea asperata pure plantation was365in1g fresh soil, soil protozoa density of spruce mixed forest was1046in1g fresh soil was significantly higher than Picea asperata pure plantation. The profile distribution of soil fauna of two stand types both have apparent surface gathering, and similar seasonal dynamics, are higher in summer than in spring and autumn.Structure and distribution of soil animal communities showed different characteristics among different treatments.7529soil animals were collected in herb removal treatment (RH); the quantities of soil animals were6103in shrub removal treatment (RS).10986soil animals were collected in CK treatment. Through RH and RS treatment, the groups of soil macro-fauna showed increasing trend in short term, but the number of micro-and meso-soil fauna were decreasing; through RH and RS treatment, the density, biomass, and DG index of soil animals showed CK>RH>RS; number and proportion of saprophagous soil animals as well as A/C ratio were decreased, value of A/C was0.92in the RH treatment, value of A/C was0.82in the RS treatment, value of A/C of CK treatment was1.43; Through RH and RS treatment, soil protozoa density decreased,there were958soil animals in1g of fresh soil in RH treatment, there were1510soil animals in1g of fresh soil in RS treatment, there were2666soil animals in CK treatment, there was a significant difference among treatments; through RH and RS treatment, the profile distribution of soil animals has not changed, but a decreasing rate showed RS>RH>CK. Overall, effects of RS treatment on soil animal communities were more than RH treatment.2. The effects of plant diversity on soil microbesThere were different component, number, biomass and temporal and spatial distribution of soil microbes in different plant types. Bacteria had the largest number in Picea asperata pure plantation and Picea asperata mixed plantation compared with other microbes, the order was Bacteria>actinomycetes>fungi, but the fungi ratio in mixed plantation was higher than that in pure plantation. The total number of microbes in Picea asperata pure plantation was significantly lower than that in Picea asperata mixed plantation, and number of actinomycetes and fungi in pure plantation were extremely lower than that in mixed plantation. Bacteria, fungi, total soil microbe number and actinomycetes in pure plantation in surface soil layer was higher than that in other soil layers, the actinomycetes had the lowest number in litter layer, and highest number in0-5cm layer compared with other soil layers. The order of Biomass in Picea asperata pure and mixed plantation was summer>spring>autumn. Biomass of soil microbes is the easy to decompose part in soil organic matter, which is an important source and sink, the profile distribution and seasonal dynamics of C/N of microbe biomass had the same trends with microbes number, and Picea asperata mixed plantation higher than that in Picea asperata pure plantation.After shrub removal, soil microbes number, biomass and profile distribution changed a lot. The number order of soil bacteria and fungi was CK>RH>RS, and the number order of actinomycetes was RH>CK>RS. There was different affection on the microbes’biomass of soil layers after shrub and herb removal. The order of microbes’biomass in litter layer was RH>CK>RS, and The order of microbes’biomass in soil layers were CK>RH>RS, microbes’ biomass had negative response after shrub removal, and had positive response after herb removal after a short period. There no huge changes in microbe profile distribution after shrub and herb removal, but microbe number and biomass reduced with the soil depth increased, the highest was RS, and the lowest was CK.3. The effects of plant diversity on soil soil enzyme activityThere were diffrent activity of soil invertase, urease, cellulase and dehydrogenase in different plant types. All enzyme activity in the Picea asperata mixed plantation was higher than that in pure plantation. And enzyme activity in surface soil layer was higher than that in other soil layers, and had the same seasonal trends. The order of invertase, urease and dehydrogenase activity was autumn<summer/spring, the order of cellulase activity was summer/autumn>spring.After shrub cutting,4enzymes’activity reduced, the order was CK>RH>RS, and the enzymes’activity effected by removing shrub are higher than that of removing herb. The lowest degressive rate of4enzymes activity with the soil depth increased was CK, the highest was RS. And cellulase had the highest degressive rate with the soil depth increased among the4enzymes, and dehydrogenase had the lowest degressive rate.4. The effects of plant diversity on litter decompositionLitter decomposition had different characteristics in the different plantation. The decomposition rate of Picea asperata pure plantation was lower than that in the Picea asperata mixed plantation, decomposition ratio of Picea asperata pure plantation and mixed plantation is65.51～99.63%. the significant difference was found in early period, and there was tiny difference in later period. The contribution of soil microbes and meso-fauna (mainly nematode and protozoa) to litter decomposition in Picea asperata pure plantation are68.71～94.03%, contribution of soil macro-fauna to litter decomposition was5.97～31.29%; The contribution of soil microbes and meso-fauna to litter decomposition in Picea asperata mixed plantation are90.29～94.22%, contribution of soil macro and meso-fauna to litter decomposition was5.78～9.71%. The interaction decomposition of soil microbes and soil fauna were higher that effect of pure soil microbes or soil fauna. The front2years’ decomposition, P、K、Ca、Mg element showed releasing, but the N showed enrichment. Releasing quantity of mixed plantation was higher that in pure plantation.After shrub and herb removal, the litter decomposition rate decreased, and litter decomposition rate decreased caused by shrub removal was higher than that in herb removal. The interaction decomposition of soil microbes and soil fauna were higher that effect of pure soil microbes or soil fauna. The front2years’ decomposition, P、K、Ca、Mg element showed releasing, but the N showed enrichment. Shrub removal had negative effect on the litter decomposition, N、P、K、Ca element showed releasing excepting Mg. Herb removal had positive effect on K releasing, and had little affection on the N、P、Ca releasing, the releasing quantity had no significant difference compared with CK. After shrub and herb removal, the changes of soil fauna, soil microbes and enzyme activity during the litter decomposition hadn’t the order CK>RH>RS, but had more complicated models. The result can be conclude that the shrub and herb removal lead to the composition and quality changes, and the soil fauna diversity and the change trends of enzyme were the main factors which lead to litter decomposition and nutrition cycle during the litter decomposition. Meanwhile, the removal is an important interference which affects the biodiversity and material cycle; the interference affection was significant in early period.To summary, compared with rich plant diversity plantation, the soil biodiversity, soil enzyme activity, and litter decomposition rate were lower than that in the poor plant diversity plantation. Stronger affection on the soil ecology process was found in shrub removal compared with herb removal. Therefore, to increase plant diversity, to enrich litter composition, to interact upper and underground organisms, to improve nutrition recycles, can enhanced the functions of forest ecosystem. |
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