Interactions Between Invertebrate And Microbial Communities In Decomposing Litter Along With The Change Of Altitude

It is well known that both invertebrate and microorganism play a vital and irreplaceable role in litter decomposition, and their interactions might run the process of litter decomposition in terrestrial ecosystems.As yet the interactions between invertebrate and microbial communities in decomposing litter along with the change of altitude remain unclear. As one of the most important branches in the upper of Yangtze River, Minjiang river basin is of ecological significance in regulating regional climate, nursing biodiversity, holding water and conserving soils. In particular, the vertical differential chacteristics of vegetations and soils with elevated altitudes provides with an ideal natural lab for studying the variations of interactions between invertebrate and microbial communities with increasing elevations and critical periods. In order to understand the changes in interactions between invertebrate and microbial communities in decomposing litter with the critical periods and altitudes, litterbags with 14 kinds of foliar litter along an altitudinal gradient in the Minjiang river basin were therefore incubated on the soil surfaces, and the dynamics of invertebrate and microbial communities in decomposing litter were measured at different critical periods.1) The results indicate the increase of elevation and the decrease of rainfall inhibit the invertebrate activity. In the time of enough rainfall and heat, not only the variety and quantity of the invertebrate were great, but also the Shannon-weiner diversity, the Pielou evenness and the Margalef richness. However some invertebrate activity restrained when there was lack of rainfall and heat which lead a high Simpson dominance index of invertebrate. That means the key factor what can control the invertebrate activity is the different of the rainfall and heat caused by elevation graduate.2) During the decomposition progress, the group density and the Shannon-weiner diversity of the invertebrate got more gradually with the Simpson dominance losing. And the individual density reached the highest point in the second December. In the diverse ecosystems, the difference of the invertebrate group and individual density had no significance during the first year amount the decomposition progress, but it appeared biggish during the second year just like the Shannon-weiner diversity, the Pielou evenness, the Simpson dominance and the Margalef richness showed in the both years. Those prove that the activity of the invertebrate in soil changes along with the decomposition progress.3) Bacteria was the main ingredient in microorganism community while microorganism was controlled by rainfall and heat which drived by altitude. When there was lack of rainfall and heat bacteria activity was inhibited while fungus activity had risen which contributed to litter decomposition.4) Microorganism diversity and evenness showed in the order Arid valley-forest ecotone (AVF)>Subalpine forest (SAF)>North subtropical forest (NST)>Alpine meadow (AM)>Mid-subtropical forest (MST)>Alpine forest (AF)>Arid valley (AV) while richness showed in the order AV>AVF>SAF>NST>MST>AF>AM. The dominance presented as AF>AV>MST>AM>SAF>NST>AVF.5) The total phospholipid fatty acid (PLFA) biocontent and bacteria PLFA biocontent were higher in the winter than in the growing season in the first year that just contrary in the second year. Fungus PLFA biocontent and ratio of fungus to bacteria in preliminary stage were higher than in other stage. Gram-positive bacteria PLFA biocontent and ration of gram-positive bacteria to gram-negative bacteria in the first year were lower than in the second year.6) Under controlling by ecosystem, litter type and sampling stage, invertebrate has a significant effect on microorganism. There was a competitive relationship between invertebrate and microorganism in alpine/ subalpine region. Invertebrate promoted microbial activity but dropped stability of microbial community structure in arid valley-forest and arid valley region. During the 2 years decomposition process, with increasing of invertebrate individual density and group density, activity of bacteria was promoted while activity of fungus was dropped.7) Invertebrate and microorganism have significant effects on litter mass loss.Invertebrate accelerated rate of herbaceous and coniferous litter mass loss, meanwhile inhibited rate of broad-leaved litter mass loss. Except litter of C.macrocarpa, mass loss ratio of rest litter had a negative correlation with fungus PLFA biocontent and a positive correlation with bacteria. The contribution of invertebrate and microorganism to litter mass loss was controlled by ecosystem, sampling stage and litter type.Litter decomposition not only changed along with gradient ascent but also controlled by litter quality and microenvironment. The interaction between invertebrate and microorganism was changed along with gradient ascent which largely in control litter decomposition process. On the whole, no matter the interaction between invertebrate and microorganism or the contribution to litter decomposition of them both regulated by litter quality, ecosystem and decomposition period.