| Soil microorganisms play a critical role in regulating litter decomposition, nutrient cyclingand humus formation and transformation, and closely associate with above-ground plantcommunites in terrestrial ecosystems. It has been well known that soil microorganisms acquirecarbon from organic source primarily supplied by plants. Above-ground plants can exert director indirect effects on microbial biomass, activities, and even shape microbial communitycomposition. Soil microorganisms, in turn, influence plant growth and community compositionthrough modifying inorganic nutrient supply that is acquired by plants. In this study, we focuson top-down effects of plants on soil microbial biomass, activities and community compositionusing a in-situ field experiment, and bottom-up effects of soil microbes, especially soil fungi, ontarget plant growth and coexistence by a pot experiment with fungi sterilization. Theexperiments were conducted in a subtropical even-green broaden-leaf forest in Gutianshan,Zhejiang Province of eastern China. Two plant species, Pinus massoniana and Lithocarpusglaber, were as target plant species. The main results are as follows:(1) The leaf litter decomposition rate of Pinus massoniana and Lithocarpus glaber showedobvious seasonal dynamics. The higher decomposition rate of Pinus massoniana emergedduring the wet season (April and September), while there were relatively lowerdecomposition rate in the dry season (Feburary and July). The decomposition rate ofLithocarpus glaber showed a gradual increasing trend. After10-months decomposition, themass loss of Pinus massoniana and Lithocarpus glaber were31.53%and27.63%,respectively.(2) Soil physicochemical factors did not vary with the distance to target tree species, i.e., Pinusmassoniana and Lithocarpus glaber, but showed significant time dynamics. In comparisonwith those within the canopy of Lithocarpus glaber (LG region) and the interval regionbetween Pinus massoniana and Lithocarpus glaber, soil organic carbon (C) and nitrogen (N)content within the canopy of Pinus massoniana (PM region) were the highest,42.37g.kg-1and1.41g.kg-1, respectively. Soil moisture in the interval region was32.66%higher thanthose in soils of LG and PM region, while soil pH in LG region was4.94, higher than thosein soils of interval region and PM region.(3) The spatial trends of soil microbial biomass, microbial respiration and soil microbial community were similar to soil physicochemical parameters. There were no significantdifferences in these microbial parameters among LG, PM and interval regions, but theyvaried with time. The highest microbial biomass C in all three regions occurred in September,while microbial biomass N and repiration significantly decreased at the same time. Thefunctional groups of microbial communities, including Gram-positive bacteria,Gram-negative bacteria, fungi and bacteria, also showed a pronounced seasonal dynamics.(4) In the pots without fungi sterilization, the height of Pinus massoniana growing in the soilscollected in the LG region in the natural forest was larger than those growing in soilscollected from interval region and PM region, indicating a positive soil feedback. Soil fungimay play a critical role in this process of soil feedback, because no simulation of Pinusmassoniana growth by LG region soils was observed under fungi sterilization.The resultcan, to some extent, support speculation that Kimi et al (2010) proposed in their modelanalysis, that is soil borne microbes may contribute to the feedbacks and consequentlyaccelerate co-existence of adjacent tree species.(5) Using universal primers Arch-amoAF/Arch-amoA ammonia oxidizing archaea AOAidentified by PCR, a690bp fragment averaging around. AOA ammonia-oxidizing archaeawere no significant differences among PM, LG and interval, and also has seasonal dynamics.Ammonia oxidizing archaea AOA was highest in July. Sterilization did not induce changesin Ammonia oxidizing archaea AOA in the pots. However, in the pots without sterilization,Ammonia oxidizing archaea AOA was significant higher under Pinus massoniana with LGand interval soils compared to those under Pinus massoniana with PM. |
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