Tree girdling affects the soil microbial community by modifying resource availability in two subtropical plantations

Abstract

We used tree girdling and phospholipid fatty acid (PLFA) analysis to evaluate the effect of nutrient availability and rhizodeposition on soil microbial community composition in two plantations (Acacia crassicarpa and Eucalyptus urophylla) in subtropical China. The magnitude of the girdling effect was also evaluated as a function of tree species and time after girdling (2 months vs. 9 months). In both plantations, tree girdling reduced the concentration of fungal PLFAs and increased the concentration of bacterial PLFAs with a consequent decrease in the fungi/bacteria ratio, but did not affect the concentration of total PLFAs. Tree girdling affected the concentration of gram-negative PLFAs and the ratio of gram-positive bacteria to gram-negative bacteria at 9 months but not at 2 months after girdling. The ratio of cy17:0 to 16:1ω7c was increased by girdling of A. crassicarpa, indicating a stressful and nutrient-deficient habitat for soil microorganisms, but was inconsistent for girdling of E. urophylla. In the A. crassicarpa plantation, responses to girdling for most microbial groups were associated with changes in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), the ratio of carbon to nitrogen, and soil pH. In the E. urophylla plantation, responses to girdling were associated with changes in DON, DOC, and NO3−-N. These results confirm that (i) recent photosynthates allocated belowground affect soil C and N availability and therefore greatly affect microbial community composition in subtropical plantations; (ii) the magnitude of the tree girdling effect increases with time after girdling and differs between plant species; and (iii) soil microbial communities are closely linked to vegetation types and plant C allocation.