دانلود رایگان مقاله اثرات ضمیمه کیسه توری و موریانه ها در تجزیه باقی مانده چوبی

Abstract

The role of insects in terrestrial decomposition remains poorly resolved, particularly for infrequently studied substrates like small diameter woody debris. Uncertainty about how mesh bags used to exclude arthropods may affect decomposition rates continues to impede progress in this area. We sought to (1) measure how insects affect the decomposition of small diameter (<2.5 cm) Triadica sebifera L. “twigs” and (2) test for unintended effects of mesh bags on wood decomposition using machined wooden dowels of similar size and specific gravity. In subtropical forests, three twig diameter classes plus dowels were enclosed in two mesh sizes (0.3 or 1 mm openings) or left unenclosed over a 20-month study period. Unenclosed twigs lost significantly more mass than those within fine mesh bags. Because this effect was consistent throughout the study (reaching nearly 80% mass loss), our findings suggest the invertebrate influence does not disappear or attenuate over time. Our dowel data (limited to dowels with no evidence of insect activity) show that fine and coarse mesh bags accelerate the decomposition of enclosed woody material, suggesting insects contributed even more to the decomposition of tallow twigs than our measure of 9 – 10%. Termites exhibited a strong preference for larger diameter twigs, resulting in temporary differences in decomposition rates among diameter classes. Our findings confirm the importance of insects to wood decomposition and highlight the need to incorporate these organisms in models of carbon and nutrient cycling.

Discussion

The dowelmethod described herein was effective in revealing the accelerative effects of both fine and coarse mesh bags on fine woody debris decomposition. The mesh bags were also shown to increase the water content of enclosed dowels, possibly explaining differences in dowel mass loss observed among the treatments. These results confirm that significant unintended effects are probable in decomposition studies involving the use of mesh bags for excluding invertebrates. Our findings suggest that mesh bags are likely to underestimate, rather than exaggerate, the effects of invertebrates on decomposition although additional research will be needed to determine how consistent this pattern is across study systems and mesh sizes. Tallow twigs completely unprotected from attack by termites and other insects lost significantly more massthan those enclosed within fine mesh bags. Beginning at 8 months, there was a consistent difference in mass loss between these treatments of 9 – 10%. This likely underestimates the true contribution of invertebrates, however, judging from the nature of the mesh bag effect reflected in our dowel data. While these data clearly indicate the direction of the mesh effect, the magnitude of this influence on tallow twig mass loss cannot be determined given differences in the decay rates and characteristics (e.g., bark coverage) between the two substrates. Despite this limitation, it is possible to conclude, with an unprecedented level of certainty, that the contribution of insects to fine woody debris decomposition, as measured in this study, is at least 9 – 10%.