Freshwater Macroinvertebrate Laboratory, Zoological Collection Dr. Eustorgio Mendez, Gorgas Memorial Institute for Health Studies (COZEM-ICGES), Ave. Justo Arosemena and Calle 35, 0816-02593 Panama City, Panama.
Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain.
Sci Total Environ. 2020 Nov 25;745:140950. doi: 10.1016/j.scitotenv.2020.140950. Epub 2020 Jul 17.
The expansion of agriculture is particularly worrying in tropical regions of the world, where native forests are being replaced by crops at alarming rates, with severe consequences for biodiversity and ecosystems. However, there is little information about the potential effects of agriculture on the functioning of tropical streams, which is essential if we are to assess the condition and ecological integrity of these ecosystems. We conducted a litter decomposition experiment in streams within a tropical catchment, which were subjected to different degrees of agricultural influence: low (protected area, PA), medium (buffer area, BA) and high (agricultural area, AA). We quantified decomposition rates of litter enclosed within coarse-mesh and fine-mesh bags, which allowed the distinction of microbial and detritivore-mediated decomposition pathways. We used litter of three riparian species representing a gradient in litter quality (Alnus acuminata > Ficus insipida > Quercus bumelioides), and examined detritivore assemblages through the contents of litterbags and benthic samples. We found that the increasing agricultural influence promoted microbial decomposition, probably due to nutrient-mediated stimulation; and inhibited detritivore-mediated and total decomposition because of reduced detritivore numbers, most likely caused by pesticides and sedimentation. Effects were evident for Alnus and Ficus, but not for Quercus, which was barely decomposed across the gradient. Our study provides key evidence about the impact of agriculture on tropical stream ecosystem functioning, which is associated to changes in stream assemblages and may have far-reaching repercussions for global biochemical cycles.
农业的扩张在世界热带地区尤其令人担忧，在这些地区，原生森林正以前所未有的速度被农作物取代，这对生物多样性和生态系统造成了严重后果。然而，关于农业对热带溪流功能的潜在影响的信息却很少，而了解这些影响对于评估这些生态系统的状况和生态完整性至关重要。我们在一个热带集水区内的溪流中进行了一项凋落物分解实验，这些溪流受到不同程度的农业影响：低（保护区，PA）、中（缓冲区，BA）和高（农业区，AA）。我们量化了包裹在粗网和细网袋内的凋落物的分解速率，这使得能够区分微生物和碎屑食者介导的分解途径。我们使用了三种河岸物种的凋落物，它们代表了凋落物质量的梯度（桤木>榕属>栓皮栎），并通过凋落物袋和底栖样本中的内容物来检查碎屑食者的组合。我们发现，农业影响的增加促进了微生物分解，这可能是由于养分介导的刺激；并抑制了碎屑食者介导的和总分解，因为碎屑食者数量减少，这很可能是由农药和沉积物造成的。桤木和榕属受到了影响，但栓皮栎没有，因为栓皮栎在整个梯度上几乎没有分解。我们的研究提供了关于农业对热带溪流生态系统功能影响的关键证据，这与溪流生物群落的变化有关，可能对全球生物化学循环产生深远影响。
