文库下机后，所有样本统一进行拆分、去除barcode和引物、拼接和初步质控，得到cleandata，将cleandata作为qiime2的输入文件。 dada2去噪时，由于输入序列没有barcode和引物，所以左端没有进行截取，–p-trim-left 默认是0，初步质控后双端拼接后的碱基质量值均很高，且拼接后的长度不确定，所以截取长度–p-trunc-len是0（不截取），其余均为dada2的默认参数

–p-max-ee Reads with number of expected errors higher than this value will be discarded. default: 2.0 –p-trunc-q Reads are truncated at the first instance of a quality score less than or equal to this value. If the resulting read is then shorter than `trunc-len`, it is discarded. default: 2 –p-pooling-method The method used to pool samples for denoising. “independent”: Samples are denoised indpendently. “pseudo”: The pseudo-pooling method is used to approximate pooling of samples. In short, samples are denoised independently once, ASVs detected in at least 2 samples are recorded, and samples are denoised independently a second time, but this time with prior knowledge of the recorded ASVs and thus higher sensitivity to those ASVs. default: 'independent'

其余参数可参考官网：https://docs.qiime2.org/2023.2/