3.3 | Diet characterization
Plant sequences from the samples were gathered into 56 taxa based on the lowest taxonomic classification (genus or species level) that could be determined confidently from GenBank and EMBL. The most abundant sequences in the pool of potential food items were those related toLespedeza sp. (30.78%). Next were those related toArtemisia sp. (16.27%), Chenopodium sp. (14.44%), andCorispermum sp. (11.83%). In total, 26–44 diet items derived from different taxa (mean = 35) were present in the diets of lambs.
PCoA via the Binary-Jaccard algorithm of diet communities revealed that diets segregated mainly by preference for a handful of plant species (Figure 1c). For all the diet item plant communities, a slightly higher dependency on grazing type than grazing period was the most important driving factor contributing to the variation in diet composition, explaining 18.25% of the variation. The second most important distinction in diet composition was the different compositional herbage species changing with the growing season. ANOVA results indicated that there was significant interaction between the grazing modes and sampling period (R2 = 0.50, P= 0.001). The predominant diet items in all samples are summarized and shown in the heatmap (Figure 1d). In general, the dominant genera in different grazing types and within the same modes in different periods had numerous differences.
The top 20 taxa accounting for 97.96% of the total sequence reads were used to investigate the diet composition of Tan sheep. Overall,Lespedeza sp ., Artemisia sp ., Chenopodium sp ., andCorispermum sp . were found to be the most predominant herbage groups, being present in 100% of samples (FOO) and comprising 73.30% of the total of diet DNA sequences (RRA) (30.81%, 16.29%, 14.40%, and 11.80%, respectively). Phellodendron amurense , Medicago sativa , Salsola sp ., Bassia scoparia , Euphorbia humifusa , Eragrostis sp ., Ixeris tamagawaensis ,Setaria italica , and Cenchrus flaccidus were also present in 100% of the samples, comprising 3.94%, 3.32%, 3.14%, 2.51%, 2.05%, 1.47%, 1.23%, 0.78%, and 0.61% of RRA, respectively. Other plant taxa included Sibbaldianthe bifurca at 95.83% (1.05% RRA) and Arnebia euchroma at 91.67% (1.59% RRA). Oxytropis halleri , Chloris pilosa , Convolvulus sp .,Astragalus peterae , and Caragana korshinskii were present at 83.33%, 33.33%, 91.67%, 75.00%, and 91.67% FOO, respectively (< 1% RRA; Table 3, Figure 2).
The multiple RRA measurements were averaged for each type-stage combination. As shown in Figure 3, the stacked bar charts indicate that the prevalent genera in the grazing group were basically the same as those in the time-limited grazing group, dominated by species such asLespedeza sp. , Artemisia sp. , Chenopodium sp. , Corispermum sp. , and Phellodendron amurense , whereas the proportions quite different (P < 0.05, Figure 3 and Table 3).