3.4 | Relationships between diet composition and fatty acid
To interpret the influences on fatty acid deposition, we conducted an association analysis to map important taxa in the desert steppe. Principal component analysis was performed to characterize the correlation structure among response variables in grazing type treatments (Figure 4 and Table 4). The eigenvalues of the first and second axes were 0.399 and 0.227, respectively. Axis 1 was dominated by Corispermum sp. , Salsola sp. , andBassia scoparia with positive values (score values: > |0.7|) and Artemisia sp . and Chenopodium sp . with the negative values (score values: > |0.7|). Axis 2 was primarily explained by three n-3 PUFAs indicators with positive values (score values: > |0.5|) and Euphorbia humifusa , Arnebia euchroma , Oxytropis halleri , andIxeris tamagavaensis with positive values (score values: > |0.6|).
RDA was conducted to further assess the association in the data set relative to all treatments (Table 4 and Figure 5). Two axes explained 59.7% of the total variance. The grazing treatment was markedly different from the time-limited grazing treatment, with more plentiful herbage species and greater n-3 fatty acids (RDA axis1,R 2 = 0.220, F = 6.20, P = 0.002).Arnebia euchroma , Euphorbia humifusa , Salsola sp. ,Bassia scoparia , Oxytropis halleri , and Ixeris tamagaxaensis positively influenced n-3 PUFAs compostion via C18:3n3, C20:5n3, and C22:6n3.
Finally, we constructed 171 herbage-PUFAs pairs consisting of 12 herbage species and 6 n-3 PUFAs. Figure 6 shows the interaction patterns among herbage-PUFAs pairs. Table S1 lists the correlation coefficients of these pairs. Of the 171 pairs, 47 (27.5%) were correlated at P< 0.05 or P < 0.01, corresponding to 10 unique herbage taxa. The correlation coefficients ranged from -0.410 to 0.959, among which Salsola sp. , Bassia scoparia ,Euphorbia humifusa , and Arnebia euchroma exerted significant influence on the n-3 PUFAs. We found that C18:2n6 was positively correlated with Lespedeza sp . (P < 0.05).