Overall, (1) low quantities of soil-derived N in combination with (2) high contents of easy available N result in rapid plant litter decomposition of L. corniculatus compared with C. epigejos due to (3) high C/N ratios and hence lower microbial degradation of C. epigejos. The application of plant
litter resulted in a significant stimulation (P<0.05) of the total microbial biomass in all treatments, irrespective of the method used (Fig. 2a and b). The highest biomass values were found in the L. corniculatus treatments 4 weeks after litter application. Surprisingly, microbial biomass at later sampling times decreased in L. corniculatus treatments and was not significantly different from that of C. epigejos. The relative content of litter-derived 13C in the microbial biomass followed the same trend. The results of the present study agree with the findings of recent EPZ-6438 chemical structure studies, which postulated
a stimulation of the microbial biomass as a result of the fast decomposition of attractive and easily available C (Xiao et Autophagy activator al., 2007; Poll et al., 2008; Jin et al., 2010). In the L. corniculatus treatment, within 4 weeks, the available plant litter nutrients were incorporated by the soil microbial biomass, whereas higher amounts of available compounds in L. corniculatus can be directly linked to a higher stimulation of the soil microbial biomass due to the increased 13C incorporation. After 12 weeks of incubation,
a decline in microbial biomass in the L. corniculatus treatment indicated a second phase in the litter much decomposition process. This process could be characterized by an increasing complexity of the available substrate, causing a shift in the microbial community structure towards slow-growing k-strategists in a community that was initially dominated by fast-growing r-strategists (Poll et al., 2008). In C. epigejos treatments, the slightly increased contents of total PLFA and the corresponding litter-derived 13C proportions at the 4-week sampling time indicated the use of easily available litter compounds; however, the maximum measured was significantly lower compared with L. corniculatus treatments. Overall, these results are in accordance with our hypothesis and show the important role of N in the microbial biomass during the decomposition process. A PCA (Fig. 3) based on individual PLFA mol% (Table S1) indicated that the litter type applied had a clear influence on the structure of microbial litter degraders. After 4 weeks, a small shift along PC1 occurred, mainly as a result of the high proportions of fungi (18:2ω6,9 and 18:3) in both litter treatments. This finding was in accordance with Poll et al. (2008), who found that an increase in fungi was detected between 2 and 4 weeks after litter application, based on ergosterol measurements.