High C input by perennial energy crops boosts belowground functioning and increases soil organic P content

Abstract C input to soil together with plant-microbial-soil organic matter (SOM) transformations are key ecological drivers for soil functioning in perennial cropping systems. In this study, we assessed the effect of three woody (poplar, black locust, willow) and three herbaceous (giant reed, miscanthus, switchgrass) perennial energy crops (PECs) on SOM pools, soil microbial biomass and metabolism and soil P forms distribution. After 9 y from plantation on a low-grade arable land, PECs significantly increased SOM content as much as 3.9 g kg−1 (+23 %) in the topsoil (0−30 cm). At the same time active C increased by 194 mg kg−1 (+ 43 %) and microbial biomass by 10.7 mg g−1 (+ 80 %). Microbial catabolic activity as measured respectively with twenty enzymes activities (EA) involved in C-, N-, P-, and S- cycling increased by 90 % and C substrate utilization profile (CSU - Microresp™) showed an increase of respiration rate by 13 % on average of all 16 substrates utilized. PERMANOVA and dbRDA analysis indicated that activity of microbial community associated with PECs differed significantly from that of arable land, with herbaceous PECs significantly increasing EA involved in C and N cycling while woody PECs increasing those involved in P-cycling. Interestingly, organic P forms content (monoester- and diester-P) along with its contribution to total NaOH-EDTA extractable soil P increased in all PECs, but more in woody than herbaceous ones. Functional diversity and evenness of microbial community resulted higher under herbaceous than woody PECs. Depth decay relationships of Bray Curtis similarity for EA patterns, more than CSU profile, was significantly smaller in woody and arable land than in herbaceous PECs, indicating a significant control of plant C inputs to soil from deep-rooting systems on proximate agents of belowground functioning. Our investigation highlighted the higher capability PECs, compared to annual cropping systems, in coupling nutrients cycling with C cycling, with the high C input being most probably the driving factor. Therefore, PECs might be ultimately considered not just as energy crops but also as a valuable strategy for revitalizing depleted soils by conventional agricultural practices.