## 4 Discussion
Consequently, it is valuable to further put forward this work with 16S rRNA sequencing technique, in order that the dominant or modified species in response to CaCO\({}_{3}\) or OM can be revealed, and their respective functions can be evaluated. In this study, we also observed the difference between plant species, including the effects on soil pH and plant growth. The soil pH in rhizosphere of _S. guianensis_ was significantly lower than that of _P. nutatum_ regardless of treatments, mainly due to the biological N fixation (BNF) in the rhizosphere of legumes [47; 48]. It is well acknowledged that the excretion of H\({}^{+}\) from legume roots is in parallel with BNF [49]. The differences in soil nutrient content (TP, AP, AK) and enzyme activity (\(\alpha\)-glucosidase, \(\beta\)-xylosidase, urase) between plant species also existed, but showed complexity due to the interaction of plant species and soil treatments. This complexity was demonstrated previously [6; 50]. Taken together, these differences led to the different response of plant growths to treatments, namely, the biomass of _S. guianensis_ was greatly increased by OM, but not by CaCO\({}_{3}\), while the biomass of _P. nutatum_ was increased by CaCO\({}_{3}\) more greatly than by OM. The different growth responses of legumes and graminoids to liming were reported elsewhere. For example, liming at 6.72 t\(\cdot\)ha\({}^{-1}\) significantly increased the aboveground biomass of barley, but not that of peas (on the average of four years, where the initial soil pH was increased by 1.9 units) [51]. An on-farm experiment indicated that the frequency of a grain yield response to liming was almost twice for corn than for soybean [52], although the different results were also reported [53]. These results highlight the necessity of selecting the appropriate treatments (liming or plant residue incorporation) for ameliorating acidic soils when growing legumes or graminoids. In this study, we demonstrated that the modification of the microbial community was achieved by both liming and plant residue incorporation, although the effect size of liming was weaker than that of plant residue incorporation. The modification can be the result of changes in pH and organic matter, as induced by liming and plant residue incorporation. It is well accepted that pH and organic matter are the two important factors altering microbial community composition and function [54; 55; 56; 57]. Soil microbe is an essential biotic component in soil ecosystems, playing critical roles in diverse soil functioning. In this study, almost all soil chemical properties except AK were increased by liming or plant residue incorporation, probably due to both elevations of pH and increase in enzyme activity. The availability of most nutrients can be promoted if soil pH shifts from acidic status to neutral status with P being the most sensitive [58]. The activity of \(\beta\)-glucosidase decreases with soil pH increasing from 4.5 to 8.5, while organic matter increases it by providing substrates [59]. This explains well why the activity of \(\beta\)-glucosidase in OM treatment was higher than that in CaCO\({}_{3}\) treatment in this study. In contrast, the activity of alkaline phosphatase in CaCO\({}_{3}\) treatment was higher than that in OM treatment, most probably due to in higher pH in CaCO\({}_{3}\) treatment. Moreover, alkaline phosphatase is mainly secreted by soil microbes [60], and thus, is linked with increased TOC or DOC as demonstrated in this study. Taking together, both liming and plant residue incorporation affect soil chemical properties and biological properties, with the former more effective on chemical processes (especially pH) and the latter more effective on the biological processes. Despite the differences, both practices are able to improve acidic soil with increased nutrient availability and biological activity.