Assessment of the influence of bamboo expansion on Si pools and fluxes in a disturbed subtropical evergreen broadleaved forest

Abstract

Silicon (Si) pools and fluxes are affected by plant community shifts in forest ecosystems. Moso bamboo (Phyllostachys pubescens) is a Si accumulating plant, and its expansion exerts various ecological effects in colonized forest ecosystems. However, it is unclear how bamboo expansion might alter the biogeochemical Si cycle. To estimate the consequences of bamboo expansion on Si availability and biochemical cycling in subtropical areas, we selected bamboo-pure forest (BPF), bamboo-broadleaved mixed forest (BMF), and adjacent secondary evergreen broadleaved forest (EBF) stands in an area of bamboo expansion and compared Si pools and fluxes of plants in each forest type. We found that the content of the soluble and exchangeable Si in soils of BPF was lower than EBF (0.18 g kg−1 versus 0.25 g kg−1), that is, bamboo expansion decreased the soluble and exchangeable Si fraction, whereas there was no significant difference among BPF, BMF and EBF. In addition, the plant Si pool in BPF (285 g Si m−2) was 32.6 % lower than EBF (428 g Si m−2), and there was a shift in Si allocation from aboveground to belowground with conversion from EBF to BPF, largely attributed to abundant roots in BPF. We found that bamboo expansion accelerated the biogeochemical Si cycle to some extent, with higher production of phytoliths and quicker turnover of fine roots in BPF than EBF. We also highlight that bamboo expansion accelerated the uptake and return of Si, and promoted the release and dissolution of phytoliths. These results have implications for assessing the impacts of vegetation shifts on the biogeochemical Si cycle.