Fenggang Luan

Litter decomposition plays a key role in nutrient cycling across ecosystems, yet to date, we lack a comprehensive understanding of the nonadditive decomposition effects in leaf litter mixing experiments. To fill that gap, we compiled 69 individual studies with the aim to perform two meta-analyses on nonadditive effects. We show that a significant synergistic effect (faster decomposition in mixtures than expected) occurs at a global scale, with an average increase of 3-5% in litter mixtures. In particular, low-quality litter in mixtures shows a significant synergistic effect, while additive effects are observed for high-quality species. Additionally, synergistic effects turn into antagonistic effects when soil fauna are absent or litter is in very late stages of decomposition (near-humus). In contrast to temperate and tropical areas, studies in boreal regions show significant antagonistic effects. Our two meta-analyses provide a systematic evaluation of nonadditive effects in mixed litter decomposition studies and show that litter quality alters the effects of litter mixing. Our results indicate that nutrient transfer, soil fauna and inhibitory secondary compounds can influence mixing effects. We also highlight that synergistic and antagonistic effects occur concurrently, and the final litter mixing effect results from the interplay between them.

Phosphate-solubilizing fungi (PSF) generally enhance available phosphorus (P) released from soil, which contributes to plants' P requirement, especially in P-limiting regions. In this study, two PSF, TalA-JX04 and AspN-JX16, were isolated from the rhizosphere soil of moso bamboo (Phyllostachys edulis) widely distributed in P-deficient areas in China and identified as Talaromyces aurantiacus and Aspergillus neoniger, respectively. The two PSF were cultured in potato dextrose liquid medium with six types of initial pH values ranging from 6.5 to 1.5 to assess acid resistance. Both PSF were incubated in Pikovskaya's liquid media with different pH values containing five recalcitrant P sources, including Ca3(PO4)2, FePO4, CaHPO4, AlPO4, and C6H6Ca6O24P6, to estimate their P-solubilizing capacity. No significant differences were found in the biomass of both fungi grown in media with different initial pH, indicating that these fungi could grow well under acid stress. The P-solubilizing capacity of TalA-JX04 was highest in medium containing CaHPO4, followed by Ca3(PO4)2, FePO4, C6H6Ca6O24P6, and AlPO4 in six types of initial pH treatments, while the recalcitrant P-solubilizing capacity of AspN-JX16 varied with initial pH. Meanwhile, the P-solubilizing capacity of AspN-JX16 was much higher than TalA-JX04. The pH of fermentation broth was negatively correlated with P-solubilizing capacity (p<0.01), suggesting that the fungi promote the dissolution of P sources by secreting organic acids. Our results showed that TalA-JX04 and AspN-JX16 could survive in acidic environments and both fungi had a considerable ability to release soluble P by decomposing recalcitrant P-bearing compounds. The two fungi had potential for application as environment-friendly biofertilizers in subtropical bamboo ecosystem.

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.

Ozone (O3) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 ± 20 nmol mol-1, 09:00-16:00 h). Elevated O3 decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (P N) and stomatal conductance (g s), inhibited maximal quantum yield (Fv/Fm) and effective quantum yield [YII] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in P N, g s, Fv/Fm, and YII. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability.