Litterfall and Element Return in an Abies faxoniana Forest in Tibet—A Five-Year Study

Forest litter is the main contributor to soil fertility and the main carrier of circulating material and energy in forest ecosystems. Abies faxoniana (Minjiang fir) is one of the dominant species in alpine forest ecosystems. Its litter input plays important roles in soil organic matter formation and biogeochemical cycles in these ecosystems, but the annual litterfall pattern and its components remain largely unknown. To determine the litter input and nutrient return of A. faxoniana, we measured the litterfall and element (carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), aluminium (Al), iron (Fe), and manganese (Mn)) contents of different litter components (branches, leaves and epiphytes) from 2016 to 2020. The results showed that the annual litterfall in the A. faxoniana forest ranged from 2055.96 to 5384.15 kg·ha−1·a−1, and the average mass proportions of branches, leaves and epiphytes were 30.12%, 62.18% and 7.7%, respectively. The litterfall yield varied significantly with time and component; not only was the yield of litter in the nongrowing season higher than that in the growing season, but it also exhibited dramatic interannual variations. We also found that time had significant effects on the contents of all elements except for Ca in the litter. The return and input amounts of each element followed the same dynamics, which closely resembled a bimodal pattern. Moreover, there was significant interannual variability in the returned amounts of each element. The ranges of annual returns of C, N and P were 744.80~2275.12, 19.80~59.00 and 1.03~2.81 kg·ha−1·a−1, respectively. The ranges of annual returns of K, Ca, Na, Mg, Al, Fe and Mn were 0.91~2.00, 7.04~18.88, 0.13~0.58, 0.33~1.20, 0.55~2.29, 0.41~1.37 and 0.16~0.48 kg·ha−1·a−1, respectively, reflecting a seasonal double-peak pattern. These results have important implications for understanding the biogeochemical cycles and material migration processes in alpine forest ecosystems.

Determinants of species assemblages of insect pests in alpine forest ecosystems of western China

Background Insect pests are a significant threat to natural resources and social development. Modeling species assemblages of insect pests can predict spatiotemporal pest dynamics. However, research gaps remain regarding the mechanism for determining species assemblages of insect pests in alpine forest ecosystems. Here, we explored these determinants using a field investigation conducted for insect pests in a region of the Qinghai-Tibet Plateau. We assessed the species assemblages of insect pests in alpine forest ecosystems based on species co-occurrence patterns and species diversity (i.e., observed diversity, dark diversity, community completeness, and species pool). A probabilistic model was used to test for statistically significant pairwise patterns of species co-occurrence using the presence-absence matrix of pest species based on species interactions. We used ordinary least squares regression modeling to explore relationships between abiotic factors (i.e., climate factors and human influence) and species diversity. Results Positive pest species interactions and many association links can occur widely across different investigation sites and parts of plant hosts in alpine forest ecosystems. We detected high dark diversity and low community completeness of insect pests in alpine forest ecosystems. High temperature and precipitation could promote pest species diversity, particularly dark diversity and species pools. Human influence could drive high levels of pest species diversity and lead to dark diversity and species pools. Community completeness could be an effective indicator for insect pest risk assessment. Conclusions Our study provides new evidence for the determinants of insect pest species assemblages in alpine forest ecosystems from the perspectives of pest species interactions and abiotic factors. The findings of our study could reveal the mechanism for shaping species assemblages and support the prevention and control of insect pests in alpine forest ecosystems.

Biodegradation Potential and Putative Catabolic Genes of Culturable Bacteria from an Alpine Deciduous Forest Site

Microbiota from Alpine forest soils are key players in carbon cycling, which can be greatly affected by climate change. The aim of this study was to evaluate the degradation potential of culturable bacterial strains isolated from an alpine deciduous forest site. Fifty-five strains were studied with regard to their phylogenetic position, growth temperature range and degradation potential for organic compounds (microtiter scale screening for lignin sulfonic acid, catechol, phenol, bisphenol A) at low (5 °C) and moderate (20 °C) temperature. Additionally, the presence of putative catabolic genes (catechol-1,2-dioxygenase, multicomponent phenol hydroxylase, protocatechuate-3,4-dioxygenase) involved in the degradation of these organic compounds was determined through PCR. The results show the importance of the Proteobacteria phylum as its representatives did show good capabilities for biodegradation and good growth at −5 °C. Overall, 82% of strains were able to use at least one of the tested organic compounds as their sole carbon source. The presence of putative catabolic genes could be shown over a broad range of strains and in relation to their degradation abilities. Subsequently performed gene sequencing indicated horizontal gene transfer for catechol-1,2-dioxygenase and protocatechuate-3,4-dioxygenase. The results show the great benefit of combining molecular and culture-based techniques.

Biodegradation of lignin monomers and bioconversion of ferulic acid to vanillic acid by Paraburkholderia aromaticivorans AR20-38 isolated from Alpine forest soil

Lignin bio-valorization is an emerging field of applied biotechnology and has not yet been studied at low temperatures. Paraburkholderia aromaticivorans AR20-38 was examined for its potential to degrade six selected lignin monomers (syringic acid, p-coumaric acid, 4-hydroxybenzoic acid, ferulic acid, vanillic acid, benzoic acid) from different upper funneling aromatic pathways. The strain degraded four of these compounds at 10°C, 20°C, and 30°C; syringic acid and vanillic acid were not utilized as sole carbon source. The degradation of 5 mM and 10 mM ferulic acid was accompanied by the stable accumulation of high amounts of the value-added product vanillic acid (85–89% molar yield; 760 and 1540 mg l−1, respectively) over the whole temperature range tested. The presence of essential genes required for reactions in the upper funneling pathways was confirmed in the genome. This is the first report on biodegradation of lignin monomers and the stable vanillic acid production at low and moderate temperatures by P. aromaticivorans. Key points • Paraburkholderia aromaticivorans AR20-38 successfully degrades four lignin monomers. • Successful degradation study at low (10°C) and moderate temperatures (20–30°C). • Biotechnological value: high yield of vanillic acid produced from ferulic acid.