Quantitative losses vs. qualitative stability of ectomycorrhizal community responses to 3 years of experimental summer drought in a beech-spruce forest.

Forest ecosystems in central Europe are predicted to face an increasing frequency and severity of summer droughts because of global climate change. European beech and Norway spruce often coexist in these forests with mostly positive effects on their growth. However, their different below-ground responses to drought may lead to differences in ectomycorrhizal (ECM) fungal community composition and functions which we examined at the individual root and ecosystem levels. We installed retractable roofs over plots in Kranzberg Forest (11°39'42″E, 48°25'12″N; 490 m a.s.l.) to impose repeated summer drought conditions and assigned zones within each plot where trees neighboured the same or different species to study mixed species effects. We found that ECM fungal community composition changed and the numbers of vital mycorrhizae decreased for both tree species over 3 drought years (2014-2016), with the ECM fungal community diversity of beech exhibiting a faster and of spruce a stronger decline. Mixed stands had a positive effect on the ECM fungal community diversity of both tree species after the third drought year. Ectomycorrhizae with long rhizomorphs increased in both species under drought, indicating long-distance water transport. However, there was a progressive decline in the number of vital fine roots during the experiment, resulting in a strong reduction in enzyme activity per unit volume of soil. Hydrolytic enzyme activities of the surviving ectomycorrhizae were stable or stimulated upon drought, but there was a large decline in ECM fungal species with laccase activity, indicating a decreased potential to exploit nutrients bound to phenolic compounds. Thus, the ectomycorrhizae responded to repeated drought by maintaining or increasing their functionality at the individual root level, but were unable to compensate for quantitative losses at the ecosystem level. These findings demonstrate a strong below-ground impact of recurrent drought events in forests.

Shorter interval and multiple flooding-drying cycling enhanced the mineralization of 14C-DDT in a paddy soil.

DDT and its main metabolites (DDTs) are still the residual contaminants in soil. Sequential anaerobic-aerobic cycling has long been approved for enhancing the degradation of DDTs in soil. However, there is a lack of study investigating whether anaerobic-aerobic cycling would enhance the mineralization of DDT, and what a kind of anaerobic-aerobic management regimes would be optimal. To fill these gaps, the fate of 14C-DDT under different flooding-drying cycles was examined in a paddy soil by monitoring its mineralization and bioavailability. The results show the total mineralization of 14C-DDT in 314 days accounted for 1.01%, 1.30%, and 1.41%, individually for the treatments subjected to one, two, and three flooding-drying cycles. By comparison, the treatment subjected to the permanently aerobic phase had only 0.12% cumulative mineralization. Shorter intervals and multiple flooding-drying cycles enhanced the mineralization of 14C-DDT, however, reduced its bioavailability. Therefore, the enhanced mineralization was explained from an abiotic pathway as predicted by the one-electron reduction potential (E1), the Fukui function for nucleophilic attack (f+) and the steps for anaerobic decarboxylation. From a practical view, it is important to investigate how the anaerobic-aerobic interval and frequency would affect the degradation and mineralization of DDT, which is very essential in developing remediation strategies.

RNA fingerprinting--a new method to screen for differences in plant litter degrading microbial communities.

Microbial activities are essential for the nutrient turnover processes in soil and play an important role in the degradation of complex organic material, for example, plant leaf litter. However, very little is known about the microorganisms and their genes involved during the course of leaf litter decomposition. In the present study, we describe the non-radioactive application of RNA arbitrarily primed-PCR (RAP-PCR) protocol in combination with the classic litter bag technique to investigate the metabolic profiles of microbial community involved in leaf litter degradation after 2 and 8 weeks of degradation in four different soil sites, without using selective primer systems for PCR. Due to the significantly reduced target sites for PCR primers, compared to the published papers about RAP fingerprinting of more complex microbial communities based on DNA analysis (only transcripts from microbes on the litter material were analysed), the patterns of parallel samples were highly reproducible (>95%). Shifts in microbial community structure and function were observed during the course of degradation. Each litter sample had its unique metabolic profile and both soil effects and litter quality effects were evident. RAP-PCR products were also cloned to generate libraries. Clone libraries were screened by restriction fragment length polymorphism (RFLP) and representative samples sequenced to identify the inserts. Both mRNA and rRNA transcripts were obtained confirming the presence of mRNA in total RNA preparations. Hence, the described protocol is a good screening method to find similarities or differences in the structure and function of microbial communities involved in litter degradation, which may be the basis for more detailed studies by cloning and sequencing approaches.