Publications

As the primary microbial substrate after shoot cutting, the element stoichiometry of root-detritus (dying or dead roots) influences the enzyme activity in root-detritusphere. However, the effect of the C/P ratio of root-detritus on the dynamics and distribution of enzyme activities is little revealed. We hypothesised that P fertilisation would decrease the C/P ratio of root-detritus, therefore affecting the hotspot areas and hot moments of C-acquiring and P-acquiring enzyme activities, as well as their activity ratio (C/P acquisition ratio). Root-detritus of low (59.0) and high (170.8) C/P ratios was produced in P-poor soil with and without P fertilisation, respectively. In situ soil zymography showed that the distribution of C-acquiring enzymes (β-glucosidase and cellobiohydrolase) was more associated with root-detritus than P-acquiring enzymes (acid and alkaline phosphomonoesterase). P fertilisation increased the hotspot areas of C-acquiring enzyme activities over the experiment, without influencing their temporal dynamics. However, its effect on phosphomonoesterase activities depended on the decomposition and delayed the appearance of the highest hotspot areas. P supply met the microbial demand in P-fertilised soil, with high C/P acquisition ratio and constant stoichiometry of microbial biomass C (MBC)/microbial biomass P (MBP). A low C/P acquisition ratio and high MBC/MBP in non-fertilised soil was observed, indicating P limitation for microorganisms. After the 150-day incubation, Olsen P significantly increased in P-fertilised soil (P < 0.05), whereas it decreased in the root-detritusphere of non-fertilised soil. We conclude that the decomposition of root-detritus with a low C/P ratio has potential to improve soil P availability; however, C-P imbalance may increase during the decomposition of root-detritus with a high C/P ratio.

Reforestation with native species and resulting understory succession can exert important influences on soil organic matter (SOM) storage and chemistry, but a mechanistic understanding of these effects is lacking. We studied different aged Masson pine (Pinus massoniana L.) plantations with and without the understory fern, Dicranopteris dichotoma (Thunb.) Berhn., in subtropical China to assess how SOM over a 30 year sequence of pine growth and fern expansion. To do this, we measured total SOM, lignin-derived phenols, soil carbon (total C and 13C), soil nitrogen (total N and 15N), and soil microbial community composition via phospholipid fatty acid (PLFA) analyses. We found that the accumulation of newly-formed SOM outweighed decomposition of old SOM, with the majority of this increase being derived from fern detrital inputs. Where ferns were present, ferns contributed 54–61% of total soil C storage in surface (0–10 cm depth) soils, which was 62–91% higher than pre-reforestation soil C storage. We found that the abundance of lignin-derived compounds was lower in fern dominated soils, perhaps because soils under ferns supported more soil fungi, the primary decomposers of the lignin in soil. Fern soils also showed higher ratios of syringyls to vanillyls and decreased δ13C values, an indicator that ferns altered the composition of SOM at the molecular level while contributing significantly to SOM accumulation. Reforestation especially when accompanied by fern expansion also improved soil N and phosphorus (P) status, with observed declines in soil δ15N in fern dominated soils aligning with increased nutrient retention and observed increases in soil C storage. Our study highlights the potentially important role of understory ferns in mediating SOM chemistry and soil C storage during ecosystem recovery.

Little is known about the effect of drought on the interactions of roots and microorganisms in the rhizosphere under different plant communities. We compared drought effects on microbial biomass carbon (MBC) and on enzyme activities in the rhizosphere of two grasses (Lolium perenne and Festuca arundinacea) and one legume (Medicago sativa) grown individually or in mixture under controlled laboratory conditions. We analysed plant biomass production and extracellular enzyme activity as well as MBC in planted and unplanted soils with and without drought. We focused on three enzymes involved in the C cycle (xylanase, β-cellobiosidase and β-glucosidase), one involved in the nitrogen (N) cycle (leucine-aminopeptidase), and one enzyme involved in both cycles (chitinase). The aim of the study was to evaluate the importance of the plant community composition for the response of these parameters to drought. Higher root-to-shoot ratio of all individual species under drought indicated that root growth was sustained under drought, whereas shoot growth was limited. Decrease of the root biomass and root-to-shoot ratio was observed for plants grown in mixture, showing that these plants competed more strongly for light than for water and nutrients compared to monocultures. MBC increased in response to drought in soil under the plant mixture, whereas it showed variable trends under monocultures. Our results further showed that drought and plant species composition were responsible for more than 90% of the variation of enzyme activities. Most enzyme activities decreased in unplanted soil in response to drought. The activity of the enzyme involved in the N cycle increased strongly under mixture and two out of three monocultures, indicating an increased N demand under drought conditions. The activities of enzymes involved in the C cycle in soil under mixture (1) generally were lower during drought compared to soil under monocultures and (2) were unchanged or tended to decrease, while they were more likely to increase under monocultures. This has an important ecological consequence: the decomposition of plant residues and soil organic matter will be slower under drought when plants are grown in mixture compared to monocultures.

Neben Stickstoff ist Phosphor (P) das wichtigste wachstumslimitierende Nahrelement in Boden. Dennoch gibt es wenig Information uber die raumliche Heterogenitat des P-Gehaltes in Waldboden. Daruber hinaus ist der Effekt einer homogenen versus heterogenen P‑Verteilung im Boden auf die mikrobielle P‑Akquirierung und Zusammensetzung der mikrobiellen Gemeinschaft weitgehend unbekannt. Ein Rhizotronexperiment mit P-armem Waldboden wurde durchgefuhrt um konkurrierende P‑Aufnahmestrategien von Mikroorganismen zu untersuchen. Um den Effekt raumlicher P‑Heterogenitat auf pflanzliche und mikrobielle P‑Aufnahme zu eruieren wurden mit F.sylvatica bepflanzte Rhizotrone mit P‑33‑Eisen(III)phosphat, einer relativ immobilen P Quelle, in verschiedenen raumlichen Verteilungen markiert. Die P‑Mobilisierung durch Mikroorganismen wurde mittels einer verbesserten P-33-PLFA-Methode verfolgt, welche die P‑33‑Inkorporierung in Mikroorganismen mit Anderungen in der Zusammensetzung mikrobieller Gemeinschaften in situ verbindet. Die mikrobielle P-Aufnahme war erhoht in Rhizotronen mit hoher P‑Verfugbarkeit, sowie in solchen mit heterogener P‑Verteilung. Charakteristische PLFA weisen auf eine Akkumulation von Ektomykorrhizapilzen, typischerweise assoziiert mit Buchenwurzeln, in P‑reichen Arealen hin. Diese Ektomykorrhizzapilze fuhren wahrscheinlich zu einer starken Zunahme der P‑Mobilisierung des ausgebrachten P‑33‑Eisen(III)phosphats in stark P-haltigen Habitaten. Im Gegensatz hierzu benotigen Habitate mit niedriger P-Verfugbarkeit eine komplexer zusammengesetzte mikrobielle Gemeinschaft um unzugangliche P-Quellen zu mobilisieren. Entsprechend fordern hohe P‑Vorkommen die Bildung von Pilzhyphen zur P-Mobilisierung – ein Effekt, der mit sinkendem P-Gehalt abnimmt. Des Weiteren zeigen grampositive und ‑negative Bakterien eine massiv erhohte P‑Aufnahme unter zunehmend heterogenen P-Verteilungen. Sie stellen jedoch einen kleineren Anteil der mikrobiellen Gemeinschaft als in homogen P‑angereicherten Rhizotronen, was auf einen Vorteil filamentoser Organismen bei heterogener P-Verteilung hindeutet. Entsprechend fordert eine heterogene P-Verteilung in Waldboden die P-Aufnahme mikrobieller Gemeinschaften aus mineralischen P-Quellen mit geringer biologischer Verfugbarkeit in Waldboden.

Straw return strategies are widely used green management practices that can alter soil organic matter transformation and dynamics through changes in microbial community structure and functions. How the exogenous input of organic materials of contrasting qualities affects the composition of dominant taxa, growth, and microbial functional properties related to nutrient acquisition in space remains unclear. In this study, we investigated the hotsopts and kinetics of C- and N-acquiring hydrolases, microbial growth, and bacterial community structure in maize rhizosphere hotspots after the addition of straw and straw-derived biochar using soil zymography, substrate-induced respiration and high-throughput sequencing. Compared with no amendment and maize straw-derived biochar, straw addition increased the growing biomass and microbial specific growth rate by 1.2–1.6 and 1.7–2.0-fold, respectively, indicating the relative dominance of fast-growing r-strategists. This corresponds to an increased relative abundance of the keystone taxa Firmicutes and their gene copies encoding β-1,4-glucosidase (BG) and β-N-acetylglucosaminidase (NAG). The potential activity and affinity (Vmax and Km) of BG increased 2.2 and 1.8 times, respectively, and those of NAG increased 4.0 and 2.0 times, respectively. In contrast, the relative abundance of Actinobacteria belonging to K-strategists increased in the biochar-amended soil. This resulted in slower growth and retarded enzymatic activity than the straw return treatment. Biochar enhanced the root biomass by 31% and increased the rhizosphere hotspot extents of BG and NAG by 26% and 47%, respectively. The highest robustness and modularity of the co-occurrence network indicated a more stable network with biochar input. In summary, the addition of straw accelerated rhizosphere nutrient cycling by triggering microbial growth, especially fast-growth r-strategists (Firmicutes), and synthesizing a large number of enzymes. In contrast, the addition of biochar increased rhizosphere nutrient mobilization by expanding the extent of rhizosphere hotspots to mobilize nutrients from a larger soil volume. This suggests that there are different strategies for nutrient mobilization in the rhizosphere with contrasting exogenous C addition.

Nitrogen (N) uptake by plant roots from soil is the largest flux within the terrestrial N cycle. Despite its significance, a comprehensive analysis of plant uptake for inorganic and organic N forms across grasslands is lacking. Here we measured in situ plant uptake of 13 inorganic and organic N forms by dominant species along a 3000 km transect spanning temperate and alpine grasslands. To generalize our experimental findings, we synthesized data on N uptake from 60 studies encompassing 148 plant species world-wide. Our analysis revealed that alpine grasslands had faster NH

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