Publications

Diversity and community composition of soil microorganisms along the elevation climosequences have been widely studied, while the microbial metabolic potential, particularly in regard to carbon (C) cycling, remains unclear. Here, a metagenomic analysis of C related genes along five elevations ranging from 767 to 4190 m at Mount Kilimanjaro was analysed to evaluate the microbial organic C transformation capacities in various ecosystems. The highest gene abundances for decomposition of moderate mineralizable compounds, i.e. carbohydrate esters, chitin and pectin were found at the mid-elevations with hump-shaped pattern, where the genes for decompositions of recalcitrant C (i.e. lignin) and easily mineralizable C (i.e. starch) showed the opposite trend (i.e. U-shaped pattern), due to high soil pH and seasonality in both low and high elevations. Notably, the gene abundances for the decompositions of starch, carbohydrate esters, chitin and lignin had positive relationships with corresponding C compounds, indicating the consistent responses of microbial functional profiles and metabolites to elevation climosequences. Understanding of adaptation of microbial communities, potential function and metabolites to elevation climosequences and their influencing factors provided a new insight for the regulation of terrestrial C storage.

The use of kinetic respiration analysis to determine soil microbial biomass its active part and maximum specific growth rate has recently increased. With this method, the increase in soil respiration rate initiated by application of carbon growth substrate, e.g. glucose, and mineral nutrients is used to estimate parameters describing microbial growth in soil. This study refines the method by developing statistical guidelines for the data analysis and processing. The kinetic respiration analysis assumes that microbial growth is not limited by substrate and energy. That is why it is critically important to identify the time period corresponding to the unlimited growth. In this work, we studied how the unlimited growth phase can be identified in less subjective ways by examining 121 datasets of respiration time series of 44 different soil samples taken from field plots. Deflection of the respiratory curve from the exponential pattern indicates growth limitation. Subjective selection of the part of respiratory curve which fits to the exponential pattern resulted in a 30% bias in specific microbial growth rates. We propose rules that are based on inspecting the patterns in a series of plots of residuals of fitted respiration rate. By comparing those rules with a set of statistical criteria we find that the weighted-coefficient of determination (r2) can be used to objectively constrain the unlimited growth phase in those cases where double-limitation does not occur. Furthermore, we discuss how the uncertainty of estimated microbial parameters is influenced by a) measurement uncertainty, b) biased measurement at the beginning of the experiment, and c) the number and timing of respiration measurements. We recommend checking plots of fits and residuals as well as reporting uncertainty bounds together with the estimated microbial parameters. A free statistical package is provided to easily deal with those aspects.

Rainwater is a vital resource and dynamic driver of terrestrial ecosystems. Yet, processes controlling precipitation inputs and interactions during storms are often poorly seen, and poorly sensed when direct observations are substituted with technological ones. We discuss how human observations complement technological ones, and the benefits of scientists spending more time in the storm. Human observation can reveal ephemeral storm-related phenomena such as biogeochemical ‘hot moments’, organismal responses, and sedimentary processes which can then be explored in greater resolution using sensors and virtual experimentation. Storm-related phenomena trigger lasting, oversized impacts on hydrologic and biogeochemical processes, organismal traits/functions, and ecosystem services. We provide examples of phenomena in forests, across disciplines and scales, to inspire mindful, holistic observation of ecosystems during storms. We conclude that technological observations alone are insufficient to trace the process complexity and unpredictability of fleeting biogeochemical or ecological events without the “shower thoughts” produced by scientists’ human sensory and cognitive systems during storms.

Reindeer grazing is a geochemical factor of carbon (C) and nutrient cycling in high-latitude ecosystems. Reindeer consume and trample aboveground biomass, and return nutrients by urine and faces on soil surface. Degradation of vegetation cover due to overgrazing induces soil warming, decreases soil organic matter (SOM) content, and affects its stability. We investigated the effects of reindeer grazing on the thermal stability and temperature sensitivity (Q10) of SOM decomposition in the Gydan Arctic tundra. Thermogravimetric analysis of the topsoil (0–5 cm) from grazed and ungrazed tundra was used to divide SOM into three thermal pools – labile, stable, and persistent. The thermally labile pool contributed 62 % to SOM, reflecting large portion of partly decomposed plant litter. The thermal stability of SOM was evaluated by the temperature, at which the half of the organic matter was lost (T50), and by the activation energy of SOM combustion (Ea TG). Reindeer grazing increased the thermal stability of SOM in tundra by decrease in the thermally labile SOM content, as well as increase in T50 and Ea TG. The decrease in the labile SOM content in grazed compared to ungrazed tundra explained the reduction of soil microbial respiration at sites under reindeer grazing. The CO2 efflux from the ungrazed and grazed soils at increasing temperatures was used to investigate the Q10 of SOM decomposition. A 10 °C increase in soil temperature accelerated microbial SOM decomposition by 3.1 and 2.9 times in ungrazed and grazed tundra soils, respectively. Concluding, reindeer grazing in the Arctic tundra decreased SOM content in topsoil and increased the thermal stability of the remaining organic matter.

http://dx.doi.org/10.13039/501100008990 Science and Technology Department of Zhejiang Province

Microbial carbon (C) use efficiency (CUE) describes the proportion of organic C used by microorganisms for anabolic processes, which increases with soil organic C (SOC) content on a global scale. However, it is unclear whether a similar relationship exists during natural vegetation restoration in terrestrial ecosystems. Here, we investigated the patterns of CUE along a 160‐year vegetation restoration chronosequence (from farmland to climax forest) estimated by stoichiometric modeling; additionally, we examined the relationship between CUE and SOC content and combined these results with a meta‐analysis. The combination indicated that vegetation restoration decreased CUE from 0.35 to 0.28. Surprisingly, SOC content increased with decreasing CUE during vegetation restoration because forest soils have low pH values and high microbial phosphorus limitations compared to early ecosystems, implying that climax forests may not sequester as much soil C as expected. The shift in soil pH was the most important predictor of CUE compared to climate, plant, and microbial factors. CUE changes were directly induced by soil pH and not by the pH‐induced microbial community. Alkaline soil acidification tended to decrease CUE. This first large‐scale estimate of the relationship between CUE and SOC during natural restoration highlights the need to strengthen C sink management in mature forests to sustain their C sequestration potential.

Soil organic carbon (SOC) decomposition is crucial in the global carbon cycle. Its sensitivity to warming significantly impacts climate change. However, the effect of soil drying-rewetting, a consequence of climate change-induced water cycling shifts, on SOC decomposition sensitivity remains poorly understood. This study investigated how drying-rewetting cycles affect the temperature sensitivity (Q10) of SOC decomposition and its underlying mechanisms. We collected soils from two farmlands with 23- and 33-year C3 C4 vegetation switches The soils were incubated at 20 °C or 30 °C for 180 days under alternate drying-rewetting cycles (100 %−20 % water holding capacity, WHC) or constant moisture (60 % WHC). Using 13C natural abundance, we differentiated CO2 sources from recent SOC (C4, <23 or <33 years) and old SOC (C3, >23 or >33 years). Results showed that warming and drying-rewetting enhanced total SOC decomposition. Across moisture conditions, the Q10 of old SOC was 0.25−0.40 units higher than that of recent SOC. Six drying-rewetting cycles decreased the Q10 of total, recent, and old SOC by 0.30−0.44 units compared to constant moisture, as warming became less dominant during the drying-rewetting process. This indicates that the commonly used Q10 might be overestimated under constant moisture, suggesting that the feedback of SOC pools to climate warming might be weaker than previously expected under real soil moisture fluctuations.

Clonal integration between ramets under heterogeneous environment has crucial implications for the clonal plants, is widely distribute in the arid ecosyste

Tree diversity strongly regulates organic matter inputs by rhizodeposition for microorganisms and microbial communities, impacting soil carbon (C) dynamics

Tropical forest conversion to agricultural land leads to a strong decrease of soil organic carbon (SOC) stocks. While the decrease of the soil C sequestration function is easy to measure, the impacts of SOC losses on soil fertility remain unclear. Especially the assessment of the sensitivity of other fertility indicators as related to ecosystem services suffers from a lack of clear methodology. We developed a new approach to assess the sensitivity of soil fertility indicators and tested it on biological and chemical soil properties affected by rainforest conversion to plantations. The approach is based on (non-)linear regressions between SOC losses and fertility indicators normalized to their level in a natural ecosystem. Biotic indicators (basal respiration, microbial biomass, acid phosphatase), labile SOC pools (dissolved organic carbon and light fraction) and nutrients (total N and available P) were measured in Ah horizons from rainforests, jungle rubber, rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis) plantations located on Sumatra. The negative impact of land-use changes on all measured indicators increased in the following sequence: forest<jungle rubber<rubber<oil palm. The basal respiration, microbial biomass and nutrients were resistant to SOC losses, whereas the light fraction was lost stronger than SOC. Microbial C use efficiency was independent on land use. The resistance of C availability for microorganisms to SOC losses suggests that a decrease of SOC quality was partly compensated by litter input and a relative enrichment by nutrients. However, the relationship between the basal respiration and SOC was non-linear; i.e. negative impact on microbial activity strongly increased with SOC losses. Therefore, a small decrease of C content under oil palm compared to rubber plantations yielded a strong drop in microbial activity. Consequently, management practices mitigating SOC losses in oil palm plantations would strongly increase soil fertility and ecosystem stability. We conclude that the new approach enables quantitatively assessing the sensitivity and resistance of diverse soil functions to land-use changes and can thus be used to assess resilience of agroecosystems with various use intensities.