Climate-land-use interactions shape tropical mountain biodiversity and ecosystem functions.

Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem functioning are largely unknown1-3. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use4,5. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa's largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained-on average-54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions.

Characteristics of annual NH3 emissions from a conventional vegetable field under various nitrogen management strategies.

High N-fertilizer applications to conventional vegetable production systems are associated with substantial emissions of NH3, a key substance that triggers haze pollution and ecosystem eutrophication and thus, causing considerable damage to human and ecosystem health. While N fertilization effects on NH3 volatilization from cereal crops have been relatively well studied, little is known about the magnitude and yield-scaled emissions of NH3 from vegetable systems. Here we report on a 2-year field study investigating the effect of various types and rates of fertilizer application on NH3 emissions and crop yields for a pepper-lettuce-cabbage rotation system in southwest China. Our results show that both NH3 emissions and direct emission factors of applied N varied largely across seasons over the 2-year period, highlighting the importance of measurements spanning entire cropping years. Across all treatments varying from solely applying urea fertilizers to only using organic manures, annual NH3 emissions ranged from 0.64 to 92.4 kg N ha-1 yr-1 (or 0.07-6.84 g N kg-1 dry matter), equivalent to 0.05-5.99% of the applied N. At annual scale, NH3 emissions correlated positively with soil δ15N values, indicating that soil δ15N may be used as an indicator for NH3 losses. NH3 emissions from treatments fertilized partially or fully with manure were significantly lower compared with the urea fertilized treatment, while vegetable yields remained unaffected. Moreover, full substitution of urea by manure as compared to the partial substitution further reduced the yield-scaled annual NH3 emissions by 79.0-92.4%. Across all vegetable seasons, there is a significant negative relationship between yield-scaled NH3 emissions and crop N use efficiency. Overall, our results suggest that substituting urea by manure and reducing total N inputs by 30-50% allows to reduce NH3 emissions without jeopardizing yields. Such a change in management provides a feasible option to achieve environmental sustainability and food security in conventional vegetable systems.

Dynamic simulation of management events for assessing impacts of climate change on pre-alpine grassland productivity.

The productivity of permanent temperate cut grasslands is mainly driven by weather, soil characteristics, botanical composition and management. To adapt management to climate change, adjusting the cutting dates to reflect earlier onset of growth and expansion of the vegetation period is particularly important. Simulations of cut grassland productivity under climate change scenarios demands management settings to be dynamically derived from actual plant development rather than using static values derived from current management operations. This is even more important in the alpine region, where the predicted temperature increase is twice as high as compared to the global or Northern Hemispheric average. For this purpose, we developed a dynamic management module that provides timing of cutting and manuring events when running the biogeochemical model LandscapeDNDC. We derived the dynamic management rules from long-term harvest measurements and monitoring data collected at pre-alpine grassland sites located in S-Germany and belonging to the TERENO monitoring network. We applied the management module for simulations of two grassland sites covering the period 2011-2100 and driven by scenarios that reflect the two representative concentration pathways (RCP) 4.5 and 8.5 and evaluated yield developments of different management regimes. The management module was able to represent timing of current management operations in high agreement with several years of field observations (r² > 0.88). Even more, the shift of the first cutting dates scaled to a +1 °C temperature increase simulated with the climate change scenarios (-9.1 to -17.1 days) compared well to the shift recorded by the German Weather Service (DWD) in the study area from 1991-2016 (-9.4 to -14.0 days). In total, the shift in cutting dates and expansion of the growing season resulted in 1-2 additional cuts per year until 2100. Thereby, climate change increased yields of up to 6 % and 15 % in the RCP 4.5 and 8.5 scenarios with highest increases mainly found for dynamically adapted grassland management going along with increasing fertilization rates. In contrast, no or only minor yield increases were associated with simulations restricted to fertilization rates of 170 kg N ha-1 yr-1 as required by national legislations. Our study also shows that yields significantly decreased in drought years, when soil moisture is limiting plant growth but due to comparable high precipitation and water holding capacity of soils, this was observed mainly in the RCP 8.5 scenario in the last decades of the century.

Simultaneous quantification of N2 , NH3 and N2 O emissions from a flooded paddy field under different N fertilization regimes.

Gaseous nitrogen (N) emissions, especially emissions of dinitrogen (N2 ) and ammonia (NH3 ), have long been considered as the major pathways of N loss from flooded rice paddies. However, no studies have simultaneously evaluated the overall response of gaseous N losses to improved N fertilization practices due to the difficulties to directly measure N2 emissions from paddy soils. We simultaneously quantified emissions of N2 (using membrane inlet mass spectrometry), NH3 and nitrous oxide (N2 O) from a flooded paddy field in southern China over an entire rice-growing season. Our field experiment included three treatments: a control treatment (no N addition) and two N fertilizer (220 kg N/ha) application methods, the traditional surface application of N fertilizer and the incorporation of N fertilizer into the soil. Our results show that over the rice-growing season, the cumulative gaseous N losses from the surface application treatment accounted for 13.5% (N2 ), 19.1% (NH3 ), 0.2% (N2 O) and 32.8% (total gaseous N loss) of the applied N fertilizer. Compared with the surface application treatment, the incorporation of N fertilizer into the soil decreased the emissions of NH3 , N2 and N2 O by 14.2%, 13.3% and 42.5%, respectively. Overall, the incorporation of N fertilizer into the soil significantly reduced the total gaseous N loss by 13.8%, improved the fertilizer N use efficiency by 14.4%, increased the rice yield by 13.9% and reduced the gaseous N loss intensity (gaseous N loss/rice yield) by 24.3%. Our results indicate that the incorporation of N fertilizer into the soil is an effective agricultural management practice in ensuring food security and environmental sustainability in flooded paddy ecosystems.

Effects of climate warming on carbon fluxes in grasslands- A global meta-analysis.

Climate warming will affect terrestrial ecosystems in many ways, and warming-induced changes in terrestrial carbon (C) cycling could accelerate or slow future warming. So far, warming experiments have shown a wide range of C flux responses, across and within biome types. However, past meta-analyses of C flux responses have lacked sufficient sample size to discern relative responses for a given biome type. For instance grasslands contribute greatly to global terrestrial C fluxes, and to date grassland warming experiments provide the opportunity to evaluate concurrent responses of both plant and soil C fluxes. Here, we compiled data from 70 sites (in total 622 observations) to evaluate the response of C fluxes to experimental warming across three grassland types (cold, temperate, and semi-arid), warming methods, and short (≤3 years) and longer-term (>3 years) experiment lengths. Overall, our meta-analysis revealed that experimental warming stimulated C fluxes in grassland ecosystems with regard to both plant production (e.g., net primary productivity (NPP) 15.4%; aboveground NPP (ANPP) by 7.6%, belowground NPP (BNPP) by 11.6%) and soil respiration (Rs) (9.5%). However, the magnitude of C flux stimulation varied significantly across cold, temperate and semi-arid grasslands, in that responses for most C fluxes were larger in cold than temperate or semi-arid ecosystems. In semi-arid and temperate grasslands, ecosystem respiration (Reco) was more sensitive to warming than gross primary productivity (GPP), while the opposite was observed for cold grasslands, where warming produced a net increase in whole-ecosystem C storage. However, the stimulatory effect of warming on ANPP and Rs observed in short-term studies (≤3 years) in both cold and temperate grasslands disappeared in longer-term experiments (>3 years). These results highlight the importance of conducting long-term warming experiments, and in examining responses across a wide range of climate.

Impacts of climate and land use on N2 O and CH4 fluxes from tropical ecosystems in the Mt. Kilimanjaro region, Tanzania.

In this study, we quantify the impacts of climate and land use on soil N2 O and CH4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured greenhouse gases (GHG) fluxes from 12 different ecosystems along climate and land-use gradients at Mt. Kilimanjaro, combining long-term in situ chamber and laboratory soil core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N2 O and CH4 respectively. N2 O emissions correlated positively with soil moisture and total soil nitrogen content. CH4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N2 O emissions of tropical montane forests were generally low (<1.2 kg N ha-1  year-1 ), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha-1  year-1 ). Forest soils with well-aerated litter layers were a significant sink for atmospheric CH4 (up to 4 kg C ha-1  year-1 ) regardless of low mean annual temperatures at higher elevations. Land-use intensification significantly increased the soil N2 O source strength and significantly decreased the soil CH4 sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non-CO2 GHG emissions following land-use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N2 O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land-use change.

Trade-offs between soil carbon sequestration and reactive nitrogen losses under straw return in global agroecosystems.

It is widely recommended that crop straw be returned to croplands to maintain or increase soil carbon (C) storage in arable soils. However, because C and nitrogen (N) biogeochemical cycles are closely coupled, straw return may also affect soil reactive N (Nr) losses, but these effects remain uncertain, especially in terms of the interactions between soil C sequestration and Nr losses under straw addition. Here, we conducted a global meta-analysis using 363 publications to assess the overall effects of straw return on soil Nr losses, C sequestration and crop productivity in agroecosystems. Our results show that on average, compared to mineral N fertilization, straw return with same amount of mineral N fertilizer significantly increased soil organic C (SOC) content (14.9%), crop yield (5.1%), and crop N uptake (10.9%). Moreover, Nr losses in the form of nitrous oxide (N2 O) emissions from rice paddies (17.3%), N leaching (8.7%), and runoff (25.6%) were significantly reduced, mainly due to enhanced microbial N immobilization. However, N2 O emissions from upland fields (21.5%) and ammonia (NH3 ) emissions (17.0%) significantly increased following straw return, mainly due to the stimulation of nitrification/denitrification and soil urease activity. The increase in NH3 and N2 O emissions was significantly and negatively correlated with straw C/N ratio and soil clay content. Regarding the interactions between C sequestration and Nr losses, the increase in SOC content following straw return was significantly and positively correlated with the decrease in N leaching and runoff. However, at a global scale, straw return increased net Nr losses from both rice and upland fields due to a greater stimulation of NH3 emissions than the reduction in N leaching and runoff. The trade-offs between increased net Nr losses and soil C sequestration highlight the importance of reasonably managing straw return to soils to limit NH3 emissions without decreasing associated C sequestration potential.

Greenhouse gas fluxes over managed grasslands in Central Europe.

Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site-specific management strategies strongly affect the biosphere-atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO2 ), nitrous oxide (N2 O), and methane (CH4 ). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO2 exchange, while long-term N2 O and CH4 flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO2 , N2 O, and CH4 fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO2 sink (-1,783 to -91 g CO2  m-2  year-1 ), but a N2 O source (18-638 g CO2 -eq. m-2  year-1 ), and either a CH4 sink or source (-9 to 488 g CO2 -eq. m-2  year-1 ). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between -2,761 and -58 g CO2 -eq. m-2  year-1 , with N2 O and CH4 emissions offsetting concurrent CO2 uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N2 O and CH4 fluxes was generally low and varied considerably within years. However, after site-specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity ("sweet spots") and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N2 O and CH4 emissions. The N2 O-N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%-8.6%). Although grassland management led to increased N2 O and CH4 emissions, the CO2 sink strength was generally the most dominant component of the annual GHG budget.

Greenhouse gas emissions and global warming potential of traditional and diversified tropical rice rotation systems.

Global rice agriculture will be increasingly challenged by water scarcity, while at the same time changes in demand (e.g. changes in diets or increasing demand for biofuels) will feed back on agricultural practices. These factors are changing traditional cropping patterns from double-rice cropping to the introduction of upland crops in the dry season. For a comprehensive assessment of greenhouse gas (GHG) balances, we measured methane (CH4 )/nitrous oxide (N2 O) emissions and agronomic parameters over 2.5 years in double-rice cropping (R-R) and paddy rice rotations diversified with either maize (R-M) or aerobic rice (R-A) in upland cultivation. Introduction of upland crops in the dry season reduced irrigation water use and CH4 emissions by 66-81% and 95-99%, respectively. Moreover, for practices including upland crops, CH4 emissions in the subsequent wet season with paddy rice were reduced by 54-60%. Although annual N2 O emissions increased two- to threefold in the diversified systems, the strong reduction in CH4 led to a significantly lower (P < 0.05) annual GWP (CH4  + N2 O) as compared to the traditional double-rice cropping system. Measurements of soil organic carbon (SOC) contents before and 3 years after the introduction of upland crop rotations indicated a SOC loss for the R-M system, while for the other systems SOC stocks were unaffected. This trend for R-M systems needs to be followed as it has significant consequences not only for the GWP balance but also with regard to soil fertility. Economic assessment showed a similar gross profit span for R-M and R-R, while gross profits for R-A were reduced as a consequence of lower productivity. Nevertheless, regarding a future increase in water scarcity, it can be expected that mixed lowland-upland systems will expand in SE Asia as water requirements were cut by more than half in both rotation systems with upland crops.

Climate change amplifies gross nitrogen turnover in montane grasslands of Central Europe in both summer and winter seasons.

The carbon- and nitrogen-rich soils of montane grasslands are exposed to above-average warming and to altered precipitation patterns as a result of global change. To investigate the consequences of climatic change for soil nitrogen turnover, we translocated intact plant-soil mesocosms along an elevational gradient, resulting in an increase of the mean annual temperature by approx. 2 °C while decreasing precipitation from approx. 1500 to 1000 mm. Following three years of equilibration, we monitored the dynamics of gross nitrogen turnover and ammonia-oxidizing bacteria (AOB) and archaea (AOA) in soils over an entire year. Gross nitrogen turnover and gene levels of AOB and AOA showed pronounced seasonal dynamics. Both summer and winter periods equally contributed to cumulative annual N turnover. However, highest gross N turnover and abundance of ammonia oxidizers were observed in frozen soil of the climate change site, likely due to physical liberation of organic substrates and their rapid turnover in the unfrozen soil water film. This effect was not observed at the control site, where soil freezing did not occur due to a significant insulating snowpack. Climate change conditions accelerated gross nitrogen mineralization by 250% on average. Increased N mineralization significantly stimulated gross nitrification by AOB rather than by AOA. However, climate change impacts were restricted to the 2-6 cm topsoil and rarely occurred at 12-16 cm depth, where generally much lower N turnover was observed. Our study shows that significant mineralization pulses occur under changing climate, which is likely to result in soil organic matter losses with their associated negative impacts on key soil functions. We also show that N cycling processes in frozen soil can be hot moments for N turnover and thus are of paramount importance for understanding seasonal patterns, annual sum of N turnover and possible climate change feedbacks.

Impacts of management and climate change on nitrate leaching in a forested karst area.

Forest management and climate change, directly or indirectly, affect drinking water resources, both in terms of quality and quantity. In this study in the Northern Limestone Alps in Austria we have chosen model calculations (LandscapeDNDC) in order to resolve the complex long-term interactions of management and climate change and their effect on nitrogen dynamics, and the consequences for nitrate leaching from forest soils into the karst groundwater. Our study highlights the dominant role of forest management in controlling nitrate leaching. Both clear-cut and shelterwood-cut disrupt the nitrogen cycle to an extent that causes peak concentrations and high fluxes into the seepage water. While this effect is well known, our modelling approach has revealed additional positive as well as negative impacts of the expected climatic changes on nitrate leaching. First, we show that peak nitrate concentrations during post-cutting periods were elevated under all climate scenarios. The maximal effects of climatic changes on nitrate concentration peaks were 20-24 mg L(-1) in 2090 with shelterwood or clear-cut management. Second, climate change significantly decreased the cumulative nitrate losses over full forest rotation periods (by 10-20%). The stronger the expected temperature increase and precipitation decrease (in summer), the lesser were the observed nitrate losses. However, mean annual seepage water nitrate concentrations and cumulative nitrate leaching were higher under continuous forest cover management than with shelterwood-cut and clear-cut systems. Watershed management can thus be adapted to climate change by either reducing peak concentrations or long-term loads of nitrate in the karst groundwater.

Divergent drivers of the spatial variation in greenhouse gas concentrations and fluxes along the Rhine River and the Mittelland Canal in Germany.

Lotic ecosystems are sources of greenhouse gases (GHGs) to the atmosphere, but their emissions are uncertain due to longitudinal GHG heterogeneities associated with point source pollution from anthropogenic activities. In this study, we quantified summer concentrations and fluxes of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and dinitrogen (N2), as well as several water quality parameters along the Rhine River and the Mittelland Canal, two critical inland waterways in Germany. Our main objectives were to compare GHG concentrations and fluxes along the two ecosystems and to determine the main driving factors responsible for their longitudinal GHG heterogeneities. The results indicated that the two ecosystems were sources of GHG fluxes to the atmosphere, with the Mittelland Canal being a hotspot for CH4 and N2O fluxes. We also found significant longitudinal GHG flux discontinuities along the mainstems of both ecosystems, which were mainly driven by divergent drivers. Along the Mittelland Canal, peak CO2 and CH4 fluxes coincided with point pollution sources such as a joining river tributary or the presence of harbors, while harbors and in-situ biogeochemical processes such as methanogenesis and respiration mainly explained CH4 and CO2 hotspots along the Rhine River. In contrast to CO2 and CH4 fluxes, N2O longitudinal trends along the two lotic ecosystems were better predicted by in-situ parameters such as chlorophyll-a concentrations and N2 fluxes. Based on a positive relationship with N2 fluxes, we hypothesized that in-situ denitrification was driving N2O hotspots in the Canal, while a negative relationship with N2 in the Rhine River suggested that coupled biological N2 fixation and nitrification accounted for N2O hotspots. These findings stress the need to include N2 flux estimates in GHG studies, as it can potentially improve our understanding of whether nitrogen is fixed through N2 fixation or lost through denitrification.

Integrated biochar solutions can achieve carbon-neutral staple crop production.

Agricultural food production is a main driver of global greenhouse gas emissions, with unclear pathways towards carbon neutrality. Here, through a comprehensive life-cycle assessment using data from China, we show that an integrated biomass pyrolysis and electricity generation system coupled with commonly applied methane and nitrogen mitigation measures can help reduce staple crops' life-cycle greenhouse gas emissions from the current 666.5 to -37.9 Tg CO2-equivalent yr-1. Emission reductions would be achieved primarily through carbon sequestration from biochar application to the soil, and fossil fuel displacement by bio-energy produced from pyrolysis. We estimate that this integrated system can increase crop yield by 8.3%, decrease reactive nitrogen losses by 25.5%, lower air pollutant emissions by 125-2,483 Gg yr-1 and enhance net environmental and economic benefits by 36.2%. These results indicate that integrated biochar solutions could contribute to China's 2060 carbon neutrality objective while enhancing food security and environmental sustainability.

Effect of vole bioturbation on N2O, NO, NH3, CH4 and CO2 fluxes of slurry fertilized and non-fertilized montane grassland soils in Southern Germany.

Populations of rodents such as common vole (Microtus arvalis) can develop impressive soil bioturbation activities in grasslands. These burrowing and nesting activities highly impact soil physicochemical properties as well as vegetation coverage and diversity. Managed grasslands in livestock production regions receive significant amounts of slurry, commonly at high loads at the beginning of the vegetation period. However, nothing is known how the combination of vole bioturbation and slurry application may affect the fluxes of C and N trace gases from grasslands. Here we report on an in-situ experiment and supporting laboratory incubations carried out during the period March to May 2020 comparing C (CH4, CO2) and N (N2O, NO, NH3) trace gas fluxes from Lolium perenne and Trifolium repens dominated montane grasslands with and without vole bioturbation and with and without slurry application, whereby, with regard to the latter, we further differentiated between acidified and non-acidified slurry. Vole bioturbation significantly (p < 0.05) increased soil NO and NH3 emissions, while N2O fluxes were only significantly (p < 0.05) enhanced in vole affected grassland patches following slurry application (+17%). Effects of vole bioturbation on CH4 fluxes were non-significant, while slurry application significantly reduced CH4 uptake. Compared to applications of non-acidified slurry, application of acidified slurry significantly (p < 0.05) reduced NH3 volatilization by approx. 38% and 50%, for vole and non-vole affected grassland patches, respectively. A significant effect of acidified slurry application on soil NO emissions was only observed for vole affected grassland patches. Significant (p < 0.05) reductions in aboveground net primary productivity and reduced plant N uptake are likely the main mechanisms explaining the stimulation of gaseous N losses following slurry application. Long-term measurements are needed to better understand effects of vole bioturbation on grassland soil C and N cycling and ecosystem GHG balance.

Soil type affects not only magnitude but also thermal sensitivity of N2O emissions in subtropical mountain area.

It is a concern whether the effect of soil type on N2O emissions has to be considered for regional mitigation strategies and emission estimates in mountainous areas with inherent spatial heterogeneities of soil type. To date, there were few field experiments which investigated soil type effects on N2O emissions. Thus a 2-year field study was conducted to measure N2O emissions and soil environmental variables from three different soils that were formed from similar parental rock under the same climate. Seasonal N2O fluxes ranged from 0.18 to 0.40 kg N ha-1 for wheat seasons and 0.40 to 1.50 kg N ha-1 for maize seasons across different experimental soils. The intra- and inter-annual variations in N2O emissions were mainly triggered by temporal dynamics of soil temperature and moisture conditions. On average, seasonal N2O fluxes for acidic soils were significantly lower than for neutral and alkaline soils in cold-dry wheat seasons while significantly greater than for neutral and alkaline soils in warm-wet maize seasons. These determined differences of N2O emissions were mainly caused by differences of initial soil properties across different soils. Moreover, seasonal N2O fluxes were positively correlated with soil pH in wheat seasons, but negatively correlated in maize seasons. The temperature sensitivity coefficient (Q10) of soil N2O emissions for acidic soil (4.06) were significantly greater than those for neutral (1.82) and alkaline (1.15) soils. Overall, N2O emissions for acidic soils were not only higher than those for neutral and alkaline soils but also more sensitive to changing temperature. The present study highlights that soil type is needed to be carefully considered for regional estimate and proposing mitigation strategy of N2O emissions especially in subtropical mountain regions with inherent great heterogeneity of soil type.

Species richness is more important for ecosystem functioning than species turnover along an elevational gradient.

Many experiments have shown that biodiversity enhances ecosystem functioning. However, we have little understanding of how environmental heterogeneity shapes the effect of diversity on ecosystem functioning and to what extent this diversity effect is mediated by variation in species richness or species turnover. This knowledge is crucial to scaling up the results of experiments from local to regional scales. Here we quantify the diversity effect and its components-that is, the contributions of variation in species richness and species turnover-for 22 ecosystem functions of microorganisms, plants and animals across 13 major ecosystem types on Mt Kilimanjaro, Tanzania. Environmental heterogeneity across ecosystem types on average increased the diversity effect from explaining 49% to 72% of the variation in ecosystem functions. In contrast to our expectation, the diversity effect was more strongly mediated by variation in species richness than by species turnover. Our findings reveal that environmental heterogeneity strengthens the relationship between biodiversity and ecosystem functioning and that species richness is a stronger driver of ecosystem functioning than species turnover. Based on a broad range of taxa and ecosystem functions in a non-experimental system, these results are in line with predictions from biodiversity experiments and emphasize that conserving biodiversity is essential for maintaining ecosystem functioning.

Earthworms offset straw-induced increase of greenhouse gas emission in upland rice production.

Increasing water scarcity and rapid socio-economic development are driving farmers in Asia to transform traditionally flooded rice cropping systems into non-flooded crop production. The management of earthworms in non-flooded rice fields appears to be a promising strategy to support residue recycling and mitigate greenhouse gas (GHG) emissions triggered by residue amendment. We conducted a field experiment on non-flooded rainfed rice fields, with and without residue amendment. In-situ mesocosms were inoculated with endogeic earthworms (Metaphire sp.), with either low (ET1: 150 individuals m-2), or high density (ET2: 450 individuals m-2), and a control (ET0: no earthworms). We measured GHG emissions (methane (CH4); nitrous oxide (N2O); carbon dioxide (CO2)) twice a week during the cropping season with static chambers. Effects of earthworms on yield and root growth were additionally assessed. Earthworms offset the enormous increase of CH4 emissions induced by straw amendment (from 4.6 ± 5 to 75.3 ± 46 kg CH4-C ha-1 in ET0). Earthworm activity significantly reduced CH4 release, particularly at ET2, by more than one-third (to 22 ± 15 kg CH4-C ha-1). In contrast, earthworm inoculation did not affect N2O emission. Straw amendment more than doubled the global warming potential (GWP). Earthworms reduced GWP by 39% at low (ET1) and 55% at high densities (ET2). Earthworm activity reduced root mass density under conditions of straw amendment but did not affect yield. Earthworms can significantly reduce detrimental effects of rice crop residue amendment on GHG release under upland rice production. Organic carbon (C) might be preserved in earthworm casts and thereby limit C availability for CH4 production. At the same time, earthworm activity might increase methanotrophic CH4 consumption, due to improved soil aeration or less root exudates. Consequently, earthworms have a strong potential for regulating ecosystem functions related to rice straw decomposition, nutrient allocation and thus GHG reduction.

Vegetation traits of pre-Alpine grasslands in southern Germany.

The data set contains information on aboveground vegetation traits of > 100 georeferenced locations within ten temperate pre-Alpine grassland plots in southern Germany. The grasslands were sampled in April 2018 for the following traits: bulk canopy height; weight of fresh and dry biomass; dry weight percentage of the plant functional types (PFT) non-green vegetation, legumes, non-leguminous forbs, and graminoids; total green area index (GAI) and PFT-specific GAI; plant water content; plant carbon and nitrogen content (community values and PFT-specific values); as well as leaf mass per area (LMA) of PFT. In addition, a species specific inventory of the plots was conducted in June 2020 and provides plot-level information on grassland type and plant species composition. The data set was obtained within the framework of the SUSALPS project ("Sustainable use of alpine and pre-alpine grassland soils in a changing climate"; https://www.susalps.de/ ) to provide in-situ data for the calibration and validation of remote sensing based models to estimate grassland traits.