The degree to which climate warming will stimulate soil organic carbon (SOC) losses via heterotrophic respiration remains uncertain, in part because different or even opposite microbial physiology ...and temperature relationships have been proposed in SOC models. We incorporated competing microbial carbon use efficiency (CUE)–mean annual temperature (MAT) and enzyme kinetic–MAT relationships into SOC models, and compared the simulated mass‐specific soil heterotrophic respiration rates with multiple published datasets of measured respiration. The measured data included 110 dryland soils globally distributed and two continental to global‐scale cross‐biome datasets. Model–data comparisons suggested that a positive CUE–MAT relationship best predicts the measured mass‐specific soil heterotrophic respiration rates in soils distributed globally. These results are robust when considering models of increasing complexity and competing mechanisms driving soil heterotrophic respiration–MAT relationships (e.g., carbon substrate availability). Our findings suggest that a warmer climate selects for microbial communities with higher CUE, as opposed to the often hypothesized reductions in CUE by warming based on soil laboratory assays. Our results help to build the impetus for, and confidence in, including microbial mechanisms in soil biogeochemical models used to forecast changes in global soil carbon stocks in response to warming.
Model simulations incorporating a positive CUE–MAT relationship are consistent with the mass‐specific soil heterotrophic respiration rates patterns found in soils across the globe. That is, at a common assay temperature, both the measured and simulated mass‐specific soil heterotrophic respiration rates are lower for soils sampled from warmer climates. A negative CUE–MAT relationship, however, is unable to predict the observed patterns.
The microbial priming effect—the decomposition of soil organic carbon (SOC) induced by plant inputs—has long been considered an important driver of SOC dynamics, yet we have limited understanding ...about the direction, intensity, and drivers of priming across ecosystem types and biomes. This gap hinders our ability to predict how shifts in litter inputs under global change can affect climate feedbacks. Here, we synthesized 18,919 observations of CO2 effluxes in 802 soils across the globe to test the relative effects (i.e., log response ratio RR) of litter additions on native SOC decomposition and identified the dominant environmental drivers in natural ecosystems and agricultural lands. Globally, litter additions enhanced native SOC decomposition (RR = 0.35, 95% CI: 0.32–0.38), with greater priming effects occurring with decreasing latitude and more in agricultural soils (RR = 0.43) than in uncultivated soils (RR = 0.28). In natural ecosystems, soil pH and microbial community composition (e.g., bacteria: fungi ratio) were the best predictors of priming, with greater effects occurring in acidic, bacteria‐dominated sandy soils. In contrast, the substrate properties of plant litter and soils were the most important drivers of priming in agricultural systems since soils with high C:N ratios and those receiving large inputs of low‐quality litter had the highest priming effects. Collectively, our results suggest that, though different factors may control priming effects, the ubiquitous nature of priming means that alterations of litter quality and quantity owing to global changes will likely have consequences for global C cycling and climate forcing.
Past vegetation and climatic conditions are known to influence current biodiversity patterns. However, whether their legacy effects affect the provision of multiple ecosystem functions, that is, ...multifunctionality, remains largely unknown. Here we analyzed soil nutrient stocks and their transformation rates in 236 drylands from six continents to evaluate the associations between current levels of multifunctionality and legacy effects of the Last Glacial Maximum (LGM) desert biome distribution and climate. We found that past desert distribution and temperature legacy, defined as increasing temperature from LGM, were negatively correlated with contemporary multifunctionality even after accounting for predictors such as current climate, soil texture, plant species richness, and site topography. Ecosystems that have been deserts since the LGM had up to 30% lower contemporary multifunctionality compared with those that were nondeserts during the LGM. In addition, ecosystems that experienced higher warming rates since the LGM had lower contemporary multifunctionality than those suffering lower warming rates, with a ~9% reduction per extra degree Celsius. Past desert distribution and temperature legacies had direct negative effects, while temperature legacy also had indirect (via soil sand content) negative effects on multifunctionality. Our results indicate that past biome and climatic conditions have left a strong “functionality debt” in global drylands. They also suggest that ongoing warming and expansion of desert areas may leave a strong fingerprint in the future functioning of dryland ecosystems worldwide that needs to be considered when establishing management actions aiming to combat land degradation and desertification.
Dryland ecosystems that have been deserts since the Last Glacial Maximum (LGM) had up to 30% lower contemporary multifunctionality compared with those that were non‐deserts during the LGM.
Responses of soil respiration (Rs) to increasing nitrogen (N) deposition and warming will have far-reaching influences on global carbon (C) cycling. However, the seasonal (growing and non-growing ...seasons) difference of Rs responses to warming and N deposition has rarely been investigated. We conducted a field manipulative experiment in a semi-arid alfalfa-pasture of northwest China to evaluate the response of Rs to nitrogen addition and warming from March 2014 to March 2016. Open-top chambers were used to elevate temperature and N was enriched at a rate of 4.42g m−2yr−1 with NH4NO3. Results showed that (1) N addition increased Rs by 14% over the two-year period; and (2) warming stimulated Rs by 15% in the non-growing season, while inhibited it by 5% in the growing season, which can be explained by decreased plant coverage and soil water. The main effect of N addition did not change with time, but that of warming changed with time, with the stronger inhibition observed in the dry year. When N addition and warming were combined, an antagonistic effect was observed in the growing season, whereas a synergism was observed in the non-growing season. Overall, warming and N addition did not affect the Q10 values over the two-year period, but these treatments significantly increased the Q10 values in the growing season compared with the control treatment. In comparison, combined warming and nitrogen addition significantly reduced the Q10 values compared with the single factor treatment. These results suggest that the negative indirect effect of warming-induced water stress overrides the positive direct effect of warming on Rs. Our results also imply the necessity of considering the different Rs responses in the growing and non-growing seasons to climate change to accurately evaluate the carbon cycle in the arid and semi-arid regions.
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•Water stress overrided the positive direct effect of warming on soil respiration.•Water stress overrided the positive direct effect of N addition on soil respiration.•Warming significantly decreased soil respiration in growing season.•Warming significantly increased soil respiration in non-growing season.•Combined warming and N addition enhanced soil respiration to acclimate temperature.
Deadly humid heat conditions exceeding human thermoregulatory capacity have been reported; however, whether and where the deadly humid heat events occur consecutively across the land surface are ...largely unknown. We calculate the maximum consecutive days of deadly humid heat, defined as daily maximum wet‐bulb temperature (TWmax) ≥35°C, for observations of 9,278 meteorological stations and for simulations of 14 global climate models. We further define short and long deadly humid heatwaves as a period of 3–4 and ≥5 consecutive days with daily TWmax ≥35°C, respectively. Our analyses show that six stations in some subtropical regions have experienced deadly humid heat with daily TWmax ≥35°C, but only occurs in individual days. Deadly humid heatwaves increase exponentially as the global mean temperature rising. When limiting global warming within 1.5°C, long deadly humid heatwaves will not occur across the land surface, and short deadly humid heatwaves will only emerge in some drylands but not in humid areas. Under 2°C warming, 0.09% of the global land, 0.42% of the human population, and 0.56% of the global centres of crop diversity are projected to be exposed to long deadly humid heatwaves. Meanwhile, 18% of the deadly humid heatwaves lasting ≥3 consecutive days will occur in humid areas; the fractions are projected to rapidly increase in humid areas as temperature rising further. At the end of the century, the percentage of land areas and human population exposed to deadly humid heatwaves lasting ≥3 consecutive days are expected to be 76‐times higher than that under 1.5°C warming level. Our finding suggests that keeping global warming within 1.5°C will significantly constrain the emergence of prolonged deadly humid heatwaves and thus reduce the risk of the human population especially outdoor agricultural workers.
Geographical distribution of the maximum consecutive days with daily maximum wet‐bulb temperature ≥35°C. (a, b) Observations of HadISD weather stations (a) and historical model runs (b) for the period 1979–2017. (c–e) Model projections for 2031–2040 under an increase in global mean temperature (ΔT) of ≤1.5°C relative to preindustrial level (c), for 2046–2055 under ΔT ≤ 2°C (d), for 2067–2076 under ΔT ≤ 3°C (e), for 2091–2100 under ΔT > 3°C (f). The multimodel ensemble mean of temporal median value during the corresponding periods is shown for each location.
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•Warming decreased Rt and Rh but had no significant effect on Ra.•N addition increased Ra whereas inhibited Rh and had no significant effect on Rt.•Warming decreased Q10 of Rt and Rh ...but had no significant effect on Q10 of Ra.•The combination of warming and N addition had a synergistic effect on Rh.•The combination of warming and N addition had an antagonistic effect on Ra.
Evaluating the responses of soil respiration and its components to global environmental change is crucial for predicting future terrestrial carbon cycle. However, the effects of warming and nitrogen (N) addition on them remain unclear. A field manipulative experiment was conducted in a semi-arid grassland on the Loess Plateau to evaluate the responses of soil total respiration (Rt), autotrophic respiration (Ra) and heterotrophic respiration (Rh) to warming and N addition from April 2015 to December 2016. Open-top chambers were used to elevate temperature and N was added as NH4NO3 at a rate of 4.42gNm−2yr−1. Warming significantly decreased Rt and Rh by 7.4% and 9.5%, respectively, but had no significant effect on Ra. N addition significantly stimulated Ra by 34%, whereas it inhibited Rh by 11% and had no significant effect on Rt. The maximum N-inducing stimulation of Rt and Ra were observed in the month with the most rainfall events in 2015. N addition significantly increased the contribution of Ra to Rt by 10%. Warming decreased the Q10 values of Rt and Rh but had no significant effect on Q10 values of Ra. N addition significantly increased the Q10 values of Rt and Rh, whereas it decreased the Q10 values of Ra. The combination of warming and N addition had a synergistic effect on the cumulant of Rh, whereas it had an antagonistic effect on Ra. No interactive effect between warming and N addition was observed on Rt. Our results emphasized that Ra and Rh responded differently to warming and/or N addition, and the extreme rainfall frequency influenced the responses of Rt and its components to N addition. Our findings suggested that Rt has the potential to resist climate warming and increasing N deposition by differentiating the responses of its inherent components.
A central role for nature-based solution is to identify optimal management practices to address environmental challenges, including carbon sequestration and biodiversity conservation. Inorganic ...fertilization increases plant aboveground biomass but often causes a tradeoff with plant diversity loss. It remains unclear, however, whether organic fertilization, as a potential nature-based solution, could alter this tradeoff by increasing aboveground biomass without plant diversity loss. Here we compile data from 537 experiments on organic and inorganic fertilization across grasslands and croplands worldwide to evaluate the responses of aboveground biomass, plant diversity, and soil organic carbon (SOC). Both organic and inorganic fertilization increase aboveground biomass by 56% and 42% relative to ambient, respectively. However, only inorganic fertilization decreases plant diversity, while organic fertilization increases plant diversity in grasslands with greater soil water content. Moreover, organic fertilization increases SOC in grasslands by 19% and 15% relative to ambient and inorganic fertilization, respectively. The positive effect of organic fertilization on SOC increases with increasing mean annual temperature in grasslands, a pattern not observed in croplands. Collectively, our findings highlight organic fertilization as a potential nature-based solution that can increase two ecosystem services of grasslands, forage production, and soil carbon storage, without a tradeoff in plant diversity loss.
Precipitation is known to have legacy effects on plant diversity and production of many terrestrial ecosystems. Precipitation regimes are expected to become more variable with increasing extreme ...precipitation events. However, how previous-year precipitation regimes affect the current-year aboveground biomass (AGB) remains largely unknown. Here we measured long-term (2004–2017) AGB in a semi-arid grassland of the Chinese Loess Plateau to evaluate the impact of previous-year precipitation amount on current-year AGB. Furthermore, to assess the response of current-year AGB to previous-year precipitation regimes, we conducted a field manipulation experiment that included three precipitation regimes during 2014–2017: (i) ambient precipitation, (ii) monthly added four 5 mm rain events, and (iii) monthly added one 20 mm event. Both the long-term (2004–2017) observations under ambient precipitation and short-term (2014–2017) measurements under manipulative treatments showed significant positive effects of previous-year precipitation on current-year AGB. Our path analysis suggested that previous-year precipitation frequency had negative effects on the current-year density and mean height of grass (Leymus secalinus) while had positive effects on forb (Artemisia capillaris). The forb had much smaller height and AGB (65% and 53% less, respectively) than the grass. Consequently, the AGB reduced in the weekly small events treatment, causing the sensitivity of AGB to precipitation to decrease. Therefore, our findings indicated that the impacts of precipitation regimes on plant community dynamics should be taken into consideration while assessing the precipitation legacy effect on ecosystem production.
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•Current-year aboveground biomass (AGB) increased linearly with previous-year precipitation.•Precipitation frequency negatively affects the sensitivity of AGB to precipitation.•Previous-year precipitation amount increases the current-year grass density.•Previous-year precipitation frequency increases the current-year forb density.
Understanding whether soil microbial respiration adapts to the ambient thermal climate with an enhanced or compensatory response, hence potentially stimulating or slowing down soil carbon losses with ...warming, is key to accurately forecast and model climate change impacts on the global carbon cycle. Despite the interest in this topic and the plethora of recent studies in natural ecosystems, it has been seldom explored in croplands. Using two recently published independent datasets of soil microbial metabolic quotient (MMQ; microbial respiration rate per unit biomass) and carbon use efficiency (CUE; partitioning of C to microbial growth vs. respiration), we find a compensatory thermal adaptive response for MMQ in global croplands. That is, mean annual temperature (MAT) has a negative effect on MMQ. However, this compensatory thermal adaptation is only half or less of that found in previous studies for noncultivated ecosystems. In contrast to the negative MMQ‐MAT pattern, microbial CUE increases with MAT across global croplands. By incorporating this positive CUE‐MAT relationship (greater C partitioning into microbial growth rather than respiration with increasing temperature) into a microbial‐explicit soil organic carbon model, we successfully predict the thermal compensation of MMQ observed in croplands. Our model‐data integration and database cross‐validation suggest that a warmer climate may select for microbial communities with higher CUE, providing a plausible mechanism for their compensatory metabolic response. By helping to identify appropriate representations of microbial physiological processes in soil biogeochemical models, our work will help build confidence in model projections of cropland C dynamics under a changing climate.
Key Points
Soil microbial respiration rates adapt to ambient temperature with a compensatory response in global croplands
The compensatory thermal adaptive capacity of soil microorganisms is lower in croplands than in natural ecosystems
A warmer climate may select for microbial communities with higher carbon use efficiency in cropland soils
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