Climate warming interacts with other global change drivers to influence plant phenology: A meta-analysis of experimental studies.

Shifts in plant phenology influence ecosystem structures and functions, yet how multiple global change drivers interact to affect phenology remains elusive. We conducted a meta-analysis of 242 published articles to assess interactions between warming (W) and other global change drivers including nitrogen addition (N), increased precipitation (IP), decreased precipitation (DP) and elevated CO2 (eCO2 ) on multiple phenophases in experimental studies. We show that leaf out and first flowering were most strongly affected by warming, while warming and decreased precipitation were the most pronounced drivers for leaf colouring. Moreover, interactions between warming and other global change drivers were common and both synergistic and antagonistic interactions were observed: interactions W + IP and W + eCO2 were frequently synergistic, whereas interactions W + N and W + DP were mostly antagonistic. These findings demonstrate that global change drivers often affect plant phenology interactively. Incorporating the multitude of interactions into models is crucial for accurately predicting plant responses to global changes.

Nitrification, denitrification, and related functional genes under elevated CO2 : A meta-analysis in terrestrial ecosystems.

Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N2 O) emissions mediated by nitrification and denitrification. We conducted a meta-analysis of the effects of elevated CO2 on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO2 experiments in terrestrial ecosystems. We investigated the effects of elevated CO2 alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO2 of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO2 increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO2 increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO2 also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO2 was larger at elevated temperature and high N (+62%). Four out of 14 two-way interactions tested between elevated CO2 and elevated temperature, elevated CO2 and increased precipitation, and elevated CO2 and N addition were marginally significant and mostly synergistic. The effects of elevated CO2 on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta-analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO2 and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N2 O emissions.

Increased precipitation and nitrogen addition accelerate the temporal increase in soil respiration during 8-year old-field grassland succession.

Ecological succession after disturbance plays a vital role in influencing ecosystem structure and functioning. However, how global change factors regulate ecosystem carbon (C) cycling in successional plant communities remains largely elusive. As part of an 8-year (2012-2019) manipulative experiment, this study was designed to examine the responses of soil respiration and its heterotrophic component to simulated increases in precipitation and atmospheric nitrogen (N) deposition in an old-field grassland undergoing secondary succession. Over the 8-year experimental period, increased precipitation stimulated soil respiration by 11.6%, but did not affect soil heterotrophic respiration. Nitrogen addition increased both soil respiration (5.1%) and heterotrophic respiration (6.2%). Soil respiration and heterotrophic respiration linearly increased with time in the control plots, resulting from changes in soil moisture and shifts of plant community composition from grass-forb codominance to grass dominance in this old-field grassland. Compared to the control, increased precipitation significantly strengthened the temporal increase in soil respiration through stimulating belowground net primary productivity. By contrast, N addition accelerated temporal increases in both soil respiration and its heterotrophic component by driving plant community shifts and thus stimulating soil organic C. Our findings indicate that increases in water and N availabilities may accelerate soil C release during old-field grassland succession and reduce their potential positive impacts on soil C accumulation under future climate change scenarios.

Declines in methane uptake in forest soils.

Forest soils are a sink for atmospheric methane (CH4) and play an important role in modulating the global CH4 budget. However, whether CH4 uptake by forest soils is affected by global environmental change is unknown. We measured soil to atmosphere net CH4 fluxes in temperate forests at two long-term ecological research sites in the northeastern United States from the late 1990s to the mid-2010s. We found that annual soil CH4 uptake decreased by 62% and 53% in urban and rural forests in Baltimore, Maryland and by 74% and 89% in calcium-fertilized and reference forests at Hubbard Brook, New Hampshire over this period. This decrease occurred despite marked declines in nitrogen deposition and increases in atmospheric CH4 concentration and temperature, which should lead to increases in CH4 uptake. This decrease in soil CH4 uptake appears to be driven by increases in precipitation and soil hydrological flux. Furthermore, an analysis of CH4 uptake around the globe showed that CH4 uptake in forest soils has decreased by an average of 77% from 1988 to 2015, particularly in forests located from 0 to 60 °N latitude where precipitation has been increasing. We conclude that the soil CH4 sink may be declining and overestimated in several regions across the globe.

Elevated CO2 does not stimulate carbon sink in a semi-arid grassland.

Elevated CO2 is widely accepted to enhance terrestrial carbon sink, especially in arid and semi-arid regions. However, great uncertainties exist for the CO2 fertilisation effects, particularly when its interactions with other global change factors are considered. A four-factor (CO2 , temperature, precipitation and nitrogen) experiment revealed that elevated CO2 did not affect either gross ecosystem productivity or ecosystem respiration, and consequently resulted in no changes of net ecosystem productivity in a semi-arid grassland despite whether temperature, precipitation and nitrogen were elevated or not. The observations could be primarily attributable to the offset of ecosystem carbon uptake by enhanced soil carbon release under CO2 enrichment. Our findings indicate that arid and semi-arid ecosystems may not be sensitive to CO2 enrichment as previously expected and highlight the urgent need to incorporate this mechanism into most IPCC carbon-cycle models for convincing projection of terrestrial carbon sink and its feedback to climate change.

Effects of livestock grazing on grassland carbon storage and release override impacts associated with global climate change.

Predicting future carbon (C) dynamics in grassland ecosystems requires knowledge of how grazing and global climate change (e.g., warming, elevated CO2 , increased precipitation, drought, and N fertilization) interact to influence C storage and release. Here, we synthesized data from 223 grassland studies to quantify the individual and interactive effects of herbivores and climate change on ecosystem C pools and soil respiration (Rs). Our results showed that grazing overrode global climate change factors in regulating grassland C storage and release (i.e., Rs). Specifically, grazing significantly decreased aboveground plant C pool (APCP), belowground plant C pool (BPCP), soil C pool (SCP), and Rs by 19.1%, 6.4%, 3.1%, and 4.6%, respectively, while overall effects of all global climate change factors increased APCP, BPCP, and Rs by 6.5%, 15.3%, and 3.4% but had no significant effect on SCP. However, the combined effects of grazing with global climate change factors also significantly decreased APCP, SCP, and Rs by 4.0%, 4.7%, and 2.7%, respectively but had no effect on BPCP. Most of the interactions between grazing and global climate change factors on APCP, BPCP, SCP, and Rs were additive instead of synergistic or antagonistic. Our findings highlight the dominant effects of grazing on C storage and Rs when compared with the suite of global climate change factors. Therefore, incorporating the dominant effect of herbivore grazing into Earth System Models is necessary to accurately predict climate-grassland feedbacks in the Anthropocene.

Simple additive simulation overestimates real influence: altered nitrogen and rainfall modulate the effect of warming on soil carbon fluxes.

Experiments and models have led to a consensus that there is positive feedback between carbon (C) fluxes and climate warming. However, the effect of warming may be altered by regional and global changes in nitrogen (N) and rainfall levels, but the current understanding is limited. Through synthesizing global data on soil C pool, input and loss from experiments simulating N deposition, drought and increased precipitation, we quantified the responses of soil C fluxes and equilibrium to the three single factors and their interactions with warming. We found that warming slightly increased the soil C input and loss by 5% and 9%, respectively, but had no significant effect on the soil C pool. Nitrogen deposition alone increased the soil C input (+20%), but the interaction of warming and N deposition greatly increased the soil C input by 49%. Drought alone decreased the soil C input by 17%, while the interaction of warming and drought decreased the soil C input to a greater extent (-22%). Increased precipitation stimulated the soil C input by 15%, but the interaction of warming and increased precipitation had no significant effect on the soil C input. However, the soil C loss was not significantly affected by any of the interactions, although it was constrained by drought (-18%). These results implied that the positive C fluxes-climate warming feedback was modulated by the changing N and rainfall regimes. Further, we found that the additive effects of [warming × N deposition] and [warming × drought] on the soil C input and of [warming × increased precipitation] on the soil C loss were greater than their interactions, suggesting that simple additive simulation using single-factor manipulations may overestimate the effects on soil C fluxes in the real world. Therefore, we propose that more multifactorial experiments should be considered in studying Earth systems.

Leaf-trait plasticity and species vulnerability to climate change in a Mongolian steppe.

Climate change is expected to modify plant assemblages in ways that will have major consequences for ecosystem functions. How climate change will affect community composition will depend on how individual species respond, which is likely related to interspecific differences in functional traits. The extraordinary plasticity of some plant traits is typically neglected in assessing how climate change will affect different species. In the Mongolian steppe, we examined whether leaf functional traits under ambient conditions and whether plasticity in these traits under altered climate could explain climate-induced biomass responses in 12 co-occurring plant species. We experimentally created three probable climate change scenarios and used a model selection procedure to determine the set of baseline traits or plasticity values that best explained biomass response. Under all climate change scenarios, plasticity for at least one leaf trait correlated with change in species performance, while functional leaf-trait values in ambient conditions did not. We demonstrate that trait plasticity could play a critical role in vulnerability of species to a rapidly changing environment. Plasticity should be considered when examining how climate change will affect plant performance, species' niche spaces, and ecological processes that depend on plant community composition.

The effects of litter input and increased precipitation on soil microbial communities in a temperate grassland.

Global warming has contributed to shifts in precipitation patterns and increased plant productivity, resulting in a significant increase in litter input into the soils. The enhanced litter input, combined with higher levels of precipitation, may potentially affect soil microbial communities. This study aims to investigate the effects of litter input and increased precipitation on soil microbial biomass, community structure, and diversity in a temperate meadow steppe in northeastern China. Different levels of litter input (0%, +30%, +60%) and increased precipitation (0%, +15%, +30%) were applied over a three-year period (2015-2017). The results showed that litter input significantly increased the biomass of bacteria and fungi without altering their diversity, as well as the ratio of bacterial to fungal biomass. Increased precipitation did not have a notable effect on the biomass and diversity of bacteria and fungi, but it did increase the fungal-to-bacterial biomass ratio. However, when litter input and increased precipitation interacted, bacterial diversity significantly increased while the fungal-to-bacterial biomass ratio remained unchanged. These findings indicate that the projected increases in litter and precipitation would have a substantial impact on soil microbial communities. In energy-and water-limited temperate grasslands, the additional litter inputs and increased precipitation contribute to enhanced nutrient and water availability, which in turn promotes microbial growth and leads to shifts in community structure and diversity.

Effects of environmental changes on soil respiration in arid, cold, temperate, and tropical zones.

Soil respiration (Rs) is projected to be substantially affected by climate change, impacting the storage, equilibrium, and movement of terrestrial carbon (C). However, uncertainties surrounding the responses of Rs to climate change and soil nitrogen (N) enrichment are linked to mechanisms specific to diverse climate zones. A comprehensive meta-analysis was conducted to address this, evaluating the global effects of warming, increased precipitation, and N enrichment on Rs across various climate zones and ecosystems. Data from 123 studies, encompassing a total of 10,377 worldwide observations, were synthesized for this purpose. Annual Rs were modeled and their uncertainties were associated with a 1-km2 resolution global Rs database spanning from 1961 to 2022. Calibrating Rs using ensemble machine learning (EML) and employing 10-fold cross-validation, 13 environmental covariates were utilized. The meta-analysis findings revealed an upsurge in Rs rates in response to warming, with tropical, arid, and temperate climate zones exhibiting increases of 12 %, 13 %, and 16 %, respectively. Furthermore, increased precipitation led to stimulated Rs rates of 11 % and 9 % in tropical and temperate zones, respectively, while N deposition affected Rs in cold (+6 %) and tropical (+5 %) climate zones. The machine learning technique estimated the global soil respiration to range from 91 to 171 Pg C yr-1, with an average Rs of 700 ± 300 g C m-2 yr-1. The values ranged between 314 and 2500 g C m-2 yr-1, with the lowest and highest values observed in cold and tropical zones, respectively. Spatial variation in Rs was most pronounced in low-latitude areas, particularly in tropical rainforests and monsoon zones. Temperature, precipitation, and N deposition were identified as crucial environmental factors exerting significant influences on Rs rates worldwide. These factors underscore the interconnectedness between climate and ecosystem processes, therefore requiring explicit considerations of different climate zones when assessing responses of Rs to global change.

Response of forage nutritional quality to climate change and human activities in alpine grasslands.

The impacts of climate change and human activities on forage nutritional quality will affect nutrient capacity, livestock development and wildlife conservation in alpine regions. However, the response of forage nutritional quality to climate change and human activities remains indistinguishable across the whole Tibet. Here, six forage variables (i.e., crude protein, CP; ether extract, EE; crude ash, Ash; acid detergent fiber, ADF; neutral detergent fiber, NDF; water-soluble carbohydrates, WSC) together represented forage nutritional quality. We estimated potential forage CP, EE, Ash, ADF, NDF and WSC contents using growing mean air temperature, total precipitation and total radiation based on random forest models. We also estimated actual forage CP, EE, Ash, ADF, NDF and WSC contents using growing mean air temperature, total precipitation and total radiation, and maximum normalized difference vegetation index based on random forest models. Climate change had nonlinear effects on potential forage CP, EE, Ash, ADF, NDF and WSC contents. Radiation change predominated the variations of potential forage nutritional quality. Human activities altered the sensitivities of forage nutritional quality to climate change. The effects of human activities on forage nutritional quality increased with increasing longitude and precipitation, and decreasing elevation and radiation. Consequently, we should pay attention to the radiation change besides climate warming and precipitation change, at least for forage nutritional quality in alpine grasslands. The effects of human activities on forage nutritional quality can vary with longitude, elevation, precipitation and radiation in alpine grasslands.

Elevated CO2, warming, N addition, and increased precipitation affect different aspects of the arbuscular mycorrhizal fungal community.

The functional diversity of arbuscular mycorrhizal fungi (AMF) affects the resistance and resilience of plant communities to environmental stress. However, considerable uncertainty remains regarding how the complex interactions among elevated atmospheric CO2 (eCO2), nitrogen deposition (eN), precipitation (eP), and warming (eT) affect AMF communities. These global change factors (GCFs) do not occur in isolation, and their interactions likely affect AMF community structure and assembly processes. In this study, the interactive effects of these four GCFs on AMF communities were explored using an open-top chamber field experiment in a semiarid grassland. Elevated CO2, eN, eT, eP, and their interactions did not affect AMF biomass. The relative abundance of Paraglomus increased with N addition across treatment combinations, whereas that of Glomus decreased with N addition, especially combined with eT and eCO2. Precipitation, temperature (T), and N affected AMF phylogenetic α-diversity, and the three-way interaction among CO2, T, and N affected taxonomic and phylogenetic α-diversity. N addition significantly affected the composition of AMF communities. Both variable selection and dispersal limitation played major roles in shaping AMF communities, whereas homogeneous selection and homogenizing dispersal had little effect on AMF community assembly. The contribution of variable selection decreased under eCO2, eN and eT but not under eP. The contribution of dispersal limitation decreased under eCO2, eT, and eP but increased under eN. The assembly of AMF communities under the sixteen GCF combinations was strongly affected by dispersal limitation, variable selection and ecological drift. Elevated CO2, warming, N addition, and increased precipitation affected different aspects of AMF communities. The interactive effects of the four GCFs on AMF communities were limited. Overall, the results of this study suggest that AMF communities in semiarid grasslands can resist changes in global climate.

[Effects of increased precipitation on growth of two ephemeral plants in the Gurbantunggut Desert, China]. / é™æ°´å¢žåŠ å¯¹å¤å°”ç­é€šå¤ç‰¹æ²™æ¼ ä¸¤ç§çŸ­å‘½æ¤ç‰©ç”Ÿé•¿çš„å½±å“.

Ephemeral plants are a major component of biodiversity in the deserts of Northwest China, with important ecological functions. Information on plant morphological characteristics and biomass accumulation and allocation during different growth stages could enhance our understanding of the functional features and survival strategy of ephemeral plants. We examined the effects of increased precipitation on ephemeral species Eremopyrum distans and Nepeta micrantha in the Gurbantunggut Desert. Changes in morphological characteristics and biomass accumulation and allocation were analyzed under increasing precipitation 30% and 50% treatments. The results showed that increased precipitation 30% and 50% treatments promoted the growth of E. distans, with leaf area and reproductive organ biomass being increased by 14.2%-188.5% and 55.9%, respectively. The effects of increased precipitation on the growth of N. micrantha varied across different growth stages. At leaf expansion stage, increased precipitation promoted growth of N. micrantha, while at fruit ripening stage, increased precipitation 50% treatment reduced leaf area, plant height, and reproduction biomass by 54.9%, 20.5%, 43.2%, respectively. Thus, the responses of the two species to increased precipitation was species-specific. Increased precipitation would change the survival strategies of the two species, with consequence on the species composition and structure of desert community.

Responses of soil extracellular enzyme activities and microbial community properties to interaction between nitrogen addition and increased precipitation in a semi-arid grassland ecosystem.

Both atmospheric nitrogen (N) deposition and precipitation can strongly impact below-ground biogeochemical processes. Soil extracellular enzymes activities (EEAs) and microorganisms are considered as the key agents in ecosystem nutrient cycling. However, how the interaction between increasing N deposition and precipitation may affect soil EEAs and microbes remain poorly understood. In a 5-year field experiment in a meadow steppe in northern China, we tested the effects of N addition (N0, 0; N1, 5; N2, 10 g N m-2 yr-1) and increased precipitation (W0, ambient precipitation; W1, increase of 15% ambient precipitation; W2, increase of 30% ambient precipitation) on soil EEAs, microbial and chemical properties. Results showed that their interaction significantly affected all hydrolase activities, except for ß-1,4-xylosidase (ßX). Furthermore, increased precipitation and N addition interactively affected bacterial gene copies (P ≤ 0.05), and increased precipitation comparatively had a stronger effects. The results on the combination of N addition and increased precipitation showed that increased precipitation alleviated the positive effects of N addition on soil EEAs. This implies that the effects of either treatment alone on grassland biogeochemical processes may be alleviated by their simultaneous occurrence. Our results suggested that soil EEAs were mainly controlled by the content of N and phosphorus (P), and the ratio of C: N and C: P. Therefore, soil element content and stoichiometry could better explain the responses of EEAs to global changes. Moreover, soil microbial communities were mainly controlled by soil P content. Overall, our study highlights that the interaction between N deposition and precipitation may play a vital role in predicting the responses of soil enzyme activities to global changes in grassland ecosystems.

N enrichment, increased precipitation, and the effect of shrubs collectively shape the plant community in a desert ecosystem in northern China.

Understanding the responses of biological communities to global climate change is pivotal to accurately forecasting future dynamics and developing effective strategies for the adaptive ecological management of desert ecosystems. Although direct demographic responses of plant species to climatic factors have been widely acknowledged, they are also regulated by interspecific interactions (i.e., the effects of shrubs on herbaceous plants). The magnitude and direction of regulation of such interspecific interactions remain unclear. To address this knowledge gap, a full factorial field experiment simulating three levels of N enrichment (ambient, 10 kg N ha-1 yr-1, and 60 kg N ha-1 yr-1) and three levels of precipitation (ambient, 20% increase, and 40% increase) were conducted in the Mu Us Desert, northern China. N enrichment and increased precipitation significantly increased herbaceous productivity by improving the soil water content and nutrient availability (e.g., soil DIN:SAP) when shrubs were not present. Taller species responded to N enrichment, whereas those with a greater specific leaf area responded to increased precipitation. When shrubs were present, they acted as a 'buffer islands' that moderated the responses of herbaceous species to N enrichment and increased precipitation by weakening the effect of the improved soil water status. The magnitude of the effect of shrubs on herbaceous biomass and richness was comparable to that of N enrichment and increased precipitation. Our results highlight the importance and complexity of both large-scale environmental changes and small-scale interspecific interactions in structuring plant communities in desert ecosystems. Moreover, abiotic environmental factors and biotic interactions should be integrated in efforts to predict the responses of plant communities to future global change in desert ecosystems.

Effects of increased precipitation on the life history of spring- and autumn-germinated plants of the cold desert annual Erodium oxyrhynchum (Geraniaceae).

Future increased precipitation in cold desert ecosystems may impact annual/ephemeral plant species that germinate in both spring and autumn. Our primary aim was to compare the life history characteristics of plants from spring-germinating (SG) and autumn-germinating (AG) seeds of Erodium oxyrhynchum. Plants in field plots with simulated increases in precipitation of 0, 30 and 50 % in spring and summer were monitored to determine seedling survival, phenology, plant size, seed production and biomass accumulation and allocation. Germination characteristics were determined in the laboratory for seeds produced by plants in all increased precipitation treatments. Increased precipitation in spring significantly improved survival of seedlings from SG and AG seeds, but survival was less for AG than SG. An increase in precipitation increased the number of seeds per plant for both SG and AG, but AG produced more seeds per plant than SG. With increased precipitation, percentage of dormant seeds from SG increased significantly, while that of AG decreased slightly. Our study suggests that with increased spring and summer rainfall AG will produce an increased number of nondormant seeds that could germinate in autumn and SG an increased number of dormant seeds that become part of the soil seed bank. However, ability of some seeds to germinate in autumn and others in spring will be maintained as long as soil moisture is limited in autumn.

Life history responses of spring-and autumn-germinated ephemeral plants to increased nitrogen and precipitation in the Gurbantunggut Desert.

Nitrogen deposition and precipitation change are not only hot topics of current global change but also the main environmental factors affecting plant growth. Thus, the effects of nitrogen and precipitation on the life history of spring-(SG) and autumn-germinated (AG) ephemeral plants of Erodium oxyrhynchum were researched in the Gurbantunggut Desert, northern China, and the aim was to understand the response of plants from different germination seasons to global change. SG and AG plants with increased nitrogen and precipitation plus nitrogen treatments were measured to determine seedling survival, phenology, plant traits, biomass accumulation and allocation and dormancy characteristics of offspring (seeds). The results showed that increased nitrogen and precipitation plus nitrogen treatments significantly improved the survival of SG and AG plants during the seedling stage, and precipitation plus nitrogen treatments also improved the growth and seed production of SG and AG plants, but increased nitrogen significantly inhibited their growth and seed production. Therefore, precipitation plays an important role in regulating nitrogen uptake by plants in arid and semiarid ecosystems. With increased nitrogen, SG and AG plants allocated more biomass into root and reproductive organs but allocated significantly less biomass into the leaf, with almost no change in biomass allocation to the stem. With nitrogen plus precipitation treatments, biomass allocation in all organs of SG and AG plants showed almost no change. Clearly, changes in soil moisture also affected biomass allocation of SG and AG plants. For offspring dormancy, SG and AG plants produced more nondormancy seeds with increased nitrogen but produced more dormancy seeds under precipitation plus nitrogen treatments. Hence, in a harsh environment, SG and AG plants produced more nondormancy offspring with low reproduction in order to occupy the habitat rapidly in the following year or produced more dormancy offspring with high reproduction in a suitable environment intended for spreading germination risk in time and conserve the population.

Distinct Drivers of Core and Accessory Components of Soil Microbial Community Functional Diversity under Environmental Changes.

It is a central ecological goal to explore the effects of global change factors on soil microbial communities. The vast functional gene repertoire of soil microbial communities is composed of both core and accessory genes, which may be governed by distinct drivers. This intuitive hypothesis, however, remains largely unexplored. We conducted a 5-year nitrogen and water addition experiment in the Eurasian steppe and quantified microbial gene diversity via shotgun metagenomics. Nitrogen addition led to an 11-fold increase in the abundance (based on quantitative PCR [qPCR]) of ammonia-oxidizing bacteria, which have mainly core community genes and few accessory community genes. Thus, nitrogen addition substantially increased the relative abundance of many core genes at the whole-community level. Water addition stimulated both plant diversity and microbial respiration; however, increased carbon/energy resources from plants did not counteract increased respiration, so soil carbon/energy resources became more limited. Thus, water addition selected for microorganisms with genes responsible for degrading recalcitrant soil organic matter. Accordingly, many other microorganisms without these genes (but likely with other accessory community genes due to relatively stable average microbial genome size) were selected against, leading to the decrease in the diversity of accessory community genes. In summary, nitrogen addition primarily affected core community genes through nitrogen-cycling processes, and water addition primarily regulated accessory community genes through carbon-cycling processes. Although both gene components may significantly respond as the intensity of nitrogen/water addition increases, our results demonstrated how these common global change factors distinctly impact each component.IMPORTANCE Our results demonstrated increased ecosystem nitrogen and water content as the primary drivers of the core and accessory components of soil microbial community functional diversity, respectively. Our findings suggested that more attention should be paid to certain components of community functional diversity under specific global change conditions. Our findings also indicated that microbial communities have adapted to nitrogen addition by strengthening the function of ammonia oxidization to deplete the excess nitrogen, thus maintaining ecosystem homeostasis. Because community gene richness is primarily determined by the presence/absence of accessory community genes, our findings further implied that strategies such as maintaining the amount of soil organic matter could be adopted to effectively improve the functional gene diversity of soil microbial communities subject to global change factors.

Life history responses of two ephemeral plant species to increased precipitation and nitrogen in the Gurbantunggut Desert.

Precipitation change and nitrogen deposition are not only hot topics of current global change but also the main environmental factors affecting plant growth in desert ecosystems. Thus, we performed an experiment of increased precipitation, nitrogen, and precipitation plus nitrogen on the ephemeral annual species Nepeta micrantha and Eremopyrum distans in the Gurbantunggut Desert. We aimed to determine the life history responses of N. micrantha and E. distans to environment changes, and the germination percentage of the offspring (seeds) was also tested in the laboratory. The results showed that increased nitrogen and precipitation plus nitrogen increased the growth of both plant species, whereas increased precipitation inhibited the growth of N. micrantha but increased the growth of E. distans. This differential response of these two species to precipitation and nitrogen also affected the germination of their offspring. In response to increased nitrogen and precipitation plus nitrogen, the germination percentage of the offspring produced by two species decreased in conjunction with the plants exhibiting high reproduction, which may prevent overcrowding during the following year; however, the N. micrantha plants produced more nondormant offspring in conjunction with low reproduction under relatively greater amounts of precipitation, and N. micrantha offspring could occupy their habitat via rapid germination in suitable environments. Therefore, with increased precipitation and nitrogen deposition, these differences in offspring dormancy may affect their ecological niche in the community.

[Effects of Short-term Exogenous Nitrogen and Carbon Input on Soil Respiration Under Changing Precipitation Pattern].

The responses of soil respiration to exogenous carbon (C) and nitrogen (N) inputs under changing precipitation patterns were explored via in-situ field experiments. In 2014, a typical temperate grassland on the Xilin River of Inner Mongolia was taken as the research site, and soil respiration was measured in the following treatments:addition of water alone (CK), addition of water + N fertilizer[CN, 2.5 g·(m2·a)-1], addition of water + labile C[CG, 24 g·(m2·a)-1], and addition of water + N fertilizer+ labile C[CNG, 2.5 g·(m2·a)-1+24 g·(m2·a) -1], and the correlations of soil respiration with soil temperature, soil moisture, soil dissolved organic C (DOC), and soil microbial biomass C (MBC) were analyzed. During the first water application event (FWE) with the frequency of natural precipitation, cumulative CO2 efflux over 168 hours significantly increased in the CG and CNG treatments, whereas there was no such change in the CN treatment. In addition, soil MBC contents in the CG and CNG treatments were significantly higher than that in the CK and CN treatments, and the correlation of average soil respiration rate with soil MBC content among these treatments was positively significant (P<0.05). In contrast with during the FWE, cumulative CO2 efflux over 168 hours and soil MBC content significantly decreased during the second water application event (SWE) with no natural precipitation (P<0.05), whereas soil DOC content significantly increased (P<0.05). The cumulative CO2 efflux over 168 hours significantly decreases in the CN and CG treatments (P<0.05).During both the water application events, soil respiration rate had a positive relationship with soil temperature and soil volume water content (P<0.05). Therefore, it is proposed that the distribution of natural precipitation influences soil water content, which controls the effects of exogenous C and N on soil respiration in semiarid grassland ecosystems.