Plant and soil responses to tillage practices change arbuscular mycorrhizal fungi populations during crop growth.

Background: Tillage practices can substantially affect soil properties depending on crop stage. The interaction between tillage and crop growth on arbuscular mycorrhizal fungi (AMF) communities remains unclear. We investigated the interactions between four tillage treatments (CT: conventional tillage, RT: reduced tillage, NT: no tillage with mulch, and SS: subsoiling with mulch), maintained for 25 years, and two wheat growth stages (elongation stage and grain filling stage) on AMF diversity and community composition. Results: The AMF community composition strongly changed during wheat growth, mainly because of changes in the relative abundance of dominant genera Claroideoglomus, Funneliformi, Rhizophagu, Entrophospora, and Glomus. Co-occurrence network analysis revealed that the grain filling stage had a more complex network than the elongation stage. Redundancy analysis results showed that keystone genera respond mainly to changes in soil organic carbon during elongation stage, whereas the total nitrogen content affected the keystone genera during grain filling. Compared with CT, the treatments with mulch, i.e., NT and SS, significantly changed the AMF community composition. The change of AMF communities under different tillage practices depended on wheat biomass and soil nutrients. NT significantly increased the relative abundances of Glomus and Septoglomus, while RT significantly increased the relative abundance of Claroideoglomus. Conclusion: Our findings indicate that the relative abundance of dominant genera changed during wheat growth stages. Proper tillage practices (e.g., NT and SS) benefit the long-term sustainable development of the Loess Plateau cropping systems.

Reduction in precipitation amount, precipitation events, and nitrogen addition change ecosystem carbon fluxes differently in a semi-arid grassland.

The increases in extent and frequency of extreme drought events and increased nitrogen (N) deposition due to global change are expected to have profound impacts on carbon cycling in semi-arid grasslands. However, how ecosystem CO2 exchange processes respond to different drought scenarios individually and interactively with N addition remains uncertain. In this study, we experimentally explored the effects of different drought scenarios (early season extreme drought, 50 % reduction in precipitation amount, and 50 % reduction in precipitation events) and N addition on net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) over three growing seasons (2019-2021) in a semi-arid grassland in northern China. The growing-season ecosystem carbon fluxes in response to drought and N addition were influenced by inter-annual precipitation changes, with 2019 as a normal precipitation year, and 2020 and 2021 as wet years. Early season extreme drought stimulated NEE by reducing ER. 50 % reduction in precipitation amount decreased ER and GEP consistently in three years, but only significantly suppressed NEE in 2019. 50 % reduction in precipitation events stimulated NEE. Nitrogen addition stimulated NEE, ER, and GEP, but only significantly in wet years. The structural equation models showed that changes in carbon fluxes were regulated by soil moisture, soil temperature, microbial biomass nitrogen (MBN), and the key plant functional traits. Decreased community-weighted means of specific leaf area (CWMSLA) was closely related to the reduced ER and GEP under early season extreme drought and 50 % reduction in precipitation amount. While increased community-weighted means of plant height (CWMPH) largely accounted for the stimulated ER and GEP under 50 % reduction in precipitation events. Our study stresses the distinct effects of different drought scenarios and N enrichment on carbon fluxes, and highlights the importance of soil traits and the key plant traits in determining carbon exchange in this water-limited ecosystem.

Nitrogen addition alleviates the adverse effects of drought on plant productivity in a temperate steppe.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Opposing responses of temporal stability of aboveground and belowground net primary productivity to water and nitrogen enrichment in a temperate grassland.

Changes in water and nitrogen availability, as important elements of global environmental change, are known to affect the temporal stability of aboveground net primary productivity (ANPP). However, evidences for their effects on the temporal stability of belowground net primary productivity (BNPP), and whether such effects are consistent between belowground and aboveground, are rather scarce. Here, we investigated the responses of temporal stability of both ANPP and BNPP to water and nitrogen addition based on a 9-year manipulative experiment in a temperate grassland in northern China. The results showed that the temporal stability of ANPP increased with water addition but decreased with nitrogen addition. By contrast, the temporal stability of BNPP decreased with water addition but increased with nitrogen enrichment. The temporal stability of ANPP was mainly determined by the soil moisture and inorganic nitrogen, which modulated species asynchrony, as well as by the stability of dominant species. On the other hand, the temporal stability of BNPP was mainly driven by the soil moisture and inorganic nitrogen that modulated ANPP of grasses, and by the direct effect of soil water availability. Our study provides the first evidence on the opposite responses of aboveground and belowground grassland temporal stability to increased water and nitrogen availability, highlighting the importance of considering both aboveground and belowground components of ecosystems for a more comprehensive understanding of their dynamics.

Density-Dependent Seed Predation of Quercus wutaishanica by Rodents in Response to Different Seed States.

The predation and/or dispersal of Quercus seeds by rodents play an important role in the creation of the tree species. The present study examined the effects of community habitats on the predation and dispersal of Quercus wutaishanica seeds by rodents. We released seeds with densities set at 2, 4, 8, 16, and 32 seed square meter with litter cover, soil burial, and bare ground in the Liupan Mountains National Nature Reserve in the Ningxia Hui Autonomous Region, northwest China. The results showed that (1) the litter cover and soil burial significantly increased the seed survival probability compared with bare ground treatments, especially the predation in situ (PIS) (p < 0.05). Both the scatter hoarding (SH) and larder hoarding (LH) for litter cover and soil burial were significantly increased compared with bare ground (p < 0.05). (2) The large seeds are preferentially predated after dispersal and their long-distance dispersal (>5 m) was significantly greater than that of small seeds (p < 0.05), while small seeds are more likely to be preyed on in situ or during short-distance dispersal (<3 m). (3) The Q. wutaishanica seed predation by rodents increased at a high density rather than at a low density, indicating a negative density-dependent predation. These findings provide insights into the ecological characteristics of Quercus tree regeneration and shed light on the coexistence between rodents and different-sized seeds.

Nitrogen addition and mowing alter drought resistance and recovery of grassland communities.

Nitrogen enrichment and land use are known to influence various ecosystems, but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood. Here we investigated the effects of increased nitrogen input and mowing on the resistance and recovery of temperate semiarid grassland experiencing a three-year drought. Nitrogen addition increased grassland biomass recovery but decreased structural recovery after drought, whereas annual mowing increased grassland biomass recovery and structural recovery but reduced structural resistance to drought. The treatment effects on community biomass/structural resistance and recovery were largely modulated by the stability of the dominant species and asynchronous dynamics among species, and the community biomass resistance and recovery were also greatly driven by the stability of grasses. Community biomass resistance/recovery in response to drought was positively associated with its corresponding structural stability. Our study provides important experimental evidence that both nitrogen addition and mowing could substantially change grassland stability in both functional and structural aspects. Our findings emphasize the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.

ß-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes.

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving ß-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected ß-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of ß-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change.

Temporal variability in production is not consistently affected by global change drivers across herbaceous-dominated ecosystems.

Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inter-annual variability in ANPP. We examined 27 global change experiments located in 11 different herbaceous ecosystems that varied in both abiotic and biotic conditions, to investigate changes in the mean and temporal variability of ANPP (measured as the coefficient of variation) in response to different GCD manipulations, including resource additions, warming, and irrigation. From this comprehensive data synthesis, we found that GCD treatments increased mean ANPP. However, GCD manipulations both increased and decreased temporal variability of ANPP (24% of comparisons), with no net effect overall. These inconsistent effects on temporal variation in ANPP can, in part, be attributed to site characteristics, such as mean annual precipitation and temperature as well as plant community evenness. For example, decreases in temporal variability in ANPP with the GCD treatments occurred in wetter and warmer sites with lower plant community evenness. Further, the addition of several nutrients simultaneously increased the sensitivity of ANPP to interannual variation in precipitation. Based on this analysis, we expect that GCDs will likely affect the magnitude more than the reliability over time of ecosystem production in the future.

Photosynthesis and Growth of Pennisetum centrasiaticum (C4) is Superior to Calamagrostis pseudophragmites (C3) During Drought and Recovery.

Global warming and changes in rainfall patterns may put many ecosystems at risk of drought. These stressors could be particularly destructive in arid systems where species are already water-limited. Understanding plant responses in terms of photosynthesis and growth to drought and rewatering is essential for predicting ecosystem-level responses to climate change. Different drought responses of C3 and C4 species could have important ecological implications affecting interspecific competition and distribution of plant communities in the future. For this study, C4 plant Pennisetum centrasiaticum and C3 plant Calamagrostis pseudophragmites were subjected to progressive drought and subsequent rewatering in order to better understand their differential responses to regional climate changes. We tracked responses in gas exchange, chlorophyll fluorescence, biomass as well as soil water status in order to investigate the ecophysiological responses of these two plant functional types. Similar patterns of photosynthetic regulations were observed during drought and rewatering for both psammophytes. They experienced stomatal restriction and nonstomatal restriction successively during drought. Photosynthetic performance recovered to the levels in well-watered plants after rewatering for 6-8 days. The C4 plant, P. centrasiaticum, exhibited the classic CO2-concentrating mechanism and more efficient thermal dissipation in the leaves, which confers more efficient CO2 assimilation and water use efficiency, alleviating drought stress, maintaining their photosynthetic advantage until water deficits became severe and quicker recovery after rewatering. In addition, P. centrasiaticum can allocate a greater proportion of root biomass in case of adequate water supply and a greater proportion of above-ground biomass in case of drought stress. This physiological adaptability and morphological adjustment underline the capacity of C4 plant P. centrasiaticum to withstand drought more efficiently and recover upon rewatering more quickly than C. pseudophragmites and dominate in the Horqin Sandy Land.

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Increasing nitrogen (N) deposition results in soil acidification in grasslands. Acid buffering capacity of soil is a critical index evaluating soil acidification, the response of which to N input is regulated by precipitation and concentration of other limiting elements. To explore the responses of soil acidification to N, phosphorus (P), and water inputs, we conducted a 13-year field experiment in an old-field grassland and calculated the acid buffering capacity (ABC) and acid neutralizing capacity (ANC) at the reference of pH=5.0 (ANCpH5.0) and 4.0 (ANCpH4.0), using quadratic curve fitting model. The results showed that, without water addition, single N addition or combined with P addition significantly decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas single P addition had no significant effect on soil pH, ANCpH5.0 or ANCpH4.0. With water addition, the addition of N or combined with P decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas P addition decreased soil pH, increased ANCpH4.0, without effect on ANCpH5.0. In contrast with treatments without water addition, water addition had positive effects on soil pH, ANCpH5.0 and ANCpH4.0. For soils with different initial soil pH values, it was better to select ANC rather than ABC as an index to evaluate soil anti-acidification capacity.

Differential roles of species richness versus species asynchrony in regulating community stability along a precipitation gradient.

Plant community may provide products and services to humans. However, patterns and drivers of community stability along a precipitation gradient remain unclear. A regional-scale transect survey was conducted over a 3-year period from 2013 to 2015, along a precipitation gradient from 275 to 555 mm and spanning 440 km in length from west to east in a temperate semiarid grassland of northern China, a central part of the Eurasian steppe. Our study provided regional-scale evidence that the community stability increased with increasing precipitation in the semiarid ecosystem. The patterns of community stability along a precipitation gradient were ascribed to community composition and community dynamics, such as species richness and species asynchrony, rather than the abiotic effect of precipitation. Species richness regulated the temporal mean (µ) of aboveground net primary productivity (ANPP), while species asynchrony regulated the temporal standard deviation (σ) of ANPP, which in turn contributed to community stability. Our findings highlight the crucial role of community composition and community dynamics in regulating community stability under climate change.

Asynchrony among local communities stabilises ecosystem function of metacommunities.

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species-level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1-315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species' populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.

Effects of nitrogen and water addition on trace element stoichiometry in five grassland species.

A 9-year manipulative experiment with nitrogen (N) and water addition, simulating increasing N deposition and changing precipitation regime, was conducted to investigate the bioavailability of trace elements, iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in soil, and their uptake by plants under the two environmental change factors in a semi-arid grassland of Inner Mongolia. We measured concentrations of trace elements in soil and in foliage of five common herbaceous species including 3 forbs and 2 grasses. In addition, bioaccumulation factors (BAF, the ratio of the chemical concentration in the organism and the chemical concentration in the growth substrate) and foliar Fe:Mn ratio in each plant was calculated. Our results showed that soil available Fe, Mn and Cu concentrations increased under N addition and were negatively correlated with both soil pH and cation exchange capacity. Water addition partly counteracted the positive effects of N addition on available trace element concentrations in the soil. Foliar Mn, Cu and Zn concentrations increased but Fe concentration decreased with N addition, resulting in foliar elemental imbalances among Fe and other selected trace elements. Water addition alleviated the effect of N addition. Forbs are more likely to suffer from Mn toxicity and Fe deficiency than grass species, indicating more sensitivity to changing elemental bioavailability in soil. Our results suggested that soil acidification due to N deposition may accelerate trace element cycling and lead to elemental imbalance in soil-plant systems of semi-arid grasslands and these impacts of N deposition on semi-arid grasslands were affected by water addition. These findings indicate an important role for soil trace elements in maintaining ecosystem functions associated with atmospheric N deposition and changing precipitation regimes in the future.

Base cations and micronutrients in soil aggregates as affected by enhanced nitrogen and water inputs in a semi-arid steppe grassland.

The intensification of grassland management by nitrogen (N) fertilization and irrigation may threaten the future integrity of fragile semi-arid steppe ecosystems by affecting the concentrations of base cation and micronutrient in soils. We extracted base cations of exchangeable calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) and extractable micronutrients of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) from three soil aggregate sizes classes (microaggregates, <0.25mm; small macroaggregates, 0.25-2mm; large macroaggregates, >2mm) from a 9-yearN and water field manipulation study. There were significantly more base cations (but not micronutrients) in microaggregates compared to macroaggregates which was related to greater soil organic matter and clay contents. Nitrogen addition significantly decreased exchangeable Ca by up to 33% in large and small macroaggregates and exchangeable Mg by up to 27% in three aggregates but significantly increased extractable Fe, Mn and Cu concentrations (by up to 262%, 150%, and 55%, respectively) in all aggregate size classes. However, water addition only increased exchangeable Na, while available Fe and Mn were decreased by water addition when averaging across all N treatments and aggregate classes. The loss of exchangeable Ca and Mg under N addition and extractable Fe and Mn in soil aggregates under water addition might potentially constrain the productivity of this semi-arid grassland ecosystem.

Responses of Soil Bacterial Communities to Nitrogen Deposition and Precipitation Increment Are Closely Linked with Aboveground Community Variation.

It has been predicted that precipitation and atmospheric nitrogen (N) deposition will increase in northern China; yet, ecosystem responses to the interactive effects of water and N remain largely unknown. In particular, responses of belowground microbial community to projected global change and their potential linkages to aboveground macro-organisms are rarely studied. In this study, we examined the responses of soil bacterial diversity and community composition to increased precipitation and multi-level N deposition in a temperate steppe in Inner Mongolia, China, and explored the diversity linkages between aboveground and belowground communities. It was observed that N addition caused the significant decrease in bacterial alpha-diversity and dramatic changes in community composition. In addition, we documented strong correlations of alpha- and beta-diversity between plant and bacterial communities in response to N addition. It was found that N enriched the so-called copiotrophic bacteria, but reduced the oligotrophic groups, primarily by increasing the soil inorganic N content and carbon availability and decreasing soil pH. We still highlighted that increased precipitation tended to alleviate the effects of N on bacterial diversity and dampen the plant-microbe connections induced by N. The counteractive effects of N addition and increased precipitation imply that even though the ecosystem diversity and function are predicted to be negatively affected by N deposition in the coming decades; the combination with increased precipitation may partially offset this detrimental effect.

[Effects of nitrogen and water addition on soil bacterial diversity and community structure in temperate grasslands in northern China].

In this study, we measured the responses of soil bacterial diversity and community structure to nitrogen (N) and water addition in the typical temperate grassland in northern China. Results showed that N addition significantly reduced microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) under regular precipitation treatment. Similar declined trends of MBC and MBN caused by N addition were also found under increased precipitation condition. Nevertheless, water addition alleviated the inhibition by N addition. N addition exerted no significant effects. on bacterial α-diversity indices, including richness, Shannon diversity and evenness index under regular precipitation condition. Precipitation increment tended to increase bacterial α-diversity, and the diversity indices of each N gradient under regular precipitation were much lower than that of the corresponding N addition rate under increased precipitation. Correlation analysis showed that soil moisture, nitrate (NO3(-)-N) and ammonium (NH4+-N) were significantly negatively correlated with bacterial evenness index, and MBC and MBN had a significant positive correlation with bacterial richness and evenness. Non-metric multidimensional scaling (NMDS) ordination illustrated that the bacterial communities were significantly separated by N addition rates, under both water ambient and water addition treatments. Redundancy analysis (RDA) revealed that soil MBC, MBN, pH and NH4+-N were the key environmental factors for shaping bacterial communities.

Effects of experimentally-enhanced precipitation and nitrogen on resistance, recovery and resilience of a semi-arid grassland after drought.

Resistance, recovery and resilience are three important properties of ecological stability, but they have rarely been studied in semi-arid grasslands under global change. We analyzed data from a field experiment conducted in a native grassland in northern China to explore the effects of experimentally enhanced precipitation and N deposition on both absolute and relative measures of community resistance, recovery and resilience--calculated in terms of community cover--after a natural drought. For both absolute and relative measures, communities with precipitation enhancement showed higher resistance and lower recovery, but no change in resilience compared to communities with ambient precipitation in the semi-arid grassland. The manipulated increase in N deposition had little effect on these community stability metrics except for decreased community resistance. The response patterns of these stability metrics to alterations in precipitation and N are generally consistent at community, functional group and species levels. Contrary to our expectations, structural equation modeling revealed that water-driven community resistance and recovery result mainly from changes in community species asynchrony rather than species diversity in the semi-arid grassland. These findings suggest that changes in precipitation regimes may have significant impacts on the response of water-limited ecosystems to drought stress under global change scenarios.

Abundance and community structure of ammonia-oxidizing Archaea and Bacteria in response to fertilization and mowing in a temperate steppe in Inner Mongolia.

Based on a 6-year field trial in a temperate steppe in Inner Mongolia, we investigated the effects of nitrogen (N) and phosphorus (P) fertilization and mowing on the abundance and community compositions of ammonia-oxidizing Bacteria (AOB) and Archaea (AOA) upon early (May) and peak (August) plant growth using quantitative PCR (qPCR), terminal-restriction fragment length polymorphism (T-RFLP), cloning and sequencing. The results showed that N fertilization changed AOB community composition and increased AOB abundance in both May and August, but significantly decreased AOA abundance in May. By contrast, P fertilization significantly influenced AOB abundance only in August. Mowing significantly decreased AOA abundance and had little effect on AOA community compositions in May, while significantly influencing AOB abundance in both May and August, Moreover, AOA and AOB community structures showed obvious seasonal variations between May and August. Phylogenetic analysis showed that all AOA sequences fell into the Nitrososphaera cluster, and the AOB community was dominated by Nitrosospira Cluster 3. The results suggest that fertilization and mowing play important roles in affecting the abundance and community compositions of AOA and AOB.

Linking ethylene to nitrogen-dependent leaf longevity of grass species in a temperate steppe.

BACKGROUND AND AIMS: Leaf longevity is an important plant functional trait that often varies with soil nitrogen supply. Ethylene is a classical plant hormone involved in the control of senescence and abscission, but its role in nitrogen-dependent leaf longevity is largely unknown. METHODS: Pot and field experiments were performed to examine the effects of nitrogen addition on leaf longevity and ethylene production in two dominant plant species, Agropyron cristatum and Stipa krylovii, in a temperate steppe in northern China. KEY RESULTS: Nitrogen addition increased leaf ethylene production and nitrogen concentration but shortened leaf longevity; the addition of cobalt chloride, an ethylene biosynthesis inhibitor, reduced leaf nitrogen concentration and increased leaf longevity. Path analysis indicated that nitrogen addition reduced leaf longevity mainly through altering leaf ethylene production. CONCLUSIONS: These findings provide the first experimental evidence in support of the involvement of ethylene in nitrogen-induced decrease in leaf longevity.

Patterns of plant biomass allocation in temperate grasslands across a 2500-km transect in northern China.

Plant biomass allocation between below- and above-ground parts can actively adapt to the ambient growth conditions and is a key parameter for estimating terrestrial ecosystem carbon (C) stocks. To investigate how climatic variations affect patterns of plant biomass allocation, we sampled 548 plants belonging to four dominant genera (Stipa spp., Cleistogenes spp., Agropyron spp., and Leymus spp.) along a large-scale (2500 km) climatic gradient across the temperate grasslands from west to east in northern China. Our results showed that Leymus spp. had the lowest root/shoot ratios among the each genus. Root/shoot ratios of each genera were positively correlated with mean annual temperature (MAT), and negatively correlated with mean annual precipitation (MAP) across the transect. Temperature contributed more to the variation of root/shoot ratios than precipitation for Cleistogenes spp. (C4 plants), whereas precipitation exerted a stronger influence than temperature on their variations for the other three genera (C3 plants). From east to west, investment of C into the belowground parts increased as precipitation decreased while temperature increased. Such changes in biomass allocation patterns in response to climatic factors may alter the competition regimes among co-existing plants, resulting in changes in community composition, structure and ecosystem functions. Our results suggested that future climate change would have great impact on C allocation and storage, as well as C turnover in the grassland ecosystems in northern China.