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Despite extensive studies on effects of elevated CO sub(2) concentration ([CO sub(2)] sub(e)) on plant growth, few studies have investigated the responses of native grassland plant species to [CO sub(2)] sub(e) in terms of nutrient acquisition. The effects of [CO sub(2)] sub(e) (769 plus or minus 23 ppm) on Artemisia frigida and Stipa krylovii, two dominant species in Inner Mongolia steppe were investigated by growing them for 7 weeks in Open-Top Chambers (OTC). Exposure to [CO sub(2)] sub(e) enhanced shoot and root growth of A. frigida and S. krylovii. Elevated [CO sub(2)] increased photosynthetic rates (Pn) by 34 % in A. frigida but decreased Pn by 52 % in S. krylovii. Moreover, root-secreted acid phosphatase activity in A. frigida was stimulated by [CO sub(2)] sub(e), while exudation of malate from roots of S. krylovii was suppressed by [CO sub(2)] sub(e). Exposure to [CO sub(2)] sub(e) led to a decrease in P concentration in shoots and roots of A. frigida and S. krylovii, but total amount of P accumulated in shoots and roots of both species was increased by [CO sub(2)] sub(e.) The two dominant species in temperate steppes differed in their responses to [CO sub(2)] sub(e), such that A. frigida was more adapted to [CO sub(2)] sub(e) than S. krylovii under low availability of soil P.

Loss of plant diversity with increased anthropogenic nitrogen (N) deposition in grasslands has occurred globally. In most cases, competitive exclusion driven by preemption of light or space is invoked as a key mechanism. Here, we provide evidence from a 9‐yr N‐addition experiment for an alternative mechanism: differential sensitivity of forbs and grasses to increased soil manganese (Mn) levels. In Inner Mongolia steppes, increasing the N supply shifted plant community composition from grass–forb codominance (primarily Stipa krylovii and Artemisia frigida, respectively) to exclusive dominance by grass, with associated declines in overall species richness. Reduced abundance of forbs was linked to soil acidification that increased mobilization of soil Mn, with a 10‐fold greater accumulation of Mn in forbs than in grasses. The enhanced accumulation of Mn in forbs was correlated with reduced photosynthetic rates and growth, and is consistent with the loss of forb species. Differential accumulation of Mn between forbs and grasses can be linked to fundamental differences between dicots and monocots in the biochemical pathways regulating metal transport. These findings provide a mechanistic explanation for N‐induced species loss in temperate grasslands by linking metal mobilization in soil to differential metal acquisition and impacts on key functional groups in these ecosystems.

FRIGIDA (FRI), as the major regulator of flowering time in Arabidopsis accessions, can activate its target FLOWERING LOCUS C (FLC) to delay flowering before vernalization. In addition to FLC, other FRI targets also exist in Arabidopsis. Although leaves sense environmental cues to modulate flowering time, it is not known if roots also regulate the floral transition. In this study, we investigated the spatio-temporal effect of FRI on flowering time. Local expression of FRI in the phloem and leaves activated FLC to delay flowering. Furthermore, we found that local expression of FRI in the roots also delayed flowering by activating other targets, MADS AFFECTING FLOWERING4 (MAF4) and MAF5, in the roots. Graft and genetic experiments revealed that the spatial expression of FRI in the root might generate a mobile signal, which is transmitted from roots to shoot and antagonizes the FT signal to delay flowering. Specifically expressing FRI in the embryo efficiently delayed flowering, even expressing FRI as early as the pro-embryo stage is enough to up-regulate FLC expression to delay flowering. Together, our findings demonstrate the spatio-temporal effect of FRI on delaying flowering, and we propose that root tissue also perceives the flowering signal to fine-tune the flowering time through MAF4/5 as novel targets of FRI.

Plasticity of root traits plays an important role in plant growth and survival under changing climate. Shift in precipitation is one of the most pertinent global change factors driving changes in structure and function of grasslands. However, few studies have investigated intraspecific variation of root traits in response to precipitation change under field conditions. We conducted a 10‐year simulated increased precipitation experiment in a temperate grassland and a 700‐km regional scale transect along a precipitation gradient ranging from 144.23 to 412.29 mm in northern China. The morphological, chemical and anatomical traits of the first two‐order roots were determined on 15 common herbaceous species in the manipulation experiment and two regionally common species (Leymus chinensis, Artemisia frigida) along a precipitation gradient. We found that most of the root traits of the herbaceous species exhibited no significant responses to water addition. The two regionally common species adjusted their root traits at sites with the annual precipitation lower than certain value, that is 250 and 160 mm for L. chinensis and A. frigida, respectively. These results indicate that root traits of the herbaceous species exhibit little plasticity in response to precipitation change and that the adjustment of root traits occurs when the range of annual precipitation exceeds a certain threshold. Root traits of L. chinensis and A. frigida varied differently both in manipulation experiment and along the precipitation gradient. Root traits of L. chinensis were relatively constant, while A. frigida adjusted their morphological root traits in response to water addition. Moreover, L. chinensis showed higher specific root length (SRL) and area, and root N contents at sites with annual precipitation lower than c. 250 mm. In contrast, A. frigida displayed thicker roots with lower SRL and area at sites with annual precipitation lower than c. 160 mm. Our results showed that root traits of herbaceous species in temperate grasslands exhibited little plasticity and that different species have evolved diverse adaptive strategies in response to precipitation change. These novel findings provide valuable information to predict responses of temperate grasslands to future climate change. 摘要 根系性状的种内变异反映了植物对变化环境的适应策略，是植物在变化环境中生存和生长的关键因素。降水变化是影响草地生态系统结构和功能重要的全球变化因子之一。然而，很少有研究探讨在野外条件下草原植物根系性状对降水变化的响应。本研究利用在内蒙古温带草原开展的野外长期（10年）增加降水控制实验和沿着从东到西的自然降水梯度(412.3–144.2 mm)设置的长约700 km的样带，分别选取了15种常见草本物种和2种区域广布种为研究对象，对其根系形态性状、化学性状和解剖结构进行测定，以期探讨草原植物对降水变化的适应策略。我们的研究结果发现：1）内蒙古典型草原植物的大部分根系性状对增加降水无显著响应，少数几个物种通过改变某几个根性状来适应降水的改变。沿着自然降水梯度，只有当降水量改变到一定程度之后，物种的表型性状才会有适应性调整。这些结果表明，内蒙古典型草原植物根系性状对降水变化响应的敏感性较小，可以适应一定范围的降水变化。2）在增加降水实验中，羊草的根系性状对增加降水无显著响应，而增加降水使冷蒿的比根长和比表面积降低而组织密度升高。沿着自然降水梯度，羊草在降水量低的样点有较高的比根长、比表面积和根N浓度，有较低的组织密度和C：N比，而冷蒿在降水量低的样点有较高的根系直径，和较低的比根长和比表面积。此结果表明，不同的物种通过多样的根系性状调整策略来适应降水的变化。 综上所述，内蒙古温带草原植物的根系性状对降水变化的响应敏感性较小，且不同植物种通过不同的表型调整策略来适应降水的变化。本研究为理解和预测温带草原植物对未来气候变化的响应提供了重要的理论基础。 A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

• Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic and sympagic (sea-ice-associated) diatom communities. We investigated the effects of light stress (shift from 20 to 380 μmol photons m−2 s−1, resembling upwelling or ice break-up) under contemporary and future pCO₂ (400 vs 1000 μatm). • The responses in growth, elemental composition, pigmentation and photophysiology were followed over 120 h and are discussed together with underlying gene expression patterns. • Stress response and subsequent re-acclimation were efficiently facilitated by T. hyalina, which showed only moderate changes in photophysiology and elemental composition, and thrived under high light after 120 h. In N. frigida, photochemical damage and oxidative stress appeared to outweigh cellular defenses, causing dysfunctional photophysiology and reduced growth. pCO₂ alone did not specifically influence gene expression, but amplified the transcriptomic reactions to light stress, indicating that pCO₂ affects metabolic equilibria rather than sensitive genes. • Large differences in acclimation capacities towards high light and high pCO₂ between T. hyalina and N. frigida indicate species-specific mechanisms in coping with the two stressors, which may reflect their respective ecological niches. This could potentially alter the balance between sympagic and pelagic primary production in a future Arctic.

Arbuscular mycorrhizal fungi (AMF) can influence plant community composition and diversity. Previous research has shown that the addition of nutrients reduces the effectiveness of AMF. However, the ways in which soil nutrient availability and AMF interact and affect plant community productivity and ecosystem stability are still poorly understood. We examined the impact of AMF suppression and phosphorus (P) addition on plant diversity, community productivity and temporal stability (TS) in a field experiment. AMF root colonization and the concentration of an AMF‐specific phospholipid fatty acid were significantly reduced after application of the fungicide benomyl as a soil drench. The TS of the plant community was higher in communities without benomyl application compared with communities with benomyl application indicating that AMF contribute to the TS of plant communities. AMF suppression increased productivity at the plant species, functional group and community levels under high P addition rates. At the zero P addition rate, AMF did not affect plant community productivity, as the dominant species Artemisia frigida was more abundant in control plots with AMF, while the subdominant species Stipa krylovii was more abundant in the benomyl‐treated plots with reduced AMF abundance. Compensatory effects between C₃ grasses and non‐N₂‐fixing forbs were observed in the control plots with AMF along the gradient of P addition rates, but these effects were not detected among plant species in the benomyl‐treated plots under AMF suppression above an addition rate of 4.76 P₂O₅ m⁻² year⁻¹. Although AMF suppression did not influence the diversity of the plant communities, it did decrease the diversity of N₂‐fixing forbs at the zero P addition rate and above an addition rate of 18.90 g P₂O₅ m⁻² year⁻¹, indicating that AMF play key roles in the maintenance of N₂‐fixing forbs at these P addition rates. P addition led to biodiversity losses at application rates below 2.36 g P₂O₅ m⁻² year⁻¹ at the community level. Synthesis. Arbuscular mycorrhizal fungi and soil P availability interact to influence the productivity and TS of a plant community by mediating compensatory effects among plant species and functional groups.

AimsPlant stoichiometry is known to influence ecological processes and element cycles in ecosystems, which in turn can all be affected by ongoing climate change. While previous studies mainly focused on warming, drought or species invasion, effects of changing water supply on plant stoichiometry have not been well explored.MethodsTo study how water supply affects plant stoichiometry (here C:N, N:P), and whether such effects differ among plant species, a manipulative experiment was conducted in which four grass species (Leymus chinensis, Stipa grandis, Artemisia frigida and Potentilla acaulis) dominant in the Inner Mongolia steppe were subjected to a gradient of water supply via changes in growing-season rainfall.ResultsWater supply significantly impacted C:N and N:P, and these effects differed among grass species. Specifically, while C:N of A. frigida and P. acaulis was unaffected by water supply, C:N of L. chinensis and S. grandis increased with increasing precipitation. Furthermore, N:P of A. frigida showed a unimodal pattern along the imposed precipitation gradient. Whereas aboveground and belowground N:P showed similar trends (but different patterns) with changing water supply, this was not the case for aboveground and belowground C:N. As a result, plant stoichiometry between aboveground and belowground parts followed an allometric pattern.ConclusionsChanges in water supply can significantly modulate plant stoichiometry. These results could improve our understanding of the dynamics of grasslands under climate change.

Overgrazing substantially contributes to global grassland degradation by decreasing plant community productivity and diversity through trampling, defoliation, and removal of nutrients. Arbuscular mycorrhizal (AM) fungi also play a critical role in plant community diversity, composition, and primary productivity, maintaining ecosystem functions. However, interactions between grazing disturbances, such as trampling and defoliation, and AM fungi in grassland communities are not well known. We examined influences of trampling, defoliation, and AM fungi on semiarid grassland plant community composition for 3 yr, by comparing all combinations of these factors. Benomyl fungicide was applied to reduce AM fungal abundance. Overgrazing typically resulted in reduced dominance of Stipa Krylovii, contributing to degradation of typical steppe grasslands. Our results indicated trampling generally had little effect on plant community composition, unless combined with defoliation or AM fungal suppression. Defoliation was the main component of grazing that promoted dominance of Potentilla acaulis over Stipa krylovii and Artemisia frigida, presumably by alleviating light limitation. In non-defoliated plots, AM fungi promoted A. frigida, with a concomitant reduction in S. krylovii growth compared to corresponding AM suppressed plots. Our results indicate AM fungi and defoliation jointly suppress S. krylovii biomass; however, prolonged defoliation weakens mycorrhizal influence on plant community composition. These findings give new insight into dominant plant species shifts in degraded semiarid grasslands.

Arbuscular mycorrhizal (AM) fungi are important components of grassland ecosystems and are sensitive to enhanced atmospheric nitrogen (N) deposition. Enhanced N deposition has been widely reported to reduce species richness and alter species composition across different types of grasslands world‐wide. Despite extensive studies on effects of N deposition on AM fungal communities of grasslands, few studies have specifically focused on effects of N deposition on AM fungi associated with dominant species in grasslands. We investigated long‐term (12‐year) effects of N addition (80 kg ha−1 year−1) on AM fungal community richness in roots and rhizosphere biomass of two dominant plant species (forb Artemisia frigida and grass Stipa krylovii) in temperate steppes of northern China. We found that AM fungi associated with the two dominant plant species differed in their responses to N addition. Nitrogen addition led to a significant reduction in AM fungal richness colonized in roots, and biomass in the rhizosphere of A. frigida, while N addition had little impacts on AM fungi colonized in roots and rhizosphere of S. krylovii. Nitrogen addition significantly reduced AM fungal colonization in roots and AM fungal spore density in the rhizosphere soils of A. frigida. In contrast, N addition had no effect on AM fungal colonization in roots and spore density in the rhizosphere of S. krylovii. Nitrogen addition markedly suppressed photosynthetic rates in A. frigida due to excessive foliar accumulation of manganese. The N‐induced reduction in photosynthetic rates reduced allocation of C into roots in A. frigida, leading to a lower root/shoot ratio, and suppression of AM fungal community associated with A. frigida. The inhibition of AM fungi would render A. frigida less competitive in terms of acquisition of mineral nutrients in soils, thus contributing to its loss in the steppe community under conditions of elevated N deposition. These findings provide a mechanistic explanation for N‐evoked differential responses of AM fungal communities associated with A. frigida and S. krylovii by linking soil properties and host plants to AM fungal communities. A plain language summary is available for this article. Plain Language Summary

We aimed to explore the mineralization characteristics of soil organic carbon(SOC) under different plant species in semi-arid grassland and provide basic soil carbon cycling data. Leymus chinensis , Stipa krylovii Roshev, Artemisia frigida , and Agrophorn cristam (L.) Gaertn were selected as the plant species. Incubation experiment were conducted on SOC mineralization in soil aggregates with particle sizes of > 2, 1–2, 0.25–1, and < 0.25 mm. The cumulative SOC mineralization amount in L. chinensis with a particle size > 2 mm was the highest, exceeding that of A. cristam (L.) Gaertn by approximately 136.14%. S. krylovii Roshev (70.73%), L. chinensis (58.05%), and A. frigida (33.73%) exhibited pronounced promotion effects on mineralization. The potential SOC mineralization of S. krylovii Roshev was the greatest among all species at the same soil particle size. The potential SOC mineralization was highest at a particle size of > 2 mm for all plant types. All plant types increased the SOC mineralization rate and cumulative mineralization in soils with large particle sizes, the mineralization reaction occurred more strongly. Organic carbon cumulative SOC mineralization rapidly increased in all tests during the first 20 days and gradually slowed thereafter.