Interactive Effects of Elevated CO2, Drought, and Warming on Plants

Adverse climate change attributed to elevated atmospheric carbon dioxide concentration (CO₂) and increased temperature components of global warming has been a central issue affecting economic and social development. Climate change, particularly global warming, imposes a severe impact on the terrestrial ecosystem. Elevated CO₂, drought, and high temperature have been extensively documented individually; however, relatively little is known about how plants respond to the interaction of these factors. To summarize current knowledge on the response of plants to global change factors, we focus on the interactive effects of CO₂ enrichment, warming, and drought on plant growth, carbon allocation, and photosynthesis. Stimulation due to elevated CO₂ might be suppressed under other negative climatic/environmental stresses such as drought, high temperature, and their combination. However, elevated CO₂ could alleviate deleterious effects of moderate drought via reducing stomatal conductance, altering leaf surface, and regulating gene expression. High CO₂ levels and rising temperatures may result in opposite responses in plant water use efficiency. Stimulation of plant growth due to elevated CO₂ for C₃ species occurs regardless of water conditions, but only under a water deficit for C₄ species. The positive effect of elevated CO₂ on C₄ species is derived mainly from the improved water status. Plant adaptive or maladaptive responses to multivariate environments are interactive; thus, researchers need to explore the ecological underpinnings involved in such responses to the multiple factors involved in climate change.     

Controls over Soil Nitrogen Pools in a Semiarid Grassland Under Elevated CO2 and Warming

Long-term responses of terrestrial ecosystems to the combined effects of warming and elevated CO₂ (eCO₂) will likely be regulated by N availability. The stock of soil N determines availability for organisms, but also influences loss to the atmosphere or groundwater. eCO₂ and warming can elicit changes in soil N via direct effects on microbial and plant activity, or indirectly, via soil moisture. Detangling the interplay of direct- and moisture-mediated impacts on soil N and the role of organisms in controlling soil N will improve predictions of ecosystem-level responses. We followed individual soil N pools over two growing seasons in a semiarid temperate grassland, at the Prairie Heating and CO₂ Enrichment experiment. We evaluated relationships of N pools with environmental factors and explored the role of plants by assessing plant biomass, plant N, and plant inputs to soil. We also assessed N forms in plots with and without vegetation to remove plant-mediated effects. Our study demonstrated that the effects of warming and eCO₂ are highly dependent on individual N form and on year. In this water-constrained grassland, eCO₂, warming and their combination appear to impact soil N pools through a complex combination of direct- and moisture-mediated effects. eCO₂ decreased NO₃ ^? but had neutral to positive effects on NH₄ ⁺ and dissolved organic N (DON), particularly in a wet year. Warming increased NO₃ ^? availability due to a combination of indirect drying and direct temperature-driven effects. Warming also increased DON only in vegetated plots, suggesting plant mediation. Our results suggest that impacts of combined eCO₂ and warming are not always equivalent for plant and soil pools; although warming can help offset the decrease in NO₃ ^? availability for plants under eCO₂, the NO₃ ^? pool in soil is mainly driven by the negative effects of eCO₂.     

Shallow Water Marine Sediment Bacterial Community Shifts Along a Natural CO2 Gradient in the Mediterranean Sea Off Vulcano,Italy

The effects of increasing atmospheric CO₂ on ocean ecosystems are a major environmental concern, as rapid shoaling of the carbonate saturation horizon is exposing vast areas of marine sediments to corrosive waters worldwide. Natural CO₂ gradients off Vulcano, Italy, have revealed profound ecosystem changes along rocky shore habitats as carbonate saturation levels decrease, but no investigations have yet been made of the sedimentary habitat. Here, we sampled the upper 2 cm of volcanic sand in three zones, ambient (median pCO₂ 419 μatm, minimum Ω_arag 3.77), moderately CO₂-enriched (median pCO₂ 592 μatm, minimum Ω_arag 2.96), and highly CO₂-enriched (median pCO₂ 1611 μatm, minimum Ω_arag 0.35). We tested the hypothesis that increasing levels of seawater pCO₂ would cause significant shifts in sediment bacterial community composition, as shown recently in epilithic biofilms at the study site. In this study, 454 pyrosequencing of the V1 to V3 region of the 16S rRNA gene revealed a shift in community composition with increasing pCO₂. The relative abundances of most of the dominant genera were unaffected by the pCO₂ gradient, although there were significant differences for some 5 % of the genera present (viz. Georgenia, Lutibacter, Photobacterium, Acinetobacter, and Paenibacillus), and Shannon Diversity was greatest in sediments subject to long-term acidification (>100 years). Overall, this supports the view that globally increased ocean pCO₂ will be associated with changes in sediment bacterial community composition but that most of these organisms are resilient. However, further work is required to assess whether these results apply to other types of coastal sediments and whether the changes in relative abundance of bacterial taxa that we observed can significantly alter the biogeochemical functions of marine sediments.     

Overstory Community Composition and Elevated Atmospheric CO2 and O3 Modify Understory Biomass Production and Nitrogen Acquisition

Elevated atmospheric CO₂ and O₃ have the potential to affect the primary productivity of the forest overstory, but little attention has been given to potential responses of understory vegetation. Our objective was to document the effects of elevated atmospheric CO₂ and O₃ on understory species composition and biomass and to quantify nitrogen (N) acquisition by the understory vegetation. The research took place at the aspen free-air CO₂ and O₃ enrichment (FACE) experiment, which has four treatments (control, elevated CO₂, elevated O₃, and elevated CO₂+O₃) and three tree communities: aspen, aspen/birch, and aspen/maple. In June 2003, each FACE ring was uniformly labeled with 15N applied as NH₄Cl. Understory biomass was harvested in June of 2004 for productivity, N, and 15N measurements, and photosynthetically active radiation (PAR) was measured below the canopy. The understory was divided into five species groups, which dominate in this young aggrading forest: Taraxacum officinale (dandelion), Solidago sp. (goldenrod), Trifolium repens and T. pretense (clover), various species from the Poaceae family (grass), and composited minor components (CMC). Understory species composition, total and individual species biomass, N content, and 15N recovery showed overstory community effects, but the direct effects of treatments was masked by the high variability of these data. Total understory biomass increased with increasing light, and thus was greatest under the open canopy of the aspen/maple community, as well as the more open canopy of the elevated O₃ treatments. Species were different from one another in terms of 15N recovery, with virtually no 15N recovered in clover and the greatest amount recovered in dandelion. Thus, understory species composition and biomass appear to be driven by the structure of the overstory community, which is determined by the tree species present and their response to the treatments. However, N acquisition by the understory does not appear to be affected by either the overstory community or the treatments at this point.     

Warming and Elevated CO<Subscript>2</Subscript> Interact to Alter Seasonality and Reduce Variability of Soil Water in a Semiarid Grassland

Global changes that alter soil water availability may have profound effects on semiarid ecosystems. Although both elevated CO₂ (eCO₂) and warming can alter water availability, often in opposite ways, few studies have measured their combined influence on the amount, timing, and temporal variability of soil water. Here, we ask how free air CO₂ enrichment (to 600 ppmv) and infrared warming (+?1.5 °C day, +?3 °C night) effects on soil water vary within years and across wet-dry periods in North American mixed-grass prairie. We found that eCO₂ and warming interacted to influence soil water and that those interactions varied by season. In the spring, negative effects of warming on soil water largely offset positive effects of eCO₂. As the growing season progressed, however, warming reduced soil water primarily (summer) or only (autumn) in plots treated with eCO₂. These interactions constrained the combined effect of eCO₂ and warming on soil water, which ranged from neutral in spring to positive in autumn. Within seasons, eCO₂ increased soil water under drier conditions, and warming decreased soil water under wetter conditions. By increasing soil water under dry conditions, eCO₂ also reduced temporal variability in soil water. These temporal patterns explain previously observed plant responses, including reduced leaf area with warming in summer, and delayed senescence with eCO₂ plus warming in autumn. They also suggest that eCO₂ and warming may favor plant species that grow in autumn, including winter annuals and C₃ graminoids, and species able to remain active under the dry conditions moderated by eCO₂.     

Elevated Temperature and Drought Interact to Reduce Parasitoid Effectiveness in Suppressing Hosts

Climate change affects the abundance, distribution and activity of natural enemies that are important for suppressing herbivore crop pests. Moreover, higher mean temperatures and increased frequency of climatic extremes are expected to induce different responses across trophic levels, potentially disrupting predator-prey interactions. Using field observations, we examined the response of an aphid host-parasitoid system to variation in temperature. Temperature was positively associated with attack rates by parasitoids, but also with a non-significant trend towards increased attack rates by higher-level hyperparasitoids. Elevated hyperparasitism could partly offset any benefit of climate warming to parasitoids, and would suggest that higher trophic levels may hamper predictions of predator-prey interactions. Additionally, the mechanisms affecting host-parasitoid dynamics were examined using controlled laboratory experiments that simulated both temperature increase and drought. Parasitoid fitness and longevity responded differently when exposed to each climatic variable in isolation, compared to the interaction of both variables at once. Although temperature increase or drought tended to positively affect the ability of parasitoids to control aphid populations, these effects were significantly reversed when the drivers were expressed in concert. Additionally, separate warming and drought treatments reduced parasitoid longevity, and although temperature increased parasitoid emergence success and drought increased offspring production, combined temperature and drought produced the lowest parasitoid emergence. The non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggest that predicting future pest outbreaks will be more challenging than previously imagined.     

Ectomycorrhizal Colonization, Biomass, and Production in a Regenerating Scrub Oak Forest in Response to Elevated CO2

The effects of CO₂ elevation on the dynamics of fine root (FR) mass and ectomycorrhizal (EM) mass and colonization were studied in situ in a Florida scrub oak system over four years of postfire regeneration. Soil cores were taken at five dates and sorted to assess the standing crop of ectomycorrhizal and fine roots. We used ingrowth bags to estimate the effects of elevated CO₂ on production of EM roots and fine roots. Elevated CO₂ tended to increase EM colonization frequency but did not affect EM mass nor FR mass in soil cores (standing mass). However, elevated CO₂ strongly increased EM mass and FR mass in ingrowth bags (production), but it did not affect the EM colonization frequency therein. An increase in belowground production with unchanged biomass indicates that elevated CO₂ may stimulate root turnover. The CO₂-stimulated increase of belowground production was initially larger than that of aboveground production. The oaks may allocate a larger portion of resources to root/mycorrhizal production in this system in elevated rather than ambient CO₂.     

Ponderosa Pine Responses to Elevated CO2and Nitrogen Fertilization

The effects of elevated CO₂ (ambient, +175, and +350 μl l⁻¹) and nitrogen fertilization (0, 100, and 200 kg N ha⁻¹ yr⁻¹ as ammonium sulfate) on C and N accumulations in biomass and soils planted with ponderosa pine (Pinus ponderosa Laws) over a 6-year study period are reported. Both nitrogen fertilization and elevated CO₂ caused increases in C and N contents of vegetation over the study period. The pattern of responses varied over time. Responses to CO₂ decreased in the +175 μl l⁻¹ and increased in the +350 μl l⁻¹ after the first year, whereas responses to N decreased after the first year and became non-significant by year six. Foliar N concentrations were lower and tree C:N ratios were higher with elevated CO₂ in the early years, but this was offset by the increases in biomass, resulting in substantial increases in N uptake with elevated CO₂. Nitrogen budget estimates showed that the major source of the N for unfertilized trees, with or without elevated CO₂, was likely the soil organic N pool. There were no effects of elevated CO₂ on soil C, but a significant decrease in soil N and an increase in soil C:N ratio in year six. Nitrogen fertilization had no significant effect on tree C:N ratios, foliar N concentrations, soil C content, soil N content, or soil C:N ratios. There were no significant interactions between CO₂ and N treatments, indicating that N fertilization had no effect on responses to CO₂ and that CO₂ treatments had no effect on responses to N fertilization. These results illustrate the importance of long-term studies involving more than one level of treatment to assess the effects of elevated CO₂.     

Responses of Rice Cultivars to the Elevated CO2

The effect of CO₂ concentration elevated to 575 – 620 µmol mol^–1 on growth, tillering, grain yield, net photosynthetic rate, dark respiration rate, stomatal conductance, sugar content and protein profile of two rice (Oryza sativa L.) cultivars Pusa Basmati-1 and Pusa-677 at flowering stage was studied using open top chambers. The cultivar Pusa Basmati-1 responded more markedly for most of the growth and physiological parameters compared to Pusa-677. The increase in grain yield in Pusa Basmati-1 attributed largely to increased grain number. The increased net photosynthetic rate and greater accumulation of sugar contributed significantly to the accelerated development of leaves and tillers in both the cultivars. The reduction in the low molecular mass proteins including Rubisco and increase in high molecular mass photosystem 2 proteins was observed in both the cultivars. Additional sugars may possibly help in balancing the profile of photosynthetic proteins and sustain greater growth and productivity in rice cultivars.     

Nematode Genera in Forest Soil Respond Differentially to Elevated CO2

Previous reports suggest that fungivorous nematodes are the only trophic group in forest soils affected by elevated CO₂. However, there can be ambiguity within trophic groups, and we examined data at a genus level to determine whether the conclusion remains similar. Nematodes were extracted from roots and soil of loblolly pine (Pinus taeda) and sweet gum (Liquidambar styraciflua) forests fumigated with either ambient air or CO₂-enriched air. Root length and nematode biomass were estimated using video image analysis. Most common genera included Acrobeloides, Aphelenchoides, Cephalobus, Ditylenchus, Ecphyadorphora, Filenchus, Plectus, Prismatolaimus, and Tylencholaimus. Maturity Index values and diversity increased with elevated CO₂ in loblolly pine but decreased with elevated CO₂ in sweet gum forests. Elevated CO₂ treatment affected the occurrence of more nematode genera in sweet gum than loblolly pine forests. Numbers were similar but size of Xiphinema decreased in elevated CO₂. Abundance, but not biomass, of Aphelenchoides was reduced by elevated CO₂. Treatment effects were apparent at the genus levels that were masked at the trophic level. For example, bacterivores were unaffected by elevated CO₂, but abundance of Cephalobus was affected by CO₂ treatment in both forests.     

Elevated CO2 affects plant responses to variation in boron availability

Aim

Effects of elevated CO₂ on N relations are well studied, but effects on other nutrients, especially micronutrients, are not. We investigated effects of elevated CO₂ on response to variation in boron (B) availability in three unrelated species: seed geranium (Pelargonium x hortorum), barley (Hordeum vulgare), and water fern (Azolla caroliniana).

Methods

Plants were grown at two levels of CO₂ (370, 700?ppm) and low, medium, and high B. Treatment effects were measured on biomass, net photosynthesis (P_n) and related variables, tissue nutrient concentrations, and B transporter protein BOR1.

Results

In geranium, there were interactive effects (P?<?0.05) of B and CO₂ on leaf, stem, and total plant mass, root:shoot ratio, leaf [B], B uptake rate, root [Zn], and P_n. Elevated CO₂ stimulated growth at 45?μM B, but decreased it at 450?μM B and did not affect it at 4.5?μM B. P_n was stimulated by elevated CO₂ only at 45?μM B and chlorophyll was enhanced only at 450?μM B. Soluble sugars increased with high CO₂ only at 4.5 and 45?μM B. High CO₂ decreased leaf [B] and B uptake rate, especially at 450?μM B. Though CO₂ and B individually affected the concentration of several other nutrients, B x CO₂ interactions were evident only for Zn in roots, wherein [Zn] decreased under elevated CO₂. Interactive effects of B and CO₂ on growth were confirmed in (1) barley grown at 0, 30, or 1,000?μM B, wherein growth at high CO₂ was stimulated more at 30?μM B, and (2) Azolla grown at 0, 10, and 1,000?μM B, wherein growth at high CO₂ was stimulated at 0 and 10?μM B.

Conclusion

Thus, low and high B both may limit growth stimulation under elevated vs. current [CO₂], and B deficiency and toxicity, already common, may increase in the future.     

Effects of Warming, Summer Drought, and CO2 Enrichment on Aboveground Biomass Production, Flowering Phenology, and Community Structure in an Upland Grassland Ecosystem

Future climate scenarios predict simultaneous changes in environmental conditions, but the impacts of multiple climate change drivers on ecosystem structure and function remain unclear. We used a novel experimental approach to examine the responses of an upland grassland ecosystem to the 2080 climate scenario predicted for the study area (3.5°C temperature increase, 20% reduction in summer precipitation, atmospheric CO₂ levels of 600 ppm) over three growing seasons. We also assessed whether patterns of grassland response to a combination of climate change treatments could be forecast by ecosystem responses to single climate change drivers. Effects of climate change on aboveground production showed considerable seasonal and interannual variation; April biomass increased in response to both warming and the simultaneous application of warming, summer drought, and CO₂ enrichment, whereas October biomass responses were either non-significant or negative depending on the year. Negative impacts of summer drought on production were only observed in combination with a below-average rainfall regime, and showed lagged effects on spring biomass. Elevated CO₂ had no significant effect on aboveground biomass during this study. Both warming and the 2080 climate change scenario were associated with a significant advance in flowering time for the dominant grass species studied. However, flowering phenology showed no significant response to either summer drought or elevated CO₂. Species diversity and equitability showed no response to climate change treatments throughout this study. Overall, our data suggest that single-factor warming experiments may provide valuable information for projections of future ecosystem changes in cool temperate grasslands.     

植物对大气CO2浓度升高的光合适应机理

光合作用对大气中CO2浓度升高适应的可能原因主要表现在以下几个方面:由于CO2浓度升高,碳水化合物过量积累,光合电子传递链中质体醌与过氧化氢(H2O2)的氧化还原信号对光合作用发生反馈抑制;核酮糖1,5-二磷酸羧化/加氧酶(Rubisco)的含量及其活性下降;气孔状态发生变化.此外,植物体内C/N平衡、生长调节物质和己糖激酶对光合基因表达水平的调控等多个方面会对光合适应产生影响.     

植物对大气CO2 浓度升高的光合适应机理

光合作用对大气中CO2浓度升高适应的可能原因主要表现在以下几个方面: 由于CO2浓度升高,碳水化合物过量积累, 光合电子传递链中质体醌与过氧化氢(H2O2)的氧化还原信号对光合作用发生反馈抑制; 核酮糖1,5-二磷酸羧化/加氧酶(Rubisco)的含量及其活性下降; 气孔状态发生变化。此外, 植物体内C/N平衡、生长调节物质和己糖激酶对光合基因表达水平的调控等多个方面会对光合适应产生影响。     

Responses of Plant Community Composition and Biomass Production to Warming and Nitrogen Deposition in a Temperate Meadow Ecosystem

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China.