Relative Abundance Of C4 Plants Research Articles

Increasing relative abundance of C4 plants mitigates a dryness-stress effect on gross primary productivity along an aridity gradient in grassland ecosystems

Increasing relative abundance of C4 plants mitigates a dryness-stress effect on gross primary productivity along an aridity gradient in grassland ecosystems

Speculation for quantifying increased C4 plants under future climate conditions: Inner Mongolia, China case study

Alternating conditions from cold to warm periods since the Late Glacial provided a significant contrast for future hydroclimatic variation, as did the corresponding variation in vegetation. To predict the potential variability in C3/C4 biomass under future warmer climatic conditions, we determined the current spatiotemporal distribution of C3 and C4 vegetation by estimating the variability of δ13Corg values in 125 topsoil samples and investigating the geological period variability of C4 plants growing in Inner Mongolia, China. We examined the factors contributing to the growth of C4 plants and the variability in C4 plants for each 1 °C increase in temperature during recent and geological times. The results revealed that the relative abundance of C4 plants in Inner Mongolia shows an increasing trend from the northwest to the southeast. The biomass of C4 plants was found to be positively correlated with temperature, although weakly correlated with precipitation, thereby indicating that temperature is the primary climatic factor determining the growth of C4 plants in this region. Furthermore, we found that in response to each 1 °C increase in temperature, there would be an approximate 2.1% increase in the spatiotemporal variation of present-day C4 plant biomass in Inner Mongolia, whereas during the geological period, there was a corresponding increase of 10.7%. Comparatively, the spatiotemporal variation in present-day C4 biomass on the Chinese Loess Plateau has undergone a 4.0% increase in response to each 1 °C increase in temperature, whereas 6.0% and 7.5% increases in the geological period were estimated based on core samples taken from the Lantian and Xingyang sections, respectively. Interestingly, for each 1 °C increase in temperature during the current growth month of C4 plants, there is a 6.6% increase in C4 biomass, which is essentially consistent with the results obtained for the geological period results (i.e., 6.0% and 7.5% for the Lantian and Xingyang sections, respectively). The findings of this study reveal a distinct contrast in the variation of C4 plants during recent and geological periods, thereby enabling us to quantitatively estimate the potential changes in C4 vegetation in response to projected climate conditions.

Variability and environmental significance of organic carbon isotopes in Ganzi loess since the last interglacial on the eastern Tibetan Plateau

The stable carbon isotope composition of total organic matter (δ13Corg) in loess deposits has been widely used as a valuable proxy for reconstructing terrestrial paleovegetation. Aeolian loess is widely distributed on the high Tibetan Plateau (TP); however, little is known about the variability and paleoenvironmental implications of the δ13Corg of Tibetan loess. We conducted detailed δ13Corg and total organic carbon analyses of the Ganzi loess sequence on the eastern TP since the last interglacial (LIG). Our results indicate that the δ13Corg values of loess during glacial periods were lower than those during interglacial periods, with more negative values associated with the cold stages since the LIG on the eastern TP. The reconstruction of vegetation from the δ13Corg data indicated that C3/C4 mixed vegetation was dominated by C3 vegetation, and that the relative abundance of C4 vegetation during the glacial stages was much lower than that during MIS 5 and MIS 3. The high relative abundance of C4 plants during MIS 5 and MIS 3 suggested an increased proportion of C4 plants during the warm period. Since the LIG, the change in the abundance of C3/C4 vegetation in the Ganzi region has been mainly controlled by climate change at the glacial–interglacial scale. The combined effect of temperature, precipitation, and atmospheric CO2 caused changes in the paleovegetation on the eastern TP.

Evolution of the relative abundance of C4 plants on the Chinese Loess Plateau since the Last Glacial Maximum and its implications

ABSTRACTUnderstanding the distribution of C3 and C4 plants and its forcing mechanisms since the Last Glacial Maximum (LGM) is important for anticipating their possible response to future climate change. The spatiotemporal pattern of C4 plant abundance on the Chinese Loess Plateau (CLP) is complex and the dominant causal factors are contentious. Here, we use δ13C records of organic matter in paleosols from the CLP to reconstruct changes in the representation of C4 plants since the LGM. The results indicate that the relative abundance of C4 plants increased after the LGM, reaching a maximum during 10–6 ka bp, and then decreased. Spatially, the representation of C4 plants was characterized by increasing values from north‐west to south‐east. In addition, the smallest spatial difference (∼10%) in the representation of C4 plants between the north‐west and south‐east parts of the CLP was during the LGM, and the largest difference (∼30%) was during the early Holocene. We combined our findings with output from the BIOME4 model to study the sensitivity of C4 plants to changes in climate and atmospheric CO2 concentration. The results suggest that increasing temperature was the dominant factor driving C4 plant expansion on the CLP since the LGM.

Factors affecting 13C enrichment of vegetation and soil in temperate grasslands in Inner Mongolia, China

Soil organic carbon (SOC) dynamics are central to understanding the effects of environmental change on the carbon cycle of ecosystems. Vegetation and soil stable carbon isotope composition (δ13C), especially the difference of δ13C between surface soils and source vegetation (Δδ13C), can provide useful information about the SOC dynamics. The variations and patterns of vegetation and soil δ13C and Δδ13C along climatic and edaphic gradients were analyzed to improve the understanding of SOC dynamics in temperate grassland ecosystems. Soil and plant samples were collected along climatic and edaphic gradients. Meteorological data were extracted from a regional climate database, which was spatially interpolated based on the records at 107 climatic stations located in Inner Mongolia. δ13C, carbon and nitrogen contents of soil and plant, soil pH, soil clay, silt, and sand contents were determined. Δδ13C and soil C:N were calculated. The integrative effects of these factors were further estimated using stepwise regression, redundancy analysis (RDA) and T value biplots. As expected, soil δ13C was positively related to vegetation δ13C, and higher than the vegetation δ13C. Vegetation and soil δ13C and Δδ13C were all related to growing season precipitation (GSP) and growing season temperature (GST). However, when climatic and edaphic factors were considered together, vegetation δ13C was positively related to GST and soil C:N, soil δ13C was positively related only to GST, and Δδ13C was negatively related only to soil C:N. Unlike previous research conducted at the species level which only included C3 species, GST, instead of precipitation, was the dominant controlling factor of vegetation δ13C. GST influences vegetation δ13C mainly through its effect on relative abundance of C4 plants. Soil C:N rather than climatic factors is the dominant controlling factor of SOC decomposition, and the effects of climatic factors on SOC decomposition are indirect and induced by their effects on soil C:N through influencing species composition and plant C:N. Measuring vegetation δ13C, soil δ13C, and △δ13C simultaneously is necessary to comprehensively understand how environmental changes influence ecosystem carbon cycles.

Distribution of C4 plants in sand habitats of different climatic regions

Sand dunes of warm regions provide suitable habitats for C4 plants because of their water and nitrogen use efficiency under high temperature and their high tolerance to ecological stress such as salinity, aridity and disturbance. We studied the distribution patterns of C4 plant species in five habitat types of sand dune ecosystems in three climatic regions (Mediterranean, Irano-Turanian and Hyrcanian). We compared the relative abundance of C4 plants in terms of richness and cover and aimed at identifying their habitat preferences in sand ecosystems. Our results revealed that C4 species notably contribute to the vegetation cover, despite their rather low contribution to the richness in comparison with C3 species. Generally, C4 plants were more prominent in mobile dunes, saltmarshes and disturbed sandy ground, but they showed regional differences in habitat preference. In northern and central Iran, C4 plants had the highest relative abundance in mobile dunes whereas in northeastern Greece they dominated disturbed sandy ground. The abundance of C4 plants appears to be influenced by climatic conditions. Central Iran, the driest and warmest among our study regions, has the highest proportion of C4 species in terms of number and cover. We observed an increasing trend in richness and cover of C4 plants with increasing aridity. As the number of C4 species alone may not fully reflect their role in a given area, the C4 plant total vegetation cover is shown to be an additional important parameter in ecological studies.

Tropical and high latitude forcing of enhanced megadroughts in Northern China during the last four terminations

Understanding the origin and evolutionary history of drought events is of great significance, providing critical insight into future hydrological conditions under the changing climate. Due to the scarcity of drought proxies from northern China, the occurrence and underlying mechanisms of the drought events remains enigmatic on longer timescales. Here we utilize microbial lipid proxies to reconstruct significant drought events over the last four ice age terminations in the southernmost section (Weinan section) of the Chinese Loess Plateau. The abundance of archaeal isoprenoid GDGTs (glycerol dialkyl glycerol tetraethers) relative to bacterial branched GDGTs, measured by Ri/b and BIT indices, is diagnostic of enhanced drought conditions. The Ri/b (and BIT) indices are stable and low (high) throughout most of the loess section spanning the last 350 thousand years, but they do exhibit sharp transient peaks (valleys) during the intervals associated with the four ice age terminations, and especially Terminations II and IV. These enhanced drought events are, non-intuitively, associated with a significant decrease in the relative abundance of C4 plants, inferred by a decrease in the carbon isotope composition of bulk organic matter. Although the microbial records show some consistency with the Weinan grain size profiles, indicative of Eastern Asian winter monsoon variability, they also show some apparent difference. In fact, some features of the microbial records exhibit strong similarities with marine sediment planktonic foraminiferal δ13C records from the western Pacific warm pool, which reflect ENSO-like changes during glacial terminations. Therefore, enhanced droughts immediately before the interglacial warming in northern China could be explained, at least in part, by teleconnections in tropical ocean–atmosphere circulation via shifts in the Intertropical Convergence Zone (ITCZ) and associated Jet Stream over the Asian continent. According to our microbial biomarker data, these enhanced megadroughts are apparently different, both in terms of severity and causal mechanism, from the more commonly discussed dry conditions observed during glacial periods.

Urban warming favours C4 plants in temperate European cities

Summary Elucidating the mechanisms responsible for the structure of urban communities is a key aim of urban ecology, but one that is often confounded by the multitude of environmental changes that are caused by urbanization. We applied trait‐based techniques to identify the specific environmental drivers that shape urban plant assemblages and predict how these drivers will further impact biotas with increasing urbanization and global environmental change. Urbanized areas across temperate Europe have significantly higher abundance and richness of plants using the C4 photosynthetic pathway, relative to the total number and species richness of all plant records, than non‐urban areas. Urban warming, mediated by the contrasting physiological responses of C3 and C4 plants to warming, is the main driver of observed patterns of plant assemblage structure. This mirrors broadscale and historical distribution patterns of C3 and C4 plants. The increased relative abundance of C4 plants in cities demonstrated here may be indicative of more geographically widespread assemblage changes to be expected in temperate environments under continuing global climate change. Synthesis. Applying a combined trait‐based, ecoinformatic and remote‐sensing approach provides new insight into the landscape‐level consequences of urbanization. Specifically, we show that localized urban warming in cities across temperate Europe favours C4 plant species, which respond positively to increased temperatures. Urban plant assemblages are shaped by environmental warming and exhibit significant increases in C4 plant relative abundance compared to non‐urban assemblages.

Grazing primarily drives the relative abundance change of C4 plants in the typical steppe grasslands across households at a regional scale

Increases in temperature and grazing intensity are believed to promote the relative abundance of C4 plants in grassland communities in Inner Mongolia. However, there is a lack of understanding as to which factor is the primary driver at the household scale. The relative abundance of C4 plants in grassland communities within 32 households was monitored over a 5-year period (2008–12) in the typical steppe region of Inner Mongolia. The relationships between the mean annual temperature, grazing intensity and their combinations on the patterns of the relative abundance of C4 plants across the land managed by these households were analysed. The results showed that (1) the herbage mass of the typical steppe grassland was mainly composed of C3 plants (87%); (2) the C4 plants were more sensitive to, and can be used as indicators of, environmental changes. These C4 species included Cleistogenes squarrosa (Trin.) Keng, Chenopodium glaucum Linn. and Salsola collina Pall.; (3) both increasing temperature and grazing intensity promoted the relative abundance of C4 plants. Grazing intensity was the primary driver of the change in relative abundance of C4 plants in this region. Not only did grazing change the micro-environment of the grasslands, but also the C3 species were preferentially grazed by the livestock. Comparison of the results with previous studies on the temporal variation in the abundance of C4 plants suggests that the relative importance of grazing and climatic factors depends on the spatial scales of the studies, with climate being of greater importance at the regional rather than the household scale.

C4 abundance in an Inner Mongolia grassland system is driven by temperature–moisture interaction, not grazing pressure

Global warming and CO2 rise is expected to change the balance of C3 and C4 plants in grassland vegetation, but disturbance, including grazing, could also affect C3/C4 community structure. We used a six-year (2005–2010) grazing experiment to test the prediction that the relative abundance of C4 plants (PC4) in the semi-arid grassland of Inner Mongolia is related to growing-period temperature and disturbance by grazing. Paddocks were stocked with sheep at six rates (0.375–2.25sheepha−1a−1) between June and September. PC4 was estimated from the relative 13C/12C composition (δ13C) of wool grown during the grazing period of each year and a two-member mixing model of the δ13C of the C3 and C4 communities in the paddocks. Stocking rate had a slight effect (<0.5‰) on the δ13C of the C3 and the C4 end-members. Annual average PC4 varied between 5% and 24%. Stocking rate had no significant effect on PC4 but the growing-season temperature had a large effect, and PC4 increased with temperature. Importantly, the growing season shifted between years due to changing seasonal distribution of rainfall and soil moisture availability from winter precipitation causing large variation in temperature of the effective growing season. Changes in temperature and in amount and seasonal distribution of rainfall as a consequence of inter-annual fluctuations and long-term change can thus have a large impact on the C4 abundance and its spatial pattern.

Climate as the dominant control on C3 and C4 plant abundance in the Loess Plateau: Organic carbon isotope evidence from the last glacial-interglacial loess-soil sequences

Abundance of C3 and C4 photosynthesis plants can be inferred relatively from stable carbon isotopic composition of organic matter in soils. The samples from five sequences of the last glacialinterglacial loesssoil in the Chinese Loess Plateau have been measured for organic carbon isotopic ratios (δ13 Corg). The organic carbon isotope data show that relative abundance (or biomass) of C4 plants was increased ca. 40% for each sampling site from the last glacial maximum (LGM) to Holocene optimum, and increased southeastward on the Loess Plateau during both periods of LGM and Holocene. Statistic analyses on the steady maximum δ13 Corg values of Holocene soils and modern climatic data from the Loess Plateau and Inner Mongolia indicate that the C4 plant abundance increases with increasing temperature and decreasing precipitation. The C4 plant abundance is related much closer with mean April temperature and precipitation than annual. These results lead us to deduce following conclusions. First, temperature is the major factor for control on variations in C4 plant abundance in the Loess Plateau from the last glacial to interglacial. In the absence of favorable temperature condition, both of low moisture and low atmospheric CO2 concentration are insufficient to drive an expansion of the C4 plants in the plateau. Second, δ13 Corg in the loess-paleosol sequences, as a proxy of the relative abundance of C4 plants in the Loess Plateau, could not be used as an indicator of changes in the summer monsoon intensity unless the temperature had changed without great amplitude. Since all C4 plants are grasses, finally, the increase of the C4 plants supports that forest has not been dominant in the ecosystem on the Loess Plateau during Holocene although precipitation and atmospheric CO2 were largely increased relative to those during LGM.