Source and Accumulation of Soil Carbon along Catena Toposequences over 12,000 Years in Three Semi-Natural Miscanthus sinensis Grasslands in Japan

Miscanthus-dominated semi-natural grasslands in Japan appear to store considerable amounts of soil C. To estimate the long-term effect of Miscanthus vegetation on the accumulation of soil carbon by soil biota degradation in its native range, we measured total soil C from the surface to a 1.2 m depth along a catena toposequence in three annually burned grasslands in Japan: Kawatabi, Soni, and Aso. Soil C stock was estimated using a radiocarbon age and depth model, resulting in a net soil C accumulation rate in the soil. C4-plant contribution to soil C accumulation was further estimated by δ13C of soil C. The range of total soil C varied among the sites (i.e., Kawatabi: 379–638 Mg, Soni: 249–484, and Aso: 372–408 Mg C ha−1). Catena position was a significant factor at Kawatabi and Soni, where the toe slope soil C accumulation exceeded that of the summit. The soil C accumulation rate of the whole horizon in the grasslands, derived C mainly from C4 plant species, was 0.05 ± 0.02 (Average ± SE), 0.04 ± 0.00, and 0.24 ± 0.04 Mg C ha−1 yr−1 in Kawatabi, Soni, and Aso, respectively. Potential exists for long-term sequestration of C under M. sinensis, but the difference in the C accumulation rate can be influenced by the catena position and the amount of vegetation.

Continuous Maize Cropping Accelerates Loss of Soil Organic Matter in Northern Thailand as Revealed by Natural 13C Abundance

AimsThe loss of soil organic matter (SOM) has widely been reported in the tropics after changing land use from shifting cultivation to continuous cropping. We tested whether continuous maize cultivation accelerates SOM loss compared to upland rice and forest fallow. Methods: Because litter sources include C4 plants (maize in maize fields and Imperata grass in upland rice fields) in Thailand, C3-derived and C4-derived SOM can be traced using the differences in natural 13C abundance (δ13C) between C3 and C4 plants. We analyzed the effects of land use history (cultivation or forest fallow period) on C stocks in the surface soil. Soil C stocks decreased with the cultivation period in both upland rice and maize fields. ResultsThe rate of soil organic carbon loss was higher in maize fields than in upland rice fields. The decomposition rate constant (first order kinetics) of C3-plant-derived SOM was higher in the maize fields than in the upland rice fields and the C4-plant-derived SOM in the forest fallow. Soil surface exposure and low input of root-derived C in the maize fields are considered to accelerate SOM loss. Soil C stocks increased with the forest fallow period, consistent with the slow decomposition of C4-plant-derived SOM in the forest fallows. ConclusionsContinuous maize cultivation accelerates SOM loss, while forest fallow and upland rice cultivation could mitigate the SOM loss caused by continuous maize cultivation.

Underutilization Versus Nutritional-Nutraceutical Potential of the Amaranthus Food Plant: A Mini-Review

Amaranthus is a C4 plant tolerant to drought, and plant diseases and a suitable option for climate change. This plant could form part of every region’s cultural heritage and can be transferred to the next generation. Moreover, Amaranthus is a multipurpose plant that has been identified as a traditional edible vegetable endowed with nutritional value, besides its fodder, medicinal, nutraceutical, industrial, and ornamental potentials. In recent decade Amaranthus has received increased research interest. Despite its endowment, there is a dearth of awareness of its numerous potential benefits hence, it is being underutilized. Suitable cultivation systems, innovative processing, and value-adding techniques to promote its utilization are scarce. However, a food-based approach has been suggested as a sustainable measure that tackles food-related problem, especially in harsh weather. Thus, in this review, a literature search for updated progress and potential uses of Amaranthus from online databases of peer-reviewed articles and books was conducted. In addition, the nomenclature, nutritional, and nutraceutical value, was reviewed. The species of focus highlighted in the review include, A. blitum, A. caudatus, A. cruentus, A. dubius, A. hypochondriacus, A. spinosus, A. thunbergii, A. tricolor, and A. viridis.

Detection of exogenous sugars in pineapple juice using compound-specific stable hydrogen isotope analysis

An improved procedure for determining 2H/1H isotope ratios, using gas chromatography-isotope ratio mass spectrometry, has been used to detect the addition of exogenous C4-plant-derived sugars to pineapple juice. Isotopic techniques are commonly used to identify the addition of low-cost sugars to fruit juices and are difficult to subvert as it is not economically viable to change the isotopic ratios of the sugars. However, the addition of cane sugar to pineapple juice has presented a significant challenge that is only detected by site-specific 13C analysis of the methyl and methylene positions of ethanol derived from pineapple sugars, measured by nuclear magnetic resonance. This new GC-IRMS-based procedure utilises the trifluoroacetate derivative of sucrose to allow direct measurement of the carbon-bound non-exchangeable hydrogen. This provides advantages over alternative isotopic methods in terms of analysis time and sensitivity. This feasibility study has demonstrated the potential to reliably differentiate between authentic pineapple juices and those adulterated with commercial beet and cane sucrose.

Setaria parviflora (knotroot foxtail).

S. parviflora is a variable, self-compatible, rhizomatous, C4 plant with a short lived seed bank, commonly regarded as an agricultural weed both in its native and introduced range (Rabinowitz and Rapp, 1981; Pensiero, 1999; Mollard et al., 2007; Mollard and Insausti, 2011; Randall, 2012). It often colonizes cultivated and disturbed soils or waste places including seasonally wet sites and salt marshes (Hubbard, 1954; Leithead et al., 1971; Pott and Pott, 2004; Edgar and Connor, 2010). It can contaminate wool (Ryves et al., 1996), seed crops, especially those of grasses such as dryland rice, lawn seed and Bahia grass (Paspalum notatum) (Silveira Filho and Aquino, 1983; Wehtje et al., 2008; Seed Regulatory and Testing Branch, 2011) and degrade and dominate sod and pastures (including alfalfa), lowering hay quality, a problem because it can cause lesions in livestock (Murphy et al., 1992; Arregui et al., 2001; Muller and Via, 2012). Land infested with it might be considered to have lower value because of poor pasture. It is regarded as a member of the alien flora of Chile (Ugarte et al., 2011).

Plant families exhibit unique geographic trends in C4 richness and cover

Numerous studies have analysed the relationship between C4 plant cover and climate. However, few have examined how different C4 taxa vary in their response to climate, or how environmental factors alter C4:C3 abundance. Here we investigate (a) how proportional C4 plant cover and richness (relative to C3) responds to changes in climate and local environmental factors, and (b) if this response is consistent among families. Proportional cover and richness of C4 species were determined at 541 one-hectare plots across Australia for 14 families. C4 cover and richness of the most common and abundant families were regressed against climate and local parameters. C4 cover and richness in Poaceae and Cyperaceae were strongly positively correlated with January temperatures, however C4 Cyperaceae occupied a more restricted temperature range. C4 Poaceae cover was also correlated with seasonal rainfall, but no such trends were identified in Cyperaceae. Soil pH and tree cover modified relative C4 cover in these families. Proportional C4 Euphorbiaceae and Chenopodiaceae cover and richness were weakly correlated with climate, but were more strongly influenced by local environmental factors, including tree cover and soil texture. However, the explanatory power of C4 Euphorbiaceae and Chenopodiaceae models were poor. Results demonstrate the unique relationships between different C4 taxa and climate, and the significant modifying effects of environmental factors on C4 distribution. Our work also reveals C4 families will not exhibit consistent responses to perturbations in climate or local conditions. These results have substantial implications for predicting C4 cover over global, continental and regional areas. This preprint is current under review following revisions with the journal Oecologia.

Corrigendum to: Does the C4 plant Trianthema portulacastrum (Aizoaceae) exhibit weakly expressed crassulacean acid metabolism (CAM)?

We examined whether crassulacean acid metabolism (CAM) is present in Trianthema portulacastrum L. (Aizoaceae), a pantropical, salt-tolerant C4 annual herb with atriplicoid-type Kranz anatomy in leaves but not in stems. The leaves of T. portulacastrum are slightly succulent and the stems are fleshy, similar to some species of Portulaca, the only genus known in which C4 and CAM co-occur. Low- level nocturnal acidification typical of weakly expressed, predominantly constitutive CAM was measured in plants grown for their entire life-cycle in an outdoor raised garden box. Acidification was greater in stems than in leaves. Plants showed net CO2 uptake only during the light irrespective of soil water availability. However, nocturnal traces of CO2 exchange exhibited curved kinetics of reduced CO2 loss during the middle of the night consistent with low-level CAM. Trianthema becomes the second genus of vascular land plants in which C4 and features of CAM have been demonstrated to co-occur in the same plant and the first C4 plant with CAM-type acidification described for the Aizoaceae. Traditionally the stems of herbs are not sampled in screening studies. Small herbs with mildly succulent leaves and fleshy stems might be a numerically significant component of CAM biodiversity.