Bottom-up redistribution of biomass optimizes energy allocation, water use and yield formation in dryland wheat improvement.

BACKGROUND: Modern wheat cultivars have been developed having distinct advantages in many aspects under drought stress, such as plasticity in biomass allocation and root system architecture. A better understanding of the biomass allocation mechanisms that enable modern wheat to achieve higher yields and yield-based water use efficiency (WUEg ) is essential for implementing best management strategies and identifying phenotypic traits for cultivar improvement. We systematically investigated the biomass allocation, morphological and physiological characteristics of three ploidy wheat genotypes under 80% and 50% field water-holding capacity (FC) conditions. Some crucial traits were also assessed in a complementary field experiment. RESULTS: The diploid and tetraploid genotypes were found to allocate more biomass to the root system, especially roots in the topsoil under drought stress. Our data illustrated that lower WUEg and yield of these old genotypes were due to excessive investment in the root system, which was associated with severely restricted canopy development. Modern hexaploid genotypes were found to allocate smaller biomass to roots and larger biomass to shoots. This not only ensured the necessary water uptake, but also allowed the plant to distribute more assimilates and limited water to the shoots. Therefore, the hexaploid genotypes have evolved a stable plant canopy structure to optimize WUEg and grain yield. CONCLUSION: This study demonstrated that the biomass shift from below ground to above ground or a more balanced root:shoot ratio tended to optimize water use and yield of the modern cultivars. This discovery provides potential guidance for future dryland wheat breeding and sustainable management strategies. © 2021 Her Majesty the Queen in Right of Canada Journal of The Science of Food and Agriculture © 2021 Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Polyethylene film mulching enhances the microbial carbon-use efficiency, physical and chemical protection of straw-derived carbon in an Entisol of the Loess Plateau.

The global use of agricultural polyethylene mulches has emerged as a widespread farming practice, however, its effects on the fate and dynamics of crop straw-derived C in soil microbial biomass C (MBC), aggregate-associated and chemical recalcitrance-related C fractions are rarely assessed in situ. A two-year field experiment using 13C-labeled maize stem was carried out to quantify the allocation and dynamics of straw-C in an Entisol with and without plastic mulching. The results indicated that across the treatments, from 49.2% to 56.4% of straw-13C was released as CO2-C, from 34.9% to 43.1% was sequestrated as SOC pool, and from 6.7% to 9.7% remained undecomposed at the end of the experiment. Compared to non-mulching, plastic mulching significantly decreased the straw-derived CO2-C emissions by 14.6%, partially owing to the increased incorporation of straw-C into SOC pool. Across the treatments, the straw-derived MBC ranged from 14.4 to 147.9 mg 13C kg-1; and plastic mulching increased straw-derived MBC and microbial C use efficiency (CUE) of straw residue by 41.2% and 35.2% compared with non-mulching, respectively. The allocation dynamics of straw-C in each soil aggregate followed a sustained upward trend with time, while a significantly higher straw-C was incorporated into both macro- (> 0.25 mm) and micro-aggregates (0.25-0.053 mm) with plastic mulching. Compared to the non-mulching, plastic mulching enhanced the inclusion of straw-13C in the chimerically more stable C fraction, especially at the late experimental period. We conclude that crop straw return combined with plastic mulching could improve SOC sequestration by enhancing microbial CUE, physical and chemical protection of straw-derived C in this dryland cropping system.

Morphological and physiological responses of different wheat genotypes to chilling stress: a cue to explain yield loss.

BACKGROUND: The eco-physiological mechanism of wheat yield loss resulting from chilling stress is a fundamental scientific issue. However, previous studies have focused on hexaploid wheats, and few studies on the morphological and physiological plasticity of wheat plants. Six different wheat genotypes were tested under chilling stress to investigate the physio-morphological parameters as well as the loss of grain yield in growth chambers. RESULTS: Chilling stress resulted in significant loss in grain yield in all genotypes. Under chilling stress, diploid wheats generated zero harvest, and tetraploid genotypes also suffered from a pronounced loss in grain yield, compared with the control group. In contrast, hexaploid genotypes acquired relatively high maintenance rate of grain yield among three species. CONCLUSIONS: Diploid and tetraploid wheat genotypes maintained relatively large leaf area and high photosynthetic rates, but they were subjected to significant declines in vascular bundle number and productive tillers as a consequence of the inhibition by sink growth under chilling stress. The hexaploid wheats were found to have relatively low leaf area and photosynthetic rates. These genotypes also stored more soluble carbohydrates and exhibited stronger sink enhancement, ensuring the translocation and redistribution of assimilates. Our findings provided a new theoretical understanding of yield stabilization in the domestication process of wheat genotypes under chilling stress. © 2017 Her Majesty the Queen in Right of Canada. Journal of The Science of Food and Agriculture © 2017 Society of Chemical Industry.

Plant architecture, plasticity, and adaptation strategies of two oat genotypes under different competition intensities.

BACKGROUND: The hypothesis that positive and negative interactions account for adaptive strategies was tested in a controlled study with two oat (Avena sativa) genotypes: 'Manotick' with erect leaves and 'Oa1316-1' with prostrate leaves. An increasing competition pattern was designed by varying the number of seeds planted in each container and the space between containers, thus creating different planting density regimes (i.e. alternative and solid treatments). RESULTS: Total biomass of individual plants tended to decrease exponentially with increasing density in both genotypes. Under high density stress, Manotick allocated more biomass to the roots and produced 50% more tillers, leading to more non-productive tillers and lower harvest index in the alternative than in the solid treatment. In contrast, Oa1316-1 allocated more biomass to panicles and stems, and less to the roots, with fewer tillers. CONCLUSIONS: With increasing density and strengthening intraspecific competition, Manotick reduced aboveground biomass allocation, leading to lower yield, while Oa1316-1 decreased allocation to the roots, but increased allocation to the panicles under an increasingly competitive environment. These adjustments were mechanically derived from negative and positive interactions, ensuring greater yield in the prostrate type. Our findings provided a novel rationale for a planting strategy based on plant type selections.

Dryland wheat domestication changed the development of aboveground architecture for a well-structured canopy.

We examined three different-ploidy wheat species to elucidate the development of aboveground architecture and its domesticated mechanism under environment-controlled field conditions. Architecture parameters including leaf, stem, spike and canopy morphology were measured together with biomass allocation, leaf net photosynthetic rate and instantaneous water use efficiency (WUE(i)). Canopy biomass density was decreased from diploid to tetraploid wheat, but increased to maximum in hexaploid wheat. Population yield in hexaploid wheat was higher than in diploid wheat, but the population fitness and individual competition ability was higher in diploid wheats. Plant architecture was modified from a compact type in diploid wheats to an incompact type in tetraploid wheats, and then to a more compact type of hexaploid wheats. Biomass accumulation, population yield, harvest index and the seed to leaf ratio increased from diploid to tetraploid and hexaploid, associated with heavier specific internode weight and greater canopy biomass density in hexaploid and tetraploid than in diploid wheat. Leaf photosynthetic rate and WUEi were decreased from diploid to tetraploid and increased from tetraploid to hexaploid due to more compact leaf type in hexaploid and diploid than in tetraploid. Grain yield formation and WUEi were closely associated with spatial stance of leaves and stems. We conclude that the ideotype of dryland wheats could be based on spatial reconstruction of leaf type and further exertion of leaf photosynthetic rate.

[The 1st International Youth Ecologist Forum in China, 2009: a review].

To promote the communication and cooperation between Chinese and overseas youth ecologists, a conference entitled "The 1st International Young Ecologist Forum" was held at Lanzhou University in June 29-30, 2009. This conference was organized by outstanding overseas ecologists and hosted by Lanzhou University. The presentations covered broad areas of ecology, including plant-soil interactions, structure and function of regional ecosystems, ecological security and ecological planning, global change ecology, and environmental sustainability, demonstrating that the development of China ecology is gradually from traditional basic research transforming into applied research. The presentations also reflected in some extent the development characteristics, evolution direction, and distribution pattern of China ecological research. China ecological research has gradually formed four centers, the Northeast, North, Northwest, and Southeast China, and each of them has its definite regional characteristics. Some suggestions about the organization form and future planning of the forum were put forward.