Systemic regulation of photosynthetic function in field-grown sorghum

The photosynthetic characteristics of developing leaves of plants grown under artificial conditions are, to some extent, regulated systemically by mature leaves; however, whether systemic regulation of photosynthesis occurs in field-grown crops is unclear. To explore this question, we investigated the effects of planting density on growth characteristics, gas exchange, leaf nitrogen concentration and chlorophyll a fluorescence in field-grown sorghum (Sorghum bicolor L). Our results showed that close planting resulted in a marked decline in light intensity in lower canopy. Sorghum plants grown at a high planting density had lower net photosynthetic rate (130), stomatal conductance (GO, and transpiration rate (E) than plants grown at a low planting density. Moreover, in the absence of mineral deficiency, close planting induced a slight increase in leaf nitrogen concentration. The decreased photosynthesis in leaves of the lower canopy at high planting density was caused mainly by the low light. However, newly developed leaves exposed to high light in the upper canopy of plants grown at high planting density also exhibited a distinct decline in photosynthesis relative to plants grown at low planting density. Based on these results, the photosynthetic function of the newly developed leaves in the upper canopy was not determined fully by their own high light environment. Accordingly, we suggest that the photosynthetic function of newly developed leaves in the upper canopy of field-grown sorghum plants is regulated systemically by the lower canopy leaves. The differences in systemic regulation of photosynthesis were also discussed between field conditions and artificial conditions. (C) 2015 Elsevier Masson SAS. All rights reserved

Effect of irrigation methods on root growth, root-shoot ratio and yield components of cotton by regulating the growth redundancy of root and shoot

Mulched drip irrigation is a common water-saving irrigation technology that can improve water resource utilization efficiency in arid areas. The change of irrigation method affects the growth of crop root system and then regulates the growth of aboveground organs. However, there have been limited comparative studies on how mulched drip irrigation affects the cotton root growth and regulates the relationship between cotton root and shoot. The objective of this study was to determine whether mulched drip irrigation could achieve water-saving and high-yield cotton cultivation by regulating the growth redundancy of root and shoot. Under field conditions, mulched drip irrigation (conventional drip irrigation and excessive drip irrigation) and traditional flood irrigation (conventional flood irrigation and reduced flood irrigation) were used in this experiment. Traditional flood irrigation was used as the control group. The results showed that compared with the traditional flood irrigation, the higher soil water content under mulched drip irrigation increased the specific root length (SRL), which promoted the growth of fine root length and biomass at the full flowering stage and prophase full boll stage. The growth of fine roots increased the root-shoot ratio (R/S) of mulched drip irrigation, and then inhibited the excessive vegetative growth of the aboveground parts. When entering the late full boll stage and boll opening stage, the fine root biomass and fine root mass fraction decreased rapidly under the mulched drip irrigation, resulting in a lower R/S. The smaller R/S of mulched drip irrigation facilitated the distribution of photosynthetic products to reproductive organs, which increased the boll number per plant by 7.30 %-25.10 %, thus increasing the boll loading of fine root system and seed cotton yield. However, compared with conventional drip irrigation, over irrigation led to excessive vegetative growth of cotton under excessive drip irrigation, which resulted in the decrease of boll opening rate and seed cotton yield by 8.71 %-17.19 % and 14.14 %-24.27 %, respectively. Moreover, the smaller R/S at the late growth stage enabled conventional drip irrigation to achieve the maximum water use efficiency (WUE). Therefore, mulched drip irrigation promoted the root growth of cotton and inhibited the vigorous vegetative growth of shoot before the prophase full boll stage, and then reduced the growth redundancy of root and increased the productive capacity of the fine root system after the prophase full boll stage, which increased boll number per plant and yield. However, only under the appropriate irrigation amount (390 mm), mulched drip irrigation can increase both yield and WUE, thus achieving the goal of water-saving and high-yield cultivation

Mulched drip irrigation increases cotton yield and water use efficiency via improving fine root plasticity

The morphological characteristics of crop roots, especially the plasticity of fine roots, are directly related to the crop's ability to obtain soil water. Mulched drip irrigation can effectively regulate soil water distribution to achieve high cotton yield with reduced water consumption. In the previous study, from the perspective of rootshoot coordination, we found that mulched drip irrigation reduced the growth redundancy of roots and improved the root productivity of cotton, thus achieving the goal of water-saving and increased yield. However, it is unclear if and how mulched drip irrigation enhances absorptive capacity of roots via regulating dry and wet soil areas and optimizing fine root morphology and distribution compared with traditional flood irrigation. To achieve this, the effects of fine root plasticity on the absorptive capacity of roots were studied in a two-year field experiment. Mulched drip irrigation (conventional drip irrigation and excessive drip irrigation) and traditional flood irrigation (reduced flood irrigation and conventional flood irrigation) were used, and soil water distribution and root distribution were determined. The results showed that compared with traditional flood irrigation, mulched drip irrigation significantly increased the soil water content (SWC) in the 0-60 cm soil layer and reduced the fluctuation amplitude of SWC at the flowering and boll stage of cotton. Mulched drip irrigation formed different dry and wet areas in the root zone, i.e., the SWC was higher in the shallow layer (0-40 cm) at 0-20 cm on both sides of the drip line, and most of the cotton roots were in the wet area. The higher SWC increased the distribution of fine roots in this area and shaped the shallow fine root system, which enhanced the cotton plant's ability to absorb soil water. Statistical analysis showed that the higher fine root biomass in the 0-40 cm soil layer at the late full boll stage of cotton under mulched drip irrigation was beneficial to increase aboveground biomass, thus increasing total bolls and seed cotton yield. However, compared with the irrigation amount of field production (390 mm), an excessive amount of irrigation (600 mm) reduced the seed cotton yield of mulched drip irrigation, resulting in the decrease of irrigation water use efficiency (IWUE). Therefore, mulched drip irrigation optimizes the distribution of fine roots and enhances water uptake by effectively regulating the water-root relationship, and thus improves seed cotton yield and IWUE

Diurnal changes in photosynthesis in Sclerocarya birrea from South Africa and Israel after introduction and acclimatization in Wenshan, Yunnan Province, China

Photosynthetic activity is one of the most important indicators for evaluating the introduction and acclimatization of trees to new geographies. The aim of this study was to investigate the photosynthetic characteristics of marula [Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro (Anacardiaceae)] and the environmental conditions relevant to its growth in China. We analyzed the diurnal dynamics of photosynthesis in two S. birrea varieties, one from South Africa and one from Israel, after introduction into China using a portable photosynthesis measuring system. Our results showed that the diurnal net photosynthetic rate (P-n) exhibited an atypical double-peak pattern that was influenced mainly by stomatal factors. Moreover, the diurnal change in stomatal conductance (G(s)) was consistent with that for P-n and showed an obvious double-peak curve, whereas the diurnal change in the transpiration rate (T-r) was opposite to that in intercellular CO2 concentration (C-i), which presented a single-peak curve. The extreme values of the environmental factors we monitored occurred at approximately the same time of day and influenced photosynthesis by affecting C-1, T-r, and leaf temperature (T-L), with light intensity exerting an especially strong effect. The P-n of the S. birrea variety from Israel was higher than that of the S. birrea variety from South Africa, while South Africa S. birrea exhibited superior growth trait in southern China. We suggest that the photosynthetic performance of S. birrea can be acclimated to a new environment. (C) 2015 SAAB. Published by Elsevier B.V. All rights reserved

Lily Cultivars Have Allelopathic Potential in Controlling Orobanche aegyptiaca Persoon

As a devastating holoparasitic weed, Orobanche aegyptiaca Persoon. (Egyptian broomrape) causes serious damage to agricultural production and threatens economic development, which has raised widespread concern. The present study was conducted to determine whether lilies have the potential to be used as 'trap crops' for controlling O. aegyptiaca Persoon. In the experiments, the ability of three popular lily cultivars (Lilium Oriental hybrids 'Sorbonne', Lilium LA (Longiflorum hybrids x Asiatic hybrids) hybrids 'Ceb Dazzle', and Lilium Longiflorum hybrids (L. formosanum x L. longiflorum) 'L. formolongo') to induce O. aegyptiaca Persoon. seed germination was assessed. Parts of the three lily cultivars, including the rhizosphere soil and underground and above-ground organs, all induced "suicidal germination" of parasitic O. aegyptiaca Persoon. seed at four growth stages. Specifically, Sorbonne and Ceb Dazzle behaved with similar allelopathy, and the bulb, scale leaf and aerial stem exhibited stronger allelopathic effects on O. aegyptiaca Pers. germination compared to other organs. Aqueous L. formolongo leaf extracts may contain more stable, effective stimulants given that they induced the highest germination rate at 76.7% even though the extracts were serially diluted. We speculate that these organs may be advantageous in further isolating and purifying economical active substances that can be substitutes for GR24. These results indicate that lilies have the potential to be used as a trap crops or can be processed into green herbicide formulations that can be applied in agriculture production to rapidly deplete the seed bank of O. aegyptiaca Persoon. parasitic weeds in soil

Enhanced thermal dissipation confers photoprotection in top leaves despite systemic regulation from lower leaves in cotton

To better understand the photosynthetic regulation between lower leaves and top leaves, leaf gas exchange and chlorophyll fluorescence were examined in field and climate chamber grown cotton (Gossypium hirsutum L. cv. Xinluzao 45). Two planting density treatments were used in the field: low planting density (LD) and high planting density (HD), and two artificial shade treatments were used in the climate chamber: no shade (NS) and lower leaves shaded (LS). Our results show that the maximum net photosynthetic rate (P-max), light saturation point (LSP) and light compensation point (LCP) of top leaves were decreased, but the apparent quantum efficiency of net carbon assimilation (AQE) of top leaves was increased in HD and LS, which had a similar trend to the lower leaves. Although top and lower leaves improved the utilization of light, the fractions of light absorbed by the PSII antenna that is utilized in PSII photochemistry Y(II) and photochemical quenching coefficient (qP) of top leaves and lower leaves were decreased in HD and LS. Furthermore, the fraction of absorbed light that is dissipated thermally via Delta pH and xanthophylls regulated processes Y(NPQ) and non-photochemical quenching (NPQ) of top leaves were increased in HD and LS. In summary, these results suggest that the light energy utilization and photochemical efficiency of the top leaves in cotton are regulated by the light environment of the lower leaves, and the activation of thermal dissipation confers photoprotection of top leaves despite systemic regulation from lower leaves in cotton. Therefore, considering that cotton is cultivated in high density in most cotton areas of the world, the systemic regulation of photosynthetic capacity in top leaves affected by light environment of lower leaves caused by high-density cultivation needs to be considered comprehensively in practical production. Then, the optimal photosynthetic capacity of the population can be obtained