•Cotton adjusts its specific leaf area in response to the spatial distribution of light within the canopy.•Cotton optimizes the canopy use efficiency of N and light by changing its specific leaf ...area.•Optimization of canopy photosynthetic capacity in the mid- and lower-canopy layer is key to maximizing whole-canopy photosynthesis.
Appropriate plant population density (PPD) is an important crop management practice for optimizing canopy light distribution and increasing canopy photosynthetic capacity in field-grown cotton (Gossypium hirsutum L.). A 2-year field experiment was conducted to determine how the PPD (7.5, 19.5 or 31.5 plantsm−2) of cotton affects canopy photosynthetic capacity and photosynthetic use efficiency of light and N. The results indicated that PPD significantly affected both leaf morphology and canopy photosynthetic characteristics. As PPD changed, cotton maximized canopy apparent photosynthetic light use efficiency (CAPLUE) and photosynthetic capacity by adjusting specific leaf area (SLA), which in turn affected leaf N distribution in the canopy. The SLA of all three canopy layers increased as PPD increased. In the upper canopy, canopy light interception and canopy apparent photosynthetic N use efficiency (CAPNUE) rose as SLA increased, but CAPLUE declined. As PPD increased, SLA in the mid- and lower-canopy layers increased significantly. This caused canopy apparent photosynthesis rate per leaf area (CAPLeaf) and CAPNUE to decline. Medium-PPD had the highest canopy apparent photosynthesis rate (CAP) and CAPLUE in the mid- and lower-canopy layers. As a result, medium-PPD had the highest whole-canopy photosynthetic capacity and CAPLUE in this study. Overall, the results indicated that optimal spatial distribution of both light and specific leaf area is key for efficient utilization of light and N in cotton canopies.
•Light intensity in densely planted maize canopies plays an important factor in lodging.•The leaves 10–12 played a very important role in the strength of the third basal internode.•Improving light ...intensity at leaves 10–12 at flowering can reduce lodging by increasing dry matter accumulation and stalk strength formation at the third basal internode.
Close planting often increases the lodging rate of maize, but the cause is unclear. Close planting reduces light intensity within the canopy; therefore, we hypothesized that light intensity may be the main factor affecting maize lodging. To test this hypothesis, three field experiments involving plant density, shading and defoliation were designed to explore how the light environment in a maize canopy affects stalk strength formation and lodging rate. The results showed that close planting and artificial shading treatments both reduced light intensity in the lower canopy. This reduced the dry weight per unit length (DWUL) and rind penetration strength (RPS) of the third basal internode and increased the lodging rate. Removal of leaves 10–12 reduced the DWUL and RPS of the third internode and increased lodging rate. This showed that leaves 10–12 play a crucial role both in the formation of RPS of the third basal internode and in lodging resistance. Removal of either all or part of leaf 16 and above not only increased ptotosynthetic active radiation (PAR) at leaves 10–12 but also increased the DWUL and RPS of the third basal internode. This resulted in a decline in lodging. Therefore, we conclude that light intensity is an important factor affecting maize lodging at high plant density. Increasing light intensity at leaves 10–12 can enhance stalk strength and reduce lodging.
Cyclic electron flow around photosystem I (CEF-PSI) is shown to be an important protective mechanism to photosynthesis in cotton leaves. However, it is still unclear how CEF-PSI is regulated in ...non-foliar green photosynthetic tissues such as bracts. In order to learn more about the regulatory function of photoprotection in bracts, we investigated the CEF-PSI attributes in Yunnan 1 cotton genotypes (
L.) between leaves and bracts. Our findings demonstrated that cotton bracts possessed PROTON GRADIENT REGULATION5 (PGR5)-mediated and the choroplastic NAD(P)H dehydrogenase (NDH)-mediated CEF-PSI by the same mechanism as leaves, albeit at a lower rate than in leaves. The ATP synthase activity of bracts was also lower, while the proton gradient across thylakoid membrane (ΔpH), rate of synthesis of zeaxanthin, and heat dissipation were higher than those of the leaves. These results imply that cotton leaves under high light conditions primarily depend on CEF to activate ATP synthase and optimize ATP/NADPH. In contrast, bracts mainly protect photosynthesis by establishing a ΔpH through CEF to stimulate the heat dissipation process.
•Cotton adjusts its canopy structure and photosynthetic capacity in response to plant density so as to maximize the CAPLUE and CAPNUE.•The light-response curves of CAPLUE and CAPNUE can reflect ...whether the canopy is optimal for photosynthate formation.•Cotton yield is influenced by the spatial distribution of vegetative and reproductive organs within canopy in different plant densities.
Plant density is a common practice for optimizing canopy photosynthetic capacity and improving cotton (Gossypium hirsutum L.) yield. The objective of this study was to evaluate the effects of plant density (14.5, 19.5 and 29 plants m−2 were adjusted by wide, medium and narrow row spacing, respectively) on canopy apparent photosynthetic use efficiency of light (CAPLUE) and N (CAPNUE), dry matter accumulation and yield formation of cotton plants (cv. SCRC24). Cotton in narrow row spacing responded to light interception and distribution within its canopy by significantly increasing the proportion of leaf area index (LAI) in the upper canopy and by increasing leaf N content per unit land area (Nland). Cotton in wide row spacing compared with narrow row spacing had a significantly greater proportion of LAI in the mid and lower canopy and a significantly lower Nland. The changes in canopy structure and leaf photosynthetic characteristics in response to row spacing affected the relationship between CAP and light within the canopies. Under low light conditions, CAPLUE and CAPNUE were greater in narrow row spacing than in wide row spacing. Under high light conditions, maximum CAPLUE and CAPNUE were greater in wide row spacing than in narrow row spacing. These light response curves support the hypothesis that CAPLUE and CAPNUE were maximized according to the light interception and distribution within its canopy, which is by adjusting canopy structure and leaf photosynthetic characteristics. Furthermore, there was no difference in leaf+boll dry weight among the three row spacing treatments. The leaf+boll dry weight was maintained in narrow row spacing by increasing leaf dry weight at the expense of boll dry weight. The cotton responded to wide row spacing both by increasing the single boll weight and the proportion of LAI in the mid- and lower canopy and by increasing the proportion of bolls in the upper canopy. Cotton in wide row spacing had better canopy leaf and boll distribution, therefore higher CAP, because a greater proportion of leaf area was allocated to the mid canopy and the canopy structure was optimal. This indicated that yield was influenced not only by maximum CAP, CAPLUE, and CAPNUE, but also by the spatial distribution of vegetative and reproductive organs.
The hot compression tests of TB9 titanium alloy sample were carried out on Gleeble-1500 thermal simulator at the temperature range of 750-1000 ℃ and the strain rate range of 0.01-10 s−1. The ...stress-strain curves obtained by the experiment were subjected to friction correction and the processing map was drawn according to the corrected stress-strain curve .The results show that the stress-strain curve after friction correction is obviously lower than that before correction, and the stress difference between them increased with the increase of strain. The corrected stress−strain curve is Math Processing Error, and can used to predict the stress of TB9 titanium alloy under different strain rates at 750 ℃ to 1000 ℃. Instable deformation of TB9 titanium alloy leads to localize the deformation bands which is about 45° to the compression direction appeared, resulting in the inhomogeneous microstructure. Stable deformation during hot working in suitable process window can bring dynamic recrystallization and recover
Cotton has many leaves and even more bolls, which results in a complicated source–sink relationship. Under water stress, the single boll weight (SBW) of cotton remains relatively stable, while both ...the leaf area and leaf photosynthetic rate decrease greatly. It is therefore difficult to understand how the formation of SBW is regulated under water stress solely by considering single-leaf photosynthesis. Considering the cotton boll–leaf system (BLS: including the main-stem leaf, sympodial leaves, and non-leaf organs) as the basic unit of the cotton canopy, we speculated that the formation of SBW may depend on photosynthesis in the corresponding BLS under water stress. To verify this hypothesis, five water treatments were set up in the field. The results showed that with increasing water stress, the relative water content (RWC) of the main-stem and sympodial leaves decreased gradually, and the decrease in the sympodial leaves was more obvious. The SBW and the number of BLSs decreased slightly with increasing water stress, while the number of bolls per plant decreased significantly. The area of the BLS decreased gradually with increasing water stress, and the area of sympodial leaves decreased more than that of the main-stem leaves. Gas exchange showed that the photosynthetic rate of the BLS (Pn
(BLS)
) decreased gradually with increasing water stress. In addition, the single-leaf photosynthesis and carboxylation efficiency (CE) decreased progressively and rapidly with the increase of water stress. Compared with the main-stem leaf, the photosynthetic function of the sympodial leaf decreased more. Further analysis showed that compared with leaf photosynthetic rate, there was a better correlation between Pn
(BLS)
and SBW. Thus, the formation of SBW mainly depends on Pn
(BLS)
under water stress, and the increase of BLS to boll is also helpful to maintain SBW to some extent. In BLS, the photosynthesis of the main-stem leaf plays a very important role in maintaining the stability of SBW, while the photosynthetic performance in sympodial leaves may be regulated plastically to influence SBW.
Estimating the boll development and boll yield from single-leaf photosynthesis is difficult as the source-sink relationship of cotton (
Gossypium hirsutum
L.) is complicated. As the boll-leaf system ...(BLS), which includes the main-stem leaf, sympodial leaf, and non-leaf organs, is the basic unit of the cotton source-sink relationship and yield formation, the concept of "BLS photosynthesis" is introduced in this study. We speculate that the characteristics of BLS gas exchange can more accurately reflect the photosynthetic function of the system, thus revealing the law of photosynthesis in the process of boll development. The results showed that the photosynthetic rate of single leaves measured by a BLS chamber was consistent with that measured by a standard single-leaf chamber. BLSs exhibited typical light response curves, and the shape of the curves was similar to those of single leaves. The light compensation point and respiration rate of BLSs were higher than those of single leaves, while the apparent quantum efficiency of BLSs was lower. Compared with single leaves, the duration of the photosynthetic function of BLSs was longer. Increasing plant density decreased the gas exchange rate per unit BLS more significantly under field conditions. There was a better linear correlation between the net CO
2
assimilation rate, respiration rate of BLSs and boll biomass. Therefore, we think that the gas exchange of BLSs can better reveal the changes in photosynthetic function of BLSs and boll development. This provides a new basis for analyzing the mechanism and regulation of cotton yield formation.
It is of great importance to explore agronomic management measures for water conservation and cotton yield in arid areas.
A four-year field experiment was conducted to evaluate cotton yield and soil ...water consumption under four row spacing configurations (high/low density with 66+10 cm wide, narrow row spacing, RS
and RS
; high/low density with 76 cm equal row spacing, RS
H and RS
L) and two irrigation amounts (CI:conventional drip irrigation; LI:limited drip irrigation) during the growing seasons in Shihezi, Xinjiang.
A quadratic relationship was observed between the maximum LAI (LAI
) and seed yield. Canopy apparent transpiration rate(CAT), daily water consumption intensity (DWCI) and crop evapotranspiration (ET
) were positively and linearly correlated with LAI. The seed yields, lint yields, and ET
under CI were 6.6-18.3%,7.1-20.8% and 22.9-32.6%higher than those observed under LI, respectively. The RS
under CI had the highest seed and lint yields. RS
L had an optimum LAI
range, which ensured a higher canopy apparent photosynthesis and daily dry matter accumulation and reached the same yield level as RS
; however, soil water consumption in RS
L was reduced ET
by 51-60 mm at a depth of 20-60 cm at a radius of 19-38 cm from the cotton row,and water use efficiency increased by 5.6-8.3%compared to RS
under CI.
A 5.0<LAI
<5.5 is optimum for cotton production in northern Xinjiang, and RS
L under CI is recommended for high yield and can further reduce water consumption. Under LI, the seed and lint yield of RS
were 3.7-6.0% and 4.6-6.9% higher than those of RS
L, respectively. In addition, high-density planting can exploit the potential of soil water to increase cotton yields under water shortage conditions.
