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Several studies have found seasonal and temporal variability in leaf photosynthesis parameters in different crops. This variability depends upon the environment, the developmental stage of the plant and the presence or absence of sinks. Girdling involves the removal of the bark and phloem down to the youngest xylem all around the stem and prevents export of photoassimilates out of the stem. The load of developing fruits has often been reported to influence the individual net leaf photosynthesis rate (Pn) in tree crops. In this study, we chose (1) to model the key parameters of photosynthesis models of leaves (Pgmax, Rd, α and θ) as a function of time and using these two means (girdling and low fruit load) to alter the source-sink balance and (2) to compare three models: the rectangular and non-rectangular hyperbola model by Thornley, as well as the non-rectangular hyperbola model by Marshall and Biscoe. Six-year-old fruit-bearing branches of 10-year-old apple trees were used to study and model the seasonal variation of photosynthetic parameters in leaves of vegetative shoots, as a function of global fruit load (at the branch level), with or without girdling, during the growing season of 2015. Three treatments were applied: control, low load (LL) or low load + girdling (LLG). For each fruit-bearing branch, light-response curves of Pn for two leaves of vegetative shoots were measured at two different positions, proximal and distal. The model of Marshall and Biscoe was the most accurate for the simulation of Pn in fruit-bearing branches of apple trees with time (season) and the three treatments applied. The present study proposed a way to model the photosynthesis rate by temporal and environmental variables only. A proper validation of this model will be necessary to extend its utilization and appreciate its predictive capacity fully.

‘Patharnakh’ and ‘Punjab Beauty’ are major pear cultivars grown under the subtropical conditions of northwestern India. These pear cultivars tend to put up profuse vegetative growth under the high density planting that leads to excessive shading of bearing zone of canopy. To facilitate light penetration into inner plant canopy, there is a need to contrive an efficient approach for vegetative growth management. The foliar applications of varying concentrations of plant bio-regulators viz. Prohexadione calcium (Pro-Ca) (100, 200, 400 mg L-1) and Paclobutrazol (PBZ) (100, 250, 500 mg L-1) were done at 10 days after full bloom (DAFB) ‘Patharnakh’ and ‘Punjab Beauty’ pear plants trained on the Y-trellis training system. Shoot length, leaf area index and trunk cross-sectional areas (TCSA) were greatly reduced by Pro-Ca200 and 400 mg L-1 concentrations. Treatments enhanced light penetration and photosynthesis. Fruit weight improved with plant bio-regulator treatments resulting in increased yield efficiency of pear plants. This study exhibited a strong positive correlation between light availability and yield efficiency of pear plants.

Summary A major challenge of modern agricultural biotechnology is the optimization of plant architecture for enhanced productivity, stress tolerance and water use efficiency (WUE). To optimize plant height and tillering that directly link to grain yield in cereals and are known to be tightly regulated by gibberellins (GAs), we attenuated the endogenous levels of GAs in rice via its degradation. GA 2‐oxidase (GA2ox) is a key enzyme that inactivates endogenous GAs and their precursors. We identified three conserved domains in a unique class of C20 GA2ox, GA2ox6, which is known to regulate the architecture and function of rice plants. We mutated nine specific amino acids in these conserved domains and observed a gradient of effects on plant height. Ectopic expression of some of these GA2ox6 mutants moderately lowered GA levels and reprogrammed transcriptional networks, leading to reduced plant height, more productive tillers, expanded root system, higher WUE and photosynthesis rate, and elevated abiotic and biotic stress tolerance in transgenic rice. Combinations of these beneficial traits conferred not only drought and disease tolerance but also increased grain yield by 10–30% in field trials. Our studies hold the promise of manipulating GA levels to substantially improve plant architecture, stress tolerance and grain yield in rice and possibly in other major crops.

Asplenium platyneuron growing at two locations (outer sunlit location and inner shaded location) in a low brick and masonry wall in upper Manhattan (New York City) was studied to assess the effects of the two different microenvironments on the ecophysiology of the two fern populations. The intensity of illumination at the inner location was ca. 40% of the intensity at the outer location, where the photosynthetic active radiation (PAR) at mid-day was ca. 1,484 µmol m–2 s–1. Generally, root space temperatures tracked air temperature, varying from 26 to 31 °C for the outer location, and 25 to 28.7 °C for the inner location. Based on prior published literature with other fern species, we hypothesized that samples of A. platyneuron growing on the outer surface exposed to maximum illumination would exhibit higher maximum photosynthesis rates, higher respiration in the light, and smaller leaves compared to the less illuminated samples growing on the inner surface. The results supported our hypothesized relationships. Mean leaf length (cm) was longer for leaves of plants at the shaded inner location (30 ± 1.1) compared to those of plants at the more illuminated outer location (9 ± 1.2). The maximum photosynthetic rate (Amax) for the outside sample of ferns (6.3 ± 0.25) was statistically significantly different from the Amax for the inside sample (4.3 ± 0.72) as hypothesized. The mean respiration in the light was significantly larger for the ferns growing outside (-0.52 ± 0.03) compared to those inside (-0.36 ± 0.04). Additionally, light response (A–Q) curves and relevant other physiological evidence are presented for ferns at the two sampling sites.

Over two growing seasons, we evaluated how irrigation strategies and lateral spacings under drip irrigation methods shape safflower physiology. A split-split plot design tested full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) across three lateral spacings (L1 = 20, L2 = 40, and L3 = 60 cm) with surface (SD) and subsurface (SSD) drip irrigation systems. We monitored leaf area index ( LAI ), photosynthesis rate ( A n ), stomatal conductance ( g s ), leaf transpiration rate ( T r ), leaf water potential ( LWP ), and leaf to air vapor pressure deficit ( VPD ) and related these to seed yield. Relative to FI, water-saving irrigation strategies reduced seasonal irrigation by ~ 25–26%, and SSD applied ~ 7% less water than SD. Peak LAI was 3.95 (2018) and 4.88 (2019), and it significantly reduced by an average of 14% and 18% with water-saving irrigation and wider later spacing, respectively, in comparison to FI and 20 cm lateral spacing. Gas exchange parameters ( A n , g s , and T r ) decreased with wider lateral spacing and peaked under FI and 20 cm lateral spacing, though PRD and 40 cm spacing resulted in an acceptable physiological performance under water scarcity. The LWP was less negative under FI by roughly 18% compared to water-saving irrigation and by 24% under L1 compared to L3. The extinction coefficient ( k ) of spring safflower for SD and SSD was 0.62 and 0.70 on average during the two growing seasons. Subsurface drip irrigation showed slightly higher light extinction coefficient, suggesting altered canopy light absorption. Collectively, treatments optimized for gas exchange properties and seed yield were FI-L1-SSD. When water is scarce, the most effective saving strategy was PRD-L2-SSD, which maintained A n , g s , LWP , and A n /T r better than DI while saving ~ 25% seasonal water compared to FI.

Cotton leafroll dwarf disease (CLRDD) caused by cotton leafroll dwarf virus (CLRDV) is an emerging threat to cotton production in the United States. The disease was first reported in Alabama in 2017 and subsequently has been reported in 10 other cotton producing states in the United States, including Georgia. A field study was conducted at field sites near Tifton, Georgia in 2019 and 2020 to evaluate leaf gas exchange, chlorophyll fluorescence, and leaf temperature responses for a symptomatic cultivar (diseased plants observed at regular frequency) at multiple stages of disease progression and for asymptomatic cultivars (0% disease incidence observed). Disease-induced reductions in net photosynthetic rate ( A n , decreased by 63–101%), stomatal conductance ( g s , decreased by 65–99%), and efficiency of the thylakoid reactions (32–92% decline in primary photochemistry) were observed, whereas leaf temperature significantly increased by 0.5–3.8°C at advanced stages of the disease. Net photosynthesis was substantially more sensitive to disease-induced declines in g s than the thylakoid reactions. Symptomatic plants with more advanced disease stages remained stunted throughout the growing season, and yield was reduced by 99% by CLRDD due to reductions in boll number per plant and declines in boll mass resulting from fewer seeds per boll. Asymptomatic cultivars exhibited more conservative gas exchange responses than apparently healthy plants of the symptomatic cultivar but were less productive. Overall, it is concluded that CLRDV limits stomatal conductance and photosynthetic activity of individual leaves, causing substantial declines in productivity for individual plants. Future studies should evaluate the physiological contributors to genotypic variation in disease tolerance under controlled conditions.

1. Projected increases in drought duration and intensity under climate change considerably affect aboveground productivity (ANPP) and associated process variables (photosynthesis rates (Pn), stomatal conductance (gs), soil respiration (Rs) and soil water content (SWC)). 2. Although ANPP has been extensively studied across the ecosystems, there is a little consensus on how the spatiotemporal patterns of ANPP will be altered with increasing drought stress. Here, we present a global meta-analysis of ANPP and the four variables (610 observations from 78 studies) for drought duration, intensity and their combination. 3. Forest-ANPP had stronger negative responses to long-term drought (34.44%; ≥4 years) than short-term drought (10.78%; ≤1 year) and decreased more in Mediterranean forests than in tropical forests. Decreases in Pn and gs were strongest under long-term moderate drought. In the short term, Rs increased by 5.66% under light drought, but decreased by 14.12% and 28.43% under moderate and severe droughts. Grass-ANPP showed a nonlinear decrease with extended duration and the rate slowed. Within light to severe intensities, ANPP decreased linearly, but became stable under extreme condition. In the short term, ANPP reduced more seriously with increasing drought intensity (12.01%-30.34%). With aggravation of drought stress, the reductions in Rs and SWC increased. There was significant heterogeneity in grassland responses to drought stress. The greatest decreases in ANPP, Pn and gs were observed in North America, and the reductions in Rs and SWC were greater in Western Europe. Shrub-ANPP showed stronger negative responses to long-term moderate drought (12.59%). Pn and gs declined significantly with increasing drought intensity. Variations in Rs to drought duration, intensity and their combination were more complex, either showing positive or negative responses (dominated). 4. Synthesis. Forest-ANPP shows high sensitivity to long-term moderate drought, whereas grass-ANPP is more responsive to short-term drought. Compared to forests and grasslands, shrub-ANPP exhibits less sensitivity to droughts. Different responses of ecosystems were predominantly driven by physiological mechanisms or species differences in turnover time, community architecture and drought adaptation strategies. Given these findings, future studies should focus on nonlinear patterns, response thresholds and adaptation mechanisms when predicting and modeling feedback between ecosystems and climate change.

Effective utilization of water is the cornerstone of maintaining plant biomass. Water use efficiency (WUE), defined as plant carbon assimilated as biomass per unit of water input, is significantly affected by global change, particularly by nitrogen (N) deposition. Generally, N availability promotes WUE by stimulating photosynthetic. However, the degree to which increased N availability may influence leaf WUE and photosynthesis properties (A, leaf net CO2 assimilation rate; gs, stomatal conductance, and E, transpiration rate), especially in salinized-alkalized grasslands, is not studied well. We conducted a randomized block manipulative experiment to evaluate the multilevel N addition (0, 5, 10, 20, 40 g N m− 2 year−1) on leaf photosynthesis properties and leaf WUE of the dominant species (Leymus chinensis (Trin.) Tzvelev) in the Songnen meadow steppe from 2016 to 2018. We have three key findings: (1) N availability increased photosynthetic and WUE properties, instantaneous WUE (Wi = A/E), intrinsic WUE (Wg = A/gs) and long-term WUE (WL) inferred from 13C composition, were all showed a non-linear increasing pattern in response to N availability; (2) N application decreased leaf mass per area and increased leaf total N content via enhancing soil inorganic N content, thus increased photosynthetic characteristics (e.g., A, E and gs), ultimately, promoted Wi and Wg; (3) N application enhanced WL was attributed to the N-induced improvement in Wi and Wg. Results of the present work are critical to our prediction of how meadow steppe dominated by L. chinensis will respond to severe N deposition in the future.

Climate change has become a concern, emphasizing the need for the development of crops tolerant to drought. Therefore, this study is designed to explore the physiological characteristics of quinoa that enable it to thrive under drought and other extreme stress conditions by investigating the combined effects of irrigation water levels (100%, 75%, and 50% of quinoa's water requirements, WR as I1, I2 and I3) and different planting methods (basin, on-ridge, and in-furrow as P1, P2 and P3) on quinoa's physiological traits and gas exchange. Results showed that quinoa’s yield is lowest with on-ridge planting and highest in the in-furrow planting method. Notably, the seed protein concentrations in I2 and I3 did not significantly differ but they were 25% higher than those obtained in I1, which highlighted the possibility of using a more effective irrigation method without compromising the seed quality. On the other hand, protein yield (PY) was lowest in P2 (mean of I1 and I2 as 257 kg ha −1 ) and highest in P3 (mean of I1 and I2 as 394 kg ha −1 , 53% higher). Interestingly, PY values were not significantly different in I1 and I2, but they were lower significantly in I3 by 28%, 27% and 20% in P1, P2, and P3, respectively. Essential plant characteristics including plant height, stem diameter, and panicle number were 6.1–16.7%, 6.4–24.5%, and 18.4–36.5% lower, respectively, in I2 and I3 than those in I1. The highest Leaf Area Index (LAI) value (5.34) was recorded in the in-furrow planting and I1, while the lowest value was observed in the on-ridge planting method and I3 (3.47). In I3, leaf temperature increased by an average of 2.5–3 o C, particularly during the anthesis stage. The results also showed that at a similar leaf water potential (LWP) higher yield and dry matter were obtained in the in-furrow planting compared to those obtained in the basin and on-ridge planting methods. The highest stomatal conductance (gs) value was observed within the in-furrow planting method and full irrigation (I1P3), while the lowest values were obtained in the on-ridge and 50%WR (I3P2). Finally, photosynthesis rate (An) reduction with diminishing LWP was mild, providing insights into quinoa’s adaptability to drought. In conclusion, considering the thorough evaluation of all the measured parameters, the study suggests using the in-furrow planting method with a 75%WR as the best approach for growing quinoa in arid and semi-arid regions to enhance production and resource efficiency.

Bamboo plantations are in high demand in the global market due to bamboo’s versatility and fast-growing nature. Dendrocalamus asper is one of the important species and is utilized in various industries, making it an economically valuable crop. Increasing yields while maintaining effective cost management is essential for planters. However, water stress possesses a significant challenge which can potentially disrupt bamboo growth and its physiological responses and thus the plant productivity. The objective of this study was to evaluate the growth and physiological responses of D. asper under different water treatments. A total of 45 seedlings were placed in a greenhouse and subjected to three different watering regimes at field capacity. The growth and physiological parameters including culm diameter, plant height, transpiration rate, photosynthesis rate, intercellular carbon dioxide concentration, and stomatal conductance were measured. The study showed that 100% of water capacity produced the best results for all the growth and physiological parameters measured. The reduction of water significantly reduced the growth of the seedlings, and the increment of water application beyond that point did not contribute to the increment of the plant growth. This indicates that excessive watering of bamboo did not improve growth performance, emphasizing the importance in optimizing water usage and conserving resources for economic sustainability.