Reduced mesophyll conductance by cell wall thickening and chloroplasts decreasing driven the decline of photosynthesis under sole NH4+ supply

The relationship between nitrogen (N) sources and photosynthetic capacity of leaf differs between species. However, the leaf anatomical variabilities related to photosynthesis (A) of shrubs under different forms of N remain imperfectly known. Here, Lonicera Japonica (a shrub) was grown hydroponically in the presence of three forms of N (sole NH4+, 50%/50% NH4+/NO3– and sole NO3–). A and photosynthetic N use efficiency significantly decreased under sole NH4+ supply, in parallel with down-regulated stomatal conductance (gs), mesophyll conductance (gm), and electron transfer rate (J). Up to the total A decline of 41.28% in sole NH4+ supply (compare with sole NO3–), the gm attributed to 60.3% of the total limitations. Besides, the decreased internal air space explained the increase of gas-phase resistance, and the increased liquid-phase resistance in sole NH4+ supply was ascribed to the thicker cell wall thickness (Tcw) and decreased chloroplasts exposed surface area per unit leaf area (Sc/S). The discrepancy of Sc/S could be interpreted by the altered chloroplasts numbers and the distance between adjacent chloroplasts (Dchl-chl). These results indicate the alteration of Tcw and chloroplast numbers were the main causes of the difference in gm in coping with varied N sources.

Phosphorus Acquisition and Utilization in Plants

Tremendous progress has been made on molecular aspects of plant phosphorus (P) nutrition, often without heeding information provided by soil scientists, ecophysiologists, and crop physiologists. This review suggests ways to integrate information from different disciplines. When soil P availability is very low, P-mobilizing strategies are more effective than mycorrhizal strategies. Soil parameters largely determine how much P roots can acquire from P-impoverished soil, and kinetic properties of P transporters are less important. Changes in the expression of P transporters avoid P toxicity. Plants vary widely in photosynthetic P-use efficiency, photosynthesis per unit leaf P. The challenge is to discover what the trade-offs are of different patterns of investment in P fractions. Less investment may save P, but are costs incurred? Are these costs acceptable for crops? These questions can be resolved only by the concerted action of scientists working at both molecular and physiological levels, rather than pursuing these problems independently. Expected final online publication date for the Annual Review of Plant Biology, Volume 73 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Revealing Soil and Tree Leaves Deposited Particulate Matter PTE Relationship and Potential Sources in Urban Environment

Trees play a pivotal role in improving urban environmental quality and provide several ecosystem services including the removal of pollutants from the air, such as particular matter (PM) and potentially toxic elements (PTE). Therefore, understanding the tree PM and PTE capturing potential, also in connection with plant species, is of great concern, especially in urban areas. This study aims to reveal the link between the elemental composition of PM deposited on tree leaves and soils PTE contents, as well as to rank the PM capturing efficiency of 10 different tree species growing under the impact of urban environments. This also allowed us to test the efficiency of PM deposited on tree leaves as a PTE biomonitoring and pollution source identification tool, in the two biggest urban areas of Armenia. Indeed, high contents of PTE are detected in both soil- and leaf-deposited PM from sites characterized by the presence of localized and active pollution sources (i.e., industrial unites, high traffic, etc.), which are identified by specific tracers (such as Mo, Cu, Zn, Pb, and Cd). Among the studied tree species, the highest PM amount per unit leaf area is observed for Platanus orientalis, but elm species are also identified as promising canditates to be considered for their PM removing potential, and need to be included in future more details studies.

Leaf surface characteristics affect the deposition and distribution of droplets in rice (Oryza sativa L.)

We studied the effects of leaf surface characteristics on canopy droplet behaviour using two rice cultivars with similar leaf shapes but significantly different leaf surface characteristics: Jia58 (glabrous rice; smooth leaf surface and no burrs) and Yongyou12 (hairy-leaved rice; rough leaf surface covered with burrs). The plants were subjected to spray tests with different spray pressures and nozzle apertures. The results showed that the deposition amount per unit leaf area was significantly higher in the Yongyou12 canopy than in the Jia58 canopy. The diameter, volume median diameter, number median diameter, and coverage of droplets were significantly higher in Yongyou12 than in Jia58, while the coverage density of droplets was significantly lower. The proportion of small droplets of Jia58 is higher than that of Yongyou12. Thus, a larger amount of large-sized droplets could retain on the leaf surface of hairy-leaved rice, and a larger number of small-sized droplets were retained on the leaf surface of glabrous rice. Smaller pressure and larger flow nozzle were conducive to the retention of the Jia58, while Yongyou12 required larger pressure and larger flow nozzles. Ultrastructural analyses revealed that the leaf surface of glabrous rice had no trichomes and more wax than hairy-leaved rice, and the critical surface tension was lower, resulting in the retention of mainly small droplets on its leaf surface and a lower deposition amount. Therefore, in order to increase the deposition of pesticide droplets on the leaf surface in production, glabrous rice should choose nozzles with smaller spray pressure and large flow rate.

Comparative analysis of the dust retention capacity and leaf microstructure of 11 Sophora japonica clones

We used fresh leaves of Sophora japonica L. variety ‘Qingyun 1’ (A0) and 10 superior clones of the same species (A1–A10) to explore leaf morphological characteristics and total particle retention per unit leaf area under natural and artificial simulated dust deposition treatments. Our objectives were to explore the relationship between the two methods and to assess particle size distribution, X-ray fluorescence (XRF) heavy metal content, and scanning electron and atomic force microscopy (SEM and AFM) characteristics of leaf surface microstructure. Using the membership function method, we evaluated the dust retention capacity of each clone based on the mean degree of membership of its dust retention index. Using correlation analysis, we selected leaf morphological and SEM and AFM indices related significantly to dust retention capacity. Sophora japonica showed excellent overall dust retention capacity, although this capacity differed among clones. A5 had the strongest overall retention capacity, A2 had the strongest retention capacity for PM2.5, A9 had the strongest retention capacity for PM2.5–10, A0 had the strongest retention capacity for PM>10, and A2 had the strongest specific surface area (SSA) and heavy metal adsorption capacity. Overall, A1 had the strongest comprehensive dust retention ability, A5 was intermediate, and A7 had the weakest capacity. Certain leaf morphological and SEM and AFM characteristic indices correlated significantly with the dust retention capacity.

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice

The source-sink relationship is key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in the source-sink relationship between a cultivated rice Oryza sativa cv. Nipponbare and a wild rice Oryza australiensis that show striking differences in biomass and grain yield. Oryza australiensis, accumulating higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves than Nipponbare. However, grain features and sugar levels suggested limited sucrose mobilization to the grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in Oryza australiensis stem utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, the source-sink relationship favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in the source-sink relationship between Nipponbare and Oryza australiensis.

CO 2 diffusion in tobacco: a link between mesophyll conductance and leaf anatomy

The partial pressure of CO 2 at the sites of carboxylation within chloroplasts depends on the conductance to CO 2 diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance ( g m ). We investigated how g m varies with leaf age and through a tobacco ( Nicotiana tabacum ) canopy by combining gas exchange and carbon isotope measurements using tunable diode laser spectroscopy. We combined these measurements with the anatomical characterization of leaves. CO 2 assimilation rate, A , and g m decreased as leaves aged and moved lower in the canopy and were linearly correlated. This was accompanied by large anatomical changes including an increase in leaf thickness. Chloroplast surface area exposed to the intercellular airspace per unit leaf area ( S c ) also decreased lower in the canopy. Older leaves had thicker mesophyll cell walls and g m was inversely proportional to cell wall thickness. We conclude that reduced g m of older leaves lower in the canopy was associated with a reduction in S c and a thickening of mesophyll cell walls.

Effect of leaf temperature on the estimation of photosynthetic and other traits of wheat leaves from hyperspectral reflectance

A growing number of leaf traits can be estimated from hyperspectral reflectance data. These include structural and compositional traits, such as leaf mass per area (LMA) and nitrogen and chlorophyll content, but also physiological traits such a Rubisco carboxylation activity, electron transport rate, and respiration rate. Since physiological traits vary with leaf temperature, how does this impact on predictions made from reflectance measurements? We investigated this with two wheat varieties, by repeatedly measuring each leaf through a sequence of temperatures imposed by varying the air temperature in a growth room. Leaf temperatures ranging from 20 °C to 35 °C did not alter the estimated Rubisco capacity normalized to 25 °C (Vcmax25), or chlorophyll or nitrogen contents per unit leaf area. Models estimating LMA and Vcmax25/N were both slightly influenced by leaf temperature: estimated LMA increased by 0.27% °C–1 and Vcmax25/N increased by 0.46% °C–1. A model estimating Rubisco activity closely followed variation associated with leaf temperature. Reflectance spectra change with leaf temperature and therefore contain a temperature signal.

Changes in Leaf Length, Width, Area, and Photosynthesis of Fruit Cucumber in a Greenhouse Production System

Changes in leaf length, width, area, weight, chlorophyll and carotenoids contents, and photosynthetic variables with different leaf positions were investigated in fruit cucumber. Plants were grown on rockwool slabs in an environmentally controlled greenhouse and irrigated by drip fertigation. Leaf measurements were conducted from the first to the 15th leaf (the oldest to the youngest). The results showed that fresh weight per unit leaf area decreased from the second to the 15th leaf. Changes in cucumber leaf length, width, and area followed quadratic models from the first to the 15th leaf. The quadratic models of leaf length, width, and area fit the measurements well, with R2 values of 0.925, 0.951, and 0.955, respectively. The leaf chlorophyll a and b and carotenoid contents increased from the oldest leaf (first leaf) to the youngest leaf and decreased after reaching the highest values. Changes in the net photosynthetic rate (Pn) also followed the quadratic model from the first to the 15th leaf, with R2 values of 0.975. The leaf transpiration rate (Tr) increased from the first to the 14th leaf. Our results revealed patterns in leaf growth and photosynthetic changes at different leaf positions in fruit cucumber and improved our understanding of the growth and development of fruit cucumber in the greenhouse production system.

Spatial Modeling of Maximum Capacity Values of Irrecoverable Rainfall Retention by Forests in a Small Watershed

When performing hydrologic calculations, the actual amount of rain precipitation falling under the tree canopies of the taiga zone is one of the most important factors in forming and estimating rainfall runoff. This is due to the fact that only a portion of rainfall reaching the soil through the forest canopy takes part in forming river runoff. At present, there is no unanimity on methods of estimating rainfall retention by the canopies of different tree species in various natural geographical zones. The existing estimation methods rely on empirical observations of net and gross rainfall rather than on the results of physical modeling of moisture on leaf surfaces in droplet form. The disadvantages of the existing methods mean that it is not possible to make a spatial estimation of rainfall captured by canopies. The purpose of this study was to map the maximum rainfall interception capacity for a small forest watershed. The authors were able to solve the following problems: (1) In situ modeling of specific water retention in droplet form on leaf surfaces of tree species of the experimental watershed in the middle taiga subzone was carried out and the specific water retention per unit leaf area was determined. Such experiments have never been conducted previously. (2) Indirect methods of estimating the leaf surface area of tree plants depending on the amount of phytomass, age and height of tree stands were developed. (3) Mapping of tree stand characteristics (such as species composition, height, canopy cover) were performed, and together with the specific rainfall interception capacity, which was determined during experiments, provided the basis for a map of maximum rainfall retention capacity by canopies, i.e., a spatial image of irrecoverable rainfall losses was obtained. Rainfall is retained on a canopy in droplet form (droplet size varies from 10.6 to 18.6 mg). Specific water retention (mass per unit leaf surface area) is determined by the leaf (needle) roughness. The overall droplet retention on canopies is determined by leaf surface area and precipitation intensity. The maximum mass of the rainfall retained on the canopies of individual deciduous trees reaches 77 kg, (3.0–4.0 mm per canopy projection area) and that of coniferous trees ranges from 24.8 to 58.0 kg (1.9 to 5.9 mm). Understanding rainfall loss values in hydrology is of key importance in distributed models of rainfall flooding. Taking into account rainfall losses due to canopy interception makes it possible to reduce the margin of error in calculations of maximum rainfall flood loss from 126% to 25%.