Application of K and Zn Influences the Mineral Accumulation More in Hybrid Than Inbred Maize Cultivars.

Maize (Zea mays L.) is an important crop used for feeding humans and cattle globally. Deficiency of potassium (K) and zinc (Zn) adversely impacts the maize crop productivity and quality. However, the application of these nutrients shows variant responses in different maize cultivars. To understand this perspective, the current study aimed at investigating K and Zn's optimal concentration in different hybrid and inbred maize cultivars. The treatments were based on three zinc levels (0, 6, and 12 mg Zn kg-1) and K levels (0, 30, and 60 mg kg-1), and their respective combinations. The experiment results showed that combined fertilization approaches of Zn and K (Zn12K60) improved the plant biometric, and physiological attributes of maize crop. The results revealed a significant increase in plant height (45%), fresh weight (70%), and dry weight (45%). Similarly, physiological attributes significantly improved the relative water content (76.4%), membrane stability index (77.9%), chlorophyll contents (170%), and photosynthetic rate (130%) in both inbred and hybrid genotypes. Furthermore, Zn and K (Zn12K60) increased transpiration rate (E), stomatal conductance (Ci), and internal CO2. In conclusion, maize hybrids (Neelam and DK-6142) were observed best compared with inbred (Afghoi and P-1543) cultivars with the combined application of Zn and K (Zn12K60). Thus, these inbred varieties should be preferred for fodder requirement with optimum fertilizer (Zn12K60) application in Zn deficient soils.

Limiting-Stress-Elimination Hypothesis: Using Non-hormonal Biostimulant to Reduce Stress and Increase Savanna Cowpea [Vigna unguiculata (L.) Walp.] Productivity.

An alternative decision axiom to guide in determining the optimal intervention strategy to maximize cowpea production is proposed. According to the decrement from the maximum concept of Mitscherlich, the decrement from the maximum for each stressor must be minimized to produce the absolute maximum production. In crop production, this means all deficient nutrients must be supplemented to ensure maximum yield and laid the foundation in fertilizer formulation. However, its implementation is not economically feasible in many situations, particularly where multiple environmental factors impact crop productivity as in the case of low resource conditions. We propose and test the hypothesis that yield allocation will increase when the most limiting stressor among prevailing stressors is eliminated at least until the next limiting stressor impacts productivity. We selected drought limiting savanna conditions and cowpea (Vigna unguiculata), adapted to nitrogen dependence. To determine the limiting condition, we measured the response of cowpea to D-sorbitol, nitrogen, and non-hormonal biostimulant (nhB) treatments. The nhB treatment increased total biomass by 45% compared to nitrogen, 13%, and D-sorbitol, 17%, suggesting osmotic stress is more limiting in the observed savanna conditions. The effect of the biostimulant is due to antioxidants and key amino acids that stimulate metabolism and stress resistance. Where nitrogen becomes the next constraining factor, biostimulants can contribute organic nitrogen. The study supports the use of biostimulants as candidate intervention under conditions where crop productivity is limited by multiple or alternating constraints during crop growth.

Estimation of short-term C-fixation in a New England temperate tidal freshwater wetland.

Wetlands provide myriad ecosystem services, yet the C-cycling of vegetation within interior freshwater tidal wetlands remains poorly understood. To this end, we estimated species'-specific plant carbon-fixation rates for the six dominant wetland plant species in a large temperate freshwater wetland in Connecticut, USA. We integrated field C-fixation rates for dominant marsh plant species with satellite-derived leaf area index and wetland aerial extent data to: 1) quantify seasonal and species-level differences in wetland plant C-fixation rates; and 2) estimate whole-marsh emergent aquatic plant C-fixation rates over the growing season. Photosynthetic rates differed significantly by species and month (P < 0.05). Acorus calamus had the highest photosynthetic rate between May and September, and Acer saccharinum had the lowest. By integrating field photosynthetic data with wetland aerial extents, we estimated that the total annual C uptake by the vegetation in this wetland, which was 2868 Mg C. Herbaceous vegetation contributed to most of that stock (herbaceous vegetation = 2099.2 Mg C, forest = 769.6 Mg C), although soil respiration likely offset those numbers substantially. Our results demonstrate the importance of short-term above-ground freshwater wetland C-fixation, and that the emergent vegetative component of these wetland systems are key components of the tidal freshwater wetland C cycle.

Gulf of Mexico estuarine blue carbon stock, extent and flux: Mangroves, marshes, and seagrasses: A North American hotspot.

The Gulf of Mexico blue carbon habitats (mangroves, seagrass, and salt marshes) form an important North American blue carbon hot spot. These habitats cover 2,161,446 ha and grow profusely in estuaries that occupy 38,000 km2 to store substantial sedimentary organic carbon of 480.48 Tg C. New investigations around GoM for Mexican mangroves, Louisiana salt marshes and seagrasses motivated our integration of buried organic carbon to elucidate a new estimate of GoM blue carbon stocks. Factors creating this include: large GoM watersheds enriching carbon slowly flowing through shallow estuarine habitats with long residence times; fewer SE Mexican hurricanes allowing enhanced carbon storage; mangrove carbon productivity enhanced by warm southern basin winter temperatures; large Preservation reserves amongst high anthropogenic development. The dominant total GoM mangrove blue carbon stock 196.88 Tg from total mangrove extent 650,482 ha is highlighted from new Mexican data. Mexican mangrove organic carbon stock is 112.74 Tg (1st sediment meter) plus USA 84.14 Tg. Mexican mangroves vary greatly in storage, total carbon depositional depths and in sediment age (to 3500 y). We report Mexican mangrove's conservative storage fraction for the normally-compared top meter, whereas the full storage depth estimates ranging above 366.78 Tg (high productivity in very deep sediment along the central Veracruz/Tabasco coast) are not reflected in our reported estimates. Seagrasses stock of 184.1 Tg C organic is derived from 972,327 ha areal extent (in 1st meter). The Louisiana marshes form the heart of GoM salt marsh carbon storage 99.5 Tg (in 1st meter), followed by lesser stocks in Florida, Texas, finally Mexico derived from salt marsh extent totaling 650,482 ha. Constraints on the partial estuarine fluxes given for this new data are discussed as well as widespread anthropogenic destruction of the GoM blue carbon. A new North American comparison of our GoM blue carbon stocks versus Atlantic coastal blue carbon stock estimates is presented.

Seagrass blue carbon dynamics in the Gulf of Mexico: Stocks, losses from anthropogenic disturbance, and gains through seagrass restoration.

Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimentary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (Corg) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n=128 cores). Mean natural seagrass Corg stocks were 25.7±6.7MgCorgha-1 around the GoM, while mean Corg stocks at adjacent barren sites that had previously hosted seagrass were 17.8MgCorgha-1. Restored seagrass beds contained a mean of 38.7±13.1MgCorgha-1. Mean Corg losses differed by anthropogenic impact type, but averaged 20.98±7.14MgCorgha-1. Corg gains from seagrass restoration averaged 20.96±8.59Mgha-1. These results, when combined with the similarity between natural and restored Corg content, highlight the potential of seagrass restoration for mitigating seagrass Corg losses from prior impact events. Our GoM basin-wide estimates of natural Corg totaled ~36.4Tg for the 947,327ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2-37.5Tg Corg. Regional US-GoM losses totaled 21.69Tg Corg. Corg losses differed significantly among anthropogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.

Pollutant tracking for 3 Western North Atlantic sea grasses by remote sensing: Preliminary diminishing white light responses of Thalassia testudinum, Halodule wrightii, and Zostera marina.

Sea grasses are foundation species for estuarine ecosystems. The available light for sea grasses diminishes rapidly during pollutant spills, effluent releases, disturbances such as intense riverine input, and tidal changes. We studied how sea grasses' remote-sensing signatures and light-capturing ability respond to short term light alterations. In vivo responses were measured over the entire visible-light spectra to diminishing white-light on whole-living-plants' spectral reflectance, including 6h of full oceanic-light fluences from 10% to 100%. We analyzed differences by various reflectance indices. We compared the sea grasses species responses of tropical vs. temperate and intertidals (Halodule wrightii, and Zostera marina) vs. subtidal (Thalassia testudinum). Reflectance diminished with decreasing light intensity that coincided with greater accessory pigment stimulation (anthocyanin, carotenoids, xanthins). Chlorophyll a and Chlorophyll b differed significantly among species (Thalassia vs. Halodule). Photosynthetic efficiency diminished at high light intensities. The NDVI index was inadequate to perceive these differences. Our results demonstrate the leaf-level utility of data to remote sensing for mapping sea grass and sea grass stress.

Changing gears during succession: shifting functional strategies in young tropical secondary forests.

Adaptations to resource availability strongly shape patterns of community composition along successional gradients in environmental conditions. In the present study, we examined the extent to which variation in functional composition explains shifts in trait-based functional strategies in young tropical secondary forests during the most dynamic stage of succession (0-20 years). Functional composition of two size classes in 51 secondary forest plots was determined using community-weighted means of seven functional traits, which were intensively measured on 55 woody plant species (n = 875-1,761 individuals). Along the successional gradient in forest structure, there was a significant and consistent shift in functional strategies from resource acquisition to resource conservation. Leaf toughness and adult plant size increased significantly, while net photosynthetic capacity (A(mass)) decreased significantly during succession. Shifts in functional strategies within size classes for A(mass) and wood density also support the hypothesis that changes in functional composition are shaped by environmental conditions along successional gradients. In general, 'hard' functional traits, e.g., A(mass) and leaf toughness, linked to different facets of plant performance exhibited greater sensitivity to successional changes in forest structure than 'soft' traits, such as leaf mass area and leaf dry matter content. Our results also suggested that stochastic processes related to previous land-use history, dispersal limitation, and abiotic factors explained variation in functional composition beyond that attributed to deterministic shifts in functional strategies. Further data on seed dispersal vectors and distance and landscape configuration are needed to improve current mechanistic models of succession in tropical secondary forests.

Reflectance of Alaskan black spruce and white spruce foliage in relation to elevation and latitude.

Leaf reflectance at visible and near-infrared wavelengths (400-1000 nm) is related primarily to pigmentation, leaf structure and water content, and is an important tool for studying stress physiology and relationships between plants and their growth environment. We studied reflectance of two co-occurring Alaskan conifers, black spruce (Picea mariana (Mill.) BSP) and white spruce (Picea glauca (Moench) Voss), at elevations from 60 to 930 m a.s.l. along a latitudinal gradient from 61 degrees to 68 degrees N. Black spruce samples were collected from 24 sites and white spruce from 30 sites. Overall, reflectance spectra of the two species were similar, but from 400 to 700 nm, needle reflectance was consistently higher in black spruce than in white spruce (all P

Changes in foliar spectral reflectance and chlorophyll fluorescence of four temperate species following branch cutting.

Spectral reflectance and chlorophyll fluorescence are rapid non-invasive methods that can be used to quantify plant stress. Because variation in ambient light (e.g., diurnal patterns of solar radiation) may have a confounding effect on these measurements, branches are often excised in the field and then measured under controlled conditions in the laboratory. We studied four temperate tree species (Abies balsamea (L.) Mill. (balsam fir), Betula papyrifera var. cordifolia (Regel) Fern. (paper birch), Picea rubens Sarg. (red spruce) and Sorbus americana Marsh. (mountain-ash)) to determine how quickly reflectance and fluorescence change following branch cutting. We hypothesized that conifer species, which have tough xeromorphic foliage, would exhibit changes more slowly than broadleaf species. Furthermore, we hypothesized that keeping broadleaf samples cool and moist would delay the onset of reflectance and fluorescence changes. In one set of experiments, we did not use any treatments to maintain the freshness of cut branches. During the first 12 h following cutting, changes in reflectance and fluorescence were slight for all species. Two or 3 days after branch cutting, the two conifers still showed only small changes in the ratio of variable to maximum fluorescence (Fv/Fm) and most reflectance indices, whereas paper birch and mountain-ash showed larger and more rapid declines in Fv/Fm and most reflectance indices. We attribute these declines to loss of water. As a consequence of xeromorphic leaf structure, the conifers were better able to minimize water loss than the two broadleaf species. In another experiment, paper birch that had been kept cool and moist after cutting showed only slight changes in fluorescence and reflectance, even after 3 days, indicating that with careful handling the time interval between collection and measurement of reflectance and fluorescence of many broadleaf specimens can be extended to several days. We conclude that measurements of reflectance and fluorescence need not be made in situ to be accurate and reliable.

Spectral reflectance and photosynthetic properties of Betula papyrifera (Betulaceae) leaves along an elevational gradient on Mt. Mansfield, Vermont, USA.

We studied relationships between spectral reflectance and photosynthesis of mountain paper birch, Betula papyrifera var. cordifolia (Regel) Fern., leaves from three different elevations on Mt. Mansfield (summit elevation 1339 m above sea level) in the Green Mountains of Vermont, USA. The different reflectance indices we used all suggested progressively increasing stress with increasing elevation. The photochemical reflectance index (PRI) indicated lower photosynthetic radiation use efficiency at higher elevations, the red edge position (λRE) indicated lower chlorophyll concentrations at higher elevations, and the structure-independent pigment index (SIPI) indicated a higher carotenoid : chlorophyll a ratio at higher elevations. The rate of change in these indices with changes in elevation was much higher than we have observed in our studies of red spruce and balsam fir reflectance along a similar elevational gradient; we take this to be an indicator of the greater susceptibility of paper birch to elevation-related stressors compared to the very stress-tolerant conifers. At all light levels, photosynthesis decreased with increasing elevation; this pattern was most noticeable in the light-saturated rate of photosynthesis (A(sat)), which was nearly twice as high in low-elevation leaves (17.0 ± 1.0 µmol·m(-2)·s(-1)) than in high-elevation leaves. The quantum yield of photosynthesis (Φ) exhibited a similar trend. Furthermore, the highest elevation leaves showed a much sharper transition from the light-limited to the light-saturated part of the light response curve than did the lowest elevation leaves. The photochemical reflectance index was highly correlated with A(sat) (r(2) = 0.99) and Φ (r(2) = 0.96). In addition to contributing to our knowledge of the ecophysiology of paper birch along a steep environmental gradient, these results are further evidence of the usefulness of reflectance measures for the rapid and noninvasive detection of plant stress, especially when used in conjunction with direct measurements of photosynthesis.