Neighbour sensing through rhizodeposits in sorghum affects plant physiology and productivity

An attempt was made to differentiate between the possible effects of high Cl- or Na+ ions on lemon leaf photosynthesis by treating grafted (Citrus limon (L.) Burm. f. cv. 'Taylor') plants with either NaCl or Na2SO4 to establish different foliar concentrations of Cl- or Na+. The rootstocks, Rangpur lime (C. reticulata var. austera hybrid?) and rough lemon (C. jambhiri), were chosen because Rangpur lime is known to be a good Cl- 'excluder' and rough lemon to be a poor Cl- 'excluder'. The grafted plants were initially treated for 7 weeks with nutrient solution (control) or nutrient solution containing 50 mol m-3 NaCl or 25 mol m-3 Na2SO4, after which time there were only marginal reductions in both photosynthetic rates and shoot growth, with the exception of 'Taylor' lemon on rough lemon roostock treated with NaCl where growth was affected more severely than the other treatments. Salinity levels were then doubled to 100 mol m-3 NaCl and 50 mol m-3 Na2SO4 and the plants treated for a further 8 weeks, causing significant increases in leaf Na+ and/or Cl- concentrations. Mature, 3-4-month-old leaves of 'Taylor' lemon on Rangpur lime rootstock treated with Na2SO4 for this period, contained c. 105 mol m-3 Na+ and c. 10 mol m-3 Cl- and had photosynthetic rates 60% lower than controls. Similar reductions in assimilation rate were seen in leaves on rough lemon roostock treated with NaCl containing c. 195 mol m-3 Cl- and c. 35 mol m-3 Na+. Smaller (35%) but significant reductions in assimilation rate were observed for trees on rough lemon roostock treated with Na2SO4, where the tagged leaves contained c. 40 mol m-3 Na+ and 50 mol m-3 SO42-. Leaf nitrogen concentrations were significantly reduced by treatment of trees with NaCl or Na2SO4 but, apart from small reductions in chlorophyll concentrations, there were no visible symptoms of nitrogen deficiency. Leaf turgor was not adversely affected. The data indicate that both Cl- and Na+ can reduce assimilation rates in salt-stressed lemon leaves, possibly because of poor compartmentation within leaves of either ion. Increases in leaf Na+ and Cl- accounted for 54-96% of the reduction in osmotic potential in 'Taylor' lemon leaves on trees treated with NaCl, whereas increases in Na+ and SO42- accounted for 33-71% of the reduction in osmotic potential in leaves on trees irrigated with Na2SO4. The greater increase in Cl- compared with the net increase of [Na+ + K+] in 'Taylor' leaves on rough lemon rootstocks was offset (65%) by reductions in malic and succinic acids. Proline increased significantly only in 'Taylor' leaves on Rangpur lime roostock treated with Na2SO4.

As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root‐permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root‐permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap‐rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd.

Environmental conditions influence phenology and physiological processes of plants. It is common for maize and sorghum to be sown at two different periods: the first cropping (spring/summer) and the second cropping (autumn/winter). The phenological cycle of these crops varies greatly according to the planting season, and it is necessary to characterize the growth and development to facilitate the selection of the species best adapted to the environment. The aim of this study was to characterize phenological phases and physiological parameters in sorghum and maize plants as a function of environmental conditions from the first cropping and second cropping periods. Two parallel experiments were conducted with both crops. The phenological characterization was based on growth analyses (plant height, leaf area and photoassimilate partitioning) and gas exchange evaluations (net assimilation rate, stomatal conductance, transpiration and water‐use efficiency). It was found that the vegetative stage (VS) for sorghum and maize plants was 7 and 21 days, respectively, longer when cultivated during the second cropping. In the first cropping, the plants were taller than in the second cropping, regardless of the crop. The stomatal conductance of sorghum plants fluctuated in the second cropping during the development period, while maize plants showed decreasing linear behaviour. Water‐use efficiency in sorghum plants was higher during the second cropping compared with the first cropping. In maize plants, in the second cropping, the water‐use efficiency showed a slight variation in relation to the first cropping. It was concluded that the environmental conditions as degree‐days, temperature, photoperiod and pluvial precipitation influence the phenology and physiology of both crops during the first and the second cropping periods, specifically cycle duration, plant height, leaf area, net assimilation rate, stomatal conductance and water‐use efficiency, indicating that both crops respond differentially to environmental changes during the growing season.

An experiment was conducted at the research farm of ICAR-Indian Agricultural Research Institute, New Delhi during 2020 and 2021 to study the genotypic differences in root architecture and physiological characteristics in mango (Mangifera indica L.) under drought. One-year-old polyembryonic 7 mango rootstock genotypes were exposed to normal irrigation and drought conditions for 24 days. The drought-induced increased total plant weight and dry weight in Kurukkan. The shoot dry weight decreased in all genotypes ranging from 5.13% in OLP-Z-6/1 to 81.82% in Kurukkan. There was a lesser reduction in membrane stability index in Kurukkan and K-5, stomata count in Kurukkan, Olour and OPK-3-7/12 at the end of the drought period. Root surface area increased under drought in Kurukkan, while it decreased more in K-5. Correlation studies confirmed a strong positive relationship between relative water content (RWC) and membrane stability index (MSI), number of stomata (SC), number of leaves (NL), root tips (RT) and root forks (NRF); MSI and number of root tips (NRT); dry weight of the whole plant and root surface area (RSA); the dry weight of roots and root volume (RV), RSA, and plant height (Ph); root length (RL) and RSA, RT, and NRF. Kurukkan was identified as drought-tolerant based on a higher SC, RWC, RV, RSA, dry mass, NRT and NRF. Results indicated that the root indices offer a promising strategy for the screening of drought-tolerant mango genotypes.

ISHS IV Balkan Symposium on Vegetables and Potatoes THE EFFECTS OF N CONCENTRATION IN PRE-TRANSPLANT NUTRIENT SOLUTION ON THE N USE EFFICIENCY AND DRY MASS PARTITIONING OF VEGETABLE SOLANACEAE SEEDLINGS

In this study, the effects of Striga hermonthica (Del.) Benth. on a sensitive and a tolerant sorghum genotype were investigated, and the underlying tolerance mechanisms were distinguished. The sensitive sorghum cv. CK60‐B and the tolerant sorghum landrace Tiemarifing were grown in pots with and without seed infestation. Both sorghum genotypes responded to infection by the parasite, but it was evident that CK60‐B was more strongly affected than Tiemarifing. Sorghum plant height, final leaf number, green leaf area, kernel yield, number of kernels and 1000‐kernel weight were significantly reduced by infection, which also had a marked effect on the phenological development of CK60‐B; the majority of the plants remained vegetative and, in the remaining plants, flowering was delayed by about 2 weeks. No effect on the phenological development of Tiemarifing was observed. The tolerant landrace showed significantly lower and delayed emergence of S. hermonthica than the sensitive cultivar, and this could be explained by a delay in the onset of attachment. Significantly higher numbers of reproductive parasitic plants were found in the pots with the sensitive sorghum plants. It is concluded that differences in root architecture and the resulting early infection and higher S. hermonthica numbers are partly responsible for the stronger effects of the parasite on the sensitive cultivar.

ABSTRACTRoot architectural traits are of fundamental importance for plant performance, especially under unfavorable soil conditions. This study examined the effect of aluminum (Al) toxicity in different growing media (nutrient solutions and soil) on root architecture of two wheat (Triticum aestivum L.) cultivars with different Al tolerances. Seedlings were grown in acidic and limed soil and in two contrasting nutrient solutions. Root systems of soil-grown plants were scanned using x-ray microcomputed tomography (µCT) while that of nutrient solution–grown plants were assesses using WinRhizo, 3 and 5 days after planting (DAP), respectively. Aluminum caused significant reduction of all examined root traits (number of seminal roots, root length, length of the longest seminal root, root surface area, and root volume). Growth in acidic soil caused significant reduction in root length, length of the longest seminal root, and root surface area at 5 DAP. Soil-grown plants produced a larger root system compared to plants grown in nutrient solutions. Aluminum toxicity–induced differences of root traits were also found between different nutrient solutions. Beside the well-known reduction of root length, Al toxicity had a profound effect on other root architectural traits. X-ray µCT has revealed root architectural changes under specific conditions of acidic, Al-toxic soil. Differences obtained in Al-induced effects on root architecture between different nutrient solutions as well as between different growing systems emphasize the need for further study of root architecture, especially under specific conditions of Al toxicity in acidic soils.

Impacts of drought stress on water relations and carbon assimilation in grassland species at different altitudes

Different methods of silicon application attenuate salt stress in sorghum and sunflower by modifying the antioxidative defense mechanism

Will nutrient-efficient genotypes mine the soil? Effects of genetic differences in root architecture in common bean ( Phaseolus vulgaris L.) on soil phosphorus depletion in a low-input agro-ecosystem in Central America

The daily (24 hour) changes in carbon balance, water loss, and leaf area of whole sorghum plants (Sorghum bicolor L. Moench, cv BTX616) were measured under controlled environment conditions typical of warm, humid, sunny days. Plants were either (a) irrigated frequently with nutrient solution (osmotic potential -0.08 kilojoules per kilogram = -0.8 bar), (b) not irrigated for 15 days, (c) irrigated frequently with moderately saline nutrient (80 millimoles NaCl + 20 millimoles CaCl(2).2H(2)O per kilogram water, osmotic potential -0.56 kilojoules per kilogram), or (d) preirrigated with saline nutrient and then not irrigated for 22 days.Under frequent irrigation, salt reduced leaf expansion and carbon gain, but water use efficiency was increased since the water loss rate was reduced more than the carbon gain. Water stress developed more slowly in the salinized plants and they were able to adjust osmotically by a greater amount. Leaf expansion and carbon gain continued down to lower leaf water potentials.Some additional metabolic cost associated with salt stress was detected, but under water stress this was balanced by the reduced cost of storing photosynthate rather than converting it to new biomass. Reirrigation produced a burst of respiration associated with renewed synthesis of biomass from stored photosynthate.It is concluded that although irrigation of sorghum with moderately saline water inhibits plant growth in comparison with irrigation with nonsaline water, it also inhibits water loss and allows a greater degree of osmotic adjustment, so that the plants are able to continue growing longer and reach lower leaf water potentials between irrigations.

Abstract:A major reason for the drought susceptibility of cultivated rice is the inability to regulate water loss as effectively as other cereals. We report studies of growth and gas exchange under well‐watered and water‐limiting conditions on selected species of Oryza and seek to relate this physiological information to the ecology of the genus. The immediate ancestor of the Oryza sativa cultigen is native to swamps and marshes, and wet habitats are typical for the genus as a whole. However, the ecological range of some species does extend to habitats that dry out seasonally. In all species studied growth was reduced by water deficit. In all species studied leaves had small absolute water contents and began to roll at a relative water content above 90%. However, there were species differences in leaf rolling and the response of stomatal conductance to an increase in vapour pressure deficit. Following re‐watering, there were persistent reductions in stomatal conductance in most of the species tested, but the assimilation rate was not reduced in all of these cases. Where there was a persistant reduction in assimilation rate, there was also a reduction in carboxylation efficiency. It was a frequent observation that plants had a stomatal conductance greater than expected for their carbon assimilation rate; that is in the range where substantial changes in conductance have little effect upon photosynthesis. It is suggested that a reason for this may be the cooling of leaves which have a small thermal capacity in environments which often combine high temperature, humidity and irradiance. Large conductances combined with small water contents may be no disadvantage in the natural habitats of Oryza, but provide some reasons for the poor regulation of water loss in cultivated rice. Although there were significant differences in gas exchange amongst species the advantages that were observed over O. sativa were not of a magnitude likely to justify wide hybridisation. This implies that improvement in the drought resistance of rice is more likely to come from increasing water acquisition than from decreasing water loss.

N AND CA CONCENTRATION OF PRE TRANSPLANT NUTRIENT SOLUTION EFFECTS ON THE STAND ESTABLISHMENT RATE OF PEPPER (C. ANNUM. L) SEEDLINGS UNDER SALINE CONDITIONS

Photosynthetic activity decreases when plants are grown under saline conditions leading to reduced growth and productivity. Leaf growth, gas exchange, and chlorophyll fluorescence of two sorghum [Sorghum bicolor (L.) Moench] varieties, Serena and Seredo, were measured in response to increasing NaCl concentration. Sorghum plants were grown in sand culture under controlled greenhouse conditions. The NaCl concentrations in complete nutrient solution were 0 (control), 50, 100, 150, 200, and 250 mM Salinity significantly (P ≤ 0.01) reduced leaf area by about 86% for both varieties of sorghum. Chlorophyll a and b, net CO2 assimilation, stomatal conductance, and transpiration rate decreased significantly (P ≤ 0.01) with the increase in salinity, and these decreases were similar for the two sorghum varieties. Salt induced decreases for these physiological traits ranged from 75 to 94%. Photochemical efficiency of PSII (Fv/Fm) and photochemical quenching coefficient (qP) decreased by about 9 and 10%, respectively, for both varieties, and electron transport rate (ETR) decreased by 20 and 25% for Serena and Seredo. In contrast, non‐photochemical quenching (NPQ) significantly (P ≤ 0.01) increased by 44 and 50% for Serena and Seredo. The results indicate that salinity affected photosynthesis per unit leaf area indirectly through stomatal closure, and to a smaller extent through direct interference with the photosynthetic apparatus. In addition, salinity decreases whole plant photosynthesis by restricting leaf area expansion. This effect starts from low levels of salinity, in contrast to that of net photosynthesis per unit leaf area, which occurs at higher levels of NaCl concentration.

Effects of P and K fertilization on Tabasco plant growth and fruit quality were evaluated in a preliminary experiment conducted in fall 2002; 4 levels of P (0.25, 1.0, 1.75, and 2.5 mM) and 4 levels of K (0.75, 1.75, 2.75, and 3.75 mM) in hydroponic culture with a factorial randomized design. The main growth experiment was conducted in spring/summer growing period of 2003. This experiment consisted of 8 treatments; 4 levels of P (P1 0.25, P2 1.25, P3 2.5, and P4 3.75 mM) and 4 levels of K (K1 0.25, K2 1.25, K3 2.5, and K4 3.75 mM). The same treatments were used to evaluate fruit quality characteristics in an experiment conducted simultaneously. Tabasco pepper "McIlhenny Select" seed were sown in trays; at the fourth true leaf stage, individual plants were transplanted into 3-gallon round plastic pots filled with agricultural grade perlite. Plants were harvested once every month; stem diameter and plant measurements were taken every fifteen days. The Preliminary growth experiment showed that P affected plant height, leaf area, root, stem and leaf dry weights as well as overall plant dry weight. Potassium affected root dry weight at both harvests with no influence on other growth variables. Dry root weights of plants grown with the highest K rate (K4) were significantly higher than the lowest k rate (K1). Potassium source was changed for the main plant growth experiment. Phosphorus and potassium rates significantly affected plant growth, increasing height, weight, stem diameter, leaf area, and dry weights of plant sections with increasing rates in nutrient solution. For fruit quality experiment, all plants grew until the flowering stage with the same nutrient solution (2 mM P; and 3.75 mM K). At the beginning of the flowering stage different nutrient treatments were applied. Increasing P and K rates also affected plant yield and some fruit quality variables. Results were consistent for most of the variables, suggesting that the 0.25 mM concentration for both P and K was insufficient for pepper production. Concentrations higher than 1.25 mM and close to 2.5 mM are the most appropriate for hydroponic tabasco pepper production.