Large Pots Research Articles

Growth responses of seedlings of early and late successional tropical forest trees to elevated atmospheric CO2

Seedlings of nine tropical forest tree species were grown outdoors in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations at the Smithsonian Tropical Research Institute, Republic of Panama. Plants were kept individually in large pots and received non-limiting supplies of water and mineral nutrients. The enhancement of biomass accumulation at elevated CO2 increased with increasing relative growth rates (RGR) of species at ambient CO2. Early successional pioneer trees (Cecropia longipes, Ficus insipida, Castilla elastica, Antirrhoea trichantha, Luehea seemannii, Pseudobombax septenatum) grew rapidly, and, at the end of 25 to 39 day treatments, dry matter accumulation was 74 +/- 26% higher at elevated than at ambient CO2 (mean increase +/- SD, n = 6). By contrast, seedlings of three late successional tree species (Calophyllum longifolium, Tetragastris panamensis, Virola surinamensis) grew slowly and, over an 84 day period, elevated CO2 led to either no (C. longifolium, T. panamensis) or only small enhancement in dry matter accumulation (V. surinamensis). These different responses to CO2 enrichment are a result of differences in growth kinetics between early and late successional species at ambient CO2 rather than a result of intrinsic physiological differences in CO2 responsiveness between plants from these two functional groups.

Limitations to Seedling Growth and Survival by the Quantity and Quality of Rooting Space: Implications for the Establishment ofThuja occidentalison Cliff Faces

Thuja occidentalis is the dominant tree of ancient, stunted cliff‐face forests of the Niagara Escarpment, Ontario, Canada, and in Michigan and Wisconsin, U.S.A. Previous field research has shown that nutrient and water limitations at the sapling stage are absent or small, yet seedling recruitment is relatively rare. To study the relationships between rooting space, nutrient supply, growth, and survival in very young seedlings, plants were grown from seed in three pot volumes (1 mL, 10 mL, and 100 mL) and under three nutrient regimes (watering with water, one‐tenth‐strength Hoagland's solution, and half‐strength Hoagland's solution). Elongation of the main axis and side branches was measured, and survival also was monitored over 2 yr. All measures of seedling growth were significantly increased by higher nutrient levels. Effects of pot size on growth were smaller and less consistent; main axis elongation tended to be greatest in the smallest pots, but branch elongation was not affected. Survival results showed trends opposite to those for growth; higher levels of nutrients did not influence seedling survival, but survival was slightly better in larger pots than in small and intermediate pots. When averaged over all treatments, 61% of seedlings survived to the end of year 1 and 14% to the end of year 2. By the beginning of the third year only 0.1% were alive and all were in large pots. The results indicate that an uncoupling of the relationship between growth and survival is possible in an environment where intraspecific competitive interactions are muted. Survival of trees on cliffs may therefore be unrelated to tree growth and may instead be primarily controlled by the chance of finding safe sites with adequate rooting volume.

Comparison of Measurement Methods of Osmotic Adjustment in Rice Cultivars

Osmotic adjustmen(OA)is a major component of drought resistance. Four different methods for measuring OA in plants are in general use, but there is no information on the comparative performance of these methods. Two similar experiments were designed to evaluate the four methods for measuring OA in diverse indica and japonica cultivars of rice (Oryza sativa L.) subjected to a drying cycle in large pots in the greenhouse. The four methods were:(i) derivation of OA from regressions of leaf relative water content (RWC) on leaf osmotic potential(OP);(ii) estimation of OA from OP of stressed plants calculated to rehydrated state; (iii) estimation of OA from OP of stressed plants that have been rehydrated; and( iv) estimation (from data used in Metho 1) of OA capacity by the sustained RWC at given OP of −3.5 MPa. Method 1 was a priori considered as the best estimate. Under relatively mild atmospherci conditions and a slow development of water deficit (first experiment), mean OA over cultivars was 0.89, 0.51, and 0.72MPa by Methods 1, 2, and 3, respectively. Mean RWC at −3.5 MPa was 6 9.3%. Significant(P ≤ 0.05) variation in OA among cultivars was observed by all methods, up to a four‐fold difference in OA among cultivars (0.35≤1.51 MPa) by Method 1. Simple correlation for OA across 12 cultivars with Method 1 was significantly higher for Method 3(r = 0.76; P = 0.04) and Method 4 (r = 0.87; P < 0.01) than for Method 2(r = 0.54; P0.07). OA by Method 4 was better correlated with Method 3(r 0.80;P < 0.01)than with Method 2(r = 0.67;P = 0.02).The coefficient of variation (CV) as a measure of error was greater for Method 1 (47%)and Method 2 (31%)than for Method 3 (21%) or 4 (24%). Both Methods 2 and 3 were less demanding on labor and plant materials than Methods 1 and 4. The results support the use of Method 3 (the “rehydration method”) as a faster and an economical replacement for Method 1.

Studies on the utilization of late‐season applied fetrilizer nitrogen in field and model experiments with winter wheat

The utilization of nitrogen (15N)‐fertilizer was studied with winter wheat grown under field conditions and in a model experiment using large pots (70 kg soil pot‐1). Fertilizer N (160 kg ha‐1, 2 g pot‐1) was applied in two or three different doses timed in the period between the beginning of tillering and that of flowering in both experiments. The field experiment contained also a fall N timing treatment. Both experiments were carried out with the same soil type and wheat variety. The N content of the tested plant parts (rachis, glumes, flag‐leaf blade, flag‐leaf sheath, upper most internode, and lower plant part) was found to be the highest in treatments including the fall applied or early spring N doses. Eighty‐eight percent of the N detected in the uppermost internode depleted during the period between 72% grain moisture content and full ripening. It is concluded that besides the uppermost internode and flag‐leaf, the glumes, as potential N sources, may also play an important role in the N translocation into the grains.The wheat plants grown in pots and watered were able to incorporate into the grains about 50% of the late N doses even though distributed at flowering. The favorable effect of late‐season N application, however, could not be statistically proved. Under field condition, the grains could not utilize the late applied N doses and there could not be detected any favorable effect of late‐season N application either in the experimental year, which was very rainless especially in the period most important from the point of view of grain development.

Monitoring of gaseous nitrogen losses from nitrogen fertilizers in model experiments

Gaseous nitrogen (N) losses were studied from N fertilizers applied to winter wheat under field conditions and in large pots in the open section of a greenhouse. The same soil type was used. Ammonium nitrate (NH4NO3), urea [CO(NH2)2], and ammonium sulphate [(NH4)2SO4] distributed at the beginning of tillering were tested in a microplot experiment (16 g N m‐2). Ammonium nitrate applied at different doses in the period between the beginning of tillering and that of flowering was tested in pots filled with 70 kg soil (2 g N pot‐1). The pots were watered. Gas traps of 4.4 dm3 and 1.8 dm3 were laid between the rows of the microplots and into the pots, respectively. Ammonia (NH3), nitric oxide (NO), nitrous oxide (NO2), dinitrogen oxide (N2O), and nitrogen (N2) contents of trapped soil air were analyzed by gas chromatography during vegetation. Nitrogen fertilizer application significantly increased the amount of nitrogenous gases in the trapped soil air and CO(NH2)2application resulted in the highest nitrogenous gas concentration. The N losses measured at the different samplings were not higher than 1.2% and 2.7% of the N doses applied in the field and pot experiment, respectively. The complete transformation of the fertilizers took place practically within 11 and six weeks after their distribution to wheat grown in the field and in the pots, respectively. The composition of the nitrogenous gases changed during vegetation depending on the applied fertilizer N form. The proportion of the “greenhouse gas”;, N2O increased within the total amount of nitrogenous gases in the field traps with all fertilizer N forms. It decreased, however, in the traps of the pots, where the soil had a higher moisture level. Among the nitrogenous gases tested, N2 showed by far the highest and NO the lowest concentration in both experiments.

Nitrate and phosphate uptake by Agropyron desertorum and Artemisia tridentata from soil patches with balanced and unbalanced nitrate and phosphate supply

To test the ability of plants to integrate small‐scale imbalances in soil nitrate and phosphate patches, plant growth and acquisition of nitrate and phosphate were measured for the perennial grass Agropyron desertorum (Fisch. ex Link) Schult. and the shrub Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle in soil where the principal supply of nitrate and phosphate came from two enriched patches. The soil was calcareous loamy‐skeletal Typic Haploxerolls. These patches were applied in two treatments: either nitrate and phosphate were applied in both patches (balanced treatment) or one patch contained only nitrate and the other only phosphate (unbalanced treatment). The same total quantity of nutrients was applied in both treatments and these included 15N and 32P tracers. The plants were in large pots in open field conditions. There were no significant differences in total biomass production and nitrogen concentration between the two treatments, indicating that both species had the physiological ability to integrate soil nutrient resources. Artemisia was able to acquire more phosphate in the unbalanced treatment, probably due to the high local solution phosphate concentration. Generally Artemisia acquired more N and P than did Agropyron.

Growth of Populus tremuloides in association with Calamagrostis canadensis

Three experiments were conducted to examine the effects of Calamagrostis canadensis (Michx.) Beauv. on the growth of Populus tremuloides Michx. Containerized seedlings of P. tremuloides were transplanted into large pots and subjected to (1) three soil temperatures (20, 12, and 6°C), (2) root competition with C. canadensis, or (3) presence or absence of C. canadensis litter, each at two nutrient regimes. In the first experiment, significant differences (p = 0.0001) in pre- and neo-formed leaf area and root and shoot dry weights were observed for plants subjected to the three different soil temperatures. In experiment two, the presence of C. canadensis significantly (p < 0.001) reduced total biomass, plant height, and root collar calliper of P. tremuloides. In the third experiment, a significant interaction (p = 0.027) between C. canadensis litter and nutrient regime was observed, with the greatest inhibitory effect on P. tremuloides growth resulting from litter at the low nutrient regime. Low soil temperature had the strongest negative effect on P. tremuloides of the four factors investigated. However, direct competition with C. canadensis, low nutrient conditions, and C. canadensis litter likely would add to the growth suppression of P. tremuloides by this grass. The results of this study have significant implications for the management of P. tremuloides after harvesting.

Response of shoot growth and transpiration to soil drying in sugarcane

The relationship between plant-available water (PAW) and shoot extension and transpiration is required to model crop response to water stress, and has not been previously defined for sugarcane (Saccharum spp. (L.)). We subjected sugarcane plants at the 5–6 leaf stage to a continuous drying cycle in large (42 L) pots to determine the threshold fraction of plant available water (PAWt) at which plants slowed shoot extension and transpiration relative to plants watered daily. Transpiration rate was measured as the daily mass loss from the pots and shoot extension as the height increase from ground level to the tip of the youngest actively expanding leaf. Three experiments were conducted with cultivar Q115 covering a range of soil types (and hence PAW) and rates of soil drying. To compare the response with sugarcane, sorghum (Sorghum bicolor (L.) Moench s.lat.), a species that has been well characterized for the relationship between PAW and transpiration and shoot extension, was grown in two additional experiments. For the same species, response curves and PAWt for either shoot extension or transpiration were very similar for the different experiments. This similarity occurred despite there being different soils, different environmental conditions, different PAW, different times taken for the pots to dry down, and hence different rates of stress development. In sugarcane, there was almost no threshold in PAWt (0.92) for shoot extension and a very small threshold in PAWt for transpiration (0.85), while in sorghum PAWt for sorghum shoot extension (0.54) and plant transpiration (0.47) were consistent with those published previously. The present data extend previous reports that sugarcane stalk extension is very sensitive to water stress, and we discuss several factors that could provide the physiological basis for the sensitivity.

Competition of five native prairie grasses with Bromus inermis under three moisture regimes

We examined the effect of moisture on the competitive ability of five native grasses (Agropyron and Stipa) in competition with the non-native grass Bromus inermis Leyss. The plants were grown in large pots in growth rooms, and the moisture treatment was imposed by the frequency of watering. The competitive ability of the five native grasses, as measured by shoot biomass ratio, increased with reduced water availability, but even under the driest conditions, they competed poorly with B. inermis. The order of competitive ability found in this experiment did not match the order predicted from field observations based on the hypothesis of a strict reciprocal relationship between stress tolerance and competitive ability. Stipa viridula Trin. was the best competitor of the five, and Stipa curtiseta (A.S. Hitchc.) Barkworth was consistently the least competitive. The order of competitive ability was more variable when measured by the effect on Bromus than when measured by the effect on the native grasses themselves. The results suggest that tolerance of abiotic stress is less important than competitive exclusion in determining species distributions on environmental gradients Key words: competitive hierarchy, competitive reversal, transitivity.

Fertilization and Harvest Technique Affect Yield of Aloe barbadensis Miller

Aloe barbadensis (Aloe vera) plants remain in production fields for several years, with their lower leaves harvested periodically. A long-term experiment was initiated in November 1993 to determine the effects of fertilization and severeness of harvest on leaf yield. Plants were grown in large pots with or without monthly applications of a 20N–8.6P–16.6K soluble fertilizer from March to October. Beginning in June 1994, the lower leaves were harvested quarterly to have 18, 15, or 12 leaves remaining. Fertilization doubled the number of leaves harvested and tripled the total yield over a 2-year period. The lower leaves on the nonfertilized plants, particularly on plants with 18 leaves remaining, sometimes became dry or partially dry at harvest. The initial quarterly yield and cumulated yield were higher in plants with 12 leaves remaining; however, this trend disappeared over time. The fertilized plants produced an average of 10 kg per plant, while the nonfertilized plants produced only 3.2 kg per plant annually. At several harvests, plants with 18 leaves remaining had higher % dry mass in the inner semi-translucent tissue than those having 12 leaves. Leaves of nonfertilized plants had high % dry mass in the inner leaf tissue when harvested in June and September 1995. Plants with 12 leaves remaining can become unstable and the tops break off in gusty wind.

Effect of Reduced Temperatures on Melon Transplant Subsequent Growth and Survival

Delays in transplanting vegetable seedlings are often a problem due to cold, wet spring weather. This results in the production of overgrown transplants, which are more difficult to transplant and often do not survive. The objective of this study was to find a non-chilling temperature at which to short-term-treat transplants in order to slow down vegetative growth. `Superstar' muskmelon and `Royal Jubilee' watermelon seedlings were greenhouse-grown at 20°C during Mar. 1996. Fifty-cell trays of transplants were grown to the first true leaf stage and then held in a dark cooler at 7.5 or 12.5°C for 4 to 8 days. Control plants were kept in the greenhouse. Transplants were repotted into larger pots after the treatment. Preliminary experiments revealed that 8 days of 7.5°C was too severe of a temperature for watermelon and cantaloupe transplants. Six days of 7.5°C was effective in significantly reducing stem and leaf area growth without seedling death for both types of melons. Shorter durations at 7.5°C or the same duration at 12.5°C was less effective in retarding stem elongation. Surface area of the transplant leaves, after the reduced temperature treatment and subsequent growth, was much more sensitive to a drop in temperature and the length of temperature treatment. In 1997, these treatments will be repeated in the greenhouse and also in the field.

Effect of mulch quality on earthworm activity and nutrient supply in the humid tropics

An experiment was conducted in 1990 and 1991 at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria to study the role of earthworms in the decomposition of plant residue mulches with different qualities. Five mulches of Dactyladenia barteri, Gliricidia sepium, Leucaena leucocephala prunings, maize ( Zea mays) stover and rice ( Oryza sativa) straw, which had a wide range of C-to-N ratio, lignin and polyphenol concentrations were studied. Based on their chemical compositions, Dactyladenia prunings were defined as low-quality mulch, Leucaena and Gliricidia prunings as high quality-mulches, and maize stover and rice straw as intermediate-quality mulches. The mean density of earthworms ( Hyperiodrilus africanus and Eudrilus eugeniae) in the experimental plots decreased in the following order: high quality > intermediate quality > low quality mulches. High quality mulch ( Leucaena and Gliricidia prunings) supported 54% higher earthworm populations than the (no mulch) control, whereas low-quality mulch ( Dactyladenia prunings) only increased earthworm density by 15%, compared to the control in 1990. Plots with Leucaena and Gliricidia prunings had the highest earthworm populations at the initial stage of the experiment, while the other treatments showed increased earthworm numbers at a later stage. Effects of earthworms on mulch decomposition were examined in the field in large pots with or without earthworms ( Eudrilus eugeniae). The effects of earthworms were more pronounced for Dactyladenia prunings (low quality), than for Leucaena and Gliricidia prunings (high quality). The results indicate that manipulation of earthworm activity with application of high- and low-quality mulches may improve the synchronization of soil nutrient supply and crop nutrient demand.

Effects of temperature and irradiance on vegetative growth of cauliflower (Brassica oleraceaL.botrytis) and broccoli (Brassica oleraceaL.italica)

Cauliflower {Brassica oleracea L. botrytis) and broccoli (Brassica oleracea L. italica) plants were grown in large pots in growth chambers for a range of temperatures (mean air temperatures from 7.0-25.3 °C) and irradiances (from 9.3-50.8 mol m~2 d1 or 4.7-25.4 MJ m~2 d ~1). The extinction coefficient for PAR decreased with plant size reaching a value of 0.55 in cauliflower and 0.45 in broccoli at plant leaf areas of 0.235 and 0.227 m2, respectively. The leaf area expansion rate was unaffected by irradiance when compared at identical leaf surface temperatures. The response of expansion rate to surface temperature was fitted to a broken stick model with a base temperature of — 0.7 C and an optimum temperature of 21.0 C. The radiation conversion coefficient increased with air temperature below 13.8°C and remained constant above this. The estimated radiation conversion coefficient above 13.8°C and for a PPFD of 20 mol m2 d~1 was 0.77 g mol 1 in cauliflower and 0.87 g mol 1 in broccoli. The radiation conversion coefficient declined with increasing irradiance level from a maximum of 1.89 g mol1 at near nil irradiance in cauliflower.

Calcium sulphate, phosphogypsum and calcium carbonate in the amelioration of acid subsoils for root growth

The chemical barrier to root development existing in the subsoils of acid soils is a subject of increasing interest. In order to better understand the factors involved in the amelioration of subsoil acidity, the effects of calcium sulphate, phosphogypsum and calcium carbonate on the properties of the solid and liquid phases of subsoil samples and on the growth and nutrient uptake by maize (Zea mays L.) were evaluated. The soils used were two alic red-yellow latosols, two acric dusky red latosols and one alic dark-red latosol from the State of Sao Paulo, Brazil. A vertical split-root technique was used in a greenhouse experiment, with the plants initially grown in a small pot with 130 g fertile soil, which was introduced in a larger pot containing 2 dm3 of the subsoil samples. The treatments consisted of a control (C) and applications of calcium carbonate (CC), calcium sulphate (CS) and phosphogypsum (PG) at the rate of 10 mmolc Ca2+ dm-3. CS and PG reduced soil acidity, but in a much smaller proportion than CC. Calcium carbonate reduced the activity of Al3+ because of the increase in pH. Total aluminum and calcium contents in the soil solution were much higher for the red-yellow latosols than for the other soils, indicating lower sorption of Ca2+ and\(SO_4^{2 - } \) in these soils. The activity of Al in the soil solution was decreased in different ways for the five soils, depending on the ionic strength and the formation of the ionic pair\(AlSO_4^ + \) and, in the case of PG, the formation of complexes of Al with F (AlF2+,\(AlF_2^ + \) and\(AlF_3^\bigcirc \)). The subsoil samples presented severe restrictions for maize root growth and all three treatments were equally effective in increasing root development, which could be attributed to the supply of calcium in one of the acric dusky red latosols and a combined effect of the amendment in reducing the activity of Al and increasing the activity of Ca in the soil solution in the other soils. As a consequence the three treatments increased in the same manner water, N and K uptake from the subsoil and the dry matter production of maize. It can be concluded that, for the soils considered in this research, phosphogypsum is an effective amendment for acid subsoils containing low calcium or toxic aluminum contents.

Growth analysis of Scots pine and lodgepole pine seedlings

Possible reasons for the superior growth rate of lodgepole pine (LP) ( Pinus contorta Dougl. var. latifolia Engelm.) compared to Scots pine (SP) ( Pinus sylvestris L.) were investigated in a trial where the species were grown in large pots with sand, till or topsoil, during 4 years following sowing. Although starting with lower seed mass, LP seedlings had greater mass than those of SP at the end of the study period. There was, however, a species × growing media interaction and the difference in final mass was greatest for seedlings growing in topsoil. Growth analyses showed that the faster relative growth rate in LP seedlings was linked with a higher leaf area ratio, specific leaf area and nitrogen use efficiency. A higher relative allocation to thin roots was another trait of LP that may contribute to its superior productivity. The fast root growth suggests shorter cultivating time of potted LP seedlings to avoid root deformation. SP allocated relatively more to stem and thick roots, components associated with physical stability. There was no species difference in allocation to needles when relating to total biomass, but LP had a larger proportion of needles in relation to above-ground biomass.

Influence of heavy metals on the functional diversity of soil microbial communities

Three soil types-Calcaric Phaeozem, Eutric Cambisol and Dystric Lithosol-in large container pots were experimentally contaminated with heavy metals at four different levels (light pollution: 300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd; medium pollution: twofold concentrations; heavy pollution: threefold concentrations; uncontaminated control). We investigated the prognostic potential of 16 soil microbial properties (microbial biomass, respiration, N-mineralization, 13 soil enzymes involved in cycling of C, N, P and S) with regard to their ability to differentiate the four contamination levels. Microbial biomass and enzyme activities decreased with increasing heavy metal pollution, but the amount of decrease differed among the enzymes. Enzymes involved in the C-cycling were least affected, whereas vartous enzyme activities related to the cycling of N, P and S showed a considerable decrease in activity. In particular, arylsulfatase and phosphatase activities were dramatically affected. Their activity decreased to a level of a few percent of their activities in the corresponding unpolluted controls. The data suggest that aside from the loss of rare biochemical capabilities-such as the growth of organisms at the expense of aromatics (Reber 1992)-heavy metal contaminated soils lose very common biochemical propertities which are necessary for the functioning of the ecosystem. Cluster analysis as well as discriminant analysis underline the similarity of the enzyme activity pattern among the controls and among the polluted soils. The trend toward a significant functional diversity loss becomes obvious already at the lowest pollution level. This implies that concentrations of heavy metals in soils near the current EC limits will most probably lead to a considerable reduction in decomposition and nutrient cycling rates. We conclude that heavy metal pollution severely decreases the functional diversity of the soil microbial community and impairs specific pathways of nutrient cycling.

Geographical Profiles of Alkalinity Levels in Greenhouse Irrigation Waters

Alkalinity of irrigation water affects pH of the plant growing media. High alkalinity water raises media pH and affects nutrient availability to plants and, thus, plant growth. Alkalinity levels in irrigation water vary in different regions. Knowledge of alkalinity levels would help growers and advisors in modifying cultural practices to suit the levels. To find out how the levels vary in different states, we searched our database of thousands of water analyses from across the country. Overall, 38% of the waters had <100 ppm CaCO3, a level not considered to be a concern for even small pots. About 74% of the waters had <200 ppm CaCO3, a level considered to be safe for large pots. The majority of the waters in the states along the eastern seaboard had <150 ppm CaCO3. In waters in the interior states, alkalinity levels varied. Pacific Northwest had most waters <150 ppm CaCO3. Detailed results—bar charts showing percent of waters at different alkalinity levels in each state and in the country will be shown.

Pot size affects expression of Mn efficiency in barley

Mn efficiency is defined here as an ability of a genotype to grow and yield well in a soil which is limiting in available Mn for a standard genotype (Graham, 1984). Screening for Mn efficiency in soil-based pot testing had been producing inconsistent results, and thus improvement of pot screening became an objective. One possible factor, pot size was examined as the cause, using two sizes of pot. In large pots, the expectation of higher dry matter and shoot Mn concentration in a Mn-efficient genotype compared to a Mn-inefficient genotype was realised over a wide range of Mn supply, whereas in small pots, the genotypic differences were expressed at only one, low rate of Mn supply (10 mg kg soil-1). Plants in the small pots strongly responded to root restriction by decreasing yields and increasing root/shoot ratios and Mn concentrations of shoots. The critical value of Mn concentration for shoot growth was not affected by the small pots, but the Mn mobilization by plants might be affected in the small pots. The practical outcome of these results is that using an adequate size of pot and measuring the Mn concentration of shoots, soil-based pot screening for Mn efficiency can be improved.

Shoot induction of ABA-requiring genes in response to soil drying

Plant responses to water deficit are dynamic and varied, requiring co-ordination between the shoot and root. Among these responses are alterations in gene expression. The expression of four genes, le4, le16, le20, and le25, which require increased ABA content for expression, was studied in tomato plants in which the root systems were divided between two large pots to impose water deficit gradually and to control signals from the root in response to soil drying without inducing a signal from the shoot. One group of plants had one-half of the roots watered, another group had both halves watered, and another group had neither halves watered. In unwatered plants, the expression of le4 and le25 correlated with ABA content, and that of le16 and le20 occurred before a detectable increase in leaf ABA content. The contrasting patterns of expression indicate a difference in sensitivity of these genes to ABA or an additional signalling mechanism. Ample evidence indicates that shoot processes such as stomatal closure are controlled by signals from the root. This study demonstrates that genes may also be induced in the shoot by signals from the root. Shoots of plants in which only half of the roots were watered showed no decrease in relative water content and no increase in ABA content ; however, three of the four genes, le4, le16, and le20, were induced. Root-to-shoot communication plays a role in changes in gene expression and in alterations in physiological processes.

Salinity Responses in Two Populations of Viviparous Rhizophora mangle L. Seedlings

Viviparous seedlings of the red mangrove, Rhizophora mangle L., were collected from adult trees growing in areas of low (59'oo) and high (360oo) surface water salinities, and planted as groups in large rectangular pots and treated with seawater corresponding to the two natural concentrations. Among individuals collected from the same site, growth was significantly enhanced in the low (5%oo) versus high (360oo) salinity treatment. Stem and leaf development exhibited larger differences between high and low salinities than did root growth. Propagules showed no increased capacity for growth when treated with salinities similar to the parent tree environments. Seedlings from the high salinity site exhibited faster growth than those from the low salinity site when treated with low salinity water. However, differences between sites were insignificant in the high salinity treatment. Results are discussed in the context of vivipary as a preconditioning mechanism for salt-tolerance and the general effects of salinity on physiological and possible genetic aspects of early development.