Belowground Dry Mass Research Articles

Breaking dormancy, alternative substrates, and the production of <i>Samanea tubulosa</i> (Benth.) seedlings

We investigated different dormancy breaking methods and substrates for Samanea tubulosa seedlings. Four substrate formulations were tested: SCO: commercial substrate; BBA: decomposed babassu biomass + soil (1:1); BBU: buriti biomass + soil (1:1); and BCA: carnauba bagana + soil (1:1), and three dormancy breaking methods: EM: mechanical scarification; IA: immersion in water; and EQ: chemical scarification. The highest seedling emergence was in BCA substrate with chemical scarification. BCA and SCO provided the highest average seedling height, root length, root volume, root density, diameter at neck height, number of leaves, aboveground dry mass, belowground dry mass, and Dickson quality index values. Therefore, BCA can be used as a substrate for the production of S. tubulosa seedlings, and the immersion in water method is optimal when combined with a BBU substrate.

Argon-ion beam induced mutants of the ectomycorrhizal agaricomycete Tricholoma matsutake defective in β-1,4-endoglucanase activity promote the seedling growth of Pinus densiflora in vitro

Tricholoma matsutake is an ectomycorrhizal agaricomycete that produces the prized matsutake mushroom in conifer forests. Here, we isolated mutants generated by the argon-ion beam irradiation of T. matsutake NBRC 33136, designated as Ar 5002 and Ar 5012, which are defective in β-1,4-endoglucanase activity, that promoted the above- and below-ground growth of the symbiotic partner Pinus densiflora in vitro, compared with the control. Pine seedlings associated with Ar 5002, compared with NBRC 33136, had significantly higher above-ground dry mass and significantly greater plant growth, while those associated with Ar 5012 had significantly higher above- and below-ground dry mass. There were no significant differences between the numbers of mycorrhizal root-tips synthesized by the wild-type and mutants, indicating that β-1,4-endoglucanase did not influence the mycorrhization of T. matsutake. In seedlings inoculated with Ar 5002- and Ar 5012, the Hartig nets resembled those of seedlings inoculated with NBRC 33136. The data suggest that T. matsutake lacking β-1,4-endoglucanase activity confer beneficial effects on the growth of P. densiflora. Further studies are necessary to determine whether the symbiotic relationship could be strengthened by such a mutated fungal trait.

Rhizobacterial species richness improves sorghum growth and soil nutrient synergism in a nutrient-poor greenhouse soil

Although microbes influence plant growth, little is known about the impact of microbial diversity on plant fitness trade-offs, intraspecific-interactions, and soil nutrient dynamics in the context of biodiversity-ecosystem functioning (BEF) research. The BEF theory states that higher species richness can enhance ecosystem functioning. Thus, we hypothesize that rhizobacterial species richness will alter sorghum (Sorghum bicolor L.) growth, soil nutrient dynamics and interactions (antagonism or synergism) in a nutrient-poor greenhouse soil. Using six rhizobacterial species in a BEF experiment, we tested the impact of a species richness gradient (0, 1, 3, 5 or 6 species per community) on plant growth, nutrient assimilation, and soil nutrient dynamics via seed-inoculation. Our experiment included, one un-inoculated control, six rhizobacterial monoculture (Pseudomonas poae, Pseudomonas sp., Bacillus pumilus., Pantoea agglomerance., Microbacterium sp., and Serratia marcescens), and their nine mixture treatments in triplicate (48). Rhizobacterial species richness enhanced per pot above- or below-ground dry mass. However, the per plant growth and plant nutrient assimilation declined, most likely, due to microbial-driven competitive interactions among sorghum plants. But nevertheless, some rhizobacterial monoculture and mixture treatments improved per plant (shoot and root) growth and nutrient assimilation as well. Soil nutrient contents were mostly lower at higher plant-associated rhizobacterial diversity; among these, the soil Zn contents decreased significantly across the rhizobacterial diversity gradient. Rhizobacterial diversity promoted synergistic interactions among soil nutrients and improved root–soil interactions. Overall, our results suggest that a higher rhizobacterial diversity may enhance soil–plant interactions and total productivity under resource limited conditions.

Effect of Nitrogen and Silicon on Rice Submerged at Tillering Stage

Core Ideas Basal silicon promotes rice growth and development at the tillering stage.After flooding, foliar spraying N or silicon timely had a better effect.Foliar spraying N had more advantages than silicon. Flooding is a major threat to rice (Oryza sativa L.) yields. We wondered if basal Si and foliar spraying fertilizer had an influence on rice submerged at tillering stage. The results showed that basal Si application promoted rice growth and development at the tillering stage, improving rice seedling tolerance to submergence stress. After the occurrence of flooding, timely foliar spraying of N or Si had significant remedial effects, and spraying N along with Si had a better effect. The combination of basal Si and post‐flooding N and Si spraying was the most promising method of nutrient application and as resistance to damage during submergence was enhanced, plants rapidly resumed growth and development. By maintaining a great number of green leaves and tillers as well as higher aboveground and belowground dry mass, sugar contents and antioxidant enzyme activities, these plants yielded significantly more grain. We conclude that reasonable use of Si leads to resistance and alleviation of the damaging effects of submergence and contributes to reducing yield losses in rice.

Effects of soil nutrient conditions on water transport properties and recovery from severe drought stress in Pinus densiflora saplings

ABSTRACTTo evaluate the acclimation of water transport properties to soil nutrient conditions, morphological and hydraulic traits were measured in 4-year-old potted saplings of Japanese red pine that were grown under differing nutrient conditions for 3 years. To compare recovery from severe drought stress under differing nutrient conditions, the well-watered saplings were subjected to drought treatments of almost Ψ50 by stopping irrigation; this is equivalent to the xylem water potential at which 50% loss of hydraulic conductivity occurs. After resuming daily watering, the xylem water potential and gas exchange rate were measured. Whole-plant transpirational demand from large total-leaf area tended to be high for plants under high-nutrient conditions. However, no differences were observed in water transport properties, such as the conducting area, hydraulic efficiency, and cavitation resistance, suggesting that acclimation of the hydraulic architecture did not occur when plants were grown under sufficient soil moisture conditions. The root dry weight tended to be large and the belowground dry mass to root dry mass (T/R ratio) tended to be low for plants under high-nutrient conditions. Plants grown under high-nutrient conditions recovered their gas exchange rate and leaf-specific hydraulic conductance slightly during the month following severe drought stress by irrigation. The recovery of Japanese red pine appears to vary under different levels of nutrient availability probably because of the influence of root water absorption capacity.

Comparison of root system architecture and rhizosphere microbial communities of Balsas teosinte and domesticated corn cultivars

The progenitor of maize is Balsas teosinte (Zea mays subsp. parviglumis) which grows as a wild plant in the valley of the Balsas river in Mexico. Domestication, primarily targeting above-ground traits, has led to substantial changes in the plant's morphology and modern maize cultivars poorly resemble their wild ancestor. We examined the hypotheses that Balsas teosinte (accession PI 384071) has a) a different root system architecture and b) a structurally and functionally different rhizosphere microbial community than domesticated cultivars sweet corn (Zea mays subsp. mays accession PI 494083) and popping corn (Zea mays subsp. mays accession PI 542713). In a greenhouse experiment, five plants from each corn variety were grown in individual pots containing a Maury silt loam – perlite (2:1) mixture and grown to the V8 growth stage at which rhizosphere bacterial and fungal community structure was assessed using terminal restriction fragment length polymorphism and fatty acid methyl ester analysis. Functional characteristics of the rhizosphere were assayed by examining the potential activity of seven extracellular enzymes involved in carbon, nitrogen and phosphorus cycling. Root system architecture was characterized by root scans of sand grown plants at the V5 growth stage. Compared to the control the sweet corn rhizosphere had different bacterial and fungal community structure, decreased fungal diversity and increased bacterial abundance. Teosinte caused a significant change in the rhizosphere bacterial and fungal community structure and increased bacterial abundance, but no significant decrease in bacterial or fungal diversity where the former was found to be significantly greater than in the sweet corn rhizosphere. Popping corn did not trigger significant changes in the bacterial or fungal diversity and bacterial abundance in the soil. The individual popping corn plants changed the bacterial and fungal communities in different directions and the overall effect on community structure was significant, but small. Of the enzymes analyzed, potential N-acetylglucosaminidase (NAG) activity was found to contributed most to the differentiation of teosinte rhizosphere samples from the other corn varieties. The teosinte root system had proportionally more very fine (diameter < 0.03 mm) roots than popping corn and sweet corn and it developed the highest root to shoot dry weight ratio, followed by popping corn. Sweet corn had significantly lower average root diameter than popping corn and teosinte and grew proportionally the least below-ground dry mass. The results allude to functional and structural differences in the rhizosphere microbial communities of the corn varieties that, with additional research, could lead to useful discoveries on how corn domestication has altered rhizosphere processes and how plant genotype influences nutrient cycling.

Competition and Niche Requirements ofCoreopsis tinctoria: A Widespread but Local High Density Annual Asteraceae

Coreopsis tinctoria (coreopsis, calliopsis, plains coreopsis, or golden wave) is an annual herbaceous Asteraceae with a broad geographic distribution mostly in the central and western United States. It co-occurs with Bouteloua curtipendula (sideoats grama) or other native C4 grasses. When grown together, C. tinctoria response variables decreased significantly in the presence of B. curtipendula aboveground, belowground, and total dry mass. The response variables included mean plant height, number of flower buds per plant, flowers per plant, as well as aboveground, belowground, and total dry mass. The presence of B. curtipendula belowground dry mass caused the greatest suppression of C. tinctoria belowground dry mass. When B. curtipendula tops were clipped to reduce grass aboveground dry mass (simulated herbivory), the percent survival of C. tinctoria plants increased from one percent in the no-clipping treatment to 18% in the neighbor removal treatment (100% clipped). Coreopsis tinctoria does not appear to be a good competitor in the presence of B. curtipendula and seems to be restricted to gaps or patches in disturbed grasslands where competition from perennial grass neighbors is reduced.

Soil Depth and Changes in Dry Mass and Competitive Intensity of Two C&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; Grasses

The presence of grassland biomes and species cannot be predicted by examining bottom up causes such as precipitation and temperature. Top down causes including herbivory and fire seem to be major controlling aspects with other factors secondary. We examined soil depth and competitive ability of two North American C4 grasses in a greenhouse experiment. Changes in dry mass were determined and competitive intensity was calculated for both species. Species were grown separately or together in pots 30, 90, or 180 cm deep. When grown in monoculture, Schizachyrium scoparium total and belowground dry mass increased from the 30 to 90 cm depth, with no further significant increase from 90 to 180 cm. Aboveground dry mass did not increase significantly with depth. Total dry mass of Buchloe dactyloides increased significantly with depth when grown in monoculture. Aboveground dry mass increased from 30 to 90 cm depth but not from 90 to 180 cm. Belowground dry mass of B. dactyloides did not increase significantly with depth. In 180 cm pots, 53% of S. scoparium root dry mass was in the top 30 cm; 74% of B. dactyloides root dry mass was in the top 30 cm. Roots of B. dactyloides were not found deeper than 90 cm. Aboveground dry mass of S. scoparium was not different in mixture or monoculture at any depth. Buchloe dactyloides aboveground dry mass in mixture was significantly lower than monoculture at the 30 cm depth, but not at 90 or 180 cm. The greatest competitive intensity was in the shallow soil pots. Soil depth could partially explain mosaics found in C4 grasslands where both species were found together with S. scoparium on deeper soils and B. dactyloides on shallower soils.

Stem biomass, C and N partitioning and growth efficiency of mature pedigreed black spruce on both a wet and a dry site

Worldwide, efforts to manage atmospheric CO2 are being explored both by reducing emissions and by sequestering more carbon (C). Stem biomass, C, and nitrogen (N) parameters were measured in plots of first-generation (F1), 32-year-old black spruce (Picea mariana (Mill.) B.S.P.) from four full-sib families studied previously for drought tolerance and differential productivity on both a dry and a wet site in central Ontario, Canada. The wet site had greater stem wood N and bark N concentrations than the dry site. Site differences in N were most likely driven by soil moisture stress impairing N uptake, as soil N was equal at both sites. Drought-tolerant (faster growing) families had lower wood density than drought-intolerant families on the wet site but there were no wood density differences between families on the dry site. Allometric analysis showed greater total stem dry mass per unit total belowground dry mass for drought-tolerant than intolerant families and for wet than dry sites, indicating a differential allocation of photosynthate dependent on both genotype and environment. Allometric analysis also showed greater total stem dry mass per unit total needle dry mass (growth efficiency) for drought-tolerant than intolerant families and for the wet than the dry site. This indicates greater productivity is a result of greater growth efficiency caused by greater net photosynthesis (shown previously) and greater partitioning of biomass to stem relative to total roots. The variation in physiological processes documented in our previous investigations and the biomass allocation variation shown here most probably underlie the increase in stem productivity from both black spruce tree improvement programs and increased water availability.

Effect of fertilization on below-ground plant mass of submontane Polygono-Cirsietum meadow

We assessed below-ground net primary productivity (BNPP) in the wet submontane Cirsium meadow occurred in the highland region of the Czech Republic. Effect of four different fertilization levels on BNPP was estimated in 1992. At the beginning of the growing season (April 29), total dry mass of rhizomes, roots and total below-ground plant parts of unfertilized stand reached 177, 1478 and 1657 g.m-2, respectively. Their living parts formed 42 % of their total dry mass. In comparison with unfertilized stands, however, the greatest accumulation of dry mass of rhizomes (504 g.m-2), roots (1503 g.m-2) and total below-ground dry mass (2008 g.m-2) was reached after application of 90 kgN.ha-1. Similarly, the highest BNPP values for living (435 g.m-2.yr-1) and total below-ground dry mass (351 g.m-2.yr-1) were calculated for the stand affected by the same amount of fertilization. These data show how variable role grasslands can play in accumulation and turn over of root biomass due to different levels of fertilization.

Effect of ambient ozone at the somma of Lake Mashu on growth and leaf gas exchange in Betula ermanii and Betula platyphylla var. japonica

We examined the effects of ambient ozone, at the somma of Lake Mashu in northern Japan, on the growth and photosynthetic traits of two common birch species in Japan (mountain birch and white birch). Seedlings of the two birch species were grown in open-top chambers and were exposed to charcoal-filtered ambient air (CF) or non-filtered ambient air (NF) at the somma of Lake Mashu during the growing season in 2009. For the mountain birch, ambient ozone significantly increased the ratio of aboveground dry mass to belowground dry mass (T/R ratio), although no difference in the whole-plant biomass was observed between the treatments. For the white birch, in contrast, ozone exposure at ambient level did not decrease in growth and photosynthesis. These results suggest that ambient O3 at the somma of Lake Mashu may shift the allocation of biomass to above-ground rather than below-ground in the mountain birch.

Contrasting response to clipping in the Asian knotweeds Fallopia japonica and Fallopia × bohemica

Invasive species are often managed with the objective of population control or eradication. Here we tested whether clipping techniques influenced the aboveground and belowground structures of 2 closely related invasive taxa: Fallopia japonica and Fallopia x bohemica. We compared the aboveground response (plant height, number of stems, and number of leaves) of rhizome fragments to clipping of both taxa. The second experiment was aimed at comparing the belowground response of both taxa to the same clipping disturbance. Rhizome fragments were planted in rhizoboxes and subjected to a clipping disturbance after 4 weeks of growth. Regrowth, belowground biomass, specific root length, total root length, and distribution of roots in 3 soil layers were measured. Aboveground plant traits of both taxa were unaffected by clipping. On the other hand, clipping induced a reduction in belowground dry mass and an increased proportion of roots in the upper layer of soil in F. japonica. Both taxa of Asian knotweeds are highly tolerant to clipping because they are able to cope with aerial biomass loss. Nevertheless, this tolerance seems to be lower in F. japonica. The potential implications for the impact of these invasive species are discussed.

Genetic effects on stand-level uniformity and above- and belowground dry mass production in juvenile loblolly pine

Genetic differences in stand-level above- and belowground dry mass production in loblolly pine ( Pinus taeda L.) may influence southern pine plantation productivity, sustainability and carbon (C) sequestration. Furthermore, deployment of more or less genetically homogeneous individuals could impact stand uniformity and ecosystem processes. In this study, we aimed to compare stand uniformity and above- and belowground dry mass production among loblolly pine genotypes of contrasting inherent genetic homogeneity. We hypothesized that stand-level uniformity would increase as within-genotype inherent genetic variation decreased (open-pollinated (half-sib) > full-sib > clone). To examine genetic effects on stand uniformity and productivity, we grew ten different genotypes (three open-pollinated families, three full-sib families, three clones, and one seed orchard mix variety) in a plantation setting for 4 years, at two different planting densities (∼539 and 1077 trees ha −1), and used allometric relationships to estimate standing dry mass and annual dry mass production. In the low planting density treatment, age 3 total standing dry mass of the most productive genotype (5824 kg ha −1) was 82% higher than that of the least productive genotype (3207 kg ha −1). In the high planting density treatment, age 3 total standing dry mass of the most productive genotype (11,393 kg ha −1) was 110% higher than that of the least productive genotype (5427 kg ha −1). Genetic differences in annual dry mass production were of a similar magnitude with peak rates during the third year as high as 4221 and 8198 kg ha −1 yr −1 in the low and high planting density treatments, respectively. More genetically homogeneous genotypes did not show greater stand-level uniformity under operational management conditions. Over time, genotypes showed no consistent differences in the coefficient of variation (CV) for ground-level diameter; however, two full-sib and two half-sib families showed significantly lower CV’s for total tree height than all three clones. Moreover, genotypes with lower CV’s for height growth displayed greater stand-level dry mass production which supports the premise that greater stand uniformity will lead to enhanced productivity. Since uniformity and stand-level productivity of loblolly pine clones will be principally governed by environmental heterogeneity, our results highlight the need for silvicultural prescriptions that maximize site uniformity. In addition, our results demonstrate how the deployment of highly productive loblolly pine genotypes may provide a means of enhancing southern pine ecosystem sustainability by sequestering C in both harvestable aboveground biomass and woody belowground biomass.

Potential impact of an introduced root-feeding flea beetle, Longitarsus bethae, on the growth and reproduction of an invasive weed, Lantana camara

A root-feeding flea beetle, Longitarsus bethae Savini & Escalona (Chrysomelidae: Altcinae), was introduced into South Africa to complement the impact of the above-ground insect agents already established on Lantana camara L. (Verbenaceae). To estimate the potential effectiveness of L. bethae for biological control of L. camara, growth of various plant components were measured under different levels of abundance of the insect under quarantine glasshouse and semi-field conditions. Populations of L. bethae larvae that developed in previously-sterilized soil from initial cohorts of 200 and 300 eggs per plant significantly stunted the growth of L. camara, causing reductions in the number of leaves, stem height, stem diameter, above-ground dry-mass, and below-ground dry-mass, of up to 54%, 21%, 31%, 34% and 40%, respectively. Compared with the controls, the larval population resulting from an inoculum of 100 eggs per plant usually had no statistically significant effect on plant growth. The degree of root damage caused by the larvae was directly proportional to the number of eggs added and to the number of adults that emerged. Under semi-field conditions, cumulative herbivory by L. bethae adults and larvae during a six-month period caused severe leaf and root damage, resulting in a cumulative decline of 148% in flower production. Overall, the ability of L. bethae to both directly suppress root growth and indirectly suppress leaf production, stem growth and flower production of L. camara, indicates that this flea beetle has the potential to make a considerable impact on the weed’s invasiveness in South Africa.

Global warming induces female cuttings of Populus cathayana to allocate more biomass, C and N to aboveground organs than do male cuttings

We investigated differences between the sexes of a dioecious species, Populus cathayana Rehd, in biomass accumulation, biomass allocation, and carbon (C) and nitrogen (N) concentrations under elevated temperature treatments. Cuttings were subjected to three temperature regimes (control, +2°C and +4°C, respectively) in closed-top chambers. Compared with the control treatment, warming significantly increased the net photosynthesis rate, height growth, leaf dry mass, stem dry mass (SM), root dry mass (RM) and total dry mass (TM), and resulted in a higher aboveground : belowground dry mass ratio (AB) in all individuals of both sexes, except in males under the +2°C warming treatment. Furthermore, warming decreased the concentration of C in the stems in both sexes, and increased the concentration of N in the leaves of females, and consequently, resulted in a lower C : N ratio in the leaves of female cuttings than in those of male cuttings. Also, further differences between males and females were detected. In the warming treatments, females exhibited significantly higher values of SM, RM, TM and AB, and lower RM : TM and RM : foliage area ratios than did the males. However, no significant differences in these traits between the two sexes were detected under ambient temperature. Our results indicated that allocation of biomass, and the concentrations of C and N in males and females are greatly affected by an elevated temperature, and that warming benefits females, which accumulate and allocate more biomass to aboveground organs than do the males.

Effect of Manipulated Rainfall on Root Production and Plant Belowground Dry Mass of Different Grassland Ecosystems

A field experiment was established to quantify the effects of different amounts of rainfall on root growth and dry mass of belowground plant parts in three types of grassland ecosystems. Mountain (Nardus grassland), highland (wet Cirsium grassland), and lowland grassland (dry Festuca grassland) ecosystems were studied in 2006 and 2007. Roofs constructed above the canopy of grass stands and gravity irrigation systems simulated three climate scenarios: (1) rainfall reduced by 50%, (2) rainfall enhanced by 50%, and (3) the full natural rainfall of the current growing season. Experimentally reduced amounts of precipitation significantly affected both yearly root increments and total root dry mass in the highland grassland. Dry conditions in 2007 resulted in considerable reduction of total belowground dry mass in highland and mountain grasslands. Although not all differences in root biomass of studied grasslands were statistically significantly, some also showed a decrease in root increment and in the amount of belowground dry mass in dry conditions.

Growth and biomass of Populus irrigated with landfill leachate

Resource managers are challenged with waste disposal and leachate produced from its degradation. Poplar ( Populus spp.) trees offer an opportunity for ecological leachate disposal as an irrigation source for managed tree systems. Our objective was to irrigate Populus trees with municipal solid waste landfill leachate or fertilized well water (control) (N, P, K) during the 2005 and 2006 growing seasons and test for differences in tree height, diameter, volume, and biomass of leaves, stems, branches, and roots. The trees were grown at the Oneida County Landfill located 6 km west of Rhinelander, Wisconsin, USA (45.6°N, 89.4°W). Eight clones belonging to four genomic groups were tested: NC13460, NC14018 [( Populus trichocarpa Torr. & Gray × Populus deltoides Bartr. ex Marsh) × P. deltoides ‘BC 1’]; NC14104, NC14106, DM115 ( P. deltoides × Populus maximowiczii A. Henry ‘DM’); DN5 ( P. deltoides × Populus nigra L. ‘DN’); NM2, NM6 ( P. nigra × P. maximowiczii ‘NM’). The survival rate for each of the irrigation treatments was 78%. The total aboveground biomass ranged from 0.51 to 2.50 Mg ha −1, with a mean of 1.57 Mg ha −1. The treatment × clone interaction was not significant for tree diameter, total volume, dry mass of the stump or basal roots, or root mass fraction ( P > 0.05). However, the treatment × clone interaction was significant for height, total tree dry mass, aboveground dry mass, belowground dry mass, and dry mass of the leaves, stems + branches (woody), and lateral roots ( P < 0.05). There was broad clonal variation within the BC 1 and DM genomic groups, with genotypes performing differently for treatments. In contrast, the performance of the NM and DN genomic groups was relatively stable across treatments, with clonal response to irrigation being similar regardless of treatment. Nevertheless, selection at the clone level also was important. For example, NC14104 consistently performed better when irrigated with leachate compared with water, while NC14018 responded better to water than leachate. Overall, these data will serve as a basis for researchers and resource managers making decisions about future leachate remediation projects.

Carbon isotope composition and water-use efficiency in plants with crassulacean acid metabolism.

The relationship between water-use efficiency, measured as the transpiration ratio (g H2O transpired g-1 above- plus below-ground dry mass accumulated), and 13C / 12C ratio (expressed as δ13C value) of bulk biomass carbon was compared in 15 plant species growing under tropical conditions at two field sites in the Republic of Panama. The species included five constitutive crassulacean acid metabolism (CAM) species [Aloe vera (L.) Webb & Berth., Ananas comosus (L.) Merr., Euphorbia tirucalli L., Kalanchoë daigremontiana Hamet et Perr., Kalanchoë pinnata (Lam.) Pers.], two species of tropical C3 trees (Tectona grandis Linn. f. and Swietenia macrophylla King), one C4 species (Zea mays L.), and seven arborescent species of the neotropical genus Clusia, of which two exhibited pronounced CAM. The transpiration ratios of the C3 and CAM species, which ranged between 496 g H2O g-1 dry mass in the C3-CAM species Clusia pratensis Seeman to 54 g H2O g-1 dry mass in the constitutive CAM species Aloe vera, correlated strongly with δ13C values and nocturnal CO2 gain suggesting that δ13C value can be used to estimate both water-use efficiency and the proportion of CO2 gained by CAM species during the light and the dark integrated over the lifetime of the tissues.

GROWTH OFPROSOPIS GLANDULOSAIN RESPONSE TO CHANGES IN ABOVEGROUND AND BELOWGROUND INTERFERENCE

Recent increases in woody plant density have occurred in grasslands worldwide, but both the cause and mechanisms involved in these changes have been elusive. Changes in grass biomass mediated by high levels of constant herbivory seem to be the pivotal reason. In this field study in central Texas, USA, effects of aboveground and belowground interference on the growth of seedlings of a deep-rooted, woody heliophyte, Prosopis glandulosa, were tested. The effects of two positions (gap or Bouteloua curtipendula grassland), two levels of aboveground interference (high or low light), and three levels of grass root interference (2, 20, and 40 cm deep root excluders) on P. glandulosa aboveground, belowground, and total dry mass were measured. The exclusion of belowground interference significantly increased aboveground, belowground, and total P. glandulosa dry mass, with the reduction of belowground interference to a depth of 20 cm maximizing P. glandulosa dry mass. Aboveground, belowground, and total dry mass of P. glandulosa were not significantly different when grown in gaps compared to grasslands, nor were there any significant differences when aboveground interference (shade) was imposed. However, the trend was for greater dry mass in gaps and high light. Data indicate that belowground interference from grass roots significantly reduces the dry mass of P. glandulosa, while aboveground interference has a lesser effect.

The Importance of Neighbors, Soil pH, Phosphorus, and Nitrogen for the Growth of Two C4Grasses

In the coastal prairies of Texas, C4 grasses dominate. However, reasons for spatial differences in composition of these prairies are uncertain, and the reasons for codominance of Schizachyrium scoparium and Paspalum plicatulum are unexplained. We completed a greenhouse experiment that examined the effects of neighbors, soil pH, added P, and N on the growth of P. plicatulum and S. scoparium, two C4 grasses. Intraspecific competition was essentially equal to interspecific competition, and soil factors seem to control dry mass of these two species. For P. plicatulum, addition of P to native soil increased above- and belowground dry mass 1.8-2.5 times, while P and N together increased dry mass 2.9-6.5 times. The response was pH dependent, with the greatest dry mass at low pH. Root: shoot ratios changed from 0.3 to ca. 1.0 as the pH decreased in native soil regardless of the P level. When N was added, ratios were ca. 0.3 across all pH and P treatments. For S. scoparium in native soil, there was little change in aboveground dry mass when P was added; however, belowground dry mass was augmented 1.5-1.9 times, with the greatest dry mass at pH 7.0. Additions of P and N increased aboveground dry mass 2.2-2.7 times, with the greatest dry mass at pH 7.0. N additions caused reductions of 79%-89% in belowground dry mass compared with that of native soil, at all levels of P and pH. Root: shoot ratios were 5-10 times higher in the native soil compared with N addition treatments and increased to 1.0 as pH decreased. Ratios were about 15% higher with P added to native soil and remained constant at ca. 0.1 in all the N addition treatments. These two C4 grasses seem to be competitively equal. Their growth was not determined by the presence of neighbors but by levels of soil resources and soil pH.