Cactus Growth Research Articles

Pengaruh Komposisi Media dan Konsentrasi Pupuk NPK Terhadap Pertumbuhan Tanaman Kaktus (Gymnocalycium damsii var.multiproliferum)

ABSTRACT
 Cactus is a type of ornamental plant that is quite popular, so its development and reproduction is important. Cactus Gymnocalycium damsii var. multiproliferum can be propagated by shoots or saplings, but its growth is very slow. The success of cactus propagation is greatly influenced by the composition of the media and the nutrients provided. By choosing the planting media and providing the right nutrients, optimal growth of cactus saplings can be achieved. Malang sand is a planting medium with fine cavities that make it porous and light. NPK is a macro nutrient that is really needed to support plant growth and development. Research to obtain the right media composition and concentration of NPK fertilizer for the growth of Gymnocalycium damsii var multiproliferum cactus saplings was carried out using a factorial experiment using a completely randomized block design with 3 replications. The composition of the media is a ratio between soil: compost: Malang sand with 3 levels, namely: (1:1:1); (1:1:2) and (1:1:3) v/v. The concentration of NPK fertilizer consists of 4 levels, namely: 0; 1; 2 and 3 g/l. The results of the research showed that there was no interaction between planting media and konsentration of NPK fertilizer on growth of cactus . Concentration of NPK fertilizer 1 g/l gave the best results on plant diameter, plant height, shoot fresh weight, total fresh weight, root fresh weight, root length and root volume of the Gymnocalycium damsii var multiproliferum cactus sapling.

Effects of Different Potting Media on the Growth of Commercial Cacti

- This research aims to study the appropriate growing media for the growth of cacti that can reduce production costs and promote cacti’s growth. The research used four genera of cacti, i.e., Gymnocalycium, Astrophytum, Mammillaria, and Echinopsis, which were famous in the commercial market in Thailand. The experimental design was completely randomized designs (CRD) with four different growing media and three replications; T1) fermented rain tree leaves (FRTL): perlite: vermiculite: pumice: vermicompost as a control, T2) FRTL: rice husk: coconut coir: charcoal: vermicompost, T3) FRTL: rice husk ash: coconut husks chips: expanded clay: vermicompost and T4) rice husk ash: vermicompost. The plant was cultivated the plastic pot 2-inches and collected the growth for six months. The result showed that Mammillaria was planted in Treatment 3 gave the greatest stem diameter and the number of roots. A similar increase in stem diameter of Echinopsis and Gymnocalycium had the newest areoles. While planted in T4, as a result, the genus Astrophytum has increased in stem diameter, the number of new areoles, and the number of roots. In the Gymnocalycium also found an increase in stem diameter. Therefore, the use of cacti growing media in T3 as an appropriate for the growth of cacti. Furthermore, it can reduce the production cost of growing media about 0.72 baht per pot (33%) when compared with the commercial media (T1) in a 2-inches plastic pot.

Improving drought tolerance ofOpuntia ficus-indicaunder field using subsurface water retention technology: changes in physiological and biochemical parameters

The prickly pear ( Opuntia ficus-indica) is an essential economic and ecological medicinal plant in arid and semi-arid areas, especially in Morocco, where water scarcity affects its survival and growth. Evidence suggests that subsurface water retention technology (SWRT) may enhance crops’ drought resistance. A field experiment was conducted to explore SWRT application effects on cactus cladodes’ growth and physiological and biochemical performance under drought conditions. Two water regimes were applied (rainfed conditions; irrigated with 4 L of water twice a week) with two treatments (without SWRT; with SWRT). The results showed that cactus cladodes’ growth and physiological and biochemical parameters cultivated for 8 months were negatively affected by drought. Drought-exposed cactus cladodes under SWRT application showed an increase in surface area and cladode stomatal densities by 65% and 29%, respectively, compared with no SWRT. This technology reduced drought-induced oxidative stress by mitigating malondialdehyde and hydrogen peroxide excess by 22% and 17%, respectively. Moreover, lower levels of enzymatic and nonenzymatic antioxidant activities were concluded, and soil organic matter and assimilable phosphorus contents were enhanced. In conclusion, our findings highlighted SWRT’s positive impacts on the tested parameters, thus presenting it as a promising technology for cactus growth and development improvement under water deficiency.

Finding a Suitable Niche for Cultivating Cactus Pear (Opuntia ficus-indica) as an Integrated Crop in Resilient Dryland Agroecosystems of India

Climate change poses a significant threat to agroecosystems, especially in the dry areas, characterized by abrupt precipitation pattern and frequent drought events. Ideal crops, tolerant to these events, such as cactus, can perform well under such changing climatic conditions. This study spatially maps land suitability for cactus (Opuntia ficus-indica) cultivation in India using the analytical hierarchical process (AHP). Nine essential growth factors that include the climate and edaphic components were considered for the period 2000 to 2007. About 32% of the total geographic area of the country is in the high to moderate suitable category. Remaining 46% falls under the marginally suitable and 22% under the low to very low suitable category. The suitability analysis, based on the precipitation anomaly (2008–2017), suggests a high probability of cactus growth in the western and east-central part of India. The relationship with aridity index shows a decreasing rate of suitability with the increase of aridity in the western and east-central provinces (β~−1 to −2). We conclude that integrating cactus into dryland farming systems and rangelands under changing climate can be one plausible solution to build resilient agro-ecosystems that provide food and fodder while enhancing the availability of ecosystem services.

Biodegradation of copolymer obtained by grafting reaction between methacrylic acid and starch

Biodegradation of methacrylic acid and starch graft copolymers was investigated for the first time in this manuscript. Synthesized copolymer was characterized by 1H nuclear magnetic resonance spectroscopy (NMR), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and elemental analysis. Copolymers with different percentage of grafting, G (%), were buried in three different types of soil. Biodegradation was monitored by measuring mass loss of the samples and using FTIR and SEM. The highest weight loss was in soil for the orchid growth (all samples had biodegradation higher than 89%), followed by soil for the cactus growth (mass loss higher than 70%) and soil rich in humus where some of the samples had biodegradation rate near or less than 50%. The correlation between G (%) and percent of weight loss after biodegradation was not significant in any types of soil. FTIR and SEM showed that after biodegradation, samples still contained both building components. Respiration test showed higher O2 consumption and CO2 production comparing to polystyrene which confirmed biodegradability of the accessible starch in copolymer. Based on the obtained results, degradation mechanism is proposed. First step is biodegradation of easily accessible starch followed by dissolution of the poly(methacrylic acid). This mechanism confirmed that biodegradation depends not only on the percentage of grafting, but also on molecular packaging, chains arrangement and the number and types of microorganisms present in the specific types of soils.

Performance of cactus pear at two geographical locations in Indian arid zone

Twenty cactus pear (Opuntia ficus-indica Mill.) genotypes were introduced in India to assess its suitability and performance at two geographical locations i.e., Jodhpur, Rajasthan (26°18’N: 73°04’E, 216 m MSL) and Kutch-Bhuj, Gujarat (23°21’N: 69°77’E, 15 m MSL) for survival and growth. The cladodes were planted in the pottingmixture of soil and compost (6: 1) with initial moisture regulated at 7–9% to prevent rotting. The rooted plantswere transplanted in the field at 2 × 3 m spacing. Mortality due to bacterial rot ranged from 50 to 100 per cent atJodhpur. The highest plant survival in the field after one year of planting was recorded in genotypes RojaxRoja-4-Pianta-25 and ARL spineless (50%) followed by 33.33% each in genotypes Bianco Macomer, Roja Castel Sardo, Gymnocarpe and clone No. 1270. Absolute mortality occurred in varieties Roja San Cono, Clone No.1287, Giall× Giall, Trunzara Red San Cono, A. Giant, Lyria and Militelo White. In contrast, better survival per cent (20–90%)was observed at Bhuj in different accessions. However, the performance and survival in pots under shade nethouse was almost 100% at both the locations but the growth was better at Bhuj as compared to Jodhpur. Theestablishment and growth of cactus pear was affected at Jodhpur due to high temperature coupled with lowrelative humidity (27.81–58.39%, 10 years mean). The coastal areas of Kutch-Bhuj have comparatively higherrelative humidity (44–76%) favoured better growth of cactus. Based on this study, it can be inferred that Kutchbhuj region is comparatively better location for growing cactus pear.

Success of long-term restoration of degraded arid land using native trees planted 11 years earlier

Restoration of degraded desert soil with three species of legume trees and the giant cardon cactus was evaluated 11 years after planting in the southern Sonora Desert. The trees in six independent field experiments were grown individually or in combination of a legume tree and cardon cactus and were originally treated with plant growth-promoting bacteria, arbuscular mycorrhizal fungi, or small amounts of cattle compost or a combination of all treatments. Survival and height of trees and cacti and cactus biovolume were measured. When data were combined from all experiments and analyzed together, the best survivor was the cardon cacti and, to a lesser extent, the legume tree mesquite amargo. Over a decade later, a combination of a legume tree with cardon cactus, while detrimental to the legume, significantly increased the chances of the cactus to survive and grow in degraded soil. The biotic and compost treatments, while enhancing the initial establishment of the plants in 2004, had only marginal benefit on the growth of cactus 11 years later. Long-term desert restoration with native trees is possible. Because this cactus is the native, long term soil stabilizer, a combination cactus-legume tree is recommended for long term desert restorations.

Quick but Odd Growth of Cacti

Let $${\mathcal {F}}$$F be a family of graphs. Given an n-vertex input graph G and a positive integer k, testing whether G has a vertex subset S of size at most k, such that $$G-S$$G-S belongs to $${\mathcal {F}}$$F, is a prototype vertex deletion problem. These type of problems have attracted a lot of attention in recent times in the domain of parameterized complexity. In this paper, we study two such problems; when $${\mathcal {F}}$$F is either the family of forests of cacti or the family of forests of odd-cacti. A graph H is called a forest of cacti if every pair of cycles in H intersect on at most one vertex. Furthermore, a forest of cacti H is called a forest of odd cacti, if every cycle of H is of odd length. Let us denote by $${\mathcal {C}}$$C and $${{\mathcal {C}}}_\mathsf{odd}$$Codd, the families of forests of cacti and forests of odd cacti, respectively. The vertex deletion problems corresponding to $${\mathcal {C}}$$C and $${{\mathcal {C}}}_\mathsf{odd}$$Codd are called Diamond Hitting Set and Even Cycle Transversal, respectively. In this paper we design randomized algorithms with worst case run time $$12^k n^{\mathcal {O}(1)}$$12knO(1) for both these problems. Our algorithms considerably improve the running time for Diamond Hitting Set and Even Cycle Transversal, compared to what is known about them.

Introduced and invasive cactus species: a global review.

Understanding which species are introduced and become invasive, and why, are central questions in invasion science. Comparative studies on model taxa have provided important insights, but much more needs to be done to unravel the context dependencies of these findings. The cactus family (Cactaceae), one of the most popular horticultural plant groups, is an interesting case study. Hundreds of cactus species have been introduced outside their native ranges; a few of them are among the most damaging invasive plant species in the world. We reviewed the drivers of introductions and invasions in the family and seek insights that can be used to minimize future risks. We compiled a list of species in the family and determined which have been recorded as invasive. We also mapped current global distributions and modelled the potential global distributions based on distribution data of known invasive taxa. Finally, we identified whether invasiveness is phylogenetically clustered for cacti and whether particular traits are correlated with invasiveness. Only 57 of the 1922 cactus species recognized in this treatment have been recorded as invasive. There are three invasion hotspots: South Africa (35 invasive species recorded), Australia (26 species) and Spain (24 species). However, there are large areas of the world with climates suitable for cacti that are at risk of future invasion-in particular, parts of China, eastern Asia and central Africa. The invasive taxa represent an interesting subset of the total species pool. There is a significant phylogenetic signal: invasive species occur in 2 of the 3 major phylogenetic clades and in 13 of the 130 genera. This phylogenetic signal is not driven by human preference, i.e. horticultural trade, but all invasive species are from 5 of the 12 cactus growth forms. Finally, invasive species tend to have significantly larger native ranges than non-invasive species, and none of the invasive species are of conservation concern in their native range. These results suggest fairly robust correlates of invasiveness that can be used for proactive management and risk assessments.

Phyllotactic pattern formation in early stages of cactus ontogeny

Representatives of the family <em>Cactaceae</em> are characterized by a wide range of phyllotaxis. To assess the origin of this diversity, early stages of phyllotactic pattern formation were examined in seedlings. The analysis of the sequence of areole initiation revealed intertribal differences. In seedlings from the <em>Trichocereeae</em> (<em>Gymnocalycium</em>, <em>Rebutia</em>) and <em>Notocacteae</em> (<em>Parodia</em>) tribes, two opposite cotyledonal areoles developed as the first elements of a pattern. Usually, next pair of areoles was initiated perpendicularly to cotyledonal areoles, starting the decussate pattern. This pattern was subsequently transformed into bijugate or into simple spiral phyllotaxis. In seedlings from the <em>Cacteae</em> tribe (<em>Mammillaria</em> and <em>Thelocactus</em>), cotyledonal areoles were never observed and the first areoles always appeared in the space between cotyledons. It was either areole pair (mainly in <em>Mammillaria</em>), starting a decussate pattern, or a single areole (mainly in <em>Thelocactus</em>) quickly followed by areoles spirally arranged, usually in accordance with the main Fibonacci phyllotaxis. Differences in the initial stages of pattern formation do not fully explain the phyllotaxis diversity in mature cacti. Only two, the most common phyllotactic patterns occurred in the early development of studied seedlings, i.e. the main Fibonacci and the decussate pattern. Discrepancy in the range of phyllotactic spectra in seedlings and in mature plants suggests that phyllotaxis diversity emerges during further plant growth. Initial phyllotactic transformations, occurring already in the very early stages, indicate great plasticity of cactus growth and seem to support the hypothesis of the ontogenetic increase of phyllotaxis diversity due to transformations.

Are cactus growth forms related to germination responses to light? A test using Echinopsis species

In this study, we investigated the effect of light regimen (white light vs. darkness) on the germination of 12 species of the Echinopsis genus (tribe Trichocereeae, Cactaceae). This genus presents a variety of growth forms and relatively small and uniform seed size. These traits allowed us to test, within the same linage and removing seed mass effect, the hypothesis that the germination response to light (indifferent to light or positive photoblastic) is related to growth form. Our results reject this hypothesis since no seeds germinated in darkness, so all of the species can be classified as being positively photoblastic. The proportion of seed germination with white light was significantly different among cactus growth forms. Columnar cacti (arborescent, creeping and short) showed a greater proportion of seed germination than barrel and globose cacti. The germination rate differed among growth forms and species. At constant temperatures, creeping columnar cacti presented a significantly higher germination rate than the other growth forms. With alternating temperatures, columnar cacti showed higher germination rates than the other growth forms. The low proportion of seeds that germinated for some species indicates that they show seed dormancy. Our results suggest that germination responses to light in the cactus family could be related to seed mass and phylogenetic constraints.

Effect of different media on the in vitro growth of cactus ( Opuntia ficus-indica ) explants

The effect of media composition on the growth of cactus explants was investigated. Two media designated A and B were used in this study. Medium A contained basal Murashige Skoog salt (MS salt) and vitamins supplemented with 5% sucrose and 1% BAP (benzyl amino purines) and media B containing vitamins and MS salt supplemented with 3% sucrose, 1.25 mg/l BAP, and 0.25 mg/l IAA (indole acetic acid). These media were used to culture cactus explants over a period of 30 days, with a view to determine the effect of difference in the supplements on days to shoot emergence, shoot height, percentage survival and percentage oxidation (secretion of phenolic compounds) of the explants in. Analysis of the results indicated that there was no significant difference between the two media used in terms of the shoot height and days to shoot emergence.

Alterations in growth and crassulacean acid metabolism (CAM) activity of in vitro cultured cactus

Unlike C-3 plants, cacti possess a crassulacean acid metabolism (CAM) physiology that can alter the pattern of carbon uptake and affect plant growth under artificial environmental conditions, especially in tissue culture. In vitro-derived plantlets of Coryphantha minima grew 7-fold larger than plants cultured under similar ex vitro conditions. Growth regulators incorporated into the culture media during shoot proliferation stage of micropropagation had a strong influence on this increased growth. Other important factors that contributed to increased growth under in vitro conditions were high relative humidity and sugar in the culture medium. An analysis of gas exchange and daily fluctuations of malic acid levels revealed an increase in net photosynthetic rate, in terms of carbon assimilation, by in vitro plants compared with that of ex vitro plants. This stimulated photosynthesis in the presence of an external carbon source was unexpected but apparently true for cacti exhibiting CAM physiology. Unlike CAM plants grown in ex vitro conditions, net CO2 uptake by in vitro-cultured cacti occurred continuously in the light as well as the dark. Once regenerated, cacti were transferred to ex vitro conditions where the normal CAM pathway resumed with a concomitant reduction in growth and CO2 uptake. These results showed that growth of cacti can be considerably accelerated by in vitro culture.

Cell Cycle Duration in the Root Meristem of Sonoran Desert Cactaceae as Estimated by Cell-flow and Rate-of-cell-production Methods

Slow rates of cactus growth in the Sonoran Desert and high productivity of some Cactaceae under cultivation suggest that relatively low growth rates are not the consequence of a long cell division cycle but of short optimal periods for growth and adverse environmental factors. To verify this hypothesis, the duration of the cell division cycle (T)in the root apical meristem of seedlings of three sympatric species from the Sonoran Desert [Ferocactus peninsulae(F. A. C. Weber) Britton & Rose ‘Townsendianus’ (Britton & Rose) N. P. Taylor, stat. nov.,Stenocereus gummosus(Engelm.) Gibson & Horak andPachycereus pringlei(S. Watson) Britton & Rose] was estimated with the rate-of-cell-production (RCP) and the cell-flow (colchicine) methods. Both methods were applied during the steady-state growth phase, which was relatively short in the first two species because of the determinate pattern of root growth. The RCP method permitted estimation ofTin each root individually. Durations of the cell division cycle were inversely proportional to the rate of root growth (r2ranged from 0.42 to 0.88,P<0.05).T,determined by the cell-flow method, ranged from 14.4 to 19.3 h in these species and was within the same range asTdetermined by the RCP method. The averageTdetermined by the RCP method was 67 to 75% of that determined by the cell-flow method. Results obtained with both methods are compared and analysed. The proposed hypothesis appears to be correct, indicating that these species can be more productive under cultivation than in the wild due to the relatively short duration of the cell division cycle. Adaptive features of these findings are also considered.

Differentiation diversity of Argentine cacti and its relationship to environmental factors

Abstract. We studied the differentiation diversity (β‐diversity or species turnover) patterns of the three main cactus growth forms (columnar, opuntioid and globose) in 318 (1° × 1°) squares covering Argentina. We analysed the degree of association between species turnover of each growth form with the spatial variation of a set of 15 environmental variables.Species turnover was estimated in two ways: (1) by calculating species turnover along latitudinal and longitudinal gradients and (2) by evaluating the species turnover between each square and its eight surrounding neighbouring grid cells.For the three growth forms, species turnover in latitudinal transects was mostly related to the mean within‐transect values of certain environmental variables, while in longitudinal transects it was related to the variation of some environmental variables within the transect rather than to their mean values. For columnar species, transect species turnover was mainly associated with variation in temperature, confirming the temperature‐sensivity of this growth form. For opuntioid species, turnover along transects was mainly related to topographic variables. In the case of globose cacti, transect turnover was associated with variation in temperature and rainfall.For the three growth forms, areas of high turnover coincided with marked transitions between different biogeographic provinces, while the areas with lowest species turnover coincide with topographically and climatically uniform plains. Species turnover between individual squares was positively associated with the proportion of summer rainfall in globose cacti, the variation of mean annual temperature in columnar cacti and was negatively related to mean annual temperature in opuntioid cacti. Compared to the other growth forms, globose cacti presented a much larger proportion of squares with a high species turnover.In general, differentiation diversity was lower for the opuntioid and the columnar species, two growth forms with higher dispersal ability and was highest for the globose cacti, which have the lowest dispersal capacity. Environmentally heterogeneous areas, where large‐scale transitions between biomes occur, have exceptionally high species turnover, and are important target areas for the conservation of biodiversity.

Interaction of diffuse competition and insect herbivory in limiting brittle prickly pear cactus, Opuntia fragilis (Cactaceae)

We tested the effects of above‐ and belowground competition and evaluated insect herbivory on the growth of a common cactus (Opuntia fragilis) in Sandhills prairie. Our purpose was to determine the independent and joint contribution of these factors to the variation observed in cactus size and local abundance. We manipulated ambient prairie vegetation and surface water availability in a full factorial design. When Opuntia fragilis was released from competition with surrounding vegetation, it grew significantly larger in the second growing season, both in terms of number and size of new cladodes. Ramets grown within live prairie vegetation averaged no net growth. These ramets were also more frequently fed upon by the larvae of two internally feeding cactus insects. As a result, insect herbivory reinforced the competitive suppression of the cactus by grasses. Water supplementation had no significant effect, either on cactus growth or on insect herbivory. We conclude that the mechanism by which dense prairie vegetation influenced net growth of O. fragilis was both direct, through competition for nonwater resources such as light, and indirect, through its mediation of feeding by specialized insect herbivores. Furthermore, since the direct growth response to treatment did not precede the indirect effect of habitat‐mediated variation in feeding by insects, our results contradict the current expectation that indirect effects require more time to be expressed than do direct effects.

Indirect versus direct effects of grasses on growth of a cactus (Opuntia fragilis): insect herbivory versus competition.

Variation in plant performance between microhabitats is usually attributed to direct mechanisms, such as plant physiological tolerances or competitive interactions. However, indirect mechanisms, such as differences in herbivore pressure mediated by microhabitat differences, could create the same pattern of variation. In this study, we investigated the effect of insect herbivore pressure on the growth of the grassland cactus Opuntia fragilis under different regimes of grassland canopy cover. Our purpose was to establish the extent to which canopy cover plays a direct, competitive role versus an indirect, mediatory role in cactus growth. We manipulated aboveground microhabitat, specifically the cover of adjacent grasses. The three treatments were: (1) open canopy, with grass pinned down away from the cactus; (2) shaded canopy, with a partial mesh cage staked over the cactus; and (3) ambient grass canopy. We measured seasonal plant growth and recorded changes in insect herbivore occurrence and damage in relation to cover. Cactus growth, defined as the change in number of live cladodes, was higher in the open than under either treatment where the plant was more shaded (P<0.05). However, allocation to new growth, measured as the proportion of new segments (cladodes) in a patch, did not differ among cover treatments. Thus, the hypothesis that physiological constraints, or competition for light, limited cactus performance in grass is rejected. Instead, we found that both cladode mortality, caused by the larvae of a cactus moth borer (Melitara dentata), and occurrence of the moth were lower in the open microhabitat than in either shaded microhabitat. Thus, higher net growth in the open, unshaded treatment, rather than representing a release from competition for light with grasses, was better explained as an indirect effect of grass cover on the activity and impact of the cactus moth. These results show that indirect effects can lead to a misinterpretation of experimental data on direct effects. These data also contribute to an improved understanding of mixed results in the biological control of weedy cacti. Clearly, future evaluations of the relative importance of physiology, competition, and insect herbivory in plant performance must be environmentally explicit.

The introduction ofMimorista pulchellalis [Lepidoptera: Pyraustidae] into South Africa for the biological control of jointed cactus,Opuntia aurantiaca 1. Biology and mass-rearing techniques

A laboratory investigation was conducted on a pyraustid moth imported from South America for jointed cactus control. It was found that the moths were crepuscular, with females laying an average of 48±3.5 eggs over a period of 4–8 days. Larvae hatched out at night and usually tunnelled into the terminal ends of cactus cladodes at a site where young cactus growth occurred. The lifecycle was completed inside the cactus, pupation typically occurring in the dry husk of the cladode on which the egg was laid. Mass-rearing of the moth was easy if plants with young cactus growth were used.

Effect of Nurse Plants on the Microhabitat and Growth of Cacti

(1) Seedlings of the cactus Carnegiea gigantea at two sites in the Sonoran Desert were found only in sheltered microhabitats, 89% occurring under the canopy of Ambrosia deltoidea and Cercidium microphyllum. In contrast, 29% of the seedlings of Ferocactus acanthodes, which tolerates higher temperatures than C. gigantea, occurred in unsheltered microhabitats, where maximum soil surface temperatures reached 71?C. Most (70%) of the sheltered seedlings of F. acanthodes occurred under the canopy of the perennial bunchgrass Hilaria rigida. (2) Shading by nurse plants reduced the total daily photosynthetically active radiation (PAR) available for their associated seedlings. Near an equinox, a seedling of C. gigantea located at the centre of an A. deltoidea shrub received 77% less total daily PAR, which reduces its predicted net CO2 uptake by 90% compared with an unshaded seedling. Similarly, a seedling of F. acanthodes located at the centre of an H. rigida plant received 64% less total daily PAR and could fix 65% less CO2 than could an unshaded seedling. (3) H. rigida and F. acanthodes have overlapping shallow root systems (mean root depth of 0 08 m for H. rigida and 0 05 m for seedlings of F. acanthodes), which accentuates competition for water. A water uptake model, which closely predicted the soil water potential in the root zone of H. rigida, indicated that a seedling of F. acanthodes located at the centre of the bunchgrass took up 32% less water than did an exposed seedling. (4) Assuming that the effects of temperatures, PAR, and soil water on net CO2 uptake are multiplicative, the predicted net CO2 uptake of a seedling of F. acanthodes under the canopy of H. rigida was only 36% of that of an exposed seedling. However, areole production by seedlings of F. acanthodes located under the nurse plant was 68% of that measured in exposed areas. This discrepancy probably reflects the 60% higher soil nitrogen levels under H. rigida. (5) Therefore, nurse plants facilitate seedling establishment by reducing high temperatures near the soil surface and provide a microhabitat with a higher soil nitrogen level. However, shading and competition for water with the nurse plants markedly reduce seedling growth. The magnitude of the reduction depends on seedling size and location under the nurse plant.

Effects of herbicides and cultivation on the growth ofOpuntiain plantations

SummaryLandraces of the genus Opuntia (Cactaceae) are important in semi-arid regions of the Mediterranean area and in Mexico, Argentina, and Chile where they provide animal fodder, and fruits and vegetable material for human use. There is little literature on current cultivars or horticultural practices for use in these plantings. Opuntia plantations when not cultivated have a low productivity. Due to the great reduction in cactus growth by weeds and the tediousness in hand weeding spiny cactus germplasm collections, herbicides were evaluated for use in Opuntia plantings. Multiple combinations of eight herbicides (hexazinone, tebuthiuron, simazine, diuron, bromacil, oryzalin, oxyfluorfen, and metolachlor) and a mechanical cultivation treatment were examined for their effect on the biomass production and survival of Opuntia lindheimeri. The vegetative cover measured 7 months from planting ranged from 0.1% to 83%. Biomass was measured by complete harvest 14 months after planting and ranged from 511 kg ha−1 ...