Aunque los pirules tienen efectos alelopáticos negativos sobre los cultivos, sus efectos sobre estas plantas nativas siguen siendo desconocidos. De hecho, la. vol número1 Alternancia de cultivos, su efecto sobre el suelo en zonas dedicadas a tabaco negro en · índice de autores · índice de materia búsqueda de . No Brasil, os estudos com alelopatia são, muitas vezes, restritos à influência de plantas cultivadas e invasoras sobre os cultivos, principalmente em manejo com .
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Differential allelopathy between genders of an invasive dioecious tree on desert plants.
The Peruvian peppertree Schinus molle is a dioecious species from South America that was introduced into central Mexico five centuries ago. This tree has invaded abandoned agricultural fields from semiarid regions, where it can be found with several native succulent plants that have recolonized these areas. Although peppertrees have negative allelopathic effects on crops, their effects on these native plants remain unknown.
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Indeed, the allelopathy of peppertrees has only been tested for female individuals, while the allelopathic potential of male peppertrees has not been assessed yet. This study focused on these issues and assessed whether peppertrees affect germination of succulent plants from the Chihuahuan Aelopatia and whether these effects differ between male and female trees.
For this we conducted a series of germination bioassays where seeds of native species were watered with aqueous extracts of staminate flowers and leaves produced by male peppertrees, and with aqueous extracts of fruits and leaves produced by female peppertrees. Additionally, we conducted experiments where seeds of native species were sowed on soils collected vultivos the canopy of both tree genders.
The results of all these experiments indicated that both peppertree genders can reduce germination of native species, but also suggested that male peppertrees would have stronger allelopathic effects than female peppertrees. To our best knowledge, this is the first study reporting allelopathic effects of peppertrees on native plants from Mexico, but this is also the first study indicating differential gender effects for invasive dioecious species with allelopathic potential. Alien plants usually colonize areas affected by human activities where native vegetation has been partially or completely removed Lozon and MacIsaac, ; Alston and Richardson, After their establishment, these invasive plants can prevent the recovery of native vegetation in several ways Levine et al.
Akelopatia competitive ability is a major mechanism by which invasive plants can cultiovs with the recovery of native communities Eliason and Allen, ; Bakker and Wilson, ; Alelopatla and Pugnaire, ; Castro et al.
Nevertheless, some invasive species also produce secondary metabolites that can inhibit the germination and growth of other plants in their surroundings Ridenour and Callaway, ; Inderjit et al. Although this allelopathic inhibition, as commonly referred to, occurs without involving direct competition among species, allelopathic plants take advantage from this process because they can monopolize the use of resources within their area of influence by excluding other potential competitors Muller, This could be the case of the Peruvian peppertree Schinus molle Cultvios.
This dioecious tree was introduced from South America by dultivos middle of the 16 th century as result of the commercial exchange between the former viceroyalties of Peru and New Alelopwtia Kramer, Peppertrees were quickly incorporated into the Mexican culture because of their rapid growth to obtain raw materials and several ethnobotanical uses in traditional medicine Bye and Linares, ; Paredes-Flores et al.
This suggests that peppertrees could interfere with the establishment of native plants. Peruvian peppertrees produce several secondary alekopatia that have been proven to reduce germination of crops, including flavonoids, oleoresins, tannins, terpenes and saponins Zahed et al. However, as far as we are aware, these negative effects on crop germination have been only evaluated for fruits and leaves produced by female peppertrees Anaya and Gomez-Pompa, ; Materechera and Hae, ; Zahed et al.
Therefore, the allelopathic effects of peppertrees on Mexican succulent plants remain unknown, as well as the differential effects that male and female trees may have on these species. In this study we performed a series of laboratory and greenhouse alelopqtia addressed to test these effects.
We specifically focused on 1 determining whether Peruvian peppertrees have the potential to reduce the germination and growth succulent plants from the Chihuahuan Desert, and 2 assessing whether male and female individuals of this invasive tree have differential allelopathic effects on these species. Mean annual temperature in this site is The density of adult peppertrees in this site is The density of recruiting peppertrees i.
Native species seed collection. Six succulent plant species were used to test the allelopathic effects of peppertrees. Seeds of all these species were obtained by collecting mature fruits between October and January For this, parental plants of each species were randomly selected in the field cuotivos and we collected alelopaatia on each of them. Fruits were carried to the laboratory and cleaned to release the seeds. Seeds were later stored in ventilated plastic flasks until their use alellpatia the experiments described below.
Allelopathic potential of peppertrees.
Influencia de la alelopatía en los cultivos 
We firstly performed a series of in vitro germination bioassays addressed to test whether the different peppertrees organs contain secondary metabolites with the potential to prevent germination of native plants, as well as to assess whether these effects differ between male and female trees.
In these bioassays, seeds of native species were watered with aqueous extracts obtained from staminate flowers and leaves produced by male individuals, and with aqueous extracts obtained from fruits and leaves produced by female trees. Plant organs of peppertrees were collected aelopatia April dry season by randomly selecting ten individuals of each gender in the field site. On male trees we collected g of mature leaves and g of staminate flowers, while on female trees we collected g of mature leaves and g of mature fruits.
Pistillate flowers were not included because most of them had already developed the fruit by the moment in which plant organs were collected. Plant organs were pooled across trees of each gender to obtain a composite sample of 1 kg per plant organ.
These samples were rinsed with distilled water during 1 min to remove dust and any other particulate materials. We did it because contaminants from urban areas neighboring the field site might reach the peppertrees and accumulate on them, which in turn could interfere with the assessment of their allelopathic effects.
Thus, although washing may remove some secondary metabolites accumulated on the surface of plant organs, we preferred assessing the allelopathic effects of secondary metabolites contained within plant organs to avoid biased effects of due to the presence of external contaminants. Aqueous extracts were prepared within 24 h after collection of plant organs.
For this, g of each plant organ staminate flowers, fruits and leaves of male and female trees were crushed it with 1 L of distilled water. Blends were later filtered and the resulting extracts were used in the germination trials described below.
This procedure concurs with those used by other authors that have assessed the allelopathic effects of peppertrees on crops Materechera and Hae, ; Borella et al. Nevertheless, since the inhibitory effects of allelopathic compounds usually depend upon their concentrations Batish et al.
Thus, for each plant organ we obtained a concentrated extract equivalent to g of plant organs per liter of distilled water, and a diluted extract equivalent 50 g of plant organs per liter of distilled water.
To test the allelopathic effects of these extracts we prepared plastic Petri dishes 50 mm diameter by 12 mm deep using sterile cotton pads as germination substrate. We assigned 45 of dishes to each native species and sowed 20 seeds of the cultivod species on these dishes.
For each culyivos, these dishes were split into nine groups 5 dishes per group ; eight groups of dishes separately received 5 mL of the different aqueous extracts male flowers, fruits, and leaves of male and female trees at the two concentrations concentrated and diluted extractswhile the ninth group of dishes only received distilled water control group.
Therefore, a total of seeds of each species received each watering treatment. Neither water nor additional extracts were added afterwards. In all cases, germination was assumed when the emergence of the radicle was observed. Allelopathy in soils beneath peppertrees. To assess whether secondary metabolites produced by peppertrees are released to the cultivoe, an also assess whether they retain their capability to inhibit germination of native species, we conducted a greenhouse germination experiment.
For this, we randomly selected five trees of each gender in the field site and collected 2 L of soil first 10 cm of the soil profile beneath their canopies. The same procedure was used to collect control soil in five open areas without vegetation cover, always maintaining a minimum distance of 20 m from the canopy of any peppertree.
Samples belonging to the same soil type male trees, female trees and control soil were pooled and meshed to remove leaf litter and other coarse materials.
Alelopatía diferencial entre los géneros de un árbol invasor dioico sobre plantas de desierto
All pots were watered every three days with 30 ml of distilled water. Since most seeds in the pots were superficially buried, it was hard to assess the emergence of the radicle. Thus, we assumed that seed germination had successfully occurred when the aerial shoots of seedlings were observed. Seedling emergence was monitored every three days during 60 days. Besides testing whether soils collected beneath peppertrees affect germination, the seedlings resulting from the greenhouse experiments were used to assess whether peppertrees affect the growth of succulent plants.
For this, the seedlings were removed from the pots at the end of the experiment, taking care of avoiding damage on their aerial shoots and radicular systems.
Each seedling was weighed in an analytical balance accuracy 0. Since several seedlings were recovered from each experimental pot, dry biomass was averaged across seedlings belonging to the same pot to avoid pseudoreplication in the statistical analyses described below Hurlbert, Failure-time-analyses were used to compare germination rates among treatments of the in vitro germination bioassays. When differences were detected, the Cox-Mantel two-sample test Lee et al.
The dry biomass of seedlings obtained in the greenhouse experiments was firstly compared among soil types with one-way ANOVA. These analyses were conducted separately for each native species and, when differences were detected, the post-hoc Tukey test was used to assess differences between soil types. Germination rates of all native species significantly differed among watering treatments in the in vitro bioassays results of statistical analyses in Table 1.
Pairwise comparisons between seeds watered with peppertree extracts and control seeds indicated that this invasive species contains secondary metabolites that can inhibit the germination of succulent plants from the Chihuahuan Desert Figure 1. Nevertheless, the magnitude of these effects varied among plant organs staminate flowers, fruits and leaves of male and female peppertreesbetween concentrations of the aqueous extracts concentrated and diluted extracts and across native species.
Symbols on the side of each figure indicate the watering treatment to which each curve belongs to.
Germination rates of Echinocactus platyacanthus were only reduced by extracts of staminate flowers, and these inhibitory effects occurred irrespectively of the aleloopatia of the aqueous extracts Figure 1A. In this case, no differences were found among the other treatments, including the control Figure 1A. In Ferocactus latispinus Figure 1B and Myrtillocactus geometrizans Figure 1Cthe concentrated and diluted extracts of staminate flowers also reduced germination rates in higher magnitudes than the other treatments.
Nevertheless, for these two cacti, extracts obtained from all other peppertree organs also led to lower germination rates than those estimated for control seeds Figure 1. Conversely to that reported for these cactus species, germination rates of Mammillaria longimamma were more strongly reduced by the concentrated extracts of fruits and leaves of female peppertrees Figure 1D. Nevertheless, the germination of this species was also inhibited by the other peppertree extracts, as compared to control seeds Figure 1D.
The two succulent monocots, Agave salmiana Figure 1E and Yucca filifera Figure 1Fdisplayed lower germination rates when watered with the concentrated extract of staminate flowers, as compared to all the other watering treatments.
The diluted extract of staminate flowers also caused lower germination rates in these two species than the other watering treatments Figure 1E and 1F.
In the case of A. Nevertheless, the diluted extracts of these plant organs did not affect germination rates of Y.
Shoot emergence rates and seedling biomass of all succulent species significantly differed among soil types results of statistical analyses in Table 1. However, the magnitude with which soil types affected these response alwlopatia varied among species. The last column of the table shows the results of the one-way ANOVA used to compare seedling dry biomass among soil types used in the greenhouse experiments.
Shoot emergence rates of Echinocactus platyacanthus Figure 2AFerocactus latispinus Figure 2B and Myrtillocactus geometrizans Figure 2C were lower in the soil collected beneath male peppertrees, as compared to the other soil types. Nevertheless, these three species also displayed lower shoot emergence rates in the soil collected beneath female peppertrees than in the control soil collected in open alelopatiia without vegetation cover Figure 2A2B and 2C.
On the other hand, shoot emergence rates of Mammillaria longimamma did not differ between soils collected beneath male and female peppertrees, but these two soil types reduced shoot emergence rates as compared with the control soil Figure 2D. The two succulent monocots, Agave salmiana Figure 2D and Yucca filifera Figure 2Fdisplayed lower shoot emergence rates in soils collected beneath male peppertrees.
Nevertheless, while shoot emergence rates of A. Seedlings of Echinocactus platyacanthus Figure 3A and Ferocactus latispinus Figure 3B showed lower biomass in soils collected culttivos both peppertrees genders than in the control soil. Nevertheless, in both cases, soil collected beneath male peppertrees had stronger negative effects than soil collected beneath alelopatiz trees Figure 3A and 3B. Myrtillocactus geometrizans and Mammillaria longimamma also displayed lower seedling biomass on soils collected beneath the canopy of rn invasive species, but no differences were found between peppertree genders Figure 3C and 3D.
Biomass of Agave salmiana seedlings was lower on soils collected beneath peppertrees than in the control soil, but seedlings grown on soil collected beneath male individuals were smaller than those grown on soil collected beneath female trees Figure 3E.
The biomass of seedlings of Yucca filiferaon the other hand, was negatively affected by the soil collected beneath male peppertrees, while no differences were found between seedlings grown on the soil collected beneath female trees and the control soil Figure 3F.