Roberto Lindig-Cisneros

WETLAND RESTORATION THRESHOLDS: CAN A DEGRADATION TRANSITION BE REVERSED WITH INCREASED EFFORT?

Previous attempts to reverse the degradation of a coastal wetland and restore nesting habitat for an endangered bird showed that adding nitrogen could temporarily increase the height of Spartina foliosa, but not produce self-sustaining tall canopies. We asked if increased effort (up to five years of N fertilization) would shift canopy attributes across the hypothesized threshold. Thirty plots were treated with 0–5 yr of urea addition, and all were followed for 5 yr. Canopies were robust while urea was being added, but Spartina reverted to short stature soon after fertilization ended, supporting R. J. Hobbs and D. A. Nortons concept of an irreversible transition. However, specific outcomes depended on the choice of response variable (six comparisons), the choice of reference data (initial conditions, same-year data, and pooled data), and the choice of statistical design (repeated measures vs. complete design), indicating the need to assess experiments thoroughly before making strong recommendations for ma...

VEGETATION OF TEPHRA DEPOSITS 50 YEARS AFTER THE END OF THE ERUPTION OF THE PARICUTÍN VOLCANO, MEXICO

Abstract Volcanic eruptions offer unique opportunities for the study of successional processes. The Paricutín Volcano eruption that started in 1943 and lasted for 9 years created different conditions for primary and secondary succession. Bare areas at the time of the eruption (mainly agricultural fields) offer an opportunity to study the effect of major natural disturbances in sites previously affected by human activities. One representative area, the Mesa de Cutzato, was surveyed to determine vegetation species composition and structure 50 years after the volcanic eruption ceased. Our results showed that few species have established and that total plant cover remained low (< 10%) and is patchy. Four species dominated these patches: Eupatorium glabratum (23% relative cover), Senecio stoechadiformis (14%), Senecio salignus (12%) and Muhlenbergia minutissima (6%). These species are either early successional or disturbance-tolerant species. No late successional species, particularly tree species, were found. Our results suggested that in old agricultural fields covered by tephra, known as arenales, succession is proceeding slowly.

Effects of domestication and agronomic selection on phytoalexin antifungal defense in Phaseolus beans

Systems of wild and cultivated relatives are good experimental systems to test chemical defense theory because they provide closely related varieties that differ in discrete traits. To determine the relationship between resistance and chemical defense diversity among wild, landrace and cultivar accessions of Phaseolus vulgaris, we measured resistance to fungal infection in laboratory and field experiments, quantified phytoalexin diversity, and assessed the effectiveness of phytoalexin mixtures extracted from live tissue. Results show a gradient of resistance to fungal infections between wild, landrace and cultivar varieties. In the laboratory, wild seedlings were more resistant (93% non-infected) than landrace seedlings (80% non-infected) and modern cultivar seedlings (68% non-infected). Under field conditions wild seedlings were more resistant (97% non-infected) than cultivar seedlings (71% non-infected). Wild seedlings presented the highest phytoalexin diversity (H′u2009=u20091.11), while those of the landrace presented an intermediate level (H′u2009=u20090.97) and cultivar seedlings presented the lowest diversity (H′u2009=u20090.93). No differences were found in total concentrations. The in vitro inhibitory properties on hyphal growth of the isoflavonoid mixtures produced by individual seedlings showed a similar trend. Our results are consistent with similar gradients in other species of Phaseolus beans and resistance to Colletotrichum sublineolum in sorghum.

Effect of tephra depth on vegetation development in areas affected by volcanism

Plant establishment on sites affected by major volcanic disturbances is limited by several factors, such as lack of suitable microsites for germination and establishment in sites affected by tephra from volcanic eruptions. Even after long periods of time, tephra deposited over un-vegetated areas (agricultural fields and other barren areas) lack closed vegetation cover and in many cases late successional species. To assess limiting factors for plant establishment, a field survey in a tephra deposit from the Paricutin volcano eruption (19°30′42.4′′xa0N, 102°12′03.0′′) and greenhouse experiments were carried out. The field survey determined the relationship between tephra depth and vegetation distribution. Greenhouse experiments determined the effect of tephra depth on establishment and growth of two dominant species in the tephra deposit surveyed, Eupatorium glabratum and Lupinus elegans. Our results suggest that size and spatial distribution of vegetation patches is related to tephra depth in the field (77% of the vegetation patches were on tephra 38.8xa0cm deep or less and only 2% on tephra of more than 46.8xa0cm). Under greenhouse conditions, Eupatorium glabratum and Lupinus elegans height sharply decreased as depth of the tephra layer increased. Lupinus elegans plants growing in tephra less than 30xa0cm deep had a mean weight of 10.56xa0g (±0.53xa0g) compared with 3.11xa0g (±0.46xa0g) for plants growing in tephra more than 30xa0cm deep. Our results suggest that tephra depth is a limiting factor for canopy development in barren areas affected by tephra deposition.

Effects of organic matter added to sand deposits of volcanic origin on recruitment of seedlings.

Abstract Vegetational development in areas covered by volcanic ash from the Paricutin Volcano shows striking differences among types of plant cover at the time of the eruption. Forests affected by deposition of ash recovered soon after the eruption (1943–1952), but areas lacking vegetation at the time of the eruption today lack a closed canopy. We tested the effect of adding organic matter, straw, and a combination of organic matter and straw on recruitment of seedlings in a sand deposit formed in agricultural fields covered by ash from the Paricutin Volcano in Michoacán, Mexico. Number of seedlings varied significantly among treatments. At the end of the rainy season, plots with organic matter showed the highest number of seedlings (154 ± 20 seedlings/m2) followed by plots with organic matter and straw (82 ± 7 seedlings/m2), plots with straw (68 ± 14 seedlings/m2), and control plots (21 ± 13 seedlings/m2). In contrast, plots with organic matter and straw accumulated significantly more biomass (61.7 ± 10.8 g/m2) than organic-matter plots (14.5 ± 3.1 g/m2) or mulched plots (9.9 ± 3.1 g/m2). Clustering of experimental plots indicated that species composition of seedlings differed between plots with organic matter and straw, and plots with straw or organic matter. Our results suggest that the nature of organic matter that accumulates in soil can have a significant effect on composition of the seedling community, and support Egglers hypothesis that lack of organic matter prevents development of vegetation in sandy substrates of volcanic origin.

Response of Pinus pseudostrobus Lindl. to fertile growing medium and tephra-layer depth under greenhouse conditions

Major disturbances that remove vegetation cover create conditions that differ greatly from those in adjacent forests. In volcanic areas, tephra deposition can be a major disturbance that eliminates vegetation cover and creates a barrier for plant establishment. The eruption of the Paricutín volcano, in Michoacán, México, from 1943 to 1952, created large tephra deposits adjacent to forest stands. Many of these deposits still lack native vegetation and understanding of the limiting factors for establishment of native tree species is necessary to restore these areas. Pinus pseudostrobus early growth in response to the amount of fertile growing medium on top of a variable-depth tephra layer was evaluated in a greenhouse experiment. Increasing amounts of fertile growing medium increased height of 28-week-old plants (no growing mediumxa0=xa05.5xa0cm tall ±1.8xa0cm, 3xa0cm of growing mediumxa0=xa021.2xa0±xa04.6xa0cm and 6xa0cm of growing medium 24.8xa0±xa04.4xa0cm). Other variables showed the same trend (diameter, number of fascicles, belowground biomass and aboveground biomass). Our results suggest that P. pseudostrobus establishment in tephra covered areas will depend on the accumulation of a fertile layer of more than 3xa0cm in thickness.

Performance of two valuable species, Pinus pseudostrobus and Eysenhardtia polystachya, in a low fertility soil mediated by mycorrhizal fungi and fertilization

AbstractnInterspecific relationships are fundamental to maintain ecological processes, and are particularly important for the recovery of plant cover in severely degraded sites. An experiment was set up to evaluate pairs of Pinus pseudostrobus–Eysenhardtia polystachya plants, the first inoculated with Pisolithus tinctorius and the second inoculated with P. tinctorius and/or Rhizophagus intraradices, plus inoculation controls, and phosphorus fertilization. Growth and biomass were measured as response variables. For the pines, only height and number of branches responded to factors directly applied to the tree: fertilization and inoculation with Pisolithus tinctorius. However, these variables also responded to inoculation of the legume with Rhizophagus intraradices, implying an indirect effect on the pine plant. Furthermore, this indirect effect was significant for pine biomass accumulation. Fertilization had a positive and significant effect for the legume plants increasing the values for almost all of the variables (apart from branch length) but for some variables the simultaneous presence of both mycorrhizal fungi was detrimental. Different combinations of fertilization and inoculation benefit growth of the pines and the legumes. When environmental restoration of production systems is considered, either conditions favoring the legume can be achieved (if protection of the soil in the short-term is desirable), or conditions favoring the pines can be implemented (if favoring the tree species is preferable).