Waterlogging and fire impacts on nitrogen availability and utilization in a subtropical wet heathland (wallum)

Protein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90- and 60-fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate, During waterlogging soil amino acids increased, particularly gamma-aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non-mycorrhizal wallum species were significantly (P < 0.05) N-15-enriched (0.3-4.3 parts per thousand) compared to species with mycorrhizal associations (ericoid-type, ecto-, va-mycorrhizal) which were strongly depleted in N-15 (-6.3 to -1.8 parts per thousand). Lignotubers and roots had delta(15)N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto-, ecto/va-, and ericoid type mycorrhizal species which were enriched in N-15 (0.1-2 4 parts per thousand). The delta(15)N signatures of delta(15)N(total soil N) and delta(15)N(soil NH4+) were in the range 3.7-4.5 parts per thousand, whereas delta(15)N(soil NO3-) was significantly (P < 0.05) more enriched in N-15 (9.2-9.8 parts per thousand). It is proposed that there is discrimination against N-15 during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium.

Effect of soil waterlogging on below-ground biomass allometric relations in Norway spruce

An increasing importance is assigned to the estimation and verification of carbon stocks in forests. Forestry practice has several long-established and reliable methods for the assessment of aboveground biomass; however we still miss accurate predictors of belowground biomass. A major windthrow event exposing the coarse root systems of Norway spruce trees allowed us to assess the effects of contrasting soil stone and water content on belowground allocation. Increasing stone content decreases root/shoot ratio, while soil waterlogging leads to an increase in this ratio. We constructed allometric relationships for belowground biomass prediction and were able to show that only soil waterlogging significantly impacts model parameters. We showed that diameter at breast height is a reliable predictor of belowground biomass and, once site-specific parameters have been developed, it is possible to accurately estimate belowground biomass in Norway spruce.

Protein changes and proteolytic degradation in red and white clover plants subjected to waterlogging

Red (Trifolium pratense L., cv. “Start”) and white clover varieties (Trifolium repens L., cv. “Debut” and cv. “Haifa”) were waterlogged for 14 days and subsequently recovered for the period of 21 days. Physiological and biochemical responses of the clover varieties were distinctive, which suggested different sensitivity toward flooding. The comparative study of morphological and biochemical parameters such as stem length, leaflet area, dry weight, protein content, protein pattern and proteolytic degradation revealed prominent changes under waterlogging conditions. Protease activity in the stressed plants increased significantly, especially in red clover cv. “Start”, which exhibited eightfold higher azocaseinolytic activity compared to the control. Changes in the protein profiles were detected by SDS-PAGE electrophoresis. The specific response of some proteins (Rubisco, Rubisco-binding protein, Rubisco activase, ClpA and ClpP protease subunits) toward the applied stress was assessed by immunoblotting. The results characterized the red clover cultivar “Start” as the most sensitive toward waterlogging, expressing reduced levels of Rubisco large and small subunits, high content of ClpP protease subunits and increased activity of protease isoforms.

Utilization Of (15)no3 (-) By Nodulated Soybean Plants Under Conditions Of Root Hypoxia.

Waterlogging of soils is common in nature. The low availability of oxygen under these conditions leads to hypoxia of the root system impairing the development and productivity of the plant. The presence of nitrate under flooding conditions is regarded as being beneficial towards tolerance to this stress. However, it is not known how nodulated soybean plants, cultivated in the absence of nitrate and therefore not metabolically adapted to this compound, would respond to nitrate under root hypoxia in comparison with non-nodulated plants grown on nitrate. A study was conducted with (15)N labelled nitrate supplied on waterlogging for a period of 48 h using both nodulated and non-nodulated plants of different physiological ages. Enrichment of N was found in roots and leaves with incorporation of the isotope in amino acids, although to a much smaller degree under hypoxia than normoxia. This demonstrates that nitrate is taken up under hypoxic conditions and assimilated into amino acids, although to a much lesser extent than for normoxia. The similar response obtained with nodulated and non-nodulated plants indicates the rapid metabolic adaptation of nodulated plants to the presence of nitrate under hypoxia. Enrichment of N in nodules was very much weaker with a distinct enrichment pattern of amino acids (especially asparagine) suggesting that labelling arose from a tissue source external to the nodule rather than through assimilation in the nodule itself.

Germinação e crescimento de Calophyllum brasiliense (Clusiaceae), uma espécie típica de florestas inundadas

Soil waterlogging and the subsequent reduction in the amount of oxygen available for the respiration of the root system selected, along the evolutive process, plants able to thrive in seasonally or permanently flooded areas. In neotropical plants there are many types of adaptations to flooding. In this paper we present the results of the work carried out with seeds and seedlings of C brasiliense subjected to hypoxia during germination and early development. C brasiliense seeds are not photoblastic and survive up to three months burried in a water saturated substrate, but germination only takes place in well-drained soils. Soil waterlogging does not inhibit seedling growth and there are no apparent morphological changes of the aerial part of flooded plants. New and aerated roots that make plant survival possible replace old and spoiled roots. In contrast to many typical species of flood-prone areas where growth is inhibited by oxygen stress. C. brasiliense seedlings seem to be well adapted to their waterlogged environment. Seed dispersion, the absence of photoblastic response as well as seed and seedling capacity of surviving and growing in waterlogged soils contribute to the wide geographic distribution of C. brasiliense always associated with areas subjected to soil waterlogging.

Adaptation trials of Atriplex and Maireana species and their response to saline waterlogged conditions in Pakistan

Utilization of salt affected wasteland by growing forage shrubs has enormous economic and environmental implication for developing countries like Pakistan, where approximately 6.3 million ha of the land is salt affected. Considering the importance of Atriplex and Maireana species, research has been conducted using their different species on the salt affected soils of Faisalabad. Most of Atriplex and Maireana species survived under the environmental conditions of Faisalabad and gave the good yield in the form of forage. Some of these species are woody and can be used for fuel purposes. Sixteen genotypes of Atriplex and Maireana were tested for their tolerance to waterlogging in order to identify halophytic fodder shrubs suitable for growth on secondary salt-affected and waterlogged farmland. The physiological and morphological responses of the species tested were typical of species with a generally poor tolerance to waterlogging. Despite this, some species (eg A. Amnicola) were surprisingly resistant, surviving up to five months of waterlogging at moderate salinity and high evapotranspirational demand. The most resistant species, A amnicola maintained higher transpiration rates, leaf water potentials and shoot extension rates than most other species during five weeks of waterlogging, and a return to control levels more quickly than other species after plots were drained. Although little morphological adaptation to waterlogged conditions was detected, a shallow and extensive lateral root system and the formation of many short aerenchymatous adventitious roots from procumbent branches appeared to advantage A. Amnicola in an environment highly heterogeneous in salinity and low in oxygen concentration. Shallow fibrous rooted species were quickly killed by waterlogging, although the procumbent branches of some individuals survived as clones if they developed adventitious roots.

Growing Atriplex and Maireana species in saline sodic and waterlogged soils

Utilization of salt affected wasteland by growing forage shrubs has enormous economic and environmental implication for developing countries like Pakistan, where approximately 6.3 million ha of the land is salt affected. Considering the importance of Atriplex and Maireana species, research has been conducted using their different species on the salt affected soils of Faisalabad. Most of Atriplex and Maireana species survived under the environmental conditions of Faisalabad and gave the good yield in the form of forage. Some of these species are woody and can be used for fuel purposes. Sixteen genotypes of Atriplex and Maireana were tested for their tolerance to waterlogging in order to identify halophytic fodder shrubs suitable for growth on secondary salt-affected and waterlogged farmland. The physiological and morphological responses of the species tested were typical of species with a generally poor tolerance to waterlogging. Despite this, some species (e.g., A. amnicola) were surprisingly resistant, surviving up to five months of waterlogging at moderate salinity and high evapotranspirational demand. The most resistant species, A amnicola maintained higher transpiration rates, leaf water potentials and shoot extension rates than most other species during five weeks of waterlogging, and a return to control levels more quickly than other species after plots were drained. Although little morphological adaptation to waterlogged conditions was detected, a shallow and extensive lateral root system and the formation of many short aerenchymatous adventitious roots from procumbent branches appeared to advantage A. amnicola in an environment highly heterogeneous in salinity and low in oxygen concentration. Waterlogging quickly killed shallow fibrous rooted species, although the procumbent branches of some individuals survived as clones if they developed adventitious roots.

Nitrate ammonification and its relationship to the accumulation of ammonium in a Vertisol subsoil

High concentrations of ammonium ( up to 270 kg N/ha) have been observed in a Vertisol soil below 1 m depth near Warra in south-east Queensland. This study examined the possibility that increased water movement into the subsoil after the removal of native vegetation, and a subsequent increase in periods of waterlogging, could have triggered nitrate ammonification and be responsible for the production of ammonium. Two incubation experiments were conducted to test this hypothesis. The first involved the incubation of repacked cores that had been amended with 30 mg N/kg of 5 atom% N-15 nitrate under low oxygen conditions for a period of 360 days. Over this time period the N-15 enrichment of the exchangeable ammonium fraction was monitored in order to detect any reduction of nitrate to ammonium. The second experiment involved the incubation of soil amended with 30 mg N/ kg of 5 atom% N-15 nitrate under waterlogged and low oxygen conditions for 75 days. During this period the redox potential of the soil was monitored using a field test to determine if reducing conditions would develop in this soil over a period of waterlogging, combined with the monitoring of any nitrate reduction to ammonium. The results of these experiments indicated that a small amount of nitrate ammonification (< 0.1 mg N/ kg) could be observed in the Warra subsoil, but that unless the rate of reduction were to significantly increase with time, this could not account for the accumulation of ammonium observed in the field. The environmental conditions that would make either dissimilatory or abiotic nitrate ammonification favourable were not observed to develop. Consequently, it has been concluded that the observed nitrate ammonification occurred via an assimilatory pathway. Due to the low rate of microbial activity in this subsoil it is considered unlikely that this process was responsible for the subsoil ammonium accumulation at Warra.

Seasonal changes of leaf Nitrogen content in trees of Amazonian floodplains

In Amazonian floodplains the trees are exposed to extreme flooding of up to 230 days a year. Waterlogging of the roots and stems affects growth and metabolic activity of the trees. An increased leaf fall in the aquatic period and annual increment rings in the wood indicate periodical growth reductions. The present study aims at documenting seasonal changes of metabolism and vitality of adult trees in the annual cycle as expressed by changes of leaf nitrogen content. Leaves of six tree species common in floodplains in Central Amazonia and typical representants of different growth strategies were collected every month between May 1994 and June 1995 in the vicinity of Manaus, Brazil. Mean leaf nitrogen content varied between 1.3% and 3.2% in the non-flooded trees. Three species showed significantly lower Ν content in the flooded period (p=0.05, 0.001, 0.001), the difference ranging 20-25% lower than in the non-flooded period. Two species showed no significant difference while Nectandra amazonum showed 32% more Ν in the flooded season (p=0.001). Leaf nitrogen content was generally high when new leaves were flushed (in the flooded period) and decreased continuously thereafter in all species. Three species showed an additional peak of nitrogen during the first month of the terrestrial phase, in leaves which had flushed earlier, indicating that flooding may disturb nitrogen uptake.

Geoecological drivers of cerrado heterogeneity and 13C natural abundance in oxisols after land-use change

The 13C natural abundance technique was applied to study C dynamics after land-use change from native savanna to Brachiaria, Pinus, and Eucalyptus in differently textured Cerrado Oxisols. But due to differences in the d13C signatures of subsoils under native savanna and under introduced species, C substitution could only be calculated based on results of cultivated soils nearby. It was estimated that after 20 years, Pinus C had replaced only 5 % of the native C in the 0-1.2 m layer, in which substitution was restricted to the top 0.4 m. Conversely, after 12 years, Brachiaria had replaced 21 % of Cerrado C to a depth of 1.2 m, where substitution decreased only slightly throughout the entire profile. The high d13C values in the subsoils of the cultivated sites led to the hypothesis that the natural vegetation there had been grassland rather than Cerrado sensu stricto, in spite of the comparable soil and site characteristics and the proximity of the studied sites. The hypothesis was tested using aerial photographs of 1964, which showed that the cultivated sites were located on a desiccated runoff head. The vegetation shift to a grass-dominated savanna formation might therefore have occurred in response to waterlogging and reduced soil aeration. A simple model was developed thereof, which ascribes the different Cerrado formations mainly to the plant-available water content and soil aeration. Soil fertility is considered of minor significance only, since at the studied native savanna sites tree density was independent of soil texture or nutrient status.

Ecophysiology and respiratory metabolism during the germination of Inga sessilis (Vell.) Mart. (Mimosaceae) seeds subjected to hypoxia and anoxia

This paper presents a study on the respiratory metabolism of germinating seeds of Inga sessilis subjected to normoxia, hypoxia and anoxia. Although it is typical of environments where waterlogging seldom occurs, 40% of its seeds are able to germinate under hypoxia; yet, anoxia periods over 96 h are lethal to the seeds. Ethanol is the main product of the seeds anaerobic metabolism, but the steep increase in lactate after 24 h anoxia or 48 h hypoxia may explain the drop in seed viability.

Dispersal modes and fruiting periods in hyperseasonal and seasonal savannas, central Brazil

Seasonal savannas are characterized by an intense drought that influences their functioning. Hyperseasonal savannas experience additionally a waterlogging during the rainy season. In South America, the largest savanna environment is the Brazilian cerrado. To assess whether a particular dispersal mode or fruiting period is associated to the waterlogging, we examined dispersal and phenological groups in hyperseasonal and seasonal cerrado plant species. We compared the proportion of species and individuals in these groups with G-tests for independence in contingency tables. We did not find differences in the proportion of species; however, based on the proportion of individuals, the main dispersal strategy was anemochory in the hyperseasonal cerrado and zoochory in the seasonal cerrado. Phenological strategies of fruiting in safe periods of the year were differently selected in both cerrados. In the hyperseasonal cerrado, most individuals fruited in non-waterlogged periods, whereas in the seasonal cerrado, most individuals fruited in wetter periods. Thus, waterlogging may drive important modifications in the efficiency of the dispersal and phenological strategies of hyperseasonal savannas plants.

Vigilancia tecnológica de los tres principales productos agrícolas base de alimentación y cultivados en Brasil y Argentina

La seguridad agroalimentaria debe ser prioridad para los gobiernos de Brasil y Argentina, debido a que deben garantizar la producción y el abastecimiento de los alimentos básicos para las futuras generaciones, entendido como alimentos básicos aquellos que más se consumen, ya sea en su forma original o por medio de sus subproductos, estos productos son el trigo, el maíz y el arroz. El garantizar la producción y el abastecimiento de estos productos en el corto y largo plazo, implica entender cuáles de los procesos productivos aplicados en la realización de los productos base de alimentación no son compatibles con el medio ambiente, generando impactos negativos sobre este. Estos impactos ambientales generados a partir de la agricultura, son identificados como el uso excesivo de recursos naturales entre ellos el agua, así como su contaminación por agentes toxico como los agroquímicos y fertilizantes. Asimismo, el uso de estos agentes tóxicos, genera la infertilidad de los suelos afectando directamente la producción en el largo plazo. Entender los impactos ambientales, implica desarrollar estrategias transversales que le permitan a los garantizar un desarrollo sostenible a lo largo de todo el ciclo del producto; estas estrategias deben estar acompañadas por un rendimiento y eficiencia de los cultivos, de nada sirve implementar estrategias compatibles con el medio ambiente si no se cumple con el principal objetivo de la producción de estos producto, que es garantizar el abastecimiento y alimentación para las generaciones presentes y futuras.

Optimal management of natural resources. Accounting for heterogeneity

Dynamic optimization methods have become increasingly important over the last years in economics. Within the dynamic optimization techniques employed, optimal control has emerged as the most powerful tool for the theoretical economic analysis. However, there is the need to advance further and take account that many dynamic economic processes are, in addition, dependent on some other parameter different than time. One can think of relaxing the assumption of a representative (homogeneous) agent in macro- and micro-economic applications allowing for heterogeneity among the agents. For instance, the optimal adaptation and diffusion of a new technology over time, may depend on the age of the person that adopted the new technology. Therefore, the economic models must take account of heterogeneity conditions within the dynamic framework. This thesis intends to accomplish two goals. The first goal is to analyze and revise existing environmental policies that focus on defining the optimal management of natural resources over time, by taking account of the heterogeneity of environmental conditions. Thus, the thesis makes a policy orientated contribution in the field of environmental policy by defining the necessary changes to transform an environmental policy based on the assumption of homogeneity into an environmental policy which takes account of heterogeneity. As a result the newly defined environmental policy will be more efficient and likely also politically more acceptable since it is tailored more specifically to the heterogeneous environmental conditions. Additionally to its policy orientated contribution, this thesis aims making a methodological contribution by applying a new optimization technique for solving problems where the control variables depend on two or more arguments --- the so-called two-stage solution approach ---, and by applying a numerical method --- the Escalator Boxcar Train Method --- for solving distributed optimal control problems, i.e., problems where the state variables, in addition to the control variables, depend on two or more arguments. Chapter 2 presents a theoretical framework to determine optimal resource allocation over time for the production of a good by heterogeneous producers, who generate a stock externalit and derives government policies to modify the behavior of competitive producers in order to achieve optimality. Chapter 3 illustrates the method in a more specific context, and integrates the aspects of quality and time, presenting a theoretical model that allows to determine the socially optimal outcome over time and space for the problem of waterlogging in irrigated agricultural production. Chapter 4 of this thesis concentrates on forestry resources and analyses the optimal selective-logging regime of a size-distributed forest.