The roll of soil N/P in drought tolerance of oak forests in Israel
Forest productivity may increasingly be limited by P shortage as indicated by declining P concentrations and increasing N:P ratios in leaves and fine roots. High atmospheric N deposition and summer droughts will further alter the availability of P. We conducted a greenhouse experiments (2 soil moisture x 2 N supply x 3 P supply levels) to study the effect of soil moisture, nitrogen and phosphorus on growth, morphology, C allocation, P uptake and use efficiencies, and rhizodeposition in saplings of oak and beech. P uptake capacity was measured by a H333PO4 feeding experiment. Main objectives were to determine (1) the influence of high drought and N on leaf and root P concentrations and associated N:P ratios, (2) the effect of decreasing P availability on P uptake and P use efficiencies, and (3) the relationship between low P or drought and root exudation. First results indicate a decrease of fine root biomass under drought under low P availability. Under drought the fine root to leaf biomass ratio decreased by trend and root exudation increased with increasing N to P ratios. Radioisotope labeling indicated an increasing P uptake capacity under low soil P in both soil moisture conditions. In dry soil, higher 33P concentration was found in coarse than in fine roots. We conclude that root exudation of oaks is stimulated by high N to P ratios and drought which may function as an adaptive response to increase P uptake efficiency.
The project is part of a collaboration with Dr. Ina Meier and PHD Candidate Julia Köhler from the Georg August University of Göttingen in Germany. The project is funded by the Volkswagen foundation.
Physiological and metabolical responses of Cabernet Sauvignon and Shiraz grapevine (Vitis vinifera) cultivars to water stress
The research focuses on two cultivars with different hydraulic behavior, Cabernet Sauvignon (near isohydric) and Shiraz (near anisohydric) in an atempt to comprehend the origins and outcomes of the differences in hydraulic behaviour. The cultivars are subjected to different irrigation regimes, and their physiological and metabolomic responses are compared. Water relations, anatomy, photosynthesis (gas exchange and flourometry), and metabolism responses are tested during different experimental conditions. Differences between the cultivars suggest hydraulic conductance and stomatal conductance are the origin of the phenomena and that metabolism of the cultivars depends on hydraulic behaviour. It apears that cultivars of different hydraulic behavior demand specific cultivar-based irrigation regime.
The role of root orders
Knowledge about the physiological function of root orders is scant. A system to monitor the water flux among different root orders was developed using miniaturized uptake chambers. Different root orders of four-year old Citrus volkameriana trees were analyzed with respect to root morphology and water flux.
Eight root orders were found. Root orders showed a broad overlap in root diameter, but differences in tissue densities and specific root area were clearly distinguishable. Thirty percent of branch biomass but 50% of branch surface area (SA) were possessed by the 1st-root order while the 5th-root order accounted for 5% of SA with 20% of biomass. First order roots showed a significantly higher rate of water uptake than the 2nd- and 3rd-root orders; whereas the 4th- and 5th-root orders showed water excess. The water excess suggested the occurrence of hydraulic redistribution, possibly as a result of differences in osmotic potentials of non-stele tissues. We suggest that plants may utilize this kind of hydraulic redistribution to prevent coarse root desiccation and/or to increase nutrient acquisition.
Our study showed that the novel ‘miniature depletion chamber’ method enabled direct measurement of water fluxes per root order and can be a major tool for future studies on root order traits. Current reserch is being conducted on the role of root orders under different abiotic stress conditions in water and nutrient uptake.
Photosynthesis and photo-protection in local annual plants
Light is essential for plant growth, since it provides the energy that drives carbon assimilation through photosynthesis. As a byproduct of this reaction, there is continuously occurring photo-damage to the PSII reaction centers that can lead to photo inhibition. One common and dynamic mechanism of photo-protection is non photochemical quenching (NPQ), which converts energy of light directly into heat.
Two different studies are conducted in order examine photo-protective and photosynthetic response in annual desert plants.
1. Wild barley (Hordeum spontaneum) ecotypes form desert and Mediterranean origins were subjected to terminal drought. The drought caused cessation of photosynthesis in both ecotypes. The desert ecotype responded to the drought by accumulation of anthocyanin. In the Mediterranean ecotype there was strong induction of NPQ under drought, however only low amount of anthocyanin was accumulated in the leaves under drought. The difference in the drought induced photo protective response might represent a difference in the adaptation of these two ecotypes to the different climates of their habitats.
2. NPQ and photosynthesis were examined in the annual desert plant species Anastatica hierochuntica (known also as Rose of Jericho). It was found that NPQ in Anastatica was very low in comparison to both model and crop plants species, as well as to other desert plants. Anastatica plants used relatively high amount of light to drive chemical processes (PSII ETR), carbon assimailtion at relatively high water use efficiencies. The photo protective and photosynthetic response in Anastatica hierochuntica plants is unique, and might serve as an adaptation to the short growing period of annual plants in deserts.
The role of pesticides as growth regulators in response to drought
Water availability is a major abiotic factor limiting plant growth and productivity in many regions of the world including agriculturally managed ecosystems. Improving plant tolerance to drought stress or reducing water use becomes increasingly important for maintaining high plant productivity in water-limiting environments. The use of plant growth regulators is an important tool for increasing plant productivity and growth.
Paclobutrazol (PBZ) is a member of the triazole family, inhibiting the synthesis of gibberellins while promoting abscisic acid, auxin and cytokinin. It has been shown to contribute to the increase of root to shoot ratio, root biomass, and fruit yield. PBZ has also been reported to increase drought tolerance in tomato plants. TMX is an insecticide in the class of neonicotinoids. Plant vigor and fruit yield of tomato plants have been increased by TMX (P.R.C. Castro et al., 2007; Rajib Karmakar and Gita Kulshrestha, 2009).
The overall objective of the current study is to assess drought stress mitigation effects of Syngenta compounds, including PBZ and TMX, on plant growth and productivity in greenhouse studies. Specific objectives include: studying the effects on the root system morphology—the changes in root architecture, water and nitrogen efficiencies, regulation of root to shoot ratios and C/N ratio in tomato plants treated by PBZ and TMX.
Root halotropism in Basia indica
Plant roots are responsible for the acquisition of nutrients and water from the soil, and have an important role in plant response to soil stress conditions. The direction of root growth is gravitropic in general. Gravitropic responses have been widely studied; however studies about other root tropisms are scarce. Soil salinity is a major environmental response factor for plants, sensed by the root and affecting the whole plant. Our observations on root architecture of Kochia (Bassia indica) indicated that salinity may cue tropism of part of the root towards increased salt concentrations. We termed this phenomenon ‘positive halotropism‘. It was observed that Kochia individuals in the field developed horizontal roots, originating from the main tap root, which grew towards saline regions in the soil. Under controlled conditions in greenhouse experiments, Kochia plants were grown in pots with artificial soil salinity gradients, achieved by irrigation with saline and fresh water. It was shown that plants grown in low salt areas developed a major horizontal root towards the higher salt concentration in the gradient. In regions of high salinity and in the absence of a salinity gradient, roots grew vertically without a major horizontal root. The novel finding of ‘positiv halotropism’ is still studied in a mechnistic approach.
Role of dew in desert plants
Water availability is a major factor influencing plant growth and survival in most terrestrial ecosystems, particularly in arid areas. Dew is a common source of water in many deserts and may constitute over 30% of the total annual water input. The importance of dew in desert environments lies in its reliability as a stable water source throughout the year as compared to the unpredictability of rains. Dew can affect plants in different ways from changing their microenvironment to being a direct water source. Although the accumulation of dew on plants is a common phenomenon, the importance of dew to ecosystems in general and particularly to plants in unclear.
We assess the importance of dew in the water balance of individual indigenous plants growing in dry environments. The research is conducted both in the field and in controlled growth chambers under different water regimes. To determine the fraction of dew directly absorbed by plants, we will use techniques of artificial exclusion (or formation) of dew and stable isotope fractionation analysis. The fact that dew has a significantly different 18/16O ratio than those of rain and soil water will enable us to distinguish between the sources of absorbed water by the plants. The findings of the study will throw light on the importance of absorption of dew to the water relations, physiology and drought tolerance of desert plants. Understanding the importance of dew for plants will have a major impact on ecology, agriculture, and basic physiology.
Role of plants in phytoremdiation
The role of plants in the treatment process of effluents by constructed wetlands (CW) is debated. Plants can affect CW processes. Among the potential attributes of plants in CWs are: (1) increasing retention time by reducing water velocities; (2) improving hydraulic conductivity by root growth; (3) root activity. By utilizing elements as (N) and phosphorus (P) plants may affect the elemental composition of WW. In addition, plants can prevent odor nuisances, enhance aesthetical appearance and provide surface area for microbial growth. In this study we reveal two novel perspective of the use of plant in CWs.
Our study focuses on the role of plant in salt phytoremediation using Bassia indica as a model plant. In addition to studynig the diffent ways in which Bassia indica can be used for phytoremdeiation we study the mechanisms which enable plants to sustain efficiant phyotremdiation.
Forest productivity may increasingly be limited by P shortage as indicated by declining P concentrations and increasing N:P ratios in leaves and fine roots. High atmospheric N deposition and summer droughts will further alter the availability of P. We conducted a greenhouse experiments (2 soil moisture x 2 N supply x 3 P supply levels) to study the effect of soil moisture, nitrogen and phosphorus on growth, morphology, C allocation, P uptake and use efficiencies, and rhizodeposition in saplings of oak and beech. P uptake capacity was measured by a H333PO4 feeding experiment. Main objectives were to determine (1) the influence of high drought and N on leaf and root P concentrations and associated N:P ratios, (2) the effect of decreasing P availability on P uptake and P use efficiencies, and (3) the relationship between low P or drought and root exudation. First results indicate a decrease of fine root biomass under drought under low P availability. Under drought the fine root to leaf biomass ratio decreased by trend and root exudation increased with increasing N to P ratios. Radioisotope labeling indicated an increasing P uptake capacity under low soil P in both soil moisture conditions. In dry soil, higher 33P concentration was found in coarse than in fine roots. We conclude that root exudation of oaks is stimulated by high N to P ratios and drought which may function as an adaptive response to increase P uptake efficiency.
The project is part of a collaboration with Dr. Ina Meier and PHD Candidate Julia Köhler from the Georg August University of Göttingen in Germany. The project is funded by the Volkswagen foundation.
Physiological and metabolical responses of Cabernet Sauvignon and Shiraz grapevine (Vitis vinifera) cultivars to water stress
The research focuses on two cultivars with different hydraulic behavior, Cabernet Sauvignon (near isohydric) and Shiraz (near anisohydric) in an atempt to comprehend the origins and outcomes of the differences in hydraulic behaviour. The cultivars are subjected to different irrigation regimes, and their physiological and metabolomic responses are compared. Water relations, anatomy, photosynthesis (gas exchange and flourometry), and metabolism responses are tested during different experimental conditions. Differences between the cultivars suggest hydraulic conductance and stomatal conductance are the origin of the phenomena and that metabolism of the cultivars depends on hydraulic behaviour. It apears that cultivars of different hydraulic behavior demand specific cultivar-based irrigation regime.
The role of root orders
Knowledge about the physiological function of root orders is scant. A system to monitor the water flux among different root orders was developed using miniaturized uptake chambers. Different root orders of four-year old Citrus volkameriana trees were analyzed with respect to root morphology and water flux.
Eight root orders were found. Root orders showed a broad overlap in root diameter, but differences in tissue densities and specific root area were clearly distinguishable. Thirty percent of branch biomass but 50% of branch surface area (SA) were possessed by the 1st-root order while the 5th-root order accounted for 5% of SA with 20% of biomass. First order roots showed a significantly higher rate of water uptake than the 2nd- and 3rd-root orders; whereas the 4th- and 5th-root orders showed water excess. The water excess suggested the occurrence of hydraulic redistribution, possibly as a result of differences in osmotic potentials of non-stele tissues. We suggest that plants may utilize this kind of hydraulic redistribution to prevent coarse root desiccation and/or to increase nutrient acquisition.
Our study showed that the novel ‘miniature depletion chamber’ method enabled direct measurement of water fluxes per root order and can be a major tool for future studies on root order traits. Current reserch is being conducted on the role of root orders under different abiotic stress conditions in water and nutrient uptake.
Photosynthesis and photo-protection in local annual plants
Light is essential for plant growth, since it provides the energy that drives carbon assimilation through photosynthesis. As a byproduct of this reaction, there is continuously occurring photo-damage to the PSII reaction centers that can lead to photo inhibition. One common and dynamic mechanism of photo-protection is non photochemical quenching (NPQ), which converts energy of light directly into heat.
Two different studies are conducted in order examine photo-protective and photosynthetic response in annual desert plants.
1. Wild barley (Hordeum spontaneum) ecotypes form desert and Mediterranean origins were subjected to terminal drought. The drought caused cessation of photosynthesis in both ecotypes. The desert ecotype responded to the drought by accumulation of anthocyanin. In the Mediterranean ecotype there was strong induction of NPQ under drought, however only low amount of anthocyanin was accumulated in the leaves under drought. The difference in the drought induced photo protective response might represent a difference in the adaptation of these two ecotypes to the different climates of their habitats.
2. NPQ and photosynthesis were examined in the annual desert plant species Anastatica hierochuntica (known also as Rose of Jericho). It was found that NPQ in Anastatica was very low in comparison to both model and crop plants species, as well as to other desert plants. Anastatica plants used relatively high amount of light to drive chemical processes (PSII ETR), carbon assimailtion at relatively high water use efficiencies. The photo protective and photosynthetic response in Anastatica hierochuntica plants is unique, and might serve as an adaptation to the short growing period of annual plants in deserts.
The role of pesticides as growth regulators in response to drought
Water availability is a major abiotic factor limiting plant growth and productivity in many regions of the world including agriculturally managed ecosystems. Improving plant tolerance to drought stress or reducing water use becomes increasingly important for maintaining high plant productivity in water-limiting environments. The use of plant growth regulators is an important tool for increasing plant productivity and growth.
Paclobutrazol (PBZ) is a member of the triazole family, inhibiting the synthesis of gibberellins while promoting abscisic acid, auxin and cytokinin. It has been shown to contribute to the increase of root to shoot ratio, root biomass, and fruit yield. PBZ has also been reported to increase drought tolerance in tomato plants. TMX is an insecticide in the class of neonicotinoids. Plant vigor and fruit yield of tomato plants have been increased by TMX (P.R.C. Castro et al., 2007; Rajib Karmakar and Gita Kulshrestha, 2009).
The overall objective of the current study is to assess drought stress mitigation effects of Syngenta compounds, including PBZ and TMX, on plant growth and productivity in greenhouse studies. Specific objectives include: studying the effects on the root system morphology—the changes in root architecture, water and nitrogen efficiencies, regulation of root to shoot ratios and C/N ratio in tomato plants treated by PBZ and TMX.
Root halotropism in Basia indica
Plant roots are responsible for the acquisition of nutrients and water from the soil, and have an important role in plant response to soil stress conditions. The direction of root growth is gravitropic in general. Gravitropic responses have been widely studied; however studies about other root tropisms are scarce. Soil salinity is a major environmental response factor for plants, sensed by the root and affecting the whole plant. Our observations on root architecture of Kochia (Bassia indica) indicated that salinity may cue tropism of part of the root towards increased salt concentrations. We termed this phenomenon ‘positive halotropism‘. It was observed that Kochia individuals in the field developed horizontal roots, originating from the main tap root, which grew towards saline regions in the soil. Under controlled conditions in greenhouse experiments, Kochia plants were grown in pots with artificial soil salinity gradients, achieved by irrigation with saline and fresh water. It was shown that plants grown in low salt areas developed a major horizontal root towards the higher salt concentration in the gradient. In regions of high salinity and in the absence of a salinity gradient, roots grew vertically without a major horizontal root. The novel finding of ‘positiv halotropism’ is still studied in a mechnistic approach.
Role of dew in desert plants
Water availability is a major factor influencing plant growth and survival in most terrestrial ecosystems, particularly in arid areas. Dew is a common source of water in many deserts and may constitute over 30% of the total annual water input. The importance of dew in desert environments lies in its reliability as a stable water source throughout the year as compared to the unpredictability of rains. Dew can affect plants in different ways from changing their microenvironment to being a direct water source. Although the accumulation of dew on plants is a common phenomenon, the importance of dew to ecosystems in general and particularly to plants in unclear.
We assess the importance of dew in the water balance of individual indigenous plants growing in dry environments. The research is conducted both in the field and in controlled growth chambers under different water regimes. To determine the fraction of dew directly absorbed by plants, we will use techniques of artificial exclusion (or formation) of dew and stable isotope fractionation analysis. The fact that dew has a significantly different 18/16O ratio than those of rain and soil water will enable us to distinguish between the sources of absorbed water by the plants. The findings of the study will throw light on the importance of absorption of dew to the water relations, physiology and drought tolerance of desert plants. Understanding the importance of dew for plants will have a major impact on ecology, agriculture, and basic physiology.
Role of plants in phytoremdiation
The role of plants in the treatment process of effluents by constructed wetlands (CW) is debated. Plants can affect CW processes. Among the potential attributes of plants in CWs are: (1) increasing retention time by reducing water velocities; (2) improving hydraulic conductivity by root growth; (3) root activity. By utilizing elements as (N) and phosphorus (P) plants may affect the elemental composition of WW. In addition, plants can prevent odor nuisances, enhance aesthetical appearance and provide surface area for microbial growth. In this study we reveal two novel perspective of the use of plant in CWs.
Our study focuses on the role of plant in salt phytoremediation using Bassia indica as a model plant. In addition to studynig the diffent ways in which Bassia indica can be used for phytoremdeiation we study the mechanisms which enable plants to sustain efficiant phyotremdiation.