Does drought limit resprouter recruitment in

Gas exchange, chlorophyll fluorescence and water potentials, together with ascorbate and glutathione concentrations, were studied during moderate and severe drought stress and in response to re-watering in Allocasuarina luehmannii seedlings. Moderate drought stress (MS) decreased stomatal conductance (g(s)) and net CO(2) assimilation rates (A) to approximately 40% and approximately 60% of control values, respectively, and caused decreases in internal CO(2) concentration (C(i)) and maximum light use efficiency of light-acclimated photosystem II (PSII) centres (Fv'/Fm'). Severe drought stress (SS) decreased g(s) and A to approximately 5% and approximately 15% of the control values, respectively, and caused increases in C(i) and PSII excitation pressure (1 - qP), as well as decreases in water potentials, effective quantum yield of PSII (PhiPSII), maximum efficiency of PSII (Fv/Fm) and Fv'/Fm'. Ascorbate and glutathione concentrations remained unaffected by drought treatments, but ascorbate became more oxidised under severe stress. MS seedlings recovered within 1 day (C(i), Fv'/Fm') to 1 week (A, g(s)) of re-watering. In comparison, SS seedlings had longer-lasting after-stress effects, with recovery of many variables (g(s), water potentials, Fv/Fm, PhiPSII, Fv'/Fm') taking between 1 and 3 weeks from re-watering. We found no indication that interaction with antioxidants played a significant role in recovery. In conclusion, A. luehmannii seedlings appear to function normally under moderate drought, but do not seem to have particular metabolic tolerance mechanisms to endure severe drought, which may have implications for its persistence under climate change at the drier margins of its distribution.

AimsWe tested two mechanisms of adaptation to extreme hydrological stresses (flooding and drought) of species making up a tropical wetland plant community by measuring leaf gas exchange and water potential. We hypothesized that anoxic conditions that occur during flooding will decrease leaf gas exchange when compared to the dry season, and that ‘super‐dominant’ species will have a distinctive physiological advantage when compared to other plants within the community.LocationNorthern Pantanal wetland, Private Natural Heritage Reserve of the Brazilian Social Service of Commerce (RPPN‐SESC Pantanal), Mato Grosso, Brazil.MethodsTwo periods representing typical extreme hydrological conditions in the Pantanal wetland were selected based on historical soil and meteorological measurements: (1) a drought period when plants experience stress due to soil moisture deficits during a dry season that persists for several months (May to Sept), and (2) a flooding period when oxidation‐reduction potential is negative for 30 d or more (Mar or Apr), indicating anoxic stress. Measurements of gas exchange and leaf water potential were made on seven species in drought and flood stress conditions. The seven species represent the majority of the plant community.ResultsAs a whole, the plant community showed significantly lower potential net photosynthesis (PN) during flooding when soil oxidation‐reduction potential reached close to −900 mV when compared to the dry season, but the magnitude of the decline in PN was species specific. Not all super‐dominant species showed higher PN compared to non‐dominant species, but they did demonstrate higher stomatal conductance and transpiration leading to lower water use efficiency. The combination of higher PN despite low soil water content suggests that the plant community had access to deep water resources. This access was also confirmed by the midday leaf water potential, which was similar for the flood and dry seasons.ConclusionsResults suggest that the plant community may have high physiological performance under a wide range of soil oxidation‐reduction potentials. Higher PN rates of super‐dominant species indicate a physiological advantage of these species in the different hydrological conditions.

In this paper standardized precipitation index (SPI) is used to assess meteorological drought for all 30 districts covering 10 agro-climatic zones in an eastern Indian state, Odisha. Monthly rainfall data of 115 years (1901-2015) for all 30 districts of Odisha are analyzed using SPI on 1, 3, 6, 9 and 12-month timescale. These timescales reflect the impact of drought on the availability of different water resources. Results indicate that in all the agro-climatic zones of Odisha, mild drought events have the highest frequencies of occurrence followed by moderate drought events for different timescales. Severe and extreme drought frequencies are comparatively lesser than mild and moderate drought frequencies. SPI analysis shows that 32-46 years are affected by mild drought, 4-16 years affected by moderate drought, 1-9 years are affected by severe drought and 1-5 years are affected by extreme drought during study period of 115 years in different agro-climatic zones of Odisha. It is observed 50.3% areas in the state are affected by drought in June out of which chances of occurrence of mild drought is maximum (28.7%). In the months of July, August and September, 51.7, 48.5 and 46.1% areas are affected by droughts. On average 49.15% areas of the entire state is affected by drought of various intensities out of which the share of mild, moderate, severe and extreme drought is 28.38, 13.28, 5.06 and 2.43%, respectively.

Effects of consolidated tailings water on red-osier dogwood ( Cornus stolonifera Michx) seedlings

Elaeis guineensis palms and its interspecific hybrid (E. oleifera x E. guineensis) were planted in 2004 in the Cuernavaca farm of Unipalma S.A., located in the municipality of Paratebueno (Cundinamarca, Colombia). The palms were planted in two fields: Mecasaragua and Aurora. The first field has never been irrigated, and the second one (Aurora) has always been flood-irrigated during the dry season according to the parameters of the plantation. In this study, physiological parameters (gas exchange and water potential) were assessed in three seasons of the year 2013 (dry season, dry-to-wet transition season and wet season). Significant gas exchange differences were found among the seasons in the field with no irrigation (Mecasaragua). Likewise, differences between the genetic materials were observed during the dry season. For example, the photosyn thesis decreased by 75% compared with the palms planted in the irrigated field. No differences among seasons or materials were found in the irrigated field (Aurora). E. guineensis palms were more sensitive to water stress compared with the OxG interspecific hybrid. Both genetic materials responded rapidly to the first rains by leveling their photosynthetic rates and demonstrated an excellent capacity to recover from water stress.

Globally, variability in canopy seed retention within closed cones (serotiny) among fire-adapted plant species is often associated with gradients in fire regime. Few studies have investigated the association of intraspecific variation in serotiny with geographical variation in fire and other environmental factors, especially climatic ones, and none has done so in the Cape Floristic Region (CFR) of South Africa. Yet the relationship between environmental gradients and intraspecific variation in reproductive traits may help us understand if those gradients partly shaped the evolution of the rich diversity or proteas in the CFR, and predict the resilience of fire-adapted Protea species to climate and fire regime changes in the CFR. We examined the association of the variability in serotiny in Protea repens (L.) L, the Common Sugarbush, with gradients in fire regime and climatic factors, and with plant age, cone age, and age of oldest closed cone across its 700 km-long longitudinal range in the CFR. Cone age was a significant covariate of the probability that a given cone was closed (our measure of serotiny), but plant age and age of oldest closed cone were not. Variability in the degree of serotiny was significant among populations. Serotiny was highest where fire intensity was historically high, where both mean annual precipitation and mean annual temperature were low, and where rainfall was least seasonal, but fire frequency was not a predictor of serotiny.

The BOREAS TE-9 team collected several data sets related to chemical and photosynthetic properties of leaves in boreal forest tree species. The purpose of the BOREAS TE-09 study was threefold: 1) to provide in situ gas exchange data that will be used to validate models of photosynthetic responses to light, temperature, and carbon dioxide (CO2); 2) to compare the photosynthetic responses of different tree crown levels (upper and lower); and 3) to characterize the diurnal water potential curves for these sites to get an indication of the extent to which soil moisture supply to leaves might be limiting photosynthesis. The gas exchange data of the BOREAS NSA were collected to characterize diurnal gas exchange and water potential of two canopy levels of five boreal canopy cover types: young jack pine, old jack pine, old aspen, lowland old black spruce, and upland black spruce. These data were collected between 27-May-1994 and 17-Sep-1994. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hydraulic architecture, height-related changes in photosynthesis and seasonal positive pressure declines in bamboo: implications for top dieback.

Drought and subsequent rewatering are common in agriculture, where recovery from mild droughts is easier than from severe ones. The specific drought threshold and factors limiting recovery are under-researched. This study subjected maize plants to varying drought degrees before rewatering, and measuring plant water status, gas exchange, hydraulic conductance, hormone levels, and cellular damage throughout. We discovered that stomatal reopening in plants was inhibited with leaf water potentials below about -1.7 MPa, hindering postdrought photosynthetic recovery. Neither hydraulic loss nor abscisic acid (ABA) content was the factor inhibited stomatal reopening on the second day following moderate drought stress and rewatering. But stomatal reopening was significantly correlated to the interaction between hydraulic signals and ABA content under severe drought. Extended drought led to leaf death at about -2.8 MPa or 57% relative water content, influenced by reduced rehydration capacity, not hydraulic failure. The lethal threshold remained relatively constant across leaf stages, but the recoverable safety margin (RSM), that is, the water potential difference between stomatal closure and recovery capacity loss, significantly decreased with leaf aging due to delayed stomatal closure during drought. Our findings indicate hydraulic failure alone does not cause maize leaf death, highlighting the importance of RSM in future research.

The objective of this study was to understand the effects of mild, moderate and severe drought stress on zoysiagrass(Zoysia japonica). Superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) content were investigated. Mild drought(60%-70% of field capacity), moderate drought(45%-55% of field capacity), and severe drought (25%-35% of field capacity) were remained for 16 days. A gradual increase was observed in SOD activity of Zoysiagrass from 1 to13 days of drought stress in all treatments. POD and CAT activity, and lipid peroxidation increased in all treatments, and maximum change was happened in severe drought group. Severe drought has more serious damage to Zoysia japonica than mild drought and moderate drough. This suggests that Zoysiagrass has excellent drought tolerance and its ability to survive in the drought environment is very strong.

A Hierarchical Bayesian model of wildfire in a Mediterranean biodiversity hotspot: Implications of weather variability and global circulation

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides, a succulent that grows in drought‐prone microenvironments in summer rainfall and all‐year rainfall regions of southern Africa. When well‐watered, this species exhibited Crassulacean acid metabolism (CAM)‐cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low‐level CAM or to CAM‐idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre‐stressed values within two days. Whole‐shoot carbon uptake rates suggested that leaf growth had continued unabated during a short‐term (≅ one week) drought. This emphasises that CAM‐idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM‐idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C3 gas exchanges when well‐watered to water‐conserving CAM‐idling during drought.

Gas Exchange and Water Relations of the Root Hemi-parasiteSantalum albumL. in Association with Legume and Non-legume Hosts

Irrigation frequency transiently alters whole plant gas exchange, water and hormone status, but irrigation volume determines cumulative growth in two herbaceous crops

Gas exchange and water relations responses to warming were compared for two shrub species, Artemisia tridentata spp. vaseyana (Asteraceae), a widely distributed evergreen species of the Great Basin and the western slope of the Rocky Mountains, and Pentaphylloides floribunda (Rosaceae), a deciduous shrub limited in distribution to moist, high-elevation meadows. Plants were exposed to an in situ infrared (IR) climate change manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, CO. Measurements of gas exchange and water relations were made on the two species in July and August, 1993 from plants growing in situ in infrared-heated and control plots. Carbon dioxide uptake, water loss, leaf temperature, water use efficiency, and water potential were compared to test the hypothesis that leaf and soil responses to IR will cause leaf level changes in photosynthesis. Photosynthetic CO2 uptake and water use efficiency increased for A. tridentata (2.9 vs. 1.9 μmol m−2 s−1 and 1.2 vs. 0.7 mmol C/mol H2O) in the heated plots compared to the controls, while water potential was significantly lower in the heated plots (−1.1 vs. −0.5 MPa). The heating treatment decreased rates of photosynthesis for P. floribunda, but not significantly so. For A. tridentata, the results are consistent with the community-level changes observed with heating. Taken together, the evidence suggests that global warming is likely to result in increasing dominance of A. tridentata in subalpine meadow habitat now dominated by forbs.