Diurnal rhythm and effect of temperature on oxygen consumption in earthworms, Amynthas gracilis and Pontoscolex corethrurus

Different species of earthworms show distinct patterns of oxygen consumption pattern. Amynthas gracilis has a diurnal rhythm of oxygen consumption, consuming more oxygen at night, whether being incubated at 20, 25, or 30 degrees C. The higher oxygen consumption of A. gracilis is directly related to its behavior, as it shows higher activity at night. In contrast, Pontoscolex corethrurus showed no obvious diurnal rhythms of oxygen consumption or behavior. In addition, its oxygen demand is not related to temperature. A. gracilis has higher oxygen consumption than P. corethrurus at 20 and 30 degrees C. The difference in temperature adaptation of oxygen consumption between these two species may be a strategy by which earthworms adapt to different temperatures. This might explain why A. gracilis disperses on the soil surface at night after a rain, in contrast to P. corethrurus for which such behavior was not been observed.     

Studies on Plover Cove Reservoir, Hong Kong

The zooplankton fauna of the Plover Cove Reservoir has been investigated using two sampling series. The first series involving a 3-year investigation using 6-ft vertical hauls at three stations in the reservoir, revealed the presence of two copepod and four cladoceran species with little variation in terms of seasonal peak occurrence and abundance in any of the stations and so no evidence of the horizontal distribution patterns referred to by other authors. In all three stations Diaptomus gracilis was the dominant copepod species and Diaphanosoma leuchtenbergianum the dominant cladoceran species. The second series, involving a 13-month investigation of vertical sets of water samples collected both day and night at 4-h intervals for 24-h periods, revealed that in terms of seasonal vertical distribution, all six species occurred at all depths during the survey, but with a tendency to be concentrated in the surface waters. In terms of diurnal vertical distribution, differences in the migration pattern occurred from season to season in the case of Diaptomus gracilis. Thus, during spring, summer and autumn, concentrations occurred at the surface at 10.00 and 22.00 hours followed by migration to greater depth, whereas in winter, surface accumulations persisted even into the daylight hours. However, both Cyclops hyalinus and Diaphanosoma leuchtenbergianum showed surface accumulations at night and a movement away from the surface by day during all seasons. Investigations of the seasonal variation in environmental parameters conducted during both sampling series revealed that, as in the case of similar surveys, water temperature was the major controlling factor governing the seasonal variation in composition of the zooplankton fauna as well as its seasonal vertical distribution since in the case of Diaptomus gracilis and Ceriodaphnia reticulata low water temperatures corresponded with peak seasonal occurrence whereas in the case of the other species high water temperatures corresponded with peak seasonal occurrence, and since Diaptomus gracilis and Diaphanosoma leuchtenbergianum showed maximum concentration near the surface when surface water temperatures were high, whereas the remaining species showed their maximum concentration near the surface when lower water temperatures prevailed. It would also appear, however, that seasonal changes in zooplankton densities closely followed algal densities since Diaptomus gracilis, Diaphanosoma leuchtenbergianum and Bosmina longirostris had their maxima in late spring and Cyclops hyalinus in late summer while algal densities in this reservoir were highest in early spring and early summer. With regard to the diurnal vertical distribution of the zooplankton, light appeared to be the only factor alternating by an amount likely to be correlated with such diurnal vertical changes in zooplankton density.     

The effect of extrinsic and intrinsic factors on oxygen consumption by the southern rock lobster, Jasus edwardsii

The oxygen consumption rate of the southern rock lobster, Jasus edwardsii, was evaluated in response to body weight, temperature, activity, handling, diurnal rhythm, feeding and oxygen saturation level. There was a positive relationship between standard oxygen consumption (M(O(2))) and both body weight and water temperature. The relationship between total oxygen consumption and wet whole body weight was described by the equation: LogM(O(2))=0.595log W-0.396 (r(2)=0.83). The relationship between weight-specific oxygen consumption and temperature was described by the equation: LogM(O(2))=0.047T-2.25 (r(2)=0.94). Activity had a significant influence on the oxygen consumption rate, causing a three-fold increase above the standard rate at the temperature of acclimation (13 degrees C). However, at temperatures approaching the upper and lower extremes, lobsters had a decreased ability to increase their oxygen consumption rates during activity. Lobsters took 4.5-5 h to return to standard oxygen consumption rates after a period of emersion and handling. A strong diurnal rhythm to oxygen consumption was recorded. J. edwardsii displayed a classic postprandial increase in oxygen consumption. A peak (1.72 times standard M(O(2))) occurred 10-13 h after feeding with an increase above standard M(O(2)) being maintained for 42 h. In its rested state J. edwardsii was an oxygen regulator down to a critical oxygen tension of 58 Torr, whilst activity resulted in the critical oxygen tension increasing to 93 Torr.     

Detection of earthworm prey by Ruff Philomachus pugnax

Ruff Philomachus pugnax staging in the Netherlands forage in agricultural grasslands, where they mainly eat earthworms (Lumbricidae). Food intake and the surface availability of earthworms were studied in dairy farmland of southwest Friesland in March–April 2011. Daily changes in earthworm availability were quantified by counting visible earthworms. No earthworms were seen on the surface during daytime, but their numbers sharply increased after sunset and remained high during the night. Nevertheless, intake rates of individual Ruff in different grasslands measured during daytime showed the typical Holling type II functional response relationship with the surfacing earthworm densities measured at night. Radiotagging of Ruff in spring 2007 revealed that most, if not all, feeding occurs during the day, with the Ruff assembling at shoreline roosts at night. This raises the question of why Ruff do not feed at night, if prey can be caught more easily than during daytime. In March–May 2013 we experimentally examined the visual and auditory sensory modalities used by Ruff to find and capture earthworms. Five males were kept in an indoor aviary and we recorded them individually foraging on trays with 10 earthworms mixed with soil under various standardized light and white noise conditions. The number of earthworms discovered and eaten by Ruff increased with light level, but only when white noise was played, suggesting that although they can detect earthworms by sight, Ruff also use auditory cues. We suggest that although surfacing numbers of earthworms are highest during the night, diurnal intake rates are probably sufficient to avoid nocturnal foraging on a resource that is more available but perhaps less detectable at that time.     

Circadian rhythm of root pressure in popular and its driving factors

Aims Our main purposes were to investigate root pressure and its circadian rhythm of excised roots in ‘84K’ popular (Populus alba × P. glandulosa) cultured in soil and solution, to explore the influencing factors and their relationships with root pressure systematically and to understand the generation and rhythm regulation of root pressure. Methods We investigated the root pressure of excised roots in ‘84K’ popular using the method of digital pressure transducer. The diurnal rhythm of excised roots was conducted through different experimental treatments including sampling in different time, defoliation and girdling, together with ambient condition like soil temperature, differential or consistant temperature during day and night. Then we discussed the effects of root respiration and hydraulic conductivity on root pressure by further using chemical inhibitor. Furthermore, diurnal variation of osmotic potential and ions content as well as soluble sugar content of exudation was determined in order to explore their relationships with root pressure rhythm. Important findings Root pressure of excised roots in popular had diurnal rhythm which was higher during daytime and lower overnight. It reached its peak value in the morning to noon and valley value at 20:00. Root pressure of excised roots sampled at different time and cultured in different medium had influence on the rhythm of root pressure to some degrees, but did not the general rhythm of high in daytime and low overnight. Defoliation, girdling and the inhibitors for root respiration or cytomembrane hydraulic conductivity could affect the maximum value of root pressure while have no significant influence on the daily rhythm. Defoliation, girdling and respiration inhibitor reduced the maximum value of root pressure, whereas the hydraulic conductivity inhibitor had little influence on root pressure. The maximum value of root pressure declined with the decrease in soil temperature which could change the rhythm of root pressure. The synchronous change in the maximum value of root pressure and root respiration rate with temperature indicated that root respiration contributed to the change of root pressure along with temperature. Osmotic potential of root exudation was higher during the daytime and lower at night. Diurnal variations of ions and soluble sugar content of exudation were consistant with that of osmotic potential. The peak of root pressure measured under the condition of differential temperature during day and night was significant higher than that measured under constant temperature. In conclusion, root pressure of the poplar ‘84K’ showed significant diurnal rhythm, i.e. higher during the daytime and lower at night. The maximum value of root pressure was mainly regulated by root respiration metabolism. The factors such as respiration inhibitor, respiration substrate and temperature influence the value of the maximum root pressure of poplar ‘84K’. Root hydraulic conductivity had no significant influence on root pressure.     

Effects of circadian phase and melatonin injection on anxiety-like behavior in nocturnal and diurnal rodents

Animals show daily rhythms in most bodily functions, resulting from the integration of information from an endogenous circadian clock and external stimuli. These rhythms are adaptive and are expected to be related to activity patterns, i.e., to be opposite in diurnal and nocturnal species. Melatonin is secreted during the night in all mammalian species, regardless of their activity patterns. Consequently, in diurnal species the nocturnal secretion of melatonin is concurrent with the resting phase, whereas in nocturnal species it is related to an increase in activity. In this research, we examined in three diurnal and three nocturnal rodent species whether a daily rhythm in anxiety-like behavior exists; whether it differs between nocturnal and diurnal species; and how melatonin affects anxiety-like behavior in species with different activity patterns. Anxiety-like behavior levels were analyzed using the elevated plus-maze. We found a daily rhythm in anxiety-like behavior and a significant response to daytime melatonin administration in all three nocturnal species, which showed significantly lower levels of anxiety during the dark phase, and after melatonin administration. The diurnal species showed either an inverse pattern to that of the nocturnal species in anxiety-like behavior rhythm and in response to daytime melatonin injection, or no rhythm and, accordingly, no response to melatonin.     

Patterns and mechanisms of transpiration in a large subalpine Norway spruce (Picea abies (L.) Karst.)

In situ water relations of a large subalpine Norway spruce (Picea abies) were analyzed by simultaneous measurements of sap flow at different crown positions. In the diurnal scale, transpiration varied greatly, both spatially and temporally. Over longer periods, however, different parts of the crown transpired in fairly constant proportions. The average estimated transpiration was about 3.5 times greater in the upper than in the lower half and decreased 1.6-fold from south to north. Water intercepted from rain, fog and dew buffered and significantly decreased the transpiration. The effect was strongest in those parts which were least coupled to the free atmosphere. The top of the crown seemed to experience a regular shortage of water shortly after starting transpiration, when it was forced to switch from internal reserves to sources in the soil. Further, lower branches then started transpiring, which may have led them to compete for the water. An enhanced nocturnal sap flow during warm and dry winds (Foehn) indicated that the tree also transpired at night. Shaded twigs had more capacity to intercept water externally than twigs in the sun. The significance of the crown structure for interaction with water in both liquid and vapour phases is discussed.     

Diurnal feeding as a potential mechanism of osmoregulation in aphids

Diurnal variation in phloem sap composition has a strong infuence on aphid performance.The sugar-rich phloem sap serves as the sole diet for aphids and a suite of physiological mechanisms and behaviors allowv them to tolerate the high osmotic stress.Here,we tested the hypothesis that night-time feeding by aphids is a behavior that takes advantage of the low sugar diet in the night to compensate for osmotic stress incurred while feeding on high sugar diet during the day.Using the electrical penetration graph(EPG)technique.we examined the eiects of diurmal rhythm on feeding behaviors of bird cherry-oat aphid(Rhopalosiphurm padi L.)on wheat.A strong diurmal rhythm in aphids as indicated by the presence of a cyclical pattern of expression in a core clock gene did not impact aphid feeding and similar feeding behaviors were observed during day and night.The major difference observed between day and night feeding was that aphids spent significantly longer time in phloem salivation during the night compared to the day.In contrast,aphid hydration was reduced at the end of the day-time feeding compared to end of the night-time fepding.Gene expression analysis of R.padi osmoregulatory genes indicated that sugar break down and water transport into the aphid gut was reduced at night.These data suggest that while diumal variation occurs in phloem sap composition,aphids use night time feeding to overcome the high osmotic stress incurred while feeding on sugar-rich phloem sap during the day.     

Simultaneous growth and emission measurements demonstrate an interactive control of methanol release by leaf expansion and stomata

Emission from plants is a major source of atmospheric methanol. Growing tissues contribute most to plant-generated methanol in the atmosphere, but there is still controversy over biological and physico-chemical controls of methanol emission. Methanol as a water-soluble compound is thought to be strongly controlled by gas-phase diffusion (stomatal conductance), but growth rate can follow a different diurnal rhythm from that of stomatal conductance, and the extent to which the emission control is shared between diffusion and growth is unclear. Growth and methanol emissions from Gossypium hirsutum, Populus deltoides, and Fagus sylvatica were measured simultaneously. Methanol emission from growing leaves was several-fold higher than that from adult leaves. A pronounced diurnal rhythm of methanol emission was observed; however, this diurnal rhythm was not predominantly determined by the diurnal rhythm of leaf growth. Large methanol emission peaks in the morning when the stomata opened were observed in all species and were explained by release of methanol that had accumulated in the intercellular air space and leaf liquid pool at night in leaves with closed stomata. Cumulative daily methanol emissions were strongly correlated with the total daily leaf growth, but the diurnal rhythm of methanol emission was modified by growth rate and stomatal conductance in a complex manner. While in G. hirsutum and in F. sylvatica maxima in methanol emission and growth coincided, maximum growth rates of P. deltoides were observed at night, while maximum methanol emissions occurred in the morning. This interspecific variation was explained by differences in the share of emission control by growth processes, by stomatal conductance, and methanol solubilization in tissue water.     

黄土高原降水年内分布差异对旱作果园蒸散特征的影响

天然降水是雨养农业区水文循环的主要驱动因子,在一定程度上决定着土壤水分生态环境,从而影响作物的蒸散特征。本研究通过分析静宁地区历年降水年内分布特征,明确了降水的集中趋势,在2018和2019年田间定位试验基础上,探究土壤水分随降水发生的变化过程以及果园蒸散特征对降水年内分布差异的响应规律。结果表明: 试验区历年降水集中度较高,集中期多分布在7和8月,8月所占比例达75%,且各年降水集中期出现的早晚变化较大。土壤水分对降水的响应主要集中在0～40 cm土层,深层水分只有在大雨量和连续性降水出现时才会发生明显变化。同为丰水年的情况下,2018年降水集中度高,集中期早,时间短,果树日耗水强度呈单峰结构,变幅较大;2019年降水分布均匀,集中期滞后,日耗水强度呈双峰结构,变幅小,大峰靠后。果树最大需水期历时长,2018年大雨的集中分布无法满足后期果树生理需水,果实产量受损,降水利用效率较2019年下降30.2%。黄土高原地区在苹果树幼果生长期往往会出现短暂干旱,影响果实品质,需加强该时段的水分管控。     

Interactive effects of global warming and ‘global worming’ on the initial establishment of native and exotic herbaceous plant species

The spread of exotic earthworms (‘worming’) and rising temperatures are expected to alter the biological, chemical and physical properties of many ecosystems, yet little is known about their potential interactive effects. We performed a laboratory microcosm experiment to investigate the effects of earthworms (anecic, endogeic, epigeic, or all three together) and 4°C warming on soil water content, litter turnover and seedling establishment of four native and four exotic herbaceous plant species. Warming and worming exerted independent as well as interactive effects on soil processes and plant dynamics. Warming reduced the water content of the upper soil layer, but only in the presence of earthworms. Litter removal increased in the presence of earthworms, the effect being most pronounced in the presence of anecic earthworms at ambient temperature. Exotic plant species were most influenced by earthworms (lower seedling number but higher biomass), whereas natives were most sensitive to warming (higher seedling number). This differential response resulted in significant interaction effects of earthworms and warming on abundance and richness of native relative to exotic plants as well as related shifts in plant species composition. Structural equation modeling allowed us to address possible mechanisms: direct effects of earthworms primarily affected exotic plants, whereas earthworms and warming indirectly and differentially affected native and exotic plants through changes in soil water content and surface litter. Invasive earthworms and warming are likely to interactively impact abiotic and biotic ecosystem properties. The invasion of epigeic and anecic species could select for plant species able to germinate on bare soil and tolerate drought, with the latter becoming more important in a warmer world. Thus earthworm invasion may result in simplified plant communities of increased susceptibility to the invasion of exotic plants.     

Respiratory and osmoregulatory responses of the hermit crab, Clibanarius vittatus (Bosc), to salinity changes

Intertidal hermit crabs were stepwise acclimated to 10, 20, and 30‰ salinity (S) and 21 ± 1 °C. Hemolymph osmolality, sodium, chloride, and magnesium were isosmotic (isoionic) to ambient sea water at 30‰ and hyperosmotic (hyperionic) at 20 and 10‰ S, while hemolymph potassium was significantly hyperionic in all acclimation salinities. Total body water did not differ significantly at any acclimation salinity. Oxygen uptake rates were higher in summer-than winter-adapted crabs. No salinity effect on oxygen consumption occurred in winter-adapted individuals. Summer-adapted, 30‰ acclimated crabs had a significantly lower oxygen consumption rate than those acclimated 10 and 20‰ S. Crabs exposed to 30 10 30‰ and 10 30 10‰ semidiurnal (12 h) and diurnal (24.8 h) fluctuating salinity regimes showed variable osmoregulatory and respiratory responses. Hemolymph osmolality followed the osmolality of the fluctuating ambient sea water in all cases, but was regulated hyperosmotically. Hemolymph sodium, chloride, and magnesium concentrations were similar to hemolymph osmolality changes. Sodium levels fluctuated the least. Hemolymph potassium was regulated hyperionically during all fluctuation patters, but corresponded to sea water potassium only under diurnal conditions. The osmoregulatory ability of Clibanarius vittatus (Bosc) resembles that reported for several euryhaline brachyuran species. The time course of normalized oxygen consumption rate changed inversely with salinity under semidiurnal and diurnal 10 30 10‰ S fluctuations. Patterns of 30 10 30‰ S cycles had no effect on oxygen consumption rate time course changes. The average hourly oxygen consumption rates during both semidiurnal fluctuations were significantly lower than respective control rates, but no statistical difference was observed under diurnal conditions.     

Oil palm and rubber expansion facilitates earthworm invasion in Indonesia

Deforestation, plantation expansion and other human activities in tropical ecosystems are often associated with biological invasions. These processes have been studied for above-ground organisms, but associated changes below the ground have received little attention. We surveyed rainforest and plantation systems in Jambi province, Sumatra, Indonesia, to investigate effects of land-use change on the diversity and abundance of earthworms—a major group of soil-ecosystem engineers that often is associated with human activities. Density and biomass of earthworms increased 4—30-fold in oil palm and rubber monoculture plantations compared to rainforest. Despite much higher abundance, earthworm communities in plantations were less diverse and dominated by the peregrine morphospecies Pontoscolex corethrurus, often recorded as invasive. Considering the high deforestation rate in Indonesia, invasive earthworms are expected to dominate soil communities across the region in the near future, in lieu of native soil biodiversity. Ecologically-friendly management approaches, increasing structural habitat complexity and plant diversity, may foster beneficial effects of invasive earthworms on plant growth while mitigating negative effects on below-ground biodiversity and the functioning of the native soil animal community.

     

Interactions of the circadian and circatidal rhythms of the littoral gastropod melanerita atramentosa Reeve

Melanerita atramentosa Reeve is active during high water and for a period after the ebb, until the substratum dries. A circatidal rhythm with an endogenous inequality between the diurnal and nocturnal high water activity is present in freshly collected snails placed under constant conditions (LL, 30 lux, temperature 21 °C, water level constant). The free-running period of the circatidal rhythm was approximately 24.3 h, slightly less than the tidal period of 24.8 h. This rhythm faded out after 4–6 days of constant conditions. Snails acclimated to non-tidal conditions were active at night. This rhythm persisted under constant conditions for 5–10 days, after which it too faded out. Shock-freezing re-initiated the circatidal rhythm, supporting a ‘multiple-clock’ hypothesis of control. Its limits entrainment are probably narrow, but an entrained periodicity persists for a number of cycles. A model of clock interaction and environmental influence is advanced.     

Relationship between a metabolic rhythm and emergence rhythm in Drosophila melanogaster

Oxygen consumption and lactic acid dehydrogenase (LDH) activity were determined for Drosophila melanogaster pupae and pharate adults exposed to 12 : 12 or 1 : 23 light-dark (LD) regime. Bimodal circadian fluctuations of oxygen consumption were found in pupae and pharate adults exposed to either LD regime and organisms appeared to demonstrate an anticipatory change in oxygen consumption associated with change in illumination. The oxygen-consumption trend for the entire period spent in the puparium showed a high at the time of emergence, but the diurnal rhythm showed a low at the time of emergence suggesting that emergence occurs at a low in the diurnal cycle. Emergence maximum showed a 3 hr lead over the oxygen-consumption maximum. Changing the LD regime produced similar changes in the phasing of both oxygen consumption and emergence rhythms. LDH activity did not demonstrate a detectable circadian rhythm but did show a steady decrease during pupal and pharate adult development.     

黄土丘陵区辽东栎和刺槐树干液流时滞效应与蒸腾特征的关联性

运用Granier热扩散探针法,于2016年7-9月对半干旱黄土丘陵区天然次生林树种辽东栎和人工林树种刺槐的树干液流进行连续测定,并同步监测气象因子和土壤含水量,用错位相关法分析液流通量密度与空气水汽压亏缺日变化的时滞长度,研究2个树种不同径级个体在不同土壤水分条件下液流通量密度与蒸腾驱动因子之间的时滞效应.结果表明:辽东栎和刺槐液流通量密度的日变化节律与气象因子显著相关,空气水汽压亏缺峰值的出现较辽东栎树干液流通量密度滞后118.2 min,较刺槐树干液流通量密度滞后39.5 min;而光合有效辐射的峰值通常滞后于辽东栎12.4 min,提前于刺槐68.5 min.液流通量密度和空气水汽压亏缺的时滞长度与树种和土壤含水量显著相关,辽东栎、刺槐在土壤含水量较高时段的时滞长度分别大于土壤含水量较低时段32.2和68.2 min.时滞长度与径级的相关性整体上未达到显著水平,但在土壤含水量较低时段小径级刺槐的时滞长度大于大径级21.4 min,差异达到了显著水平.两树种液流通量密度与空气水汽压亏缺之间的时滞效应反映了对蒸腾驱动因子的敏感性,较好的土壤水分条件有利于液流通量密度提早达到峰值,较低土壤水分会导致树干液流对气象环境因子响应的敏感性降低;刺槐树干液流受土壤水分的影响更显著.     

Wintering behaviour and spatial ecology of Eurasian Woodcock Scolopax rusticola in western France

The spatial ecology of wintering Eurasian Woodcocks Scolopax rusticola was investigated to determine whether hunting-free forest reserves offer adequate protection to all individuals. The analysis of movements performed by 65 radiotagged Woodcocks during three consecutive winters in Brittany revealed the existence of three types of individual strategies. During daylight hours, 34% of birds remained in a unique core area (of 1.1 ha) during January and February while 18% used several core areas successively (never came back to a previously used core) and 48% alternated between several core areas (exploratory movements around several core areas visited several times). Alternating diurnal strategies seemed to result from a lower abundance of food (earthworms), whereas this was not the case in the unique core-use strategy. The successive core-use strategy was considered as a subset of the 'unique' strategy, for which birds were forced to change sites because of a lower abundance of food after depletion. During the night, 62% of birds showed alternative core-use whereas 33% lived in a unique core and the 'successive' strategy was almost absent. As food abundance was similar in the night cores used by birds under each strategy, we discuss the reasons for the nocturnal strategies in relation to individual differences in territoriality or the ability to detect predators. Both diurnal and nocturnal strategies led most of the birds to leave the reserve, and the important use of bocage and hedges by day (by 39% of birds) and meadows at night (83% of birds used meadows on more than 70% of nights), around the protected forest, call for their inclusion in management plans around reserves.     

Thermoregulation in the meerkat (Suricata suricatta Schreber, 1776)

Tre of the suricates exhibits a marked diurnal rhythm (mean Tre at night 36.3 +/- 0.6 degrees C and 38.3 +/- 0.5 degrees C during the day). Oxygen consumption is lowest at Ta 30-32.5 degrees C (mean 0.365 +/- 0.022 ml O2 g-1 hr-1); this is 42% below the value expected from body mass. At Ta below the TNZ, oxygen uptake rises rapidly, minimal thermal conductance (0.040 ml O2 g-1 h-1 degrees C-1) being 18% above the mass-specific level. Lowest heart rates occur at Ta 30 degrees C (mean 109.6 +/- 9.8 beats min-1) and oxygen pulse is minimal at Ta 30-35 degrees C with 40-45 microliter O2 beat-1. At Ta 15-32.5 degrees C total evaporative water loss is between 0.46-0.63 ml H2O kg-1 hr-1 and increases markedly during heat stress (to a mean of 5.35 ml H2O kg-1 hr-1 at Ta 40 degrees C). This rise of TEWL is mainly attributable to the onset of panting at Ta above 35 degrees C.     

Drought stress in rice (Oryza sativa L.) is enhanced in the presence of the compacting earthworm Millsonia anomala

Earthworms increase growth of most plant species through a number of poorly investigated mechanisms. We tested the hypothesis that earthworm modifications of soil structure and the resulting changes in water availability to plants explain this positive effect. Addition of endogeic earthworms Millsonia anomala induced a 40% increase in shoot biomass production and a 13% increase in CO₂ assimilation rate of well watered rice plants grown in pots. Conversely, when plants were subjected to water deficit, presence of earthworms had no effect on shoot biomass production and a negative impact on CO₂ assimilation rate (−21%). Early stomatal closure in presence of earthworms indicated lower water availability. The hypothesis that earthworms improve plant biomass production through soil physical structure modification was thus rejected. Three hypotheses were tested to explain this decrease in water availability: (i) a decrease in soil water retention capacity, (ii) an increase in evaporation from the soil or/and (iii) an increase in plant transpiration. Results showed that earthworms significantly reduced soil water retention capacity by more than 6%, but had no effect on evaporation rate. Water losses through transpiration were greater in the presence of earthworms when the soil was maintained at field capacity, but this was not the case under drought conditions. This experiment showed that the endogeic compacting earthworm M. anomala significantly increased plant photosynthesis by an undetermined mechanism under well-watered conditions. However, photosynthesis was reduced under drought conditions due to reduced soil water retention capacity.     

High temperature-adapted plants of Kalancho daigremontiana show changes in temperature dependence of the endogenous CAM rhythm

Plants of the CAM species Kalanchodaigremontiana grown at elevatedtemperatures (34/25C day/night) did not show endogenous netCO₂-exchange rhythm at 34C whereas at 30–32C the rhythmwas present. In contrast, the endogenous rhythm never occursabove 30C in plants grown at 25/15C day/night. Key words: Crassulacean acid metabolism (CAM), endogenous rhythm, Kalancho daigremontiana, temperature adaptation, tonoplast