Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae)

The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake.     

Flavonoids from Serratula komarovii Iljin (the Asteraceae Family)

Russian Journal of Bioorganic Chemistry - The genus Serratula L. (the Asteraceae family) is represented by two species in the Russia’s Far East: Serratula manshurica Kitag. and Serratula...     

An empirical predictive model for the flight period of Platypus koryoensis (Coleoptera: Platypodinae)

Between 2007 and 2009, field studies were conducted in four Quercus mongolica Fischer ex Ledebour forests in Korea to develop an empirical degree-day model for the flight period of the ambrosia beetle, Platypus koryoensis (Murayama). The lower developmental threshold temperature was estimated using an iterative method based on field trap catches and temperatures. The pooled proportion of the total number of beetles found in the traps at the end of the experiment was plotted against the accumulated degree-days at selected baseline temperatures, and these plots were fitted by the Weibull function. The baseline temperature with the highest coefficient of determination was considered the lower developmental threshold temperature, and this was estimated to be 5.8 °C. The explanatory power of the model was 89 %. Moreover, the model accurately predicted the time distributions of P. koryoensis flights in 2011 and 2012 at one of the sites. The estimated median flight dates in 2011 and 2012 were 4 days earlier and 5 days later than the corresponding observed flight dates, respectively. The estimated median date of flight advanced progressively during 1970–2010 by a total of 9 days due to an increase in annual mean temperature.     

Stem photosynthesis in Psorothamnus spinosus (smoke tree) in the Sonoran desert of California

Summary Stem photosynthetic responses to environmental parameters were investigated with Psorothamnus spinosus in the Sonoran Desert of California. Light saturation of stem photosynthesis was equal to maximum midday summer irradance (1600–2000 mol·m^-2·s^-1). The optimum temperature for stem photosynthesis was 39°C, and lower stem temperatures (27–35°C) caused significant decreases (up to 50%) in stem photosynthesis. Positive stem photosynthesis was maintained up to 51°C. Stem photosynthesis was relatively insensitive to increasing vpd up to 5 kPa; However, stem conductance decreased by 25% at a vpd of 5 kPa. At vpd greater than 5 kPa stem photosynthesis decreased relatively more than that of stem conductance causing a decrease in water use efficiency and an increase an intercellular carbon dioxide concentration. Maximum stem photosynthetic rates were low (6.2–10.6 mol·m^-2·s^-1) on a stem surface area, but, stem photosynthetic rates of young shoots were substantially higher (19.5–33.3 mol· m^-2·s^-1) on a projected area basis.Dedicated to the memory of Dr. W.H. Muller     

荒漠草原异质生境下猪毛蒿种群动态

以荒漠草原猪毛蒿种群为对象,设置风沙土、灰钙土和基岩风化沉积土3个生境下增水30%、减水30%和对照3个处理,编制猪毛蒿种群的动态生命表,绘制种群存活和死亡曲线,分析异质生境下猪毛蒿种群动态规律,研究猪毛蒿年内年际间种群动态特征.结果表明: 猪毛蒿种群存活曲线趋于Deevey-Ⅰ型,即生长前期存活率较高,趋于稳定状态,死亡率基本维持在较低的水平,生育期末种群死亡率则上升较快.各生境下猪毛蒿个体的存活数均呈前期波动后期下降的趋势,风沙土和灰钙土生境下死亡率的波动变幅较大,增减水处理对猪毛蒿种群死亡率的影响无显著差异.土壤类型对猪毛蒿株高、冠幅、密度、盖度和生物量均有显著影响,降水处理对猪毛蒿株高、冠幅和盖度影响显著,对密度和生物量无显著影响,而土壤类型和降水处理的交互作用仅对株高和冠幅有显著影响.基岩风化沉积土生境下猪毛蒿生物量的可塑性指数显著高于风沙土和灰钙土,灰钙土和基岩风化沉积土生境下盖度可塑性显著高于风沙土.增水处理的密度可塑性指数显著高于对照和减水处理.株高和冠幅的可塑性指数较高,说明在不同的生境压力下,猪毛蒿可以通过优先调节这两个参数来应对生境的变化.     

Herbaceous layer determines the relationship between soil respiration and photosynthesis in a shrub-dominated desert plant community

Plant and Soil - Although the linkages between aboveground photosynthates production and belowground respiration processes have been well studied, doubts remain as to the extent that photosynthate...     

Water use efficiency,photosynthesis, extreme temperature and drought tolerance of desert plant seedlings

The seedlings of twenty eight annual and perennial desert plants belonging to fifteen families were raised under controlled growth conditions and subjected to a range of tests. The water use efficiency, photosynthesis, extreme temperatures and drought tolerance were monitored. The results were discussed for their ecological significance as a basic information to applied research. Seedlings which were more tolerant to extreme high and low temperatures and drought were more capable of controlling water loss through better water use efficiency. At temperatures below 25°C, the annual plants had higher photosynthetic rate than perennials, whereas at higher temperatures, the perennials were advantaged.     

A dynamic model for photosynthesis by an aquatic plant, Egeria densa

Abstract This paper describes a dynamic model for photosynthesis by an aquatic plant, Egeria densa. The model takes into account an HCO^?₃ pump, high diffusion resistances and PEP carboxylase, and develops a set of differential equations to form the time-dependent solutions for photosynthesis. The predicted changes in pH, [CO₂]_aq and total inorganic carbon are compared with experimental data and the model is found to describe the data. The model is then used to examine the effect of O₂ on photosynthesis under these conditions, and shows that the increase in internal CO₂ concentration due to the recycling of photorespiratory CO₂ directly stimulates gross CO₂ fixation and can more than compensate for the O₂ inhibition of gross photosynthesis. The importance of the HCO^?₃ pump in O₂ inhibition is also examined. The CO₂ compensation point (where inorganic carbon influx and efflux are equal) is examined and the importance of the HCO^?₃ pump and PEP carboxylase in reducing the compensation concentration is discussed. The model was developed in order to study the photosynthesis of an aquatic weed, which will be reported in a later paper.     

An empirical codon model for protein sequence evolution

In the past, 2 kinds of Markov models have been considered to describe protein sequence evolution. Codon-level models have been mechanistic with a small number of parameters designed to take into account features, such as transition-transversion bias, codon frequency bias, and synonymous-nonsynonymous amino acid substitution bias. Amino acid models have been empirical, attempting to summarize the replacement patterns observed in large quantities of data and not explicitly considering the distinct factors that shape protein evolution. We have estimated the first empirical codon model (ECM). Previous codon models assume that protein evolution proceeds only by successive single nucleotide substitutions, but our results indicate that model accuracy is significantly improved by incorporating instantaneous doublet and triplet changes. We also find that the affiliations between codons, the amino acid each encodes and the physicochemical properties of the amino acids are main factors driving the process of codon evolution. Neither multiple nucleotide changes nor the strong influence of the genetic code nor amino acids' physicochemical properties form a part of standard mechanistic models and their views of how codon evolution proceeds. We have implemented the ECM for likelihood-based phylogenetic analysis, and an assessment of its ability to describe protein evolution shows that it consistently outperforms comparable mechanistic codon models. We point out the biological interpretation of our ECM and possible consequences for studies of selection.     

The diurnal time course of net photosynthesis of soybean leaves: Analysis with a physiologically based steady-state photosynthesis model

Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to analyze observed net photosynthesis daily time courses of soybean, Glycine max (L.) Merr., leaves. Observations during two time periods of the 1978 growing season are analyzed and compared. After adjustment of the model for soybean, net photosynthesis rates are calculated with the model in response to measured incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance. The steady-state calculations closely approximate observed net photosynthesis. Results of the comparison reveal a decrease in photosynthetic capacity in leaves sampled during the second time period, which is associated with decreasing ability of leaves to respond to light intensity and internal air space carbon dioxide concentration, increasing mesophyll resistance, and increasing stomatal resistance.     

An empirical model for sediment resuspension in shallow lakes

Suspended solids concentrations were measured at routine 2–3 week intervals and on additional windy days for at least one year in each of seven shallow (mean depth < 2 m) south Island, New Zealand lakes. Surface wave characteristics were estimated from water depths and local meteorological data using a shallow-water wave forecasting model for fetch-limited waves. Bottom shear stresses were computed from surface wave characteristics for the sampling stations and for a hypothetical lake-average station. The calculated shear stresses were, on average, much better predictors of suspended solids concentrations than alternative models using two different functions of wind speed, wave height²/depth or wavelength/depth. A combination of the sample station and lake average shear stresses provided slightly better predictions than the sample station values alone, suggesting that currents also contribute significantly to the concentration at a given point. Regressions of suspended solids on the combined functions had r ² values ranging from 0.74–0.73 in the seven lakes. The slopes of these regressions were negatively related to the settling velocity of the lowest quartile of the sediment, and to macrophyte biomass, in multiple regression (r ² = 0.94, p < 0.01).     

Microsatellite DNA loci from the drought desert plant Calligonum mongolicum Turcz. (Polygonaceae)

Calligonum mongolicum Turcz. (Polygonaceae) is a typical drought desert plant which can tolerate extreme drought, cold, and other stress in the northern extreme drought desert of China. They are playing an important role in maintaining the local ecosystems in these regions. In order to understand the adaptive evolution and develop effective conservation methods of this species in the arid habitats, it is important to know its genetic structure. In this study, 14 polymorphic microsatellite loci were isolated and characterized from an enrichment genomic library of this species. We further assessed the polymorphisms of each locus in 18 individuals from six geographically distant populations. The number of alleles per locus ranged from three to six. The observed and expected heterozygosity ranged from 0.24 to 0.35 and 0.38 to 0.57, respectively. These markers have been crossed checked in another congeneric species, C. mongolicum. These microsatellite markers will be useful for investigating the genetic structure and devising conservation strategies of this species, and morphological divergence between and it and the closely related species.     

Effects of seed colour heterogeneity on germination behaviour of the desert plant Lotononis platycarpa (Fabaceae)

We aimed to determine the ecological role of three seed morphs observed for the first time in a desert population of Lotononis platycarpa (Fabaceae), with respect to their germination requirements. Seeds sorted by seed coat colour (olive green, orange and brown) were germinated under laboratory conditions under two photoperiods (12/12‐h light and continuous dark) and three alternating temperature regimes (15/25, 20/30, 25/35°C). We found that the three distinct seed types differ in their seed mass, germination percentage and speed of germination. Overall, the light‐incubated seeds germinated with higher percentages than seeds in the total darkness. Furthermore, seeds with orange coat germinated with higher percentages at 15/25 and 25/35°C (up to 60%, for both) and significantly faster than the other two colour morphs. Our results suggest an adaptive significance of seed colour heterogeneity in the harsh desert habitat inhabited by the study species.     

An empirical model of primary productivity (14C) using mesocosm data along a nutrient gradient

The two parameters of the hyperbolic tangent equation, P_m and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) ¹⁴C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (P_d). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m^–2 year^–1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m^–2 day^–1and was significantly correlated, in all treatments, with acomposite parameter BI₀/k (where B is phytoplankton biomass;I₀ is daily radiation and k is the extinction coefficient).Linear regressions of P_d against BI₀/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI₀/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production.     

An empirical model for describing the effects of nitrogen sources on nisin production

AIMS: A study on the effects of tryptone and yeast extract on nisin production by Lactococcus lactis was carried out using a second order rotatable factorial design. METHODS AND RESULTS: The results show that both ingredients increased nisin production, although a small decrease in nisin levels was noted at high tryptone concentrations. In view of the low vitamin content of tryptone, the amino acids present in both tryptone and yeast extract may be responsible for these observations. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: The observed response suggests that maintaining tryptone concentrations in the centre of the domain and increasing the concentration of yeast extract would be ideal conditions for nisin production. However, when the economic aspects are considered, it appears that low concentrations of yeast extract and reasonably high concentrations of tryptone are optimal.