Eco-physiological studies on desert plants

Summary The Egyptian Zygophyllum species, though limited in number, contribute in considerable measure to the desert vegetation. They represent a group of succulent plants which are drought resistant or salt tolerant living under severe dry climatic conditions. Their abundance is attributed to these characteristics in addition to their unpalatibility.The distribution of the studied species is deduced from the data collected by the present authors and others working in the Egyptian desert. The growth and distribution of some Zygophyllum species are dependant on the chemical nature of the substratum. Z. occineum is a widespread species in the limestone territories of the Eastern desert. Z. decumbens is confined to a limited area within the borders of the area inhabited by Z. coccineum. Z. album is a salt tolerant plant with wide geographical range growing in dry littoral or inland salt marshes. Z. simplex, the only ephemeral species, has wide geographical and ecological ranges. The soil carbonate content does not exercise any significant effect on its distribution though it is more ecologically related to Z. occineum than the other species. Z. decumbens is ecologically related to Z. coccineum, while Z. album has its own ecological amplitude.     

Eco-physiological studies on desert plants X. Contribution to the autecology of the desert chasmophyte Stachys aegypticca Pers.

Summary Stachys aegyptiaca Pers. is a desert calcicolous chasmophyte. Its growth in the Egyptian Desert is confined to the limestone formations of the Northern Arabian Desert, Sinai and the Isthmic Desert. The plant lives under harsh climatic conditions: high summer temperatures with mean maxima above 35°C and low rainfall ranging from 9.4 mm/annum at El-Tor to 87.3 mm/annum at Hemme.The vegetation dominated by Stachys aegyptiaca is a pioneer stage in the development of the wadi bed ecosystem. Other chasmophytes are the main associates of the Stachys community. The studied plant has been recorded among the associates of numerous plant communities.Runoff, accelerated by the rugged topography in areas where the plant grows, and the stoniness of the substratum contribute to securing ample water supply to the plant.The daily march of the transpiration rate was investigated in two seasons. It has been clear that there is an obvious regulation of transpiration in summer.The osmotic pressure of the plant sap was determined at regular monthly intervals throughout one year. The average osmotic value is 17 atm, ranging from 13.8 atm in April to 19.3 atm in November.Dedicated to Prof. M. Evenari and Dr. K. Springer     

Eco-physiological studies on Indian arid zone plants

Summary The separate and combined effects of sodium chloride and gibberellin (GA) on growth and the activities of alanine aminotransferase (GPT), aspartate aminotransferase (GOT) and glutamate dehydrogenase (GLDH) have been studied in the aerial parts of Pennisetum typhoides seedlings. Salt concentrations higher than 8.55×10³ M inhibited growth and reduced GLDH activity, but strongly stimulated the activity of GPT and, to a lesser extent, that of GOT. GA alone, on the other hand, stimulated growth but did not affect activity of any of the enzymes tested. In combination with salt, however, GA tended to counteract the effect of salt on both growth and enzyme activity. The possible significance of the results in explaining adaptation of plants under conditions of stress has been discussed.     

Eco-physiological studies on Indian arid zone plants

Summary Photosynthetic characteristics of two important grasses of Indian desert have been studied. Pennisetum typhoides, an important cereal crop, known to have Kranz-type leaf anatomy and low CO₂-compensation point, shows the C-4-dicarboxylic acid pathway for photosynthetic carbon reduction. Lasiurus sindicus, a promising forage grass, has also been shown to possess, for the first time, a typical Kranz-type leaf anatomy and a very similar CO₂-fixation pattern like Pennisetum typhoides. It is remarkable that both species after short time exposure to ¹⁴CO₂ show a high labelling not only in malate but also in alanine. This may be due to the activity of an aspartic acid decarboxylase.     

四种荒漠植物的光合响应

研究了胡杨（Populus euphratica Oliv）、疏叶骆驼刺（Alhagi sparsifolia B.Keller et Shap)、多枝柽柳（Tamarix ramosissima Lbd)和头状沙拐枣（Calligonum caput-medusae Schrenk)等四种塔克拉玛干荒漠植物的光合响应曲线,结果表明：（1）四种植物中,疏叶骆驼刺光呼吸（Rp)和CO2补偿点（Г）最高,净光合速率（An）以及水分利用效率（WUE）最低;而C4植物头状沙拐枣无论Rp还是Г都最低,它的An、光补偿点（LCP）及光饱和点（LSP）都显著高于其它3种植物（P≤0．05）,而且因为非常低的蒸腾速率（E）,沙拐枣的WUE也较高。（2）4种植物都为喜光植物,但仍然表现出一定的差异。根据它们光曲线中LCP以及暗呼吸速率（Rd),4种喜光植物的喜光顺序为：头状沙拐枣,疏叶骆驼枣刺,多枝柽柳,胡杨。（3）柽柳光合响应曲线与日变化中的An,gs等值差异较大,可能是该植物的温度生态位较其它三种植物范围较窄,设置的25℃不在其最适温度范围内,或者是在这个温度下气孔对光强变化的不敏感。（4）综合前人的结果表明,在特定的环境条件,发育阶段以及经过一定的诱导处理,胡杨可以因诱导而表现出一些C4植物特征。     

两种沙生植物抗旱生理指标的比较研究

以沙坡头地区自然生长和人工灌溉条件下的沙冬青（Ａｍｍｏｐｉｐｔａｎｔｈｕｓ ｍｏｎｇｏｌｉｃｕｓ）和柠条（Ｃａｒａｇａｎａ ｋｏｒｓｈｉｎｓｋｉｉ）为材料,对它们部分抗旱生理指标的变化进行了研究,结果表明,沙冬青对干办迫最敏感,这些生理指标随着个体发育阶段的不同变化,并具种间差异性。可溶性糖和游离氨基酸（特别是Ｐｒｏ）在干旱环境植物中均有较高含量,沙冬青有较高的热值,类黄酮水平未见差异性变化。     

几种荒漠植物地上生物量估算的初步研究

在调查植物样方的基础上,利用植株冠幅特征如冠幅长与宽、株高、基径、新生枝条数、总枝条数等作为变量建立了估算典型荒漠植物地上生物量的模型,利用植株冠幅长与宽所建拟合方程对估算琵琶柴灌丛生物量的精确度较高,经验证,预测值与实测值的相关系数为O．9989,相对误差在4．79％～10．12％之间利用植株株高、基径所建拟合方程对估算梭梭、多枝柽柳生物量计算值与实测值的相关系数在0.9418以上,显著性检验表明相关系数均为极显著经验证,预测值与实测值的相关系数分别为0．9902和0．9875．相对误差分别为6．87％～19．22％和7．49％～18．47％。研究表明,在大面积荒漠植物生物量研究中,利用植株冠幅特征作为变量来估算琵琶柴灌丛地上生物量方法简便可行,用来估算梭梭、多枝柽柳等灌木地上生物量时存在一定误差     

硅缓解植物镉毒害的生理生态机制

镉是对生物毒性最强的污染物之一。过量的镉能够抑制植物的生长和光合作用,干扰矿质代谢并诱发氧化胁迫。硅作为一种有益元素,主要以Si(OH)_4的形态通过主动或被动方式被植物体吸收并转运到地上部分。硅对植物镉毒害具有缓解作用,但其缓解机制在不同物种、品种或生态型之间存在显著差异,并表现出一定的硅/镉浓度依赖性。总体上可概括为避性机制和耐性机制。避性机制包括:(1)在器官水平,减少植物根系对镉的吸收及其向地上部的转运;(2)在细胞水平,增强细胞壁对镉的吸附能力,减少共质体中镉的含量。耐性机制包括:(1)诱导细胞产生小分子螯合剂,增强对镉的螯合作用,减少细胞中游离态镉的含量;(2)增强抗氧化机制,减轻氧化胁迫;(3)改善光合作用和无机营养,促进植物生长。从植物对硅的吸收和转运、镉对植物的毒害作用以及硅对缓解植物镉毒害的生理生态机制3个方面进行了综述,并基于目前的研究现状和薄弱之处,对今后的研究重点进行了展望。     

Oxygen effects on photosynthesis and C metabolism in desert plants

The effect of 1% and 21% O₂ upon ¹⁴CO₂ assimilation by desert plants exposed for 10 to 90 seconds has been studied. The plants studied can be divided into three groups with respect to O₂. The C₃ plants display the usual Warburg effect. No changes could be observed in the intensity of photosynthesis as a function of O₂ content in another group of plants (showing signs of Crassulacean acid metabolism). In still another group of plants (C₄ plants) the stimulating effect of O₂ on photosynthesis could be detected. In C₃ plants, O₂ inhibits the processing of carbon through the Calvin cycle intermediates. The involvement of carbon in the glycolate pathway fails to explain completely the inhibiting effect of O₂ on photosynthesis. It is assumed that O₂ inhibits the enzymes of the Calvin cycle. In C₄ plants O₂ stimulates the incorporation of ¹⁴C into malate and aspartate. The incorporation of ¹⁴C into the intermediates of the Calvin cycle in C₄ plants is inhibited much like that in typical C₃ plants.     

Eco-physiological studies of the semiarid grasses Aristida leptopoda and Astrebla lappacea

The perennial grasses (Aristida spp.) are invaders of the Mitchell (Astrebla spp.) grasslands of semiarid Queensland. The possible role of a number of physiological factors influencing the establishment and maintenance of Aristida leptopoda (white spear grass) and Astrebla lappacea (curly Mitchell grass) populations were examined in a series of experiments. Under controlled conditions, both seedling growth and root extension rates of curly Mitchell grass were far superior to white spear grass at a temperature of 30°C. However, at temperatures of 25°C and less, little species differences in these rates occurred White spear required a lower soil phosphorus concentration for optimum growth compared with curly Mitchell grass, but its yield response to increasing phosphorus concentration was much smaller than this species. Results of other studies suggested that relative drought endurance of established plants of these species to be related more to the amount and vertical distribution of the root system rather than to differences in stomatal control.     

Predator-mediated interactions among the seeds of desert plants

In theory, seed predators are capable of inducing indirect interactions among the seeds they consume. However, empirical evidence of predator-mediated interactions among seeds is rare. Rodents in the Heteromyidae are highly granivorous and therefore likely to induce indirect interactions among the seeds of desert plants. The indirect interactions may be in the form of apparent competition and apparent mutualism between seeds within a patch. Apparent competition exists when the survival of seeds of a focal species is lessened because of the presence of additional seeds of other species in the patch. Apparent mutualism exists when the presence of the other seeds results in an increase in survival of seeds of the focal species. By measuring seed removal from trays placed in the field, apparent competition between the seeds of several plant species was detected. Apparent mutualism might also exist, but there was no strong evidence of it. Apparent competition appeared most likely to occur among the species whose seeds were the most heavily predated. For instance, predation on seeds of Astragalus cicer, Oryzopsis hymenoides, and Sphaeralcea coccinea was substantial with more than 50% of the seeds removed from the trays, on average. The intensity of apparent competition (measured by the indirect effect, IS) between these species and two others was significant; IS ranged from –0.02 to –0.39 on a scale of 0 to –1. This indicates that, in some communities, indirect effects are most likely to exist when direct effects are strong. Received: 5 August 1999 / Accepted: 2 March 2000     

Differential utilization of summer rains by desert plants

Summary Seasonal changes in the hydrogen isotope ratios of xylem waters were measured to determine water sources used for growth in desert plants of southern Utah. While all species used winter-spring recharge precipitation for spring growth, utilization of summer rains was life-form dependent. Annuals and succulent perennials exhibited a complete dependence on summer precipitation. Herbaceous and woody perennial species simultaneously utilized both summer precipitation and remaining winter-spring precipitation, with herbaceous species much more reliant on the summer precipitation component. Several of the woody perennials exhibited no response to summer precipitation. Currently, precipitation in southern Utah is evenly partitioned between winter and summer time periods; however, global circulation models predict that summer precipitation will increase in response to anticipated climate change. Our data indicate that components within the community will differentially responde to the change in precipitation patterns. These results are discussed in relation to impact on competition and possible changes in community structure.     

Annual plants in arid and semi-arid desert regions

Annual plants are the main vegetation in arid and semi-arid desert regions.Because of their unique traits,they are the optimal experimental subjects for eco-logical studies.In this article,we summarize annual plants' seed germination strategies,seedling adaptability mechanism to environments,seed dispersal,and soil seed banks.We also discuss the biotic and abiotic factors affecting the composition and dynamics of annual plant populations and communities.Because annual plants have important ecological functions in desert vegetation systems,this study on annual plants will be of great bene-fit to the conservation and restoration of desert ecosys-tems,the rational utilization of resources,and the sustainable development of desert regions.     

Annual plants in arid and semi-arid desert regions

Annual plants are the main vegetation in arid and semi-arid desert regions. Because of their unique traits, they are the optimal experimental subjects for ecological studies. In this article, we summarize annual plants’ seed germination strategies, seedling adaptability mechanism to environments, seed dispersal, and soil seed banks. We also discuss the biotic and abiotic factors affecting the composition and dynamics of annual plant populations and communities. Because annual plants have important ecological functions in desert vegetation systems, this study on annual plants will be of great benefit to the conservation and restoration of desert ecosystems, the rational utilization of resources, and the sustainable development of desert regions. __________ Translated from Chinese Journal of Ecology, 2006, 25(7): 851–856 [译自: 生态学杂志]