Contrasts between Citrus species in response to salinisation: An analysis of photosynthesis and water relations for different rootstock-scion combinations

Leaf gas exchange, water relations and ion content were measured on two-year-old Valencia orange (Citrus sinensis [L.] Osbeck), Washington Navel orange (C. sinensis) and Marsh grapefruit (C. parodisi Macfad) scions budded to either Trifoliata (Poncirus infoliata [L] Raf) or Cleopatra mandarin (C. reticuLua Blanco) rootstoeks. Trees were watered with dülute nutrient solution containing either 0 or 50 _mM NaCl for 77 days. Leaf chloride concentrations (cell sap basis) were higher in all scions budded on “Trifoliata but sodium levels were lower than in equivalent foliage budded on Cleopatra mandarin rootstock. Foliar salt levels also varied according to scion. Leaves of Marsh grapefruit had higher levels of both sodium and chloride than leaves of either Valencia orange or Washington Navel orange on both rootstocks. Accumulation of sodium and chloride in salinised leaves caused a reduction in leaf osmotic potential of 0.2–1.4 MPa. and leaf water potential declined by as much as 0.5 MPa. Turgor pressure in salinised leaves was thus maintained at or above the control level. Osmotic potentials determined by psychrometry compared with pressure-volume curves were taken to imply that some accumulation of sodium or chloride in the apoplast of salinised leaves may have occurred. Despite turgor maintenance both _co2 assimilation and stomatal conductance were reduced by salinity. Following onset of leaf response to salinisation, gas exchange was impaired to a greater extent in scions budded to Cleopatra mandarin compared to those on Trifoliata. Amongst those scions. leaves of salt-treated Marsh grapefruit showed greater reductions in gas exchange than Valencia orange or Washington Navel orange budded on either rootstock. Increased sensitivity of 1Marsh grapefruit was correlated with a higher foliar sodium and chloride content in this scion. Scion differences in sensitivity of leaf gas exchange to solute concentration were independent of rootstock and appeared unrelated to leaf prolinebetaine concentrations. This implies an inherent difference between scion species with respect to salt tolerance, rather than variation in their capacity to acquire that type of compatible solute. In terms of rootstock effects, all scions proved more sensitive to salinity when budded to Cleopatra mandarin compared with Trifoliata. That response was attributed to a disproportionately higher concentration of leaf sodium in scions on Cleopatra mandarin.     

新疆塔里木河下游生态输水与胡杨叶片的生理及形态响应

选择塔里木河下游3个典型断面的15个研究样地,分析和测定了塔里木河下游2000～2002年生态输水前后不同研究样地的地下水位、地下水含盐量和胡杨(Populus euphratica Oliv.)叶片中脯氨酸、可溶性糖、植物内源激素脱落酸和细胞分裂素的含量以及胡杨叶片的形态结构变化,研究了塔里木河下游主要建群种胡杨对生态输水的生理与形态的响应和适应性.结果表明,塔里木河下游胡杨生长已受到不同程度的干旱胁迫;输水后各样地地下水位均有所上升,胡杨对浅层地下水位的变化表现出明显响应,胡杨受到的生理胁迫降低,胡杨叶片角质层厚度、维管束导管官腔直径及管壁厚度皆随地下水位的上升而减少;随着地下水位的上升,地下水含盐量分别提高1.76～2.47倍,输水效果由于盐对植物的生理胁迫作用的增加而有所减弱;在塔里木河下游极端干旱环境下,胡杨林保育恢复的合适地下水位埋深为3.15～4.12 m,地下水含盐量为67.15～72.65 mm.     

新疆塔里木河下游生态输水与胡杨叶片的生理及形态响应

选择塔里木河下游3个典型断面的15个研究样地,分析和测定了塔里木河下游2000￣2002年生态输水前后不同研究样地的地下水位、地下水含盐量和胡杨(Populus　euphratica　Oliv.)叶片中脯氨酸、可溶性糖、植物内源激素脱落酸和细胞分裂素的含量以及胡杨叶片的形态结构变化,研究了塔里木河下游主要建群种胡杨对生态输水的生理与形态的响应和适应性。结果表明,塔里木河下游胡杨生长已受到不同程度的干旱胁迫;输水后各样地地下水位均有所上升,胡杨对浅层地下水位的变化表现出明显响应,胡杨受到的生理胁迫降低,胡杨叶片角质层厚度、维管束导管官腔直径及管壁厚度皆随地下水位的上升而减少;随着地下水位的上升,地下水含盐量分别提高1.76　￣　2.47倍,输水效果由于盐对植物的生理胁迫作用的增加而有所减弱;在塔里木河下游极端干旱环境下,胡杨林保育恢复的合适地下水位埋深为3.15　￣　4.12　m,地下水含盐量为67.15　￣　72.65　mm。     

黑河下游河岸绿洲区包气带土壤水分与植被生长状况的研究

黑河下游荒漠平原区近年来由于河水流入量的持续减小,致使依赖河水补给来源的地下水呈减少趋势,造成区域性地下水位下降,从而引起一系列生态环境问题。通过研究黑河下游河岸绿洲区非饱和带的含水量、地下潜水埋深、土壤类型结构等与河岸绿洲植被生长状况之间的关系,发现土壤结构、地下水位埋深和土壤盐分是决定研究区植被生长状况的3个主要因素,而土壤结构是不可改变的,土壤盐分又与地下水关系密切,因此,地下水是极端干旱区植被生长状况的决定因素。     

Growth Characteristics of Cowpea (Vigna unguiculata) Seedlings as Affected by Depth to Water Table

Seedlings of two Nigerian varieties of cowpea (IT82D and IT84E716)were grown together from seeds on loamy soil for 8 weeks intwo identical sloping moisture gradient boxes established outdoorsduring the dry season. Gradients of 13 cm to 79 cm depth towater table were maintained. For all growth characters determined,differences between the two varieties did not differ statisticallythough variety IT84E716 showed marginal improvement over varietyIT82D. Depth to water table had significant effects on all growthcharacteristics determined except for number of lateral shoots.No significant depth to water table x variety interactions wererecorded for any characters examined. Nodules and nodulatedroots showed maximum development in the wettest soils wherethey were relatively thick and large. The main pattern of growththat emerged was limited growth in very wet soil, maximum growthin wet soil and increasingly limited growth as the soil becamedrier. The experiment supported the hypothesis that depth towater table may provide a major edaphic control of cowpea unlessthere is frequent rainfall or irrigation. Cowpea (Vigna unguiculata cylindrica (L.) Walp.), growth characteristics, moisture gradient boxes, phenotypic plasticity, water table     

Efficient propagation and rooting of three citrus rootstocks using different plant growth regulators

The influence of various basal medium and plant growth regulators on the efficient micropropagation of nodal explants from mature trees of alemow, sour orange, and ??Cleopatra?? mandarin citrus rootstocks was studied. All three citrus rootstock shoot cultures showed a preference for high-salt media, like Murashige and Skoog or Driver and Kuniyuki Walnut medium. Several combinations of N ⁶-benzyladenine (BA) and adenine (AD), kinetin (KIN) or gibberellic acid (GA) were tested to optimize the shoot proliferation phase. BA/GA combinations improved the proliferation of all the rootstocks studied, especially alemow. The addition of BA and AD to the culture medium improved shoot proliferation in sour orange and ??Cleopatra?? mandarin in the same way as BA and GA. The addition of different combinations of BA/KIN did not result in further improvement of any of the studied variables. The transfer of in vitro shoots to rooting media, containing different concentrations of indolebutyric acid (IBA) and indoleacetic acid (IAA), resulted in regeneration of complete plantlets. Alemow and ??Cleopatra?? mandarin shoots rooted well using these plant growth regulators; however, all combinations of IBA and IAA tested resulted in very low rooting percentages in sour orange. To improve rooting in sour orange and ??Cleopatra?? mandarin, different combinations of naphthaleneacetic acid (NAA) and IBA were tested. All NAA/IBA combinations produced higher rooting percentages than did the IBA/IAA combinations, and in sour orange nearly 100 % of explants developed roots. An efficient and simple protocol for the micropropagation of three citrus rootstocks, alemow, ??Cleopatra?? mandarin, and sour orange, by culturing nodes from mature plants, has been established.     

Effects of Salinity on Some Citrus Scion-Rootstock Combinations

Chloride and sodium concentrations, water relations and gasexchange parameters were measured on leaves of Clementine (CitrusClementine Hort. ex. Tan) and Navel orange [C. sinensis (L.)Osb] scions grafted on Cleopatra mandarin (C. reticulata Blanco)and Troyer citrange (C. sinensis x Poncirus trifoliata) rootstocksgrown at increasing levels of NaCl in the external medium. Otherparameters affected by salinity such as growth and defoliationwere also recorded. Scions on Cleopatra mandarin accumulated less Cl^- in their leavesthan did scions on Troyer citrange. Also, leaf Cl^- levels inClementine scions were lower than in Navel orange when bothwere grafted on the same rootstock. However, sodium concentrationwas lower in scions on Troyer citrange than in Cleopatra mandarin. Leaf water potential, stomatal conductance, photosynthesis andgrowth were reduced more in grafted plants of salt-treated Navelorange than those of salt-treated Clementine. However, choiceof rootstock had little effect on salt-induced changes in theseparameters. For each scion, reduction in leaf stomatal conductancewas closely correlated with decrease in leaf water potential.Also, a significant correlation between photosynthesis and stomatalconductance was found. The results indicate that reductions in gas exchange parametersand growth at increasing salinity levels depended more on thescion type than on Cl^- or Na⁺ concentration in leaves. Otherwise,leaf injury and defoliation were closely correlated with leafCl^- concentration.Copyright 1995, 1999 Academic Press Citrus, photosynthesis, salinity, water relations     

The Impact of Water Table Drawdown and Drying on Subterranean Aquatic Fauna in In-Vitro Experiments

The abstraction of groundwater is a global phenomenon that directly threatens groundwater ecosystems. Despite the global significance of this issue, the impact of groundwater abstraction and the lowering of groundwater tables on biota is poorly known. The aim of this study is to determine the impacts of groundwater drawdown in unconfined aquifers on the distribution of fauna close to the water table, and the tolerance of groundwater fauna to sediment drying once water levels have declined. A series of column experiments were conducted to investigate the depth distribution of different stygofauna (Syncarida and Copepoda) under saturated conditions and after fast and slow water table declines. Further, the survival of stygofauna under conditions of reduced sediment water content was tested. The distribution and response of stygofauna to water drawdown was taxon specific, but with the common response of some fauna being stranded by water level decline. So too, the survival of stygofauna under different levels of sediment saturation was variable. Syncarida were better able to tolerate drying conditions than the Copepoda, but mortality of all groups increased with decreasing sediment water content. The results of this work provide new understanding of the response of fauna to water table drawdown. Such improved understanding is necessary for sustainable use of groundwater, and allows for targeted strategies to better manage groundwater abstraction and maintain groundwater biodiversity.     

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi‐arid coastal ecosystem

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi‐arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water‐use functional types? We examined a suite of physiological parameters and water‐uptake depths of the dominant, functionally distinct woody vegetation along a water‐table depth gradient in a Mediterranean semi‐arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water‐source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi‐arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi‐arid coastal ecosystems to groundwater drawdown.     

1-Aminocyclopropane-1-Carboxylic Acid Transported from Roots to Shoots Promotes Leaf Abscission in Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) Seedlings Rehydrated after Water Stress

The effect of water stress and subsequent rehydration on 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity, ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in ACC synthase activity were observed. Neither increase in ACC content nor significant ethylene production were detected in leaves of water-stressed plants. After rehydration, a sharp rise in ACC content and ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after water stress than in nonstressed plants. Leaf abscission induced by rehydration after drought stress was inhibited when roots or shoots were treated before water stress with aminooxyacetic acid (AOA, inhibitor of ACC synthase) or cobalt ion (inhibitor of ethylene-forming enzyme), respectively. However, AOA treatments to shoots did not suppress leaf abscission. The data indicate that water stress promotes ACC synthesis in roots of Cleopatra mandarin seedlings. Rehydration of plants results in ACC transport to the shoots, where it is oxidized to ethylene. Subsequently, this ethylene induces leaf abscission.     

The relationship of oxalic acid to the translocation and utilization of calcium inNicotiana tabacum

Summary Burley tobacco varieties (Nicotiana tabacum L.) which differed in degrees of susceptibility to calcium deficiency were analyzed for calcium and oxalic acid content. Calcium accumulated by the total plant top was not related to susceptibility to calcium deficiency. Upper leaves and buds of plants of susceptible varieties contained less calcium per unit weight than did upper leaves and buds of non-susceptible varieties.The upper half of stalks of susceptible varieties contained more oxalic acid per unit weight than did stalks of non-susceptible varieties. The calcium content minus the oxalic acid content in buds and young leaves of the plants of the susceptible varieties was considerably less than that of buds and young leaves of the plants of the non-susceptible varieties. High levels of oxalic acid in the upper stalks and young leaves of varieties susceptible to calcium deficiency apparently induce calcium deficiency by interfering with the translocation and utilization of absorbed calcium.Contribution of the Department of Agronomy, Kentucky Agr. Exp. Sta., Lexington, and published with the approval of the Experiment Station Director. This paper is based on a portion of a thesis submitted by the senior author to the Graduate School, University of Kentucky, in partial satisfaction of the requirements for the Master's degree, 1963.     

Growth and root hydraulic conductivity of several citrus rootstocks under salt and polyethylene glycol stresses

The water relations responses to salt of several important citrus rootstocks such as Swingle citrumelo, sour orange, and Milam lemon have not been studied in detail before. Studies were set up to compare growth and root hydraulic properties of these rootstocks to other citrus rootstocks by exposing them to NaCl and polyethylene glycol (PEG) stresses. Seedlings of 7 citrus rootstocks were irrigated for 5 months with nutrient solutions containing NaCl or PEG that had been adjusted to osmotic potentials of -0.10, -0.20 or -0.35 MPa. The 7 rootstocks studied were sour orange (Citrus aurantium), Cleopatra mandarin (Citrus reticulata Blanco), Swingle citrumelo (C. paradisi x P. trifoliata), Carrizo citrange (C. sinensis x P. trifoliata), rough lemon (Citrus jambhiri Lush), Milam lemon (C. jambhiri hybrid), and trifoliate orange (Poncirus trifoliata [L.] Raf.). In both shoot and root growth, Cleopatra mandarin and sour orange were the least sensitive to salt, Milam and trifoliate orange were the most sensitive, and rough lemon, Swingle, and Carrizo were intermediate in sensitivity. Even though the roots were exposed to solutions of equal osmotic potentials, plant growth and root conductivity were reduced more by the PEG treatments than the corresponding NaCl treatments. At -0.10 and -0.20 MPa, shoot and root dry weights were reduced 16 to 55% by NaCl and 24 to 68% by PEG. Shoot root ratio was lowered at the higher concentrations, particularly by PEG. There was a major decrease in root conductivity caused by NaCl at -0.10 MPa (19 to 30% in sour orange and Cleopatra mandarin and 78 to 85% in trifoliate orange and Milam). Conductivity decreased more at -0.20 and -0.35 MPa, but not proportionally as much as at -0.10 MPa. Root weight per unit length increased at the higher salt levels, particularly in trifoliate orange. Water flow rate through root systems followed the same trend as root conductivity; salt affected sour orange and Cleopatra mandarin the least and trifoliate orange and Milam the most. However, reductions in fibrous root length by salt treatment differed. Root lengths of Swingle and Carrizo were least affected by salt while sour orange. Milam, and rough lemon were the most affected. Hence, even though sour orange and Cleopatra mandarin were more tolerant than the other rootstocks in terms of water flow rate or root conductivity, these 2 rootstocks showed a proportionally greater decrease in root length than Carrizo, Swingle, or trifoliate orange.     

干旱胁迫对科尔沁沙地榆树幼苗C、N、P化学计量特征的影响

设置适宜水分、轻度、中度和重度干旱胁迫处理(即80%、65%、50%和35%田间持水量),研究干旱胁迫对榆树幼苗不同器官C、N、P化学计量的影响.结果表明:与适宜水分处理相比,干旱胁迫导致C含量在叶、茎、粗根和细根中增加,N含量在叶、茎和粗根中增加,P含量在叶、茎和粗根中下降,在细根中增加,C:N在叶和茎中下降,C:P及N:P在叶、茎和粗根中增加,在细根中下降.各器官间C含量呈显著正相关,而各器官间N与P相关性均不显著.土壤含水量与各器官C含量,叶N含量,细根P含量及C:N,叶、茎和粗根C:P及N:P呈显著负相关,而与细根N含量,叶、茎和粗根P含量,细根C:P及N:P呈显著正相关.因此,干旱胁迫影响榆树幼苗对N、P的吸收及向上运输,幼苗生长主要受N限制;随着干旱胁迫的加剧,叶、茎和粗根生长受P限制作用增强.     

新疆塔里木河下游荒漠河岸(林)植被合理生态水位

 该文依据塔里木河下游地下水位多年监测资料, 将地下水位按不同埋深划分为0~2、2~4、4~6、6~8、8~10和>10 m 6个梯度, 并设置植 被调查样方进行连续监测, 以分析地下水位变化对植物物种多样性与种群生态位的影响。研究结果表明: 在地下水位2~4 m时, 物种多样性最高 , 其次为4~6 m, 再次为0~2 m; 当地下水位在6 m以下时, 物种多样性锐减, Hill多样性指数曲线变化趋势趋于平直化。荒漠河岸(林)植被主要 植物种群生态位随着地下水位的逐步下降而扩展, 并在地下水位4~6 m处达到最宽; 尔后, 生态位又显著变窄; 地下水位4~6 m时, 种群间生态 位重叠最不显著, 物种数较为丰富。因此, 该文分析得出结论: 塔里木河下游植被恢复的地下水位应确保达到6 m以上, 大部分地区地下水位应 维持在4~6 m, 而部分河道附近地区地下水位争取达到2~4 m。     

Some physiological and morphological characteristics of citrus plants for drought resistance

Tolerance and avoidance mechanisms to drought stress were studied in 6-month-old plants of Newhall orange (Citrus sinensis (L.) Osbeck) and Ellendale tangor (orange × mandarin hybrid) (Citrus sinensis (L) Osbeck × Citrus reticulata Blanco) during a drought/rewatering cycle under controlled conditions. Drought stress did not promote osmotic adjustment, while elastic adjustment (tissue elasticity increase) was noted in stressed orange and tangor plants. Both citrus plants showed a parallel decrease in leaf conductance (g₁) and leaf water potential (Ψ₁) under water stress. Tangor plants had a more efficient water conservative strategy than orange, based on the characteristics of canopy architecture (lower canopy area and a more closed canopy with leaves nearly vertically oriented) together with a significant decrease in cuticular transpiration rates (TRc) under stress.     

The role of carotenoid cleavage dioxygenases in the regulation of carotenoid profiles during maturation in citrus fruit

To investigate the relationship between a carotenoid profile and gene expression for carotenoid cleavage dioxygenases, three citrus varieties that exhibit different 9-cis-violaxanthin levels in their juice sacs, Satsuma mandarin (Citrus unshiu Marc.; a variety accumulating a low level of 9-cis-violaxanthin), Valencia orange (Citrus sinensis Osbeck; variety accumulating a high level of 9-cis-violaxanthin), and Lisbon lemon (Citrus limon Burm.f.; a variety accumulating an undetectable level of 9-cis-violaxanthin) were used. Three cDNAs (CitCCD1, CitNCED2, and CitNCED3) were cloned. The recombinant CitCCD1 protein cleaved beta-cryptoxanthin, zeaxanthin, and all-trans-violaxanthin at the 9-10 and 9'-10' positions and 9-cis-violaxanthin at the 9'-10' position. The recombinant CitNCED2 and CitNCED3 proteins cleaved 9-cis-violaxanthin at the 11-12 position to form xanthoxin, a precursor of abscisic acid (ABA). The gene expression of CitCCD1 increased in the flavedos and juice sacs of the three varieties during maturation. In Satsuma mandarin, the gene expression of CitNCED2 and CitNCED3 increased noticeably, accompanying a massive accumulation of ABA in the flavedo and juice sacs. In Valencia orange, the gene expression of CitNCED3 increased with a slight elevation of the ABA level in the flavedo, whereas neither the gene expression of CitNCED2 nor the ABA level increased noticeably in the juice sacs. In Lisbon lemon, the gene expression of CitNCED2 increased remarkably, accompanying increases in the ABA level in the flavedo and juice sacs. These results suggest that, in the juice sacs, the efficient cleavage reaction for ABA synthesis reduces the 9-cis-violaxanthin level in Satsuma mandarin and Lisbon lemon, whereas the low cleavage reaction maintains the predominant 9-cis-violaxanthin accumulation in Valencia orange.     

Regeneration and characterization of somatic hybrids combining sweet orange and mandarin/mandarin hybrid cultivars for citrus scion improvement

Protoplast fusion between sweet orange and mandarin/mandarin hybrids scion cultivars was performed following the model ??diploid embryogenic callus protoplast?+?diploid mesophyll-derived protoplast??. Protoplasts were isolated from embryogenic calli of ??Pera?? and ??Westin?? sweet orange cultivars (Citrus sinensis) and from young leaves of ??Fremont??, Nules??, and ??Thomas?? mandarins (C. reticulata), and ??Nova?? tangelo [C. reticulata?×?(C. paradisi?×?C. reticulata)]. The regenerated plants were characterized based on their leaf morphology (thickness), ploidy level, and simple sequence repeat (SSR) molecular markers. Plants were successfully generated only when ??Pera?? sweet orange was used as the embryogenic parent. Fifteen plants were regenerated being 7 tetraploid and 8 diploid. Based on SSR molecular markers analyses all 7 tetraploid regenerated plants revealed to be allotetraploids (somatic hybrids), including 2 from the combination of ??Pera?? sweet orange?+???Fremont?? mandarin, 3 ??Pera?? sweet orange?+???Nules?? mandarin, and 2 ??Pera?? sweet orange?+???Nova?? tangelo, and all the diploid regenerated plants showed the ??Pera?? sweet orange marker profile. Somatic hybrids were inoculated with Alternaria alternata and no disease symptoms were detected 96?h post-inoculation. This hybrid material has the potential to be used as a tetraploid parent in interploid crosses for citrus scion breeding.     

不同柑桔品种上桔全爪螨的生长和种群动态差异

通过田间调查、室内盆栽苗接螨、离体叶片饲养等方法,考察了14个柑桔品种上桔全爪螨种群动态,组建了其实验种群生命表,结果表明：该螨在各柑桔品种上的种群密度有明显差异,平均密度以北碚447、台湾晚白柚和垫江白柚上较高,柑新生系最低。雌成螨寿命在台湾晚白柚上最长,垫江白柚次之,柑新生系最短;产卵量以取食台湾晚白柚时最多,垫江白柚、五步红心柚次之,以柑新生系最少;在垫江白柚上的内禀增长率（r_m）最大,沙田柚、台湾晚白柚次之,金弹最小。根据桔全爪螨实验种群的参数判断,金弹和柑新生系属抗螨品种,台湾晚白柚、垫江白柚和北碚447是感螨品种。从品种归类上来看,柚类品种和甜橙中的北碚447感螨程度较高,金柑属的金弹和宽皮柑桔类的柑新生系感螨程度较低。甜橙类与宽皮柑桔类比较,前者感螨程度较高,后者相对较低,但宽皮柑桔类的早津感螨程度相对较高。     

Effect of flooding and cropping on the changes in the inorganic phosphate fractions in some rice soils

Summary Greenhouse experiments were conducted to evaluate the significance to flooded rice of the various forms of inorganic soil phosphate on Aborlan, Luisiana and Pili soils with and without phosphate. Changes in the various inorganic soil phosphate fractions with time under cropped and uncropped conditions were measured. Results showed that the iron phosphate fraction was the most important source of phosphate to the rice plant. It was also evident that phosphate added to the soils was slowly converted into the iron phosphate form. Transformation of soil phosphate seemed to be greatly affected by the presence of plant roots. Changes in the phosphate fractions were marked in the cropped soils.Data presented in this paper form part of Ph.D. dissertation submitted by the first author to the University of the Philippines, College of Agriculture, Los Banos, The Philippines.Professor of Agr. Chemistry, Dept. of Agr. Chemistry, Univ, of the Philippines, College of Agriculture.Rice Agronomist, Univ. of Agr. Sciences, Regional Research Station, Mandaya, Mysore, India.     

盐渍化灌区土壤盐分的时空变异特征及其与地下水埋深的关系

土壤盐分空间变异特征和地下水埋深状况是指导灌区合理用水和防治土壤盐碱化的重要依据。运用经典统计学和地质统计学方法,结合GIS技术,分析了河套灌区沙壕渠灌域0-20 cm、20-40 cm、40-60 cm土壤EC值的空间变异特征及地下水埋深对土壤盐分分布的影响。结果表明:沙壕渠灌域土壤盐分Cv值在不同灌溉时期和不同土壤深度均大于36%,表现为强变异特征;各灌水时期和不同土壤深度土壤EC值均表现为中等强度的空间自相关性,表层0-20 cm土壤空间自相关程度最高;秋浇前不同层次土壤EC值的空间分布在灌域内从南到北呈增大趋势,秋浇后土壤含盐量的高值区在西北部或东北部;土壤盐分受地下水埋深影响显著,灌域内地下水埋深南深北浅,土壤盐分随地下水埋深的增大而减小,二者之间满足指数关系。因此,应采取合理措施控制地下水埋深,防止区域土壤盐渍化加剧。