Realized pollen and seed dispersal within a continuous population of the dioecious coniferous Brazilian pine [Araucaria angustifolia (Bertol.) Kuntze]

Extensive realized pollen and seed flow across populations reduces inbreeding and spatial genetic structure (SGS) and increases the genetic diversity and effective size within populations. Inbreeding, SGS and realized patterns of pollen and seed dispersal of the dioecious, wind pollinated Araucaria angustifolia were investigated based on microsatellite loci. The study was conducted in a 7.2 ha plot established within a continuous Araucaria Forest in Southern Brazil. In the plot, all 290 adult trees were mapped, measured (diameter at breast height, dbh), sexed, sampled and genotyped. We also sampled, measured (total height), mapped and genotyped 223 juveniles. A total of 86 alleles were detected in the sample (n = 513). Adults and juveniles showed a positive and significant fixation index (minimum of 0.096), suggesting inbreeding or Wahlund effect. Juveniles presented a significant aggregated distribution which was associated with a genetic aggregation (significant SGS up to 20 m), indicating that near neighbor trees may be related due the limited seed dispersal. However, the intensity of SGS was not significantly higher among juveniles (Sp = 0.0041) than adults (Sp = 0.0026). Realized pollen and seed immigration into the plot was low (pollen = 6 %; seeds = 5 %) and the patterns of pollen and seed dispersal were similar. Pollen was dispersed over long distances (343 m), but 50 % was dispersed up to 124 m. Seeds also reached long distances (318 m), with 50 % being dispersed up to 133 m. Our results are discussed in terms of auto-ecology and the genetic conservation of A. angustifolia populations.     

Initial growth of Brazilian pine (Araucaria angustifolia) under equal soil volumes but contrasting rooting depths

Araucaria angustifolia is a critically endangered tall tree species of valuable wood, and field observations led to the suggestion that limitations imposed to the vertical growth of its tap root system greatly restrict the height of mature individuals. However, experimental studies dealing with the effects of soil depth on the species growth are mostly lacking. This study evaluated and compared the growth responses of young plants of A. angustifolia to distinct rooting depths but same soil volumes. Seeds were planted in pots of different heights and diameters, all containing 3 liters of soil mixture. Plants were submitted to four available rooting depths: 65 (T1), 35 (T2), 20 (T3), and 10 (T4) cm. There were eight experimental units in each treatment, arranged in a randomized complete block design, each block containing two units per treatment. Contrary to what was expected, the T3 and T4 plants had accumulated more mass and attained the same height as the other two groups, after a 10-month growth period in a green house. Those plants also had thicker stems, longer shoot branches, and thicker and longer lateral roots, which were interpreted as compensatory responses to increase plant anchorage and stability. The inverse relationship between rooting depth and plant mass was attributed to a down-regulation of shoot growth because or restricted lateral space and/or poor soil aeration of the longer and narrower pots. This experiment allowed us to demonstrate that is not the possibility of the tap root to grow deep into the soil that ensures a better growth to plants of A. angustifolia: provided that the offer of soil volume and resources are the same, the vertical extension of the tap root does not result in greater growth of the plants. In fact, much greater growth impairment is expected from lateral than from vertical restriction to root growth.     

Past century changes in Araucaria angustifolia (Bertol.) Kuntze water use efficiency and growth in forest and grassland ecosystems of southern Brazil: implications for forest expansion

Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer tree restricted to the southern region of South America that plays a key role in the dynamics of regional ecosystems where forest expansion over grasslands has been observed. Here, we evaluate the changes in intrinsic water use efficiency (iWUE) and basal area increment (BAI) of this species in response to atmospheric CO₂, temperature and precipitation over the last century. Our investigation is based on tree-rings taken from trees located in forest and grassland sites in southern Brazil. Differences in carbon isotopic composition ( δ ¹³C), ¹³CO₂ discrimination (Δ¹³C) and intracellular carbon concentration ( C _i ) are also reported. Our results indicate an age effect on Δ¹³C in forest trees during the first decades of growth. This age effect is not linked to an initial BAI suppression, suggesting the previous existence of nonforested vegetation in the forest sites. After maturity all trees show similar temporal trends in carbon isotope-derived variables and increasing iWUE, however, absolute values are significantly different between forest and grassland sites. The iWUE is higher in forest trees, indicating greater water competition or nutritional availability, relative to grassland, or both. BAI is also higher in forest trees, but it is not linked with iWUE or atmospheric CO₂. Nevertheless, in both forest and grassland sites A. angustifolia has had growth limitations corresponding to low precipitation and high temperatures observed in the 1940s.     

Cloning and expression of embryogenesis-regulating genes in Araucaria angustifolia (Bert.) O. Kuntze (Brazilian Pine)

Angiosperm and gymnosperm plants evolved from a common ancestor about 300 million years ago. Apart from morphological and structural differences in embryogenesis and seed origin, a set of embryogenesis-regulating genes and the molecular mechanisms involved in embryo development seem to have been conserved alike in both taxa. Few studies have covered molecular aspects of embryogenesis in the Brazilian pine, the only economically important native conifer in Brazil. Thus eight embryogenesis-regulating genes, viz., ARGONAUTE 1, CUP-SHAPED COTYLEDON 1, WUSCHEL-related WOX, S-LOCUS LECTIN PROTEIN KINASE, SCARECROW-like, VICILIN 7S, LEAFY COTYLEDON 1, and REVERSIBLE GLYCOSYLATED POLYPEPTIDE 1, were analyzed through semi-quantitative RT-PCR during embryo development and germination. All the eight were found to be differentially expressed in the various developmental stages of zygotic embryos, seeds and seedling tissues. To our knowledge, this is the first report on embryogenesis-regulating gene expression in members of the Araucariaceae family, as well as in plants with recalcitrant seeds.     

土壤干旱对沙棘苗木生长及水分利用的影响

研究了土壤干旱条件下盆栽沙棘苗木生长、光合和水分关系的变化。结果表明,同样环境条件下,蒸腾速率随干旱胁迫程度加重而降低,而蒸腾日进程差异不大,均为单峰曲线,峰值出现在11：00;轻、中度干旱胁迫下沙棘叶含水量、水势、渗透势、膨压下降幅度较小,光合速率、侧枝生长速率保持在较高水平,能维持基本的生长量,表现出耐旱植物的生理特征;重度干旱胁迫使上述指标下降较显著,且长时间胁迫后,33．3％沙棘幼苗死亡。     

Root and Crown Rot of Brazilian Pine (Araucaria angustifolia) Caused by Phytophthora cinnamomi

In an area reforested with Brazilian pine (Araucaria angustifolia) located in Paraná State, southern Brazil, 20‐ to 40‐year‐old trees representing 0.2% of the surveyed area had symptoms of root and crown rot, yellowing and browning of leaves from the uppermost branches and death. Three Phytophthora isolates obtained from diseased plant tissue were tested against 1‐year‐old Brazilian pine seedlings and found to display positive pathogenicity. Based on their morphological and physiological characteristics, the isolates were identified as Phytophthora cinnamomi. A GenBank BLAST search of partial sequences from the β‐tubulin and elongation factor‐1α genes, as well as the ITS regions and 5.8S gene of rDNA, confirmed the species identification. This is the first report of the involvement of this pathogen on the aetiology of Brazilian pine root and crown rot.     

Soybean leaf growth and gas exchange response to drought under carbon dioxide enrichment

This study was conducted to determine the response in leaf growth and gas exchange of soybean (Glycine max Merr.) to the combined effects of water deficits and carbon dioxide (CO₂) enrichment. Plants grown in pots were allowed to develop initially in a glasshouse under ambient CO₂ and well-watered conditions. Four-week old plants were transferred into two different glasshouses with either ambient (360 μmol mol^-1) or elevated (700 μmol mol^-1) CO₂. Following a 2-day acclimation period, the soil of the drought-stressed pots was allowed to dry slowly over a 2-week period. The stressed pots were watered daily so that the soil dried at an equivalent rate under the two CO₂ levels. Elevated [CO₂] decreased water loss rate and increased leaf area development and photosynthetic rate under both well-watered and drought-stressed conditions. There was, however, no significant effect of [CO₂] in the response relative to soil water content of normalized leaf gas exchange and leaf area. The drought response based on soil water content for transpiration, leaf area, and photosynthesis provide an effective method for describing the responses of soybean physiological processes to the available soil water, independent of [CO₂].     

Simulation model of soil compaction and root growth

Soil compaction is a widespread cause of reduced plant productivity. If the effects of soil compaction on plant growth are to be reproduced in simulation models, then the processes through which compaction reduces root elongation must be expressed mathematically and then tested against experimental data. The mathematical theory by which these processes may be represented is given in the accompanying article. In this article, the behavior of a simulation model based on this theory is tested against data for root growth and soil gas concentration recorded from soil columns of which the middle layers were compacted to different bulk densities. The model was able to reproduce the failure of the root system to penetrate the compacted middle layer within the period of the experiment when bulk density exceeded 1.55 Mg m^-3. The model also reproduced decreases in O₂ concentrations, and increases in CO₂ concentrations, in the atmospheres of the compacted layer and of the uncompacted layer below it as bulk density of the compacted layer increased. The simulated time course of O₂ and nutrient uptake and of O₂ concentrations in the compacted layer at different depths is presented and its consistency with experimental findings is examined. As part of a larger ecosystem model, this model will be useful in estimating site-specific effects of soil compaction on carbon cycling in agroecosystems.     

异株荨麻（Urtica dioica）生长及光合特性对不同土壤水分含量的响应

异株荨麻是我国一种重要中药植物,如何对其进行人工定向培植具有重要意义。以异株荨麻扦插苗为实验材料,采用盆栽水分梯度法,按土壤相对含水量93．58％、80．74％、67．90％、55．06％和42．22％分为对照组CK,实验处理组T1,T2,T3和T4五个处理组,通过观测不同水分条件下,异株荨麻生长量、生物量变化和光合特征变化,试图探讨异株荨麻的水分适应性,寻找出适合其生长的水分范围及对生物量分配的影响,为北方地区种植栽培此类植物提供科学依据。结果发现：随土壤水分含量的降低,异株荨麻生长量和生物量积累呈先上升后下降趋势,在土壤相对含水量80．74％生长达到高峰,土壤相对含水量67．90％～80．74％为异株荨麻生长的适宜范围。净光合速率、蒸腾速率、气孔导度、气孔限制值及叶绿体色素含量的变化趋势与之相近似。在上述水分范围以外其光合功能下降、同化作用减弱,使异株荨麻生长衰退和干物质积累的减少。此外,土壤水分直接调控光合产物在地上和地下的分配以及植株个体形状,生产实践中,通过控水可以达到控制株形和根冠比的作用,用以诱导植株朝种植的预期方向生长,以达到获取植株不同部位产量的实际应用需求。     

Stable isotope analysis of water extraction from subsoil in upland rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) as affected by drought and soil compaction

Water extraction from subsoil in upland rice (Oryza sativa L.) was examined as related to topsoil desiccation and subsoil compaction. The water extraction was observed by measurements of heavy water concentrations in transpiring plants. The plants were grown in pots that were filled with sandy soil and vertically compartmented into two columns. Heavy water was applied to the subsoil. Plants exposed to mild topsoil desiccation (–120 kPa in water potential) eventually increased water extraction from the subsoil and maintained photosynthetic rate and stomatal conductance at the wet condition level. The rates of the plants subjected to severely droughted topsoil (–190 kPa) were significantly lowered due to less water uptake from the subsoil. Subsoil compaction at bulk densities of 1.45 and 1.50 Mg m^–3 inhibited increase of root length densities. Limited water extraction from the subsoil was insufficient to maintain plant productivity under drought conditions. Daily water uptake per unit of root length in the lower tube did not apparently increase even if water demand on the unit root length increased. When water to topsoil was completely withheld, water extraction from the subsoil gradually increased as the topsoil dried out. Plants that were watered and rewatered took up very little water from the subsoil. The extraction from the subsoil occurred only when water potential of the topsoil was below about –190 kPa.     

干旱条件下AM真菌对植物生长和土壤水稳定性团聚体的影响

采用分室培养系统,模拟正常水分和干旱胁迫两种环境条件,探讨不同丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)对紫花苜蓿(Medicago sativa L.)生长和土壤水稳性团聚体的影响.试验条件下,Glomus intraradices对苜蓿根系的侵染率均显著高于Acaulospora scrobiculata和Diversispora spurcum接种处理.正常水分条件下,供试AM真菌均能显著提高植株生物量及磷浓度.干旱胁迫显著抑制了植株生长和菌根共生体发育,总体上菌根共生体对植株生长没有明显影响,接种D.spurcum甚至趋于降低植株生物量;同时,仅有G.intraradices显著提高了植株磷浓度.AM真菌主要影响到＞2mm的水稳性团聚体数量,以G.intraradices作用效果最为显著.在菌丝室中,G.intraradices显著提高了总球囊霉素含量.研究表明AM真菌对土壤大团聚体形成具有积极作用,而菌根效应因土壤水分条件和不同菌种而异,干旱胁迫下仅有G.intraradices对土壤结构和植物生长表现出显著积极作用.在应用菌根技术治理退化土壤时,需要选用抗逆性强共生效率高的菌株,对于不同AM真菌抗逆性差异的生物学与遗传学基础尚需进一步研究.     

Growth features of Acacia tortilis and Acacia xanthophloea seedlings and their response to cyclic soil drought stress

Seedlings of Acacia tortilis (Forsk) Hyne and Acacia xanthophloea Benth. were raised under controlled glasshouse conditions. Control plants were watered daily while other treatments involved withholding water for 2, 4 and 6 days with 1‐day rehydration to container capacity. Compared to A. tortilis, A. xanthophloea seedlings showed higher leaf area, relative growth rates and total dry weight production under adequate water supply conditions. However, with increased water stress, A. xanthophloea seedlings could not alter their pattern of carbon allocation, retaining their root : shoot (r : s) ratio of about 0.5. By comparison, A. tortilis seedlings shifted carbon allocation to the roots, leading to a r : s ratio of 1.5 in water‐stressed seedlings, compared to 0.5 in the control plants. The ability of A. tortilis to reallocate carbon to the roots away from the shoots and to actually increase root growth compared to A. xanthophloea was a dehydration postponement strategy that may be important in species survival during drought.     

Commercially available plant growth regulators and promoters modify bulk tissue abscisic acid concentrations in spring barley, but not root growth and yield response to drought

Field and lysimeter experiments were conducted in 2002 to investigate the effects of an antigibberellin growth regulator (Moddus, active ingredient trinexapac‐ethyl, Syngenta Crop Protection UK Ltd, Whittlesford, Cambridge, UK) and an auxin‐stimulating (Route, active ingredient zinc ammonium acetate, De Sangosse Ltd, Swaffham Bulbeck, Cambridge, UK) growth promoter on root growth, soil water extraction and the drought response of spring barley. The effects on root growth and distribution were investigated in the field. The effects on the drought response were studied in 1.2‐m‐deep lysimeters packed with a loamy sand subsoil and sandy loam topsoil. Lysimeters were located under a fixed rain shelter, and drought was imposed by withholding irrigation. In both field and lysimeter experiments, growth regulator/promoters were applied to cv. Optic at early tillering according to the manufacturers’ recommendations. After withholding irrigation from lysimeters at Zadoks growth stage (GS) 21 (37 days after sowing), 50% of the profile available water had been depleted by flag leaf emergence (GS 37/39; 62 days after sowing). Drought significantly reduced stem biomass at ear emergence (GS 59; 78 days after sowing) but not leaf or ear dry weight; this was before there was any significant reduction in leaf water potential or stomatal conductance to water vapour. The reduction in stem biomass may reflect a change in partitioning between shoot and root in response to soil drying. When averaged over growth regulator/promoter treatments, drought reduced grain yield by approximately 1 t ha^?1. This was associated with a reduction in both ears per m² and grains per ear. The mean grain weight was not reduced by drought, in spite of significant reductions in stomatal conductance and canopy lifespan post‐anthesis. Route, and to a lesser extent Moddus, significantly increased abscisic acid accumulation in the stem base of droughted plants, and there was some indication of a possible delay in stomatal closure in Route‐treated plants as the soil moisture deficit developed. However, there was no significant effect on the amount of soil water extracted or grain yield under drought. Similarly, in field experiments, neither Route nor Moddus significantly altered total root length, biomass or distribution. There is little evidence from these experiments or in the literature to support the use of antigibberellin or auxin‐simulating growth regulator/promoters to modify root growth and drought avoidance of spring barley.     

The transition of proembryogenic masses to somatic embryos in Araucaria angustifolia (Bertol.) Kuntze is related to the endogenous contents of IAA,ABA and polyamines

In somatic embryogenesis (SE) of conifers, the inability of many embryogenic cell lines to form well-developed somatic embryos may results from failure and constraints during the transition of proembryogenic masses (PEMs) to early somatic embryos. In the present work, we propose the inclusion of a preculture and prematuration steps looking at enhancing PEM III-to-early somatic embryos transition. It was further hypothesized that these results would correlate with the contents of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and polyamines (PA). To test these hypotheses, the embryogenic culture was subjected to preculture with fluridone (FLD) and prematuration treatments with different combinations of carbon source and polyethylene glycol (PEG). The frequency of PEM III was increased after FLD preculture and the contents of IAA and ABA decreased, while the contents of PA increased. Putrescine (Put) was the most abundant PA present at this stage, followed by spermidine (Spd) and spermine (Spm). In early embryogenesis, prematuration treatments supplemented with maltose or lactose plus PEG enhanced the PEM III-to-early somatic embryos transition. IAA and ABA contents increased at this stage, while a decrease of the total free PA levels was observed. Put was the most abundant PA, followed by Spd and Spm, mainly in the treatment supplemented with PEG. This resulted in a decrease of PA ratio (Put/Spd + Spm) and, hence, PEM III-to-early somatic embryos transition. It was concluded that the preculture with FLD and prematuration treatments promote the PEM III-to-early somatic embryos transition throughout the whole early developmental process in Araucaria angustifolia.     

黄土丘陵半干旱区柠条林密度对土壤水分和柠条生长的影响

研究密度对土壤水分和植物生长的影响对森林植被恢复和生态建设具有重要的意义。以黄土丘陵半干旱区人工柠条为研究对象,对相同立地条件下不同密度柠条林生长与林地土壤水分进行了长期定位观测和分析。研究表明,1—5年生柠条不同密度林地土壤水资源量差异显著,从第3年开始,土壤水资源量随着密度增加而增加;10—12年生柠条密度越低土壤水资源量越高(Treatment4除外,T4),不同密度之间水资源量差异不显著。1—3年生柠条密度越高会促进其株高生长;从第四年开始,柠条密度过高会抑制其株高生长;1—5年生柠条密度越高基径生长越快,不同密度生长差异不显著;10—12年生密度过高(Treatment1,T1)或过低(T4)均会抑制柠条株高与基径生长。在柠条播种后第5年,高密度试验小区(T1和Treatment2,T2)柠条林地最大入渗深度土壤水资源量降到水资源利用限度,此时需要依据土壤水分植被承载力通过平茬来降低林分密度,以达到减少土壤水分消耗和可持续利用土壤水资源之目的。     

Nutrient uptake and growth of barley as affected by soil compaction

A field experiment with different levels of compaction was carried out on a mouldboard ploughed silty clay, with the objective of studying the effects on plant nutrient uptake and growth. Soil from the field was also used in laboratory studies of carbon and nitrogen mineralization, and plant uptake of water and nutrients. In the field, low as well as high bulk densities reduced biomass production and nutrient uptake of barley (Hordeum vulgare L.) compared to intermediate bulk densities, where grain yield was approximately 20% higher. In the beginning of the growing season, the concentration of phosphorus and potassium was lowest in plants grown in the loosest and in the most compacted soil, and suboptimal for plant growth. The uptake of nutrients transported by diffusion was more affected by compaction than for nutrients transported by mass flow. The reasons for lowered uptake in loose compared to moderately compacted soil could be reduced root-to-soil contact, a low diffusion coefficient for nutrients and/or reduced mass transport of water to seed and roots. Differences in plant nutrient concentrations between treatments gradually declined until harvest. Immediately after compaction there was probably oxygen deficiency in the compacted soil since the air-filled porosity was critically low, but as the soil dried out, mechanical resistance to root growth may have become a more important growth-limiting factor. In the laboratory study, severe compaction reduced carbon mineralization and uptake of water and nutrients by roots, and caused denitrification. There were only small differences between loose and moderately compacted soil in carbon mineralization, nitrogen concentration in the soil, uptake of water and nutrients and dry matter yield. The large yield increase due to recompaction in the field was not reproduced in the laboratory. Possible reasons are differences in soil temperature between the field and laboratory, in the sowing and fertilizing methods, the pretreatment of the soil and in the spatial variability of bulk density. It is possible that recompaction is needed only in the uppermost part of the soil, which is the loosest, dries out first, and is where the seed as well as the fertilizer are placed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tolerance of soil algae and cyanobacteria to drought stress

Tolerance to drought stress in soil crust microorganisms is essential for exploiting suitable organisms for restoring soil. In this study, the responses to drought stress of two drought‐tolerant species, a green alga and a cyanobacterium, were compared with those of two non‐tolerant green algae. In response to drought stress, induced by treatment with polyethylene glycol, the intracellular proline levels increased and were associated with increases in malondialdehye, pigment contents, and enzyme activities such as superoxide dismutase (SOD) and peroxidase (POD). Our results suggest that tolerance to drought stress could be indicated by the intracellular levels of proline, SOD, and carotenoids. This study provides insights into the drought physiology of the photosynthetic microorganisms and suggests that Leptolyngbya boryana and Chlorella vulgaris are suitable pioneer organisms for soil restoration.     

Changes in IAA, tryptophan and activity of soluble peroxidase associated with zygotic embryogenesis in Araucaria angustifolia (Brazilian pine)

In A. angustifolia seeds the highest values of freeIAA occurred in the embryonic axis, at the initial phases of development. Thesevalues decreased sharply coincident with the increase of IAA with thedifferentiation of cotyledons and seed elongation. During seed development,tryptophan concentrations varied inversely with free IAA and directly withconjugated IAA. An increase in peroxidase activity was followed by a decreaseinfree IAA in the embryo axis, and in conjugated IAA in the megagametophyte.Megagametophyte tissues did not exhibit significant variation in free IAAduringseed development. Following the stage where cotyledons arise, tryptophandecreased in the megagametophyte and increased in the cotyledons and embryonicaxis.     

AaMps1 protein inhibition regulates the protein profile,nitric oxide,carbohydrate and polyamine contents in embryogenic suspension cultures of Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae)

Plant Cell, Tissue and Organ Culture (PCTOC) - The Monopolar Spindle 1 (Mps1) protein is a dual-specificity kinase that plays a critical role in the progression of the cell cycle. Studies on...