Interactions between plants: the role of mycorrhizae

Summary We present and discuss evidence, mostly from our own research, on some possible roles of mycorrhizae in interactions between plants. Experiments investigating whether seedlings become more rapidly infected with mycorrhiza if they are near large, already infected plants have shown that contact between the seedling's roots and established mycelium sometimes speeds up infection but on other occasions it does not. The reason for the discrepancies is not clear. Mycorrhiza can substantially alter the balance between competing plant species in a way that would not be predicted from their response when growing separately. An experiment involving large and small plants of the same species growing together showed little effect of mycorrhiza on the balance between plants of different sizes. The rate of transfer of ³²P between plants of Lolium perenne or Plantago lanceolata was so slow, even when they were mycorrhizal, that phosphorus transfer between living plants seems unlikely to be of major ecological importance. However, nitrogen was found to be transferred much more freely than phosphorus between P. lanceolata plants. Situations are discussed in which there could be a source-sink relationship between plants causing net flow of carbon or mineral nutrients from one to the other. If nutrients pass from dying roots to living plants via mycorrhizal links, this could result in preferential nutrient cycling between species that share the same type of mycorrhiza. Some evidence is presented that this does happen.     

基于DRIS法的短枝木麻黄苗期综合营养诊断

以我国东南沿海沙地主要造林树种短枝木麻黄（Casuarina equisetifolia）一年生苗木为研究对象,应用氮（N）、磷（P）、钾（K）三元二次旋转回归法,根据现实生物量的差异,划分为2种不同的产量类型,同时结合室内养分含量分析,以高产量类型为最适值,制定了诊断施肥综合法（Diagnosis and Recommendation Integrate Sys-tem,简称DRIS）及指数法的营养诊断标准,研究氮、磷、钾不同施肥配比条件下苗木体内氮、磷、钾的养分含量及其需求程度,对短枝木麻黄进行苗期综合营养诊断分析。结果表明：施肥配比对短枝木麻黄苗木生物量积累规律有较大影响,苗木生物量最优解为19.84 g/株,对应的最佳施肥方案为氮、磷、钾分别施肥0.329 g/株、2.298 g/株、0.154 g/株。短枝木麻黄苗期小枝3种元素浓度的最佳比值范围为P/N=0.3174±0.1302;K/N=1.1010±0.506;K/P=3.5564±0.5075,以生长末期12月份各处理苗木为例,列出各元素的DRIS诊断指数及相对需肥次序,证实了营养诊断的准确性。     

Ecological implications of seed characteristics of the native Prosopis cineraria and the alien P. juliflora

Seed weight, percentage germination, seedling growth, and nutrient concentrations (Mg, Na, K, Zn, Cu and P) of whole seeds, and of seed coats and embryos separately of two tree species, the native Prosopis cineraria and the invasive alien P. juliflora from semi-arid and arid areas of north and north-west India, were analysed to understand the differences in their ecology. Seeds of P. cineraria were heavier than those of P. juliflora. Percent germination was similar in the two species, but seedling growth was faster in P. juliflora than in P. cineraria. Nutrient concentrations of seeds of the two species were similar (except Cu). Nutrient concentrations in the embryo were higher in P. cineraria, while those in the seed coat were higher in P. juliflora. The relative allocation of nutrients to seed coat was higher in P. juliflora than in P. cineraria. Nutrient-rich embryos and slow growth, along with a staggered seed germination pattern in the native P. cineraria could be linked to delayed establishment as well, in the substratum. Faster growth of the nutrient-poor embryos in P. juliflora along with its simultaneous seed germination pattern, and creation of a favourable microenvironment through leaching of nutrients from a nutrient-rich seed coat can facilitate immediate and successful establishment of this alien species in the invaded habitats.     

Comparative phenology and growth in different species of the Mediterranean maquis of central Italy

A phenomorphological survey was carried out in central Italy to study the effects of increasing water stress on some characteristic species of the Mediterranean maquis. Nutrient content and leaf water potential were examined. The results show that three different groups exist which diverge in the modulation of growth activity. 1) Evergreen sclerophyllous species (e.g. Pistacia lentiscus, Phillyrea media, Arbutus unedo, Ruscus aculeatus), which were supposed to be drought-tolerant, in fact limited their growth activity to a brief period before aridity increased. A similar growth pattern was exhibited by those species (e.g. Quercus ilex, Erica arborea, Smilax aspera) that stopped producing new leaves and branches during the driest season and that recovered after the first rain; i.e., their growth period lasted longer. 2) Drought-deciduous species (e.g. Calicotome villosa) that adopted the drought-avoidance strategy had two vegetative periods interrupted by a phase during which they completely shed their leaves. 3) Semideciduous species (Cistus monspeliensis) with mesophitic leaves adopted an intermediate response. These grew even in the dry and cold season.     

Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure

Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem.     

Nitrogen mineralisation in soils of varying texture,moisture and organic matter

Summary Estimates of nitrogen availability based on the nitrogen mineralisation potential,N₀, and the mineralisation rate constant,k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July.There was a significant relationship between values calculated fromN₀ andk and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising.The time required for mineralisation of 50% ofN₀ indicated that less than half the potential value would become available in a normal temperature growing season.     

Seed germination and seedling performance of two Mediterranean tree species,holm oak (shape Quercus ilex L.) and Aleppo pine (shape Pinus halepensis Mill.): a multifactor experimental approach

A two-level multifactor experimental approach was used to compare seed germination and seedling performance of two Mediterranean tree species: the early successional Aleppo pine (Pinus halepensis Mill.) and the late successional holm oak (Quercus ilex L.). In a first experiment germination rate was evaluated under the combined effects of shade, nitrogen availability, and pine or holm oak leaf litter. In a second experiment we tested for the effects of shade, nutrient availability, and litter type on seedling survival, growth and biomass allocation. Holm oak showed higher germination rates under shaded than under unshaded conditions, while Aleppo pine showed no differences between shaded and unshaded conditions. Nitrogen availability and litter type had no significant effect on germination of either species. Both species showed increased RGR, but also higher mortality rates, when grown in an enriched nutrient environment. While Aleppo pine showed no differences in RGR and mortality rate under different shading levels, RGR decreased and mortality increased for holm oak in full light. Increased radiation decreased LAR, SLA and height:diameter ratio, and increased RWR and R/S in both species, although Aleppo pine showed more pronounced changes. Unlike Aleppo pine, holm oak responded to increased nutrient availability by decreasing R/S and increasing LAR. From these results, no seed-seedling conflicts were found in either species, but a trade-off does seem to exist for holm oak between biomass allocation traits deployed in response to increased nutrient availability and radiation. Aleppo pine outperformed holm oak under most environmental conditions tested and showed a wider regeneration niche.     

Nutrient deprivation improves field performance of woody seedlings in a degraded semi-arid shrubland

The performance of planted seedlings in drylands is affected by seedling morphological and physiological traits. Recent studies support a positive relationship between seedling size and field performance. However, exceptions to this paradigm suggest that this relationship may be dependent on species and degree of stress. To test the hypothesis that small seedlings would be favored under harsh semi-arid conditions over large seedlings, we produced seedlings of five Mediterranean woody species (Pistacia lentiscus, Quercus coccifera, Rhamnus lycioides, Rhamnus alaternus and Tetraclinis articulata) under contrasted fertilization regimes, and evaluated their performance after planting in a semi-arid area. Seedlings were cultivated under full sunlight and received either slow release fertilizer or bi-weekly applications of complete nutrient solution, diluted fertirrigation, or nutrient solutions containing no nitrogen or no phosphorus. Fertilization had a strong effect on nutrient status, above and belowground biomass accumulation, and biomass allocation patterns. Root: shoot ratio was higher in nitrogen- and phosphorus-deficient seedlings than in seedlings receiving complete nutrient solution or slow-release fertilizer. One year after planting, seedling survival was negatively correlated with plant size for all species. The effect of nutritional regime on field survival decreased over the 2 following years. Our results show that nutrient-deprived seedlings are more likely to establish under semi-arid conditions than well-fertilized seedlings, suggesting that morphological and functional characteristics associated with nutrient deficiency may outbalance the scarcity of nutrient reserves in seedling tissues.     

大棚繁育克氏原螯虾种苗对养殖水体营养盐的影响

为探讨利用温室大棚进行克氏原螯虾(Procambarus clarkia)种苗繁育对养殖水体的水质影响, 文章通过对繁育期间的水样和表层底泥营养盐的定期监测, 研究了整个育苗期间水质和表层底泥中营养盐的变化动态。结果表明, 水体DO、WT变幅为5.75—6.33 mg/L、12.6℃—22.9℃, 水温要高于同期外部水温5—10℃; 受饲料投喂和虾活动等影响, 上覆水中TN、TP和COD含量快速增加, 在养殖期间的变幅分别为2.091—2.688、0.196—0.480和42.400—53.200 mg/L; 表层底泥的TN、TP和有机质含量变幅分别为1032—1279、623—1004 和12.00—14.28 mg/kg, 其增幅分别为24%、23%和41%。受水体浊度较高、水体中亲本虾数量不明等影响, 无法判定投入的饲料是否全部为虾子摄食, 造成了短期内较高的饲料投入量带来养殖水体营养盐的急剧增加, 较高的营养盐含量为后期养殖尾水的治理带来新的要求。     

Frequency of MEFV gene mutations in Hatay province,Mediterranean region of Turkey and report of a novel missense mutation (I247V)

In the present study, 1000 patients with clinical suspicion of FMF were retrospectively reviewed to determine the spectrum of MEFV gene mutations by using DNA sequence analysis between September, 2008 and April, 2012. Sixteen different mutations and 55 different genotypes were detected in 618 of 1000 patients. Among 16 different mutations, R202Q (21.35%) was the most frequently observed mutation; followed by E148Q (8.85%), M694V (7.95%), M680I (2.40%), V726A (1.85%), M694I (0.95%), A744S (0.80%), R761H (0.55%), P283L (0.35%), K695R (0.20%), E230K (0.15%), L110P (0.10%), I247V (0.05%), G196W (0.05%) and G304R (0.05%). In the present study, a novel missense mutation (I247V) and a silent variant (G150G) were identified in the MEFV gene. On the other hand, P238L, G632A and G304R mutations are the first cases reported from Turkey. Our results indicated that MEFV mutations are highly heterogeneous in our study population as in other regions of Turkey and mutation screening techniques such as PCR-RFLP, amplification refractory mutation system or reverse hybridization do not adequately detect uncommon or novel mutations. Therefore, it was proven that sequence analysis of the MEFV gene could be useful for detection of rare or unknown mutations.     

Factors affecting radial growth of Quercus ilex L. in a coppice stand in southern France

Quercus ilex woodlands in the south of France are characterized by low productivity. Several hypotheses have been put forward to provide an explanation for this phenomenon: (i) senescence of coppice stumps; (ii) limited availability of water and nutrient resources; (iii) intershoot and inter-plant competition. To test some of these hypotheses, growth response to rainfall distribution and nutrient supply (NPK), and the influence of edge effects after clear-cutting were studied in a 40-yr old stand.Curves of radial increment were compared with precipitation and umbrothermic patterns for the 6 years studied. Water availability apparently accounted for some inter-annual differences in growth. However, it was not mean annual rainfall, but rather rainfall occurring in late spring-summer (June, July) which played a large role in determining radial growth. Radial growth was also increased by nutrient supply. Its positive effect was strengthened by favourable rainfall in 1987. Edge-effects following a clear-cut were also found, both in the first year and in four succeeding years following the cut. This comprised in greater radial growth rate for all shoots, with reduced repression of smaller shoots by the larger ones. The effect decreased over a distance of 10 m with increasing distance from the cut field. This could be explained by increased availability of water, nutrient resources, and light.     

基于LF-NMR探究板栗失水过程中质构和色差变化

板栗（Castanea mollissima Blu.）果实中的水分组成在其生理代谢及品质变化过程中具有重要作用。本研究以贵州黔西南望谟县板栗为实验材料,利用低场核磁共振技术,对不同水分含量（48%、38%、28%、18%）的板栗果中氢核的横向弛豫衰减信号进行测试,并利用 SIRT 模型对数据进行反演,得出横向弛豫时间T₂ 的反演数据。采用自旋回波脉冲序列对板栗果的质子密度加权成像;使用物性测试仪分析质构特性,利用色差仪分析板栗失水过程中果肉颜色的变化。结果显示,自然失水改变了板栗果中水分的结合状态,水分发生明显迁移,自由水和不易流动水的信号幅值随失水程度的加剧而逐渐减弱。不同含水率板栗的反演峰总面积不同,随着含水率的增加,核磁共振信号增强,峰面积增大,两者具有显著的相关性。核磁共振成像技术通过图片明暗不同,可直观反映不同阶段的水分含量。板栗果实自然贮藏过程中发生石灰化,果实质地发生硬化,挤压咀嚼时抵抗力增大,失水初期内聚性和弹性变化不显著,后期下降;粘附性前期降低,但后期变化不明显;板栗失水初期果肉发生氧化,颜色逐渐呈暗红色,失水后期石灰化较为严重,果肉颜色变白,亮度增加。本研究结果可为板栗加工过程中的水分迁移机制探讨以及产品的品质控制提供参考。     

Germination and emergence of annual species and burial depth: Implications for restoration ecology

Due to the high content of viable seeds, topsoil is usually spread on ground left bare during railway and motorway construction to facilitate the regeneration of vegetation cover. However, during handling of the topsoil, seeds are often buried deeply and they cannot germinate or the seedlings cannot emerge from depth. This study experimentally explores the predictive value of seed mass for seed germination, mortality and seedling emergence at different burial depths for 13 common annual species in semiarid Mediterranean environments. We separate the effect of burial depth on germination and emergence by means of two experiments. In the germination experiment, five replicates of 20 seeds for each species were buried at depths ranging from 0 to 4 cm under greenhouse conditions. Germinated and empty or rotten seeds were counted after 8 weeks. In the emergence experiment, five replicates of four newly-germinated seeds per species were buried at the same depths under controlled conditions and emergence was recorded after 3 weeks. The effect of burial depth on percentage of germination and seedling emergence was dependent on seed size. Although all species showed a decrease in germination with burial depth, this decrease was greater for small-than large-seeded species. Percentage of emergence was positively related to seed mass but negatively related to burial depth. Seed mortality was higher for small-than large-seeded species, but there was no general effect of burial depth on this variable. Thus, the current practice of spreading 30 cm deep layers of topsoil in post-construction restoration projects is unadvisable. In this restoration scenario, thinner layers of topsoil should be used to achieve the maximum potential of the topsoil for germination and seedling establishment.     

Effects of microsite disturbances and herbivory on seedling performance in the perennial herb <Emphasis Type="Italic">Helleborus foetidus</Emphasis> (Ranunculaceae)

The impact of small scale disturbances on the early seedling performance components of Helleborus foetidus (Ranunculaceae) was studied through a transplant experiment. The aims of this study were: (i) to determine if the herbivory pattern depends on microsite disturbance, by the analysis of two of its components, seedling encounter (the probability of at least one seedling being harmed) and seedling exploitation (the proportion of seedling tissue removed once encountered); (ii) to test if seedlings of H. foetidus in disturbed microsites will survive in a greater proportion than seedlings in undisturbed microsites; (iii) to investigate if seedling survival is correlated with the degree of herbivory. Microsite disturbances had a large effect on the herbivory pattern. Seedlings growing in undisturbed vegetation had a 2-fold higher likelihood of being grazed and suffered 1.38-fold higher damage than those growing in disturbed plots. At the end of this experiment, after fourteen months, only 10.4% of the seedlings transplanted were still alive due to seedling desiccation, but no differences on seedling survival were found between disturbed and undisturbed plots. The effect of herbivory and the interactive effect of herbivory and disturbance on seedling survival only reached statistical significance dependent upon site. We concluded that although small scale disturbances had a large impact on herbivory patterns; they had only a minor role in the early seedling survival of H. foetidus. Only locally, small scale disturbances showed an effect on seedling survival through herbivory. Abiotic factors like summer drought and spatial variations determined the early survival of H. foetidus seedlings to a major extent.