Woody plant richness and NDVI response to drought events in Catalonian (northeastern Spain) forests

The role of species diversity on ecosystem resistance in the face of strong environmental fluctuations has been addressed from both theoretical and experimental viewpoints to reveal a variety of positive and negative relationships. Here we explore empirically the relationship between the richness of forest woody species and canopy resistance to extreme drought episodes. We compare richness data from an extensive forest inventory to a temporal series of satellite imagery that estimated drought impact on forest canopy as NDVI (normalized difference vegetation index) anomalies of the dry summer in 2003 in relation to records of previous years. We considered five different types of forests that are representative of the main climatic and altitudinal gradients of the region, ranging from lowland Mediterranean to mountain boreal-temperate climates. The observed relationship differed among forest types and interacted with the climate, summarised by the Thorntwaite index. In Mediterranean Pinus halepensis forests, NDVI decreased during the drought. This decrease was stronger in forests with lower richness. In Mediterranean evergreen forests of Quercus ilex, drought did not result in an overall NDVI loss, but lower NDVI values were observed in drier localities with lower richness, and in more moist localities with higher number of species. In mountain Pinus sylvestris forests NDVI decreased, mostly due to the drought impact on drier localities, while no relation to species richness was observed. In moist Fagus sylvatica forests, NDVI only decreased in plots with high richness. No effect of drought was observed in the high mountain Pinus uncinata forests. Our results show that a shift on the diversity-stability relationship appears across the regional, climatic gradient. A positive relationship appears in drier localities, supporting a null model where the probability of finding a species able to cope with drier conditions increases with the number of species. However, in more moist localities we hypothesize that the proportion of drought-sensitive species would increase in richer localities, due to a higher likelihood of co-occurrence of species that share moist climatic requirements. The study points to the convenience of considering the causes of disturbance in relation to current environmental gradients and historical environmental constraints on the community.     

吉林西部退化草地修复方案的仿真优化

退化草地的恢复已成为吉林西部农牧业发展的重要任务.为使吉林省西部草地步人可持续发展的良性轨道,如何对退化草地进行恢复就成为研究工作面临的主要问题.首先,运用用RS和GIS技术,建立1989和2004年吉林西部土地利用/土地覆盖空间数据库,研究15年来的吉林西部草地退化情况,草地从1989年至2004年,其总面积减少26.752×104 hm2,15年间减少将近32%.针对吉林西部草地退化状况,提出不同的草地修复规划方案,在系统动力学的指导下,运用VENSIM软件建立了吉林西部草地退化典型区大安市的草地修复规划方案的仿真优化模型,对生产建设型、生态恢复型和生态修复型3种方案进行了仿真优化,其中生态修复型方案,大安市的草地面积以2%的速度恢复,到2020年草地面积为8.23×10.hm2,耕地面积为7.54×104hm2,草地耕地面积比为1.1:1,草地面积占大安市可利用土地面积的41%.农民人均收入达到3 299元,生态效益良好,为吉林西部受损草地生态系统修复的最佳方案.     

Shrub and tree establishment on coal spoils in northern High Plains — USA

Trickle irrigation, during establishment, increased survival two fold for seven species of shrubs and trees planted on coal mine spoil in the semiarid area of northeastern Wyoming, USA. Increased survival of irrigated plants persisted for five years after initiation of this study, which included two growing and winter seasons after cessation of irrigation. Species included green ash (Fraxinus pennsylvanica), Russian olive (Elaeagnus angustifolia), silver buffaloberry (Shepherdia argentea), Siberian peashrub (Caragana arborescens), American plum (Prunus americana), ponderosa pine (Pinus ponderosa), and Rocky Mountain juniper (Juniperus scopulorum).     

退化沙质草地恢复过程土壤颗粒组成变化对土壤-植被系统稳定性的影响

通过对不同恢复程度的6个退化沙质草地群落样地的土壤取样,分析了土壤颗粒组成,进行了饱和持水量和土壤粘结力与结持性能的室内试验与测定.结果表明:在退化最为严重和沙漠化程度最高的群落1,土壤颗粒组成以0.25～0.10 nm的细砂和0.50～0.25 mm的中砂等粗粒成分为主,其质量分数分别为77.62%和19.02%;而0.10～0.05 mm的极细砂和<0.05 mm的粘粉粒等细粒成分的质量分数极低,分别为1.65%和1.67%.土壤颗粒组成的这种特征是沙漠化过程土壤各级颗粒受到强烈分选、土壤组成粗粒化的反映.退化沙质草地恢复过程土壤颗粒组成的变化主要表现为:粘粉粒和极细砂质量分数显著上升,在恢复程度最高的群落6分别达到了16.27%和27.38%;细砂质量分数则显著降低,在恢复程度最高的群落6下降到33.85%.极细砂和粘粉粒能够提高土壤持水能力,其质量分数每提高1%,相当于使土壤饱和持水质量分数分别提高0.18%和0.32%;增强土壤的粘结力和抗风蚀能力,是土壤基质的稳定剂,其质量分数每提高1%,相当于使土壤粘结力分别提高0.078 3 kg·cm-2和0.1363 kg·cm-3.退化沙质草地恢复过程土壤颗粒组成变化是土壤-植被系统互馈作用、良性发展的指示器,其生态意义在于:引起水分人渗和分配变化,使表层土壤截存的降水量增加,有利于浅根系草本植被发育,而深层土壤水分补给减少,沙地旱化;使土壤基质的黏结力和结持性能增强,稳定性增强,抗风蚀能力提高,进一步推动土壤-植被系统的良性发展,加速恢复进程.     

石斛气生的兰科菌根组织结构及其对御旱研究

基于过去对铁皮石斛（Dendrobium candidum Wall．Ex Lindl．）气生的兰科菌根适应干旱环境胁迫机理的研究鲜为涉及,现开展了培养基质的不同水分质量分数（W（水）1=43．6％、16．8％、5．5％）对兰科菌根的外部形态以及内部组织结构影响的研究。研究结果表明：基质水分质量分数降低使石斛菌根外部形态发生多样变化;随着基质水分质量分数的不断降低,石斛的生长受到显著的抑制。当基质水分质量分数为5．5％时,石斛的多数生长指标均小于其它处理,但是根冠比（R／S）增加显著,高达2．22;通过不同切片多重镜检测定和图像分析,发现菌根的形态结构产生了天然的适应突变,独特的根被组织细胞层数多达5层以上,细胞壁相对加厚,细胞腔内网、羽状结构比其它两处理明显增多,石斛菌根通过形态结构的改变来适应水分胁迫并维持其生长发育,石斛菌根组织结构的这些改变大大提高了石斛御旱的能力;水分质量分数高低与菌根感染率呈负相关,越是干旱条件菌根真菌繁衍越活跃,菌丝团结构相持时间越长,菌根的这些适应性响应都提高了石斛的抗旱能力。     

Effect of MS-222 on response to light and rate of metabolism of the little skate Raja erinacea

The effect of tricaine methanesulfonate (MS-222) on the standard (SMR) and routine (RMR) metabolic rates of Raja erinacea was estimated from oxygen-consumption measurements. Data were gathered from a computerized, flow-through respirometry system. Individual trials were run for 96 h at 10 °C on anesthetized and untreated fish. The resulting rates, SMR = 20.1 ± 1.99 SE and RMR = 48.3± 2.5 SE mg O₂ kg⁻¹ h⁻¹, for an unanesthetized skate of 0.5 kg standardized weight, are the lowest reported for any elasmobranch. Periodogram analysis revealed a significant light-response component to the oxygen consumption of these fish, indicating a pattern of nocturnal and crepuscular activity. This activity pattern was disrupted in skates subjected to anesthesia. The use of low-dosage MS-222 in conjunction with the respirometry trials provides positive preliminary evidence that this technique may be useful in giving quick, accurate estimates of SMR in the more intractable elasmobranch fishes. Received: 15 January 1997 / Accepted: 6 February 1997     

石斛气生的兰科菌根组织结构及其对御旱研究

基于过去对铁皮石斛(Dendrobium candidum Wall.Ex Lindl.)气生的兰科菌根适应干旱环境胁迫机理的研究鲜为涉及,现开展了培养基质的不同水分质量分数(w(水分)=43.6%、16.8%、5.5%)对兰科菌根的外部形态以及内部组织结构影响的研究。研究结果表明:基质水分质量分数降低使石斛菌根外部形态发生多样变化;随着基质水分质量分数的不断降低,石斛的生长受到显著的抑制。当基质水分质量分数为5.5%时,石斛的多数生长指标均小于其它处理,但是根冠比(R/S)增加显著,高达2.22;通过不同切片多重镜检测定和图像分析,发现菌根的形态结构产生了天然的适应突变,独特的根被组织细胞层数多达5层以上,细胞壁相对加厚,细胞腔内网、羽状结构比其它两处理明显增多,石斛菌根通过形态结构的改变来适应水分胁迫并维持其生长发育,石斛菌根组织结构的这些改变大大提高了石斛御旱的能力;水分质量分数高低与菌根感染率呈负相关,越是干旱条件菌根真菌繁衍越活跃,菌丝团结构相持时间越长,菌根的这些适应性响应都提高了石斛的抗旱能力。     

13C-labeling shows the effect of hierarchy on the carbon gain of individuals and functional groups in dense field stands

Measurements of resource capture by individuals, species, or functional groups coexisting in field stands improve our ability to investigate the ecophysiological basis of plant competition. But methodological and technical difficulties have limited the use of such measurements. Carbon capture, in particular, is difficult to asses in heterogeneous, dense field stands. Here we present a new approach to measure in situ daily gross carbon gain of individuals. It is based on measuring the 13C content of shoots after a few hours of continuous labeling of all assimilated CO2. The technique is simple and has few assumptions. A new, fully mobile facility was developed, capable of providing a labeling environment with a CO2 concentration close to atmospheric air and known, constant 13C-enrichment, while maintaining temperature and relative humidity within ambient values. This facility was used in seminatural grasslands of Germany and Argentina to explore the relationship between size and carbon gain of individuals of coexisting species growing in contrasting hierarchical positions, and to analyze the carbon gain of functional groups. In general, carbon gain per unit shoot mass increased with increasing size among small individuals, but it became independent of size among the largest ones. In consequence, competition appeared to be size asymmetric between subordinate individuals but size symmetric between dominant individuals. When comparing functional groups, the carbon gain per unit shoot mass of rosette dicots vs. grasses reflected not their relative contribution to stand biomass, but their hierarchical position: irrespectively of mass or growth form, being taller than neighbors was most important in determining carbon gain per unit shoot mass. We believe these results show that in situ measurements of carbon gain can provide valuable insight in field studies of plant competition.     

The effect of species response form on species distribution model prediction and inference

Ecological theory and current evidence support the validity of various species response curves according to a variety of environmental gradients. Various methods have been developed for building species distribution models but it is not well known how these methods perform under various assumptions about the form of the underlying species response. It is also not well known how spatial correlation in species occurrence affects model performance. These effects were investigated by applying an environmental envelope method (BIOCLIM) and three regression-based methods: logistic regression (LR), generalized additive modelling (GAM), and classification and regression tree (CART) to simulated species occurrence data. Each simulated species was constructed as a sum of responses with varying weights. Three basic species response curves were assumed: Gaussian (bell-shaped), Beta (skew) and linear. The two non-linear responses conform to standard ecological niche theory. All three responses were applied in turn to three simulated environmental variables, each with varying degrees of spatial autocorrelation. GAM produced the most consistent model performance over all forms of simulated species response. BIOCLIM and CART were inclined to underrate the performance of variables with a linear response. BIOCLIM was less sensitive to data density. LR was susceptible to model misspecification. The use of a linear function in LR underestimated the performance of variables with non-linear species response and contributed to increased spatial autocorrelation in model residuals. Omission of important environmental variables with non-linear species response also contributed to increased spatial autocorrelation in model residuals. Adding a spatial autocovariate term to the LR model (autologistic model) reduced the spatial autocorrelation and improved model performance, but did not correct the misidentification of the dominant environmental determinant. This is to be expected since the autologistic approach was designed primarily for prediction and not for inference. Given that various forms of species response to environmental determinants arise commonly in nature: (1) higher order functions should always be tested when applying LR in modelling species distribution; (2) spatial autocorrelation in species distribution model residuals can indicate that environmental determinants with non-linear response are missing from the model; and (3) deficiencies in LR model performance due to model misspecification can be addressed by adding a spatial autocovariate to the model, but care should be taken when interpreting the coefficients of the model parameters.     

Acute and chronic toxic effect of lead (Pb) and zinc (Zn) on biomarker response in post larvae of Penaeus monodon (Fabricus, 1798)

Metal pollution produces damage to marine organisms at the cellular level possibly leading to ecological imbalance. The present investigation focused on the acute and chronic toxicity of lead (Pb) and zinc (Zn) by examining the effects of biomarker enzymes in post-larvae of Penaeus monodon (Tiger prawn). Antioxidant biomarker responses such as lipid peroxidation (LPO) and catalase (CAT) activity for Pb and Zn were determined following chronic exposure. Acute Lethal Concentration ₅₀ (LC₅₀) values observed in the study at 96?h for Pb and Zn at 5.77?±?0.32?mg?L^?1 and 3.02?±?0.82?mg?L^?1, respectively. The estimated No Observed Effect Concentration and Lowest Observed Effect Concentration values for Pb were 0.014 and 0.029?mg?L^?1 and that recorded for Zn was 0.011 and 0.022?mg?L^?1, respectively. Among the two metals studied, toxicity of Zn was found to be greater to P. monodon than Pb. The activities of antioxidant defense enzymes and total protein content differed significantly from control following exposure to both metals. Overall, the biomarker studies demonstrated that alterations in antioxidant enzymes and induction of LPO reflect the consequences of heavy metal exposure in P. monodon.     

The effect of hunger on the strength and duration of the antipredator behavioral response of green frog (<Emphasis Type="Italic">Rana clamitans</Emphasis>) tadpoles

The activity level of prey reflects a trade-off between predation risk and foraging gain. A number of theoretical and empirical studies have shown that a prey's energetic state or the level of its resource should influence this trade-off (i.e., what the optimal activity level at a level of predation risk is). Here, I show that the energetic state of prey may also influence the duration of their antipredator behavioral response. Green frog tadpoles (Rana clamitans) reduced their activity level for a shorter time during exposure to the chemical cue of predatory larval dragonflies (Anax spp.) as their time since last feeding increased (i.e., as their energetic state decreased). Interestingly, the tadpoles strongly reduced their activity level upon cue exposure in all treatments. Thus, the relative activity level of tadpoles at different energetic states varied over time.     

Growth and metal accumulation response of <Emphasis Type="Italic">Vigna radiata</Emphasis> L. var PDM 54 (mung bean) grown on fly ash-amended soil: effect on dietary intake

Plants of Vigna radiata L. var. PDM 54 (mung bean) were grown in soil amended with different amounts (10 and 25%) of fly ash (FA). Although total metal content increased with increasing FA amendment, DTPA-extractable metals were higher for 10% FA. Accumulation of metals by the plants increased with increasing FA amendment and was greater in shoots than in roots (except for Mn and Cu) and seeds (except Mn). The total daily intake (TDI) of all the tested metals in seeds was within the recommended dietary allowance (RDA)/provisional tolerable daily intake (PTDI) for adults, except for Cd, which was higher than recommended values. Principal-components analysis (PCA) based on studies of physicochemical properties, DTPA-extractable metals, and metal accumulation in the different parts of V. radiata showed that physicochemical properties such as cation-exchange capacity, organic carbon, and organic matter had significant positive effects on accumulation of Cd, Co, Ni, and Pb by the plant, whereas EC had a significant negative effect. Although addition of fly ash (10%) initially increased the rate of growth, toxic symptoms were observed for 25% FA. Results from analysis of antioxidants (carotenoids, ascorbic acid, non-protein thiol, and free proline) revealed that these increased more in plants grown in 10% FA than in those grown in garden soil. Cysteine and malondialdehyde (MDA) content increased with increasing FA amendment. PCA also showed that all the antioxidants studied behaved similarly except cysteine, for which there was a close relationship with MDA content. Thus, the results obtained during this study revealed that V. radiata L. var. PDM 54 may be grown in 10% FA and/or contaminated agricultural soil.