海河流域14种农作物对土壤库中磷的输出量和输入量初步研究

 海河流域14种农作物平均含磷量为0.127±0.053%,变化范围0.023—0.214%,不同器官中最高可达0.419%,最低仅为0.019%。对土壤库中磷输出量最大者为谷子,磷可达99.758±56.931kg·ha-1·a-1,其次是玉米和棉花;磷输入量以白薯为最大,为12.557±5.020kg·ha-1·a-1(但包括可食部分块根的输出部分在内),然后是谷子和花生,其余作物均较低,<2kg·ha-1·a-1。具高输出量的作物的部位有玉米、谷子、花生、棉花等果实,谷子、花生、白薯等茎叶;就输入量而言,除白薯为高输入和谷子为低输入类型外,其余均属很低输入型,上述特点揭示了海河流域因作物的收获而大量损失土壤库中的磷,如种植谷子、玉米、棉花等分别以99.758、32.661和26.591kg·ha-1·a-1的速率损失有效态磷。并对不同子流域作物磷的输出(入)量差异以及针对上述问题应采取的对策作了探讨。     

Effects of nutrient availability and neighbours on shoot growth,resprouting and flowering of Erica multiflora

Abstract. To test if low soil fertility and competition limit the performance of Mediterranean shrubs, and if the effects of competition on plant performance were modified by soil fertility, we subjected shrubs of Erica multiflora to a factorial field experiment of fertilization and removal of neighbours around target plants. After 18 months of treatment, fertilization had stimulated the growth of pre-existent sprouts and biomass allocation to stems into new sprouts, but decreased the frequency of sprout flowering. Removal of neighbours increased the number and biomass of new sprouts, the probability of sprout flowering and the biomass of flowers. Fertilization slightly enhanced sprout recruitment and the probability of sprout flowering when neighbours were removed, but did not modify the other parameters of plant performance. According to our results, both low soil fertility and competition limited plant performance. Competition was slightly more intense in fertilized plants, but only in determining sprout and flowering bud stimulation.     

藻－菌生态系统代谢功能的生态学研究

在室内模拟条件下,研究了一些生态因子对藻－菌（Ａ＋Ｂ）生态系统代谢有机碳（Ｃ６Ｈ１２Ｏ６）、ＮＨ３－Ｎ和无机磷（ＩＰ）的影响．研究结果表明,当藻－菌生态系统中藻（Ａ）或菌（Ｂ）的起始数量一定时,其代谢Ｃ６Ｈ１２Ｏ６的速率,随与之组合的Ｂ或Ａ的起始数量增加（数量比则相应降低）而增加．在光照和黑暗条件下,Ａ＋Ｂ系统代谢上述３种营养物质的速率均有一定的差异．黑暗下Ｃ６Ｈ１２Ｏ６的平均代谢速率较光照下高１２．３％（Ｐ＜０．０５）,ＩＰ和ＮＨ３－Ｎ的平均代谢速率则分别较光照下低１４．４％（Ｐ＜０．０５）和１６．２％（Ｐ＜０．００１）．在Ａ＋Ｂ系统和Ａ、Ｂ单培养物中,３种营养物质的代谢速率均随有机负荷量增加而增加,而且Ａ＋Ｂ系统的代谢速率分别高于单培养的Ａ和Ｂ,其中ＮＨ３－Ｎ代谢尤为显著．文章还就生态系统结构与功能的关系问题进行了讨论．     

Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.     

Hyposensitive canopy conductance renders ecosystems vulnerable to meteorological droughts

Increased meteorological drought intensity with rising atmospheric demand for water (hereafter vapor pressure deficit [VPD]) increases the risk of tree mortality and ecosystem dysfunction worldwide. Ecosystem-scale water-use strategy is increasingly recognized as a key factor in regulating drought-related ecosystem responses. However, the link between water-use strategy and ecosystem vulnerability to meteorological droughts is poorly established. Using the global flux observations, historic hydroclimatic data, remote-sensing products, and plant functional-trait archive, we identified potentially vulnerable ecosystems, examining how ecosystem water-use strategy, quantified by the percentage bias (δ) of the empirical canopy conductance sensitivity to VPD relative to the theoretical value, mediated ecosystem responses to droughts. We found that prevailing soil water availability substantially impacted δ in dryland regions where ecosystems with insufficient soil moisture usually showed conservative water-use strategy, while ecosystems in humid regions exhibited more pronounced climatic adaptability. Hyposensitive and hypersensitive ecosystems, classified based on δ falling below or above the theoretical sensitivity, respectively, achieved similar net ecosystem productivity during droughts, employing different structural and functional strategies. However, hyposensitive ecosystems, risking their hydraulic system with a permissive water-use strategy, were unable to recover from droughts as quickly as hypersensitive ones. Our findings highlight that processed-based models predicting current functions and future performance of vegetation should account for the greater vulnerability of hyposensitive ecosystems to intensifying atmospheric and soil droughts.     

Ecosystem-level effects of re-oligotrophication and N:P imbalances in rivers and estuaries on a global scale

Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two–three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides phytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the other hand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries.     

The ecosystem wilting point defines drought response and recovery of a Quercus-Carya forest

Soil and atmospheric droughts increasingly threaten plant survival and productivity around the world. Yet, conceptual gaps constrain our ability to predict ecosystem-scale drought impacts under climate change. Here, we introduce the ecosystem wilting point (Ψ_EWP), a property that integrates the drought response of an ecosystem's plant community across the soil–plant–atmosphere continuum. Specifically, Ψ_EWP defines a threshold below which the capacity of the root system to extract soil water and the ability of the leaves to maintain stomatal function are strongly diminished. We combined ecosystem flux and leaf water potential measurements to derive the Ψ_EWP of a Quercus-Carya forest from an “ecosystem pressure–volume (PV) curve,” which is analogous to the tissue-level technique. When community predawn leaf water potential (Ψ_pd) was above Ψ_EWP (=−2.0 MPa), the forest was highly responsive to environmental dynamics. When Ψ_pd fell below Ψ_EWP, the forest became insensitive to environmental variation and was a net source of carbon dioxide for nearly 2 months. Thus, Ψ_EWP is a threshold defining marked shifts in ecosystem functional state. Though there was rainfall-induced recovery of ecosystem gas exchange following soaking rains, a legacy of structural and physiological damage inhibited canopy photosynthetic capacity. Although over 16 growing seasons, only 10% of Ψ_pd observations fell below Ψ_EWP, the forest is commonly only 2–4 weeks of intense drought away from reaching Ψ_EWP, and thus highly reliant on frequent rainfall to replenish the soil water supply. We propose, based on a bottom-up analysis of root density profiles and soil moisture characteristic curves, that soil water acquisition capacity is the major determinant of Ψ_EWP, and species in an ecosystem require compatible leaf-level traits such as turgor loss point so that leaf wilting is coordinated with the inability to extract further water from the soil.     

Identifying historical and future global change drivers that place species recovery at risk

Ecosystem management in the face of global change requires understanding how co-occurring threats affect species and communities. Such an understanding allows for effective management strategies to be identified and implemented. An important component of this is differentiating between factors that are within (e.g. invasive predators) or outside (e.g. drought, large wildfires) of a local manager's control. In the global biodiversity hotspot of south-western Australia, small- and medium-sized mammal species are severely affected by anthropogenic threats and environmental disturbances, including invasive predators, fire, and declining rainfall. However, the relative importance of different drivers has not been quantified. We used data from a long-term monitoring program to fit Bayesian state-space models that estimated spatial and temporal changes in the relative abundance of four threatened mammal species: the woylie (Bettongia penicillata), chuditch (Dasyurus geoffroii), koomal (Trichosurus vulpecula) and quenda (Isoodon fusciventor). We then use Bayesian structural equation modelling to identify the direct and indirect drivers of population changes, and scenario analysis to forecast population responses to future environmental change. We found that habitat loss or conversion and reduced primary productivity (caused by rainfall declines) had greater effects on species' spatial and temporal population change than the range of fire and invasive predator (the red fox Vulpes vulpes) management actions observed in the study area. Scenario analysis revealed that a greater extent of severe fire and further rainfall declines predicted under climate change, operating in concert are likely to further reduce the abundance of these species, but may be mitigated partially by invasive predator control. Considering both historical and future drivers of population change is necessary to identify the factors that risk species recovery. Given that both anthropogenic pressures and environmental disturbances can undermine conservation efforts, managers must consider how the relative benefit of conservation actions will be shaped by ongoing global change.     

Litter and soil biodiversity jointly drive ecosystem functions

The decomposition of litter and the supply of nutrients into and from the soil are two fundamental processes through which the above- and belowground world interact. Microbial biodiversity, and especially that of decomposers, plays a key role in these processes by helping litter decomposition. Yet the relative contribution of litter diversity and soil biodiversity in supporting multiple ecosystem services remains virtually unknown. Here we conducted a mesocosm experiment where leaf litter and soil biodiversity were manipulated to investigate their influence on plant productivity, litter decomposition, soil respiration, and enzymatic activity in the littersphere. We showed that both leaf litter diversity and soil microbial diversity (richness and community composition) independently contributed to explain multiple ecosystem functions. Fungal saprobes community composition was especially important for supporting ecosystem multifunctionality (EMF), plant production, litter decomposition, and activity of soil phosphatase when compared with bacteria or other fungal functional groups and litter species richness. Moreover, leaf litter diversity and soil microbial diversity exerted previously undescribed and significantly interactive effects on EMF and multiple individual ecosystem functions, such as litter decomposition and plant production. Together, our work provides experimental evidence supporting the independent and interactive roles of litter and belowground soil biodiversity to maintain ecosystem functions and multiple services.