Effects of rainfall patterns on annual plants in Horqin Sandy Land, Inner Mongolia of China

Growth of annual plants in arid environments depends largely on rainfall pulses. An increased understanding of the effects of different rainfall patterns on plant growth is critical to predicting the potential responses of plants to the changes in rainfall regimes, such as rainfall intensity and duration, and length of dry intervals. In this study, we investigated the effects of different rainfall patterns（e.g. small rainfall event with high frequency and large rainfall event with low frequency） on biomass, growth characteristics and vertical distribution of root biomass of annual plants in Horqin Sandy Land, Inner Mongolia of China during the growing season（from May to August） of 2014. Our results showed that the rainfall patterns, independent of total rainfall amount, exerted strong effects on biomass, characteristics of plant growth and vertical distribution of root biomass. Under a constant amount of total rainfall, the aboveground biomass（AGB）, belowground biomass（BGB）, plant cover, plant height, and plant individual and species number increased with an increase in rainfall intensity. Changes in rainfall patterns also altered the percentage contribution of species biomass to the total AGB, and the percentage of BGB at different soil layers to the total BGB. Consequently, our results indicated that increased rainfall intensity in future may increase biomass significantly, and also affect the growth characteristics of annual plants.

Annual plants in arid and semi-arid desert regions

Annual plants are the main vegetation in arid and semi-arid desert regions.Because of their unique traits,they are the optimal experimental subjects for eco-logical studies.In this article,we summarize annual plants’seed germination strategies,seedling adaptability mechanism to environments,seed dispersal,and soil seed banks.We also discuss the biotic and abiotic factors affecting the composition and dynamics of annual plant populations and communities.Because annual plants have important ecological functions in desert vegetation systems,this study on annual plants will be of great benefit to the conservation and restoration of desert ecosystems,the rational utilization of resources,and the sustainable development of desert regions.

Dynamics of arbuscular mycorrhizal fungi associated with desert ephemeral plants in Gurbantunggut Desert

Previous studies documented that most desert plants can be colonized by arbuscular mycorrhizal （AM） fungi, however, little is known about how the dynamics of AM fungi are related to ephemerals in desert ecosystems. The dynamics of AM fungi with desert ephemerals were examined to determine the effects of host plant life stages on the development of AM fungi. Mean colonization of ephemeral annual plants was 45% lower than that of ephemeral perennial plants. The colonizations were much higher in the early part of the growing season than in later parts, peaking at flowering times. The phenology of AM fungi in root systems varied among different ephem- erals. The density of AM fungal spores increased with the development of ephemeral annual plants, reached its maximum at flowering times, and then plateaued about 20 days after the aboveground senescence. A significant positive correlation was found between AM fungi spore density and biomass of ephemeral annual plants. The life cycles of AM fungi associated with desert ephemerals were very shod, being about 60-70 days. Soil temperature and water content had no direct influence on the development of AM fungal spores. We concluded that the development of AM fungi was in response to desert ephemeral phenology and life history strategy.

Effects of hydrological connection and human disturbance on genetic variation of submerged Vallisneria natans populations in four lakes in China

With the increase in the need for flood prevention and lake resource used by humans,the construction of floodgates and sluices has changed the hydrological connection between rivers and lakes,and between adjacent lakes.In river-disconnected lakes,exploitation and use of lake resources have resulted in water quality decline and mechanical disturbance intensification to a different degree.Of the large number of river-disconnected lakes in the middle-lower reaches of the Changjiang(Yangtze)River,the Futou Lake,and the Xiliang Lake lie close together and are,historically,directly connected,and so do Liangzi Lake and Baoan Lake.The extent of human disturbance is severe in the Futou Lake and the Baoan Lake,but relatively mild in the Xiliang Lake and Liangzi Lake.The freshwater rosette-forming submerged plant Vallisneria natans is one of the dominant species in the four lakes.Using microsatellite markers,we studied the genetic variation of V.natans subpopulations in lakes with different intensities of human disturbance and historical direct hydrological connections.Our results showed that human disturbance decreased plant density and clonal growth in V.natans,but might increase genetic and clonal diversity at a subpopulation level and enhance gene flow among subpopulations by sexual propagule movement.Under similar climatic conditions,different intensities of disturbance seem to have such a high selective potential to differentiate genetically adjacent lake populations that they outperform the forces of gene flow through historical direct hydrological interconnection,which tends to produce genetic homogeneity.Our findings imply that human disturbance has a profound eff ect on the evolutionary process of natural populations of submerged plants.Moreover,increased subpopulation genetic diversity can enhance resistance and resilience to environmental disturbances.To a certain degree,we could expect that disturbed populations have the possibility of restoring spontaneously if humans cease to perturb natural ecosystems in the future.

Diverse outcomes of species interactions in an invaded annual plant community

Aims Despite acknowledgement that interactions among native and exotic species are important for determining the structure and diversity of novel communities,directed experiments using mul-tiple exotics from the same system are rare.Recent observational studies have highlighted distinct ways that exotic species interface with resident natives across invaded communities.The correlative nature of these studies,however,has provided few details about the mechanisms driving distinct interaction outcomes within the same communities.Our aim was to determine how three exotic annual plant species with distinct relationships with local plant diversity impact the performance of a co-occurring native annual in the York gum-jam woodlands of Western Australia.Methods We grew species in experimental communities in growth chambers at varying total planting densities to assess how interaction out-comes varied among natives and exotics across a gradient of com-petition intensity.We measured a variety of performance responses,including survival,biomass and population-level and individual-level reproductive investment.Important Findings Overall,the effects of interspecific versus intraspecific competi-tion on performance varied with the identity and density of exotic competitors.The exploitative exotic grass Bromus madritensis was dominant in polyculture,whereas the diminutive grass Pentameris airoides conferred weak intraspecific competition and interspe-cific facilitation on native Waitzia nitida.The exotic broadleaf forb,Hypochaeris glabra,suppressed growth and survival of W.nitida,while W.nitida had weakly negative,neutral or positive effects on all exotics.These outcomes highlight the complexity of interac-tions impacting the diversity,stability and structure of novel plant communities.As few of these communities contain a single exotic species,understanding the competitive dynamics occurring in diverse novel communities is critical for their conservation and restoration.

GLOBALLY ASYMPTOTIC STABILITY IN A MODEL FOR AN ANNUAL PLANT

In this paper, some conditions for the globally asymptotic stability in a model for an annual plant are obtained.

The central role of stem cells in determining plant longevity variation

Vascular plants display a huge variety of longevity patterns,from a few weeks for several annual species up to thousands of years for some perennial species.Understanding how longevity variation is structured has long been considered a fundamental aspect of the life sciences in view of evolution,species distribution,and adaptation to diverse environments.Unlike animals,whose organs are typically formed during embryogenesis,vascular plants manage to extend their life by continuously producing new tissues and organs in apical and lateral directions via proliferation of stem cells located within specialized tissues called meristems.Stem cells are the main source of plant longevity.Variation in plant longevity is highly dependent on the activity and fate identity of stem cells.Multiple developmental factors determine how stem cells contribute to variation in plant longevity.In this review,we provide an overview of the genetic mechanisms,hormonal signaling,and environmental factors involved in controlling plant longevity through long-term maintenance of stem cell fate identity.

以色列严重退化旱地长期恢复对土壤和植被的影响

Land degradation affects extensive drylands around the world.Due to long-term misuse,the Israeli Sde Zin dryland site has faced severe degradation.The study objective was to assess the feasibility of passive restoration in recovering the site.The study was conducted in four land-units along a preservation-degradation continuum:(1)an area that has not faced anthropogenic disturbances(Ecological land);(2)an area that was proclaimed as a national park in the 1970s(Rehabilitation);(3)an area that was prone,until recently,to moderate anthropogenic pressures(Triangle);and(4)a dirt road that was subjected to long-term off-road traffic(Dirtroad).Soil was sampled and analyzed for its properties.The soil physical quality followed the trend of Ecological land>Rehabilitation>Triangle>Dirtroad.Specifically,high soil salinity in the latter three land-units is attributed to long-term erosional processes that exposed the underlying salic horizons.Herbaceous and shrubby vegetation cover was also monitored.The herbaceous vegetation cover followed the trend of Ecological land(86.4%)>Rehabilitation(40.3%)>Triangle(26.2%)>Dirtroad(2.1%),while the shrubby cover was 2.8%in the Ecological land-unit,and practically zero in the other land-units.It seems that despite the effectiveness of passive restoration in recovering the soil’s physical properties,the recovery of vegetation is limited by the severe soil salinity.