Litterfall is the largest source of nutrients to for-est soils of tropical rainforests.However,variability in lit-terfall production,nutrient remobilization,and changes in leaf nutrient concentration with climate seasonality remain largely unknown for the central Amazon.This study meas-ured litterfall production,leaf nutrient remobilization,and leaf area index on a forest plateau in the central Amazon.Litterfall was measured at monthly intervals during 2014,while nitrogen,phosphorus,potassium,calcium and mag-nesium concentrations of leaf litter and canopy leaves were measured in the dry and rainy seasons,and remobilization rates determined.Leaf area index was also recorded in the dry and rainy seasons.Monthly litterfall varied from 33.2(in the rainy season)to 87.6 g m^(-2) in the dry season,while leaf area index increased slightly in the rainy season.Climatic seasonality had no effect on concentrations of nitrogen,calcium,and magnesium,whereas phosphorous and potassium responded to rainfall seasonality oppositely.While phosphorous increased,potassium decreased during the dry season.Over seasons,nitrogen,potassium,and phosphorous decreased in leaf litter;calcium increased in leaf litter,while magnesium remained unaffected with leaf aging.Regardless,the five nutrients had similar remobilization rates over the year.The absence of climate seasonality on nutrient remobilization suggests that the current length of the dry season does not alter nutrient remobilization rates but this may change as dry periods become more prolonged in the future due to climate change.
Ricardo Antonio MarencoSaul Alfredo Antezana-VeraDaniela Pereira DiasLuiz Antonio Candido
Forest productivity is closely linked to seasonal variations and vertical differentiation in leaf traits.However,leaf structural and chemical traits variation among co-existing species,and plant functional types within the canopy are poorly quantified.In this study,the seasonality of leaf chlorophyll,nitrogen(N),and phosphorus(P)were quantified vertically along the canopy of four major tree species and two types of herbs in a temperate deciduous forest.The role of shade tolerance in shaping the seasonal variation and vertical differentiation was examined.During the entire season,chlorophyll content showed a distinct asymmetric unimodal pattern for all species,with greater chlorophyll levels in autumn than in spring,and the timing of peak chlorophyll per leaf area gradually decreased as shade tolerance increased.Chlorophyll a:b ratios gradually decreased with increasing shade tolerance.Leaf N and P contents sharply declined during leaf expansion,remained steady in the mature stage and decreased again during leaf senescence.Over the seasons,the lower canopy layer had significantly higher chlorophyll per leaf mass but not chlorophyll per leaf area than the upper canopy layer regardless of degree of shade tolerance.However,N and P per leaf area of intermediate shade-tolerant and fully shade-tolerant tree species were significantly higher in the upper canopy than in the lower.Seasonal variations in N:P ratios suggest changes in N or P limitation.These findings indicate that shade tolerance is a key feature shaping inter-specific differences in leaf chlorophyll,N,and P contents as well as their seasonality in temperate deciduous forests,which have significant implications for modeling leaf photosynthesis and ecosystem production.
Jiajia ZengFan LiuYuan ZhuJiayi LiYing RuanXiankui QuanChuankuan WangXingchang Wang
We examine whether management earnings forecasts(MEFs)help reduce the stock return seasonality associated with earnings seasonality around earnings announcements(EAs)in Chinese A-share markets.We find that firms in historically low earnings seasons outperform firms in high earnings seasons by 2.1%around MEFs.Firms in low earnings seasons also have higher trading volume and return volatility than their counterparts around EAs and MEFs.MEFs significantly reduce the ability of historical seasonal earnings rankings to negatively predict announcement returns,volume and volatility around EAs.The reduction effects are stronger when MEFs are voluntary or made closer to EAs.The evidence suggests that MEFs facilitate the correction of investors’tendency to extrapolate earnings seasonality and its resulted stock mispricing.
A series of medical and biological studies have identified a strong link between the season during which a child is born and early childhood development and adult health.While providing an explanation for the seasonal determinants of birth remains one of the key challenges for demographers,understanding seasonal birth peaks and troughs can inform both public health planning and efforts to prevent childhood diseases.The seasonality of births varies across and within countries.Nonetheless,there has been scant research into the seasonality of births in China.This study takes an in depth look at the seasonal fluctuations in China’s births since 1960 and investigates the effects on seasonality of several key factors such as parity,residence(urban or rural area),and changes to fertility policies.Traditionally,winter has been the peak season of births in China,while spring and summer have been lean seasons,a pattern which is quite different than patterns in Europe and the United States.After 1990,the sweeping implementation of one-child policy and the wider use of modern contraceptives among Chinese women prompted a fundamental shift in the seasonality of births,with the deviation of births from month to month gradually diminishing over time.People’s self-control may serve as a key determinant accounting for such seasonal changes.First births exhibit pronounced and steady seasonality,while second and subsequent births follow a vague seasonal pattern,suggesting that later births are more likely affected by self-choice and self-intervention.The analysis also reveals that the monthly distribution pattern of second births experienced a dramatic change following the roll-out of the selective-two-child policy and the Universal Two-child Policy in 2014 and 2016,changes that reflects the adjustments people made to achieve their fertility plans under the new policy.
