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Studying community phylogenetic diversity within forest stands of different diameter classes (i.e. size classes) is helpful for understanding relationships among species at different ages while at the same time community phylogenetic structure. However, little research has been focused on the influence of species abundance on phylogenetic structure of community. This study was conducted in the Jianfengling tropical montane rainforest on Hainan Island. First, we assessed the impact of species abundance on four widely used phylogenetic diversity indices at different size classes. Next, two of the indices (i.e. net relatedness index, •研究报告• 618 生 物 多 样 性 Biodiversity Science 第 24 卷 NRI and nearest taxon index, NTI) were standardized and used to quantify phylogenetic relatedness of woody plants at different size classes across a series of local habitat types. The results showed that: (1) The unweighted MPD (mean pairwise distance) index significantly overestimated phylogenetic diversity relative to MPD weighted according to species abundance. This overestimation when using unweighted MPD was greatest for small trees and shrubs (1 cm≤DBH 0). However, this pattern continued to show overdispersion within communities made up of large trees (DBH≥15 cm) (NTI

Remnant trees, remaining after large-scale disturbance of forests, have been shown to exhibit noticeable ecological effects on the recovery of ecosystem functions. Although it is well known that remnant trees may serve as dispersal foci, their effects on the spatial pattern of later stages of dominant tree species in natural secondary forest have not been fully appreciated. To explore the spatial influences of remnant trees on later stages of dominant tree species of a secondary Abies-Betula forest on the eastern edge of the Qinghai–Tibetan Plateau, we mapped all the trees in a 200 m × 200 m plot. We used spatial point pattern analysis including O-ring statistics to analyze the spatial associations between old-growth remnant trees and two dominant tree species of later stages. Abies faxoniana and Betula albo-sinensis, comparing different size-classes at different spatial scales. Our results showed that saplings, small trees, and medium trees of the shade-tolerant species, A. faxoniana, showed significantly positive associations to the old-growth remnant trees of both dominant species, suggesting that remnant trees provided favourable sites for the regeneration of shade-tolerant species. In contrast, small, and medium trees of the shade-intolerant species, B. albo-sinensis, showed significantly negative associations to old-growth remnant trees of both dominant species, suggesting that the remnant trees hinder their regeneration. For old-growth remnant trees, the O12(r) function value (density) of their seedlings, saplings, small trees, and medium trees was calculated at increasingly greater concentric scales (with radius from 0 to 100 m from the remnant trees). Tree density first increased rapidly from 0 to 10 m or 20 m radius (distance from remnant tree) and then decreased continually away from remnant trees, consistent in part with the population recruitment curve proposed by the Janzen–Connell model. We found that saplings, small trees, and medium trees of A. faxoniana tended to distribute within a particular range of annuli around the remnant trees of A. faxoniana, with the densities of the three largest size-classes reaching a maximum within 3–6 m of the remnant tree. The densities beyond the parent remnant trees continued to show an increasingly expanding zone of attraction around the remnant tree. In effect, the small and medium A. faxoniana trees coalesced around remnant trees to create increasingly enlarged canopy cover areas, which served simultaneously as protected zones for A. faxoniana regeneration and extended exclusion zones for B. albo-sinensis and similar shade intolerant species.

Carbon and nitrogen storage in different plantation ecosystems of Erythrophleum fordii,Castanopsis hystrix and Pinus massoniana in subtropical south China were studied.The results showed that the allocation of C in the organs of the different tree species had no significant correlation with their age,while that of N had closer relationship with the age.The N concentration in young organs was higher than that in aged ones and the C/N ratio was higher in aged organs than that in young ones.The N concentration was higher in all components of the nitrogen-fixing species(E.fordii plantation) than that in other species(C.hystrix and P.massoniana plantations).There was an obvious enrichment of C and N in the topsoil of the plantation ecosystems.The total ecosystem carbon storage of E.fordii,C.hystrix and P.massoniana plantations was 236.22 t/hm2,267.84 t/hm2 and 200.57 t/hm2 and nitrogen storage was 17.91 t/hm2,12.38 t/hm2 and 10.59 t/hm2,respectively.Carbon storage of tree layer occupied 42.57%,36.31% and 40.28% while 0—100 cm soil occupied 55.77%,62.52% and 57.83%,respectively.Nitrogen storage of soil occupied 92.00%,93.72% and 95.53%.Our study indicated that most ecosystem carbon and nitrogen storage of the plantations stored in soil.Carbon sequestration ability of C.hystrix plantation is higher compared to other two plantations.

In order to reveal the relationships between seed chemical compositions and climatic factors,seven Quercus species from eight core distribution areas were selected in temperate zone of North-South Transect of Eastern China(NSTEC).The relationships between climatic factors and seed chemical compositions of the Quercus species,including starch,protein,lipid,soluble total sugars,tannin and proline were discussed.The results shown that temperature was the most important factor affected the compositions of the seeds and the annual sunlight taken the second place,while the precipitation had no significant effect on compositions of the seeds.In temperate zone of NSTEC,with increasing of latitude,the temperature decrease,the mean annual sunlight increase,and length of growing season of the trees become shorter and shorter due to the decrease of the growing degree day;starch content of Quercus seeds decreased,and tended to hydrolyze to soluble sugar.From the south to the north,the species had to improve the cold resistance of their seeds by increasing the content of total soluble sugar,protein and proline for adapting the environment of lower temperature.Moreover,there were positive relationships among the content of total soluble sugar,protein and amino acid praline of the seeds,and all of them had negative relations to starch.It is one kind of ecological strategies for the plants to adapt their living environment.

Subalpine dark coniferous forests in western Sichuan,China include natural old-growth forests and natural regenerated forests after logging over the past 50 years.Both the bamboo-forest type and moss-forest type are comprised of three different restoration stages: broad-leaved forest of 20—40 years old(BBLF,MBLF),conifer/broad-leaved mixed forest of 50 years old(BCBLF,MCBLF),and old-growth dark coniferous forest of 160—200 years old(OBDCF,OMDCF).Our objectives were to understand the consume of the soil seed of Betula albo-sinensis and Abies faxoniana through analyzing the number,components,and the distributions pattern,and 1-year old seedlings at different forest restoration stages of the two forest types.We conducted field sampling to determine the number of the remainder soil seed and the density of 1-year old seedlings in August,2009 before the seed riped,and used sieve and stereoscopic microscope to identify components,density and distribution pattern of soil seed at different forest restoration stages.We tested viability of Betula albo-sinensis and Abies faxoniana seeds with tetrazolium method and seed germination experiments in laboratory.The results showed as below: 1) The total number of remainder soil seeds,complete shape seeds,undeveloped seeds,empty seeds and decayed seeds of Betula albo-sinensis had a decreasing trend with forests restoration,but an increasing trend occurred in Abies faxoniana.The total number of remainder soil seeds,complete shape seeds,undeveloped seeds,empty seeds and decayed seeds of Betula albo-sinensis in each one of the forest restoration stages of the bamboo-forest types had more than in the corresponding restoration stages of the moss-forest types.The maximum value of the total number of remainder soil seeds,complete shape seeds,undeveloped seeds,empty seeds and decayed seeds of Abies faxoniana have been occurred at the moss-old-growth dark coniferous forest;2) At the broad-leaved forest and conifer/broad-leaved mixed forest stages,the maximal proportion of the components of seeds of Betula albo-sinensis and Abies faxoniana were decayed seeds and undeveloped seeds,respectively.At the dark coniferous forest stages,the proportion of the decayed seeds and empty seeds of Betula albo-sinensis cut the top class,however,the maximal proportion occurred at complete shape seeds of Abies faxoniana;3) The number of complete shape seeds,undeveloped seeds,empty seeds and decayed seeds of Betula albo-sinensis and Abies faxoniana had a decreasing trend with the increasing soil depth.The proportion of different components of seeds of Betula albo-sinensis and Abies faxoniana varied between 72.85%—94.28% at the litter layer;4) The density of 1-year old seedling of Betula albo-sinensis decreased gradually with forest restoration,however,Abies faxoniana had an opposite trend.The viability seed of Betula albo-sinensis and Abies faxoniana in soil was lost in August,which indicated that the seeds of Betula albo-sinensis and Abies faxoniana just formed transient soil seed bank.

Both soil temperature and soil water condition are important factors that influencing soil respiration at different temporal scales.There is still intra and inter-seasonal variations in soil temperature and soil water content although they are seasonally correlated.In this study,a field experiment was carried out to explore effects of diurnal variations in soil temperature and soil water on soil respirations(RS) in the alpine meadows in Balang Mountain in West Sichuan of China.The objectives of our study are to: 1) understand the seasonal pattern of day-and night-time RS,in particular,nocturnal variations of RS,2) elucidate the partitioning pattern of day-and night-time RS,and 3) compare Q10 values of day-and night-time RS.We examined both day-and night-time RS by using LI-8100 Automated Soil CO2 Flux System on monthly basis from April to November,2011.The effects of soil temperature and soil water on RS of alpine meadow were analyzed based on field measurements of diurnal soil respiration.The results indicated that RS showed large seasonal variations in day-and night-time during the measurements period,with a two-peak curve in the day-time and parabola curve at the night-time.During the measurements period(April to November),the means of RS in the day-and night-time are 1.83 μmol · m-2 · s-1 and 1.61μmol · m-2 · s-1,respectively.The means of daytime and nighttime RS were significantly higher in growing seasons(Jun to September) than that in green up period(April to May) and withering period(October to November) which accounted largest contribution to annual soil respiration.The nocturnal soil respiration appeared to have similar tendency of variations among measurements,and it was relatively low at night-time,with the lowest between 06:30 and 07:00am.During the measurement period,Van′t Hoff equation and Lloyd Taylor function were the same to be used for describing the relationships between soil respiration and soil temperature.The two-factor equations(soil temperature and moisture content) were much better to describe responses of nocturnal soil respiration compared to the single-factor equations.Soil respiration rates in the day-time and night-time exhibited a significantly exponential correlation with soil temperature during green up period,growing season and weathering periods,while the linear positive relationships between soil respiration and soil water content were found for nocturnal respiration in green up period and for both day-time and nocturnal respirations in weathering period.Q10 values were estimated to be 3.90 and 3.74 for the day-time and night-time respirations respectively,during the whole measurement period.Soil Q10 values varied with season,but daytime soil respiration during the green up period was most sensitive to temperature,and the nocturnal soil respiration during the peak months of growing seasons was least sensitive to temperature.Our results demonstrated that soil temperature,soil water,and their interactive effects had distinct effects on soil respiration of either the day-time or night-time during the measurements period in the subalpine meadow.Therefore,more measurements of the soil nocturnal CO2 efflux are essential to accurately estimate the seasonal and annual carbon fluxes based on instantaneous measurements of soil respiration.At the same time,soil temperature,soil water and other biotic factors affecting soil respiration should be taken into account.