Functional diversity drives ecosystem multifunctionality in a Pinus yunnanensis natural secondary forest.

It is essential to understand how the loss of biodiversity impacts both ecosystem function (EF) and multifunctionality (EMF). Previous studies have mostly focused on predicting how species richness (SR) impacts EMF, while the effect of functional diversity (FD) on EMF remains unclear. Specifically, we know little about the primary functional drivers impacting EMF compared with SR. Therefore, we analysed 8 ecosystem functions within 58 natural secondary forest plots to investigate the effect of FD on both individual EF and EMF. Our results suggest that SR and FD had very significant positive effects on plant phosphorus, soil available phosphorus, and soil total nitrogen. FD explained significantly more variations in these functional responses than SR for individual ecosystem functioning. We also used a multiple threshold approach to test the effect of SR and FD on EMF. We found that FD and SR were positively related to EMF regardless of whether low-level function or high-level function was desired, but FD had a larger effect than SR. Based on the averaging approach, OLS regression, multivariate linear regression model and random forest analysis, we found that SR and FD were both drivers of EMF but that FD had a stronger effect and could explain more variation. As such, we conclude that FD drives ecosystem multifunctionality more than SR.

Dormancy release and germination of Taxus yunnanensis seeds during wet sand storage.

Dormancy is an innate constraint on germination that occurs across all life forms. In this study, we investigated the seed dormancy release and germination characters of Taxus yunnanensis by exploring the seed morphology, permeability, germination inhibitors, endogenous hormones, and embryo germination in vitro during wet sand storage. Our results showed that seeds and embryos grew to a critical size to germination and permeability increased with the extension of storage. Seed coat and kernel methanol extracts reduced Brassica campestris seed vigor index. The in vitro embryo germination rate increased by 12.20% after storage for 30-360 d, whereas seed germination occurred after 450 d. Gibberellic acid and zeatin riboside contents were relatively stable, whereas abscisic acid (ABA) content decreased; indole acetic acid (IAA) content and the IAA/ABA ratio showed increasing trends. These results indicate that ABA is the key inhibitor of germination in Taxus. The chemical(s) in seed coat and kernel cause the inhibition of seed germination. Taken together, Taxus seeds have morphophysiological dormancy, in which the embryos can continue to grow and hormone imbalance inhibits further development and germination. Further, seed dormancy is active even during the middle of storage and shows "double peaks" during the entire dormancy process.

Positive relationship between species richness and aboveground biomass across forest strata in a primary Pinus kesiya forest.

Both biodiversity and biomass are important variables in forest ecosystems, and the relationship between them is critical for ecosystem functioning and management. The primary Pinus kesiya forest is increasingly threatened by human disturbance in Yunnan Province. We observed that species richness had a positive impact on aboveground biomass across all forest vegetation layers, and this relationship was strongest in the herb layer. The asymptotic relationship between cumulative species number and aboveground biomass suggested that individual of Pinus kesiya trees with relatively large diameters contributed the majority of the aboveground biomass in the tall tree strata due to their strong competitive advantage over other tree species. Although aboveground biomass increased with stand age in the tall tree strata, climate factors and the soil nutrient regime affected the magnitude of the diversity-productivity relationship. Stand age had no significant effect on species richness and aboveground biomass in the forest understory. The effect of the positive diversity-productivity relationship of the tall trees on the shrub layer was negligible; the diversity-productivity relationship in the forest understory was significantly affected by the tall tree aboveground biomass. The tall trees have increased the strength of the positive diversity-productivity relationship in the forest understory.

The relationship between species richness and aboveground biomass in a primary Pinus kesiya forest of Yunnan, southwestern China.

The relationship between biodiversity and biomass is an essential element of the natural ecosystem functioning. Our research aims at assessing the effects of species richness on the aboveground biomass and the ecological driver of this relationship in a primary Pinus kesiya forest. We sampled 112 plots of the primary P. kesiya forests in Yunnan Province. The general linear model and the structural equation model were used to estimate relative effects of multivariate factors among aboveground biomass, species richness and the other explanatory variables, including climate moisture index, soil nutrient regime and stand age. We found a positive linear regression relationship between the species richness and aboveground biomass using ordinary least squares regressions. The species richness and soil nutrient regime had no direct significant effect on aboveground biomass. However, the climate moisture index and stand age had direct effects on aboveground biomass. The climate moisture index could be a better link to mediate the relationship between species richness and aboveground biomass. The species richness affected aboveground biomass which was mediated by the climate moisture index. Stand age had direct and indirect effects on aboveground biomass through the climate moisture index. Our results revealed that climate moisture index had a positive feedback in the relationship between species richness and aboveground biomass, which played an important role in a link between biodiversity maintenance and ecosystem functioning. Meanwhile, climate moisture index not only affected positively on aboveground biomass, but also indirectly through species richness. The information would be helpful in understanding the biodiversity-aboveground biomass relationship of a primary P. kesiya forest and for forest management.

Non-structural carbohydrates regulated by season and species in the subtropical monsoon broad-leaved evergreen forest of Yunnan Province, China.

Non-structural carbohydrates (NSC) play important roles in adapting to environments in plants. Despite extensive research on the seasonal dynamics and species differences of NSC, the relative contributions of season and species to NSC is not well understood. We measured the concentration of starch, soluble sugar, NSC, and the soluble sugar:starch ratio in leaves, twigs, trunks and roots of twenty dominant species for dry and wet season in monsoon broad-leaved evergreen forest, respectively. The majority of concentration of NSC and starch in the roots, and the leaves contained the highest concentration of soluble sugar. A seasonal variation in starch and NSC concentrations higher in the dry season. Conversely, the wet season samples had higher concentration of soluble sugar and the sugar:starch ratio. Significant differences exist for starch, soluble sugar and NSC concentrations and the sugar:starch ratio across species. Most species had higher starch and NSC concentrations in the dry season and higher soluble sugar concentration and the sugar:starch ratio in wet season. Repeated variance analysis showed that starch and NSC concentrations were strongly affected by season although the effect of seasons, species, and the interaction of the two on the starch, soluble sugar, and NSC concentrations were significant.

Effects of light acclimation on shoot morphology, structure, and biomass allocation of two Taxus species in southwestern China.

Acclimation to changing light conditions plays a crucial role in determining the competitive capability of tree species. There is currently limited information about acclimation to natural light gradient and its effect on shoot structure and biomass in Taxus species. We examined the acclimation of the leaf and shoot axis morphology, structure and biomass allocation of Taxus yunnanensis and T. chinensis var. mairei under three different natural light environments, full daylight, 40-60% full daylight and <10% full daylight. The leaf biomass, nitrogen content per unit area, leaf carbon content per dry mass and leaf dry mass to fresh mass ratio increased with light in both species, demonstrating an enhanced investment of photosynthetic biomass and structural investment under high light. The number of leaves per unit shoot axis length and the leaf dry mass per unit shoot axis length increased with light in both species. However, the light increase did not result in the increase of the total shoot mass. T. yunnanensis produced larger leaves under low light and a higher shoot axis length per unit dry mass under high light, whereas the leaf size and biomass yield of T. chinensis var. mairei were not sensitive to light.

Changes in Biomass Carbon and Soil Organic Carbon Stocks following the Conversion from a Secondary Coniferous Forest to a Pine Plantation.

The objectives of this study were to estimate changes of tree carbon (C) and soil organic carbon (SOC) stock following a conversion in land use, an issue that has been only insufficiently addressed. For this study, we examined a chronosequence of 2 to 54-year-old Pinus kesiya var. langbianensis plantations that replaced the original secondary coniferous forest (SCF) in Southwest China due to clearing. C stocks considered here consisted of tree, understory, litter, and SOC (0-1 m). The results showed that tree C stocks ranged from 0.02±0.001 Mg C ha-1 to 141.43±5.29 Mg C ha-1, and increased gradually with the stand age. Accumulation of tree C stocks occurred in 20 years after reforestaion and C stock level recoverd to SCF. The maximum of understory C stock was found in a 5-year-old stand (6.74±0.7 Mg C ha-1) with 5.8 times that of SCF, thereafter, understory C stock decreased with the growth of plantation. Litter C stock had no difference excluding effects of prescribed burning. Tree C stock exhibited a significant decline in the 2, 5-year-old stand following the conversion to plantation, but later, increased until a steady state-level in the 20, 26-year-old stand. The SOC stocks ranged from 81.08±10.13 Mg C ha-1 to 160.38±17.96 Mg C ha-1. Reforestation significantly decreased SOC stocks of plantation in the 2-year-old stand which lost 42.29 Mg C ha-1 in the 1 m soil depth compared with SCF by reason of soil disturbance from sites preparation, but then subsequently recovered to SCF level. SOC stocks of SCF had no significant difference with other plantation. The surface profile (0-0.1 m) contained s higher SOC stocks than deeper soil depth. C stock associated with tree biomass represented a higher proportion than SOC stocks as stand development proceeded.

[Species-area relationship at different succession stages of monsoon evergreen broad-leaved forest in south subtropical area of Yunnan Province].

Based on the investigation data of monsoon evergreen broad-leaved forest at its different succession stages (primary, CP; 15 years of succession, CF; and 30 years of succession, CT) in Pu' er of Yunnan Province, this paper studied the species-area relationship of this forest at each succession stage. It was found that in the communities at each succession stage, the number of total species, trees, shrubs, and lianas had a significant correlation with sampling area, with the area explained over 94% of the total variation. The Z value of the total species (0.334) and trees (0.394) was the lowest at CT, whereas that of shrubs (0.437) and lianas (0.326) was the lowest at CF. No significant differences were observed in the intercepts of the species-area curve of total species, trees, shrubs, and lianas among different succession stages, but the coefficient of determination (R2) of the species-area curve of total species and lianas was the highest at CP. The richness of trees and shrubs at CF explained 99.9% of the variance of Z value, but the richness of total species, trees, shrubs, and lianas at CP and CT had no significant correlations with the Z value.

[Biodiversity of tree species, their populations' spatial distribution pattern and interspecific association in mixed deciduous broadleaved forest in Changbai Mountains].

Based on the data collected from the sampling plot with an area of 1 hm2 at the Experimental and Management Bureau of Jiaohe in Jilin Province, this paper analyzed and researched the community structure, biological diversity, spatial distribution pattern and interspecific association between tree species populations in a mixed deciduous broadleaved forest. The results indicated that there was no obvious dominant order among tree species populations, and the indices of tree species diversity such as Shannon-Wiener index (H'), Pielou evenness index (E) and Simpson ecological dominant index (D) were all low. Shrub and herb species diversity indices were also not high. The spatial distribution pattern of five dominant tree species all presented aggregative. Based on 2 x 2 contigency table, the interspecific associations of 15 tree species in the community were examined by means of chi2-test, together with the association coefficient (AC). The results showed that there were 14 species pairs in 15 species showing significantly negative association. The proportion of species pairs showing negative association was much more than that of showing positive association. It could be deduced that the community was instable and at the stage of autogenic succession from soft deciduous broadleaved forest to hard deciduous broadleaved forest, and then, the Korean pine broadleaved forest.