Zaifu Xu

Tropical rain forest fragmentation and its ecological and species diversity changes in southern Yunnan

Three fragmented rain forests and one primary forest in southern Yunnan were plotted. The microclimate and soil conditions of these forests were also studied. The following conclusions were drawn: (1) The microclimatic differences between inside and outside forest are less in the fragmented forests than in the primary forest, which indicates that the buffer effects to climatic change have been reduced in the fragmented forests. The soil has deteriorated to some extent due to forest fragmentation. (2) In species composition, especially the abundance of some species and the dominant ranks of some families have changed with fragmentation. Barringtonia macrostachya, the most dominant species in the control primary forest, disappeared from the fragmented forests, while Antiaris toxicaria, which is a characteristic but not dominant species in the primary forest, is dominant in fragmented forests. (3) The total number of species per plot was reduced in the fragmented forests and the more seriously disturbed the fragment was, the more the species richness diminished. (4) In life form spectra, the liana and microphanerophyte species increased, but epiphyte, megaphanerophyte, mesophanerophyte and chamaephyte species decreased in the fragmented forests. (5) The plant species diversity is generally lower in the fragmented forests than in the primary forest, although for some life forms it could be higher. (6) The tree species with small populations could be lost first in the process of rain forest fragmentation. (7) The heliophilous or pioneer tree species increased and the shade-tolerant species were reduced in the fragmented forests.

Pollination - Flexible style that encourages outcrossing

Despite the convenience of self-pollination (selfing) in flowering plants , the detrimental effects of inbreeding that follow repeated selfing have promoted strong natural selection for mating systems that ensure successful cross-fertilization (outcrossing). Here we describe a mechanism deployed by some tropical ginger flowers to avoid self-pollination — the flower moves its stigma (style), which normally acts as the pollen receptor, out of the way while its anther is releasing pollen. This cunning evasion adds to the diversity of pollination strategies that have contributed to the evolutionary success of flowering plants.

Ex situ genetic conservation of endangered Vatica guangxiensis (Dipterocarpaceae) in China

RAPD polymorphisms were applied to check the efficiency of ex situ genetic conservation of endangered Vatica guangxiensis X. L. Mo. endemic to southwestern China. Low level of genetic variation was revealed in three remaining natural populations. Twenty random primers, each with 10 base pairs, generated 231 bands with 53.68% being polymorphic, and with an average of 32.46% being polymorphic in each natural population. Strong Population differentiation was revealed by AMOVA (analysis of molecular variance) and Gst value was 0.3764. The population ML ex situ conserved in the Xishuangbanna Tropical Botanical Garden contained an intermediate genetic variation compared with natural Populations. with 30.74% bands being polymorphic. Of the total 231 bands generated in V. guangxiensis, 204 bands were also detected in population M L, indicating that 88.31% of the total genetic variations of this species were conserved in ex situ population. If only the alleles with moderate to high frequency (P>0.05) were considered, 204 out of 209 bands (97.61%) occurred in ex situ population M L. RAPD analysis also detected one exclusive band in natural population NS, and five in natural population NP, three of these exclusive bands were generated in every samples of natural population (NP), and other three had moderate to high frequencies. While none of these exclusive bands were detected in ex situ conserved population ML. Our conclusions Lire that the ex situ conserved population ML contains representative genetic variation to maintain long-term survival and evolutionary process of V. guangxiensis, and that more extensive ex situ sampling in natural population NS and NP is needed to conserve more exclusive alleles in ex situ population. The tropical area in the Botanical Garden would play a more important role in the ex situ conservation of rare and endangered plants

Leaf litter decomposition of canopy trees, bamboo and moss in a montane moist evergreen broad-leaved forest on Ailao Mountain, Yunnan, south-west China

Litter decomposition and nutrient release of selected dominant synusiae in an old-growth, evergreen, broad-leaved mossy forest on Ailao Mountain, Yunnan, south-west China, were studied over a 22-month period. The species studied were three dominant tall tree species, Lithocarpus xylocarpus Markg., Lithocarpus chintungensis Hsu et Qian and Castanopsis wattii A. Camus; one dominant understory species (the bamboo Sinarundinaria nitida Nakai); and a mixture of dominant mosses (including Homaliodendron scalpellifolium Fleisch, Symphyodon perrottetti Mont., Herberta longifolissa Steph. and Bazzania albicans Horik.). Fast initial litter decomposition was followed by lower rates. Decomposition rates of canopy species and bamboo leaf litter appear to be controlled by the initial concentration of lignin, nitrogen (N) and phosphorus (P) more than by morphological features of the leaves. The decay rate of moss litter was less correlated with nutrient composition and lignin concentration in initial mass. The order of decomposition rates was Castanopsis wattii > L. xylocarpus > L. chintungensis > bamboo > moss. The decomposition rate constants (k) of the leaf litter for the canopy species L. xylocarpus, L. chintungensis and Castanopsis wattii were 0.62, 0.50 and 0.64, respectively, and 0.40 and 0.22 for bamboo and moss, respectively. Turnover time (1/k) for the three canopy species was 1.61 years, 2.0 years and 1.55 years, respectively, and 2.50 years and 4.55 years for bamboo and moss, respectively. The N and P concentration in the decomposing leaf litter increased in the first 6 months and then decreased over the remaining period. There was a relatively rapid initial loss of potassium (K), followed by a slight increase. Each of calcium (Ca) and magnesium (Mg) decreased with time whereas iron (Fe) and manganese (Mn) increased with time to some extent. Nutrient release from decomposing leaf litter was in the order of K > Mg > Ca > N > P > Mn > Fe, except for bamboo (Sinarundinaria nitida) K > Ca > P > N > Mg > Mn > Fe.

Nutrient fluxes in bulk precipitation, throughfall and stemflow in montane subtropical moist forest on Ailao Mountains in Yunnan, south-west China

A study of nutrient movement through rainfall, throughfall and stemflow, as well as epiphytic bryophyte (moss and liverwort) biomass and its effect on nutrient composition of stemflow, was conducted for 2 y in subtropical montane moist forest (Lithocarpus-Castanopsis association) at Xujiaba, Ailao Mountain National Nature Reserve, Yunnan, south-west China. Base cation and fluxes were increased in throughfall, while NH 4 + -N and NO 3 - -N were reduced relative to precipitation. Annual throughfall inputs of N, P, Ca and S were mainly from precipitation, while most K and two-thirds of Mg throughfall input was due to canopy leaching. Input of Na in the precipitation and throughfall was low in this forest. Net flux (throughfall flux minus bulk precipitation) and deposition ratios (ratio of throughfall flux to bulk precipitation flux) were in the low part of the range reported for other tropical montane rain forests. The throughfall data for this forest reveal generally low cycling rates for mineral elements. Abundant epiphytic bryophytes on bole bark affected the chemical composition of stemflow by selective uptake or release of elements. Relative to trees without epiphytic bryophytes, the annual amounts of total N, NH 4 +-N, Mg, Na and SO 4 2- -S were enhanced, while NO 3 - -N, K, P and Ca were depleted in stemflow. Contributions of N from nitrogen-fixing organisms are likely to be constrained by low temperatures.

Litterfall and nutrient dynamics in a montane moist evergreen broad-leaved forest in Ailao Mountains, SW China

Montane moist evergreen broad-leaved forest, dominated byLithocarpus and Castanopsis species,is the most extensive stand of subtropical mountain in Yunnan Province, SWChina. Litter production, standing crop of litter on forest floor and nutrientreturn patterns were studied over nine years (1991–1999) in a stand ofprimary evergreen broad-leaved forest in northern crest of the Ailao MountainRange. There were significant yearly variations in litter production, which ismainly related with the masting year of canopy species, and exceptionalphysicalevents (strong winds and snow) in the natural forest. The mean annual smalllitterfall is 7.12 t ha−1 yr−1ofwhich leaf litter account for 65% of the total litterfall. The seasonality ofsmall litterfall was bia-modal, with the main one in the late dry season(April–May) and a lesser one in early winter (October–November).Decomposition quotient value was relatively low with 0.58 for total smalllitterfall. Mean large-wood (≥ 2.5 cm in diameter) ranged from0.21 to 1.41 t ha−1 yr−1 with amean of 0.52 t ha−1 yr−1.Concentrations of most elements in leaf and twig were slightly greater in wetmonths than dry months, except for C and K. Woody litter had low N and Pconcentrations compared with the leaf and reproductive parts. Nutrient returntothe soil through small litterfall decrease in the orderC>N>Ca>K>Mg>Mn>Al>P>Fe, while nutrient reserve inlitteron the forest floor was in the declining sequenceC>N>Ca>K>Mg>P>Fe>Al>Mn.

Mating system and stigmatic behaviour during flowering of Alpinia kwangsiensis (Zingiberaceae)

Abstract. Little is known about the breeding systems of tropical perennial ginger species. In this paper, we provide information about the breeding system of Alpinia kwangsiensis in Yunnan, Southwest China, specifically self-compatibility, mechanisms promoting outcrossing, and the visitation characteristics of pollinators. Populations of A. kwangsiensis have two specific phenotypes that differ in flowering behaviour: 1) “cataflexistyle” individuals in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes decurved under the anther at noon and 2) “anaflexistyle” individuals in which the receptive stigma is decurved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen at mid-day. The stigmatic movements in the two floral phenotypes, which occur in a ratio of 1:1 in natural populations, are synchronous and correlate with the foraging behaviour of floral visitors; pollination is effected only between floral forms. Field experiments indicate that A.kwangsiensis is self-compatible and dependent upon insects for fertilization. This newly reported floral mechanism, which we have named “flexistyly,” adds to the repertoire of devices that have evolved in flowering plants to insure outcrossing.

Allozyme variation and conservation genetics of common wild rice (Oryza rufipogon Griff.) in Yunnan, China

In order to reveal levels and distribution of genetic variation within Oryza rufipogon Griff. of Yunnan, China, where one of the centers of genetic diversity for Asian cultivated rice O. sativa L. is located, allozyme variation encoded by 22 loci was electrophoretically analyzed in 149 individuals of all three existing populations as well as five from other regions (Guangxi, Hainan and Jiangxi provinces) of China. As compared to the level of genetic diversity (the mean A = 1.2, P = 24.1%, Ho = 0.045 and He = 0.079) for the populations from other regions, a rather low genetic diversity (the mean A = 1.1, P = 7.6%, Ho = 0.007 and He = 0.011) was found in Yunnan, which may originate from marginal nature of these populations, recent reduction of populations and consequent drift. The result suggests that the current center of genetic diversity for O. rufipogon fail to agree with that for cultivated rice in China. The genetic differentiation for all the eight populations(FST = 0.254) was slightly lower than that for three populations from Yunnan (FST = 0.302), indicating a fairly high genetic differentiation in the region. Finally, a conservation plan for sampling/preserving fewer populations but more individuals from each population for the species was given, and an appropriate strategy for conserving the three surviving populations from Yunnan was proposed.

Acclimation to irradiance in seedlings of three tropical rain forest Garcinia species after simulated gap formation

We investigated the acclimation of seedlings of three tropical rain forest sub-canopy Garcinia species (G. xanthochymus, G. cowa, and G. bracteata) after transfer from 4.5 (LI) to 40 % (HI) sunlight and 12.5 (MI) sunlight to HI (LH1 and LH2 denoting transfer from LI to HI and MI to HI transfer, respectively). The changes of chlorophyll (Chl) fluorescence, net photosynthetic rate (PN), dark respiration rate (RD), Chl content per unit area (Chlarea), leaf mass per unit area (LMA), and seedling mortality were monitored over two months after transfer. These parameters together with leaf anatomy of transferred and control seedlings (kept in LI, MI, and HI) were also examined after two months. No seedlings died during the two months. Fv/Fm, PN, and Chlarea of the transferred seedlings decreased in the first 3 to 12 d. LH1 leaves showed larger reduction in Fv/Fm (>23 % vs. <16 %) and slower recovery of Fv/Fm than LH2 leaves. PN started to recover after about one week of I transfer and approached higher values in all G. cowa seedlings and G. xanthochymus LH1 seedlings than those before the transfer. However, PN of G. bracteata seedlings approached the values before transfer. The final PN values in leaves of transferred G. xanthochymus and G. cowa seedlings approached that of leaves kept in HI, while the final PN values of transferred leaves of G. bracteata were significantly lower than that of leaves grown under HI (p<0.05). RD of G. xanthochymus LH1 seedlings and all G. cowa seedlings increased and approached the value of the seedlings in HI. The final Chlarea of both G. xanthochymus and G. cowa approached the values before transfer, but that of G. bracteata did not recover to the level before transfer. The final Chlarea of all transferred seedlings was not significantly different from that of seedlings in HI except that G. cowa LH1 seedlings had higher Chlarea than that in HI. LMA decreased within 2 d and then increased continuously until about 30 d and approached the value under HI. Spongy/palisade mesophyll ratio decreased after transfer because of the increase in palisade thickness. Leaf thickness did not change, so LMA increase of transferred seedlings was mainly due to the increase of leaf density. Thus the mature leaves under LI and MI of G. xanthochymus and G. cowa are able to acclimate to HI by leaf physiological and anatomical adjustment, while G. bracteata had limited ability to acclimate to HI.

Genetic evaluation of the efficacy of in situ and ex situ conservation of Parashorea chinensis (Dipterocarpaceae) in southwestern China

The majority of research in genetic diversity yields recommendations rather than actual conservation achievements. We assessed the efficacy of actual in situ and ex situ efforts to conserve Parashorea chinensis (Dipterocarpaceae) against the background of the geographic pattern of genetic variation of this species. Samples from seven natural populations, including three in a nature reserve, and one ex situ conservation population were studied. Across the natural populations, 47.8% of RAPD loci were polymorphic; only 20.8% on average varied at the population level. Mean population genetic diversity was 0.787 within natural populations and 1.410 for the whole species. Significant genetic differentiation among regions and isolation by distance were present on larger scales (among regions). AMOVA revealed that the majority of the among-population variation occurred among regions rather than among populations within regions. Regression analysis, Mantel test, principal coordinates analysis, and cluster analysis consistently demonstrated increasing genetic isolation with increasing geographic distance. Genetic differentiation within the region was quite low compared to that among regions. Multilocus spatial autocorrelation analysis of these three populations revealed random distribution of genetic variation in two populations, but genetic clustering was detected in the third population. The ex situ conserved population contained a medium level of genetic variation compared with the seven natural populations; it contained 77.1% of the total genetic variation of this species and 91% of the moderate to high frequency RAPD fragments (f > 0.05). Exclusive bands were detected in natural populations, but none were found in the ex situ conserved population. The populations protected in the nature reserve contained most of the genetic variation of the whole species, with 81.4% of the total genetic variation and 95.7% of the fragments with moderate to high frequency (f > 0.05) of this species conserved. The results show that the ex situ conserved population does not contain enough genetic variation to meet the need of release in the future, and that more extensive ex situ sampling in natural populations TY, NP, HK, and MG is needed. The in situ conserved population contains representative genetic variation to maintain long-term survival and evolutionary processes of P. chinensis.