Qianmei Zhang

A climate change-induced threat to the ecological resilience of a subtropical monsoon evergreen broad-leaved forest in Southern China

Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought-induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of Chinas forested land. In this study, we describe how the monsoon evergreen broad-leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad-leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long-term climate change.

Wild Plant Species with Extremely Small Populations Require Conservation and Reintroduction in China

For reintroduction of rare and endangered plants, plants protected and propagated via ex situ conservation are returned to their original natural and semi-natural ecosystems or to suitable wild habitats. The goal is to establish a population with sufficient numbers and genetic resources to enable it to adapt to change and to be self-sustaining and self-renewing (Griffith et al. 1989; IUCN 1998). International organizations have also published guidelines for the reintroduction of wild species, and at least 249 reintroduction trials involving 172 taxa have been conducted worldwide (Godefroid et al. 2011). More than 890 papers related to reintroduction have been published (Polak and Saltz 2011). To date, there have been 62 successful reintroduction cases in the world (Albrecht et al. 2011). Based on ex situ conservation and research on threatened plants, China has performed several reintroduction experiments. Until now, 38 plant species have been successfully reintroduced. Reintroduced herbs include Primulina tabacum, Paphiopedilum wardii, Paphiopedilum armeniacum, Paraisometrum mileense, Tigridiopalma magnifica, Metabriggsia ovalifolia, Paphiopedilum malipoense, and Doritis pulcherrima. Reintroduced shrubs include Myricaria laxiflora (Chen et al. 2005), Loropetalum subcordatum, and Cycas debaoensis (Ren et al. 2008). Reintroduced trees include Disanthus cercidifolius subdp longipes, Nageia nagi, Manglietia longipedunculata, Bretschneidara sinensis, Parakmeria lotungensis, Davidia involucrate, Dipteronia sinensis, Lirianthe odoratissima, Manglietia aromatica, Euryodendron excelsum, Formanodendron doichangensis, Pachylarnax sinica, Cyclobalanopsis sichourensis, Nyssa yunnanensis, and Diploknema yunnanensis (Sun et al. 2006; Zheng and Sun 2009). The lower plant Adiantum reniforme. var. sinense has also been successfully reintroduced (Ren 2012). The reintroduction of plant species with extremely small populations in China involves a number of main features and problems. Botanical gardens play an important role in the early stage of wild plant reintroduction because such gardens research introduction techniques are related to ex situ conservation. The government is important because it promotes interactions with international organizations and it develops and implements the relevant laws and regulations. For example, the State Forestry Administration approved the “Implementation Plan for Saving Wild Plants of Extremely Small Populations” in 2012; Botanical Garden Conservation International launched a “10 species program” in China aiming at insuring species survival and population recovery. Those works are conducted mainly in relatively developed areas, such as Guangdong and Zhejiang provinces, or biodiversity-rich regions (such as Yunnan province), and over a short period of time, but few related papers have been published. The plant species that have been systematically studied include Primulina tabacum, Tigridiopalma magnifica, Bretschneidara sinensis, Pachylarnax sinica, and Cyclobalanopsis sichourensis. The species that have been reintroduced are confined to those in single-species families and genera, and relic species or rare and endangered species. With respect to the reintroduction of wild plants, researchers in China have studied the ecological characteristics, population genetics, and breeding biology of 28 species. The research has confirmed that these species have narrow distribution areas and shrinking population sizes related to anthropogenic disturbance and climate change. Primulina tabacum, Tigridiopalma magnifica, and Cycas changjiangensis have had 3, 1, and 2 wild distribution points (populations), respectively, that became extinct in the past decade (Ren et al. 2010, 2012). The genetic diversity of these plants is generally low. These plants have varying degrees of natural reproduction barriers (Jian et al. 2010). To increase the successful reintroduction of rare and endangered species, researchers have combined methods of biotechnology and ecological restoration. Our investigations showed that reintroduction of Primulina tabacum often required the use of bryophytes as nurse plants (Ren et al. 2010). Successful reintroduction of Tigridiopalma magnifica indicated that rare and endangered species can be transplanted and established with anthropogenic assistance under the conditions of global climate change, which clarified current academic debate (Ren et al. 2012). We have also successfully reintroduced some trees (including species of Magnoliaceae) and produced substantial numbers of plants from seeds. Some of these seedlings have been used for urban landscaping. Most importantly, we have established the following protocol for the reintroduction of rare and endangered plants: first, select the appropriate target plant species; second, conduct basic research on their breeding and other aspects of their biology and ecology; and then, reintroduce them to the wild while also developing their market-oriented production. By consulting with regional and national agencies concerned with ecological planning, we have promoted this protocol for the reintroduction of rare and endangered plants throughout China.

Substantial reorganization of China's tropical and subtropical forests: based on the permanent plots

There is evidence that climate change induced tree mortalities in boreal and temperate forests and increased forest turnover rates (both mortality and recruitment rates) in Amazon forests. However, no study has examined Chinas tropical and subtropical evergreen broadleaved forests (TEBF) that cover >26% of Chinas terrestrial land. The sustainability of this biome is vital to the maintenance of local ecosystem services (e.g., carbon sequestration, biodiversity conservation, climatic regulation), many of which may influence patterns of atmospheric circulation and composition at regional to global scales. Here, we analyze time-series data collected from thirteen permanent plots within Chinas unmanaged TEBF to study whether and how this biome has changed over recent decades. We find that the numbers of individuals and species for shrub and small tree have increased since 1978, whereas the numbers of individuals and species for tree have decreased over this same time period. The shift in species composition is accompanied by a decrease in the mean diameter at breast height (DBH) for all individuals combined. Chinas TEBF may thereby be transitioning from cohorts of fewer and larger individuals to ones of more and smaller individuals, which shows a unique change pattern differing from the documented. Regional-scale drying is likely responsible for the biomes reorganization. This biome-wide reconstitution would deeply impact the regimes of carbon sequestration and biodiversity conservation and have implications for the sustainability of economic development in the area.

Direct somatic embryogenesis and shoot organogenesis from leaf explants of Primulina tabacum

AbstractsAn efficient propagation system via somatic embryogenesis and shoot organogenesis and plant regeneration system for endangered species Primulina tabacum Hance was established. Thidiazuron (TDZ) was the key plant growth regulator for inducing somatic embryogenesis and kinetin (KIN) and 6-benzylaminopurine (BAP) were the key cytokinins for inducing shoot organogenesis from leaf explants. TDZ combined with BAP or KIN in the induction Murashige and Skoog medium induced both somatic embryos and adventitious shoots. Leaf explants with abaxial site in contact with the medium induced less somatic embryos or adventitious shoots compared to inversely placed leaf explants and the optimum pH was 6.5–7.0. Secondary somatic embryos or adventitious shoot could be induced from primary somatic embryos using TDZ and BAP. Shoots developed adventitious roots on rooting medium containing 0.5 μM indole-3-butyric acid and 0.2 % activated carbon. Over 90 % of plantlets survived following acclimatization and transfer to potting mixture (sand:Vermiculite:limestone; 1:2:1).

Are functional traits a good predictor of global change impacts on tree species abundance dynamics in a subtropical forest

Significant changes in the composition of tree species have been observed in various forests worldwide. We hypothesised that these changes might result from variable sensitivities of species to global change, and species sensitivities might be quantified, using functional traits. Employing long-term (1978-2010) species abundance data of 48 tree species from a permanent subtropical forest plot, where multiple global change factors have been observed, including soil drying, we examined the relationships between temporal trends in abundance and suits of functional traits. We found that species with high photosynthesis rates, leaf phosphorus and nitrogen concentrations, specific leaf area, hydraulic conductivity, turgor loss point and predawn leaf water potential had increased in abundance, while species with opposite trait patterns had decreased. Our results demonstrate that functional traits underlie tree species abundance dynamics in response to drought stress, thus linking traits to compositional shifts in this subtropical forest under global changes.

Characteristics of sun- and shade-adapted populations of an endangered plant Primulina tabacum Hance

Primulina tabacum Hance is an endangered perennial herb distributed in calcium-rich and nitrogen-limited soil of the karst limestone areas in southern China. The morphological, ultrastructural, and physiological traits were determined for P. tabacum populations growing in three different environment conditions: twilight zone of a cave (site TZ, extremely low light intensity), at a cave entrance (site EZ, low light intensity), and in an open area (site OA, high light intensity). At site OA, P. tabacum plants were exposed to high light (635 μmol m−2 s−1 of mean daily photosynthetically active radiation) with drought stress, and expressed traits to minimize light capture and water loss. Compared to plants at sites EZ and TZ, those at site OA had thicker leaves with higher densities of stomata and pubescence, higher palisade/spongy ratio, higher light-saturated rate of net photosynthetic rate (Pmax), higher biomass, higher non-photochemical quenching coefficient (NPQ), and higher light saturation point (LSP) but fewer grana per chloroplast and less thylakoid stacking per granum. In contrast, P. tabacum growing at the cave vicinities: EZ (mean daily irradiance 59 μmol m−2 s−1) and TZ (mean daily irradiance 11 μmol m−2 s−1) showed typical shade-adapted characteristics for optimum light capture. The presence of sun- and shade-adapted characteristics indicates that P. tabacum has different strategies to cope with different environments but whether these strategies reflect genetic selection or phenological plasticity is yet to be determined. Such variability in physiological and morphological traits is important for the survival of P. tabacum in heterogeneous light conditions.

Isolation and characterization of microsatellite markers for Primulina tabacum, a critically endangered perennial herb

Primulina tabacum is a rare and endangered perennial herb with highly restricted limestone distribution in southern China. To enrich our scientific conservation for this species, we developed ten microsatellite markers using repetitive DNA enriched libraries. The number of alleles per microsatellite locus varied from two to six. The expected (HE) and observed (HO) heterozygosities varied from 0.4059 to 0.7294 and from 0.1364 to 0.5217, respectively. These markers will be employed in future studies of genetic structure in P. tabacum.

Distribution, status, and conservation of Camellia changii Ye (Theaceae), a Critically Endangered plant endemic to southern China

The distribution of the endemic threatened plant Camellia changii Ye (Family Theaceae) is restricted to a small area in southern China, and little else is known about its status in the wild. To provide information for the conservation of C. changii we investigated its distribution, population size and structure, and habitat, and assessed its conservation status. Surveys confirmed that the species grows in a narrow band along both sides of a 4 km long segment of a stream in Ehuangzhang Nature Reserve, under the discontinuous canopy of a secondary evergreen broadleaved forest on well-drained, acidic sandy loam soil. We found a total of 1,039 individuals of C. changii . The population has a high flowering rate but a low seed-setting rate. The population appears to be in decline because no seedlings and few young plants were evident. Our findings indicate that C. changii should be categorized as Critically Endangered on the IUCN Red List. We have recommended an integrated species-conservation plan for the species that includes patrolling the Ehuangzhang Nature Reserve to prevent plant removal, establishing an ex situ living collection that contains the entire wild genetic diversity (accomplished by grafting of short cuttings from all wild individuals), facilitating propagation for commercial use, and implementing reintroduction to augment the wild population.

Pollen and seed flow under different predominant winds in wind-pollinated and wind-dispersed species Engelhardia roxburghiana

In most plants, the contributions of pollen and seed flow to their genetic structures are generally difficult to disentangle. For typical wind-pollinated and wind-dispersed species Engelhardia roxburghiana in a 20-ha natural forest plot in lower subtropic China, because the prevailing wind directions change during its pollen release and seed dispersal seasons, we could compare its genetic structures in different directions, which could result primarily from pollen or seed flow. Furthermore, because the plot has undergone from an open to a closed canopy stage historically, we also examined forest canopy effects on gene flow in different generations and different directions. Using 522 E. roxburghiana individuals mapped in the plot, our results revealed that greater pollen flow led to biased gene flow in the pollen dispersal-predominant direction (pollen direction), while greater seed flow generated less spatial genetic structure in the seed dispersal-predominant direction (seed direction). The results predicted from generalized additive models indicated that canopy closure enhanced resistance to gene flow from the old generation to the new generation. Analyses by landscape genetic models for the new generation revealed that gene flow associated with pollen direction was more strongly affected by canopy than with seed direction. Our study is new by proposing an alternative way to separate effects of the pollen and seed flow on spatial variation patterns in E. roxburghiana. To our knowledge, our study is also the first attempt to use landscape genetic models to represent canopy effects for different dispersal vectors in spatial scales only up to a few hundred meters.

Spatial and Temporal Patterns of Carbon Storage in Forest Ecosystems on Hainan Island, Southern China

Spatial and temporal patterns of carbon (C) storage in forest ecosystems significantly affect the terrestrial C budget, but such patterns are unclear in the forests in Hainan Province, the largest tropical island in China. Here, we estimated the spatial and temporal patterns of C storage from 1993–2008 in Hainans forest ecosystems by combining our measured data with four consecutive national forest inventories data. Forest coverage increased from 20.7% in the 1950s to 56.4% in the 2010s. The average C density of 163.7 Mg C/ha in Hainans forest ecosystems in this study was slightly higher than that of Chinas mainland forests, but was remarkably lower than that in the tropical forests worldwide. Total forest ecosystem C storage in Hainan increased from 109.51 Tg in 1993 to 279.17 Tg in 2008. Soil C accounted for more than 70% of total forest ecosystem C. The spatial distribution of forest C storage in Hainan was uneven, reflecting differences in land use change and forest management. The potential carbon sequestration of forest ecosystems was 77.3 Tg C if all forested lands were restored to natural tropical forests. To increase the C sequestration potential on Hainan Island, future forest management should focus on the conservation of natural forests, selection of tree species, planting of understory species, and implementation of sustainable practices.