Guolei Li

Ostryopsis davidiana seedlings inoculated with ectomycorrhizal fungi facilitate formation of mycorrhizae on Pinus tabulaeformis seedlings

Reforestation in China is important for reversing anthropogenic activities that degrade the environment. Pinus tabulaeformis is desired for these activities, but survival and growth of seedlings can be hampered by lack of ectomycorrhizae. When outplanted in association with Ostryopsis davidiana plants on reforestation sites, P. tabulaeformis seedlings become mycorrhizal and survival and growth are enhanced; without O. davidiana, pines often remain without mycorrhizae and performance is poorer. To better understand this relationship, we initiated an experiment using rhizoboxes that restricted root and tested the hypothesis that O. davidiana seedlings facilitated ectomycorrhizae formation on P. tabulaeformis seedlings through hyphal contact. We found that without O. davidiana seedlings, inocula of five indigenous ectomycorrhizal fungi were unable to grow and associate with P. tabulaeformis seedlings. Inocula placed alongside O. davidiana seedlings, however, resulted in enhanced growth and nutritional status of O. davidiana and P. tabulaeformis seedlings, and also altered rhizosphere pH and phosphatase activity. We speculate that these species form a common mycorrhizal network and this association enhances outplanting performance of P. tabulaeformis seedlings used for forest restoration.

Combined effects of cotyledon excision and nursery fertilization on root growth, nutrient status and outplanting performance of Quercus variabilis container seedlings

Artificial excision of the distal part of acorns in order to promote germination is well researched in oak seedling cultivation studies. However, studies of combined effects of cotyledon excision and nursery fertilization on container seedlings are lacking, especially for seedling root growth and outplanting performance. This study aimed to explore the main effects of cotyledon excision on Quercus variabilis seedling emergence characteristics and demonstrated the combined effects of cotyledon excision and nursery fertilization on seedling quality to improve Quercus variabilis seedling outplanting performance. Four cotyledon excision treatments and two classes of nursery fertilization were implemented. Seedling emergence was noted every week after sowing. Seedling dry mass, morphology, and nutrient status were assessed at the end of the nursery season. After the first outplanting season, the aforementioned measurements along with seedling survival were determined once again. The results showed that cotyledon excision generally induced greater and more rapid seedling emergence, but did not affect shoot emergence synchronicity. The highest total emergence and emergence rate occurred with Intermediate excision (1/2 of the distal end of acorn was excised). Effects of nutrient loss due to cotyledon excision on seedling quality and outplanting performance were somewhat compensated by nursery fertilization. Nursery fertilization promoted dry mass increment (the net increment from T0 to T2 for dry mass) for excised seedlings after outplanting, resulting in better performance for Slight (1/3 of the distal end of acorn was excised) and Intermediate excision treatments in the field. Thus we conclude Intermediate excision combined with reasonable nursery fertilization can be recommended for production of nursery grown seedlings for afforestation.

A Study on Biodiversity Mechanism by the Creativity Theory of Ecosystem

The mechanisms of biodiversity have been intensively studied in recent decades. Significant attention has been given to finding those mechanisms that explain the patterns of species richness found changing with latitudinal gradients (Hubbell, 1979; Jablonski, 2006; Lyons, 1999; Root, 1988). A large number of these species richness hypotheses have been proposed, and new ones continue to appear, with the total now exceeding thirty (Hawkins et al., 2003; Huston, 1979; Ritchie & Olff 1999). Yet there remains considerable controversy about the hypotheses that underlie the observed patterns of biodiversity (Kerswell, 2006; Willing et al., 2003). The theories of local determinism generally try to find a few key environmental factors and establish their simple relationships with species richness in that distinct environment (Ricklefs, 2006). By doing so, the species richness could hopefully be predicted by measuring these environmental factors and their results could then become the principles of biodiversity conservation. Initially a single prominent factor is regressed against species richness, for example, the species-energy hypothesis, species-area hypothesis, or species-productivity hypothesis treats the single factor of energy, area, and productivity, respectively, as the most important factor to influence species richness (Allen et al., 2002; Mittelbach et al., 2001; Turner et al., 1988). Later on multiple factors are used to explain the causes of biodiversity, such as the hypothesis of water-energy dynamics that suggests the link between water-energy and species richness is widespread and generally strong (Hawkins et al., 2003). Ironically, more and more environmental factors are found to be important, and the relationships between these factors and species richness are variants according to different locations and scales. The theories of community explain the forces that maintain species diversity from the aspect of community ecology, for example the niche-assembly theory asserts that species co-occur in a community only when they differ from one another in resource use. But this theory has some difficulties to explaining the diversity often observed in species-rich communities such as tropical forests (Zhou & Zhang, 2006). The neutral theory, on the other hand, assumes that all individuals of all species in a trophically similar community are ecologically equivalent. The number of species in a community is controlled by species extinction and immigration, and speciation of new species (Hubbell, 2001). Based on the fundamental processes of birth, death, dispersal and speciation, neutral theory presented a mechanism that generates species abundance distributions remarkably similar to those observed in nature, however controversy persists (McGill, 2003). Some ecologist believe that the most important task