[Spatial pattern of plant community in original karst tiankeng: A case study of Zhanyi tiankeng in Yunnan, China]. / å–€æ–¯ç‰¹åŽŸç”Ÿå¤©å‘æ¤ç‰©ç¾¤è½ç©ºé—´æ ¼å±€ç‰¹å¾­­ä»¥äº‘南沾益天坑为例.

Damaosi is one of original karst tiankengs with underground virgin forest in Yunnan Pro-vince. The spatial point pattern analysis and the woody individual spatial structure parameters, including the uniform angle index, mingling degree and storey index, were used to estimate spatial pattern of the tiankeng's underground forest community. We also analyzed the intraspecific spatial distribution characteristics and interspecific spatial association on the basis of the individual relative position information of plant community. The results showed that the spatial distribution of plant community in Damaosi tiankeng was random. Plant species in the forest were moderately mixed. The vertical stratification of this forest was relatively simple, with stable structure and mature development characteristics of climax forest community. The populations in this community were mainly clustered in spatial distribution, negatively correlated between species and stronger negative correlation on the same vertical level. The larger the difference in the vertical level, the smaller the space competition was. The negative correlation in space became weaker with the increases of spatial scale. Tiankeng ecosystem was one type of precious natural habitats and plant refuges with high ecological stability. The stable structure of tiankeng plant community had important implications for the ecological resto-ration in karst areas.

[Interspecific relationships of dominant species in the grassland community of moderately degraded tiankeng of Yunnan, China.] / äº‘å—ä¸­åº¦é€€åŒ–çš„å–€æ–¯ç‰¹å¤©å‘è‰åœ°æ¤ç‰©ç¾¤è½ä¼˜åŠ¿ç§ç§é—´å ³ç³».

Karst tiankeng is a special grand negative landform. The environment of tiankeng inside are independent of that outside, showing a unique characteristics of plant community. Taking a moderately degraded tiankeng with good accessibility, Bajiaxiantang as the focus, the dominant species with importance value >1 were selected to clarify the interspecific association of 11 dominant species by the multi-disciplinary approach including the variance ratio (VR) of overall association, Φ2 test, association coefficient (AC) and Spearman rank correlation coefficient. The results showed that VR of overall association in this grassland community was 1.377 (which was larger than 1), indicating that this community had overall significantly positive interspecific association. Given the great difference between the positive and negative association and significantly negative correlation between heliophiles and sciophiles, the community had independent distribution. The number of positive pairs of species (26) was less than that with negative correlation (29) in Spearman correlation analysis. Combined with the difference of tiankeng's micro-environment, dominant plant species of degraded tiankeng could be divided into three ecological groups. The grassland community in tiankeng showed circle distribution pattern.

Effects of multi-environmental factors on physiological and biochemical responses of large yellow croaker, Larimichthys crocea.

Land-based recirculating aquaculture systems (RAS) and cage culture are important methods of Larimichthys crocea production. The effects of environmental factors on physiological and biochemical aspects of L. crocea require clarification. Temperature and salinity are controlled in RAS and directly affect L. crocea growth and survival. To explore optimal parameters, the oxygen consumption rate (RO), ammonium excretion rate (RN), and O/N ratio at different temperatures (8, 14, 20, 26, and 32 °C) and salinities (5, 15, 25, and 35‰) were determined. RO, RN, and O/N first increased and then decreased with elevated temperature and salinity, peaking at 26 °C and 25‰, respectively. This suggests that the metabolism of L. crocea was maximal at 26 °C and 25‰ salinity, which promote its growth and survival. Additionally, hypoxia affects cage culture, and has significant effects on enzymatic activities and stress-inducible gene expression. To accelerate the selective breeding of hypoxia-tolerant L. crocea in cage culture, we measured adenosine triphosphatase (ATPase), lactate dehydrogenase (LDH), and succinate dehydrogenase (SDH) activities, and hypoxia-inducing factor 1 (HIF-1) mRNA expression in the myocardium under hypoxia (2.5, 3.5, and 4.5 mg L-1). ATPase and SDH activities first decreased and then increased under hypoxia, whereas LDH activity and HIF-1α expression first increased and then decreased. Thus, under hypoxia, the myocardial mitochondria switched from being susceptible to being resistant to injury induced by energy metabolism, and respiration in L. crocea likely converted from aerobic to anaerobic during adaptation. Furthermore, the upregulation of HIF-1α mRNA suggests it has an active role in protection against anoxic damage.

Physiological responses and changes in gene expression in the large yellow croaker Larimichthys crocea following exposure to hypoxia.

Organisms at all levels of evolutionary complexity react to hypoxic stress. To clarify the effects of acute hypoxia on physiological and biochemical responses of Larimichthys crocea, we measured the activity levels of the antioxidant enzymes superoxide dismutase and catalase, hemoglobin concentration, functional indices of the liver (aspartate transaminase, alanine transaminase), heart (phosphocreatine kinase), and immune system (alkaline phosphatase), as well as mRNA expression levels of the immunity-related genes Hsp70 and HIF-1α at different time points of hypoxic. In addition, liver, gill, and kidney samples were histologically analyzed. We found that hemoglobin concentration and all enzyme activities increased during hypoxia, although these effects were transient and most indices returned to basal levels thereafter. The extent of the increase in the parameter values was inversely proportional to the dissolved oxygen content. Hsp70 and HIF-1α mRNA expression levels increased significantly in the blood, liver, gills, and kidneys following exposure to hypoxia, which may play an important role in protecting fish against oxidative damage. However, we found histological evidence of hypoxia-induced injuries to the gills, liver, and kidneys, which are involved in breathing, detoxification, and osmotic balance maintenance, respectively. Thus, despite the upregulation of defensive mechanisms, acute hypoxia still caused irreversible damage of organs. In conclusion, we observed that, in response to acute hypoxic stress, L. crocea enhances immune defensive function and antioxidant capacity. A better understanding of the regulation of the molecular anti-hypoxia mechanisms can help speeding up the selective breeding of hypoxia-tolerant L. crocea.