Effects of different altitudes on the nutrient and amino acid contents of bamboo (Fargesia denudata ),staple food of the giant panda,in Minshan,Sichuan, China
Nutritional components of plant species (e.g.,contents of crude protein,crude fat,and amino acids),as well as the contents of fiber that influence animals' food digestibility,collectively determine animal food preferences. Animals would prefer to feed on leaves or stems with higher contents of crude protein,crude fat,and amino acids and a lower content of fiber. Many studies have demonstrated that nutritional components or fiber contents are differently impacted by various environmental factors. It is possible that differences in the nutrient or fiber content of vegetation under different conditions would potentially affect animal distribution through food choice. Dwarf-bamboo species dominate the underground layer of subalpine forests. However,the distribution or growth of these bamboo species is predicted to be markedly affected by global warming. As the main food source for the panda,changes in temperature may influence their preference for bamboo by altering bamboo nutrition. Although the temperature difference along vertical altitudinal gradients is obvious, there have been few studies focusing on the effects of different temperatures on bamboo due to altitudinal gradients,which could potentially influence panda food preference and distribution. We designed an in situ experiment to examine the effects of different altitudes on the contents of nutrients,such as crude protein and amino acids,and parameters related to animal food digestibility,such as fiber content,of dwarf bamboo ( Fargesia denudate) in Wanglang Nature Reserve in the northwest Sichuan Province,China. Samples ( leaf,shoot,and culm) of F. denudata were selected from three altitudes (2600 m,2850 m,and 3100 m) to study differences that may be attributable to differences in altitude. The results indicated that the nutrient compositions and amino acid contents of different parts of F. denudata showed different change patterns among the different altitudes. Our main results were as follows. (1) At the same altitude,nutrients of different F. denudata tissues (leaf,shoot,and culm) were significantly different from each other. For instance,the crude protein and crude fat contents of the leaf were the highest,whereas those of the stem were the lowest. In the shoot,these parameters were in the middle range. ( 2) Most interestingly,the amount of crude protein and total amino acids were markedly influenced by the altitudinal gradient,being significantly higher at 3100 m than at 2600 m. For example,the contents of crude protein and total amino acids of bamboo shoots were highest at 3100 m. However,crude fat and crude fiber showed no significant differences among the different altitudes. ( 3) In addition to the threonine,glycine,and cysteine in shoots, serine and methionine in culms,and cysteine in leaves,contents of the other amino acids were significantly affected by the altitudinal gradient. For example,the histidine content in shoots increased with increasing altitude. Altitude had significant effects on the ratios of crude protein /crude fat and crude protein /crude fiber; however,no significant effects were observed on the ratios of cellulose /crude fiber and crude fat /crude fiber. Our results demonstrate that at higher altitude,F. denudata accumulates higher contents of crude protein and total amino acids. Warmer climates would probably affect the distribution of F. denudata and characters related to panda food preference,such as crude protein content,which may,to a certain extent,determine panda movement or migration to higher altitudes to feed on relatively nutritious food.