Katjiua Mutjinde L J, Ward David
Department of Natural Resources and Conservation, University of Namibia, Windhoek.
J Chem Ecol. 2006 Jul;32(7):1431-43. doi: 10.1007/s10886-006-9060-9. Epub 2006 May 25.
Resource availability, degree of herbivore damage, genetic variability, and their interactions influence the allocation of investment by plants to resistance and tolerance traits. We evaluated the independent and interactive effects of soil nutrients and moisture, and simulated the effects of herbivore damage on condensed tannins (resistance) and growth/regrowth (tolerance) traits of Terminalia sericea, a deciduous tree in the Kalahari desert that constitutes a major component of livestock diet. We used a completely crossed randomized-block design experiment to examine the effects of nutrients, water availability, and herbivore damage on regrowth and resistance traits of T. sericea seedlings. Plant height, number of branches, internode length, leaf area, leaf mass for each seedling, combined weight of stems and twigs, and root mass were recorded. Condensed tannin concentrations were 22.5 and 21.5% higher under low nutrients and low soil moisture than under high nutrient and high water treatment levels. Tannin concentrations did not differ significantly between control and experimental seedlings 2 mo after simulated herbivore damage. Tannin concentrations correlated more strongly with growth traits under low- than under high-nutrient conditions. No trade-offs were detected among individual growth traits, nor between growth traits and condensed tannins. T. sericea appeared to invest more in both resistance and regrowth traits when grown under low-nutrient conditions. Investment in the resistance trait (condensed tannin) under high-nutrient conditions was minimal and, to a lesser degree, correlated with plant growth. These results suggest that T. sericea displays both resistance and tolerance strategies, and that the degree to which each is expressed is resource-dependent.
资源可用性、食草动物的损害程度、遗传变异性及其相互作用会影响植物对抗性和耐受性特征的投资分配。我们评估了土壤养分和水分的独立及交互作用，并模拟了食草动物损害对绢毛榄仁（Terminalia sericea）（卡拉哈里沙漠中的一种落叶乔木，是牲畜饮食的主要组成部分）缩合单宁（抗性）和生长/再生长（耐受性）特征的影响。我们采用完全交叉随机区组设计实验，来研究养分、水分可用性和食草动物损害对绢毛榄仁幼苗再生长和抗性特征的影响。记录了每株幼苗的株高、分枝数、节间长度、叶面积、叶质量、茎和小枝的总重量以及根质量。与高养分和高水分处理水平相比，低养分和低土壤水分条件下缩合单宁浓度分别高出22.5%和21.5%。模拟食草动物损害2个月后，对照幼苗和实验幼苗的单宁浓度没有显著差异。在低养分条件下，单宁浓度与生长特征的相关性比高养分条件下更强。在个体生长特征之间，以及生长特征与缩合单宁之间均未检测到权衡关系。绢毛榄仁在低养分条件下生长时，似乎在抗性和再生长特征上都投入更多。在高养分条件下，对抗性特征（缩合单宁）的投入极少，且在较小程度上与植物生长相关。这些结果表明，绢毛榄仁展现出抗性和耐受性策略，且每种策略的表达程度都依赖于资源。
