Oleksyn J, Karolewski P, Giertych M J, Zytkowiak R, Reich P B, Tjoelker M G
Polish Academy of Sciences, Institute of Dendrology, Parkowa 5, PL-62-035 Kórnik, Poland.
University of Minnesota, Department of Forest Resources, 1530 Cleveland Ave. N, St. Paul, MN 55108-1027, USA.
New Phytol. 1998 Oct;140(2):239-249. doi: 10.1046/j.1469-8137.1998.00270.x.
Field-grown trees of Alnus incana (L.) Moench, Alnus glutinosa (L.) Geartner and Betula pendula Roth displayed pronounced differences in responses of light-saturated net photosynthesis (A ) to herbivory by the alder beetle (Agelastica alni L., Galerucinae), a specialized insect which primarily defoliates alders. We found that photosynthetic rates of grazed leaves increased following herbivory in Alnus but not in Betula. Area- and mass-based A of grazed leaves declined linearly with increasing amount of leaf perforation in B. pendula, by as much as 57%. By contrast Alnus glutinosa and Alnus incana increased area-based rates of A by 10-50% at all levels of leaf grazing. Given increased A in the remaining portion of grazed leaves, a net reduction in photosynthesis per leaf occurred only when the proportion of leaf area grazed exceeded 40% for Alnus incana and 23% for Alnus glutinosa. Since vein perforation by Agelastica alni was observed much more frequently in leaves of Betula than in Alnus, we hypothesized that declining A in herbivorized Betula was related to this disruption of water transport. A field experiment with artificial leaf perforation demonstrated a greater decline in A in vein-perforated Betula leaves than perforated leaves with midrib veins intact. However, regardless of leaf perforation regime, birch never showed post-perforation increases in A . In all species, rates of transpiration of grazed leaves linearly increased and water-use efficiency decreased with increased amount of leaf perforation. In grazed Alnus incana leaves, increasing leaf area consumption by Agelastica alni resulted in an increase of total phenols, a reduction in starch content and no changes in nitrogen concentration in the remaining portion. The increase in photosynthesis in Alnus incana might be related to declining leaf starch concentration or increasing stomatal conductance, but was unrelated to leaf nitrogen concentration. These gas exchange and leaf chemistry measurements suggest that in contrast to B. pendula, Alnus incana and Alnus glutinosa, which are the major host species for Agelastica alni, possess leaf-level physiological adaptations and defence mechanisms which can attenuate negative effects of herbivory by the alder leaf-beetle.
在野外生长的灰桤木（Alnus incana (L.) Moench）、欧洲桤木（Alnus glutinosa (L.) Geartner）和垂枝桦（Betula pendula Roth），在光饱和净光合速率（A）对桤木叶甲（Agelastica alni L.，叶甲亚科）取食的响应方面表现出显著差异。桤木叶甲是一种专门取食桤木的昆虫，主要造成桤木落叶。我们发现，在桤木中，被啃食叶片的光合速率在取食后会增加，但在桦树中则不会。垂枝桦中，被啃食叶片基于面积和质量的A随着叶片穿孔数量的增加呈线性下降，降幅高达57%。相比之下，在所有叶片啃食水平下，欧洲桤木和灰桤木基于面积的A速率增加了10% - 50%。鉴于被啃食叶片其余部分的A增加，只有当灰桤木叶面积被啃食的比例超过40%、欧洲桤木叶面积被啃食的比例超过23%时，单叶光合作用才会出现净减少。由于桤木叶甲造成的叶脉穿孔在桦树叶中比在桤木叶中更频繁地被观察到，我们推测，被取食的桦树中A下降与这种水分运输的破坏有关。一项人工叶片穿孔的田间试验表明，叶脉穿孔的桦树叶中A的下降幅度比中脉完整的穿孔叶片更大。然而，无论叶片穿孔情况如何，桦树在穿孔后A从未出现增加。在所有物种中，被啃食叶片的蒸腾速率随着叶片穿孔数量的增加呈线性增加，水分利用效率降低。在被啃食的灰桤木叶中，桤木叶甲对叶面积的消耗增加导致总酚增加、淀粉含量降低，而其余部分的氮浓度没有变化。灰桤木光合作用的增加可能与叶片淀粉浓度下降或气孔导度增加有关，但与叶片氮浓度无关。这些气体交换和叶片化学测量结果表明，与垂枝桦不同，作为桤木叶甲主要寄主物种的灰桤木和欧洲桤木具有叶片水平的生理适应和防御机制，能够减轻桤木叶甲取食的负面影响。
