College of Life Sciences, Zhejiang University, Hangzhou, China.
Ann Bot. 2011 Mar;107(3):407-13. doi: 10.1093/aob/mcq249. Epub 2010 Dec 17.
Plant biomass-density relationships during self-thinning are determined mainly by allometry. Both allometry and biomass-density relationship have been shown to vary with abiotic conditions, but the effects of biotic interactions have not been investigated. Arbuscular mycorrhizal fungi (AMF) can promote plant growth and affect plant form. Here experiments were carried out to test whether AMF affect plant allometry and the self-thinning trajectory.
Two experiments were conducted on Medicago sativa L., a leguminous species known to be highly dependent on mycorrhiza. Two mycorrhizal levels were obtained by applying benomyl (low AMF) or not (high AMF). Experiment 1 investigated the effects of AMF on plant growth in the absence of competition. Experiment 2 was a factorial design with two mycorrhizal levels and two plant densities (6000 and 17 500 seeds m(-2)). Shoot biomass, root biomass and canopy radius were measured 30, 60, 90 and 120 d after sowing. The allometric relationships among these aspects of size were estimated by standardized major axis regression on log-transformed data.
Shoot biomass in the absence of competition was lower under low AMF treatment. In self-thinning populations, the slope of the log (mean shoot biomass) vs. log density relationship was significantly steeper for the high AMF treatment (slope = -1·480) than for the low AMF treatment (-1·133). The canopy radius-biomass allometric exponents were not significantly affected by AMF level, but the root-shoot allometric exponent was higher in the low AMF treatment. With a high level of AMF, the biomass-density exponent can be predicted from the above-ground allometric model of self-thinning, while this was not the case when AMF were reduced by fungicide.
AMF affected the importance of below-ground relative to above-ground interactions and changed root vs. shoot allocation. This changed allometric allocation of biomass and altered the self-thinning trajectory.
自疏过程中植物生物量-密度关系主要由异速生长决定。异速生长和生物量-密度关系都已被证明会随非生物条件而变化，但生物相互作用的影响尚未被研究。丛枝菌根真菌（AMF）可以促进植物生长并影响植物形态。本研究进行了实验来检验 AMF 是否影响植物的异速生长和自疏轨迹。
在豆科植物紫花苜蓿（已知高度依赖菌根）上进行了两项实验。通过施用苯菌灵（低 AMF）或不施用（高 AMF）来获得两种 AMF 水平。实验 1 研究了 AMF 在无竞争情况下对植物生长的影响。实验 2 是一个具有两种 AMF 水平和两种植物密度（6000 和 17500 粒 m(-2))的析因设计。播种后 30、60、90 和 120 d 测量地上生物量、根生物量和冠层半径。通过对对数转换数据进行标准化主轴回归来估计这些大小方面之间的异速生长关系。
在低 AMF 处理下，无竞争时的地上生物量较低。在自疏种群中，高 AMF 处理的对数（平均地上生物量）与密度关系的斜率（-1.480）明显比低 AMF 处理（-1.133）陡峭。冠层半径-生物量的异速生长指数不受 AMF 水平的显著影响，但在低 AMF 处理中，根-茎的异速生长指数较高。在高 AMF 水平下，生物量-密度指数可以从自疏的地上异速生长模型中预测，而当用杀菌剂减少 AMF 时则不行。
AMF 影响了地下与地上相互作用的重要性，并改变了根与茎的分配。这改变了生物量的异速生长分配并改变了自疏轨迹。
